Synthesis and Reactivity of Rhodium Complexes Bearing [E(o-C6H4PPh2)3]-Type Tetradentate Ligands (E = Si, Ge, and Sn)

Abstract

Rhodium complexes {(Ph2P)C6H4}3ERh(CO) (1: E = Si; 2: E = Ge; 3: E = Sn) bearing EP3-type tetradentate ligands were synthesized by the reaction of the corresponding ligand precursors HE(o-C6H4PPh2)3 with tris(triphenylphosphine) carbonyl rhodium hydride RhH(CO)(PPh3)3. In these complexes, the group 14 elements E exhibited a high σ-electron donor ability and elongated the Rh–CO bond trans to E in the order (H ≪) Sn ≈ Ge < Si. The Rh–E strength has influence on the CO/P(OMe)3 substitution reactions. The substitution of 1 is remarkably slower than those of 2 and 3, and the relative ratios of the pseudo-first-order rate constants kobs for 1, 2, and 3 are 1:7.7:8.5. The kinetic study indicated that heavy group 14 elements E could induce the dissociation of a phosphine ligand cis to E, which eventually leads to CO/L substitution.