Synthesis, reactions, and rearrangement of X(PEt3)2Pt[C(=PR)X] (X = Cl, Br; R = 2,4,6-tri-tert-butylphenyl), a synthetic precursor for bridged cyaphide, semi-bridged isocyaphide metal complexes

Oxidative addition reactions of X[subscript]2C = PR (X = Cl, Br; R = 2,4,6-tri-tert-butylphenyl) with M(PEt[subscript]3)[subscript]4 (M = Pt, Pd) or (C[subscript]2H[subscript]4)Pt(PPh[subscript]3)[subscript]2 initially yield the cis isomer of square planar (X)(PR[subscript]sp3\u27)[subscript]2M (C(=PR)X); these complexes, where PR[subscript]sp3\u27 is PEt[subscript]3, rearrange rapidly in the presence of free PEt[subscript]3 to give the trans isomers. In contrast, the cis isomers, where PR[subscript]sp3\u27 is PPh[subscript]3 and M is Pt, react further to give R-C≡P and cis-X[subscript]2Pt(PPh[subscript]3)[subscript]2. In polar solvents (CH[subscript]2Cl[subscript]2 and CHCl[subscript]3), all the addition products (cis and trans) convert to R-C≡P and cis- or trans-X[subscript]2M(PR[subscript]sp3\u27)[subscript]2 via the surprising phosphabicyclo intermediate (X)(PR[subscript]sp3\u27)[subscript]2M(X-PBC); the structure of (Cl)(PEt[subscript]3)[subscript]2Pt(Cl-PBC) was established crystallographically. In the presence of H[subscript]2O, (X)(PR[subscript]sp3\u27)[subscript]2M (C(=PR)X) gives the oxy-phosphabicyclo complex (X)(PR[subscript]sp3\u27)[subscript]2M ((H)O=PBC); the structure (Cl)(PEt[subscript]3)[subscript]2Pt ((H)O=PBC) was characterized by X-ray diffraction. A mechanism for the conversion of (X)(PR[subscript]sp3\u27)[subscript]2M (C(=PR)X) to R-C≡P and X[subscript]2M(PR[subscript]sp3\u27)[subscript]2 is also proposed;The halophosphaalkene platinum complexes, trans-(X)(PEt[subscript]3)[subscript]2Pt (C(=PR)X) (X = Cl, Br; R = 2,4,6-tri-tert-butylphenyl) react with Pt(PEt[subscript]3)[subscript]4 to yield (X)(PEt[subscript]3)Pt([mu]-C=PR)Pt(PEt[subscript]3)[subscript]2(X). The molecular structure of (Cl)(PEt[subscript]3)Pt([mu]-C=PR)Pt(PEt[subscript]3)[subscript]2(Cl) shows that it contains a semi-bridging isocyaphide (C≡P-R) ligand;The platinum complexes trans-(X)(PEt[subscript]3)[subscript]2Pt (C(=PR)X) (X = Cl, Br) react with Pd(PEt[subscript]3)[subscript]4 to give (X)(PEt[subscript]3)[subscript]2Pt(C≡P) and (X)(PEt[subscript]3)[subscript]2Pd(R). The complexes (X)(PEt[subscript]3)[subscript]2Pt(C≡P), which are tentatively assigned a structure with a terminal cyaphide (C≡P[superscript]-) ligand, react with Pt(PEt[subscript]3)[subscript]4 to give bridging cyaphide di-platinum complexes (PEt[subscript]3)[subscript]2Pt([mu]-C=P)Pt(PEt[subscript]3)[subscript]2(X) (X = Cl, Br). The molecular structure of (PEt[subscript]3)[subscript]2Pt([mu]-C=P)Pt(PEt[subscript]3)[subscript]2(Cl) exhibits a bridging C≡P[superscript]- ligand carbon-bonded to Pt(1) and [eta][superscript]2-bonded to Pt(2). In the structure (Cl)(PEt[subscript]3)[subscript]2Pd(R) (R = 2,4,6-tri-tert-butylphenyl), a methyl group of each of the two o-tert-butyl groups of the R ligand sits above (and below) the Pd; however, NMR studies suggest there is little if any agostic interaction