Metallacycle formation through the linking of an alkyne with phosphido and acetyl groups at an iron centre: X-ray structure of (Cp = η5-C5H5)

Article abstract of DOI:10.1016/0022-328X(93)80360-N

The diphenylphosphine ligand of (Cp = η⁵-C5H5) can be deprotonated with DBU (DBU = 1,8-diazabicyclo<5.4.0>undec-7-ene) or n-butyllithium; subsequent alkylation with RI (R = Me, Et) gives the complexes . Reaction of the anionic phosphido complex with the electrophilic alkyne methyl propiolate (HC<*>CCO2Me) followed by reprotonation with CH3COOH gives the vinylphosphine complex , whereas a similar reaction sequence with dimethyl acetylenedicarboxylate (DMAD, MeO2CC<*>CCO2Me) produces two isomers of the complex , in which linking of the alkyne with both the phosphido and acetyl ligands has occurred to form a six-membered metallacycle. The structure of one of the two isomers has been determined by X-ray diffraction and shows that the metallacyclic ring is bound to the iron atom through the phosphorus and the carbonyl oxygen of the acetyl group, and adopts a boat conformation in the solid state.