Synthesis and Characterization of Silyl-Bridged Dinuclear Cobalt

4 days ago - A cobalt dialkyl with an N-heterocyclic carbene [Co(CH2SiMe3)2(IPr)] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene) underwent ...
0 downloads 0 Views 1MB Size
Download PDF
Article Cite This: Organometallics XXXX, XXX, XXX−XXX

pubs.acs.org/Organometallics

Synthesis and Characterization of Silyl-Bridged Dinuclear Cobalt Complexes Supported by an N‑Heterocyclic Carbene Yusuke Ishizaka and Yumiko Nakajima* Interdisciplinary Research Center for Catalytic Chemistry, National Institute of Advanced Industrial Science and Technolo-gy (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan Graduate School of Pure and Applied Sciences, University of Tsukuba 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8577, Japan

Downloaded via WEBSTER UNIV on February 12, 2019 at 20:28:56 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: A cobalt dialkyl with an N-heterocyclic carbene [Co(CH2SiMe3)2(IPr)] (IPr = 1,3-bis(2,6diisopropylphenyl)imidazole-2-ylidene) underwent successive Si−H bond cleavage of hydrosilanes. The reaction paths were highly dependent on the bulkiness of the hydrosilanes, which led to the formation of various μ-silyl-bridged dicobalt complexes, [{Co(IPr)} 2 (μ-SiH 2 Hex) 4 ], [{Co(IPr)} 2 (μSiH2Ph)3(H)3], and [{Co(IPr)}2(μ-SiHPh2)(μ-H)2].

■

INTRODUCTION Transition-metal silyl complexes are widely recognized as an important class of reagents and intermediates in various catalytic reactions.1 To date, their chemistry has been intensely studied using complexes of precious transition metals, such as platinum,2,3 palladium,2,4 iridium,2,5 and rhodium,2,6 because these complexes exhibit high catalytic performance toward a range of synthetic organic reactions such as hydrosilylation and dehydroganative silylation reactions. Cobalt complexes are also known to exhibit diverse catalytic activities. For example, cobalt carbonyls catalyze olefin hydrosilylation reactions.7 Recently, significant progress has been made in this research area by the development of anti-Markovnikov hydrosilylation of alkenes by the Chirik group, Deng group, Holland group, etc.8 However, in comparison with the intense studies on silyl complexes of 4d and 5d metals, the study of the chemistry of cobalt silyl complexes, which have to date been performed mainly on the basis of cobalt(0) carbonyl species,9 is still limited. 1 0 In this study, the reactions of [Co(CH2SiMe3)2(IPr)] (1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with various silanes have been studied.11 It was found that the reaction pathway is highly dependent on the substituents of the hydrosilanes, and various silyl-bridged dicobalt complexes were formed.

Scheme 1. Reaction of 1 with HexSiH3

formation of H2 as well as Me4Si and Me3SiCH2SiH2Hex (1 equiv/Co). Although 2 possesses two paramagnetic Co(II) centers, which are bridged by four silyl ligands, it possesses a Co−Co bond and exhibits signals in the typical diamagnetic region for 1H NMR spectra. Complex 2 showed fluxional behavior at room temperature, and identification was performed on the basis of the rather sharper signals recorded at 80 °C. In the 1H NMR spectrum, four μ-SiH2Hex groups exhibited one set of terminal-SiH and agostic-SiH signals, which appeared at δ 3.63 and −10.24 ppm with integral intensities of 4H, respectively. The iPr groups of IPr and Hex groups on the Si atom significantly overlapped and were

■

RESULTS AND DISCUSSION The reaction of 1 with HexSiH3 (5 equiv) proceeded rapidly at room temperature to give the dinuclear cobalt complex [Co(μSiHexH2)2(IPr)]2 (2) in 86% yield (Scheme 1). In the reaction, gas evolution was detected. Thus, the reaction was followed by 1H NMR spectroscopy, which confirmed the © XXXX American Chemical Society

Received: November 29, 2018

A

DOI: 10.1021/acs.organomet.8b00865 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics observed as complicated broad signals in the range of δ 1.01− 1.57 ppm with an integral intensity of 100H. However, the signal that was assignable to the backbone CH of two IPr groups equivalently appeared as a singlet at δ 6.43 ppm. The observation strongly supports the rotation of the IPr ligands around the Co−C(IPr) bond. The signals become broadened according to the decrease in the temperature, and unfortunately, the signals remain broad even at −76 °C and the fluxional behavior could not be fully defined. The dinuclear structure bearing four μ-SiH2Hex ligands of 2 was fully determined by a single-crystal X-ray diffraction study. The ORTEP diagram of 2 is shown in Figure 1. The molecule

