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Article

Studies Toward Persilylation of π-Cyclopentadienyl Complexes of Fe and Ru. Molecular Structures of [Fe(C5H5){C5(SiMe2H)5}], [Fe(C5H5){C5Br3(SiMe3)2}] and [Fe(C5H5){C5Br2(SiMe3)3}]

by
Stefanie Bernhartzeder
,
Tobias Blockhaus
,
Markus Lang
and
Karlheinz Sünkel
*
Department Chemistry, Ludwig Maximilians University Munich, 81377 Munich, Germany
*
Author to whom correspondence should be addressed.
Inorganics 2025, 13(2), 42; https://doi.org/10.3390/inorganics13020042
Submission received: 28 December 2024 / Revised: 24 January 2025 / Accepted: 27 January 2025 / Published: 1 February 2025
(This article belongs to the Special Issue State-of-the-Art Inorganic Chemistry in Germany)
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Abstract

:
Increasing the number of SiMe3 substituents on a cyclopentadienyl ring has, in addition to a stabilizing effect of unusual coordination geometries and oxidation states, the effect of increasing the solubility in unpolar solvents and increasing the volatility. Starting from pentabromoferrocene and pentabromo(pentamethyl)ruthenocene, we could achieve the introduction of up to five silyl (SiMe2H or SiMe3) groups to give [Fe(C5H5){C5(SiMe2R)5}], R = H, Me, and [Ru(C5Me5){C5(SiMe2H)5}]. However, yields were very low, and nearly all intermediate steps afforded mixtures of similar silyl-substituted compounds, which were difficult to separate. The crystal structures of [Fe(C5H5){C5(SiMe2H)5}] (13a), [Fe(C5H5){C5Br3(SiMe3)2}] (4b), and [Fe(C5H5){C5Br2(SiMe3)3}] (8b) were determined.

1. Introduction

Trimethylsilyl (SiMe3) groups have been introduced as substituents into π-cyclopentadienyl groups mainly because of three reasons: Firstly, SiMe3 groups are supposed to increase the solubility in unpolar solvents, and, for example, it was possible to prepare hexane-soluble ionic titanocene derivatives with a {C5H2(SiMe3)3} ligand [1]. However, such a high solubility in unpolar solvents does not always occur [2]. Second, the volatility of such complexes is significantly raised, which is important for possible OMCVD (organometallic chemical vapor deposition) applications [3,4,5,6]. Third, and most important, the increasing bulkiness with the increasing number of SiMe3 substituents has allowed for the synthesis of rather stable compounds with unusual coordination geometries, magnetic properties, and oxidation states using the {C5H2(SiMe3)3} ligand. For example, the stabilization of [Fe(C5R5)X] [7], [Cu(C5R5)(PBu3)] [8], [Cr(C5R5)2] [9], [Mn(C5R5)2] [10], [(Ca, Sr, Ba)(C5R5)2] [11], and several lanthanoid (Y, Dy, Ce) [12,13] or uranium complexes [14] was possible using the tris(trimethylsilyl)cyclopentadienyl ligand. On the other hand, it has been shown that multiple substitution with SiMe3 substituents has hardly any influence on the electronic properties including the redox potentials [15]. What is obvious is the fact that none of these complexes contain more than three SiMe3 ligands per cyclopentadienyl ring, and, in general, they are in 1,2,4 position of the Cp ring. Thus, the question arises, why? One obvious reason is the ease of synthesis. All these compounds could be prepared by standard salt metathesis reactions between a metal halide and an alkali metal salt (Li, Na, or K) of 1,2,4-tris(trimethylsilyl)cyclopentadiene, which can easily be prepared, and which for some time was even commercially available. The two regio-isomers 1,1′,2,2′,4,4′- and 1,1′,2,2′,3,3′-hexakis (trimethylsilyl)ferrocene as well as the ferricenium derivative of the latter have been prepared and characterized spectroscopically and by X-ray diffraction [16,17,18]. While the former was prepared via salt metathesis between FeX2 and the lithium salt of 1,2,4-tris(trimethylsilyl)cyclopentadiene, the latter used a different approach: starting from 1,2,3,1′,2′,3′-hexabromoferrocene, the corresponding hexalithioferrocene was generated in situ via multiple Br-Li exchanges followed by an electrophilic quench with SiMe3Cl. There are, to the best of our knowledge, no reports on ferrocene derivatives with more than three SiMe3 groups on one Cp ring (there is, however, one compound that contains, in addition to three SiMe3 substituents, a CH(Me)(NMe2) substituent on the same Cp ring [19]. There was also one other compound with a 1,2,3-tris(trimethylsilyl)cyclopentadienyl ligand reported before by us, i.e., [Mn{C5(SiMe3)3H2} (CO)3] [20]. In fact, there are also very few reports on cyclopentadienyl complexes of other metals with more than three SiMe3 groups on the Cp ring: [Mn{C5(SiMe3)4X}(CO)3]. (X = H, Br, SiMe3) were reported by us in 1993 [21,22], and a Japanese/US patent from 2011 postulates the synthesis of [{C5(SiMe3)5}Rh(µ-CH2)]2 [23]. While the Mn complexes were characterized by NMR and HRMS spectra (and one of them by X-ray diffraction), no characterization data were given for the Rh complex. But in contrast to the rich literature on the trimethylsilyl-substituted Cp complexes, there are hardly any reports on complexes with more than one SiMe2H group on a Cp ligand [24]. Until very recently, the only complex with a {C5(SiMe2H)5} ligand had been reported by us in 1992 [25]. This compound was prepared using, similar to the mentioned synthesis of 1,2,3,1′,2′,3′-hexakis(trimethylsilyl)ferrocene, the post-functionalization of an already coordinated cyclopentadienyl ligand. Starting from pentabromocymantrene [Mn(C5Br5)(CO)3], up to five SiMe2H groups could be introduced via a series of alternate Br-Li exchange reactions (using n-BuLi in Et2O) followed by an electrophilic quench with SiMe2HCl. Similarly, starting from [Mn(C5Br4SiMe3)(CO)3], the synthesis of [Mn{C5(SiMe2H)4SiMe3}(CO)3] could be achieved, from which, via chlorination by PdCl2 followed by a reaction with MeMgCl, a mixture of [Mn{C5(SiMe3)4X}(CO)3] (X = H, Br, SiMe3) could be obtained. Now, a very recent publication on the “persilylation of ferrocene” used a similar approach, starting with decabromoferrocene and consecutive Br-Li exchange reactions (using t-BuLi). Reactivity studies showed a strong solvent dependence of both the stability of lithiated intermediates and reactivity toward silylation. The best compromise was starting the lithiations in pentane at −80 °C followed by silylation at T > −50 °C, then changing to THF as solvent for both Li-Br exchange and silylation. Quite interestingly, in Et2O, the lithiated compounds decomposed before a reaction with the silylating agent took place. This synthetic procedure yielded a complicated mixture of highly silylated ferrocenes including [Fe{C5(SiMe2H)5}2] [26], which could be successfully separated via RP-HPLC and be fully characterized. This achievement prompts us to report on our studies toward the introduction of five SiMe2R (R = H, Me) substituents into only one Cp ring in the ferrocene and ruthenocene system.

