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Article

Synthesis and Characterization of N-Heterocyclic Carbene-Coordinated Silicon Compounds Bearing a Fused-Ring Bulky Eind Group

1
Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University 3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502, Japan
2
Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
3
Department of Biomolecular Functional Engineering, College of Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, Ibaraki 316-8511, Japan
4
Graduate School of Natural Sciences, Nagoya City University Yamanohata 1, Mizuho-cho, Mizuho-ku, Nagoya, Aichi 467-8501, Japan
5
RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
*
Author to whom correspondence should be addressed.
Inorganics 2018, 6(1), 30; https://doi.org/10.3390/inorganics6010030
Submission received: 23 December 2017 / Revised: 13 February 2018 / Accepted: 14 February 2018 / Published: 23 February 2018
(This article belongs to the Special Issue Coordination Chemistry of Silicon)

Abstract

:
The reactions of the fused-ring bulky Eind-substituted 1,2-dibromodisilene, (Eind)BrSi=SiBr(Eind) (1a) (Eind = 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl (a)), with N-heterocyclic carbenes (NHCs) (Im-Me4 = 1,3,4,5-tetramethylimidazol-2-ylidene and Im-iPr2Me2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) are reported. While the reaction of 1a with the sterically more demanding Im-iPr2Me2 led to the formation of the mono-NHC adduct of arylbromosilylene, (Im-iPr2Me2)→SiBr(Eind) (2a′), a similar reaction using the less bulky Im-Me4 affords the bis-NHC adduct of formal arylsilyliumylidene cation, [(Im-Me4)2→Si(Eind)]+[Br] (3a). The NHC adducts 2a′ and 3a can also be prepared by the dehydrobromination of Eind-substituted dibromohydrosilane, (Eind)SiHBr2 (4a), with NHCs. The NHC-coordinated silicon compounds have been characterized by spectroscopic methods. The molecular structures of bis-NHC adduct, [(Im-iPr2Me2)2→Si(Eind)]+[Br] (3a′), and 4a have been determined by X-ray crystallography.

Graphical Abstract

1. Introduction

Over many years, a number of unsaturated silicon compounds have been successfully obtained by virtue of the complexation of metal ions and/or coordination of ligands (mainly Lewis bases) in addition to steric protection with bulky substituents [1,2,3,4,5,6,7,8,9,10,11]. Among them, the coordination chemistry of highly-reactive halosilylenes, i.e., halogen-substituted divalent Si(II) species, have attracted a lot of attention as potentially useful precursors for the construction of a wide range of silicon-containing compounds [12,13,14,15,16,17]. Figure 1 shows recent examples of coordination-stabilized arylhalosilylenes and their derivatives [18,19,20,21,22,23,24]. In 2010, Filippou’s group reported the first N-heterocyclic carbene (NHC) adducts of arylchlorosilylenes bearing sterically large m-terphenyl groups, (Im-Me4)→SiCl(Ar) (Ic and Id) (Ar = 2,6-(Mes)2C6H3 (Mes = 2,4,6-Me3C6H2) (c) and 2,6-(Tip)2C6H3 (Tip = 2,4,6-iPr3C6H2) (d)), which were prepared by the dehydrochlorination of the aryldichlorohydrosilanes, (Ar)SiHCl2, with NHC (Im-Me4 = 1,3,4,5-tetramethylimidazol-2-ylidene) along with the formation of imidazolium chloride, [(Im-Me4)H]+[Cl] [18]. The NHC adduct Id reacted with [Li+][CpMo(CO)3] to afford the silylidene complex, Cp(CO)2Mo=Si(Ar)(Im-Me4) (IId), and the subsequent treatment with B(C6H4-4-Me)3 produced the first silylidyne complex, Cp(CO)2Mo≡Si(Ar) (IIId), featuring a metal-silicon triple bond [19,25].
In 2011, we reported on the 4-pyrrolidinopyridine (PPy) adducts of arylbromosilylenes with fused-ring bulky Rind groups, PPy→SiBr(Rind) (IVa and IVb) (Rind = 1,1,3,3,5,5,7,7-octa-R-substituted s-hydrindacen-4-yl; Eind (a: R1 = R2 = Et) and EMind (b: R1 = Et, R2 = Me)) [26,27], which were formed by the addition of PPy to 1,2-dibromodisilenes, (Rind)BrSi=SiBr(Rind) (1a and 1b) [20]. Also in 2011, Cui reported on the related NHC-coordinated aminochlorosilylene [28], and recently Driess’s group reported on the aminochlorosilylene-nickel complex [29]. In 2012, a platinum complex of arylbromosilylene, (Bbt)BrSi=Pt(PCy3)2 (Ve), was synthesized by the treatment of 1,2-dibromodisilene, (Bbt)BrSi=SiBr(Bbt) (1e), bearing the bulky Bbt groups (Bbt = 2,6-{CH(SiMe3)2}2-4-C(SiMe3)3-C6H2 (e)) [30] with Pt(PCy3)2 [21,31]. In this context, some arylbromosilylidene and arylsilylidyne complexes of nickel and platinum were reported [32,33,34]. In 2013, Filippou’s group reported the unprecedented dicationic NHC complexes of silicon(II) and NHC adducts of iodesilyliumylidene cation SiI+ [35]. Subsequently, we reported the reaction of 1,2-dibromodisilenes (1b, 1e, and 1f) having EMind, Bbt, and Tbb groups (Tbb = 2,6-{CH(SiMe3)2}2-4-tBu-C6H2 (f)) with NHCs (Im-Me4 and Im-iPr2Me2) (Im-iPr2Me2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) leading to the formation of mono-NHC adducts of arylbromosilylenes, NHC→SiBr(Ar) (VIb′ and VIe), and the bromide salts of the bis-NHC adducts of formal arylsilyliumylidene cations, [(NHC)2→Si(Ar)]+[Br] (VIIb, VIIb′, and VIIf) [22]. Inoue’s group also reported the synthesis of chloride salts of bis-NHC adducts of formal arylsilyliumylidene cations, [(Im-Me4)2→Si(Ar)]+[Cl] (VIIIc and VIIIg) (Ar = Tip (g)) [23] and their unique conversion to silicon analogues of acylium ions, [(Im-Me4)2→Si(O)(Ar)]+[Cl] (IXc and IXg) [24]. Recently, Inoue’s group reported on the chalcogen-atom transfer and exchange reactions of NHC-bound heavier silaacylium ions, [(Im-Me4)2→Si(E)(Ar)]+[Cl] (E = S, Se, and Te) [36].
In this article, we describe the preparation and characterization of NHC-coordinated silicon compounds bearing the bulky Eind group, which have been obtained by two different synthetic procedures, i.e., the NHC-induced fragmentation of the Eind-based 1,2-dibromo-disilene and the dehydrobromination of the Eind-based dibromohydrosilane with NHCs.

