SYNTHESIS, REACTIONS, AND REARRANGEMENT OF X(PR'3)2M[C(=PR)X] (M=PT, PD, X=CL, BR, R'=ET, PH, R = 2,4,6-TRI-TERT-BUTYLPHENYL), MECHANISM OFTHE TRANSITION-METAL PROMOTED CONVERSION OF X2C=PR TO R-C-EQUIVALENT-TO-P

Oxidative addition reactions Of X2C=PR (X=Cl, Br; R=2,4,6-tri-tert-but ylphenyl) with M(PEt3)4 (M=Pt, Pd) or (C2H4)Pt(PPh3)2 initially yield the cis isomer of square planar (X)-(PR'3)2M[C(=PR)X] (II); these comp lexes (IIa-IId), where PR'3 is PEt3, rearrange rapidly in the presence of free PEt3 to give the trans isomers (Ia-Id). In contrast, the cis isomers (IIe and IIf), where PR'3 is PPh3 and M is Pt, react further t o give R-C=P and CiS-X2Pt(PPhs)2. In polar solvents (CH2Cl2 and CHCl3) , all the addition products (I and II) convert to R-C=P and cis- or tr ans-X2M(PR'3)2 via the surprising phosphabicyclo intermediate (X)(PR'3 )2Pt-(X-PBC) (III and IV); the structure of IIIa was established cryst allographically. In the presence of H2O, (X)(PEt3)2Pt[C(=PR)X] (Ia and Ib where X=Cl, Br) give the oxophosphabicyclo complex (X) (PEt3)2Pt[( H)O=PBC] (Va and Vb) which was characterized by X-ray diffraction. A m echanism for the conversion of (X)(PR'3)2M[C(=PR)X] to R-C=P and X2M-( PR'3)2 is proposed.