2. Results

2.1. Synthesis

2.1.1. Dimethylsilylferrocenes

1-Dimethylsilylferrocene “FcSiMe2H” was described in 1990 [27], but there are no other ferrocenes which have SiMe2H groups only on one Cp ring. We decided to first try an approach that worked on the cymantrene system: treating pentabromoferrocene 1a with one or two equivalents of n-butyl lithium followed by an electrophilic quench with SiMe2HCl. However, when using one equivalent of n-BuLi at −50 °C, a 73:4:6:15 mixture of the desired [Fe(C5Br4SiMe2H)(C5H5)] (2a) with 3a and 4a (for structures, see Scheme 1) and the hydrolysis product 1b (in addition to traces of 1a and 1c) was obtained. Using two equivalents of n-BuLi afforded an even more complicated mixture of compounds 2a, 3a, 4a, and 8a in a 13:22:27:3 relation, together with contamination with traces of 1a and the hydrolysis products 1b (28%) and 1c (9%). These apparently “unexpected” results are, however, not without precedent. Complicated product mixtures were also obtained when we tried an electrophilic cyanation with the pentabromoferrocene/n-BuLi system [28].
We reasoned that this outcome might be a consequence of the slow reaction of the electrophile with a presumed lithiated ferrocene, combined with the presence of unreacted n-BuLi. Therefore, we tried a different approach next. The deprotonation of 1b or 1c, with lithium tetramethylpiperidinide (LiTMP) and electrophilic quench with SiMe2HCl, should avoid further reactions of the silylated products with the sterically demanding LiTMP, if present in excess. When 1b was treated with 1.0 equiv. LiTMP, a 76:8:16 mixture of the desired 2a with 1a and 1b together with traces of 3a was obtained. Increasing the amount of LiTMP to 1.5 equiv. yielded an 88:3 mixture of 2a and 3a together with 9% of 1b + c and traces of 1a (see Scheme 2). This corresponds to a yield of approximately 95% with a recovery of ca. 5% of 1b.
The treatment of 1c with 2.5 equiv. LiTMP, followed by electrophilic quench with SiMe2HCl, yielded a 7:1 mixture of 3a and 2a with a recovery of 19% of apparently unreacted 1c. Increasing the amount of LiTMP to 3.5 eq., a 93:7 mixture of the desired 4a, the partial hydrolysis product 5a together with traces of several unidentified products could be obtained (the mass spectrum showed some weak high mass peaks, attributable to the formulations [C10Br4(SiMe2H)2H4Fe] and [C10Br4(SiMe2H)3H3Fe]). This corresponds to a yield of ca. 91% based on 1c. Attempts to purify 4a (either by column chromatography or by recrystallization) without the substantial loss of product was met with failure.
Although we did not succeed in the complete purification of 4a, we decided to use this impure product for further synthetic studies. The treatment of a THF solution of 4a (containing 5a) with ca. 1 equiv. of n-BuLi gave mainly an 86:10:4 mixture of the desired 8a, 5a, and 9a together with a series of very minor impurities. This corresponds to a yield of 94% based on 4a alone. Again, several high mass peaks attributable to compounds with substituents on both rings [C10(SiMe2H)5Br2H3Fe] (m/z = 679.9) were found in the MS. It was not possible to achieve the complete purification of 8a by recrystallization without substantial losses in yield.
The treatment of this impure 8a with approximately 1 equiv. n-BuLi and SiMe2HCl yielded an 89:10:1 mixture of 11a, 9a, and 6a with traces of unreacted starting material (the mass spectrum also showed minor amounts of 13a). This corresponds to a yield of 100% based on 8a alone. Repeating this lithiation and electrophilic quench step twice yielded a product that consisted of a 76:14:9:1 mixture of 13a, 11a, 9a, and 6a together with traces of other unidentified impurities (the mass spectrum also shows the presence of 12a) (Scheme 3). This corresponds to a yield of 90% based on 11a alone. The recrystallization of this mixture yielded very few crystals of 13a that were suitable for X-ray diffraction.
While none of the compounds described here could be isolated in sufficient purity for elemental analysis, the key compounds 2a, 4a, 8a, 11a, and 13a could be characterized by 1H and 13 C NMR spectroscopies as well as by HRMS.

2.1.2. Trimethylsilylferrocenes

To achieve a higher degree of SiMe3 substitution, we decided to use a similar approach as for the synthesis of the poly(dimethylsilyl)ferrocenes (Scheme 4).
The treatment of 1c with three equivalents of LDA in THF at −78 °C, followed by an addition of SiMe3Cl, gave the desired bis-silylated ferrocene 4b in good yield (71%) and high purity (>98%) after recrystallization. The consecutive treatment of 4b with 1.4 equiv. of n-BuLi in Et2O at −78 °C followed by an electrophilic quench with SiMe3Cl yielded a 50:15:26:9 mixture of 8b, 9b, 4b, and 5b and a series of unidentified compounds. This corresponds to a yield of 61% for 8b with a 28% recovery of 4b. Recrystallization from methanol gave a few crystals suitable for X-ray diffraction.
The treatment of this mixture in Et2O with an excess of n-BuLi and SiMe3Cl produced a multi-component mixture consisting mainly of a 67:25:8 mixture of 9b, 5b, and 6b, which corresponds to a yield of nearly 100% for 9b based on 8b alone. Preparative RP-TLC allowed the separation and isolation of almost (86–90%) pure compounds 5b, 9b, and 11b. The mass spectrum of the latter showed contamination with small amounts of the “ultimate goal compound”, pentakis(trimethylsilyl)ferrocene 13b. All attempts to isolate 13b from this mixture, as well as by the renewed treatment of 11b with n-BuLi and SiMe3Cl, were met with failure. The treatment of 9b with one equivalent of n-BuLi in THF followed by hydrolysis allowed the isolation of the known 1,2,4-tris(trimethylsilyl)ferrocene 10b.
The key compounds 4b, 8b, and 11b could be characterized by NMR and mass spectroscopy, and except for 11b, also by X-ray diffraction. As a consequence of the low yield, it was not possible to extract—besides the MS—any other spectroscopic data for 13b.

