*Article* **Low-Dimensional Architectures in Isomeric** *cis***-PtCl2{Ph2PCH2N(Ar)CH2PPh2} Complexes Using Regioselective-N(Aryl)-Group Manipulation**

**Peter De'Ath, Mark R. J. Elsegood , Noelia M. Sanchez-Ballester and Martin B. Smith \***

Department of Chemistry, Loughborough University, Loughborough LE11 3TU, UK; P.DeAth@lboro.ac.uk (P.D.); m.r.j.elsegood@lboro.ac.uk (M.R.J.E.); n.m.sanchez-ballester@lboro.ac.uk (N.M.S.-B.) **\*** Correspondence: m.b.smith@lboro.ac.uk

**Abstract:** The solid-state behaviour of two series of isomeric, phenol-substituted, aminomethylphosphines, as the free ligands and bound to PtII, have been extensively studied using single crystal X-ray crystallography. In the first library, isomeric diphosphines of the type Ph2PCH2N(Ar)CH2PPh<sup>2</sup> [**1a**–**e**; Ar = C6H<sup>3</sup> (Me)(OH)] and, in the second library, amide-functionalised, isomeric ligands Ph2PCH2N{CH2C(O)NH(Ar)}CH2PPh<sup>2</sup> [**2a**–**e**; Ar = C6H<sup>3</sup> (Me)(OH)], were synthesised by reaction of Ph2PCH2OH and the appropriate amine in CH3OH, and isolated as colourless solids or oils in good yield. The non-methyl, substituted diphosphines Ph2PCH2N{CH2C(O)NH(Ar)}CH2PPh<sup>2</sup> [**2f**, Ar = 3-C6H<sup>4</sup> (OH); **2g**, Ar = 4-C6H<sup>4</sup> (OH)] and Ph2PCH2N(Ar)CH2PPh<sup>2</sup> [**3**, Ar = 3-C6H<sup>4</sup> (OH)] were also prepared for comparative purposes. Reactions of **1a**–**e**, **2a**–**g**, or **3** with PtCl<sup>2</sup> (η 4 -cod) afforded the corresponding square-planar complexes **4a**–**e**, **5a**–**g**, and **6** in good to high isolated yields. All new compounds were characterised using a range of spectroscopic (1H, <sup>31</sup>P{1H}, FT–IR) and analytical techniques. Single crystal X-ray structures have been determined for **1a**, **1b**·CH3OH, **2f**·CH3OH, **2g**, **3**, **4b**·(CH<sup>3</sup> )2SO, **4c**·CHCl<sup>3</sup> , **4d**· 1 2 Et2O, **4e**· 1 <sup>2</sup>CHCl<sup>3</sup> · 1 <sup>2</sup>CH3OH, **5a**· 1 2 Et2O, **5b**, **5c**· 1 <sup>4</sup>H2O, **5d**·Et2O, and **6**·(CH<sup>3</sup> )2SO. The free phenolic group in **1b**·CH3OH, **2f**·CH3OH, **2g**, **4b**·(CH<sup>3</sup> )2SO, **5a**· 1 2 Et2O, **5c**· 1 <sup>4</sup>H2O, and **6**·(CH<sup>3</sup> )2SO exhibits various intra- or intermolecular O–H···X (X = O, N, P, Cl) hydrogen contacts leading to different packing arrangements.

**Keywords:** amide groups; isomers; late-transition metals; P-ligands; phenols; secondary interactions; single crystal X-ray crystallography

### **1. Introduction**

Tertiary phosphines, and their phosphine oxides, have played an important role in the study of supramolecular and self-assembly processes [1–3]. Their synthetic versatility, coupled with ease of substituent modification, has no doubt played a significant contribution over the years. Hydrogen bonding interactions are routinely encountered in supramolecular ligand systems as illustrated by the elegant studies from Breit [4], Reek [5], and others [6,7]. More recently, amongst other common types of non-covalent interactions, those based on halogen bonding [8,9] and Hδ<sup>+</sup> ···Hδ<sup>−</sup> have been reported [10].

For a number of years, we [11–16], and others [17–22], have been interested in aminomethylphosphines, readily amenable by Mannich condensation reactions. Such interest stems from the relative ease of accessing *P*-monodentate ligands based on a P–C–N linker [11,15,16,19,20,22] or *P*/*P*-bidentate derivatives bearing a P–C–N–C–P backbone [12–14,17–19,21]. Previously, we have shown that the N-arene group can be easily tuned with, for example, various H-bonding donor/acceptor sites based on –CO2H/OH groups [12–16]. In continuation of these studies, we report here our work on the regioselective positioning of amide/hydroxy and methyl groups within a series of aminomethylphosphines, both as the free ligands and when coordinated to a square-planar Pt(II) metal centre. Our rationale for introducing an –C(O)NH– group is based on the known use of

**Citation:** De'Ath, P.; Elsegood, M.R.J.; Sanchez-Ballester, N.M.; Smith, M.B. Low-Dimensional Architectures in Isomeric *cis*-PtCl2{Ph2PCH2N(Ar)CH2PPh2} Complexes Using Regioselective-N(Aryl)-Group Manipulation. *Molecules* **2021**, *26*, 6809. https://doi.org/10.3390/ molecules26226809

Academic Editors: William T. A. Harrison, R. Alan Aitken and Paul Waddell

Received: 28 September 2021 Accepted: 7 November 2021 Published: 11 November 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

**Compound <sup>a</sup> <sup>δ</sup>(P) <sup>b</sup>**

**δ(H) /OH (NH)** 

**1a** (79) −27.5 8.62 7.33–7.23,

**1b** (56) −27.3 9.06 7.36–7.26,

**1c** (97) <sup>−</sup>27.5 8.77 7.44–7.22,

**1d** (38) <sup>−</sup>26.7 8.63 7.40–7.30,

**1e** (96) −26.4 9.06 7.49–7.33,

(8.68)

7.55–7.32, 6.95,

**2c** (88) <sup>−</sup>26.5 <sup>c</sup> 9.34

**2d** (65) <sup>−</sup>27.1 9.05

**δ(H) /arom. H.** 

this functionality in supramolecular chemistry [23] and, furthermore, the recent interest in amide-modified phosphines for their variable coordination chemistry [24–26], binding nitroaromatics [27], and relevance to catalysis based on Pd [28]. Our choice of metal fragment in this work, "*cis*-PtCl2", is based on its capability to support a relatively small bite angle diphosphine ligand in a *cis*, six-membered ring conformation, and to provide up to two "acceptor" sites for potential H-bonding [29]. For this purpose, we elected to pursue a double Mannich condensation reaction of Ph2PCH2OH with a series of isomeric primary amines bearing either OH/CH<sup>3</sup> groups and/or an amide spacer between the arene and P–C–N–C–P backbone (Chart 1). ality in supramolecular chemistry [23] and, furthermore, the recent interest in amide-modified phosphines for their variable coordination chemistry [24–26], binding nitroaromatics [27], and relevance to catalysis based on Pd [28]. Our choice of metal fragment in this work, "*cis*-PtCl2", is based on its capability to support a relatively small bite angle diphosphine ligand in a *cis*, six-membered ring conformation, and to provide up to two "acceptor" sites for potential H-bonding [29]. For this purpose, we elected to pursue a double Mannich condensation reaction of Ph2PCH2OH with a series of isomeric primary amines bearing either OH/CH3 groups and/or an amide spacer between the arene and P–C–N–C– P backbone (Chart 1).

16]. In continuation of these studies, we report here our work on the regioselective positioning of amide/hydroxy and methyl groups within a series of aminomethylphosphines, both as the free ligands and when coordinated to a square-planar Pt(II) metal centre. Our rationale for introducing an –C(O)NH– group is based on the known use of this function-

*Molecules* **2021**, *26*, x FOR PEER REVIEW 2 of 22

**Chart 1.** Potential modification sites of a Ph2P–C–N(Ar)–C–PPh2 backbone. **Chart 1.** Potential modification sites of a Ph2P–C–N(Ar)–C–PPh<sup>2</sup> backbone.

#### **2. Results and Discussion 2. Results and Discussion**

*2.1. Ligand Synthesis 2.1. Ligand Synthesis*

We [11–16,29], and others [17,19–22], have previously used Mannich condensations as a versatile method for the synthesis of aminomethylphosphines. Accordingly, two equivalents of Ph2PCH2OH were reacted with one equivalent of the amine, for 24 h at r.t. under N2, yielding the desired phenol-substituted ditertiary phosphines **1a**–**e** and **3** (Scheme 1). We [11–16,29], and others [17,19–22], have previously used Mannich condensations as a versatile method for the synthesis of aminomethylphosphines. Accordingly, two equivalents of Ph2PCH2OH were reacted with one equivalent of the amine, for 24 h at r.t. under N2, yielding the desired phenol-substituted ditertiary phosphines **1a**–**e** and **3** (Scheme 1). *Molecules* **2021**, *26*, x FOR PEER REVIEW 3 of 22

.