Scheme 2. Reaction of 1 with PhSiH3

range of 243−298 K. Therefore, rapid site exchange between the agostic SiH and the hydrides was supported. Eight iPr groups of the IPr ligands appeared as four doublets at δ 0.91 × 2, 1.00, and 1.13 ppm and two septets at δ 2.82 × 2 ppm. On the basis of these spectra, we assigned 3a as a dinuclear cobalt species with three magnetically equivalent μ-SiH2Ph ligands. Although the quality of the crystals was poor, the dinuclear structure of 3a, which exhibits a mirror plane including the midpoint of the Co−Co bond and three Si atoms, was confirmed by a single-crystal X-ray diffraction study.15 In the structure of 3a, three Si atoms were located in pseudoequilateral triangular positions around the Co−Co bond. Different from 3a, 3b exhibited three inequivalent singlets at δ 46.3, 49.6, and 67.5 ppm in the 29Si NMR spectrum. Accordingly, three SiH signals were observed at δ 4.05, 4.57, and 5.54 ppm in the 1H NMR spectrum. IPr ligands exhibited one singlet for the backbone methine proton, four doublets, and two septets for iPr groups. These observations supported the dinuclear structure of 3b with a mirror plane, which is composed of three Si atoms and the midpoint of the Co−Co bond, bridged by three magnetically inequivalent μ-SiPhH2 ligands. Signals that were assignable to the hydrides and agostic SiH were equivalently observed at δ −10.48 ppm with an integral intensity of 6H, which again supported the site exchange between the agostic SiH and the hydride.16 The correlation of the Si atom and agostic protons was confirmed by twodimensional NMR spectroscopic analysis, 29Si−1H HSQC. In the infrared (IR) spectrum of the mixture of 3a,b, the stretching signal of Si−H bonds was observed at 2082 cm−1 as a strong, broad signal. On the other hand, Co−H(terminal) or agostic Si−H stretching was not observed in the typical region (800−1400 cm−1 for hydride and 1650−1800 cm−1 for agostic SiH).17,2a Therefore, a rapid site exchange between the hydrides and the agostic SiH was also indicated on the time scale of the IR measurement (10−10−10−11 s). To shed light on the coordination mode of the Si−H moieties in the solid-state structures of 3a,b, DFT calculations were performed using the model complex 3a′, in which diisopropylphenyl groups were replaced with phenyl groups. Optimization was performed by starting from two possible structures, a dinuclear Co(III) complex with three hydrido and three silyl ligands, [{Co(IPr)}2(H)3(μ-SiH2Ph)3], and a dinuclear Co(0) complex with three silane ligands, [{Co(IPr)}2(μ-η2:η2-SiH3Ph)3]. It was revealed that both of them resulted in a dinuclear structure composed of Co(II) bridged by two silyl ligands and a silane ligand, [{Co(IPr)}2(H)2(μ-SiH2Ph)2(μ-η2:η2-SiH3Ph)] (3a′)

Figure 1. Molecular structure of 2 with 50% probability ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Co1−Co1*, 2.4465(9); Co1−Si1, 2.2534(11); Co1−Si1*, 2.3923(11); Co1−Si2, 2.2808(13); Co1*−Si1, 2.3923(11); Co1*−Si2, 2.4045(13); Co1−C1, 1.912(3); Co1− Si1−Co1* 63.47(3); Co1−Si2−Co1*, 62.89(3); Si1−Co1−Si1* 116.53(3); Si1−Co1−Si2, 73.72(4).

possesses a crystallographic inversion center at the midpoint of the Co−Co* bond. The Co1−Co1* bond length is smaller than the sum of the covalent radii of Co (2.46 Å) and exhibits a rather short bond length (2.4465(9) Å) among the typical Co−Co single bonds.12 Thus, reflective of the diamagnetic NMR spectrum of 2, the Co−Co single bond is also supported. The Co1−Si1 and Co1−Si2 distances are 2.2534(11) and 2.2808(13) Å, which are in the range of typical Co−Si single bonds.10d,13 In contrast, the Co1*−Si1 and Co1*−Si2 bonds are elongated by ca. 0.1 Å (2.3923(11) and 2.4045(13) Å, respectively), and thus a Si−H agostic interaction is supported.14 The reaction of 1 with PhSiH3 (5 equiv) proceeded similarly at ambient temperature, resulting in the quantitative formation of dinuclear Co complexes 3a,b with three μ-SiH2Ph ligands (3a/3b = 1/1) (Scheme 2). Concomitant formation of Me3SiCH2SiH2Ph (1 equiv/Co) as well as Me4Si was also confirmed by 1H NMR spectroscopic analysis. Complexes 3a,b, which were obtained as a mixture, were identified by NMR analysis. In the 29Si NMR spectrum of 3a, signals of three μ-SiH2Ph groups were equivalently observed at δ 48.5 ppm. Consistently, 3a exhibited one SiH signal at δ 4.99 ppm with an integral intensity of 3H in the 1H NMR spectrum. A sharp singlet was observed in the high-field region at δ −10.48 ppm with an integral intensity of 6H. The signal became broad in accordance with a decrease in temperature, although the SiH signal remained sharp in the temperature B

DOI: 10.1021/acs.organomet.8b00865 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics (Figure 2). The Co1−Si2 and Co2−Si1 bond lengths are 2.22 and 2.23 Å, respectively, which correspond to a normal Co−Si

