Synthesis and Reactivity of Rhodium Complexes Bearing [E( o -C 6 H 4 PPh 2 ) 3 ]-Type Tetradentate Ligands (E = Si, Ge, and Sn)

Rhodium complexes {(Ph 2 P)C 6 H 4 } 3 ERh(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 -C 6 H 4 PPh 2 ) 3 with tris(triphenylphosphine) carbonyl rhodium hydride RhH(CO)(PPh 3 ) 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 k obs 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.