**Microanalysis (CHN)** 

Calc. for C33H31NOP2, C, 76.29; H, 6.01; N, 2.70 Found, C, 76.07; H, 6.13; N, 2.78

Calc. for C33H31NOP2.2MeOH, C, 72.03; H, 6.74; N, 2.40 Found, C, 72.45; H, 6.04; N, 2.58

Calc. for C33H31NOP2, C, 76.29; H, 6.01; N, 2.70 Found, C, 75.99; H, 6.00; N, 2.76

Calc. for C33H31NOP2, C, 76.29; H, 6.01; N, 2.70 Found, C, 75.53; H, 6.05; N, 2.74

Calc. for C33H31NOP2.MeOH, C, 74.03; H, 6.40; N, 2.54 Found, C, 74.81; H, 5.93; N, 2.61

> Calc. for C35H34N2O2P2, C, 72.91; H, 5.94; N, 4.86

**Scheme 1.** Synthesis of **1a**–**e**, **2a**–**g**, and **3**. **Scheme 1.** Synthesis of **1a**–**e**, **2a**–**g**, and **3**.

**δ(H) /CH2**

**δ(H) /CH3**

**νOH (νNH) <sup>e</sup>**

(3228)

**Table 1.** Selected spectroscopic and analytical data for compounds **1a**–**3** <sup>a</sup>

6.76, 6.69–6.57 4.15 (2.4) 2.10 3398

7.15, 6.50, 6.44 3.96 (5.6) 1.74 3282

6.86, 6.54, 6.48 4.09 (3.4) 2.12 3389

6.85, 6.50, 6.27 3.88 (3.6) 2.08 3387

6.61, 6.41 3.69 3.81 (4.8) 2.04 <sup>3047</sup>

**2a** (81) −26.0 8.15 7.77–7.19 5.06 3.62 (8.0) 1.19 - - **2b** (89) −26.0 7.83 7.60–7.21 5.07 3.69 (3.6) 1.63 - -

6.55 4.02 (3.2) 1.96 3432

(8.17) 7.71–7.19 5.27 3.61 (4.8) 1.63 - -

**δ(H) /CH2** 

For **1a**–**e**, colourless solids were isolated in 38–97% yields and found to be air stable in the solid state, but oxidise rapidly in solution. Compounds **1a**–**e** and **3** exhibit single resonances in their <sup>31</sup>P{1H} NMR spectra (in d<sup>6</sup> -dmso) around δ(P) −26 ppm [12–15,29], indicating the presence of only one PIII environment. The ligands were also characterised by <sup>1</sup>H NMR, FT–IR, and elemental analysis (Table 1). In particular, the absence of an NH resonance, in the <sup>1</sup>H NMR spectra, confirmed that double condensation had occurred.


**Table 1.** Selected spectroscopic and analytical data for compounds **1a**–**3** a .

a Isolated yields in parentheses. <sup>b</sup> Recorded in (CD3)2SO unless otherwise stated. <sup>c</sup> Recorded in CDCl3. d 2*J*(PH) coupling in brackets.

<sup>e</sup> Recorded as KBr discs.

The synthesis of ditertiary phosphines, containing a flexible backbone presenting extra donor/acceptor sites with additional H-bonding capability, is described here with the opportunity to enhance solid-state packing behaviour. The precursors for the synthesis of the desired functionalised ditertiary phosphines **2a**–**g** were prepared using, in step (i), 1 equiv. of primary amine, *N*-carbobenzyloxyglycine (1 equiv.) and dicyclohexylcarbodi-

imide (DCC, 1 equiv.) in THF affording the corresponding carbamates followed by, in step (ii), treatment with Pd/C and cyclohexene in C2H5OH, to give the desired primary alkylamines in moderate to good yields [30,31]. Using a similar procedure to that described for **1a**–**e**, the amide-functionalised diphosphines **2a**–**e** were prepared in 65–89% yields by condensation using 1 equiv. of primary amine and two equiv. of Ph2PCH2OH at r.t. in CH3OH (Scheme 1). Furthermore, the phenol-substituted phosphines **2f** and **2g** were synthesised to investigate what effect, if any, an absent methyl group on the N-arene ring displays. In the case of **2d**–**g**, the diphosphines were obtained as solids whereas **2a**–**c** were obtained as yellow oils that were sufficiently pure to be used in complexation studies. All compounds displayed a single <sup>31</sup>P NMR resonance around <sup>δ</sup>(P) <sup>−</sup>26 ppm [12–15,29] indicating the inclusion of an amide spacer has negligible effect on the <sup>31</sup>P chemical shift. Other spectroscopic and analytical data are given in Table 1.

### *2.2. Single Crystal X-ray Studies of* **1a***,* **1b**·*CH3OH,* **2f**·*CH3OH,* **2g***, and* **3**

X-ray quality crystals of **1a**, **1b**·CH3OH, **2f**·CH3OH, **2g**, and **3** were obtained by slow evaporation of a methanol solution, while for **2g** diethyl ether was diffused into a deuterochloroform/methanol solution (Table 2).

**Table 2.** Details of the X-ray data collections and refinements for compounds **1a**, **1b**·CH3OH, **2f**·CH3OH, **2g**, and **3**.


<sup>a</sup> *<sup>R</sup>* <sup>=</sup> <sup>∑</sup>||*F*o| <sup>−</sup> <sup>|</sup>*F*c||/∑|*F*o|. <sup>b</sup> *wR*2 = [∑[*w*(*F*<sup>o</sup> <sup>2</sup> <sup>−</sup> *<sup>F</sup>*<sup>c</sup> 2 ) 2 ]/∑[*w*(*F*o 2 ) 2 ]]1/2 .

The geometry around each phosphorus atom is essentially pyramidal as would be anticipated (Figures 1–5). The PIII atoms are in an *anti* conformation, presumably to minimise steric repulsions between the phenyl groups. The geometry about the N(1) centre is approx. pyramidal [Σ(C–N(1)–C) angles: 337.0(3)◦ for **1a**; 335(2)◦ for **1b**·CH3OH; 335.2(2)/336.6(2)◦ for **2f**·CH3OH; 333.7(2)◦ for **2g**] and approximately trigonal planar for **3** [Σ(C–N–C) = 359.05(11)◦ ]. In **1a** and **1b**·CH3OH, the N-arene ring [C(3) > C(8)] is twisted by ca. 88◦ (**1a**) and 86◦ (**1b**·CH3OH) [12,32] such that it is almost perpendicular to the C(1)–N(1)–C(2) plane, whereas for **3**, the twist of the C(1)–N(1)–C(2) fragment is around 9◦ from co-planarity with the N-arene group, apparently as a result of the intermolecular H-bonding requirements (*vide infra*). *Molecules* **2021**, *26*, x FOR PEER REVIEW 6 of 22

*Molecules* **2021**, *26*, x FOR PEER REVIEW 7 of 22

**Figure 1.** Molecular structure of **1a**. All hydrogens, except on C(1), C(2) and O(1), have been omitted for clarity. **Figure 1.** Molecular structure of **1a**. All hydrogens, except on C(1), C(2) and O(1), have been omitted for clarity.

N–H∙∙∙Nintra [2.714(3), 117(2)] 2.748(4), 114(3) **Figure 2.** Molecular structure of **3** showing a dimer pair. All hydrogens, except on C(1), C(2) and O(1), have been omitted for clarity. Symmetry code: A = 1 − x, 1 − y, 1 − z. **Figure 2.** Molecular structure of **3** showing a dimer pair. All hydrogens, except on C(1), C(2) and O(1), have been omitted for clarity. Symmetry code: A = 1 − x, 1 − y, 1 − z.

2.671(3), 171(3) [2.659(3), 165(3)]

2.695(3), 114(2)

Compound **3**, where the −OH functional group is in the *meta* position with respect to

Compound **1b**∙CH3OH, which contains the −OH group in a *para* position with respect to the N-arene, displays a similar structure to **3** with intramolecular O–H∙∙∙P interactions

gen bonds, O−H∙∙∙P [*d* = 2.60(2) Å], form between symmetry-related molecules, creating dimers in which two ligands are held in an *R*22(16) H-bonding motif (Figure 2). The distance between symmetry-related nitrogen atoms is 8.257 Å. The structure of **3** shows a 0D

direction (Figure 3). The *para* hydroxyl oxygen acts as an acceptor for an O–H∙∙∙O intermolecular H-bond from approximately alternate CH3OH molecules of crystallisation with *d* = 2.05 Å. These CH3OH molecules are 50/50 disordered with the second component Hbonding to its neighbour with *d* = 1.95 Å. Selected hydrogen parameters for **1b**∙CH3OH

**Figure 3.** Crystal structure packing plot for **1b**∙CH3OH. Most H atoms, two Ph groups per P atom

asymmetric unit. A pair of H-bonded molecules, related by inversion symmetry, and with *d* = 1.81(3) Å for the intermolecular O–H∙∙∙O interaction [1.78(3) Å for molecule 2] affords *R*22(16) ring motifs (Figure 4). The intramolecular N–H∙∙∙N *S*(5) H-bond motif with *d* = 2.25(3) Å [2.26(3) Å for molecule 2] results in an intermediate twist angle of 64.23(13)° [but a rather more perpendicular 78.70(8)° for molecule 2] between planes C(1)/N(1)/C(2) and ring C(5) > C(10) [plane C(35)/N(4)/C(36) and ring C(39) > C(44) for molecule 2]. The *meta*

Compound **2f**∙CH3OH crystallises with two, similarly behaved, molecules in the

have been omitted for clarity. Symmetry code: A = x, −y + ½, z + ½.

2.706(4), 169(4)

167(2)

arrangement.

are listed in Table 3.

<sup>a</sup> Values in parentheses are for the second independent molecule.

are listed in Table 3.

O(1), have been omitted for clarity. Symmetry code: A = 1 − x, 1 − y, 1 − z.