2. Results and Discussions

2.1. Reactions of (Eind)BrSi=SiBr(Eind) (1a) with NHCs

We first performed an NMR tube scale reaction of Eind-based 1,2-dibromodisilene, (Eind)BrSi=SiBr(Eind) (1a) [20], in C6D6 with two equivalents of the sterically more bulky NHC, Im-iPr2Me2, relative to Im-Me4. The progress of the reaction was monitored by 1H NMR spectroscopy, indicating the selective formation of the mono-NHC adduct of the arylbromosilylene, (Im-iPr2Me2)→SiBr(Eind) (2a′), after overnight heating at 70 °C. In the 29Si NMR spectrum, only one signal was observed at δ = 18.0 ppm, which is comparable to those of (Im-iPr2Me2)→SiBr(EMind) (VIb′) (δ = 13.1 ppm) and (Im-Me4)→SiBr(Bbt) (VIe) (δ = 10.9 ppm) [22]. The 13C signal at δ = 170.6 ppm for 2a′ is characteristic of a carbene carbon atom, similar to those for VIb′ (δ = 169.7 ppm) and VIe (δ = 167.5 ppm) [22]. Based on the NMR tube experiment, the mono-NHC adduct 2a′ was synthesized as an orange solid in 88% crude yield (Scheme 1).
We also examined the reaction of 1a with four equivalents of Im-iPr2Me2. After 1-day heating at 70 °C in C6D6, the 29Si NMR spectrum indicated the formation of a mixture containing the mono-NHC adduct 2a′ (δ = 18.0 ppm) as the major product and the bis-NHC adduct of the arylsilyliumylidene cation, [(Im-iPr2Me2)2→Si(Eind)]+[Br] (3a′) (δ = −59.6 ppm), as the minor product. The latter 29Si signal was shifted upfield compared to the former, and was similar to those of the formal arylsilyliumylidene cations, [(NHC)2→Si(EMind)]+[Br] (VIIb and VIIb′) (δ = −60.8 and −75.9 ppm) and [(Im-Me4)2→Si(Tbb)]+[Br] (VIIf) (δ = −70.9 ppm) [22]. However, we found that the reaction was not completed even after prolonged heating (longer than 1 week), probably due to the severe steric repulsion between the Eind group and Im-iPr2Me2 molecules. Thus, we were unable to isolate 3a′. Nevertheless, single red crystals of 3a′ could be obtained from the reaction mixture, whose structure was determined by X-ray crystallography (Figure 2).
Figure 2 shows a separated ion pair of 3a′ in the crystal. The closest Si⋯Br distance (7.6669(6) Å) is analogous to that of VIIb′ (7.732(3) Å) [22], thus being much longer than the sum of the van der Waals radii of Si and Br (3.95 Å). The Si atom is three-coordinate adopting a distorted pyramidal geometry, which can be explained by the presence of a lone pair of electrons. The sum of the surrounding angles around the Si atom (ΣSi = 327.3°) is almost the same as that of VIIb′ (ΣSi = 327.0°) [22]. The Si–C(Rind) bond length in 3a′ (Si1–C1 = 1.9482(19) Å) is similar to that in VIIb′ [1.927(8) Å] [22] and longer than typical Si–C bonds (ca. 1.88 Å), suggesting the high s-character of the lone pair of electrons on the Si atom and the high p-character of the Si–C(Rind) bond. The Si←C(NHC) coordination distances in 3a′ (Si1–C29 = 1.953(2) and Si1–C40 = 1.942(2) Å) are comparable to those observed in VIIb′ (1.955(9) and 1.979(8) Å) [22].
We next investigated the reaction of 1a with two equivalents of the less bulky NHC, Im-Me4, and C6D6. After 1 day at room temperature, two signals mainly appeared at δ = 73.3 and −63.3 ppm in the 29Si NMR spectrum, corresponding to the unreacted 1a and the bis-NHC adduct of the arylsilyliumylidene cation, [(Im-Me4)2→Si(Eind)]+[Br] (3a). This indicated that the NHC-arylbromosilylene adduct, (Im-Me4)→SiBr(Eind) (2a), which serves as a potential intermediate, is more reactive toward Im-Me4 compared to 1a. When the dibromodisilene 1a was treated with four equivalents of Im-Me4 in benzene, the bis-NHC adduct 3a was efficiently formed (Scheme 1). We obtained 3a as an orange powder in 54% crude yield. The upfield-shifted 29Si resonance for 3a (δ = −63.3 ppm) suggests the contribution of the canonical form due to the bis(imidazolium) adduct of a silyl anion, whose electronic structure was previously supported by the theoretical calculations of VIIb′ and VIIf [22]. In the 13C NMR spectrum of 3a in CD3CN, one NHC carbene signal was observed at δ = 162.0 ppm, comparable to those for VIIb (δ = 160.5 ppm), VIIb′ (δ = 162.4 ppm), and VIIf (δ = 160.4 ppm) [22].

