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

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 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.

带有EP3型四齿配体（tetradentate ligand）的铑配合物{(Ph₂P)C₆H₄}₃ERh(CO)（配合物1：E=硅（Si）；配合物2：E=锗（Ge）；配合物3：E=锡（Sn）），通过配体前体HE(o-C₆H₄PPh₂)₃与三(三苯基膦)羰基氢化铑（tris(triphenylphosphine) carbonyl rhodium hydride）RhH(CO)(PPh₃)₃的反应合成得到。在该类配合物中，第14族元素E展现出优异的σ电子给体能力；在取代反应中，其可按照(H ≪) Sn ≈ Ge的顺序拉长与E处于反位的Rh-CO键。配合物1的取代反应速率显著慢于配合物2与3，三者的准一级速率常数kobs（pseudo-first-order rate constant）的相对比值为1:7.7:8.5。动力学研究表明，较重的第14族元素E可诱导与E处于顺位的膦配体发生解离，最终引发CO/L配体取代反应。