**Figure 3.** Crystal structure packing plot for **1b**∙CH3OH. Most H atoms, two Ph groups per P atom have been omitted for clarity. Symmetry code: A = x, −y + ½, z + ½. **Figure 3.** Crystal structure packing plot for **1b**·CH3OH. Most H atoms, two Ph groups per P atom have been omitted for clarity. Symmetry code: A = x, <sup>−</sup>y + <sup>1</sup> 2 , z + <sup>1</sup> 2 . hydroxy group in **2f** facilitates 0D dimer formation, as opposed to the chains observed in **2g** (*vida infra*).

**Figure 2.** Molecular structure of **3** showing a dimer pair. All hydrogens, except on C(1), C(2) and

Compound **1b**∙CH3OH, which contains the −OH group in a *para* position with respect to the N-arene, displays a similar structure to **3** with intramolecular O–H∙∙∙P interactions at *d* = 2.60 Å. However, instead of forming dimers, there are 1D zig-zag chains in the *c* direction (Figure 3). The *para* hydroxyl oxygen acts as an acceptor for an O–H∙∙∙O intermolecular H-bond from approximately alternate CH3OH molecules of crystallisation with *d* = 2.05 Å. These CH3OH molecules are 50/50 disordered with the second component Hbonding to its neighbour with *d* = 1.95 Å. Selected hydrogen parameters for **1b**∙CH3OH

**Figure 4.** Dimers of **2f** forming *R*22(16) graph set motifs. Most H atoms omitted for clarity. The second unique molecule which adopts a similar, centrosymmetric motif, is not shown. **Figure 4.** Dimers of **2f** forming *R* 2 2 (16) graph set motifs. Most H atoms omitted for clarity. The second unique molecule which adopts a similar, centrosymmetric motif, is not shown. between planes C(1)/N(1)/C(2) and arene ring C(5) > C(10). The *para* hydroxy group promotes chain formation.

**Figure 5.** Intra- and intermolecular interactions in the crystal structure of **2g**. Most H atoms omitted for clarity. Symmetry operator A = x, −y + 3/2, z − ½. the region of 1653–1675 cm–1, indicative of ν(C=O amide). **Figure 5.** Intra- and intermolecular interactions in the crystal structure of **2g**. Most H atoms omitted for clarity. Symmetry operator A = x, <sup>−</sup>y + <sup>3</sup>/<sup>2</sup> , z <sup>−</sup> <sup>1</sup> 2 .

**Figure 5.** Intra- and intermolecular interactions in the crystal structure of **2g**. Most H atoms omitted

ratio) in CH2Cl2 for 1.5 h with displacement of the cod ligand. The products were isolated in good yields as colourless solids. Downfield shifts of the 31P NMR resonances were observed for all complexes, with 1*J*PtP coupling constants of approx. 3400 Hz, indicative of a *cis* conformation [29]. This was further supported by two characteristic νPtCl IR vibrations in the range of 279–316 cm−1 (Table 4). Furthermore, compounds **4a**–**e**, **5a**–**g**, and **6** present ν(NH) and ν(OH) IR absorptions in the range 3050–3465 cm–1 and also a strong band in

The synthesis of *P,P*-chelate complexes *cis*-PtCl2(**1a**–**e**) [**4a**–**e**], *cis*-PtCl2(**2a**–**g**) [**5a**–**g**], and *cis*-PtCl2(**3**) [**6**] (Chart 2) was achieved by stirring the ligands and PtCl2(η4-cod) (1:1 ratio) in CH2Cl2 for 1.5 h with displacement of the cod ligand. The products were isolated in good yields as colourless solids. Downfield shifts of the 31P NMR resonances were observed for all complexes, with 1*J*PtP coupling constants of approx. 3400 Hz, indicative of a *cis* conformation [29]. This was further supported by two characteristic νPtCl IR vibrations in the range of 279–316 cm−1 (Table 4). Furthermore, compounds **4a**–**e**, **5a**–**g**, and **6** present ν(NH) and ν(OH) IR absorptions in the range 3050–3465 cm–1 and also a strong band in

*2.4. Dichloroplatinum(II) Complexes of* **1a**–**e***,* **2a***–***g***, and* **3**

*2.4. Dichloroplatinum(II) Complexes of* **1a**–**e***,* **2a***–***g***, and* **3**

the region of 1653–1675 cm–1, indicative of ν(C=O amide).

for clarity. Symmetry operator A = x, −y + 3/2, z − ½.

### *2.3. Secondary Interactions in* **1a***,* **1b**·*CH3OH,* **2f**·*CH3OH,* **2g***, and* **3**

The synthons observed in the solid state for these highly modular ligands may be dictated by various factors including the nature of the ligand, the flexibility of the P–C– N–C–P backbone, the predisposition of the OH/CH<sup>3</sup> groups about the N-arene ring, and the solvent used in the crystallisation. In order to probe the OH/CH<sup>3</sup> interplay of groups, the crystal structure of **1a**, with the –OH group in the *ortho* position with respect to the N(1) atom, is described first. Ligand **1a** crystallises with an intramolecular *S*(5) [33–35] H-bonded ring with *d* = 2.26(5) Å [denoting the hydrogen (H) to acceptor (A) distance in an H-bond D–H···A] [36] for the O–H···N interaction (Figure 1). The intramolecular Hbonding in **1a** limits the dimensionality of the packing of the diphosphine ligand. Therefore, the structure of **1a** is essentially zero-dimensional (Table 3).

**Table 3.** Selected data (*D*···*A*/Å, ∠*D*–H···*A*/ ◦ ) for key inter- and intramolecular contacts for compounds **1a**, **1b**·**CH3OH**, **2f**·**CH3OH**, **2g**, and **3**.


<sup>a</sup> Values in parentheses are for the second independent molecule.

Compound **3**, where the −OH functional group is in the *meta* position with respect to the tertiary N(1) atom, aggregates in the solid state in such a way that fairly weak hydrogen bonds, O−H···P [*d* = 2.60(2) Å], form between symmetry-related molecules, creating dimers in which two ligands are held in an *R* 2 <sup>2</sup>(16) H-bonding motif (Figure 2). The distance between symmetry-related nitrogen atoms is 8.257 Å. The structure of **3** shows a 0D arrangement.

Compound **1b**·CH3OH, which contains the −OH group in a *para* position with respect to the N-arene, displays a similar structure to **3** with intramolecular O–H···P interactions at *d* = 2.60 Å. However, instead of forming dimers, there are 1D zig-zag chains in the *c* direction (Figure 3). The *para* hydroxyl oxygen acts as an acceptor for an O–H···O intermolecular H-bond from approximately alternate CH3OH molecules of crystallisation with *d* = 2.05 Å. These CH3OH molecules are 50/50 disordered with the second component H-bonding to its neighbour with *d* = 1.95 Å. Selected hydrogen parameters for **1b**·CH3OH are listed in Table 3.

Compound **2f**·CH3OH crystallises with two, similarly behaved, molecules in the asymmetric unit. A pair of H-bonded molecules, related by inversion symmetry, and with *d* = 1.81(3) Å for the intermolecular O–H···O interaction [1.78(3) Å for molecule 2] affords *R* 2 <sup>2</sup>(16) ring motifs (Figure 4). The intramolecular N–H···N *S*(5) H-bond motif with *d* = 2.25(3) Å [2.26(3) Å for molecule 2] results in an intermediate twist angle of 64.23(13)◦ [but a rather more perpendicular 78.70(8)◦ for molecule 2] between planes C(1)/N(1)/C(2) and ring C(5) > C(10) [plane C(35)/N(4)/C(36) and ring C(39) > C(44) for molecule 2]. The *meta* hydroxy group in **2f** facilitates 0D dimer formation, as opposed to the chains observed in **2g** (*vida infra*).

For **2g**, molecules form H-bonded, 1D, zig-zag chains in the *c* direction via strong O–H···O interactions with *d* = 1.83(5) Å (Figure 5). The intramolecular N–H···N *S*(5), H-bond motif with *d* = 2.29(3) Å again results in an almost perpendicular twist angle of 82.09(15)◦ between planes C(1)/N(1)/C(2) and arene ring C(5) > C(10). The *para* hydroxy group promotes chain formation.

**4e** (81) <sup>−</sup>7.8 <sup>d</sup>

**5a** (89) <sup>−</sup>9.8 d,e

**5b** (65) <sup>−</sup>11.0 <sup>d</sup>

**5c** (73) <sup>−</sup>9.9 <sup>d</sup>

**5d** (99) <sup>−</sup>9.8 c,d

 (3421)

(3398)

(3397)

(3406)

 (3405) 9.01

9.45 (8.91)

9.16 (8.61)

9.56 (8.94)

9.17 (8.90)

7.59–7.45, 6.75, 6.27, 6.03

7.84–7.80,

7.83–7.80, 7.57–7.41, 7.05, 6.48

7.85–7.77, 7.59–7.38, 6.63, 6.51

7.98–7.50, 6.97–6.84, 6.68, 6.73

### *2.4. Dichloroplatinum(II) Complexes of* **1a***–***e***,* **2a***–***g***, and* **3**

The synthesis of *P*,*P*-chelate complexes *cis*-PtCl2(**1a**–**e**) [**4a**–**e**], *cis*-PtCl2(**2a**–**g**) [**5a**–**g**], and *cis*-PtCl2(**3**) [6] (Chart 2) was achieved by stirring the ligands and PtCl2(η 4 -cod) (1:1 ratio) in CH2Cl<sup>2</sup> for 1.5 h with displacement of the cod ligand. The products were isolated in good yields as colourless solids. Downfield shifts of the <sup>31</sup>P NMR resonances were observed for all complexes, with <sup>1</sup> *J*PtP coupling constants of approx. 3400 Hz, indicative of a *cis* conformation [29]. This was further supported by two characteristic νPtCl IR vibrations in the range of 279–316 cm−<sup>1</sup> (Table 4). Furthermore, compounds **4a**–**e**, **5a**–**g**, and **6** present ν(NH) and ν(OH) IR absorptions in the range 3050–3465 cm–1 and also a strong band in the region of 1653–1675 cm–1, indicative of ν(C=O amide). *Molecules* **2021**, *26*, x FOR PEER REVIEW 9 of 22

.

