An investigation into the photochemical reactions of MCp(CO)4 (Cp = η5-C5H5) and M(η5-C9H7)(CO)4 (η5-C9H7 = indenyl; M = Nb or Ta) with CO, H2 and N2 in solution at room temperature

Abstract

Time resolved step-scan FTIR spectroscopy (s²-FTIR) has been used to characterise MCp′(CO)₃L (Cp′ = Cp or indenyl (η⁵-C₉H₇); M = Nb or Ta; L = n-heptane, H₂ or N₂) in solution at room temperature. TaCp′(CO)₄ formed the classical dihydrides, TaCp′(CO)₃H₂ upon irradiation in n-heptane saturated with H₂. However, photolysis of Nb(η⁵-C₉H₇)(CO)₄ under the same conditions led to the non-classical complex, Nb(η⁵-C₉H₇)(CO)₃(η²-H₂), whereas irradiation of NbCp(CO)₄ resulted in both NbCp(CO)₃H₂ and NbCp(CO)₃(η²-H₂). Photolysis of MCp′(CO)₄ in n-heptane saturated with N₂ resulted in formation of MCp′(CO)₃(N₂) in all cases. No evidence for disubstitution of these complexes was obtained in these s²-FTIR experiments. The rate constants for the reaction of M(η⁵-C₉H₇)(CO)₃(n-C₇H₁₆) with CO, H₂ and N₂ have been determined. Comparison of these rate constants with those obtained for the analogous cyclopentadienyl complexes showed that the indenyl complexes are more reactive (ca. 10 times). Additionally, the Nb(η⁵-C₉H₇)(CO)₃(L) (L = η²-H₂ or N₂) complexes were found to be less stable (ca. 20–30 times) than NbCp(CO)₃(L), and Ta(η⁵-C₉H₇)(CO)₃(N₂) was more reactive (ca. 25 times) than TaCp(CO)₃(N₂).