2.1.3. Dimethylsilylruthenocenes

Overall, 1′-trimethylsilyl-(1,2,3,4,5-pentamethyl) ruthenocene, 1,3-bis(trimethylsilyl)ruthenocene, and 1,1′,3,3′-tetrakis(trimethylsilyl)ruthenocene were prepared [4,15,29]. Notably, 1,1′-Bis(dimethylsilyl)ruthenocene has also been described [27], but no dimethylsilyl derivatives of pentamethylruthenocene are known. As we had described the synthesis of [Ru(C5Br5)(C5Me5)] (1d) previously [30], we regarded it as a suitable starting material for the multiple introductions of SiMe2H groups. First, we treated 1d with one or two equivalents of n-BuLi followed by electrophilic quench with SiMe2HCl. However, no silylated products were obtained. Instead, only the hydrolysis products 1e,f of the anticipated intermediate lithiated species could be isolated (Scheme 5).
Therefore, we turned to the stronger base t-BuLi, which also has the advantage in halogen–lithium exchange reactions that—when used in excess—it removes the side product t-BuBr by an elimination reaction. And, indeed, the reaction of 1d with two equivalents of t-BuLi yielded a 10:1 mixture of 4c and 3c (and very small amounts of other unidentified compounds) in ca. 84% yield (Scheme 6).
The treatment of this impure 4c with two equivalents of t-BuLi and SiMe2HCl yielded, somehow unexpectedly, compound 8c, contaminated by apparently unreacted 4c and other unidentified products. Without further purification, the treatment of this product mixture with an excess of t-BuLi (>3 equiv.) followed by SiMe2HCl gave a mixture that mainly consisted of 11c, 12c, and 13c in an approximately 1:2:1 ratio, and pentamethylruthenocene, which made up nearly 50% of the mixture. Several attempts of purification were pursued: column chromatography, recrystallization, and fractional sublimation. Many such steps were performed that led mainly to substantial product loss, but in the end, about 1 mg of the desired pentasilyl complex 13c could be isolated as off-white microcrystals, unfortunately not suitable for X-ray diffraction.
The key compounds 4c, 8c, 11c, and 13c could be characterized by NMR and mass spectrometry, but either the purity or the low yield prevented characterization by elemental analysis.

2.2. Crystallography

2.2.1. Pentakis(dimethylsilyl)ferrocene, 13a

Compound 13a crystallizes in the hexagonal space group P63/m with four half molecules in the asymmetric unit. Platon analysis showed the presence of 5.6% solvent-accessible voids, and therefore, the dataset was “squeezed”. In the original structure solution, the four Fe atoms as well as one cyclopentadienyl C atom on each ring together with the attached silicon atoms were situated on a crystallographic plane, while two cyclopentadienyl C atoms on each ring together with the attached silicon atoms were “unique”. Further refinement showed that the Si atoms were disordered, and so were the attached Cp ring carbons. Applying the mirror symmetry operator produced very unfavorable interactions in the SiMe2H groups, together with unreasonable bond lengths and angles. Therefore, a large number of restraints (283; mostly “same distance” restraints) had to be applied to produce a reasonable structure model. Due to the symmetry requirements of the mirror plane, the disorder had to be fixed at a 50:50 ratio. Figure 1 shows an ortep3 representation of molecules A and B, while the structures of molecules C and D are displayed in the Supporting Information.
The structure shows the typical chiral “paddle-wheel” orientation of such molecules (the corresponding enantiomer is automatically generated by the application of the mirror operator), which has also been described for the structures of [Mn{C5(SiMe2H)5}(CO)3] [17] and [Fe{C5(SiMe2H)5}2] [21]. Due to a lack of further crystallographic symmetry restrictions, the disorder also found in these structures could be refined to different values from 1:1. Similar cyclic tongue-and-groove arrangements are observed for hexakis(dimethylsilyl)benzene, and the stereochemistry was proven to be dynamic in solution [31], while at the same time, disorder was observed in the crystals of [C6(SiMe2H)6] and its M(CO)3 (M = Cr, Mo, W) complexes [32]. Although the steric congestion between silyl substituents at a five-membered ring is smaller than on a six-membered ring, it still prevents the easy rotation of the SiMe2H substituents. It therefore seems justified that the chosen restraints correspond to a “real” situation and are not an artifact. On the other hand, the large number of distance restraints makes a detailed discussion of bond lengths and angles senseless. The distances from the Fe atoms to the centroids of the substituted Cp rings average at 1.647(7) Å and to the centroids of the unsubstituted Cp rings at 1.665(9) Å. Apparently, and quite surprising, despite the expected steric crowding at the substituted Cp ring, the unsubstituted C5H5 ring is further away from the metal. However, a similar observation was made in the crystal structure of pentakis(isopropyl)ferrocene, which has also one sterically crowded Cp ligand [33]. Individual Fe–C distances vary between 2.006 and 2.116 Å for the substituted and between 2.044 and 2.064 Å for the unsubstituted Cp ring. Angles between Fe-Ct vectors at Fe atoms Fe1, Fe2, and Fe3 are close to 180° (the highly disordered C5H5 ring at Fe4 is excluded from discussion). The average distance of the Si atoms from the corresponding Cp carbon atoms is 1.874(5) Å. For comparison, in the structure of decakis(dimethylsilyl)ferrocene, the Fe centroid distance is 1.716 Å, very much longer than in 13a, and the C–Si distances average at 1.879 Å, quite similar to the value found in our compound [26]. Figure 2 displays a packing plot of 13a, which shows that the different molecules A-D arrange very differently.

2.2.2. 1,2,4-Tribromo-2,5-bis-trimethylsilyl-ferrocene 4b

Compound 4b crystallizes in the monoclinic space group P21/c with one molecule in the asymmetric unit. Figure 3 shows an ortep3 plot of its molecular structure.
Important bond parameters are collected in Table 1. The structure can be compared with the structure of the analogous Mn(CO)3 complex of the [C5Br3(SiMe3)2] ligand, “A”. As can be seen from the Table, the C–Br bonds are slightly longer and the C–Si bonds are slightly shorter than in the Mn(CO)3 complex.

2.2.3. 1,3-Dibromo-2,4,5-tris-trimethylsilyl-ferrocene 8b

Compound 8b crystallizes in the triclinic space group P1 with two independent molecules in the asymmetric unit. Figure 4 shows an ortep3 top view of both independent molecules. The major difference between both molecules is in the relative orientation of the Cp rings. While molecule A shows nearly staggered conformation, molecule B is close to eclipsed.
The bond parameters of both molecules are nearly identical. When comparing with the structure of 4a, the Fe atom is closer to the substituted Cp ring than to the unsubstituted in both molecules, but both distances are longer in 8a, while the difference in distances becomes smaller on increasing silyl substitution. In 4a, both silicon atoms are very close to the Cp ring plane, while in both molecules of 8a, only one Si atom is in the Cp ring plane (the Si atom between the Br substituents), while the other two deviate in both directions significantly from this plane.

