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)]