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.