3. Discussion

In nearly all cases, the individual synthetic steps yielded mixtures of the products, which were characterized by the replacement of one or more Br atoms by hydrogen. This behavior is most likely due to the high moisture sensitivity of chlorosilanes, particularly of SiMe2HCl, which inevitably produce small amounts of HCl. Although we tried to minimize the impact of water by the storage of the chlorosilanes over polyvinylpyridine (Reillex®) and distillation over CaH2 prior to reaction, remaining traces of moisture stayed in the system. As with an increasing substitutional degree, apparently, the reactivity of the lithiated mixed bromo-silyl metallocenes at low temperatures toward the silylchlorides diminished, and the present traces of HCl reacted quickly at these low temperatures. In addition to the direct protonation of lithiated species, the HCl could also induce protiodesilylation of the already present silyl substituents.
But in addition to hydrolysis reactions, there were also other side reactions at work that led to complicated product mixtures. In several cases, products could be identified that contained more Br substituents than the starting materials. In some cases, mass spectrometry revealed that products had formed that contained substituents on both Cp rings. Such observations are usually made when “halogen dance reactions” are at work. This type of reaction is usually observed with halogen-substituted heterocycles, especially with iodides and bromides, and has been known for quite a while [34], but its mechanism is still being discussed today [35]. Only recently it could be shown that bases like KOtBu or KN(SiMe3)2 catalyze halogen dance reactions in bromopyridines, if added in small amounts to the stoichiometric base LDA [36]. More important in the present context is that such reactions also occur in metallocene chemistry [37], and that it is possible to use them for stereoselective synthesis [17,38,39]. Scheme 7 shows how such a halogen dance can produce a complex product mixture just by occurring once.
The purification of these mixtures also turned out to be very difficult. Standard column chromatography using silica gel or alumina did not work at all, as in addition to incomplete separation, substantial desilylation, most likely due to acidic surface OH groups, was also observed. The pretreatment of silica gel with SiMe3Cl gave “silanized” silica gel (which, however, does not completely remove all surface OH groups), which allowed some separation using MeOH as eluent. Alternatively, commercial RP18-modified TLC plates allowed for the partial separation of the SiMe3–ferrocenes (we did not try these on the SiMe2H derivatives); however, complete separations were not possible either, if not repeated several times, with concomitant substantial losses in yields (most likely due to desilylation on the chromatography material).
The lower steric strain in SiMe2H-substituted derivatives allowed repeated treatments with n-BuLi in the case of the ferrocenes, as the remaining Br and H substituents were still reactive. However, in the ruthenocene system, apparently no Br-Li exchange at low temperatures with n-BuLi took place, and therefore, the more reactive t-BuLi had to be used. Unfortunately, this reagent does not only exchange with H and Br substituents but also with SiMe2H substituents (presumably during the warming up of the reaction mixture), and in the last synthetic steps, large contamination with the de-brominated and desilylated pentamethylruthenocene was observed, becoming the main product in the end. In this context, it should also be mentioned that the pentamethylcyclopentadienyl ligand cannot be regarded as “innocent” when it comes to reaction with t-BuLi [40]. Although we did not perform mechanistic studies, it seems likely that lithiated positions at the brominated Cp ring might also be able to abstract protons from the methyl groups of the Cp* ring.
The higher steric strain of SiMe3 groups prevented the direct formation of pentasilylated ferrocene 13b from its presumed tetra-silylated “precursors” 11b or 12b. Actually, it was not even possible to prepare 12b from isolated 11b by a reaction with n-BuLi, followed by hydrolysis, while the analogous reaction of the tris-silylated 9b gave 10b without problems. It has to be assumed, therefore, that the observed formation of 13b occurred from a different precursor than 11b. The molecular structures of compounds 4b and 8b show that as soon as two SiMe3 groups are “forced” into two neighboring positions, they try to avoid each other by shifting to two different sides of the Cp ring plane. Such an “up–down” alternation is also possible in a tetrasilylated Cp ring, but not in a pentasilylated derivative: high steric strain is unavoidable. This can be seen to an even higher extent in the distorted structure of hexakis(trimethylsilyl)benzene [41].

4. Materials and Methods

4.1. Chemicals and Instrumentation

Solvents for reactions (THF, Et2O) were obtained commercially in the highest available anhydrous quality and stored under dry N2. Solvents for chromatography were of analytical grade and were used as obtained. Reagents HTMP, 1.6 m n-BuLi, 1.6 m t-BuLi, and 1.0 m LDA were obtained commercially and were used as obtained (it is advisable, however, to use either freshly opened commercial vials, or titrate the reagents prior to use!). Reagents SiMe2HCl and SiMe3Cl were obtained commercially, stored over Reillex ®, and freshly distilled over CaH2 prior to use. LiTMP was freshly prepared from HTMP and n-BuLi in THF prior to use. The ferrocenes pentabromoferrocene 1a, tetrabromoferrocene 1b, and 1,2,4-tribromoferrocene 1c as well as pentabromo-pentamethyl-ruthenocene 1d were prepared as reported earlier [30,42]. All reactions were performed under dry N2 or Ar, using standard Schlenk techniques (Schlenk flasks/tubes were stored in a hot oven at 160 °C for at least 24 h and were assembled under a purge of inert gas while still being hot. The assembled flasks were then evacuated using standard oil vacuum pump (ca. 0.01 Torr) and then flushed with inert gas.
For standard column chromatography, silica gel 100 C18 Reversed Phase (Fluka) was used, or standard silica gel (0.035–0.070 mm, 60A, Merck, Rahway, NJ, USA) was pretreated with sufficient dry Et2O and SiMe3Cl with stirring for several days; then solvents were evaporated, and the residue was kept in high vacuum for 8 h, and finally flashed with dry argon. For preparative TLC, RP8 F254S (Merck) was used, applying 20–30 mg of substance per plate.
NMR spectra were measured on a jeol ecp-270 or ex-400 instrument, (both jeol Germany, Freising, Germany) using C6D6 or CDCl3 as solvent. The chemical shifts were obtained relative to the residual solvent signals, as defined by the MestReNova software (Version 14.1.1–24751, Mestrelab Research S.L., Santiago de Compostela, Spain) (δCDCl3 = 7.260 and 77.16 ppm, respectively; δCHD5 = 7.160 and 128.06 ppm, respectively). Mass spectra were obtained on Finnigan MAT 90 and JEOL Mstation 700 (jeol Germany, Freising, Germany) instruments, in DEI mode.
Crystals were measured on a Bruker Kappa CCD (13a) or a Bruker D8Venture (4a,8a) diffractometer. The obtained datasets were solved using shelxt [43] and refined using shelxl 2018/3 [44]. An examination of the structure solutions was performed with the program platon as part of the wingx program suite [45]. Graphics were prepared using either ortep3 for windows or mercury, both being part of the wingx program suite. For further details of the crystal structure determinations see Table S1 of the Supporting Information.