.

C, 50.46; H, 3.98; N, 1.78 Found, C, 50.66; H, 4.61; N, 1.70

Calc. for C35H34Cl2N2O2P2Pt.0.5CH2Cl2, C, 48.63; H, 3.74; N, 3.15 Found, C, 49.00; H, 4.07; N, 3.13

Calc. for C35H34Cl2N2O2P2Pt, C, 49.89; H, 4.07; N, 3.32 Found, C, 49.32; H, 4.17; N, 3.25

Calc. for C35H34Cl2N2O2P2Pt, C, 49.89; H, 4.07; N, 3.32 Found, C, 49.28; H, 4.05; N, 2.91

Calc. for C35H34Cl2N2O2P2Pt.0.5C4H10O, C, 50.52; H, 4.47; N, 3.19

**Chart 2.** Structures of compounds **4a**–**e**, **5a**–**g**, and **6**. **Chart 2.** Structures of compounds **4a**–**e**, **5a**–**g**, and **6**.

**Table 4.** Selected spectroscopic and analytical data for compounds **4a**–**6** a. **Table 4.** Selected spectroscopic and analytical data for compounds **4a**–**6** a


4.03 4.03 1.80 <sup>3050</sup>

3.17 4.05 2.17 <sup>3075</sup>

3.20 4.66 2.13 <sup>3323</sup>

7.53–7.44, 6.69 3.49 4.05 2.22 <sup>3051</sup>

4.33 2.09 3416 316, 284

(3249) 305, 283

(3350) 316, 283

(3347) 315, 290

(3465) 309, 283


**Table 4.** *Cont.*

a Isolated yields in parentheses. <sup>b</sup> Recorded in (CD3)2SO unless otherwise stated. <sup>c</sup> Recorded in CDCl3. d 1*J*(PtP) coupling in parentheses. <sup>e</sup> Recorded in CDCl3/CD3OD. <sup>f</sup> Recorded as KBr discs.

#### *2.5. Single Crystal X-ray Studies of Complexes* **4b**·*(CH3)2SO,* **4c**·*CHCl3,* **4d**· 1 2 *Et2O,* **4e**· 1 2 *CHCl3*· 1 2 *CH3OH,* **5a**· 1 2 *Et2O,* **5b***,* **5c**· 1 <sup>4</sup>*H2O,* **5d**·*Et2O, and* **6**·*(CH3)2SO*

Detailed single crystal X-ray analysis (Tables 5 and 6) of complexes **4b**·(CH3)2SO, **4c**·CHCl3, **4d**· 1 2 Et2O, **4e**· 1 <sup>2</sup>CHCl3· 1 <sup>2</sup>CH3OH, **5a**· 1 2 Et2O, **5b**, **5c**· 1 <sup>4</sup>H2O, **5d**·Et2O, and **6**·(CH3)2SO shows that the geometry about each Pt(II) centre is approximately square planar [P–Pt–P range 90.23(9)–96.52(3)◦ ] (Tables 7 and 8). The Pt–Cl and Pt–P bond distances are consistent with literature values [29] and the conformation of the Pt–P–C–N–C–P six-membered ring in each complex is best described as a boat. The dihedral angle measured between the P2C<sup>2</sup> plane and N-arene ring least-squares planes varies between 50.98(12)◦ [in **6**·(CH3)2SO] and 90◦ (in **5d**·Et2O), the difference of ca. 39◦ may tentatively be explained by the predisposition of the –OH group about the N-arene group and subsequent H-bonding requirements. Upon metal chelation, a degree of freedom, compared with the free ligands **1a**, **1b**·CH3OH, **2f**·CH3OH, **2g**, and **3** has been removed, as the P–C–N–C–P backbone is locked into a specific conformation. Unfortunately, we were unable to obtain suitable X-ray quality crystals of compounds **4a** and **5e**–**g**.


**Table 5.** Details of the X-ray data collections and refinements for compounds **4b**·**(CH3)2SO**, **4c**·**CHCl3**, **4d**· **1 <sup>2</sup>OEt2**, and **4e**· **1 <sup>2</sup>CHCl3**· **1 <sup>2</sup>CH3OH**.

<sup>a</sup> *<sup>R</sup>* <sup>=</sup> <sup>∑</sup>||*F*o| <sup>−</sup> <sup>|</sup>*F*c||/∑|*F*o|. <sup>b</sup> *wR*2 = [∑[*w*(*F*<sup>o</sup> <sup>2</sup> <sup>−</sup> *<sup>F</sup>*<sup>c</sup> 2 ) 2 ]/∑[*w*(*F*o 2 ) 2 ]]1/2 .

**Table 6.** Details of the X-ray data collections and refinements for compounds **5a <sup>1</sup> <sup>2</sup>OEt2**, **5b**, **5c**· **1 <sup>4</sup>H2O**, **5d OEt2**, and **6 (CH3)2SO**.



**Table 6.** *Cont.*

<sup>a</sup> *<sup>R</sup>* <sup>=</sup> <sup>∑</sup>||*F*o| <sup>−</sup> <sup>|</sup>*F*c||/∑|*F*o|. <sup>b</sup> *wR*2 = [∑[*w*(*F*<sup>o</sup> <sup>2</sup> <sup>−</sup> *<sup>F</sup>*<sup>c</sup> 2 ) 2 ]/∑[*w*(*F*o 2 ) 2 ]]1/2 .

**Table 7.** Selected bond distances and angles for dichloroplatinum(II) compounds **4b**·**(CH3)2SO**, **4c**·**CHCl3**, **4d**, and **4e**· **1 <sup>2</sup>CHCl3**· **1 <sup>2</sup>CH3OH**.


<sup>a</sup> Values in parentheses are for the second independent molecule.

**Table 8.** Selected bond distances and angles for dichloroplatinum(II) compounds **5a**· **1 <sup>2</sup>OEt2**, **5b**, **5c**· **1 <sup>4</sup>H2O**, **5d**·**OEt2**, and **6**·**(CH3)2SO**.


<sup>a</sup> Values in parentheses are for the second independent molecule. <sup>b</sup> 2-fold disorder. <sup>c</sup> Molecule lies on a mirror plane.

Despite the *ortho* position of the hydroxy group in **4c**·CHCl3, molecules do not form an intramolecular *S*(5) O–H···N interaction as seen in **1a** (Figure 1), instead forming a bifurcated H-bond with the two coordinated chloride ligands of an adjacent molecule (Figure 6). This generates a 1D chain, and also attracts a bifurcated H-bonded chloroform

Observed reflections

Largest difference map

a

molecule. There are somewhat asymmetric distances *d* for H(1C) to Cl(1) and Cl(2) are 2.45(4) and 2.76(4) Å, while those from H(34) to Cl(1) and Cl(2) are 2.66 and 2.86 Å, so are also asymmetric. The twist angle between planes P(1)/P(2)/C(1)/C(2) and ring C(3) > C(8) is 84.83(8)◦ , so is almost perpendicular. Atoms N(1) and Pt(1) lie 0.795(4) and 0.024(2) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively. The hinge angle across the P(1)–P(2) vector is 2.51(5)◦ . Selected hydrogen bonding geometric parameters for **4c**·CHCl<sup>3</sup> are shown in Table 9. *Molecules* **2021**, *26*, x FOR PEER REVIEW 11 of 22

**Figure 6.** H-bonded packing arrangement in the crystal structure of **4c**∙CHCl3. Most H atoms omitted for clarity. Symmetry operator A = x+½, –y+½, z+½. **Figure 6.** H-bonded packing arrangement in the crystal structure of **4c**·CHCl<sup>3</sup> . Most H atoms omitted for clarity. Symmetry operator A = x+<sup>1</sup> 2 , –y+<sup>1</sup> 2 , z+<sup>1</sup> 2 .

**Table 5.** Details of the X-ray data collections and refinements for compounds **4b·(CH3)2SO**, **4c·CHCl3**, **4d·½OEt2**, and **4e·½CHCl3·½CH3OH**. **Table 9.** Selected data (*D*···*A*/Å, ∠*D*–H···*A*/ ◦ ) for key inter- and intramolecular contacts for compounds **4b**·**(CH3)2SO**, **4c**·**CHCl3**, **4e**· **1 <sup>2</sup>CHCl3**· **1 <sup>2</sup>CH3OH**, 5**a**· **1 <sup>2</sup>OEt2**, **5b**, **5c**· **1 <sup>4</sup>H2O**, **5d**·**OEt2**, and **6**·**(CH3)2SO**.


Density (calcd.)/Mg/m3 1.657 1.713 1.458 1.735 μ/mm−1 4.391 4.500 3.425 4.666 <sup>a</sup> Values in parentheses are for the second independent molecule. <sup>b</sup> For the major disorder component; 2.658(12), 117 for the minor component.

