Photochemistry of some iron and ruthenium (η5-cyclopentadienyl) carbonyl dimers in frozen gas matrices at ca. 12 K

Abstract

The photochemistry of [M₂(η⁵-C₅H₅)₂(CO)₄][M = Fe, (1); or Ru, (2)] and [CH₂{(η⁵-C₅H₄)M(CO)₂}₂][M = Fe, (5); or Ru, (6)] has been studied in frozen-gas matrices (Ar, CH₄, and N₂) at ca. 12 K and that of (2) in poly (vinyl chloride)(pvc) films at ca. 12 K. Low-energy photolysis of compounds (1) and (2) was found to induce opening of trans-carbonyl-bridged species affording terminal carbonyl species. Photolyses into the electronic absorption band maxima of these new terminal-carbonyl species yielded 17-electron radical species [M(η⁵-C₅H₅)(CO)₂]˙ as well as small amounts of triply carbonyl-bridged species, [M₂(η⁵-C₅H₅)₂(µ-CO)₃]. At the corresponding maxima of trans-carbonyl-bridged complexes (1) and (2) photolysis yielded the triply-carbonyl-bridged species directly. Photolysis of (5), which is exclusively bridging and is constrained by the methylene linkage between the rings to be in a cis conformation, at a range of wavelengths showed no evidence for carbonyl-bridge opening. At its electronic absorption maxima photolysis resulted in carbonyl ejection and formation of a new species whose spectrum is consistent with its having three terminal carbonyl groups and an Fe–Fe double bond. Photolysis of compound (6) which exists in a cis-terminal conformation also resulted in carbonyl loss and formation of a species similar to that observed for (5). These results are discussed in terms of their relationship to previous photochemical studies of (1) and (2) and an overall model for the photochemical behaviour of (1) and (2) is presented.