4.2. Synthesis

4.2.1. 1,2,3,4-Tetrabromo-5-dimethylsilylferrocene, [Fe(C5H5)(C5Br4SiMe2H)], 2a

Notably, 1,2,3,4-tetrabromoferrocene 1b (0.11 g, 0.22 mmol) was dissolved in 9 mL of THF. At –30 °C, this solution was added to freshly prepared LiTMP (0.34 mmol) in 1 mL of THF. After aging for 4 h at –30 °C, the mixture was cooled to –78 °C, and SiMe2HCl (0.04 mL, 0.37 mmol) was added. The solution was allowed to warm to room temperature over a period of 16 h. The solvent was removed, and the residue was extracted with hexane. The evaporation of the extract gave a yellowish-brown oil. Yield: 0.13 g (Figures S1 and S2; NMR purity ca. 88%, contamination by 1b and traces of 1c and 3a and, according to MS (Figure S32), also traces of products with 5, 6, and 7 Br atoms).
HRMS (DEI): m/z = 559.6747 (calc. for C12H1279Br281Br2SiFe: 559.6752)

4.2.2. 1,2,4-Tribromo-3,5-bis(dimethylsilyl)ferrocene, [Fe(C5H5){C5Br3(SiMe2H)2}], 4a

Notably, 1,2,4-tribromoferrocene 1c (0.15 g, 0.35 mmol) was dissolved in 9 mL of THF. At –30 °C, this solution was added to freshly prepared LiTMP (1.24 mmol) in 1 mL of THF. After aging for 3 h at –30 °C, the mixture was cooled to –78 °C, and SiMe2HCl (0.14 mL, 1.29 mmol) was added. The solution was allowed to warm to room temperature over a period of 16 h. The solvent was removed, and the residue was extracted with hexane. The evaporation of the extract gave an orange oil. Yield: 0.23 g (Figures S5 and S6, NMR purity 90%, contamination by 5a, and additionally, some “organics” like HTMP and BHT, and according to MS (Figure S33), traces of products with higher Br and silyl content).
HRMS (DEI): m/z = 539.7863 (calc. for C14H1979Br81Br2Si2Fe: 539.7866)

4.2.3. 1,3-Dibromo-2,4,5-tris(dimethylsilyl)ferrocene, [Fe(C5H5){C5Br2(SiMe2H)3}], 8a

A solution of impure 4a (0.52 g, ca. 0.79 mmol, together with ca. 0.05 mmol 5a) in 25 mL of Et2O was treated with n-BuLi solution (0.55 mL, 0.88 mmol) at –78 °C. After stirring for 1 h at this temperature, SiMe2HCl (0.10 mL, 0.92 mmol) was added. The solution was allowed to warm to room temperature over a period of 16 h. The solvent was removed, and the residue was extracted with hexane. The evaporation of the extract gave an orange oil. Yield: 0.48 g (Figures S7 and S8, NMR purity 81%, contamination by 5a, 9a, and about 5% “organics”, and according to MS (Figure S34), also possibly by 13a, m/z = 475.8).
HRMS (DEI): m/z = 517.9052 (calc. for C16H2679Br81BrSi3Fe: 517.9040

4.2.4. 1-Bromo-2,3,4,5-tetrakis(dimethylsilyl)ferrocene, [Fe(C5H5){C5Br(SiMe2H)4}], 11a

A solution of impure 8a (0.34 g, containing ca. 0.56 mmol 8a, in addition to ca. 0.04 mmol 9a and 0.02 mmol 5a) in 25 mL of Et2O was treated with BuLi solution (1.17 mL, 1.87 mmol) at –78 °C. After stirring for 3 h at this temperature, SiMe2HCl (0.14 mL, 1.29 mmol) was added. The solution was allowed to warm to room temperature over a period of 16 h. The solvent was removed, and the residue was extracted with hexane. The evaporation of the extract gave an orange oil. Yield: 0.32 g (Figures S9 and S10, NMR purity 86%, contamination by 9a and 6a, ca. 3% “organics” and, according to MS (Figure S35), also traces of 8a).
HRMS (DEI): m/z = 496.0188 (calc. for C18H3379BrSi4Br: 496.0194)

4.2.5. 1,2,3,4,5-Pentakis(dimethylsilyl)ferrocene, [Fe(C5H5){C5(SiMe2H)5}], 13a

A solution of 11a (0.43 g, containing ca. 0.69 mmol 11a and 0.12 mmol 9a) in 25 mL of Et2O was treated with BuLi solution (1.04 mL, 1.66 mmol) at –78 °C. After stirring for 7 h at this temperature, SiMe2HCl (0.18 mL, 1.66 mmol) was added. The solution was allowed to warm to room temperature over a period of 16 h. The solvent was removed, and the residue was extracted with hexane. The evaporation of the extract gave an orange solid. Yield: 0.39 g (Figures S11 and S12, NMR purity 75%, contamination by 6a, 9a, and 11a, and according to MS (Figure S36), also traces of 12a). Recrystallization from hexane yielded crystals suitable for X-ray structure determination.
HRMS (DEI): m/z = 476.1338 (calc. for C20H40Si5Fe: 476.1327)
EA: calc. C, 50.38; H, 8.46%; found: C, 51.16; H, 7.86%

4.2.6. 1,2,4-Tribromo-3,5-bis(trimethylsilyl)ferrocene, [Fe(C5H5){C5Br3(SiMe3)2}], 4b

Notably, 1c (0.106 g, 0.25 mmol) was dissolved in THF (5 mL) and treated with LDA solution (0.75 mL, 0.75 mmol) and SiMe3Cl (0.090 mL, 0.80 mmol) at -78 °C for 2h and then warmed to r.t. within 16 h. After re-dissolution in Et2O (5 mL) and filtration through silica gel, an orange-colored viscous fluid was obtained (Yield: 0.145 g). Recrystallization from MeOH gave orange crystals, suitable for X-ray diffraction (0.100 g, 0.18 mmol, 71%, Figures S13 and S14, NMR purity >98%; according to MS (Figure S37), traces of 5b and [Fe(C5H4Br){C5Br3(SiMe3)2}].
29Si NMR (54 MHz, C6D6) δ 1.95
MS (EI): m/z = 568.06 (calc. 567.82)

