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. 2026 Apr 28;65(18):10087–10095. doi: 10.1021/acs.inorgchem.6c00544

1,3-Disilabicyclo[1.1.0]butane and η2‑Silene Nickel Complex Derived from a Bromosilene

Shunya Honda 1, Shintaro Ishida 1,*, Takeaki Iwamoto 1,*
PMCID: PMC13169367  PMID: 42048255

Abstract

The reactivity of halogen-substituted silenes (silicon–carbon doubly bonded compounds) is not well understood relative to alkenyl halides. Herein, we report the reductive dimerization and complexation of a stable bromosilene (1). The reaction of 1 with an equimolar amount of KC8 furnished a 1,3-disilabicyclo[1.1.0]­butane (trans-3) featuring a remarkably short bridgehead Si–Si bond [2.204(1) Å] and a very wide Si–Si–Cexocyclic angle of 173.0(1)°. Bulky alkyl groups on the bridgehead silicon atoms and less steric hindrance at the bridging carbon atoms lead to the short bridgehead bond. Bromosilene 1 reacted with Ni­(PMe3)4 to afford the corresponding η2-bromosilene nickel complex (4) as a minor product. Complex 4 exhibits a twisted square planar structure in the solid state. Structural and spectroscopic properties of 4 indicate considerable metallacyclic character.

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Introduction

Silenes (Silicon–carbon doubly bonded compounds, R1R2SiCR3R4) possess an intrinsically polarized Siδ+Cδ− double bond due to the difference of the electronegativity between Si (1.90) and C (2.55) and a narrow π–π* gap owing to the poor 3p­(Si)–2p­(C) orbital overlap. − Hence, the characteristic properties and reactivity of functionalized silenes receive broad attention. , Among these, halogen-substituted silenes should enable us to access low-valent silicon-containing π-electron systems via functionalization of the halogen groups. − However, their chemical transformations remain scarce relative to alkenyl halides. For instance, the treatment of NHC-coordinated trimethylsilyl­(chloro)­silene A with potassium amide furnishes the CSiSiC cumulene derivative B via transmetalation and salt elimination (Scheme a). Bis-chlorosilene C reacts with B­(C6F5)3 to provide 1,4-disilabenzene D with elimination of chlorosilylene E (Scheme b). In this reaction, the two-electron oxidation of C to afford F is accompanied. Previously, we have reported the synthesis of stable bromosilene 1 and its substitution reactions using tert-butyllithium, lithium diphenylamide, and tris­(trimethylsilyl)­silylpotassium to deliver new silenes 2a–c (Scheme a). Given that alkenyl halides, lighter congeners of halosilenes, are a versatile feedstock and useful reagents for numerous chemical transformations including coupling reactions, we decided to further examine Wurtz-coupling using alkaline metals and related reagents and Yamamoto-type homocoupling using Ni(0) complexes of 1 to obtain extended SiC frameworks. Herein we report the reductive debromination of 1 with KC8 giving a 1,3-disilabicyclo[1.1.0]­butane trans-3 and the complexation with Ni­(PMe3)4 furnishing an η2-silene nickel complex 4 (Scheme b).

1. (a) Reaction of NHC-Coordinated Chlorosilene A. (b) Reaction of Bis-Chlorosilene C .

1

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2. (a) Substitution Reactions of Bromosilene 1 with Nucleophiles to Afford 2a–c. (b) 1,3-Disilabicyclo[1.1.0]­butane trans-3 and η2-Silene Nickel Complex 4 .

2

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Results and Discussion

Reaction of Bromosilene 1 with KC8

Treatment of 1 with an equivalent amount of KC8 in diethyl ether at 10 °C for 3 h furnished 1,3-disilabicyclo[1.1.0]­butane trans- 3 instead of a homocoupling product, 2,3-disila-1,3-butadiene 3′. Trans-3 was isolated as a yellow crystalline solid in 33% yield by recrystallization from a saturated hexane solution at −25 °C (Scheme a). This is the first example of the formation of 1,3-disilabicyclo[1.1.0]­butane from halosilenes. , No other stereoisomers of trans-3 were detected in the reaction mixture. Previously, we reported that 2,3-disila-1,3-butadiene 5a thermally isomerizes into 1,3-disilabicyclo[1.1.0]­butane 6a (Scheme b). Computational studies suggested that the transformation of 5a to 6a proceeds via conrotatory ring closure. Consequently, it is reasonable to consider that the homocoupling of 1 provides 3′ as an initial product, which undergoes the subsequent conrotatory cyclization to afford trans-3 selectively (Scheme a).