θ range/° 1.79–26.09 1.67–31.09 1.78–31.10 2.94–27.49 Measured reflections 29848 32600 48268 84353 Independent reflections 6852 10997 13239 15063 (*F*2 > 2*σ*(*F*2)) 5560 8926 10918 12905 Compound **6**·(CH3)2SO, in which the –OH group is *meta* to the N-arene group Hbonds to the DMSO molecule of crystallisation resulting in a 0D structure (Figure 7). The distance *d* for this H-bond is 1.79(2) Å. The twist angle between plane P(1)/P(2)/C(1)/C(2) and ring C(3) > C(8) is 50.98(12)◦ . Atoms N(1) and Pt(1) lie 0.758(4) and 0.404(2) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively, so is more chair-shaped than some of the

> 2 − *F*c 2 ) 2 ]/∑[*w*(*F*o 2 ) 2 ]]1/2 .

*<sup>R</sup>* = ∑||*F*o| − |*F*c||/∑|*F*o|. <sup>b</sup> *wR*2 = [∑[*w*(*F*<sup>o</sup>

*R*int 0.110 0.043 0.039 0.049 *R*[*F*2 > 2*σ*(*F*2)] a 0.0473 0.0303 0.0266 0.0561 *wR*2 [all data] b 0.1015 0.0660 0.0646 0.1202

other platinum(II) complexes reported here. The hinge angle across the P(1)–P(2) vector is 11.87(13)◦ . other platinum(II) complexes reported here. The hinge angle across the P(1)–P(2) vector is 11.87(13)°. 11.87(13)°.

and ring C(3) > C(8) is 50.98(12)°. Atoms N(1) and Pt(1) lie 0.758(4) and 0.404(2) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively, so is more chair-shaped than some of the

and ring C(3) > C(8) is 50.98(12)°. Atoms N(1) and Pt(1) lie 0.758(4) and 0.404(2) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively, so is more chair-shaped than some of the other platinum(II) complexes reported here. The hinge angle across the P(1)–P(2) vector is

*Molecules* **2021**, *26*, x FOR PEER REVIEW 14 of 22

*Molecules* **2021**, *26*, x FOR PEER REVIEW 14 of 22

**Figure 7.** Crystal structure of **6**∙(CH3)2SO showing the hydroxyl group H-bonding to the (CH3)2SO molecule of crystallisation. Most H-atoms omitted for clarity. **Figure 7.** Crystal structure of **6**·(CH<sup>3</sup> )2SO showing the hydroxyl group H-bonding to the (CH<sup>3</sup> )2SO molecule of crystallisation. Most H-atoms omitted for clarity. molecule of crystallisation. Most H-atoms omitted for clarity.

For **4d**∙½Et2O (Figure 8) a molecule of badly disordered diethyl ether, modelled by

For **4d**∙½Et2O (Figure 8) a molecule of badly disordered diethyl ether, modelled by the Platon Squeeze procedure, is not shown, but is in the vicinity of the hydroxy group and may H-bond to it resulting in a 0D structure. The twist angle between plane P(1)/P(2)/C(1)/C(2) and ring C(3) > C(8) is 67.82(7)°. Atoms N(1) and Pt(1) lie 0.797(3) and 0.2378(16) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively. The hinge angle across For **4d**· 1 2 Et2O (Figure 8) a molecule of badly disordered diethyl ether, modelled by the Platon Squeeze procedure, is not shown, but is in the vicinity of the hydroxy group and may H-bond to it resulting in a 0D structure. The twist angle between plane P(1)/P(2)/C(1)/C(2) and ring C(3) > C(8) is 67.82(7)◦ . Atoms N(1) and Pt(1) lie 0.797(3) and 0.2378(16) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively. The hinge angle across the P(1)–P(2) vector is 9.20(9)◦ . the Platon Squeeze procedure, is not shown, but is in the vicinity of the hydroxy group and may H-bond to it resulting in a 0D structure. The twist angle between plane P(1)/P(2)/C(1)/C(2) and ring C(3) > C(8) is 67.82(7)°. Atoms N(1) and Pt(1) lie 0.797(3) and 0.2378(16) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively. The hinge angle across the P(1)–P(2) vector is 9.20(9)°.

**Figure 8.** Crystal structure of **4d**∙½Et2O. Most H atoms and the disordered OEt2 molecule omitted **Figure 8.** Crystal structure of **4d**∙½Et2O. Most H atoms and the disordered OEt2 molecule omitted for clarity. **Figure 8.** Crystal structure of **4d**· 1 2 Et2O. Most H atoms and the disordered OEt<sup>2</sup> molecule omitted for clarity.

for clarity. The crystal structure of **4b**∙(CH3)2SO shows the hydroxy group H-bonding to the DMSO molecule of crystallisation (Figure 9a). The distance *d* for this H-bond is 1.89 Å. The twist angle between plane P(1)/P(2)/C(1)/C(2) and ring C(3) > C(8) is 72.2(4)°. Atoms N(1) and Pt(1) lie 0.781(17) and 0.180(10) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively. The hinge angle across the P(1)–P(2) vector is 8.7(6)°. Molecules form 1D, weakly H-bonded, undulating chains in the *c* direction via the methylene H atoms on C(1) The crystal structure of **4b**∙(CH3)2SO shows the hydroxy group H-bonding to the DMSO molecule of crystallisation (Figure 9a). The distance *d* for this H-bond is 1.89 Å. The twist angle between plane P(1)/P(2)/C(1)/C(2) and ring C(3) > C(8) is 72.2(4)°. Atoms N(1) and Pt(1) lie 0.781(17) and 0.180(10) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively. The hinge angle across the P(1)–P(2) vector is 8.7(6)°. Molecules form 1D, weakly H-bonded, undulating chains in the *c* direction via the methylene H atoms on C(1) and C(2) to a single, coordinated chloride ligand in an adjacent molecule (Figure 9b). Se-The crystal structure of **4b**·(CH3)2SO shows the hydroxy group H-bonding to the DMSO molecule of crystallisation (Figure 9a). The distance *d* for this H-bond is 1.89 Å. The twist angle between plane P(1)/P(2)/C(1)/C(2) and ring C(3) > C(8) is 72.2(4)◦ . Atoms N(1) and Pt(1) lie 0.781(17) and 0.180(10) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively. The hinge angle across the P(1)–P(2) vector is 8.7(6)◦ . Molecules form 1D, weakly H-bonded, undulating chains in the *c* direction via the methylene H atoms on C(1) and C(2) to a single, coordinated chloride ligand in an adjacent molecule (Figure 9b). Selected hydrogen bonding parameters for **4b**·(CH3)2SO are shown in Table 9.

lected hydrogen bonding parameters for **4b**∙(CH3)2SO are shown in Table 9.

and C(2) to a single, coordinated chloride ligand in an adjacent molecule (Figure 9b). Se-

(**b**)

**Figure 9.** (**a**) Crystal structure of **4b**∙(CH3)2SO showing the hydroxyl group H-bonding to the DMSO molecule of crystallisation. Most H-atoms removed for clarity. (**b**) Packing interactions in the crystal structure of **4b**∙(CH3)2SO. Most H atoms omitted for clarity. Symmetry operator A = y − 1, 1 − x, ¼ + z. **Figure 9.** (**a**) Crystal structure of **4b**·(CH<sup>3</sup> )2SO showing the hydroxyl group H-bonding to the DMSO molecule of crystallisation. Most H-atoms removed for clarity. (**b**) Packing interactions in the crystal structure of **4b**·(CH<sup>3</sup> )2SO. Most H atoms omitted for clarity. Symmetry operator A = y <sup>−</sup> 1, 1 <sup>−</sup> x, <sup>1</sup> 4 + z.

For compound **4e**∙½CHCl3∙½CH3OH there are two independent Pt complexes, one CH3OH, and one CHCl3 in the asymmetric unit. Both Pt complexes form 1D chains aligned parallel to *b*, but these chains are different (Figure 10). The chain involving Pt(2) forms simple O–H∙∙∙Cl H-bonds with the adjacent molecules via the *para* hydroxy group with *d* = 2.39(4) Å. For the chain involving the Pt(1)-containing molecules, the intermolecular Hbond has an inserted methanol molecule. The distances, *d*, are 2.32(5) and 1.82 Å for H(3)∙∙∙Cl(2) and H(1A)∙∙∙O(3), respectively. Atoms N(1)/N(2) and Pt(1)/Pt(2) lie 0.765(9)/0.798(9) and 0.424(5)/0.364(5) Å away from the P(1)/P(2)/C(1)/C(2) or P(3)/P(4)/C(34)/C(35) planes, respectively. So, as in **6**∙(CH3)2SO, the core 6-membered Pt– P–C–N–C–P rings adopt more chair-shaped conformations. The hinge angles across the P(1)–P(2)/P(3)–P(4) vectors are 13.44(16)/12.47(16)°. The twist angles between planes P(1)/P(2)/C(1)/C(2) or P(3)/P(4)/C(34)/C(35) and rings C(3) > C(8) or C(36) > C(41) are 88.17(19)/54.62(15)°. So, while the other geometric parameters are similar between the two For compound **4e**· 1 <sup>2</sup>CHCl3· 1 <sup>2</sup>CH3OH there are two independent Pt complexes, one CH3OH, and one CHCl<sup>3</sup> in the asymmetric unit. Both Pt complexes form 1D chains aligned parallel to *b*, but these chains are different (Figure 10). The chain involving Pt(2) forms simple O–H···Cl H-bonds with the adjacent molecules via the *para* hydroxy group with *d* = 2.39(4) Å. For the chain involving the Pt(1)-containing molecules, the intermolecular H-bond has an inserted methanol molecule. The distances, *d*, are 2.32(5) and 1.82 Å for H(3)···Cl(2) and H(1A)···O(3), respectively. Atoms N(1)/N(2) and Pt(1)/Pt(2) lie 0.765(9)/0.798(9) and 0.424(5)/0.364(5) Å away from the P(1)/P(2)/C(1)/C(2) or P(3)/P(4) /C(34)/C(35) planes, respectively. So, as in **6**·(CH3)2SO, the core 6-membered Pt–P–C–N–C– P rings adopt more chair-shaped conformations. The hinge angles across the P(1)–P(2)/P(3)– P(4) vectors are 13.44(16)/12.47(16)◦ . The twist angles between planes P(1)/P(2)/C(1)/C(2) or P(3)/P(4)/C(34)/C(35) and rings C(3) > C(8) or C(36) > C(41) are 88.17(19)/54.62(15)◦ . So, while the other geometric parameters are similar between the two molecules, this twist angle is significantly different.

molecules, this twist angle is significantly different.