2.2 Reactions of (Eind)SiHBr2 (4a) with NHCs

We also examined another synthetic route for the NHC-coordinated silicon compounds, i.e., the dehydrobromination of the Eind-substituted dibromohydrosilane, (Eind)SiHBr2 (4a), with NHCs (Scheme 2). The precursor (4a) was prepared as pale brown crystals by the dibromination of the Eind-based trihydrosilane, (Eind)SiH3 [37,38], with allyl bromide in the presence of a catalytic amount of PdCl2 [39]. We found that this reaction exclusively afforded 4a even using an excess amount of allyl bromide with prolonged heating (longer than 1 week), most likely due to the steric bulkiness of the Eind group. In this context, Kunai, Ohshita, and their co-workers previously reported the selective dibromination of trihydrosilanes with CuBr2 in the presence of CuI [40]. The formation of 4a was deduced on the basis of the spectroscopic data (Figures S1–S4). In the 1H NMR spectrum, the Si–H signal was found at δ = 6.89 ppm with satellite signals, due to the 29Si nuclei [1J(29Si–1H) = 288 Hz]. The 29Si NMR signal appeared at δ = −28.7 ppm, similar to that of (Bbt)SiHBr2 (δ = −28.47 ppm) [41]. The infrared spectrum exhibited a Si–H stretching band at 2317 cm–1 in the KBr-pellet (Figure S4) and at 2298 cm–1 in THF [42,43]. The molecular structure of 4a was determined by single-crystal X-ray diffraction analysis (Figure 3). The hydrogen atom on the silicon atom was located on difference Fourier maps and isotropically refined. In the crystal, the SiHBr2 group is fixed in one conformation with respect to the rotamer around the Si–C bond. A similar conformation was also observed in the crystal of (Eind)PCl2 [44]. The Si–C bond length for 4a (1.8746(18) Å) is comparable to those of typical Si–C bonds (ca. 1.88 Å).
As shown in Scheme 2, the reaction of 4a with two equivalents of Im-iPr2Me2 proceeded more smoothly at room temperature in comparison to the reaction of 1a with Im-iPr2Me2 (Scheme 1), producing the mono-NHC adduct 2a′ in 59% crude yield. The reaction of 4a with three equivalents of Im-Me4 also afforded the bis-NHC adduct 3a on the basis of the NMR data. In these reactions, it is essential to remove the byproducts, imidazolium bromides, [(NHC)H]+[Br], for the isolation procedure of the silicon products, which may be considered as a disadvantage when compared to the no-byproduct strategy of using 1a as a precursor (vide supra). Actually, the separation of 3a and [(Im-Me4)H]+[Br] was found to be difficult in our experiments. However, dibromodisilene 1a can only be obtained by a two-step synthesis from the trihydrosilane, (Eind)SiH3; thus the bromination of (Eind)SiH3 with N-bromosuccinimide (NBS) first affords the tribromosilane, (Eind)SiBr3, then the reduction of (Eind)SiBr3 with two equivalents of lithium naphthalenide (LiNaph) produces 1a [20]. Therefore, the dehydrobromination of 4a with NHCs can be considered as a convenient short-step synthesis for NHC-coordinated silylene derivatives.

3. Materials and Methods

3.1. General Procedures

All manipulations of the air- and/or moisture-sensitive compounds were performed either using standard Schlenk-line techniques or in a glove box under an inert atmosphere of argon. Anhydrous hexane, benzene, and toluene were dried by passage through columns of activated alumina and supported copper catalyst supplied by Nikko Hansen & Co., Ltd. (Osaka, Japan). Anhydrous pentane and acetonitrile were purchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan), and used without further purification. Deuterated benzene (C6D6, benzene-d6) was dried and degassed over a potassium mirror in vacuo prior to use. Deuterated acetonitrile (CD3CN, acetonitrile-d3) was dried and distilled over calcium hydride (CaH2) prior to use. (Eind)SiH3 [37,38], (Eind)BrSi=SiBr(Eind) (1a) [20], 1,3,4,5-tetramethylimidazol-2-ylidene (Im-Me4) [45] and 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene(Im-iPr2Me2) [45] were prepared by the literature procedures. All other chemicals and gases were used as received.
Nuclear magnetic resonance (NMR) measurements were carried out using a JEOL ECS-400 spectrometer (399.8 MHz for 1H, 100.5 MHz for 13C, and 79.4 MHz for 29Si) or JEOL JNM AL-300 spectrometer (300 MHz for 1H, 75 MHz for 13C, and 59 MHz for 29Si) (JEOL Ltd., Tokyo, Japan). Chemical shifts (δ) are given by definition as dimensionless numbers and relative to 1H chemical shifts of the solvents for 1H (residual C6D5H in C6D6, 1H(δ) = 7.15, residual CD2HCN in CD3CN, 1H(δ) = 1.94), and 13C chemical shifts of the solvent for 13C (C6D6: 13C(δ) = 128.06 and CD3CN: 13C(δ) = 118.26). The signal of tetramethylsilane (29Si(δ) = 0.0) was used as an external standard in the 29Si NMR spectra. The absolute values of the coupling constants are given in Hertz (Hz) regardless of their signs. Multiplicities are abbreviated as singlet (s), doublet (d), triplet (t), quartet (q), multiplet (m), and broad (br). The mass spectra were recorded by a JEOL JMS-T100LC AccuTOF LC-plus 4G mass spectrometer (ESI-MS) with a DART source. The elemental analyses were performed in the Microanalytical Laboratory at the Institute for Chemical Research (Kyoto University, Uji, Japan). Melting points (m.p.) were determined by a Stanford Research Systems OptiMelt instrument. We were unable to obtain a satisfactory elemental analysis for 2a′ and 3a, probably due to their extremely high air- and moisture-sensitivity as well as a contamination of NHCs and unidentified compounds associated with some thermal decomposition (Figures S5–S10).

