An investigation into the photochemical reactions of M(η5-C5H5)(CO)4 and M(η5-C9H7)(CO)4 (M = Nb or Ta) with H2 and N2 in polyethylene matrices and liquid xenon at low temperature

Abstract

The photolysis of MCp′(CO)4 (Cp′ = Cp or indenyl; M = Nb or Ta) in polyethylene (PE) matrices at low temperature under a high pressure of reactant gas led to formation of a wide range of photoproducts. Under an inert atmosphere (helium), NbCp′(CO)3 and NbCp′(CO)2 are observed following irradiation of the parent tetracarbonyl. However, only TaCp′(CO)3 is observed for the analogous reactions of the corresponding tantalum compounds. Similarly, NbCp′(CO)3(N2) and NbCp′(CO)2(N2)2 are seen following irradiation of NbCp′(CO)4 under a high pressure of N2, whereas only TaCp′(CO)3(N2) was observed following irradiation of TaCp′(CO)4. Under hydrogen, the classical dihydride TaCp′(CO)3H2 is formed following irradiation of TaCp′(CO)4. The non-classical dihydrogen complex Nb(C9H7)(CO)3(η2-H2) is formed following irradiation of Nb(C9H7)(CO)4. NbCp(CO)4 forms both the classical hydride and non-classical dihydrogen complex. Using a high pressure-low temperature cell, the thermal reaction of TaCp′(CO)3(N2) with hydrogen to form TaCp′(CO)3H2 was observed. Preliminary room temperature studies suggest that Ta(C9H7)(CO)3H2 is ca. 50 times more reactive than TaCp(CO)3H2 in PE.