Preparations and reactions of alkylcobalt complexes and diphenylacetylenecobalt complexes having a π-cyclopentadienyl group as a ligand

Abstract

Methyl- and benzyl-cobalt complexes of type π-C 5H 5Co(L)RR' [L = Ph 3P, Ph 2CH 3P, and Ph 3As;R,R' = CH 3, PhCH 2 and I] were prepared from the reaction of π-C 5H 5Co(L)I 2 with Grignard reagents. The reaction of I(L = Ph 3P) with isopropylmagnesium bromide in the presence of diphenylacetylene afforded an acetylene complex, π-C 5H 5Co(PPh 3)(PhCCPh) (VI), a cobaltacyclopentadiene complex, π-C 5H 5Co(PPh 3)(PhCCPh) 2 (VII), or a stilbenyl complex of divalent cobalt, π-C 5H 5Co(PPh 3)(CPhCHPh) (VIII), depending on the conditions applied. The diphenylacetylene group in (VI) was readily replaced by fumaronitrile, dimethyl-fumarate and -maleate to give complexes of type π-C 5H 5Co(PPh 3)(olefin). On the other hand, reactions of (VI) with substituted acetylenes resulted in the formation of cobaltacyclopentadiene complexes without loss of diphenylacetylene. The reaction of (VII) with ethylene gave π-cyclopentadienyl-π-1,2,3,4-tetraphenylcyclohexadienecobalt (XV). The structures of some of these new compounds are discussed briefly on the basis of their proton NMR spectra.