Reaction of a diphenylacetylenecobalt complex with alkyl diazoacetates

Abstract

The diphenylacetylene-cobalt complex, η 5-C 5H 5Co(PPh 3)(PhCCph) (I) reacted with alkyl diazoacetates (II, alkyl = methyl, ethyl, and t-butyl) at room temperature to give two isomers of the mononuclear cobalt complex, η 5-C 5H 5Co- (PhC 2Ph)(CHCO 2R) 2 (III and IV) and two isomers of the dinuclear cobalt complex [η 5-C 5H 5Co(PhC 2Ph)(CHCO 2R)] 2 (V and VI). The complexes III and IV are diene complexes, syn,syn- and syn,anti- (dialkyl 2,3-diphenylmuconate)-η 5-cyclopentadienylcobalt, respectively. The structure of Vb (R = C 2H 5) was determined by X-ray diffraction as η-[1–3-η 3 : 1,4,5-μ 3- 1,6-bis(ethoxycarbonyl)-2,3,4,5-tetraphenylhexa-2,4-diene-1,1-diyl]bis(η 5-cyclopentadienylcobalt)( CoCo. The complex VI is the bis(η 3-allyl)cobalt complex, μ-[1–3-η 3 : 4–6η 3-1,6- anti,anti-bis(alkoxycarbonyl)-2,3,4,5,-tetraphenylhexa- 1,3,5-triene]bis(η 5-cyclopentadienylcobalt)( CoCo) according to its 1H NMR spectrum. The formation of these products was rationalizes in terms of a cobaltacyclobutene intermediate.