Titanium Phosphinidene and Phosphide Moieties from Oxidative Phosphorylation and Desilylation

Abstract

A unique entry into mononuclear titanium complexes bearing phosphinidene and phosphide ligand moieties is reported. Reaction of [K(crypt)][(PN)₂TiCl] (1, crypt = 2.2.2-cryptand) with [Na(OCP)] results in [K(crypt)][(PN)₂Ti(OCP)] (2) and such species can be oxidized to the derivative [(PN)₂Ti(OCP)] (3), both of which do not undergo decarbonylation. However, the reaction of 1 and [NaP(SiMe₃)₂] leads to an unprecedented Ti^III phosphinidene, [K(crypt)][(PN)₂Ti═PSiMe₃] (4), through an oxidative phosphorylation reaction. To promote the formation of a Ti≡P bond, complex 4 was treated with 0.5 equivalent XeF₂, resulting in an oxidative desilylation step forming a molecular titanium phosphide complex, [K(crypt)][(PN)₂Ti≡P] (5), which showed a characteristic downfield chemical shift at 1449.8 pmm in the ³¹P NMR spectrum. Complex 5 can be further functionalized to generate a terminal Ti^IV phosphinidene, [(PN)₂Ti═PSiMe₃] (6), and the latter can be independently accessed through oxidation of 4. All new complexes were characterized structurally and as appropriate by multinuclear NMR, CW X-band EPR (for Ti^III), and HFEPR (for Ti^II) spectroscopies.