3. (a) Reaction of 1 with KC8; (b) Thermal Isomerization of 5a to 6a .

3

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In the 1H NMR spectrum of trans-3 in C6D6 at room temperature, diastereotopic methylene protons of 1,1-bis­(trimethylsilyl)-3,3-dimethylbutyl groups appeared as a set of two doublet signals. Two singlet signals due to bridging CAr*H units [Ar* = 3,5-di­(tert-butyl)­phenyl] appeared at 3.69 and 4.96 ppm. These spectroscopic characteristics confirm the trans-configuration of the bridging carbon atoms in the folded disilabicyclo[1.1.0]­butane skeleton. In the 13C­{1H} NMR spectrum, two tertiary signals and two quaternary signals due to the para- and ipso-positions of Ar* groups appeared in the aromatic region, indicating two chemically inequivalent Ar* groups. The signals of ortho-carbons are missing probably due to the signal broadening, which could result from the restricted ring rotation around the Ar*–C bond at room temperature.

The geometry around the bridgehead bond in bicyclo[1.1.0]­butanes involving heavy elements (heavy bicyclo[1.1.0]­butanes) such as trans- 3 has been discussed as an important issue because heavy bicyclo[1.1.0]­butanes are predicted to provide bond-stretch isomers which differ primarily in the distance between bridgehead atoms. , The short-bond isomer (SBI) is characterized by a shorter bridgehead bond associated with a smaller hinge angle between the two three-membered rings, while the long-bond isomer (LBI) has the opposite trend. The molecular structure of trans-3 in the solid state was determined by single crystal X-ray diffraction study (sc-XRD) as shown in Figure , and the obtained structural parameters represent marked characteristics of an SBI (Table ). The bridgehead Si1–Si1* distance (d) of trans-3 [2.204(1) Å] is much shorter than standard Si–Si bond lengths (2.36 Å) and the shortest value among hexaorganodisilanes (in the CSD, 215 entries in ConQuest Ver. 2025.3.1).

1.

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ORTEPs of trans-3. Hydrogen atoms except for those on the C1 and C2 atoms and tert-butyl groups on the aryl groups are omitted for clarity. Thermal ellipsoids are drawn at the 50% probability level. The 3,5-di­(tert-butyl)­phenyl (Ar*) rings and C1 and C2 atoms are located on the crystallographic mirror plane.

1. Selected Metric Parameters of trans-3 and Related 1,3-Disilabicyclo[1.1.0]­butanes.

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compound d SiSi/Å α/° β/° Σθ/° φ/Å reference
trans-3 2.204(1) 173.0(1) 120.43 347.0 –0.387 this work
6a 2.3854(12) 119.19(5) 139.8(2) 338.95(14) +0.548
119.78(5) 340.50(14) +0.526
2.3867(13) 118.38(4) 140.2(2) 338.78(15) +0.551
119.51(4) 340.11(15) +0.531
6b 2.2303(6) 144.96(2) 124.76(8) 359.96(5) +0.022
144.21(2) 359.91(5) +0.034
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a

The angle sums around the bridgehead silicon atom except for the bridgehead bond.

b

Distance of the central silicon atom and the reference plane, where the reference plane is defined by the three substituent atoms whose angle sum is closest to 360°. Negative φ indicates tetrahedral geometry at the silicon atom, while positive φ indicates hemispheroidal geometry.

c

A crystallographic mirror plane exists in the molecule.

d

Two crystallographically independent molecules exist in the asymmetric unit.

