Photochemistry of dicarbonylcyclopentadienylcobalt in frozen gas matrices at 12 K. Infrared spectroscopic evidence for tricarbonylcyclopentadienylcobalt and carbonylcyclopentadienyl(dinitrogen)cobalt complexes

Abstract

Infrared spectroscopic evidence, including ¹³CO labelling and energy-factored CO force-field fitting, is presented to show that on photolysis of [CO(η⁵-C₅H₅)(CO)₂] at high dilution in CO and N₂ matrices at 12 K new species [Co(η⁵-C₅H₅)(CO)₃] and [Co(η₅-C₅H₅)(CO)(N₂)] are produced. No evidence has been found for the formation of [Co(η⁵-C₅H₅)(CO)] and CO on photolysis of [Co(η⁵-C₅H₅)(CO)₂] at high dilution in the inert matrices of Ar and CH₄. The reversibility of the reaction [Co(η⁵-C₅H₅)(CO)₂]+ CO ⇌[Co(η³-C₅H₅)(CO)₃] is interpreted as confirming the existence of an expanded-co-ordination-number species as the intermediate in the substitution reactions of [Co(η⁵-C₅H₅)(CO)₂]. This is the first time that an expanded-co-ordination-number species, corresponding to an intermediate proposed in an associative mechanism, has been observed by matrix-isolation studies. At low dilutions, photolysis of [Co(η⁵-C₅H₅)(CO)₂] in Ar, CH₄, and N₂ matrices is shown to produce [{Co(η⁵-C₅H₅)(CO)}₂] and this is supported by ¹³CO labelling and energy-factored CO force-field fitting together with comparison with the matrix i.r. spectrum of ¹³CO-enriched [{Ni(η⁵-C₅H₅)(CO)}₂].