A BIMETALLIC TANTALUM ZINC COMPLEX WITH AN ANCILLARY ARYLDIAMINE LIGAND AS PRECURSOR FOR A REACTIVE ALKYLIDYNE SPECIES - ALKYLIDYNE-MEDIATED C-H ACTIVATION AND A PALLADIUM-MEDIATED ALKYLIDYNE FUNCTIONALIZATION

The 1:1 reaction of TaCl2{C6H3(CH2NMe2)2-2,6}(=CH-t-Bu) with neopentylzinc chloride affords the bimetallic complex TaCl2{C6H3(CH2NMe2)2-2,6}(mu-C-t-Bu) (mu-ZnCI) (2) in high yield. Crystals of 2 belong to the space group P2(1)2(1)2(1) with a = 9.725(2) angstrom, b = 10.436(2) angstrom, c = 20.766(3) angstrom, Z = 4, M(r) = 613.11, V = 2107.5(7) angstrom3, p(calcd) = 1.932 g.cm-3. The pentacoordinate tantalum center has a coordination geometry between trigonal bipyramidal and square pyramidal while the zinc center has a distorted tetrahedral ligand array; the alkylidyne functionality and the aryl ipso-carbon bridge between the zinc and tantalum centers. The p-orbital at C(ipso) of the aryldiamine ligand forms a 2-electron bond to the zinc center, and this aryldiamine ancillary thus functions as an 8-electron donor. The reaction of 2 with tmeda at 60-degrees-C leads to elimination of zinc chloride and formation of the alkylidene complex TaCl{C6H3(CH2N(Me)CH2)-2-(CH2-NMe2)-6}(=CH-t-Bu); this is an alkylidyne-mediated activation reaction of a methyl C-H bond in a NMe2 group. In the presence of [Pd(C6H4CH2NMe2-2)(mu-X)]2 (X = Cl, I) the reaction of bimetallic 2 with tmeda [Me2N(CH2)2NMe2] appears to generate TaCl2(C6H4CH2NMe2-2)[=C(t-Bu){C6H3(CH2NMe2)2-2,6}] and, as such, is an unanticipated, new palladium-mediated alkylidyne functionalization reaction.