4.2.7. 1,3-Dibromo-2,4,5-tris(trimethylsilyl)ferrocene, [Fe(C5H5){C5Br2(SiMe3)3}], 8b

A solution of 4b (0.100 g, ca. 0.18 mmol) in Et2O (10 mL) was treated with n-BuLi solution (0.160 mL, 0.25 mmol) and SiMe3Cl (0.030 mL, 0.26 mmol) at -78 °C for 1 h and then brought to r.t. within 16 h. After re-dissolution in petroleum ether and filtration through silica gel, the crude product was obtained (0.122 g; Figure S15): NMR purity ca. 50%, contamination with 4b and 9b, and according to MS (Figure S38), also 5b. Preparative RP-TLC (RP8, using MeOH) removed 9b. Yield: 0.070 g for a 86:3:11 mixture of 8b, 5b, and 4b (NMR: Figure S16, MS: Figure S39). NMR shows relatively large amounts of Et2O. Recrystallization from MeOH gave some crystals suitable for X-ray diffraction.
29Si NMR (79MHz, C6D6): 1.52 (Si), −0.29 (2Si)
MS (EI+, 70 eV) m/z = 560.23 (calc. 559.95)

4.2.8. Reaction of 8b with n-BuLi and SiMe3Cl

Impure 8b (0.070 g, ca. 0.11 mmol 8b, contaminants 4b, ca. 0.014 mmol, and traces of 5b) was dissolved in Et2O (10 mL) and treated at -78 °C with n-BuLi solution (0.17 mL, 0.28 mmol), and after stirring for 2 h at this temperature, SiMe3Cl (0.035 mL, 0.28 mmol) was added. The mixture was brought to r.t. within 16 h and then filtered through silica gel, using additional Et2O. the evaporation of the solvent in vacuo left an oily residue (0.080 g). 1H NMR spectroscopy showed that this crude product consisted mainly of 9b, 5b, and 6b (Figures S17 and S18), while MS (Figure S40) showed the additional presence of 11b as well as very small amounts of 8b, 12b, and 13b. Preparative TLC (RP18, MeOH) gave four fractions, which still contained mixtures. Two fractions were isolated and re-chromatographed by TLC (RP18, MeOH). Thus, it was possible to separate 5b (Fraction F3.2; Figures S19 and S20; NMR purity, 86%; MS (Figure S41) showed the presence of small amounts of 9b, 6b, and 10b), 9b (Fraction F3.3; Figures S21 and S22, NMR purity, 90%; 5b as main contaminant (MS, Figure S42, showed further traces of 10b and 6b)), and 11b (Fraction F4.10; Figure S23; according to MS (Figure S43; contaminated by small amounts of 13b)). Another fraction (F4.7) also contained 11b, but it was contaminated with 8b and 12b, and some other unidentified products (Figure S44).
5b: 29Si NMR (79 MHz, C6D6) δ = 0.45, −2.01
HRMS (EI): m/z = 487.9062 (calc. For C16H2479Br 81BrFeSi2: 487.9114)
9b: 29Si NMR (79 MHz, C6D6) δ = −1.52, −1.97, −2.25
HRMS (EI): m/z = 480.0407 (calc. For C19H3379BrFeSi3: 480.0425)

4.2.9. 1,2,4-Tris(trimethylsilyl)ferrocene, [Fe(C5H5){C5H2(SiMe3)3}] 10b

A solution of 9b (0.020 g, 0.042 mol) in THF (2 mL) was treated with n-BuLi solution (0.030 mL, 0.048 mmol) for 30 min at -78° C and then hydrolyzed with MeOH (1 mL). After the evaporation of the solvent, the residue was taken up in petroleum ether and filtered through silica gel. The evaporation of the solvent left [Fe(C5H5){C5H2(SiMe3)3}] (0.020 g). The spectroscopic data agree with the literature data (Figures S24 and S25) [7].
29Si NMR (79 MHz, C6D6) δ −2.96, −4.05

4.2.10. (1,2,4-Tribromo-2,5-bis(dimethylsilyl)(6,7,8,9,10-pentamethyl)ruthenocene, [Ru(C5Me5){C5Br3(SiMe2H)2}] (4c)

A solution of 1d (0.200 g, 0.28 mmol) in THF (50 mL) was treated at -78 °C with t-BuLi solution (0.35 mL, 0.56 mmol) with stirring for 10 min. Then, SiMe2HCl (0.060 mL, 0.56 mmol) was added, and stirring was continued for 16 h. After the evaporation of the solvent in vacuo, the residue was extracted with pentane (50 mL) for 12 h. The obtained suspension was filtered through a glass frit and the filtrate was evaporated in vacuo. Compound 4c was obtained as an orange-yellow solid (0.174 g, ca. 0.23 mmol 4c, 84% yield), with NMR purity (Figure S26) ca. 85%; mass spectroscopy (Figure S45) showed the presence of 3c.
MS (EI+, 70 eV) m/z = 655.62 (calc. 655.84)

4.2.11. (1,3-Dibromo-2,4,5-tris(dimethylsilyl)(6,7,8,9,10-pentamethyl)ruthenocene, [Ru(C5Me5){C5Br2(SiMe2H)3}] (8c)

A solution of (impure) 4c (0.174 g, < 0.26 mmol) in THF (25 mL) was treated at −78 °C with t-BuLi solution (0.33 mL, 0.52 mmol) with stirring for 10 min. Then, SiMe2HCl (0.060 mL, 0.56 mmol) was added, and stirring was continued for 16 h. After the evaporation of the solvent in vacuo, the residue was extracted with pentane (50 mL) for 12 h. The obtained suspension was filtered through a glass frit, and the filtrate was evaporated in vacuo. Compound 8c was obtained as an off-white powder (0.151 g, <0.23 mmol), with NMR purity ca. 80% (Figure S27); mass spectrometry (Figure S46) shows the presence of 4c.
MS (EI+, 70 eV) m/z = 634.2 (calc. 633.95)

4.2.12. Reaction of Crude 8c with Excessive t-BuLi and SiMe2HCl

A solution of impure 8c (0.125 g, <0.20 mmol) in THF (25 mL) was treated at −78 °C with t-BuLi solution (0.40 mL, 0.64 mmol) with stirring for 10 min. Then, SiMe2HCl (0.070 mL, 0.65 mmol) was added, and stirring was continued for 16 h. After the evaporation of the solvent in vacuo, the residue was extracted with pentane (50 mL) for 12 h. The obtained suspension was filtered through a glass frit, and the filtrate was evaporated in vacuo, leaving an off-white powder. 1H NMR spectroscopic (Figure S28) and mass spectroscopic (Figure S47) examination of the residue showed that it mainly consisted of 11c, 12c, and 13c. Using a combination of purification steps (column chromatography, recrystallization, sublimation; Figures S29–S31) yielded compound 13c in purity of >90% in very low yield (ca. 1%).

