The coordination chemistry of 2,4,6-oxy functionalised 1,3,5-triphosphinines.

A number of stable group 6 metal complexes bearing 2,4,6-oxy functionalised 1,3,5-triphosphinines, phosphorus containing heterocyclic ligands with a central CP core, were synthesised such that a complete series of [M{PC(OX)}(CO)] compounds is obtained [M = Cr(0), Mo(0), W(0); X = H, SiBuPh, B(ipc)]. In all complexes, the triphosphinine coordinates in a η-binding mode the delocalized 6π-system of the ring. The ligand properties can be tuned by changing the substituent on the oxygen centre. The π-electron accepting properties of the ligand increases in the following order: PC(OH) < PC(OSiBuPh) < PC(OB(ipc)). This trend is reflected in the structures determined by X-ray crystallography, and the (CO) stretching frequencies determined by IR spectroscopy. The collected data raise questions with respect to the frequently made assumption that phosphinines act as stronger π-acceptors with respect to arenes and thereby deplete electron density at the metal centres. With PC(OH) as an η-coordinated ligand further molecules can be coordinated in the second coordination sphere hydrogen bonds, which may be of interest for the construction of coordination polymers.