**Figure 10.** H-bonded packing motifs in the crystal structure of **4e**∙½CHCl3∙½CH3OH. Most H atoms, two Ph groups per P atom, and the disordered chloroform of crystallisation which is not involved in any significant intermolecular interactions, are omitted for clarity. Symmetry operators are x, y − 1, z and x, y + 1, z. **Figure 10.** H-bonded packing motifs in the crystal structure of **4e**· 1 <sup>2</sup>CHCl<sup>3</sup> · 1 <sup>2</sup>CH3OH. Most H atoms, two Ph groups per P atom, and the disordered chloroform of crystallisation which is not involved in any significant intermolecular interactions, are omitted for clarity. Symmetry operators are x, y − 1, z and x, y + 1, z.

In **5c**, the amide and ring atoms from C(4) > C(11) are disordered over two sets of almost equally occupied positions. The disorder highlights two or more chain-forming possibilities for this structure, analogous to that observed in in **4e**∙½CHCl3∙½CH3OH, with one possibility being simple (hydroxyl)O–H∙∙∙O(amide) links (Figure 11a), while the other, shown in Figure 11b, shows an alternative, water-inserted linkage. There is also likely to be some alternation of these motifs, given the random disorder and approx. 25% occupancy observed for water atom O(3). Unlike almost all of the other structures herein, the core 6-membered Pt–P–C–N–C–P ring adopts a conformation with atoms Pt(1)/P(1)/P(1)/C(2) being in a plane and atoms C(1) and N(2) being 1.021(6) and 1.237(6) Å, respectively, away from that plane. There is no C=O∙∙∙HN intermolecular H-bonding observed between molecules. Instead, the amide N*H* forms a bifurcated H-bond with the two neighbouring acceptor atoms N(1) and the *ortho* hydroxyl O(2) with *d* = 2.37 and 2.28 Å, respectively, while *d* = 2.89 Å for H(2)∙∙∙O(1A). In the second motif, adjacent molecules have an inserted water molecule in the Hbond pattern (Figure 11b). The amide N*H* again forms a bifurcated H-bond with the two neighbouring acceptor atoms N(1) and O(2X) with *d* = 2.14 and 2.25 Å, respectively, while In **5c**, the amide and ring atoms from C(4) > C(11) are disordered over two sets of almost equally occupied positions. The disorder highlights two or more chain-forming possibilities for this structure, analogous to that observed in in **4e**· 1 <sup>2</sup>CHCl3· 1 <sup>2</sup>CH3OH, with one possibility being simple (hydroxyl)O–H···O(amide) links (Figure 11a), while the other, shown in Figure 11b, shows an alternative, water-inserted linkage. There is also likely to be some alternation of these motifs, given the random disorder and approx. 25% occupancy observed for water atom O(3). Unlike almost all of the other structures herein, the core 6-membered Pt–P–C–N–C–P ring adopts a conformation with atoms Pt(1)/P(1)/P(1)/C(2) being in a plane and atoms C(1) and N(2) being 1.021(6) and 1.237(6) Å, respectively, away from that plane. There is no C=O···HN intermolecular H-bonding observed between molecules. Instead, the amide N*H* forms a bifurcated H-bond with the two neighbouring acceptor atoms N(1) and the *ortho* hydroxyl O(2) with *d* = 2.37 and 2.28 Å, respectively, while *d* = 2.89 Å for H(2)···O(1A). *Molecules* **2021**, *26*, x FOR PEER REVIEW 17 of 22

**Figure 11.** Most H atoms and 2 Ph groups per P atom have been omitted for clarity. (**a**) Packing motif 1 in the crystal structure of **5c**. Symmetry operator A = x + 1, y, z. (**b**) Packing motif 2 in the crystal structure of **5c**. The true structure is most likely an alternation of motifs 1 and 2. Symmetry operator A = x + 1, y, z. **Figure 11.** Most H atoms and 2 Ph groups per P atom have been omitted for clarity. (**a**) Packing motif 1 in the crystal structure of **5c**. Symmetry operator A = x + 1, y, z. (**b**) Packing motif 2 in the crystal structure of **5c**. The true structure is most likely an alternation of motifs 1 and 2. Symmetry operator A = x + 1, y, z.

Complex **5a**∙½Et2O was crystallised from a diethyl ether solution, including half a solvent molecule per complex molecule in the crystal lattice. There are two Pt complexes

The packing adopted by this second complex with an *ortho* hydroxyl group is very different to **5c** (Figure 12). Here there is no intramolecular N–H∙∙∙N H-bond, instead the ortho hydroxyl forms an intramolecular H-bond with the amide oxygen with *d* = 1.80 and 1.77(4) Å in the molecules containing Pt(1) and Pt(2), respectively. This does leave the two unique amide N*H* atoms free to form intermolecular interactions, which they do via highly asymmetric, bifurcated H-bonds with the coordinated chloride ligands on adjacent Pt complexes. From H(2) *d* = 2.60(11) and 2.95(13) Å to Cl(3) and Cl(4), respectively, while *d* = 2.52(7) and 3.12(15) Å from H(4) to Cl(1A) and Cl(2A), respectively. N(1)/N(3) and Pt(1)/Pt(2) lie 0.771(13)/0.781(14) and 0.349(8)/0.346(8) Å out of the planes P(1)/P(2)/C(1)/C(2) and P(3)/P(4)/C(37)/C(38), respectively. The twist angle between planes P(1)/P(2)/C(1)/C(2) and P(3)/P(4)/C(37)/C(38) relative to the rings C(5) > C(10) and C(41) > C(46) are 51.3(5) and 51.71(4)°, respectively. Hinge angles across P(1)–P(2) and P(3)–P(4) are 12.3(5) and 12.0(4)°, respectively. Differences between the two systems involving *ortho* hydroxyl groups are the position of the methyl ring substituent in the *meta* or *para* position, and the co-crystallised solvent being a small amount of water or Et2O. Either, or both of these differences might account for the different intra- and intermolecular packing motifs observed. Selected hydrogen bonding parameters for **5a**∙½Et2O are

shown in Table 9.

In the second motif, adjacent molecules have an inserted water molecule in the Hbond pattern (Figure 11b). The amide N*H* again forms a bifurcated H-bond with the two neighbouring acceptor atoms N(1) and O(2X) with *d* = 2.14 and 2.25 Å, respectively, while *d* = 2.89 Å for H(2X)···O(3), which is a little long, and *d* for O(3)···O(1XA) = 2.21(3) Å, which is rather short. The distance *d* from water oxygen O(3) to O(1A), however, is entirely reasonable for an H-bond at 2.74 Å, suggesting a predominantly alternating pattern between the two disorder options is most likely.

Complex **5a**· 1 2 Et2O was crystallised from a diethyl ether solution, including half a solvent molecule per complex molecule in the crystal lattice. There are two Pt complexes and two, half-occupied, Et2O solvent molecules of crystallisation in the asymmetric unit. The packing adopted by this second complex with an *ortho* hydroxyl group is very different to **5c** (Figure 12). Here there is no intramolecular N–H···N H-bond, instead the ortho hydroxyl forms an intramolecular H-bond with the amide oxygen with *d* = 1.80 and 1.77(4) Å in the molecules containing Pt(1) and Pt(2), respectively. This does leave the two unique amide N*H* atoms free to form intermolecular interactions, which they do via highly asymmetric, bifurcated H-bonds with the coordinated chloride ligands on adjacent Pt complexes. From H(2) *d* = 2.60(11) and 2.95(13) Å to Cl(3) and Cl(4), respectively, while *d* = 2.52(7) and 3.12(15) Å from H(4) to Cl(1A) and Cl(2A), respectively. N(1)/N(3) and Pt(1)/Pt(2) lie 0.771(13)/0.781(14) and 0.349(8)/0.346(8) Å out of the planes P(1)/P(2)/C(1)/C(2) and P(3)/P(4)/C(37)/C(38), respectively. The twist angle between planes P(1)/P(2)/C(1)/C(2) and P(3)/P(4)/C(37)/C(38) relative to the rings C(5) > C(10) and C(41) > C(46) are 51.3(5) and 51.71(4)◦ , respectively. Hinge angles across P(1)–P(2) and P(3)–P(4) are 12.3(5) and 12.0(4)◦ , respectively. Differences between the two systems involving *ortho* hydroxyl groups are the position of the methyl ring substituent in the *meta* or *para* position, and the co-crystallised solvent being a small amount of water or Et2O. Either, or both of these differences might account for the different intra- and intermolecular packing motifs observed. Selected hydrogen bonding parameters for **5a**· 1 2 Et2O are shown in Table 9. *Molecules* **2021**, *26*, x FOR PEER REVIEW 18 of 22

**Figure 12.** Packing motif in the crystal structure of **5a**∙½Et2O. Most H atoms, two Ph groups per P atom and the two, half-occupied, Et2O molecules have been omitted for clarity. **Figure 12.** Packing motif in the crystal structure of **5a**· 1 2 Et2O. Most H atoms, two Ph groups per P atom and the two, half-occupied, Et2O molecules have been omitted for clarity.