5. Conclusions

We showed that pentasilylated metallocenes [Fe(C5R5)(C5H5)], R = SiMe2H, SiMe3, and [Ru(C5Me5){C5(SiMe2H)5}] can be prepared. Due to various side reactions (hydrolysis, halogen dance reactions, desilylation) multi-component mixtures were always obtained. These mixtures were very difficult to separate, both because the products were structurally very similar and because of the reactions of the products with the chromatography material. Consequently, the obtained yields were very low. Future research is needed to find better reaction conditions (solvent, temperature range, pretreatment of reagents) and better separation methods (chromatography materials, HPLC).

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/inorganics13020042/s1. Figure S1: 1H NMR of the crude reaction product according to Section 4.2.1; Figure S2: 13C{1H} NMR of the crude reaction product according to Section 4.2.1; Figure S3: 1H NMR of the crude reaction product obtained from 1c and 2.5 eq. LiTMP; Figure S4: 13C{1H} NMR of the crude reaction product obtained from 1c and 2.5 eq. LiTMP; Figure S5: 1H NMR of the crude reaction product obtained from 1c and 3.5 eq. LiTMP (Section 4.2.2); Figure S6: 13C{1H} NMR of the crude reaction product obtained from 1c and 3.5 eq. LiTMP (Section 4.2.2); Figure S7: 1H NMR of the crude reaction product obtained acc. Section 4.2.3; Figure S8: 1H NMR of the crude reaction product obtained acc. Section 4.2.3; Figure S9: 1H NMR of the crude reaction product obtained acc. Section 4.2.4; Figure S10: 13C{1H} NMR of the crude reaction product obtained acc. Section 4.2.4; Figure S11: 1H NMR of the crude reaction product obtained acc. Section 4.2.5; Figure S12: 13C{1H} NMR of the crude reaction product obtained acc. Section 4.2.5; Figure S13: 1H NMR of compound 4b (Section 4.2.6); Figure S14: 13C{1H} NMR) of compound 4b (Section 4.2.6.); Figure S15: 1H NMR of the crude reaction product obtained acc. Section 4.2.7; Figure S16: 1H NMR) of purified 8b (Section 4.2.7); Figure S17: 1H NMR of the crude reaction product obtained acc. Section 4.2.8; Figure S18: 13C{1H} NMR of the crude reaction product obtained acc. Section 4.2.8; Figure S19: 1H NMR of 5b (Section 4.2.8); Figure S20: 13C{1H} NMR of 5b (Section 4.2.8); Figure S21: 1H NMR of 9b (Section 4.2.8); Figure S22: 13C{1H} NMR of 9b (Section 4.2.8); Figure S23: 1H NMR of 11b (Section 4.2.8); Figure S24: 1H NMR of 10b (Section 4.2.9); Figure S25: 13C{1H} NMR of 10b (Section 4.2.9); Figure S26: 1H NMR of 4c (Section 4.2.10); Figure S27: 1H NMR of the crude reaction product obtained according Section 4.2.11; Figure S28: 1H NMR of the crude reaction product obtained according Section 4.2.12; Figure S29: 1H NMR of the product of the first purification step (Section 4.2.12); Figure S30: 13C{1H} NMR of the product of the first purification step (Section 4.2.12); Figure S31: 1H NMR of the product of the second purification step (Section 4.2.12); Figure S32 MS (DEI) of the crude reaction product according to Section 4.2.1; Figure S33: MS (DEI) of the crude reaction product according to Section 4.2.2; Figure S34: MS (DEI) of the crude reaction product according to Section 4.2.3; Figure S35 MS (DEI) of the crude reaction product according to Section 4.2.4; FigureS36: MS (DEI) of the crude reaction product according to Section 4.2.5; Figure S37: MS (EI) of 4b (Section 4.2.6); Figure S38: MS (EI) of the crude reaction product obtained acc. Section 4.2.7; Figure S39: MS (EI) of 8b; Figure S40: MS (EI): of the crude reaction product obtained acc. Section 4.2.8; Figure S41: MS(EI) of the product of the second purification step, fraction F3.2, Section 4.2.8; Figure S42: MS(EI) of the product of the second purification step, fraction F3.3, Section 4.2.8; Figure S43: MS(EI) of the product of the third purification step, fraction F4.10., Section 4.2.8; Figure S44: MS (EI) of 4c (Section 4.2.10); Figure S45: MS (EI) of 8c (Section 4.2.11); Figure S46: MS (EI) of the product obtained according to Section 4.2.12; Figure S47: ortep3 plots of the molecular structure of 13a, molecules C and D; Table S1: experimental details of the crystal structure determinations; Table S2: 1H- and 13C NMR as well as MS data of all identified compounds.

Author Contributions

Conceptualization, T.B., M.L. and K.S.; Data Curation, K.S.; Formal Analysis, S.B., T.B. and M.L.; Investigation, S.B., T.B. and M.L.; Methodology, S.B., T.B. and M.L.; Project Administration, K.S.; Resources, K.S.; Supervision, K.S.; Visualization, K.S.; Writing—Review and Editing, K.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Statement CCDC 2407160-2407162 contains the supplementary crystallographic data referenced in this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, by emailing data_request@ccdc.cam.ac.uk or by contacting the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; Fax: +44-1223336033.

Acknowledgments

We would like to express our appreciation of the experimental work performed by the undergraduate student Anja Layer within the studies of the Ru system. Furthermore, we appreciate that we could use the NMR facilities of T.M. Klapötke, and our special thanks goes to Peter Mayer for performing the crystal structure measurements and data processing.

Conflicts of Interest

The authors declare no conflicts of interest.