3.1.1. Synthesis of (Eind)SiHBr2 (4a)

To a solution of (Eind)SiH3 (4.09 g, 9.91 mmol) in toluene (30 mL) was added PdCl2 (38.0 mg, 0.21 mmol) and allyl bromide (4.2 mL, 48.5 mmol). The reaction mixture was heated at 80 °C for 8 days. After the solvent was removed in vacuo, the residue was dissolved in hexane and the resulting mixture was centrifuged to remove the insoluble materials. The supernatant was concentrated to dryness and the resulting residue was recrystallized from pentane to afford 4a as pale brown crystals in 81% yield (4.58 g, 8.02 mmol).
1H NMR (399.8 MHz, C6D6, 30 °C): δ = 0.78 (t, J = 7.3 Hz, 12 H, CH2CH3), 0.80 (br. s, 12 H, CH2CH3), 1.48–1.65 (m, 8 H, CH2CH3), 1.76 (s, 4 H, CH2), 2.11 (br. s, 8 H, CH2CH3), 6.89 (s, 1 H, satellite, JSi–H = 288 Hz, SiH), 7.01 (s, 1 H, ArH). 13C NMR (100.5 MHz, C6D6, 25 °C): δ = 9.3, 10.5 (br), 33.5, 34.2 (br), 42.6 (br ×1), 44.8 (br ×1), 47.9 (br ×2), 54.7 (×2), 123.6, 125.1, 150.8 (one aromatic peak is broadened at 155–158); 29Si NMR (79.4 MHz, C6D6, 30 °C): δ = −28.7 (d, JSi–H = 288 Hz). IR (KBr, cm−1): ν = 2317 (Si−H); IR (THF, cm−1): ν = 2298 (Si−H). DART-HRMS (positive-mode) Calcd. for C28H46Br2Si + H: 569.1814. Found: 569.1820. Anal. Calcd. for C28H46Br2Si: C, 58.94; H, 8.13. Found: C, 59.41; H, 8.19. Melting point (argon atmosphere in a sealed tube) 102–105 °C.

3.1.2. Synthesis of (Im-iPr2Me2)→SiBr(Eind) (2a′)

(Method A) Reaction of (Eind)BrSi=SiBr(Eind) (1a) with Im-iPr2Me2

A mixture of 1a (158 mg, 0.16 mmol) and Im-iPr2Me2 (63.0 mg, 0.35 mmol) was dissolved in benzene (5 mL). The reaction mixture was heated overnight at 70 °C. After the solvent was removed in vacuo, the residue was washed with pentane to afford 2a′ as an orange solid in 88% crude yield (190 mg, 0.28 mmol). We were unable to isolate 2a′ in pure form, because 2a′ was not thermally stable in solution, gradually giving Im-iPr2Me2 and unidentified compounds (Figure S5).
1H NMR (399.8 MHz, C6D6, 60 °C): δ = 0.81–1.00 (m, 24 H, CH2CH3), 1.12 (br. s, 6 H, CH(CH3)2–(Im-iPr2Me2)), 1.19 (d, J = 7.0 Hz, 6 H, CH(CH3)2–(Im-iPr2Me2)), 1.61 (s, 6 H, CH3–(Im-iPr2Me2)), 1.62–1.95 (m, 20 H, CH2 + CH2CH3), 5.00–5.27 (m, 2 H, CH(CH3)2–(Im-iPr2Me2)), 6.71 (s, 1 H, ArH). 13C NMR (100.5 MHz, C6D6, 70 °C): δ = 9.3, 9.4, 9.9, 10.0, 10.5, 20.7, 21.4, 24.6, 33.7 (br, overlapped, Im-iPr2Me2 and CH2CH3), 42.8, 48.4, 51.1 (Im-iPr2Me2), 54.5, 119.9, 125.9 (Im-iPr2Me2), 147.2, 148.5, 153.7, 170.6 (Im-iPr2Me2); 29Si NMR (79.4 MHz, C6D6, 25 °C): δ = 18.0. HRMS (ESI, positive) Calcd. for C39H65BrN2Si + H: 669.4179. Found: 669.4211. Melting point (argon atmosphere in a sealed tube) 152–156 °C (dec.).

(Method B) Reaction of (Eind)SiHBr2 (4a) with Im-iPr2Me2

A mixture of 4a (476 mg, 0.97 mmol) and Im-iPr2Me2 (352 mg, 1.95 mmol) was dissolved in benzene (7 mL). After stirring overnight at room temperature, the resulting orange suspension was filtered through a polytetrafluoroethylene (PTFE) syringe filter to remove the insoluble materials. The filtrate was concentrated to dryness and the resulting residue was washed with pentane to afford 2a′ as an orange solid in 59% crude yield (197 mg, 0.29 mmol).

3.1.3. Synthesis of [(Im-Me4)2→Si(Eind)]+[Br] (3a)

(Method A) Reaction of (Eind)BrSi=SiBr(Eind) (1a) with Im-Me4

A mixture of 1a (102 mg, 0.11 mmol) and Im-Me4 (54 mg, 0.43 mmol) was dissolved in benzene (6 mL). After stirring for 1 day at room temperature, the resulting orange solid was separated and washed with a mixture of hexane and benzene to afford 3a as an orange powder in 54% crude yield (85.2 mg, 0.12 mmol). We were unable to isolate 3a in pure form, because 3a was not thermally stable in solution leading to the contamination of Im-Me4 and unidentified compounds (Figure S8).
1H NMR (399.8 MHz, CD3CN, 20 °C): δ = 0.61 (br. t, J = 6.3 Hz, 12 H, CH2CH3), 0.80 (t, J = 7.3 Hz, 12 H, CH2CH3), 1.50–1.70 (m, 8 H, CH2CH3), 1.75 (br. s, 4 H, CH2), 1.93−1.97 (m, overlapped, 8 H, CH2CH3), 2.15 (s, 12 H, CH3–(Im-Me4)), 3.25 (br. s, 12 H, CH3–(Im-Me4)), 6.75 (s, 1 H, ArH). 13C NMR (100.5 MHz, CD3CN, 19 °C): δ = 9.2, 9.4, 10.0 (br, Im-Me4), 34.1 (br, overlapped, Im-Me4 and CH2CH3), 42.8, 48.1, 54.2, 121.8, 128.5 (Im-Me4), 136.5, 150.7, 162.0 (Im-Me4) (one aromatic peak is overlapped). 29Si NMR (79.4 MHz, CD3CN, 25 °C): δ = −63.3. DART-HRMS (positive-mode) Calcd. for C42H69BrN4Si + H: 737.4553. Found: 737.4562. Melting point (argon atmosphere in a sealed tube) 169–174 °C (dec.).

