Palladium(II) Terminal Phosphido Complexes Derived from Cyclometalated Dimesitylphosphine: Synthesis, Structure, and Low-Barrier Phosphorus Inversion

The cyclometalated cationic Pd(II) and Pt(II) complexes [M(diphos)(CH 2 C 6 H 2 Me 2 P(Mes)(H))][X] ( 5 − 8: M = Pd, Pt; diphos = dppe (Ph 2 PCH 2 CH 2 PPh 2 ), dppen ( cis -Ph 2 PCH CHPPh 2 ); Mes = 2,4,6-Me 3 C 6 H 2; X = OTf, BF 4 ) were prepared by thermolysis of the cations [M(diphos)(Me)(PMes 2 H)][X]. Deprotonation of 5 − 8 gave the neutral phosphido complexes M(diphos)(CH 2 C 6 H 2 Me 2 P(Mes)) ( 9 − 12 ); the Pd(II) compounds 9 and 11 are the first examples of stable palladium terminal phosphido alkyl complexes, and their crystal structures were determined. Fluxional processes in complexes 9 − 12 were studied by variable-temperature NMR spectroscopy; the spectra are consistent with low barriers to phosphorus inversion.