It should be worth comparing the structures of 1,3-disilabicyclo[1.1.0]­butanes. We have reported 1,3-disilabicyclo[1.1.0]­butanes 6a 12a and 6b 12b (Table ), and 6a bearing tert-butyldimethylsilyl groups at the bridgehead positions exhibits an LBI character, while its triisopropylsilyl derivative 6b is an SBI. 1,3-Disilabicyclo[1.1.0]­butanes having bulky substituents at the bridgehead positions tend to prefer the SBI. The unusually short Si–Si bond in trans-3 could arise mainly from steric effect imposed by the substituents and the bicyclic skeleton. The bridgehead Si1–Si1* bond lengths of 1,3-disilabicyclo[1.1.0]­butanes increase in the order: trans-3 [2.204(1) Å] < 6b [2.2303(6) Å] < 6a [2.3854(12) and 2.3867(13) Å]. The hinge angles between two CSi2 three-membered rings (β) increase in the same order: trans-3 [120.43°] < 6b [124.76(8)°] < 6a [144.1(1)°]. The short bridgehead bond and small β values are characteristic of the SBI and are consistent with the increasing bulkiness of the bridgehead substituents [t-BuCH2(Me3Si)2C (Rs) > i-Pr3Si > t-BuMe2Si]. In trans-3, the smaller bridging CHAr* group also allows a narrower β. The Rs–Si–Si angle (α) of trans-3 [173.0(1)°] is much wider than the corresponding angles of 6a [118.34(4)–119.78(5)°] and 6b [144.21(2)° and 144.96(2)°]. A large α is typical of the SBI in heavy bicyclo[1.1.0]­butanes and would be enhanced by steric repulsion between the bulky Rs groups on the bridgehead silicon atoms. The geometry around the bridgehead silicon atoms can be categorized by (1) the angle sum at silicon excluding the bridgehead bond ∑θ­(Si), and (2) the hemispheroidality parameter φ. According to these parameters, 6a [∑θ­(Si) = 339.59° and φ = +0.539 Å] and 6b [∑θ­(Si) = 359.94° and φ = +0.028 Å] have hemispheroidal and trigonal pyramidal bridgehead silicon atoms, respectively, while the bridgehead silicon atoms in trans-3 adopt a distorted tetrahedral geometry [∑θ­(Si) = 347.0° and φ = −0.387 Å]. These results indicate that the geometry of the bridgehead silicon atoms in the 1,3-disilabicyclo[1.1.0]­butanes is strongly influenced by the neighboring substituents.

UV–vis spectrum of trans- 3 in hexane exhibits an absorption band at 348 nm (band-I, ε 5200) as shown in Figure S13. We conducted TD-DFT calculations for the optimized structure of trans-3 (3 opt ) at the M06–2X-D3/6–31+G­(d,p)//M06–2X-D3/6–31G­(d) level of theory to obtain insight into the electronic structure of trans- 3. The calculated lowest energy transition of 3 opt (347 nm) well reproduced the observed absorption band. Accordingly, the longest-wavelength absorption band of trans-3 is assignable to the HOMO–LUMO transition. The HOMO and LUMO are bent σ- and σ*-orbitals at the bridgehead Si–Si bond (Figure ). The calculated Mayer bond order (MBO) of the bridgehead silicon–silicon bond (0.75) is only slightly smaller than that of the Si–Si bond in hexamethyldisilane (0.86), which indicates a significant bonding interaction between the bridgehead silicon atoms. QTAIM analysis of 3 opt also exhibits an outward-curved bond path between the bridgehead silicon atoms (Figure S14). The bond-path length (2.300 Å) is notably longer than the interatomic Si–Si distance (2.189 Å). The bond ellipticity at the bond critical point (BCP) on the Si–Si bond path is 0.182. The nonzero ellipticity value reflects a deviation from cylindrical symmetry of the electron density at the BCP, as observed for disilacyclopropane (ellipticity at the BCP of Si–Si bond: 0.359). Together, these computational features suggest a considerably bent banana-bond, as illustrated by the shape of the HOMO. Natural bond orbital (NBO) analysis provides information on the hybridization of the bridgehead Si–Si bond. The hybridization ratios of the bridgehead bonds are as follows: trans-3 (s 16.79%, p 82.96%; sp4.94), 6a (s 0.02%, p 99.78%; sp99.99), and 6b (s 7.10%, p 92.69%; sp13.05). Bridgehead Si–Si bonds show high p-character in both the LBI and SBI structures, which is consistent with their large ∑θ­(Si) values and other bonding analyses. Among the SBI structures, trans-3 has a larger s-character than 6b. The difference may reflect the more electron-withdrawing alkyl substituent (Rs) relative to the silyl group and may also be relevant to the shorter Si–Si bond in trans-3.

2.

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Frontier orbitals of 3 opt . Hydrogen atoms are omitted for clarity. Isosurface = 0.04.