(Method B) Reaction of (Eind)SiHBr2 (4a) with Im-Me4

A mixture of 4a (70.3 mg, 0.12 mmol) and Im-Me4 (50.6 mg, 0.41 mmol) was dissolved in benzene (6 mL). After stirring for 1 day at room temperature, an orange suspension was formed. An insoluble orange solid was collected by filtration, whose 1H NMR spectrum indicated the formation of a mixture of 4a and [(Im-Me4)H]+[Br].

3.2. X-ray Crystallographic Studies of 3a′ and 4a

Single crystals suitable for X-ray diffraction measurements were obtained from benzene for 3a′ and from hexane for 4a. Intensity data were collected using a Rigaku XtaLAB P200 with a PILATUS 200K detector for 3a′ and a Rigaku AFC-8 with a Saturn 70 CCD detector for 4a (Rigaku Corporation, Tokyo, Japan). All measurements were carried out using Mo Kα radiation (λ = 0.71073 Å). The integration and scaling of the diffraction data were carried out using the programs CrysAlisPro [46] for 3a′ and CrystalClear [47] for 4a. Lorentz, polarization, and absorption corrections were also performed. The structures were solved by an iterative method with the program of SHELXT [48], and refined by a full-matrix least-squares method on F2 for all the reflections using the program SHELXL-2017/1 [49]. The non-hydrogen atoms were refined by applying anisotropic temperature factors. Positions of all the hydrogen atoms were geometrically calculated, and refined as riding models. The Si–H hydrogen atom was located on difference Fourier maps and isotropically refined. Full details of the crystallographic analysis and accompanying CIF files can be obtained free of charge from the Cambridge Crystallographic Data Centre (CCDC numbers 1811699 and 1811700) via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44-1223-336033; E-mail: [email protected]).

3.2.1. [(Im-iPr2Me2)2→Si(Eind)]+[Br] (3a′)

C50H85BrN4Si·C6H6, M = 928.32, crystal size 0.36 × 0.15 × 0.12 mm, triclinic, space group P−1 (#2), a = 10.6548(3) Å, b = 12.0149(2) Å, c = 21.7366(5) Å, α = 80.5199(18)°, β = 82.343(2)°, γ = 72.816(2)°, V = 2611.54(11) Å3, Z = 2, Dx = 1.181 g cm−3, μ(Mo Kα) = 0.849 mm−1, 65594 reflections collected, 13761 unique reflections, and 579 refined parameters. The final R(F) value was 0.0491 [I > 2σ(I)]. The final Rw(F2) value was 0.1364 (all data). The goodness-of-fit on F2 was 1.031.

3.2.2. (Eind)SiHBr2 (4a)

C28H46Br2Si, M = 570.56, crystal size 0.16 × 0.17 × 0.41 mm, triclinic, space group P−1 (#2), a = 7.972(3) Å, b = 11.070(4) Å, c = 16.621(5) Å, α = 89.972(4)°, β = 80.770(3)°, γ = 73.314(5)°, V = 1385.1(8) Å3, Z = 2, Dx = 1.368 g cm−3, μ(Mo Kα) = 2.992 mm−1, 22599 reflections collected, 6332 unique reflections, and 292 refined parameters. The final R(F) value was 0.0298 [I > 2σ(I)]. The final Rw(F2) value was 0.0803 (all data). The goodness-of-fit on F2 was 1.016.

4. Conclusions

We have synthesized some new NHC-coordinated silicon species having the fused-ring bulky Eind group by two methods; one is via the reactions of the stable diaryldibromodisilene, (Eind)BrSi=SiBr(Eind) (1a), with NHCs, and the other is the dehydrobromination of the aryldibromohydrosilane, (Eind)SiHBr2 (4a), with NHCs. In both synthetic pathways, we have mainly obtained the mono-NHC adduct of the arylbromosilylene, (Im-iPr2Me2)→SiBr(Eind) (2a′), and the bis-NHC adduct of the formal arylsilyliumylidenecation, [(Im-Me4)2→Si(Eind)]+[Br] (3a), depending on the steric bulk of the NHCs (Im-iPr2Me2 vs. Im-Me4). Further studies on the reactivities of the NHC-coordinated silicon compounds are now in progress.

Supplementary Materials

The following are available online at https://www.mdpi.com/2304-6740/6/1/30/s1, S1: NMR spectra of 4a, 2a′, and 3a and IR spectrum of 4a (PDF), S2: crystallographic details for 4a and 3a′ (CIF) and S3: cif-checked files (PDF).
Supplementary File 1

Acknowledgments

This study was supported by Grants-in-Aid for Scientific Research on Innovative Areas “Stimuli-responsive Chemical Species for the Creation of Functional Molecules (No. 2408)” (JSPS KAKENHI Grant Nos. JP20109003 for Tsukasa Matsuo, JP15H00964 for Daisuke Hashizume, and JP20109013 for Norihiro Tokitoh), Scientific Research (B) (No. JP15H03788 for Tsukasa Matsuo and JP15H03777 for Takahiro Sasamori), Young Scientists (A) (No. 15H05477 for Tomohiro Agou) and Challenging Exploratory Research (No. 16K13953 for Tomohiro Agou). This study was partially supported by a MEXT-Supported Program for the Strategic Research Foundation at Private Universities 2014–2018 subsidy from MEXT and Kindai University. We thank the Collaborative Research Program of The Institute for Chemical Research, Kyoto University (grants #2016-94 and #2017-99). Naoki Hayakawa and Tomohiro Sugahara acknowledge the support by Grants-in-Aid for JSPS Fellows from JSPS (Nos. JP16J01036 and JP16J05501).