Molecules of **5d**∙Et2O lie on a mirror plane, passing through Pt(1), between pairs of P and Cl atoms, and including the atoms from N(1) to the terminal hydroxy-substituted ring. Again, here the amide N*H* is involved in the 1D chain propagation (Figure 13), forming a symmetrical bifurcated H-bond with the two coordinated chloride ligands on the adjacent molecule with *d* = 2.66(15) Å. Supporting this is an additional (Ar)C–H(5)∙∙∙Pt(1) interaction at 2.78 Å. The twist angle between the P(1)/P(1A)/C(1)/C(1A) plane and the ring C(4) > C(9) = 90° due to the imposed crystallographic symmetry. The hinge angle at P(1)–P(1A) = 29.5(5)°. Atoms N(1) and Pt(1) lie 0.79(2) and 0.782(14) Å away from the Molecules of **5d**·Et2O lie on a mirror plane, passing through Pt(1), between pairs of P and Cl atoms, and including the atoms from N(1) to the terminal hydroxy-substituted ring. Again, here the amide N*H* is involved in the 1D chain propagation (Figure 13), forming a symmetrical bifurcated H-bond with the two coordinated chloride ligands on the adjacent molecule with *d* = 2.66(15) Å. Supporting this is an additional (Ar)C–H(5)···Pt(1) interaction at 2.78 Å. The twist angle between the P(1)/P(1A)/C(1)/C(1A) plane and the ring C(4) > C(9) = 90◦ due to the imposed crystallographic symmetry. The hinge angle at P(1)–P(1A) = 29.5(5)◦ . Atoms N(1) and Pt(1) lie 0.79(2) and 0.782(14) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively. So, this is the most chair shaped core

P(1)/P(2)/C(1)/C(2) plane, respectively. So, this is the most chair shaped core Pt–P–C–N–

**Figure 13.** Packing plot of **5d**∙Et2O. Most H atoms, two Ph groups per P atom, and a diordered Et2O molecule modelled by the Platon Squeeze procedure, are omitted for clarity. Symmetry operators:

For compound **5b**, the *para* position of the hydroxyl group facilitates 1D chain formation, forming an H-bond with one of the chloride ligands on an adjacent molecule with *d* = 2.09(6) Å (Figure 14). The amide N*H* here forms the familiar, but not universal, H-bond with the amine N(1) with *d* = 2.29(5) Å. The twist angle between the P(1)/P(2)/C(1)/C(2) plane and the ring C(5) > C(10) = 68.39(12)°. The hinge angle at P(1)–P(1A) = 4.95(10)°. Atoms N(1) and Pt(1) lie 0.810(4) and 0.164(3) Å away from the P(1)/P(2)/C(1)/C(2) plane,

(i) for the mirror x, y, −z + ½, (ii) for the chain direction x + 1, y, z.

respectively.

make an H-bond with the solvent of crystallisation.

Pt–P–C–N–C–P 6-membered ring. The *meta* hydroxyl group is not involved in the chain propagating intermolecular interactions and points into a cleft between a pair of Ph rings. It does not make an H-bond with the solvent of crystallisation. C–P 6-membered ring. The *meta* hydroxyl group is not involved in the chain propagating intermolecular interactions and points into a cleft between a pair of Ph rings. It does not make an H-bond with the solvent of crystallisation.

**Figure 12.** Packing motif in the crystal structure of **5a**∙½Et2O. Most H atoms, two Ph groups per P

Molecules of **5d**∙Et2O lie on a mirror plane, passing through Pt(1), between pairs of P and Cl atoms, and including the atoms from N(1) to the terminal hydroxy-substituted ring. Again, here the amide N*H* is involved in the 1D chain propagation (Figure 13), forming a symmetrical bifurcated H-bond with the two coordinated chloride ligands on the adjacent molecule with *d* = 2.66(15) Å. Supporting this is an additional (Ar)C–H(5)∙∙∙Pt(1) interaction at 2.78 Å. The twist angle between the P(1)/P(1A)/C(1)/C(1A) plane and the ring C(4) > C(9) = 90° due to the imposed crystallographic symmetry. The hinge angle at P(1)–P(1A) = 29.5(5)°. Atoms N(1) and Pt(1) lie 0.79(2) and 0.782(14) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively. So, this is the most chair shaped core Pt–P–C–N–

atom and the two, half-occupied, Et2O molecules have been omitted for clarity.

*Molecules* **2021**, *26*, x FOR PEER REVIEW 18 of 22

**Figure 13.** Packing plot of **5d**∙Et2O. Most H atoms, two Ph groups per P atom, and a diordered Et2O molecule modelled by the Platon Squeeze procedure, are omitted for clarity. Symmetry operators: (i) for the mirror x, y, −z + ½, (ii) for the chain direction x + 1, y, z. **Figure 13.** Packing plot of **5d**·Et2O. Most H atoms, two Ph groups per P atom, and a diordered Et2O molecule modelled by the Platon Squeeze procedure, are omitted for clarity. Symmetry operators: (i) for the mirror x, y, <sup>−</sup>z + <sup>1</sup> 2 , (ii) for the chain direction x + 1, y, z.

For compound **5b**, the *para* position of the hydroxyl group facilitates 1D chain formation, forming an H-bond with one of the chloride ligands on an adjacent molecule with *d* = 2.09(6) Å (Figure 14). The amide N*H* here forms the familiar, but not universal, H-bond with the amine N(1) with *d* = 2.29(5) Å. The twist angle between the P(1)/P(2)/C(1)/C(2) plane and the ring C(5) > C(10) = 68.39(12)°. The hinge angle at P(1)–P(1A) = 4.95(10)°. Atoms N(1) and Pt(1) lie 0.810(4) and 0.164(3) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively. For compound **5b**, the *para* position of the hydroxyl group facilitates 1D chain formation, forming an H-bond with one of the chloride ligands on an adjacent molecule with *d* = 2.09(6) Å (Figure 14). The amide N*H* here forms the familiar, but not universal, H-bond with the amine N(1) with *d* = 2.29(5) Å. The twist angle between the P(1)/P(2)/C(1)/C(2) plane and the ring C(5) > C(10) = 68.39(12)◦ . The hinge angle at P(1)–P(1A) = 4.95(10)◦ . Atoms N(1) and Pt(1) lie 0.810(4) and 0.164(3) Å away from the P(1)/P(2)/C(1)/C(2) plane, respectively. *Molecules* **2021**, *26*, x FOR PEER REVIEW 19 of 22

**Figure 14.** Packing plot in the crystal structure of **5b**. Phenyl groups and hydrogen atoms not involved in hydrogen bonding have been omitted for clarity. **Figure 14.** Packing plot in the crystal structure of **5b**. Phenyl groups and hydrogen atoms not involved in hydrogen bonding have been omitted for clarity.

### **3. Conclusions**

**3. Conclusions**  In summary, we have shown that the position of the OH/CH3 groups with respect to the N-arene, the inclusion of an amide spacer, and the solvent used in the crystallisation can dictate the solid-state packing behaviour of both non coordinated and *cis*-PtCl2 bound diphosphine ligands. Unsurprisingly, the use of highly polar solvents (DMSO, CH3OH) in this study has been shown to play an important role in disrupting packing behaviour. Our work reinforces the importance of substituent effects, not only those commonly associated with −PR2 groups which may be alkyl or aryl based [37,38], but also those functional In summary, we have shown that the position of the OH/CH<sup>3</sup> groups with respect to the N-arene, the inclusion of an amide spacer, and the solvent used in the crystallisation can dictate the solid-state packing behaviour of both non coordinated and *cis*-PtCl<sup>2</sup> bound diphosphine ligands. Unsurprisingly, the use of highly polar solvents (DMSO, CH3OH) in this study has been shown to play an important role in disrupting packing behaviour. Our work reinforces the importance of substituent effects, not only those commonly associated with −PR<sup>2</sup> groups which may be alkyl or aryl based [37,38], but also those functional moieties positioned on the arene group of the central tertiary amine.

### **4. Materials and Methods**

#### **4. Materials and Methods**  *4.1. General Procedures*

*4.2. Instrumentation* 

*4.1. General Procedures*  The synthesis of ligands **1a**–**e**, **2a**–**g**, and **3** were undertaken using standard Schlenkline techniques and an inert nitrogen atmosphere. Ph2PCH2OH was prepared according to a known procedure [39]. All coordination reactions were carried out in air, using rea-The synthesis of ligands **1a**–**e**, **2a**–**g**, and **3** were undertaken using standard Schlenkline techniques and an inert nitrogen atmosphere. Ph2PCH2OH was prepared according to a known procedure [39]. All coordination reactions were carried out in air, using reagent grade quality solvents. The compound PtCl2(η 4 -cod) (cod = cycloocta-1,5-diene) was

gent grade quality solvents. The compound PtCl2(η4-cod)(cod = cycloocta-1,5-diene) was

Infrared spectra were recorded as KBr pellets on a Perkin-Elmer Spectrum 100S (4000–250 cm−1 range) Fourier-Transform spectrometer. 1H NMR spectra (400 MHz) were recorded on a Bruker DPX-400 spectrometer with chemical shifts (δ) in ppm to high frequency of Si(CH3)4 and coupling constants (*J*) in Hz. 31P{1H} NMR (162 MHz) spectra were recorded on a Bruker DPX-400 spectrometer with chemical shifts (δ) in ppm to high frequency of 85% H3PO4. NMR spectra were measured in CDCl3 or (CD3)2SO at 298 K. Elemental analyses (Perkin-Elmer 2400 CHN Elemental Analyser) were performed by the Loughborough University Analytical Service within the Department of Chemistry.

