The CO/PC analogy in coordination chemistry and catalysis

Abstract

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 crosscoupling 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.

Synthesis of 1-Phosphabarrelene Phosphine Sulfide Substituted Palladium(II) Complexes: Application in the Catalyzed Suzuki Cross-Coupling Process and in the Allylation of Secondary Amines

“…Indeed, though the ligand itself proves to be too reactive to be employed in standard catalytic transformations, its reactivity offers interesting structural possibilities. Thus, reactions with nucleophiles yield λ 4 -phosphinine anions, which bind transition-metal centers in an η 1 (type A), , η 2 (type B), or η 5 fashion (type C), depending on the substitution scheme of the ring (Scheme ). The first class of complex (type A), incorporating a phosphino sulfide as ancillary ligand and a λ 4 -phosphinine as the central subunit, exhibits an interesting activity for the activation of several metal centers and was employed, for example, with Rh(I) complex to activate small molecules such as O 2 , CO 2 , and CS 2 .…”

From P‐Functional Thiazol‐2‐thione Derivatives to Phosphaalkenes

“…These fascinating compounds I , II , possessing a formal P=C bond due to (3p‐2p)π‐overlap, marked the beginning of what is now a highly active field that has had major impact on both fundamental and applied inorganic chemistry. As the field has matured, there is growing interest to use P=C bonds in areas such as polymer science and catalysis …”

Copper(I) Complexes of Pyridine-Bridged Phosphaalkene-Oxazoline Pincer Ligands

“…3,4 The PC double bond features a low-energy π*-orbital that leads to excellent π-accepting properties. 5 The most studied 6 phosphaalkene-containing pincer ligand motif is the symmetric ligand D [i.e., 2,6-bis(phosphaethylene)pyridine or BPEP, R = H 7 and R = Ph 8 ]. This class of ligand has attracted attention due to its highly delocalized π-electron backbone that is not found in analogous bisphosphine derivatives.…”

“…There is considerable interest in the coordination chemistry of compounds containing low coordinate phosphorus, such as phosphaalkenes or phosphinines, for potential applications in catalysis. , The PC double bond features a low-energy π*-orbital that leads to excellent π-accepting properties . The most studied phosphaalkene-containing pincer ligand motif is the symmetric ligand D [i.e., 2,6-bis­(phosphaethylene)­pyridine or BPEP, R = H and R = Ph].…”