Reaction of a diphenylacetylenecobalt complex with alkyl diazoacetates

The diphenylacetylene-cobalt complex, η⁵-C₅H₅Co(PPh₃)(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, η⁵-C₅H₅Co- (PhC₂Ph)(CHCO₂R)₂ (III and IV) and two isomers of the dinuclear cobalt complex η⁵-C₅H₅Co(PhC₂Ph)(CHCO₂R)]₂ (V and VI).The complexes III and IV are diene complexes, syn,syn- and syn,anti- (dialkyl 2,3-diphenylmuconate)-η⁵-cyclopentadienylcobalt, respectively. The structure of Vb (R = C₂H₅) was determined by X-ray diffraction as η-1–3-η³ : 1,4,5-μ³- 1,6-bis(ethoxycarbonyl)-2,3,4,5-tetraphenylhexa-2,4-diene-1,1-diyl]bis(η⁵-cyclopentadienylcobalt)(CoCo. The complex VI is the bis(η³-allyl)cobalt complex, μ-1–3-η³ : 4–6η³-1,6-anti,anti-bis(alkoxycarbonyl)-2,3,4,5,-tetraphenylhexa- 1,3,5-triene]bis(η⁵-cyclopentadienylcobalt)(CoCo) according to its ¹H NMR spectrum.The formation of these products was rationalizes in terms of a cobaltacyclobutene intermediate.