Transition metal-cyanocarbon chemistry: VI. Insertions of cyano- and dicyano-acetylenes into the iron-hydride bonds in (C5H5)(CO)LFeH (L  CO, PPh3) and [(C5H5)(CO)FeH]2 [μ-(C6H5)2PCH2CH2P(C6H5)2] complexes

Abstract

Monocyanoacetylene (HCCCN, mca) and dicyanoacetylene (NCCCCN, dca) have been shown to insert into the FeH bonds of various mononuclear and dinuclear iron hydrides. In the presence of dca, [(η5-C5H5)(CO)2FeH] and [(η5-C5H5)(CO)(PPh3)FeH] give [(η5-C5H5)(CO)2Fe(σ-(Z)-C(CN)CH(CN)] and [(η5-C5H5)(CO)(PPh3)Fe(σ-(Z)-C(CN)CH(CN)] respectively. The reaction involving [(η5-C5H5)(CO)(PPh3)FeH] provides the first evidence for non-regioselectivity of an insertion of mca; the isomers [(η5-C5H5)(CO)(PPh3)Fe(σ-(Z)-CHCH(CN)] and [(η5-C5H5)(CO)(PPh3)Fe(σ-C(CN)CH2)] being obtained in a 4/1 ratio. However regioselectivity is observed for insertion of mca into the FeH bonds of dinuclear [(η5-C5H5)(CO)FeH]2(μ-dppe) (dppe = 1,2-bis(diphenylphosphido)ethane); in this case the CN groups are attached only to the Cα carbon atom. The reaction of dca with the dinuclear hydride gives products analogous to those from the mononuclear ones. The mechanisms of these various insertions are discussed in terms of the degree of hydridic nature of the hydridic hydrogen in the initial iron complexes.