Formation of α,ω-dienes upon photooxidation of alkenyl carbyne complexes

Photolysis of the alkenyl carbyne complexes (eta(5)-C5H5)(CO){P(OMe)(3)}Mo = CCH2(CH2)(n)CH=CH2 (n = 2 (1b), 3 (1c) and 4 (1d)) in CHCl3 results in the formation of the corresponding alpha,omega-dienes CH2 = CH(CH2)(n)CH=CH2. Also produced are the dichloromolybdenum carbynes (eta(5)-C5H5)Cl-2{P(OMe}(3)Mo = C-CH2(CH2)(n)CH=CH2 (n = 2 (8b), 3 (8c), and 4 (8d)). Both sets of products arise following the generation of highly reactive 17-electron complexes via photochemical electron transfer from 1b-d to the solvent. These radical cations either undergo H-abstraction at the carbyne carbon followed by H-shift to form the dienes or they undergo exchange of Cl- for the CO ligand and Cl- abstraction at the metal to yield 8b-d. The product ratios reflect partitioning of the 17-electron species between reactivity at the metal center vs. the carbyne carbon. (C) 1998 Elsevier Science S.A.