Scheme 3. Reaction of 1 with Ph2SiH2

Figure 2. Optimized structure of 3a′. Selected bond distances (Å) and angles (deg): Co1−Co2, 2.55; Co1−Si1, 2.41; Co1−Si2, 2.22; Co2−Si1, 2.23; Co2−Si2, 2.42; Co1−Si3, 2.36, Co2−Si3, 2.35, Co1− C1, 1.93; Co1−H1, 1.46; Co2−H1*, 1.45; Co1−Si1−Co2 66.53; Co1−Si2−Co2, 66.48; Co1−Si3−Co2, 65.63.

single bond. The Co1−Si1 and Co2−Si2 bonds (2.41 and 2.42 Å) are slightly longer due to the Si−H agostic interaction. The Si3PhH3 moiety coordinates with the Co1 and Co2 atoms in a μ-η2:η2 fashion, which exhibits elongated Co−Si bond lengths (2.36, 2.35 Å). The Mayer bond index of the Co−Co bond was calculated to be 0.45, which strongly supported the Co− Co bond interaction. In the HOMO-27 of 3a′, a bonding interaction of the hydride H1* with both the Co2 and Si1 atoms was confirmed (Figure 3). A similar agostic interaction of H1 with Si2 and

Figure 4. Molecular structure of 4 with 50% probability ellipsoids. Hydrogen atoms except those attached to the Si and/or Co atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Co1−Co1*, 2.4527(8); Co1−Si1, 2.2267(8); Co1−Si1*, 2.3274(8); Co1−C1, 1.939(2); Co1−Si1−Co1* 65.13(3); Si1−Co1−Si1* 114.87(3); Si1−Co−C1, 122.34(8); Si*−Co−C, 124.04(8).

bond length was found to be 2.4527(8) Å. As observed in 2, two slightly different Co−Si bond lengths (2.2267(8) Å for Co1−Si1 and 2.3274(8) Å for Co1*−Si1) are confirmed, indicating the agostic Si1*−H1* and Si1−H1 coordination to Co1 and Co1* atoms, respectively. The existence of agostic SiH atoms is also supported by the inequivalent bond angles of Si−Co−C(IPr): that is, the IPr ligands tilt to avoid steric repulsion with the agostic protons and thus the Si1*−Co1−C bond angle (124.04(8)°) is larger than that of Si1−Co−C (122.34(8)°). Related to this observation, two hydride atoms, which exist as μ-H ligands, are detected by difference Fourier synthesis. As a result, the structure of 4 was concluded to be a dinuclear structure composed of formal Co(II) centers with a Co−Co single bond.19 A possible reaction path for the formation of 2−4 is proposed in Scheme 4. Complex 1 reacts with 2 equiv of silane to form the hydridosilyl intermediate A. In this step, two reactive alkyl groups in 1 are converted into RR′HSiCH2SiMe3 and Me4Si, which is probably initiated with σ-bond metathesis. Such reactivity is also reported for the analogous amido complex [Co(N(SiMe3)2)2(IPr)], which reacts with HSi(OEt)3 to form (Me3Si)2NSi(OEt)3.20 In the case of Ph2SiH2, 4 is obtained after the dimerization of A. Primary silane is further incorporated in the reaction sphere, i.e., successive reaction with PhSiH3 results in the formation of 3, whereas two molecules of the smaller HexSiH3 are involved in the reaction to give 2 accompanied by the formation of H2.

Figure 3. HOMO-27 of 3a′.

Co1 was also observed in the HOMO-26 of 3a′ (Figure S6). Given that H atoms which coordinate both a metal and a silicon atom through a three-centered two-electron interaction are often obscured due to a significant blue shift,2b,18 such a coordination mode could be one reason for the absence of νCoH in the IR spectrum. The reaction of 1 with the bulkier secondary hydrosilane Ph2SiH2 was then performed. The reaction of 1 with Ph2SiH2 (5 equiv) proceeded much more slowly to give 4 (88% yield) after 16 h at room temperature, accompanied by the formation of Ph2SiH2CH2SiMe3 and SiMe4 (Scheme 3). Complex 4 was sparingly soluble in organic solvents, and it was difficult to characterize by NMR spectroscopy. Luckily, single crystals were obtained when the reaction was performed overnight without stirring. Thus, a single-crystal X-ray diffraction study was performed (Figure 4). The Co1−Co1* C

DOI: 10.1021/acs.organomet.8b00865 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

