Rh(I) and Rh(III) silyl PMe 3 complexes. Syntheses, reactions and 103Rh NMR spectroscopy

Abstract

Synthetic approaches to Rh(I) silyls are described. The complexes L n RhSiR 3 (L=PMe 3; 6, n=4, R 3=(OEt) 3; 7, n=4, R 3=Me(OMe) 2; 21, n=3, R 3=Ph 3) resulted from the reactions of MeRhL 4 ( 1) with the corresponding silanes HSiR 3. Complex 21 was prepared alternatively from PhRhL 3 ( 2) and HSiPh 3, while analogous reactions of HSi(OEt) 3, HSiMe(OMe) 2 and HSi(OMe) 3 led to the bis(silyl)hydrides fac-L 3Rh(SiR 3) 2(H) ( 8, R 3=(OEt) 3; 9, R 3=Me(OMe) 2; 13, R 3=(OMe) 3). Like in analogous iridium-based systems, the outcome of these reactions largely depends on the nature of substituents at the silicon atom. Synthesis of Rh(I) silyls inaccessible by this route, namely those with alkyl substituents at the silicon, L n RhSiR 3 ( 19, n=3, R 3=PhMe 2; 22, n=4, R 3=Me 3), was achieved utilizing nucleophilic attack of the corresponding silyllithiums at [L 4Rh]Cl. The solid-state structure of 19 was determined by X-ray crystallography. C 17H 38P 3SiRh, Fw=466.38 monoclinic, C2/m, a=13.304(3) Å, b=13.814(2) Å, c=13.123(4) Å, β=110.66(3) deg, V=2257(1) Å 3, Z=4, d calcd=1.373 g cm −3, μ=1.019 mm −1. A series of di(hydrido)silyls fac-L 3Rh(H) 2(SiR 3) ( 10, R 3=(OEt) 3; 15, R 3=PhMe 2; 16, R 3=Ph 3) was synthesized using oxidative additions of HSiR 3 to HRhL 4 ( 3). Complexes 10, 15, 16 are thermodynamically stable with respect to H–H and Si–H reductive-elimination reactions at ambient conditions. Complex 8 reductively eliminates HSi(OEt) 3 reversibly at room temperature and complex 13 is capable upon heating of mediating dehydrogenative Si–Si coupling of HSi(OMe) 3 and redistribution of [(MeO) 3Si] 2. 103Rh NMR data obtained for MeRhL 4 ( 1), HRhL 4 ( 3), L 3RhSiPhMe 2 ( 19), L 3RhSiPh 3 ( 21) and for the di(hydrido) silyls ( 10, 15, 16) allowed to qualitatively evaluate steric and electronic effects of methyl, silyl, and hydride ligands on the 103Rh chemical shift.