Photolysis of (η5-C5H4C4H9)2Mo2(CO)4(μ-η2:2-RCCR′) in frozen Nujol matrices

A series of compounds, (eta (5)-C5H4C4H9)(2)Mo-2(CO)(4)(mu-eta (2:2)-acetylene), where acetylene = 3-hexyne, diphenylacetylene, phenylacetylene and 1-phenylpropyne, was prepared and characterized by IR,H-1- and C-13-NMR spectroscopies and MS. Photolysis of these compounds was carried out in frozen Nujol at 77 K. IR spectra established the presence of two isomeric carbonyl-loss species, (eta 5-C5H4C4H9)(2)Mo-2(CO)(2)(mu -eta(1),eta(2)-CO)(mu-eta(2:2)-acetylene), A, and (eta(5)-C5H4C4H9)(2)Mo-2(mu-CO)(3)(mu-eta(2:2)-acetylene), B. A is formed by photolysis into low energy electronic transitions associated with the tetrahedrane core of the parent molecule, while B is formed by either photolysis into electronic bands associated with A, or photolysis into the high energy charge-transfer bands of the parent molecule. These photointermediates are likely to be involved in the formation of 'fly-over' compounds, resulting from thermally or photochemically induced multiple substitution of acetylenes. (C) 1998 Elsevier Science S.A. All rights reserved.