−10.24 (s, 4H, Co−H−Si), 1.01−1.57 (br, 100H, CH3(CH2)5, CH(CH3)2), 2.91−3.22 (m, 8H, CH(CH3)2), 3.63 (s, 4H, Si−H), 6.43 (s, 4H, IPr-backbone CH). Anal. Calcd for Co2Si4N4C78H132: C, 69.08; H, 9.81; N 4.13. Found: C, 68.97; H, 9.59; N, 4.53. IR spectrum (KBr, cm−1): νSiH 2102 (m). Synthesis of 3a,b. In a J. Young NMR tube was placed a C6D6 solution (300 μL) of 1 (18.6 mg, 30 μmol) and mesitylene (2.8 μL, 20 μmol), and PhSiH3 (16.3 mg, 150 μmol) was added at room temperature. 3a,b were obtained in yields of 48% and 45%, respectively, which were decided by the signal intensity of IPrbackbone signals. Isolation was carried out by scale up. To a C6H6 solution (3 mL) of 1 (372 mg, 600 μmol) was added PhSiH3 (324 mg, 3.00 mmol) at room temperature. After the solution was stirred for 1 h, the volatiles were removed under vacuum. The residue was extracted with hexane and passed through an Al2O3 pad (eluent C6H6). After removal of the solvent, a mixture of 3a and 3b was obtained as a brown powder (183.8 mg, 150 μmol, 50%). Crystals of 3a was obtained from cold hexane solution (−35 °C). Data for 3a are as follows. 1H NMR (C6D6, 25 °C): δ −10.48 (s, 6H, CoH), 0.91 (d, J = 6.9 Hz, 12H ×2, CH(CH3)2), 1.00 (d, J = 6.9 Hz, 12H, CH(CH3)2), 1.13 (d, J = 6.9 Hz, 12H, CH(CH3)2), 2.82 (m, 8H, CH(CH3)2), 4.99 (s, 3H, SiH), 6.50 (s, 4H, CH-IPr), 6.83 (m, 4H, ArH), 6.91 (m, 4H, ArH), 7.00 (m, 4H, ArH), 7.08 (m, 3H, SiPh), 7.14 (m, 6H, SiPh), 7.15 (m, 6H, SiPh). 13C{1H} NMR (C6D6, 25 °C): δ 22.2 (CH(CH3)2), 22.4 (CH(CH3)2), 25.8 (CH(CH3)2), 25.9 (CH(CH3)2), 29.0 × 2 (CH(CH3)2), 124.0 (Ar), 124.3 (CHIPr), 124.4 (Ar), 126.7 (SiPh), 128.3 (SiPh), 129.6 (Ar), 136.1 (SiPh), 139.1 (Ar), 145.3 (Ar), 145.3 (Ar), 144.9 (SiPh) 197.3 (carbene-C). 1H−13C HSQC (C6D6, 25 °C): δ 0.91−25.8, 0.91−25.9, 1.00−22.2, 1.13−22.4, 2.82−29.0, 6.50−124.3, 6.83−124.0, 6.91− 124.4, 7.00−129.6, 7.08−126.7, 7.14−136.1, 7.15−128.3. 29Si{1H} NMR (C6D6, 25 °C): δ 48.5. 1H−29Si HSQC (C6D6, 25 °C): δ −10.48, 4.99−48.5. Data for 3b are as follows. 1H NMR (C6D6, 25 °C): δ −10.48 (s, 6H, CoH), 0.94 (d, J = 6.9 Hz, 12H, CH(CH3)2), 0.96 (d, J = 6.9 Hz, 12H, CH(CH3)2), 0.10 (d, J = 6.9 Hz, 12H, CH(CH3)2), 1.20 (d, J = 6.9 Hz, 12H, CH(CH3)2) 2.77 (sept, 4H, CH(CH3)2), 2.99 (sept, 4H, CH(CH3)2), 4.05 (s, 1H, SiH), 4.57 (s, 1H, SiH), 5.54 (s, 1H, SiH), 6.43 (s, 4H, CH-IPr), 6.77 (m, 4H, ArH), 6.85 (m, 4H, ArH), 6.95 (m, 4H, ArH), 7.07 (m, 1H, SiPh), 7.12 (m, 2H, SiPh), 7.17 (m, 1H, SiPh), 7.17 (m, 1H, SiPh), 7.20 (m, 2H, SiPh), 7.22 (m, 2H, SiPh), 7.35 (m, 2H, SiPh), 7.52 (m, 2H, SiPh), 7.57 (m, 2H, SiPh). 13 C{1H} NMR (C6D6, 25 °C): δ 21.8 (CH(CH3)2), 22.5 (CH(CH3)2), 25.9 (CH(CH3)2), 26.1 (CH(CH3)2), 29.0 (CH(CH3)2 × 2), 29.0 (CH(CH3)2), 124.4 (Ar × 2), 124.6 (CH-IPr), 126.7 (SiPh), 126.9 (SiPh), 127.0 (SPh), 127.1 (SiPh), 129.6 (Ar), 135.3 (SiPh), 135.6 (SiPh), 136.1 (SiPh), 136.3 (SiPh), 136.5 (SiPh), 139.1 (Ar), 144.9 (SiPh), 145.0 (SiPh), 145.4 (Ar), 145.6 (Ar), 146.2 (SiPh), 198.5 (carbene-C). 1H−13C HSQC (C6D6, 25 °C): δ 0.94−26.1, 0.96−25.9, 0.10−21.8, 1.20−22.5, 2.77, 2.99−29.0, 6.43−124.6, 6.77, 6.85−124.4, 6.95−129.6, 7.07−127.0, 7.12−126.9, 7.17−126.7, 127.1, 7.20−136.5, 7.22−136.1, 7.35−135.6, 7.52−135.3, 7.57−136.3. 29Si{1H} NMR (C6D6, 25 °C): δ 46.3, 49.6, 67.5. 1H−29Si HSQC (C6D6, 25 °C): δ −10.48−46.3, −10.48−49.6, −10.48−67.5, 4.05−46.3, 4.57−67.5, 5.54−49.6. Anal. Calcd for Co2Si3N4C72H96: C, 70.90; H, 7.93; N 4.59. Found: C, 71.12; H, 7.47; N, 4.61. Synthesis of Complex 4. To a C6H6 solution (4 mL) of 1 (279.8 mg, 600 μmol) was added Ph2SiH2 (415.1 mg, 3.00 mmol) at room temperature. The solution was stirred for 16 h and then kept overnight at room temperature to give a brown powder. Successive decantation and evaporation gave 4 (250.3 mg, 264.0 mmol, 88%). Deep red crystals of 4 were obtained when the reaction was performed without stirring. Anal. Calcd for Co2Si2N4C78H96·0.4C6H6: C, 74.54; H, 7.44; N, 4.34. Found: C, 74.29; H, 7.67; N, 4.29. Single-Crystal X-ray Diffraction Studies. The single-crystal Xray diffraction measurements of 2 and 4 were performed under a cold nitrogen stream on a Rigaku XtaLAB P200 diffractometer with a Pilatus 200 K detector using multilayer mirror monochromated Mo Kα radiation. The determination of crystal systems and unit cell

