Molybdenum complexes with polymer-bound cysteine and their catalysis in acetylene reduction

Water soluble polymers with cysteine residues (Pcys) were synthesized by the copolymerization of S‐benzyl‐N‐benzyloxycarbonyl‐4'‐vinyl‐L‐cysteineanilide and acrylic acid or methacrylic acid. These copolymers were reacted with Mo(V)2O 42− to Mo(V)‐Pcys complexes with di‐μ‐oxo bridged binuclear structure. The absorption maximum of these complexes appears at 330 nm in aqueous solution. ESR study suggests that mononuclear Mo(III)‐Pcys complexes (g = 1,997) are formed by reduction of Mo(V)‐Pcys complexes with NaBH4. These Mo(III)‐Pcys complexes are effective catalysts for the reduction of acetylene in the presence of NaBH4 and their catalytic activities are 2—3 times greater than that of the corresponding low molecular weight Mocysteine complex. The higher activity of the polymer complexes is explained by the enhancement of the proportion of monomuclear species due to the stretching of the polymer chain caused by the electrostatic repulsions between the carboxyl anions on the side chains.