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 C 3 P 3 core, were synthesised such that a complete series of [M{P 3 C 3 (OX) 3 }(CO) 3 ] compounds is obtained [M = Cr(0), Mo(0), W(0); X = H, Si t BuPh 2 , B(ipc) 2 ]. In all complexes, the triphosphinine coordinates in a η 6 -binding mode via 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: P 3 C 3 (OH) 3 < P 3 C 3 (OSi t BuPh 2 ) 3 < P 3 C 3 (OB(ipc) 2 ) 3 . This trend is reflected in the structures determined by X-ray crystallography, and the ν (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 P 3 C 3 (OH) 3 as an η 6 -coordinated ligand further molecules can be coordinated in the second coordination sphere via hydrogen bonds, which may be of interest for the construction of coordination polymers.