Reaction of primary silanes with dinuclear rhodium hydride complexes: silane coupling reactions

Abstract

The reaction of the dinuclear rhodium hydride dimer [(dippe)Rh] 2(μ-H) 2 (dippe=l,2-bis(diisopropylphosphino)ethane) with primary silanes is described. In the presence of two equivalents of RSiH 3 (R=Bu n and Tol P), dinuclear bis(μ-silylene) complexes of the formula [(dippe)Rh] 2(μ-SiHR) 2 result. Attempts to generate silylhydride complexes of the formula [(dippe)Rh] 2(μ-H)(μ-H-SiHR) by the addition of one equiv. of RSiH 3 failed. The bis(μ-silylene) complexes react with hydrogen to form adducts wherein two equivalents of H 2 per dimer unit have been activated; on the basis of NMR spectral studies these complexes are proposed to have the following formula: [(dippe)RhH] 2(μ-H-SiHR) 2. These molecules are extremely fluxional and lose H 2 rather readily. Addition of more than three equivalents of primary silane to 1 generated dinuclear rhodium derivatives with three silicon-containing ligands, having the formula [(dippe)Rh] 2(μ-SiHR)(μ-H-SiHR) 2. In the presence of excess primary silane, the dinuclear rhodium hydride 1 acts as a catalyst precursor for the dehydrogenative coupling of silanes. With the p-tolylsilane, dimerization does occur but the process is complicated by dispro- portionation reactions to generate (Tol P) 2SiH 2 and (Tol P) 3SiH; with butylsilane, SiSi chains with up to five silicons have been produced with no evidence of disproportionation. Crystals of [(dippe)Rh] 2(μ-SiHBu n) 2 ( 2a) are monoclinic, a=10.889(1), b=13.105(2), c=16.676(2) Å,β=104.06(1)°, Z=2, space group P2 1/n.; and those of [(dippe)Rh] 2(μ-η 2-H-SiHTol P) 2(μ-SiHTol P) ( 4b) are monoctinic, a=25.839(4), b=13.084(3), c=17.133(3) Å, β=107.10(1)°, Z=4, space group P21/ a. The structures were solved by Patterson ( 2a) and direct ( 4b) methods and were refined by full-matrix least-squares procedures to R=0.035 and 0.047 ( R w=0.030 and 0.060) for 3184 and 5997 reflections with 1⩾3η( I), respectively.