Metallacycle formation through the linking of an alkyne with phosphido and acetyl groups at an iron centre: X-ray structure of [Cp [formula omitted]}] (Cp =η 5-C 5H 5)

Abstract

The diphenylphosphine ligand of [CpFe(CO)(PPh 2H)(COMe)] (Cp  η 5-C 5H 5) 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 [CpFe(CO)(PPh 2R)COMe)]. Reaction of the anionic phosphido complex with the electrophilic alkyne methyl propiolate (HOCCO 2Me) followed by reprotonation with CH 3COOH gives the vinylphosphine complex [CpFe(CO)(PPh 2CHCHCO 2Me) (COMe)], whereas a similar reaction sequence with dimethyl acetylenedicarboxylate (DMAD, MeO 2CCCCO 2Me) produces two isomers of the complex [Cp Fe(CO){Ph 2PCH(CO 2Me)C(CO 2Me)C(Me)O }], 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.