Author Contributions

Naoki Hayakawa, Kazuya Sadamori, Shinsuke Mizutani, Tomohiro Agou, and Tomohiro Sugahara performed the experiments. Naoki Hayakawa and Daisuke Hashizume carried out the X-ray crystallographic analysis. Tomohiro Sugahara, Norihiro Tokitoh, and Tsukasa Matsuo designed the experiments and co-directed the project. Naoki Hayakawa, Kazuya Sadamori, and Tsukasa Matsuo co-wrote the paper. Takahiro Sasamori, Norihiro Tokitoh, Daisuke Hashizume, and Tsukasa Matsuo reviewed and approved the final manuscript. All authors contributed to the discussions.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Kira, M.; Iwamoto, T. Progress in the chemistry of stable disilenes. Adv. Organomet. Chem. 2006, 54, 73–148. [Google Scholar]
  2. Wang, Y.; Robinson, G.H. Unique homonuclear multiple bonding in main group compounds. Chem. Commun. 2009, 5201–5213. [Google Scholar] [CrossRef] [PubMed]
  3. Mizuhata, Y.; Sasamori, T.; Tokitoh, N. Stable heavier carbene analogues. Chem. Rev. 2009, 109, 3479–3511. [Google Scholar] [CrossRef] [PubMed]
  4. Fischer, R.C.; Power, P.P. π-Bonding and lone pair effect in multiple bonds involving heavier main group elements: Developments in the new millennium. Chem. Rev. 2010, 110, 3877–3923. [Google Scholar] [CrossRef] [PubMed]
  5. Lee, V.Y.; Sekiguchi, A. Organometallic Compounds of Low-Coordinate Si, Ge, Sn and Pb: From Phantom Species to Stable Compounds; John Wiley & Sons Ltd.: Chichester, UK, 2010; ISBN 978-0-470-72543-6. [Google Scholar]
  6. Asay, M.; Jones, C.; Driess, M. N-Heterocyclic carbene analogues with low-valent group 13 and group 14 elements: Syntheses, structures, and reactivities of a new generation of multitalented ligands. Chem. Rev. 2011, 111, 354–396. [Google Scholar] [CrossRef] [PubMed]
  7. Yao, S.; Xiong, Y.; Driess, M. Zwitterionic and donor-stabilized N-heterocyclic silylenes (NHSis) for metal-free activation of small molecules. Organometallics 2011, 30, 1748–1767. [Google Scholar] [CrossRef]
  8. Kira, M. Bonding and structure of disilenes and related unsaturated Group-14 element compounds. Proc. Jpn. Acad. Ser. B Phys. Biol. Sci. 2012, 88, 167–191. [Google Scholar] [CrossRef] [PubMed]
  9. Scheschkewitz, D. Functional Molecular Silicon Compounds II: Low Oxidation States; Springer: Basel, Switzerland, 2014; ISBN 978-3-319-03734-9. [Google Scholar]
  10. Wang, Y.; Robinson, G.H. N-heterocyclic carbene—Main-group chemistry: A rapidly evolving field. Inorg. Chem. 2014, 53, 11815–11832. [Google Scholar] [CrossRef] [PubMed]
  11. Ghadwal, R.S.; Azhakar, R.; Roesky, H.W. Dichlorosilylene: A high temperature transient species to an indispensable building block. Acc. Chem. Res. 2013, 46, 444–456. [Google Scholar] [CrossRef] [PubMed]
  12. Ghadwal, R.S.; Roesky, H.W.; Merkel, S.; Henn, J.; Stalke, D. Lewis base stabilized dichlorosilylene. Angew. Chem. Int. Ed. 2009, 48, 5683–5686. [Google Scholar] [CrossRef] [PubMed]
  13. Filippou, A.C.; Chernov, O.; Schnakenburg, G. SiBr2(Idipp): A stable N-heterocyclic carbene adduct of dibromosilylene. Angew. Chem. Int. Ed. 2009, 48, 5687–5690. [Google Scholar] [CrossRef] [PubMed]
  14. Roy, S.; Stollberg, P.; Herbst-Irmer, R.; Stalke, D.; Andrada, D.M.; Frenking, G.; Roesky, H.W. Carbene-dichlorosilylene stabilized phosphinidenes exhibiting strong intramolecular charge transfer transition. J. Am. Chem. Soc. 2015, 137, 150–153. [Google Scholar] [CrossRef] [PubMed]
  15. Hickox, H.P.; Wang, Y.; Xie, Y.; Wei, P.; Schaefer, H.F., III; Robinson, G.H. Push-pull stabilization of parent monochlorosilylenes. J. Am. Chem. Soc. 2016, 138, 9799–9802. [Google Scholar] [CrossRef] [PubMed]
  16. Geiβ, D.; Arz, M.I.; Straβmann, M.; Schnakenburg, G.; Filippou, A.C. Si=P double bonds: experimental and theoretical study of an NHC-stabilized phosphasilenylidene. Angew. Chem. Int. Ed. 2015, 54, 2739–2744. [Google Scholar]
  17. Ghana, P.; Arz, M.I.; Das, U.; Schnakenburg, G.; Filippou, A.C. Si=Si double bonds: Synthesis of an NHC-stabilized disilavinylidene. Angew. Chem. Int. Ed. 2015, 54, 9980–9985. [Google Scholar] [CrossRef] [PubMed]
  18. Filippou, A.C.; Chernov, O.C.; Blom, B.; Stumpf, K.W.; Schnakenburg, G. Stable N-heterocyclic carbene adducts of arylchlorosilylenes and their germanium homologues. Chem. Eur. J. 2010, 16, 2866–2872. [Google Scholar] [CrossRef] [PubMed]
  19. Filippou, A.C.; Chernov, O.C.; Stumpf, K.W.; Schnakenburg, G. Metal-silicon triple bonds: The molybdrnumsilylidyne complex [Cp(CO)2Mo≡Si-Ar]. Angew. Chem. Int. Ed. 2010, 49, 3296–3300. [Google Scholar] [CrossRef] [PubMed]
  20. Suzuki, K.; Matsuo, T.; Hashizume, D.; Tamao, K. Room-temperature dissociation of 1,2-dibromodisilenes to bromosilylenes. J. Am. Chem. Soc. 2011, 133, 19710–19713. [Google Scholar] [CrossRef] [PubMed]
  21. Agou, T.; Sasamori, T.; Tokitoh, N. Synthesis of an arylbromosilylene-platinum complex by using a 1,2-dibromodisilene as a silylene source. Organometallics 2012, 31, 1150–1154. [Google Scholar] [CrossRef]
  22. Agou, T.; Hayakawa, N.; Sasamori, T.; Matsuo, T.; Hashizume, D.; Tokitoh, N. Reactions of diaryldibromodisilenes with N-heterocyclic carbenes: Formation of formal bis-NHC adducts of silyliumylidene cations. Chem. Eur. J. 2014, 20, 9246–9249. [Google Scholar] [CrossRef] [PubMed]
  23. Ahmad, S.U.; Szilvási, T.; Inoue, S. A facile access to a novel NHC-stabilized silyliumylidene ion and C–H activation of phenylacetylene. Chem. Commun. 2014, 50, 12619–12622. [Google Scholar] [CrossRef] [PubMed]
  24. Ahmad, S.U.; Szilvási, T.; Irran, E.; Inoue, S. An NHC-stabilized silicon analogue of acylium ion: Synthesis, structure, reactivity, and theoretical studies. J. Am. Chem. Soc. 2015, 137, 5828–5836. [Google Scholar] [CrossRef] [PubMed]
  25. Mork, B.V.; Tilley, T.D. Multiple bonding between silicon and molybdenum: A transition-metal complex with considerable silylyne character. Angew. Chem. Int. Ed. 2003, 42, 357–360. [Google Scholar] [CrossRef] [PubMed]
  26. Matsuo, T.; Suzuki, K.; Fukawa, T.; Li, B.L.; Ito, M.; Shoji, Y.; Otani, T.; Li, L.C.; Kobayashi, M.; Hachiya, M.; et al. Synthesis and structures of a series of bulky “Rind-Br” based on a rigid fused-ring s-hydrindacene skeleton. Bull. Chem. Soc. Jpn. 2011, 84, 1178–1191. [Google Scholar] [CrossRef]
  27. Matsuo, T.; Tamao, K. Fused-ring bulky “Rind” groups producing new possibilities in elemento-organic chemistry. Bull. Chem. Soc. Jpn. 2015, 88, 1201–1220. [Google Scholar] [CrossRef]
