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

Neutral diphenylcarbenerhodium(I) complexes of the general composition trans-[RhX(=CPh2)((PPr3)-Pr-t)(2)] (X = F (3), OCN (4), CF3CO2 (5), PhCO2 (6), CF3SO3 (7)) were prepared from the chloro or bromo precursors trans-[RhCl(=CPh2)((PPr3)-Pr-i)(2)] (1) and trans-[RhBr(=CPh2)((PPr3)-Pr-i)(2)] (2) by salt metathesis in acetone and isolated in excellent yields. While treatment of 1 with Tl(acac[F-6]) afforded the substitution product trans-[Rh(kappa (1)-acac[F-6])(=CPh2)((PPr3)-Pr-i)(2)] (8), the corresponding reaction of 1 with Tl(acac) gave the chelate compound [Rh(kappa (2)-acac)(=CPh2)((PPr3)-Pr-i)] (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)((PPr3)-Pr-i)(2)](+) which after addition of NaBAr4F precipitates as the BAr4F 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=(PPr3)-Pr-i (17), (SbPr3)-Pr-i (18)). The BAr4F salt of the cation trans-[Rh(CH3CN)(=CPh2)((SbPr3)-Pr-i)(2)](+) (19) was characterized by X-ray crystallography. Compounds 11, 16-19 and the bis(pyridine) derivative cis-[Rh(=CPh2)(NC5H5)(2)((PPr3)-Pr-i)]PF6 (12) are the first representatives of four-coordinate cationic ;diphenylcarbenerhodium(I) complexes. (C) 2001 Elsevier Science B.V. All rights reserved.