The CO/PC analogy in coordination chemistry and catalysis

This short account summarizes recent results obtained in the coordination chemistry of phosphinines and emphasizes their analogy with CO ligands. Reduced complexes can be easily assembled through the reaction of reduced 2,2′-biphosphinine dianions with transition metal fragments. Theoretical calculations were performed to establish the oxidation state of the metal in these complexes. Though many reduced complexes are available, phosphinines proved to be too sensitive toward nucleophiles to be used as efficient ligands in most catalytic processes. However, the high electrophilicity of the phosphorus atom can be exploited to synthesize phosphacylohexadienyl anions which exhibit a surprising coordination chemistry. When phosphino sulfide groups are incorporated as ancillary tridentate anionic SPS ligands can be easily produced. These ligands can bind different transition metal fragments such as M–X (M = group 10 metal, X = halogen), Rh–L (L = 2 electron donor ligand), Cu–X and Au–X (X = halogen). Palladium(II) complexes proved to be active catalyst in the Miyaura cross-coupling reaction. Bidentate anionic PS ligands were also synthesized following a similar approach. Their Pd(II) (allyl) derivatives showed a very good activity in the Suzuki catalyzed cross-coupling process that allows the synthesis of biphenyl derivatives through the reaction of phenylboronic acid with bromoarenes.