Low-temperature infrared spectral study of the photochemical reaction of (CO)5Cr=C(OMe)Ph with solvent and alkynes

Article abstract of DOI:10.1021/om00018a010

The photochemical behavior of the Fisher carbene (CO)₅Cr=C(OMe)Ph (1) under a variety of low-temperature conditions is studied. Photolysis of 1 with low-pressure mercury lamps at 95 K in a 3-methylpentane (3MP) glass is followed by FTIR observation during programmed warmup in the range from 95 K to 295 K. Photolysis of 1 in 3MP glass results in loss of CO with low quantum yield and formation of a cis-solvento species. Recombination with CO occurs in the temperature range to 140 K. When THF is present in low concentration, photolysis results in formation of cis-(CO)₄(THF)Cr=C(OMe)Ph. In the temperature interval 95-160 K this species undergoes changes of uncertain origins, before reverting to 1 upon THF loss and recombination with CO, at temperatures above 165 K. In the presence of dilute p-CF₃C₆H₄-CCH, photolysis at 95 K results in formation of a single intermediate which remains unchanged upon warming until, in the temperature range 200-235 K, it converts to the final phenol annulation product. When THF is present in addition to the alkyne, the cis-THF complex is formed at low temperature and then converts to the same alkyne intermediate as THF dissociates from the complex. The results of these experiments are discussed in terms of the various intermediates previously proposed for the reactions of 1 with alkynes.