BINUCLEAR SIGMA-BENZYLIC AND ETA-3-BENZYLIC DERIVATIVES OF NICKEL

The stepwise reaction of the dibromides m- and p-BrCH2C6H4Br with [Ni(cod)(PMe3)2] (cod = cycloocta-1,5-diene) affords the sigma-benzylic derivatives trans-[Ni(CH2C6H4Br)Br(PMe3)2] 1a (meta) or lb (para) and the binuclear species trans,trans-[(Me3P)2BrNi(mu-sigma:sigma-CH2C6H4)NiBr(PMe3)2] 2a (meta) or 2b (para). If the second oxidative addition is carried out using equimolar amounts of [Ni(cod)2] and PMe3 the pseudo-allyl complexes trans-[(Me3P)BrNi(mu-eta-3:sigma-CH2C6H4)NiBr(PMe3)2] 5a (meta) or 5b (para) are obtained instead. Carbonylation of the binuclear compounds 2 yields the stable bis(acyl) derivatives trans,trans-[(Me3P)2BrNi(mu-COCH2C6H4CO)NiBr(PMe3)2] 3a (meta) or 3b (para) while excess of PMe3 induces a reductive elimination process that furnishes the bis(aryl) species trans,trans-[(Me3P)2BrNi-(mu-C6H4CH2CH2C6H4)NiBr(PMe3)2] 4a (meta) or 4b (para). A crystal structure determination of complex 2b has been undertaken: monoclinic, space group P2(1)/c, with cell dimensions a = 11.241 (1), b = 8.866(2), c = 29.323(8) angstrom, beta = 90.22(1)-degrees and Z = 4. The geometry around both nickel atoms is distorted square planar, with a dihedral angle between the two co-ordination planes of 103.77(9)-degrees.