Reaction of Bromosilene with Ni­(PMe3)4

Treatment of 1 with Ni­(PMe3)4 in benzene at room temperature furnished a small amount of nickel η2-silene complex 4 together with an intractable mixture. Under these conditions, trans-3 was not observed in the reaction mixture. After repeated recrystallizations, 4 was isolated in 8% yield as thermally unstable red crystals (Scheme ). Because 1 decomposed in the presence of P­(t-Bu)3 to give a similar intractable mixture, decomposition of 1 induced by PMe3 released through ligand exchange is likely a major competing pathway in this reaction. Isolable group 10 metal η2-silene complexes are scarce, and structural information on this class of compounds is still very limited. Dinuclear nickel complex 7 and platinum complex 8 have been reported as isolable transition metal complexes of silenes and discussed in terms of their significant metallacyclic character. ,, Accordingly, we evaluate the bonding character of 4 in the context of the Dewar–Chatt–Duncanson model, using the upfield shifts in the NMR signals of the silene moiety and the structural changes upon complexation to access the relative contributions of metallacyclic and π-complex character. The methine proton on the silene ligand appeared at 1.90 ppm as a doublet (3 J PH = 11.0 Hz), which was upfield-shifted by 4.22 ppm compared to that of free silene 1 (6.12 ppm). In the 13C and 29Si NMR spectra, the signal of the silene center was observed at 26.8 and 24.2 ppm, respectively, which are also considerably upfield-shifted upon complexation (13C and 29Si NMR chemical shifts of the silene moiety in 1 in C6D6: 100.9 and 85.2 ppm, respectively).

4. Reaction of 1 with Ni­(PMe3)4, Resonance Structures of 4, and Previously Reported Silene-Nickel Complex 7 and Silene-Platinum Complex 8 .

4

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The structure of 4 in the solid state was determined by sc-XRD (Figure ). Compound 4 was crystallized in the monoclinic P21 space group, and two crystallographically independent but structurally similar molecules of 4 exist in the unit cell. Hereafter, only the molecule containing Ni1 is discussed. In complex 4, the Z-configuration of the bromosilene moiety remains intact. The nickel atom adopts a slightly twisted square-planar coordination; the interplane angle between NiP2 and NiCSi planes is 14.8°. The steric repulsion among substituents on the silene and phosphines would cause the twisted structure. The bond length of the silene moiety (Si1–C1) [1.800(8) Å] is elongated by 4.9% from that of 1 [1.7157(15) Å] and falls into the range of the standard bond lengths of Si–C single bond (1.87 Å) and SiC double bonds (1.70 Å). The SiC bond length of 4 is comparable to those of 7 (1.825 Å) and 8 (1.838 Å), and the Si1–Ni1 and Ni1–C13 bond lengths [2.221(3) and 2.035(8) Å] are also similar to those of 7 [2.181 and 2.000 Å]. The Ni1–P2 (trans-position toward Si1) bond length of 2.206(3) Å is longer than that of Ni1–P1 (cis-position toward Si1) [2.156(2) Å] because of the trans influence of the σ-donating silyl ligand. The bromosilene unit of 4 diminished its planarity: the bent back angles, defined as an angle between an R2Si (R2C) plane and a C–Si bond, of the bromosilene moiety in 4 were 46.3° (Si1) and 21.2° (C1). Based on the observed upfield shifts in the NMR signals and the structural changes of the silene moiety, 4 has a significant metallacyclic character (4a), similar to that proposed for the previously reported η2-silene complexes 7 and 8. ,

3.

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Molecular structures of 4. Two crystallographically independent molecules exist in the unit cell, and one molecule is shown. Hydrogen atoms were omitted for clarity. Thermal ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å): Si1–C13 1.800(8), Si1–Br1 2.269(2).

