Photochemistry of dicarbonyl(η5-cyclopentadienyl)-methyl- and -ethyl-iron and -ruthenium complexes in solutions at –30 °C and in frozen gas matrices at 12 K

Abstract

The photolysis reactions of [M(CO)₂R(η⁵-C₅H₅)](M = Fe or Ru, R = Me or Et) complexes have been studied by a combination of solution (–30 °C) and matrix-isolation (12 K) techniques. In pentane solutions (–30 °C) photolysis of [M(CO)₂Me(η⁵-C₅H₅)](M = Fe or Ru) alone yields the dimers [{M(CO)₂(η⁵-C₅H₅)}₂], whereas that of [M(CO)₂Et(η⁵-C₅H₅)](M = Fe or Ru) leads to the known dimers, [{M(CO)₂(η⁵-C₅H₅)}₂], and the new dimer[{Ru(CO)(η⁵-C₅H₅)}₂(µ-H)₂]. Photolysis of [M(CO)₂Me(η⁵-C₅H₅)](M = Fe or Ru) in pentane (–30 °C) in the presence of C₂H₄ results in the formation of the new complexes [M(CO)(C₂H₄)Me(η⁵-C₅H₅)]. The ethyl complex [Fe(CO)₂Et(η⁵-C₅H₅)] reacts photochemically with C₂H₄ to produce [Fe(CO)₂H(η₅-C₅H₅)], [{Fe(CO)₂(η⁵-C₅H₅)}₂] and the new dimer[{Fe(CO)(C₂H₄)(η⁵-C₅H₅)}₂], while the complex [Ru(CO)₂Et(η⁵-C₅H₅)] dealkylates to give only [Ru(CO)₂H(η⁵-C₅H₅)]. In gas matrices (12 K) the trapping of [Ru(¹²Co)Me(η⁵-C₅H₅)] and [Ru(¹³CO)Me(η⁵-C₅H₅)] species provided direct evidence for the CO-dissociation pathway. The [M(CO)Me(η⁵-C₅H₅)] species readily recombined with ejected CO or reacted with N₂ or C₂H₄ to give the complexes [Fe(CO)(C₂H₄)Me(η⁵-C₅H₅)], [Ru(CO)(N₂)Me(η⁵-C₅H₅)], and [Ru(CO)(C₂H₄)Me(η⁵-C₅H₅)]. Photolysis of [M(CO)₂Et(η⁵-C₅H₅)](M = Fe or Ru) in CH₄ matrices afforded the β-elimination products [M(CO)₂H(η⁵-C₅H₅)] together with [Ru(CO)(C₂H₄)H(η⁵-C₅H₅)]. The photolysis of [Ru(CO)₂Et(η⁵-C₅H₅)] in N₂ and C₂H₄-doped CH₄ matrices yielded [Ru(CO)(N₂)H(η⁵-C₅H₅)] and [Ru(CO)(C₂H₄)H(η⁵-C₅H₅)], respectively. Using ¹³CO-doped CH₄ matrices and energy-factored force-field fitting to investigate the possibility of competing reactions, it was found that the initial process was β elimination which was followed by CO exchange. Photolysis in CO matrices revealed the existence of a further pathway possibly involving ring-slippage products, e.g. [Fe(CO)₃R(η³-C₅H₅)](R = Me or Et) and [Ru(CO)₃H(η³-C₅H₅)]