A new family of carbenerhodium(I) complexes: Ligand variation as the key to success

A synthetic methodology to obtain square-planar carbenerhodium(I) complexes of the general composition trans-[RhCl(= CRR')(L)(2)] where L is a tertiary phosphane, arsane, or stibane has been developed. The starting material trans-[RhCl(C2H4)(SbiPr(3))(2)] (3) reacts with diazoalkanes RR'CN2 [RR' = Ph-2, Ph(C6H4X), (C6H4X)(2), Ph(CF3), C12H8] under mild conditions to give the compounds trans-[RhCl(= CRR')(SbiPr(3))(2)] (4-11) almost quantitatively. On treatment of 3 with EtO2CCHN2 and PhC(N-2)C(O)R, the olefinrhodium and diazoalkanerhodium compounds trans-[RhCl{(E)-C2H2(CO2Et)(2)}(SbiPr(3))(2)] (12) and trans-[RhCl{N2C(R)C(O)Ph}(SbiPr(3))(2)] (13, 14) are obtained instead of carbene complexes. Displacement of the SbiPr(3) ligands in 4 (R = R' = Ph) by PiPr(3), PiPr(2)Ph, PiPrPh(2), PPh3, PPh2Me, AsiPr(3), and SbEt3 leads to the corresponding carbene complexes trans-[RhCl(= CPh2)(L)(2)] (15-21) in high yields. The results of the X-ray crystal structure analyses of 4 and 15 (L = PiPr(3)) illustrate that the different donor-acceptor properties of SbiPr(3) and PiPr(3) have little influence on the Rh-C bond length. The reactions of 4 and 15 with CO and CNtBu afford, by metal-assisted C-C coupling, diphenylketene Ph2C=C=O (23) and the corresponding imine Ph2C=C=NtBu (26). On treatment of 4 and 15 with ethene, however, two different olefinic products, 3,3-diphenyl-1-propene (31) and 1,1-diphenyl-1-propene (32), are formed. Compound 15 reacts with KBr, NaOPh, and NaC5H5 by substitution of the chloride to give trans-[RhBr(= CPh2)-(PiPr(3))(2)] (33), trans-[Rh(OPh)(= CPh2)-(PiPr(3))(2)] (34) and [C5H5Rh(= CPh2)- (PiPr(3))] (35), and wit HCl by oxidative a addition to yield [RhCl2(CHPh2)-(PiPr(3))(2)] (36).