To obtain insight into the electronic structure of 4, computational studies were carried out. The MBO analysis of 4 opt at the M06–2X/B1 [B1 basis: SDD for Br and Ni atoms: 6–31G­(d) for H, C, Si, and P atoms] level of theory also confirmed the NiSiC metallacycle character. The MBOs of Si–Ni (0.70) and Ni–C13 (0.64) indicate the substantial bonding interaction between the nickel center and the silene moiety. The MBO of the Si–C13 bond (1.02) is significantly decreased from that of free bromosilene 1 opt (1.68) at the same level of theory, demonstrating that the SiC bond order is substantially reduced upon coordination to nickel, consistent with the structural changes observed upon complexation. Intrinsic bonding orbital (IBO) analysis provides a set of localized bonding orbitals without empirical inputs and further clarifies the bonding situations. − The IBO analysis of 4 opt at the PBE/def2-TZVP level of theory exhibits two n­(P), four d­(Ni), σ-donation, and π-backdonation orbitals (Figure ). The σ-donation orbital is mainly localized on the carbon atom. The π-backdonation orbital is a bonding orbital between nickel and silicon atoms. The unsymmetric σ-donation and π-backdonation orbitals arise from the Siδ+C δ− polarization. In the π-backdonation orbital, d-electron number on the nickel atom (1.251) is smaller than that of (Me3P)2Ni­(η2-ethylene), a typical Ni(0)-alkene complex (1.525, Figure S15). Hence, 4 opt has a substantial metallacycle character compared to the π-complex (Me3P)2Ni­(η2-ethylene). The low-lying LUMO of 1 would enhance the π-backdonation, which is responsible for the metallacycle character of 4.

4.

4

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Selected IBOs of 4 opt calculated at the PBE/def2-TZVP//M06–2X/B1 [B1 basis: SDD for Br and Ni atoms: 6–31G­(d) for H, C, Si, and P atoms] level of theory. Values indicate electron numbers on atoms in each IBO.

Conclusion

Reductive debromination of bromosilene 1 with KC8 afforded a new 1,3-disilabicyclo[1.1.0]­butane (trans-3), which is a new route to 1,3-disilabicyclo[1.1.0]­butane from halosilene. trans-3 features a large Si–Si–Rs bond angle [173.0(1)°] and a short Si–Si bond length [2.204(1) Å]. These findings suggest that a Si–Si single bond can be shortened by embedding it within a small bicyclic skeleton bearing bulky substituents at the bridgehead positions. In the reaction of 1 with Ni­(PMe3)4, a small amount of η2-silene nickel complex (4) was isolated. The spectroscopic, structural, and computational data for 4 indicate a considerable contribution from metallacycle 4a.

General Procedures

All reactions treating air-sensitive compounds were carried out under nitrogen atmosphere using a high-vacuum line and standard Schlenk techniques, or a glovebox as well as dry and oxygen-free solvents. 1H (500 MHz), 13C (126 MHz), 29Si (99 MHz), and 31P (202 MHz) NMR spectra were recorded on a Bruker Avance III 500 FT NMR spectrometer. 1H and 13C NMR chemical shifts were referenced to residual 1H and 13C of signals of benzene-d 6 (1H δ 7.16 and 13C δ 128.0). 29Si NMR and 31P chemical shifts in benzene-d 6 were referenced to external standards [Me4Si (δ 0.0) and 85% phosphoric acid (δ 0.0)]. Mass spectra were recorded on a Bruker Daltonics SolariX 9.4T and JEOL JMS-Q1050 spectrometers. UV–vis-NIR spectra were recorded in a JASCO V-770 spectrometer. X-ray analysis was carried out using a Bruker AXS APEX II CCD diffractometer. Measurement of melting point was measured on an SRS OptiMelt MPA100. Elemental analysis was performed with a J-SCIENCE LAB JM-11 at Research and Analytical Center for Giant Molecules, Graduate School of Science, Tohoku University.

Materials

Diethyl ether (Et2O) and heptane were dried with LiAlH4 and distilled prior to use by using a vacuum line. Hexane and benzene were dried with a VAC-103991 type solvent purifier. Benzene-d 6 was dried with molecular sieves 4Å. Materials unless otherwise noted are commercially available and used without further purification. KC8 and bromosilene 1 were prepared according to the literatures.

Safety Statement

Caution! LiAlH4 and KC8 are extremely pyrophoric. They must be handled in a glovebox or using Schlenk lines.

X-ray Crystallographic Analysis

Single crystals suitable for X-ray diffraction study were obtained by recrystallization from Et2O solution at −25 °C for trans-3 and from heptane solution at −25 °C for 4. The single crystals for data collection coated by Apiezon grease were mounted on a thin glass fiber and transferred to a cold nitrogen gas stream of the diffractometer. Diffraction data was collected by a Bruker AXS APEX II CCD diffractometer with graphite monochromated Mo–Kα radiation (0.71073 Å). An empirical absorption correction based on the multiple measurement of equivalent reflections was applied using the program SADABS and the structures were solved by direct methods and refined by full-matrix least-squares against F 2 using all data (SHELXL-2019). Molecular structure was analyzed by Yadokari-XG software.

