Metal-ligand cooperation with NHC-phosphonium ylide pincer complexes

Work package:
Among the large variety of ligands made available, carbon ligands have become essential, especially with the emergence of N-heterocyclic carbenes (NHC). Phosphonium ylides (PY: R3P+−CR2− <-> R3P=CR2), which represent an alternative class of carbon ligands act also as effective Lewis bases in coordination chemistry. Electron-rich NHC-phosphonium ylide Pd(II) complexes were thus recently prepared in the bidentate (A),[1] and in the pincer series (B),[2] the latter being active in the catalytic allylation of aldehydes. In parallel, a bidentate NHC-based Mn(I) complex (C) featuring a phosphonium ylide (PYr) bound in a reversed fashion to the metal was reported to activate H2 through a new mode of metal-ligand cooperation acting as one of the most efficient pre-catalyst for ketone hydrogenation in manganese series.[3] Based on these results, it is envisioned now to prepare unprecedented pincer complexes of type D exhibiting NHC ligand N-substituted by two phosphonium ylides, one ylide being bound to the metal in a conventional manner by its C-atom to provide strong electron density and the other one in an unconventional manner by its P-atom to bring non-innocent character. The synthesis of Pd(II) and Ni(II) complexes D could constitute a step forward in the design of new cooperative carbon-based systems, both from a fundamental point of view but also in the perspective of catalytic applications (See corresponding illustration as attached file).