The following general procedure was used for the synthesis of **1a**–**e**, **2a**–**g**, and **3**. A mixture of Ph2PCH2OH (2 equiv.) and the appropriate amine (1 equiv.) in CH3OH (20 mL) was stirred under N2 for 24 h. The volume of the solution was evaporated to ca. 2–3 mL, under reduced pressure, to afford the desired ligands which were collected by suction filtration (except **2a**–**c**) and dried *in vacuo*. Isolated yields in range 38–97%. Characterising

*4.3. Preparation of Ligands 1a–e, 2a–g, and 3* 

details are given in Table 1.

commercial sources and used directly without further purification

moieties positioned on the arene group of the central tertiary amine.

prepared according to a known procedure [40]. All other chemicals were obtained from commercial sources and used directly without further purification

### *4.2. Instrumentation*

Infrared spectra were recorded as KBr pellets on a Perkin-Elmer Spectrum 100S (4000–250 cm−<sup>1</sup> range) Fourier-Transform spectrometer. <sup>1</sup>H NMR spectra (400 MHz) were recorded on a Bruker DPX-400 spectrometer with chemical shifts (δ) in ppm to high frequency of Si(CH3)<sup>4</sup> and coupling constants (*J*) in Hz. <sup>31</sup>P{1H} NMR (162 MHz) spectra were recorded on a Bruker DPX-400 spectrometer with chemical shifts (δ) in ppm to high frequency of 85% H3PO4. NMR spectra were measured in CDCl<sup>3</sup> or (CD3)2SO at 298 K. Elemental analyses (Perkin-Elmer 2400 CHN Elemental Analyser) were performed by the Loughborough University Analytical Service within the Department of Chemistry.

### *4.3. Preparation of Ligands* **1a***–***e***,* **2a***–***g***, and* **3**

The following general procedure was used for the synthesis of **1a**–**e**, **2a**–**g**, and **3**. A mixture of Ph2PCH2OH (2 equiv.) and the appropriate amine (1 equiv.) in CH3OH (20 mL) was stirred under N<sup>2</sup> for 24 h. The volume of the solution was evaporated to ca. 2–3 mL, under reduced pressure, to afford the desired ligands which were collected by suction filtration (except **2a**–**c**) and dried *in vacuo*. Isolated yields in range 38–97%. Characterising details are given in Table 1.

### *4.4. Preparation of cis-Dichloroplatinum(II) Phosphine Complexes* **4a***–***e***,* **5a***–***g***, and* **6**

The following general procedure was used for the synthesis of **4a**–**e**, **5a**–**g**, and **6**. To a solution of PtCl2(η 4 -cod) (1 equiv.) in CH2Cl<sup>2</sup> (5 mL) was added a solution of the appropriate ligand (1 equiv.) in CH2Cl<sup>2</sup> (5 mL). The colourless (or pale yellow) solution was stirred for 30 min at r.t., evaporated to ca. 2–3 mL under reduced pressure, and diethyl ether (10 mL) added. The solids were collected by suction filtration and dried *in vacuo*. Isolated yields in range 73–99%. Characterising details are given in Table 4.

### *4.5. Single Crystal X-ray Crystallography*

Suitable crystals of **1a**, **1b**·CH3OH, **2f**·CH3OH, and **3** were obtained by slow evaporation of a CH3OH solution whereas **2g** was obtained by vapour diffusion of Et2O into a CDCl3/CH3OH solution. Crystals of **4b**·(CH3)2SO, **5a**· 1 2 Et2O, **5b**, and **5c**· 1 <sup>4</sup>H2O were obtained by slow diffusion of Et2O into a CDCl3/(CH3)2SO/CH3OH solution. Slow diffusion of hexanes [for **6**·(CH3)2SO] into a CDCl3/(CH3)2SO solution or vapour diffusion of Et2O into a CHCl3/(CH3)2SO/CH3OH [for **4c**·CHCl3, **4e**· 1 <sup>2</sup>CHCl3· 1 <sup>2</sup>CH3OH) or CH2Cl2/CH3OH (for **5d**·Et2O)]. Slow evaporation of a CH2Cl2/Et2O/hexanes solution gave suitable crystals of **4d**· 1 2 Et2O. Tables 2, 5 and 6 summarise the key data collection and structure refinement parameters. Diffraction data for compounds **1a**, **1b**·CH3OH, **2f**·CH3OH **3**, **4b**·(CH3)2SO, **4c**·CHCl3, **4d 4e**· 1 <sup>2</sup>CHCl3· 1 <sup>2</sup>CH3OH, **5d**·Et2O, and **6**·(CH3)2SO, were collected using a Bruker or Bruker-Nonius APEX 2 CCD diffractometer using graphitemonochromated Mo-K<sup>α</sup> radiation. Data for compounds **5b** and **5c**· 1 <sup>4</sup>H2O, were collected using a Bruker APEX 2 CCD diffractometer using synchrotron radiation at Daresbury SRS Station 9.8 or 16.2 SMX for **5a**· 1 2 Et2O. Data for compound **2g** was collected using a Bruker SMART 1000 CCD diffractometer using graphite-monochromated Mo-K<sup>α</sup> radiation. All structures were solved by direct methods [except structures **4b**·(CH3)2SO, **5a**· 1 2 Et2O, and **5b** which were solved using Patterson synthesis] and refined by full-matrix least-squares methods on *F* 2 . All C*H* atoms were placed in geometrically calculated positions and were refined using a riding model (aryl C–H 0.95 Å, methyl C–H 0.98 Å, methylene C–H 0.99 Å. Where data quality allowed, O*H* and N*H* atom coordinates and *U*iso were freely refined, or refined with mild geometrical restraints; otherwise, they were placed geometrically with O/N–H = 0.84 Å. *U*iso(*H*) values were set to be 1.2 times *U*eq of the carrier atom for aryl C*H* and N*H*, and 1.5 times *U*eq of the carrier atom for O*H* and C*H*3. Throughout the text and tabulated data, where H atom geometry does not include a SU, the coordinates were

constrained. Unless stated, all structural determinations proceeded without the need for restraints or disorder modelling. Where disorder was modelled it was supported with appropriate geometrical and *U* value restraints. In **1b**·CH3OH, the methanol was modelled as disordered over two equally occupied sets of positions. In **2f**·CH3OH the methanol was modelled using the Platon Squeeze procedure [41]. Compound **3** was found to contain a disordered methanol and was modelled over two sets of positions, each at half weight. In **4d**· 1 2 Et2O, atoms C(1) > C(7) and N(1) were modelled with *U* value restraints. The Et2O was modelled using Platon Squeeze due to significant disorder. In **4e**· 1 <sup>2</sup>CHCl3· 1 <sup>2</sup>CH3OH the chloroform molecule was modelled over two sets of positions with major occupancy 57.1(7)% Restraints were applied to that molecule and also ring C(55) > C(60). In **5a**· 1 2 Et2O three Ph rings were modelled as disordered over two sets of positions with occupancies close to 50%. Restraints were applied to these rings and also the two half-occupancy Et2O solvent molecules of crystallisation. In **5c**· 1 <sup>4</sup>H2O, atoms Cl(1) and C(3) > C(11), O(1), O(2) and N(1) were modelled as split over two sets of positions with major occupancy 56(4) and 50.9(6)%, respectively and restraints were applied. In **5d**·Et2O the Et2O was modelled as a diffuse area of electron density by the Platon Squeeze procedure and restraints were applied to atoms C(1) > C(10), C(11) > C(22) and N(2) O(2). In **6**·(CH3)2SO the DMSO was modelled with restraints as disordered over two sets of positions with major component 71.0(5)% and with C(33) coincident for both components Programs used during data collection, refinement and production of graphics were Bruker SMART, Bruker APEX 2, SAINT, SHELXTL, COLLECT, DENZO and local programs [41–51]. CCDC 2101643-2101656 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures (accessed on 3 November 2021).

**Author Contributions:** Conceptualisation, M.B.S.; synthesis and characterisation of the compounds, N.M.S.-B., P.D.; single crystal X-ray crystallography, N.M.S.-B., M.R.J.E.; writing-original draft preparation, M.B.S.; writing-review and editing, M.R.J.E., M.B.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** We thank the EPSRC Centre for Doctoral Training in Embedded Intelligence under grant reference EP/L014998/1 for financial support (PD). Johnson Matthey are acknowledged for their kind donation of precious metals and the UK National Crystallography Service at the University of Southampton for three of the data collections. The STFC is thanked for the allocation of beam time at Daresbury Laboratory.

**Conflicts of Interest:** The authors declare no conflict of interest.

**Sample Availability:** Samples of the compounds in this article are not available from the authors.

### **References**