Computational Study

All theoretical calculations were performed using Gaussian 09 and GRRM 14 − programs. Geometry optimization, frequency analysis, and NBO analysis of 3 opt , 6a, and 6b were carried out at the M06–2X-D3/6–31G­(d) level of theory. Geometry optimization and frequency analysis of 4 opt and 1 opt were carried out at the M06–2X-D3/B1 (B1: SDD for Ni, Br, 6–31G­(d) for C, H, Si, P) level of theory. No imaginary frequencies were found in the optimized structures. Atomic coordinates of the optimized structures are listed in an xyz-format file (computational_study.xyz). Twenty excited states of 3 opt calculated at the TD-M06–2X/6–31+G­(d,p) level of theory (Table S3). Mayer bond order (MBO) was calculated using Multiwfn software. Intrinsic bond orbital (IBOs) and Molecular graphs on QTAIM analysis are visualized by using IBOview and AIMALL programs.

Synthesis

Reductive Debromination of Bromosilene 1 with KC8

In a test tube (20 mL) equipped with a magnetic stirring bar under argon atmosphere, bromosilene 1 (51 mg, 94 μmol) and potassium graphite (13 mg, 93 μmol) were placed. To the vial, Et2O (1 mL) was added. After stirring for 3 h at 10 °C, the volatiles of the reaction mixture were removed under reduced pressure. Then, hexane (ca. 5 mL) was added to the residue, and the insoluble material was filtered off using a PTFE filter, and the filtrate was concentrated under reduced pressure. The crude solid was recrystallized from hexane at −25 °C. Thus, obtained product was washed with cold heptane to yield trans-3 (14 mg, 15 μmol) as pale-yellow crystals in 33% yield.

trans- 3: pale-yellow crystals; 1H NMR (500 MHz, C6D6, 291 K, δ) 0.16 (s, 18H, SiMe3), 0.26 (s, 18H, SiMe3), 1.13 (s, 18H, t-Bu), 1.48 (s, 36H, t-Bu), 1.98 (d, 2H, CH2, J = 14.7 Hz), 2.04 (d, 2H, CH2, J = 14.7 Hz), 3.69 (s, 1H, Ar*CH), 4.96 (s, 1H, Ar*CH), 7.268 (s, 1H, p-CH), 7.270 (s, 1H, p-CH), 7.60 (very broad, 4H, o-CH); 13C­{1H} NMR (126 MHz, C6D6, 292 K, δ) 3.7 (SiMe3), 3.9 (SiMe3), 14.5 [C(SiMe3)2], 32.0 [C­(CH3)3], 32.1 [C­(CH3)3], 32.2 [CH2C­(CH3)3], 33.9 (CH2 CMe3), 35.1 (CMe3), 35.2 (CMe3), 41.4 (Ar*CH), 45.2 (CH2), 56.5 (Ar*CH), 117.3 (p-CH), 118.1 (p-CH), 145.5 (ipso-C), 148.0 (ipso-C), 150.4 (m-C), 150.7 (m-C); 29Si­{1H} NMR (99 MHz, C6D6, 291 K, δ) −14.9 (bridgehead Si), 2.1 (SiMe3), 3.3 (SiMe3); HRMS (APCI) m/z [M]+ calcd for C54H102Si6, 918.6592; Found, 918.6592; Anal. Calcd for C54H102Si6: C, 70.51; H,11.18%. Found: C, 70.61; H, 11.25%; UV–vis (hexane, 298 K) λ/nm (ε) 348 (5.61 × 103). In the 13C­{1H} NMR spectrum, the signals for ortho-carbon atoms of 3,5-di­(tert-butyl)­phenyl groups were missing. As 1H NMR signals of ortho-protons were remarkably broadened, the reason for the absence of the corresponding ortho-carbon signals would also be broadening.

