Base induced additions of coordinated phosphines to acetylenes to give metal complexes of chelating diphosphine ligands

Reactions occur with [M(CO)₄ (PPh₂H)(PPh₂)]^- (M - Cr, Mo) and [Mn(CO)₃ (PPh₂H)(PPh₂)Br]^- (each generated from the corresponding bisphosphine metal carbonyl and BuLi at -78°C) and several acetylenes with electron-withdrawing substituents (MeOOCC CCOOMe, PhC CCOOEt, PhC CH) to give after protonation, moderate yields of complexes of chelating diphosphines. These reactions are believed to be a type of Michael addition, proceeding via carbanion intermediates. Several isomers are possible in these reactions depending on the orientation of the acetylene substituent groups. Trans-stereochemistry of the single product derived from the manganese complex and MeOOCC CCOOMe was determined from NMR data; this preference is likely a consequence of steric constraints.