INSERTION OF ISOCYANIDE INTO (DELTA-ALLENYL)PLATINUM(II) AND (DELTA-ALLENYL)PALLADIUM(II) COMPOUNDS - SYNTHESIS AND MECHANISM OF FORMATION OF NEW ORGANOPLATINUM COMPOUNDS CONTAINING A DELTA-BONDED VINYLKETENIMINE LIGAND - X-RAY CRYSTAL-STRUCTURE OF [PTBR(C(CME2)(CH=C=N-T-BU))(PPH3)2]

The insertion reactions of isocyanides into the metal-carbon bond of (sigma-allenyl)platinum(II) and -palladium(II) complexes trans-[MX{C(H)=C=CRR''}(PPh3)2] (1a-j) are described. When the R groups of the allenyl ligand are small, these insertion reactions give rise to the formation of new (metallovinyl)ketenimine compounds trans-[MX{C(CRR')(CH=C=NR'')}(PPh3)2] (2a-d, 2i, and 2j). The platinum vinylketenimine complexes 2a-d and 2i are stable compounds, whereas the palladium vinylketenimine compound 2j cannot be isolated. The structure of the (metallovinyl)ketenimine complexes has been confirmed by an X-ray crystal structure determination of trans-[PtBr{C(CMe2)(CH=C=N-t-Bu)}(PPh3)2], 2a: space group P1BAR, a = 11.907(2) angstrom, b = 12.603(2) angstrom, c = 14.862(3) angstrom, alpha = 81.74(2)degrees, beta = 78.50(2)degrees, gamma = 72.43(2)degrees, V = 2075.8(3) angstrom3, Z = 2, R = 0.037, and R(w) = 0.069. When the R groups of the allenyl ligand are large, the insertion of isocyanide is sterically hindered and the ionic complexes trans-[Pt-{C(H)=C=CRR'}(CN-t-Bu)(PPh3)2]Br (3e-h) are formed. The mechanism of isocyanide insertions in (sigma-allenyl)platinum(II) complexes was shown to be solvent dependent. When apolar or polar coordinating solvents were used, the reactions resulted in the formation of the platinum vinylketenimine complexes. When the reactions were performed in a polar noncoordinating solvent, or with (sigma-allenyl)platinum(II) compounds containing large R groups, no formation of the platinum vinylketenimine complexes was observed, but the ionic [Pt-{C(H)=C--CRR'}(CN-t-Bu)(PPh3)2]Br complexes were formed instead.