From chelating to bridging diphosphine ligands in quadruply-bonded bimetallic complexes: a non-dissociative phosphine exchange mechanism

Abstract

The exchange of phosphine ligands in the bimetallic Mo₂Cl₄[H₂P–(CH₂)₂–PH₂]₂ complex was studied by means of DFT calculations with the B3LYP functional. A non-dissociative mechanism was fully characterized (minima, transition states) for the isomerization reaction, which transforms the α isomer, with two chelating diphosphines, into the β isomer, with two bridging diphosphines. It involves the non-concerted migration of one end of each diphosphine ligand from one metal center to the other. The computed activation energy (about 30 kcal mol⁻¹) is associated with the jumping of the first phosphine end, which bridges the two metal centers in the transition state structure (TS1).