Photoreactions of Aminepentacarbonylmolybdenum(0) and -tungsten(0) Complexes

The ligand photosubstitution processes in M(CO)₅L (M = Mo and W; L = NH₃, n-PrNH₂, and piperidine) upon excitation with 366-, 405-, or 436-nm light have been investigated. Photosubstitution of both L and CO is found and the quantum yields are dependent on the excitation wavelength. Photosubstitution of L dominates the chemical decay paths of the excited state with CO substitution becoming more important at shorter excitation wavelengths. Photosubstitution of CO for M = Mo is generally higher than for M = W in the M(CO)₅L complexes investigated. Typical quantum yields for M-L cleavage at 405 nm are of the order of 0.5 as determined by measuring the formation of M(CO)₆ by photolysis of Mo(CO)₅NH₃ or W(CO)₅(piperidine) in the presence of CO. Substitution yields for CO release are in the range of 10^-2-10^-1 as determined by photolysis of M(CO)₅L in the presence of excess L yielding M(CO)₄L₂ complexes, Importantly, the total reaction quantum yields are less than unity.