  28. Cui, H.; Cui, C. Silylation of N-heterocyclic carbene with aminochlorosilane and -disilane: Dehydrohalogenation vs. Si–Si bond cleavage. Dalton Trans. 2011, 40, 11937–11940. [Google Scholar] [CrossRef] [PubMed]
  29. Hadlington, T.J.; Szilvási, T.; Driess, M. Silylene-nichkel promoted cleavage of B–O bonds: From catechol borane to the hydroborylene ligand. Angew. Chem. Int. Ed. 2017, 56, 7470–7474. [Google Scholar] [CrossRef] [PubMed]
  30. Sasamoti, T.; Hironaka, K.; Sugiyama, Y.; Takagi, N.; Nagase, S.; Hosoi, Y.; Furukawa, Y.; Tokitoh, N. Synthesis and reactions of a stable 1,2-diaryl-1,2-dibromodisilene: A precursor for substituted disilenes and a 1,2-diaryldisilyne. J. Am. Chem. Soc. 2008, 130, 13856–13857. [Google Scholar] [CrossRef] [PubMed]
  31. Liao, W.-H.; Ho, P.-Y.; Su, M.-D. Mechanisms for the reactions of Group 10 transition metal complexes with metal-group 14 element bonds, Bbt(Br)E=M(PCy3)2 (E = C, Si, Ge, Sn, Pb; M = Pd and Pt). Inorg. Chem. 2013, 52, 1338–1348. [Google Scholar] [CrossRef] [PubMed]
  32. Filippou, A.C.; Hoffmann, D.; Schnakenburg, G. Triple bonds of niobium with silicon, germanium and tin: The tetrylidyne complexes [(κ3-tmps)(CO)2Nb≡E–R] (E = Si, Ge, Sn; tmps = MeSi(CH2OMe2)3; R = aryl). Chem. Sci. 2017, 8, 6290–6299. [Google Scholar] [CrossRef]
  33. Blom, B. Reactivity of Ylenes at Late Transition Metal Centers. Dissertation, University of Bonn, Göttingen, Germany, 2011. [Google Scholar]
  34. Papazoglou, I. Unprecedented Tetrylidyne Complexes of Group 6 and Group 10 Metals. Dissertation, University of Bonn, Dr. Hut Verlag, München, Germany, 28 May 2017. [Google Scholar]
  35. Filippou, A.C.; Lebedev, Y.N.; Chernov, O.; Straβmann, M.; Schnakenburg, G. Silicon(II) coordination chemistry: N-Heterocyclic carbene complexes of Si2+ and SiI+. Angew. Chem. Int. Ed. 2013, 52, 6974–6978. [Google Scholar] [CrossRef] [PubMed]
  36. Sarkar, D.; Wendel, D.; Ahmad, S.U.; Szilvási, T.; Pöthig, A.; Inoue, S. Chalcogen-atom transfer and exchange reactions of NHC-stabilized heavier silaacylium ions. Dalton Trans. 2017, 46, 16014–16018. [Google Scholar] [CrossRef] [PubMed]
  37. Fukazawa, A.; Li, Y.; Yamaguchi, S.; Tsuji, H.; Tamao, K. Coplanar oligo(p-phenylenedisilenylene)s based on the octaethyl-substituted s-hydrindacenyl groups. J. Am. Chem. Soc. 2007, 129, 14164–14165. [Google Scholar] [CrossRef] [PubMed]
  38. Kobayashi, M.; Hayakawa, N.; Nakabayashi, K.; Matsuo, T.; Hashizume, D.; Fueno, H.; Tanaka, K.; Tamao, K. Highly coplanar (E)-1,2-di(1-naphthyl)disilene involving a distinct CH–π interaction with the perpendicularly oriented protecting Eind group. Chem. Lett. 2014, 43, 432–434. [Google Scholar] [CrossRef]
  39. Iwata, A.; Toyoshima, Y.; Hayashida, T.; Ochi, T.; Kunai, A.; Ohshita, J. PdCl2 and NiCl2-catalyzed hydrogen-halogen exchange for the convenient preparation of bromo- and iodosilanes and germanes. J. Organomet. Chem. 2003, 667, 90–95. [Google Scholar] [CrossRef]
  40. Kunai, A.; Ochi, T.; Iwata, A.; Ohshita, J. Synthesis of bromohydrosilanes: Reactions of hydrosilanes with CuBr2 in the presence of CuI. Chem. Lett. 2001, 1228–1229. [Google Scholar] [CrossRef]
  41. Agou, T.; Sugiyama, Y.; Sasamori, T.; Sakai, H.; Furukawa, Y.; Takagi, N.; Guo, J.-D.; Nagasa, S.; Hashizume, D.; Tokitoh, N. Synthesis of Kinetically Stabilized 1,2-Dihydrodisilenes. J. Am. Chem. Soc. 2012, 134, 4120–4123. [Google Scholar] [CrossRef] [PubMed]
  42. Simons, R.S.; Haubrich, S.T.; Mork, B.V.; Niemeyer, M.; Power, P.P. The Syntheses and Characterization of the Bulky Terphenylsilanes and Chlorosilanes 2,6-Mes2C6H3SiCl3, 2,6-Trip2C6H3SiCl3, 2,6-Mes2C6H3SiHCl2, 2,6-Trip2C6H3SiHCl2, 2,6-Mes2C6H3SiH3, 2,6-Trip2C6H3SiH3 and 2,6-Mes2C6H3SiC12SiCl3. Main Group Chem. 1998, 2, 275–283. [Google Scholar] [CrossRef]
  43. Weidemann, N.; Schnakenburg, G.; Filippou, A.C. Novel silanes with sterically demanding aryl substituents. Z. Anorg. Allg. Chem. 2009, 635, 253–259. [Google Scholar] [CrossRef]
  44. Li, B.; Tsujimoto, S.; Li, Y.; Tsuji, H.; Tamao, K.; Hashizume, D.; Matsuo, T. Synthesis and characterization of diphosphenes bearing fused-ring bulky Rind groups. Heteroat. Chem. 2014, 25, 612–618. [Google Scholar] [CrossRef]
  45. Kuhn, S.; Kratz, T. Synthesis of imidazol-2-ylidenes by reduction of imidazole-2(3H)-thiones. Synthesis 1993, 561–562. [Google Scholar] [CrossRef]
  46. CrysAlisPro; Agilent Technologies Ltd.: Yarnton, Oxfordshire, UK, 2014.
  47. CrystalClear; Rigaku/MSC. Inc.: The Woodlands, TX, USA, 2005.
  48. Sheldrick, G.M. SHELXT—Integrated space-group and crystal-structure determination. Acta Crystallogr. Sect. A 2015, A71, 3–8. [Google Scholar] [CrossRef] [PubMed]
  49. Sheldrick, G.M. Crystal structure refinement with SHELXL. Acta Crystallogr. Sect. C 2015, C71, 3–8. [Google Scholar]
Figure 1. Examples of coordination-stabilized arylhalosilylenes and their derivatives. Each one of the possible canonical forms is depicted.
Figure 1. Examples of coordination-stabilized arylhalosilylenes and their derivatives. Each one of the possible canonical forms is depicted.
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Scheme 1. Reactions of 1a with N-heterocyclic carbenes (NHCs).
Scheme 1. Reactions of 1a with N-heterocyclic carbenes (NHCs).
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Figure 2. Molecular structure of 3a′. The thermal ellipsoids are shown at the 50% probability level. All hydrogen atoms and benzene molecule are omitted for clarity.
Figure 2. Molecular structure of 3a′. The thermal ellipsoids are shown at the 50% probability level. All hydrogen atoms and benzene molecule are omitted for clarity.
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Scheme 2. Reactions of 4a with NHCs.
Scheme 2. Reactions of 4a with NHCs.
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Figure 3. Molecular structure of 4a: Side view (left), front view (right). The thermal ellipsoids are shown at the 50% probability level. The hydrogen atoms, except for the Si–H group, are omitted for clarity.
Figure 3. Molecular structure of 4a: Side view (left), front view (right). The thermal ellipsoids are shown at the 50% probability level. The hydrogen atoms, except for the Si–H group, are omitted for clarity.
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MDPI and ACS Style