Reaction of 1 with Ni­(PMe3)4

In a Schlenk tube (20 mL) equipped with a magnetic stirring bar under argon atmosphere, Ni­(PMe3)4 (33 mg, 92 μmol) and benzene (1 mL) were placed. To the flask, a benzene solution (2 mL) of bromosilene 1 (50 mg, 93 μmol) was added as four portions. Then, the flask was carefully evacuated for 1 min to remove the resulting volatile trimethylphosphine. After stirring for 15 min under slightly reduced pressure and for 1 h under ambient pressure, the solution turned from yellow to orange. Volatiles were removed by reduced pressure, and hexane was added to the residue. The insoluble material was filtered off using a PTFE filter, and the filtrate was concentrated under reduced pressure. The crude product was recrystallized twice from hexane at −25 °C, and η2-bromosilene nickel complex 4 was obtained as red crystals in 8% yield (6 mg, 8 μmol).

4: red crystals; decomposed (>30 °C) before melting; 1H NMR (500 MHz, C6D6, 296 K, δ) 0.55 (s, 9H, SiMe3), 0.57 (s, 9H, SiMe3), 0.69 (d, 9H, PMe3, 2 J PH = 6.0 Hz), 1.18 (d, 9H, PMe3, 2 J PH = 6.5 Hz), 1.35 (s, 9H, CH2CMe 3), 1.44 (s, 18H, t-Bu on Ar*), 1.90 (d, 1H, silene-CH, 3 J PH = 11.0 Hz), 2.15 (d, 1H, CH 2 tBu, J = 14.8 Hz), 2.42 (d, 2H, CH 2 tBu, J = 14.8 Hz), 7.09 (s, 1H, p-CH), 7.45 (brs, 2H, o-CH); 13C­{1H} NMR (126 MHz, C6D6, 297 K, δ) 4.6 (SiMe3), 5.5 (SiMe3), 11.5 [d, C(SiMe3)2, 3 J PC = 19.9 Hz], 16.2 (dd, PMe3, 1 J PC = 17.2, 3 J PC = 2.7 Hz), 19.6 (dd, PMe3, 1 J PC = 22.2, 3 J PC = 5.5 Hz), 26.8 (d, silene-CH, 2 J PC = 3.9 Hz), 32.1 [C­(CH3)3], 33.4 [CH2C­(CH3)3], 33.9 (CH2 CMe3), 35.0 (CCMe3), 45.2 (CH2), 114.0 (CH), 122.0 (CH), 148.7 (C), 149.2 (C); 29Si­{1H} NMR (99 MHz, C6D6, 299 K, δ) 1.9 (SiMe3), 7.7 (SiMe3), 24.2 (dd, 2 J PSi = 117.2, 24.0 Hz, silene-Si); 31P­{1H} NMR (202 MHz, C6D6, 296 K, δ) −20.9 (d, PMe3, 2 J PP = 27.4 Hz), −16.3 (d, PMe3, 2 J PP = 27.4 Hz); HRMS (APCI) m/z [M – PMe3 + 2O]+ calcd for C30H61BrNiO2PSi3, 705.2248; found; 705.2251, [M + 3O + H]+ calcd for C33H70BrNiO3P2Si3, 797.2639; found; 797.2643; Anal. Calcd for C33H69BrNiP2Si3: C, 52.80; H, 9.26%. Found: C, 52.75; H, 9.52%.

Supplementary Material

ic6c00544_si_001.pdf (4MB, pdf)
ic6c00544_si_002.xyz (32.4KB, xyz)

Acknowledgments

This work was supported by JSPS KAKENHI [No JP25620020 (S.I.)].

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.6c00544.

  • NMR and UV–vis spectra, crystallographic data, and computational study data (PDF)

  • Cartesian coordinates of all computed molecules (XYZ)

Conceptualization: S.H. and S.I.; Methodology: S.H. and S.I.; Investigation: S.H. and S.I.; Visualization: S.H. and S.I.; Funding acquisition: S.I.; Project administration: S.I.; Supervision: T.I.; Writingoriginal draft: S.H. and S.I.; Writingreview and editing: S.H., T.I., and S.I. The manuscript was written through the contributions of all authors. All authors have given approval to the final version of the manuscript.

The authors declare no competing financial interest.

Published as part of Inorganic Chemistry special issue “Current Advancements in Main Group Chemistry”.

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Supplementary Materials

ic6c00544_si_001.pdf (4MB, pdf)
ic6c00544_si_002.xyz (32.4KB, xyz)

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