Scheme 4. Possible Reaction Path for Cobalt Silyl Complexes 2−4

■

CONCLUSION Reactions of IPr-supported Co dialkyl complex 1 with various hydrosilanes proceeded via facile multiple Si−H bond cleavage of both primary and secondary silanes to give silyl-bridged dicobalt complexes. The mode of the reaction was highly dependent on the size of the hydrosilane; thus, reaction with HexSiH3 resulted in the formation of a complex with four μsilyl ligands, and the reaction with the larger PhSiH3 resulted in the formation of a complex with three μ-silyl ligands. Only two bulkier μ-SiHPh2 ligands were incorporated in the dicobalt skeleton in the reaction of 1 with Ph2SiH2. These results demonstrate one of the rare examples of well-defined silylbridged dinuclear cobalt complexes.

■

EXPERIMENTAL SECTION

General Considerations. Unless otherwise noted, all manipulations were performed under a nitrogen atmosphere using either Schlenk techniques or a glovebox. All organic solvents were dried with a solvent purification system (MBraun SPS-800 or Glass Contour Ultimate Solvent System). C6D6 was dried over sodium benzophenone ketyl and distilled. Complex 1 was synthesized by following the reported procedures.11 All other reagents were purchased from commercial suppliers and used without further purification unless otherwise noted. 1H, 13C{1H}, and 29Si{1H} NMR spectra (1H, 600 MHz; 13C, 150 MHz; 29Si, 119 MHz) were recorded with a Bruker AVANCE 600 spectrometer. Chemical shifts are reported in δ (ppm) and are referenced to 1,4-bis(trimethylsilyl)benzene for 29Si (C6D6, −4.20 ppm) and to the residual solvent signals for 1H (7.16 ppm for C6D6, 2.08 ppm for Tol-d8) and 13C (128.06 ppm for C6D6). In the case of variable-temperature experiments, 1H NMR measurements were performed on a Bruker Avance III HD 400 spectrometer. Infrared (IR) spectra were recorded with a Bruker Alpha-T ATRFTIR Fourier transform infrared spectrometer. Elemental analyses were performed with a Yanaco CHN CORDER MT-6 instrument. Synthesis of Complex 2. To a C6H6 solution (3 mL) of 1 (279.1 mg, 450 μmol) was added HexSiH3 (261.5 mg, 2.25 mmol) at room temperature. After the solution was stirred for 1 h, the volatiles were removed under vacuum. The residue was extracted with hexane and passed through an Al2O3 pad (eluent C6H6). After removal of the solvent, crystallization from hexane at −35 °C gave 2 as red plate crystals (262.2 mg, 193 mmol, 86%). 1H NMR (Tol-d8, 70 °C): δ D

DOI: 10.1021/acs.organomet.8b00865 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics ORCID

parameters and data processing were performed with the CrystalClear program package.21 All structures were solved by direct methods using the ShelxT program22 and refined by full-matrix least-squares calculations on F2 for all reflections (SHELXL-2014/7)23 using the Yadokari-XG 2009 program.24 Crystallographic parameters for 2 and 4 are given in Table 1.

Yumiko Nakajima: 0000-0001-6813-8733 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by a MEXT Grant-in-Aid for Scientific Research on Innovative Areas “Precise Formation of a Catalyst Having a Specified Field for Use in Extremely Difficult Substrate Conversion Reactions” (no. 18H04280) and by KAKENHI (no. 18H01986) from JSPS.

