Synthesis and molecular structure of four-coordinate neutral and cationic diphenylcarbenerhodium(I) complexes

Neutral diphenylcarbenerhodium(I) complexes of the general composition trans-[RhX(CPh2)(PiPr3)2] (X=F (3), OCN (4), CF3CO2 (5), PhCO2 (6), CF3SO3 (7)) were prepared from the chloro or bromo precursors trans-[RhCl(CPh2)(PiPr3)2] (1) and trans-[RhBr(CPh2)(PiPr3)2] (2) by salt metathesis in acetone and isolated in excellent yields. While treatment of 1 with Tl(acac[F6]) afforded the substitution product trans-[Rh(κ1-acac[F6])(CPh2)(PiPr3)2] (8), the corresponding reaction of 1 with Tl(acac) gave the chelate compound [Rh(κ2-acac)(CPh2)(PiPr3)] (9) with only one phosphine ligand attached to the metal center. In acetone solution, the triflato complex 7 is in equilibrium with the cation trans-[Rh{OC(CH3)2}(CPh2)(PiPr3)2]+ which after addition of NaBArF4 precipitates as the BArF4 salt 11. The starting material 1 as well as the bis(triphenylphosphine) and bis(triisopropylstibine) analogues 14 and 15 react with pyridine or acetonitrile in the presence of KPF6 to yield the cationic complexes trans-[Rh(py)(CPh2)(PPh3)2]PF6 (16) and trans-[Rh(CH3CN)(CPh2)(L)2]PF6 (L=PiPr3 (17), SbiPr3 (18)). The BArF4 salt of the cation trans-[Rh(CH3CN)(CPh2)(SbiPr3)2]+ (19) was characterized by X-ray crystallography. Compounds 11, 16–19 and the bis(pyridine) derivative cis-[Rh(CPh2)(NC5H5)2(PiPr3)]PF6 (12) are the first representatives of four-coordinate cationic diphenylcarbenerhodium(I) complexes.