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 C3P3 core, were synthesised such that a complete series of [M{P3C3(OX)(3)}(CO)(3)] compounds is obtained [M = Cr(0), Mo(0), W(0); X = H, SitBuPh(2), B(ipc)(2)]. In all complexes, the triphosphinine coordinates in a eta(6)-binding mode via the delocalized 6 pi-system of the ring. The ligand properties can be tuned by changing the substituent on the oxygen centre. The pi-electron accepting properties of the ligand increases in the following order: P3C3(OH)(3) < P3C3((OSiBuPh2)-Bu-t)(3) < P3C3(OB(ipc)(2))(3). This trend is reflected in the structures determined by X-ray crystallography, and the nu(CO) stretching frequencies determined by IR spectroscopy. The collected data raise questions with respect to the frequently made assumption that phosphinines act as stronger pi-acceptors with respect to arenes and thereby deplete electron density at the metal centres. With P3C3(OH)(3) as an eta(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.

Automated summary

A series of stable group 6 metal complexes with 2,4,6-oxy functionalised 1,3,5-triphosphinines as ligands were synthesized, resulting in the formation of [M{P3C3(OX)(3)}(CO)(3)] compounds (M = Cr(0), Mo(0), W(0); X = H, SitBuPh(2), B(ipc)(2)]. The triphosphinines coordinate in an eta(6)-binding mode via the 6 pi-system of the ring. The ligand properties can be tuned by changing the substituent on the oxygen centre, and the order of pi-electron accepting properties is P3C3(OH)(3) < P3C3((OSiBuPh2)-Bu-t)(3) < P3C3(OB(ipc)(2))(3).