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

Abstract

Reactions occur with [M(CO) 4 (PPh 2H)(PPh 2)] − (M — Cr, Mo) and [Mn(CO) 3 (PPh 2H)(PPh 2)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.