Double bond shifts induced by reaction of hex-5-en-2-one with triosmium clusters

Abstract

Carbonhydrogen bond cleavage at the terminal 6-position occurs when hex-5-en-2-one (CH 2CHCH 2CH 2COMe) oxidatively adds to [Os 3(CO) 10(MeCN) 2] to give [Os 3H(μ-CHCHCH 2CH 2COMe)(CO) 10], which is completely analogous to the simple vinyl complex [Os 3H(μ-CHCH 2)(CO) 10]. A minor product from the reaction is [Os 3(CH 3CHCHCH 2COMe)(CO) 10], an isomer in which double-bond migration has occurred to give the βγ-unsaturated ketone; stabilisation occurs through chelation and ketone coordination. [Os 3H 2(CO) 10] reacts with CH 2CHCH 2CH 2COMe in refluxing cyclohexane to give a third isomer, [Os 3H(CH 3CH 2CCHCOMe)(CO) 10], in which further double bond migration has occurred to give the αβ-unsaturated ketone. Metallation at the β-site gives an OsC bond as part of a 5-membered chelate ring. Thermolysis of each of the three isomeric decarbonyl species in refluxing cyclohexane or heptane leads to the elimination of an Os(CO) 4 group to give the dinuclear compound [Os 2H(EtCCHCOMe)(CO) 6] in varying yield. Pathways from γδ to the βγ and finally the αβ unsaturated ketones may be mapped out.