Hayakawa, N.; Sadamori, K.; Mizutani, S.; Agou, T.; Sugahara, T.; Sasamori, T.; Tokitoh, N.; Hashizume, D.; Matsuo, T. Synthesis and Characterization of N-Heterocyclic Carbene-Coordinated Silicon Compounds Bearing a Fused-Ring Bulky Eind Group. Inorganics 2018, 6, 30. https://doi.org/10.3390/inorganics6010030

AMA Style

Hayakawa N, Sadamori K, Mizutani S, Agou T, Sugahara T, Sasamori T, Tokitoh N, Hashizume D, Matsuo T. Synthesis and Characterization of N-Heterocyclic Carbene-Coordinated Silicon Compounds Bearing a Fused-Ring Bulky Eind Group. Inorganics. 2018; 6(1):30. https://doi.org/10.3390/inorganics6010030

Chicago/Turabian Style

Hayakawa, Naoki, Kazuya Sadamori, Shinsuke Mizutani, Tomohiro Agou, Tomohiro Sugahara, Takahiro Sasamori, Norihiro Tokitoh, Daisuke Hashizume, and Tsukasa Matsuo. 2018. "Synthesis and Characterization of N-Heterocyclic Carbene-Coordinated Silicon Compounds Bearing a Fused-Ring Bulky Eind Group" Inorganics 6, no. 1: 30. https://doi.org/10.3390/inorganics6010030

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