Table 1. Crystallographic Parameters for 2 and 4 empirical formula formula wt temp, K wavelength, Å cryst syst space group a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z calcd density, Mg/m3 F(000) goodness of fit on F2 final R indices (I > 2σ(I)) R indices (all data)

2

4

C78H132Co2N4Si4 1356.09 93(2) 0.71075 monoclinic P21/c 12.458(3) 18.877(5) 17.377(4) 90 102.772(7) 9 3985.4(17) 2 1.130 1476 1.291 R1 = 0.0656, wR2 = 0.1791 R1 = 0.1032, wR2 = 0.1964

C84H102Co2N4Si2 1341.73 93(2) 0.71075 monoclinic P21/n 12.767(2) 13.947(3) 20.546(4) 90 99.274(4) 90 3610.6(12) 2 1.234 1432 1.062 R1 = 0.0458, wR2 = 0.0824 R1 = 0.0857, wR2 = 0.0956

■

Computational Methods. The geometry of 3a′ was optimized with the DFT method, where the B3LYP functional was used for exchange-correlation terms.25 We ascertained that each equilibrium geometry exhibited no imaginary frequency. For the calculations, core electrons of Co were replaced (up to 3d) with effective core potentials (ECPs), where a Lanl2DZ basis set was used for valence electrons of Co.26 The 6-31G(d,p) basis sets were used for Si and N atoms as well as C and H atoms attached to the Co atoms. For other C and H atoms, 6-31G basis sets were used. The Gaussian 09 program package was used for all calculations.27

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00865. NMR, IR, and UV−vis spectra of 2-4, single-crystal Xray diffraction data of 3a, and computational details (PDF) Cartesian coordinates for the calculated structures (XYZ) Accession Codes

CCDC 1877985 and 1880255 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

■

REFERENCES

(1) (a) Marciniec, B. Comprehensive Handbook on Hydrosilylation; Pergamon Press: Oxford, New York, 1992. (b) Marciniec, B.; Maciejewski, H.; Pietraszuk, C.; Pawluć, P. Hydrosilylation: A Comprehensive Review on Recent Advances; Springer: Berlin, 2009. (c) Marciniec, B. Catalysis by Transition Metal Complexes of Alkene Silylation−Recent Progress and Mechanistic Implications. Coord. Chem. Rev. 2005, 249, 2374−2390. (2) (a) Corey, J. Y. Reactions of Hydrosilanes with Transition Metal Complexes and Characterization of the Products. Chem. Rev. 2011, 111, 863−1071. (b) Osakada, K.; Tanabe, M. Platinum and Palladium Complexes with Metal−Silicon Bonds. New Bonding, Structures, and Chemical Properties. Bull. Chem. Soc. Jpn. 2005, 78, 1887−1898. (c) Ogino, H.; Tobita, H. Bridged Silylene and Germylene Complexes. Adv. Organomet. Chem. 1998, 42, 223−290. (3) (a) Speier, J. L.; Webster, J. A.; Bernes, G. H. The Addition of Silicon Hydrides to Olefinic Double Bonds. Part II. The Use of Group VIII Metal Catalysts. J. Am. Chem. Soc. 1957, 79, 974−979. (b) Lewis, L. N.; Sy, K. G.; Bryant, G. L., Jr.; Donahue, P. E. Platinum− Catalyzed Hydrosilylation of Alkynes. Organometallics 1991, 10, 3750−3759. (c) Roy, A. K.; Taylor, R. B. The First Alkene− Platinum−Silyl Complexes: Lifting the Hydrosilation Mechanism Shroud with Long-Lived Precatalytic Intermediates and True Pt Catalysts. J. Am. Chem. Soc. 2002, 124, 9510−9524. (d) Ozawa, F.; Kamite, J. Mechanistic Study on the Insertion of Phenylacetylene into cis-Bis(silyl)platinum(II) Complexes. Organometallics 1998, 17, 5630−5639. (e) Pfeiffer, J.; Kickelbick, G.; Schubert, U. Synthesis of a Bis(silanolate) Complex from a Bis(silyl) Complex by Air Oxidation: Evidence for the Participation of Silanolate Complexes in the Transition-Metal-Catalyzed Formation of Disiloxanes from Hydridosilanes. Organometallics 2000, 19, 957−959. (4) (a) Suginome, M.; Ito, Y. Transition-Metal-Catalyzed Additions of Silicon−Silicon and Silicon−Heteroatom Bonds to Unsaturated Organic Molecules. Chem. Rev. 2000, 100, 3221−3256. (b) Yamanoi, Y. Palladium-Catalyzed Silylations of Hydrosilanes with Aryl Halides Using Bulky Alkyl Phosphine. J. Org. Chem. 2005, 70, 9607−9609. (5) (a) Auburn, M. J.; Holmes-Smith, R. D.; Stobart, S. R. (Phosphinoalkyl)silyl Complexes 3. “Chelate-Assisted” Hydrosilylation: Formation of Enantiomeric and Diastereoisomeric Iridium(III) Complexes with Chelating (Phosphinoethyl)silyl Ligands. J. Am. Chem. Soc. 1984, 106, 1314−1318. (b) Fernández, M. J.; Esteruelas, M. A.; Jiménez, M. S.; Oro, L. A. Synthesis and Reactions of Dlhydrldo(trlethylsllyl)(1,5-cyclooctadlene)-Iridium(III) Complexes: Catalysts for Dehydrogenatlve Sllylatlon of Alkanes. Organometallics 1986, 5, 1519−1520. (c) Karshtedt, D.; Bell, A. T.; Tilley, T. D. Stoichiometric and Catalytic Reactions Involving Si−H Bond Activations by Rh and Ir Complexes Containing a Pyridylindolide Ligand. Organometallics 2006, 25, 4471−4482. (d) Nishihara, Y.; Takemura, M.; Osakada, K. Comparative reactivity of triorganosilanes, HSi(OEt)3 and HSiEt3, with IrCl(CO)(PPh3)2. Formation of IrCl(H)2(CO)(PPh3)2 or Ir(H)2(SiEt3)(CO)(PPh3)2 depending on the substituents at Si. Inorg. Chim. Acta 2009, 362, 2951−2956. (6) (a) Ojima, I.; Kumagai, M. The Stereochemistry of the Addition of Hydrosilanes to Alkyl Acetylenes Catalyzed by Tris(triphenylphosphine)chlororhodium. J. Organomet. Chem. 1974, 66,