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Scheme 1. Structural formulae of the compounds described in this publication. ML = “metal–ligand”, Cp* = η5-(C5Me5). For all compounds with planar chirality (5, 6, 7, 9), only one enantiomer is shown.
Scheme 1. Structural formulae of the compounds described in this publication. ML = “metal–ligand”, Cp* = η5-(C5Me5). For all compounds with planar chirality (5, 6, 7, 9), only one enantiomer is shown.
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Inorganics 13 00042 sch002
Scheme 2. Synthesis of 2a from 1b. Reaction conditions: (A): (1) 1.5 equiv. LiTMP/THF/−30 °C; (2) excess SiMe2HCl, −78 °C.
Scheme 2. Synthesis of 2a from 1b. Reaction conditions: (A): (1) 1.5 equiv. LiTMP/THF/−30 °C; (2) excess SiMe2HCl, −78 °C.
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Scheme 3. Stepwise synthesis of 13a. Reaction conditions: (A) (1) 3.5 equiv. LiTMP/THF/−30 °C; (2) excess SiMe2HCl/−78 °C; (B) 1.0 equiv. n-BuLi/Et2O/−78 °C, then SiMe2HCl; (C) 3.0 equiv. n-BuLi/Et2O/−78 °C, then SiMe2HCl; (D) 2 equiv. n-BuLi/Et2O/−78 °C, then SiMe2HCl.
Scheme 3. Stepwise synthesis of 13a. Reaction conditions: (A) (1) 3.5 equiv. LiTMP/THF/−30 °C; (2) excess SiMe2HCl/−78 °C; (B) 1.0 equiv. n-BuLi/Et2O/−78 °C, then SiMe2HCl; (C) 3.0 equiv. n-BuLi/Et2O/−78 °C, then SiMe2HCl; (D) 2 equiv. n-BuLi/Et2O/−78 °C, then SiMe2HCl.
Inorganics 13 00042 sch003
Inorganics 13 00042 sch004
Scheme 4. Synthesis of 13b. Reaction conditions: (A) 3 equiv. LDA/THF/−78 °C, then excess SiMe3Cl; (B) 1.4 equiv. n-BuLi/Et2O/−78 °C, then excess SiMe3Cl; (C) excess n-BuLi/Et2O/−78 °C, then excess SiMe3Cl.
Scheme 4. Synthesis of 13b. Reaction conditions: (A) 3 equiv. LDA/THF/−78 °C, then excess SiMe3Cl; (B) 1.4 equiv. n-BuLi/Et2O/−78 °C, then excess SiMe3Cl; (C) excess n-BuLi/Et2O/−78 °C, then excess SiMe3Cl.
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Scheme 5. The reaction of 1d with n-BuLi in THF.
Scheme 5. The reaction of 1d with n-BuLi in THF.
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Scheme 6. The synthesis of 13c. Reaction conditions: (A) and (B) 2.0 equiv. t-BuLi/THF/−78 °C, then SiMe2HCl; (C) >3 equiv. t-BuLi/THF/−78 °C, then SiMe2HCl.
Scheme 6. The synthesis of 13c. Reaction conditions: (A) and (B) 2.0 equiv. t-BuLi/THF/−78 °C, then SiMe2HCl; (C) >3 equiv. t-BuLi/THF/−78 °C, then SiMe2HCl.
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Figure 1. ortep3 representations of the molecular structure of compound 13a, molecules A and B. Displacement ellipsoids are drawn at the 50% probability level.
Figure 1. ortep3 representations of the molecular structure of compound 13a, molecules A and B. Displacement ellipsoids are drawn at the 50% probability level.
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Figure 2. Packing plot of 13a, viewed along c. mercury; color coding “by symmetry equivalence”.
Figure 2. Packing plot of 13a, viewed along c. mercury; color coding “by symmetry equivalence”.
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Figure 3. Molecular structure of 4b. Displacement ellipsoids are drawn at the 50% probability level.
Figure 3. Molecular structure of 4b. Displacement ellipsoids are drawn at the 50% probability level.
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Figure 4. Molecular structure of 8b; molecule A (left); molecule B (right). Displacement ellipsoids are drawn at the 50% probability level.
Figure 4. Molecular structure of 8b; molecule A (left); molecule B (right). Displacement ellipsoids are drawn at the 50% probability level.
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Scheme 7. Halogen dance reaction starting with mono-lithiated 1b.
Scheme 7. Halogen dance reaction starting with mono-lithiated 1b.
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Table 1. Important bond parameters of 4b and 8b and some related structures.
Table 1. Important bond parameters of 4b and 8b and some related structures.
4b“A”8b/Mol. A8b/Mol. B
C–Br [Å]1.889(3)/1.888(3)/1.902(3)1.87/1.885(9)1.907(3)/1.905(3)1.910(3)/1.896(3)
Ccp–Si1.898(3)/1.862(4)1.909(9)1.894(4)/1.898(3)/1.888(4)1.892(4)/1.889(3)/1.905(4)
Fe–CTsub1.6292(14){1.753}1.6435(14)1.6415(14)
Fe–CTC5H51.6589(15)–1.6682(16)1.6686(19)
CTsub-Fe-CTC5H5 [°]178.52(7)–178.26(9)179.51(10)
Br-CTsub-CTC5H5-Hcp [°]16.3–19.75.5
Δ Si—Cp [Å]0.064(1)/0.008(1) −0.092(1)/−0.318(1)/0.196(1)−0.009(1)/−0.109(1)/0.290(1)
CTsub is the centroid of the substituted Cp ring; Hcp is the H atom on the C5H5 ring closest to the projection of a Br atom on the C5H5 ring plane. Δ Si—Cp is the perpendicular distance of the silicon atoms from the plane of the substituted Cp ring.
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Bernhartzeder, S.; Blockhaus, T.; Lang, M.; Sünkel, K. Studies Toward Persilylation of π-Cyclopentadienyl Complexes of Fe and Ru. Molecular Structures of [Fe(C5H5){C5(SiMe2H)5}], [Fe(C5H5){C5Br3(SiMe3)2}] and [Fe(C5H5){C5Br2(SiMe3)3}]. Inorganics 2025, 13, 42. https://doi.org/10.3390/inorganics13020042

AMA Style

Bernhartzeder S, Blockhaus T, Lang M, Sünkel K. Studies Toward Persilylation of π-Cyclopentadienyl Complexes of Fe and Ru. Molecular Structures of [Fe(C5H5){C5(SiMe2H)5}], [Fe(C5H5){C5Br3(SiMe3)2}] and [Fe(C5H5){C5Br2(SiMe3)3}]. Inorganics. 2025; 13(2):42. https://doi.org/10.3390/inorganics13020042

Chicago/Turabian Style

Bernhartzeder, Stefanie, Tobias Blockhaus, Markus Lang, and Karlheinz Sünkel. 2025. "Studies Toward Persilylation of π-Cyclopentadienyl Complexes of Fe and Ru. Molecular Structures of [Fe(C5H5){C5(SiMe2H)5}], [Fe(C5H5){C5Br3(SiMe3)2}] and [Fe(C5H5){C5Br2(SiMe3)3}]" Inorganics 13, no. 2: 42. https://doi.org/10.3390/inorganics13020042

APA Style

Bernhartzeder, S., Blockhaus, T., Lang, M., & Sünkel, K. (2025). Studies Toward Persilylation of π-Cyclopentadienyl Complexes of Fe and Ru. Molecular Structures of [Fe(C5H5){C5(SiMe2H)5}], [Fe(C5H5){C5Br3(SiMe3)2}] and [Fe(C5H5){C5Br2(SiMe3)3}]. Inorganics, 13(2), 42. https://doi.org/10.3390/inorganics13020042

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