Diphosphinine derivatives of terpyridine: a newclass of neutral p-accepting pnp-pincer ligands

Phosphinines (phosphabenzenes, phosphorins), the higher homologues of pyridines are low-coordinated phosphorus compounds that possess significantly different steric and electronic properties compared to common ligands based on trivalent phosphorus.[1, 2] We have recently started to investigate the preparation of functionalized phosphinines via the pyrylium salt route, originally described by M#rkl for the synthesis of 2,4,6-triphenylphosphinine.[ 1a] It turned out that this procedure allowed us to introduce substituents into specific positions of the heterocyclic framework; a feature which is essential for ligand design and their potential application in homogeneous catalytic reactions. In this way a variety of donor-functionalized and axially chiral monophosphinines, as well as a trans-coordinating diphosphinine have been designed and prepared by us lately.[3, 4]