AUTHOR INFORMATION

Corresponding Author

*E-mail for Y.N.: [email protected]. E

DOI: 10.1021/acs.organomet.8b00865 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics C14−C16. (b) Ojima, I.; Donovan, R. J.; Shay, W. R. Silylcarbocyclization Reactions Catalyzed by Rh and Rh−Co Complexes. J. Am. Chem. Soc. 1992, 114, 6580−6582. (c) Duckett, S. B.; Perutz, R. N. Mechanism of Homogeneous Hydrosilation of Alkenes by (η5Cyclopentadieny) Rhodium. Organometallics 1992, 11, 90−98. (d) Muraoka, T.; Matsuda, I.; Itoh, K. Rhodium-Catalyzed Silylative Cyclization of 1,6-Heptadiyne Derivatives: A Versatile Route for the Synthesis of a 1,2-Dialkylidenecyclopentane Skeleton. Organometallics 2002, 21, 3650−3660. (e) Cheng, C.; Hartwig, J. F. Mechanism of the Rhodium-Catalyzed Silylation of Arene C−H Bonds. J. Am. Chem. Soc. 2014, 136, 12064−12072. (7) (a) Sun, J.; Deng, L. Cobalt Complex-Catalyzed Hydrosilylation of Alkenes and Alkynes. ACS Catal. 2016, 6, 290−300. (b) Harrod, J. F.; Chalk, A. J. Dicobalt Octacarbonyl as a Catalysts for Hydrosilylation of Olefins. J. Am. Chem. Soc. 1965, 87, 1133. (8) (a) Atienza, C.C. H.; Diao, T.; Weller, K. J.; Nye, S. A.; Lewis, K. M.; Delis, J. G. P.; Boyer, J. L.; Roy, A. K.; Chirik, P. J. Bis(imino)pyridine Cobalt-Catalyzed Dehydrogenative Silylation of Alkenes: Scope, Mechanism, and Origins of Selective Allylsilane Formation. J. Am. Chem. Soc. 2014, 136, 12108−12118. (b) Liu, Y.; Deng, L. Mode of Activation of Cobalt(II) Amides for Catalytic Hydrosilylation of Alkenes with Tertiary Silanes. J. Am. Chem. Soc. 2017, 139, 1798−1801. (c) Chen, C.; Hecht, M. B.; Kavara, A.; Brennessel, W. W.; Mercado, B. Q.; Weix, D. J.; Holland, P. L. Rapid, Regioconvergent, Solvent-Free Alkene Hydrosilylation with a Cobalt Catalyst. J. Am. Chem. Soc. 2015, 137, 13244−13247. (9) (a) Wekel, H.-U.; Malisch, W. Synthese und Reaktivität von Silicium-Ü bergangsmetall-Komplexen: XVIII. Trihydrosilylkomplexe des Eisens: Darstellung und Metallierung mit Dicobaltoctacarbonyl. J. Organomet. Chem. 1984, 264, C10−C13. (b) Kreisz, J.; Sisak, A.; Markó, L. Reaction of Silylcobalt Tetracarbonyls with Oxiranes. Kinetics and Mechanism. J. Organomet. Chem. 1993, 451, 53−57. (c) Anderson, F. R.; Wright, M. S. Direct Observation of the Intermediate in the Photochemical Reaction of R3SiCo(CO)4 with R′3SiH and Establishment of the Mechanism for R′3SiCo(CO)4 Formation. J. Am. Chem. Soc. 1984, 106, 995−999. (10) (a) Brookhart, M.; Grant, B. E.; Lenges, C. P.; Prosenc, M. H.; White, P. S. High Oxidation State Organocobalt Complexes: Synthesis and Characterization of Dihydridodisilyl Cobalt(V) Species. Angew. Chem., Int. Ed. 2000, 39, 1676−1679. (b) Lyons, T. W.; Brookhart, M. Cobalt-Catalyzed Hydrosilation/Hydrogen-Transfer Cascade Reaction: A New Route to Silyl Enol Ethers. Chem. - Eur. J. 2013, 19, 10124−10127. (c) Ampt, K. A. M.; Duckett, S. B.; Perutz, R. N. Low Temperature in situ UV Irradiation of [(η5-C5H5)Co(C2H4)2] in the NMR Probe: Formation of Co(III) Silyl Hydride Complexes. Dalton Trans. 2007, 2993−2996. (d) Sun, J.; Gao, Y.; Deng, L. Low-Coordinate NHC-Cobalt(0)-Olefin Complexes: Synthesis, Structure, and Their Reactions with Hydrosilanes. Inorg. Chem. 2017, 56, 10775−10784. (11) Przyojski, J. A.; Arman, H. D.; Tonzetich, Z. J. NHC Complexes of Cobalt(II) Relevant to Catalytic C−C Coupling Reactions. Organometallics 2013, 32, 723−732. (12) Pauling, L. Metal−Metal Bond Lengths in Complexes of Transition Metals. Proc. Natl. Acad. Sci. U. S. A. 1976, 73, 4290−4293. (13) (a) Yong, L.; Hofer, E.; Wartchow, R.; Butenschön, H. Oxidative Addition of Hydrosilanes, Hydrogermane, and Hydrostannane to Cyclopentadienylcobalt(I) Bearing a Pendant Phosphane Ligand: Cyclopentadienylhydridocobalt(III) Chelate Complexes with Silyl, Germyl, and Stannyl Ligands. Organometallics 2003, 22, 5463− 5467. (c) Sun, J.; Luo, L.; Luo, Y.; Deng, L. An NHC−Silyl−NHC Pincer Ligand for the Oxidative Addition of C−H, N−H, and O−H Bonds to Cobalt(I) Complexes. Angew. Chem., Int. Ed. 2017, 56, 2720−2724. (14) (b) Ohki, Y.; Kojima, T.; Oshima, M.; Suzuki, H. {(η5C5Me5)Fe}2(μ-H)2(μ-η2:η 2-H2SitBu2), a Versatile Precursor for Bimetallic Active Species. Organometallics 2001, 20, 2654−2656. (c) Ohki, Y.; Suzuki, H. [{(η5-C5Me5)Fe}2(μ-H)4]: A Novel Dinuclear Iron Tetrahydrido Complex. Angew. Chem., Int. Ed. 2000, 39, 3120−3122. (d) Tanabe, M.; Takahashi, A.; Yamada, T.; Osakada,

