BINUCLEAR COMPLEXES OF NICKEL WITH THE BRIDGING ORTHO-CH2C6H4 LIGAND - SYNTHESIS AND REACTIONS - X-RAY CRYSTAL-STRUCTURE OF TRANS-(ME3P)2BRNI(C(O)C6H4-ORTHO-CH2)NIBR(PME3), A COMPLEX CONTAINING A BRIDGING MU-2-ETA-1-ETA-1-AROYL LIGAND

The reaction of Ni(cod)(PMe3)2 with equimolar amounts of BrCH2C6H4-omicron-Br affords trans-Ni(eta-1-CH2C6H4-omicron-Br)Br(PMe3)2 (1), which oxidatively adds to a second equivalent of Ni(cod)(PMe3)2 to yield binuclear cis,trans-(Me3P)2BrNi(mu-2-eta-1:eta-1-CH2-omicron-C6H4)NiBr(PMe3)2 (2). The latter complex readily loses one molecule of PMe3 with the formation of the pseudoallyl trans-(Me3P)BrNi(mu-2-eta-3:eta-1-CH2-omicron-C6H4)NiBr(PMe3)2 (3). Complex 2 selectively inserts CO into the Ni-benzyl bond (to give 4), but under the same conditions, the pseudoallyl 3 furnishes a bridging aroyl, trans-(Me3P)2BrNi(C(O)C6H4-omicron-CH2)NiBr(PMe3) (6), i.e., the product of the insertion of CO into the Ni-aryl bond. Complex 6 crystallizes in the monoclinic space group P2(1)/n with a = 6.907 (1) angstrom, b = 14.782 (2) angstrom, c = 24.660 (3) angstrom, beta = 95.07 (1)-degrees, and Z = 4. The bridging aroyl ligand is characterized by C-O, Ni-C, and Ni'-O separations of 1.233 (18), 1.824 (16), and 1.982 (11) angstrom, respectively. Interaction of the pseudoallylic species 3 with PMe3 produces the binuclear complex trans,trans-(Me3P)2BrNi(C6H4-omicron-CH2CH2-omicron-C6H4)NiBr(PMe3)2 (7), while the chelating ligands dmpm and dppm (dmpm = Me2PCH2PMe2; dppm = Ph2PCH2PPh2) yield respectively (dmpm)BrNi(mu-2-eta-1:eta-1-CH2-omicron-C6H4)NiBr(dmpm) (8) and [(Me3P)BrNi(mu-2-eta-3:eta-1-CH2-omicron-C6H4)Ni)PMe3)(dppm)Br (9). Obviously, compound 7 results from a C-C bond-forming reaction that involves the dimerization of the eta-1-benzylic ligand through methylene coupling. The reaction of 3 with NaCp to give trans-(C5H5)(PMe3)Ni(mu-2-eta-1:eta-1-CH2-omicron-C6H4)NiBr(PMe3)2 (10) has also been studied.