An Unusual P-P Double Bond Formed via Phospha-Wittig Transformation of a Terminal PO Complex

Abstract

The terminal phosphorus monoxide complex [(OP)Mo(N[superscript t Bu]Ar) subscript 3], 1 (Ar = 3,5-Me2C6H3) [1 (Ar = 3,5-Me subscript 2 C subscript 6 H subscript 3)], undergoes an O-for-PSiR3 [O-for-PSiR subscript 3] metathesis reaction with the niobium phosphinidene complex iPr3SiPNb(N[CH2tBu]Ar)3 [superscript i Pr subscript 3 SiPNb(N[CH subscript 2 superscript t Bu]Ar) subscript 3], 2, to generate the oxoniobium complex ONb(N[CH2tBu]Ar)3 [ONb(N[CH subscript 2 superscript t Bu]Ar) subscript 3], 3, and the diphosphenido complex iPr3SiPPMo(N[tBu]Ar)3 [superscript i Pr subscript 3 SiPPMo(N[superscript t Bu]Ar) subscript 3], 4. The structure of 4, as determined by X-ray crystallography, contains a “singly bent” diphosphenido moiety, suggesting that the diphosphenido ligand serves as a 3e− donor to a formally d2 [d superscript 2] metal center. This bonding characterization was supported by DFT calculations and is unique among known diphosphenido complexes. Diphosphenido 4 was found to react over time to produce products consistent with a bimolecular degradation pathway where the terminal phosphide complex [PMo(N[superscript t Bu]Ar) subscript 3], 5, serves as a stable leaving group. Mixtures of 4 and PPh3 [PPh subscript 3] were observed to set up an equilibrium (Keq = 0.7) [(K subscript eq = 0.7)] between 4, PPh3 [PPh subscript 3], and the products of phosphinidene transfer, 5 and iPr3SiP═PPh3 [superscript i Pr subscript 3 SiP═PPh subscript 3].