K. Dipalladium Complexes with Bridging Monoalkyl or Monophenyl Silyl Ligands in the Solid State and in Solution. Organometallics 2013, 32, 1815−1820. (15) For more details, please see the Supporting Information. (16) The high-field signal of 3b occasionally appears at the same position as for 3a with a w1/2 value of 8.1 Hz in C6D6. However, the signal was resolved into two signals at δ −10.58 and −10.59 in tol-d8. (17) Kaesz, H. D.; Saillant, R. B. Hydride Complexes of the Transition Metals. Chem. Rev. 1972, 72, 231−281. (18) Takao, T.; Yoshida, S.; Suzuki, H. Synthesis, Characterization, and Reactivities of Diruthenium Complexes Containing a μ-Silane Ligand and Structural Studies of the μ-Silane Complex [Cp′Ru(CO)]2(μ-H2SitBu2). Organometallics 1995, 14, 3855−3868. (19) The structurally similar dicobalt(I) complex [{Co(IPr)}2(μ-η2HSiPh2)2] has been reported,10d which exhibited bond lengths and angles around the Co atom almost identical with those of 4, whereas its IR spectrum was significantly different. (20) Liu, Y.; Deng, L. Mode of Activation of Cobalt(II) Amides for Catalytic Hydrosilylation of Alkenes with Tertiary Silanes. J. Am. Chem. Soc. 2017, 139, 1798−1801. (21) Crystal Clear; Rigaku Corp., The Woodlands, TX, USA, 2011. (22) Sheldrick, G. M. SHELXT−Integrated Space-Group and Crystal-Structure Determination. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71, 3−8. (23) Sheldrick, G. M. A. Short History of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (24) (a) Kabuto, C.; Akine, S.; Nemoto, T.; Kwon, E. Release of Software(Yadokari-XG 2009)for Crystal Structure Analyses. Nippon Kessho Gakkaishi 2009, 51, 218−224. (25) Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648−5652. (26) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for the Transition Metal Atoms Sc to Hg. J. Chem. Phys. 1985, 82, 270−283. (c) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for Main Group Elements Na to Bi. J. Chem. Phys. 1985, 82, 284−298. (d) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for K to Au Including the Outermost Core Orbitals. J. Chem. Phys. 1985, 82, 299−310. (27) Gaussian 09, Revision D.01; Gaussian, Inc., Wallingford, CT, 2016. See the Supporting Information for the full citation.

F

DOI: 10.1021/acs.organomet.8b00865 Organometallics XXXX, XXX, XXX−XXX