Binuclear σ- and η3-benzylic derivatives of nickel

Abstract

The stepwise reaction of the dibromides m- and p-BrCH₂C₆H₄Br with [Ni(cod)(PMe₃)₂](cod = cycloocta-1,5-diene) affords the σ-benzylic derivatives trans-[Ni(CH₂C₆H₄Br)Br(PMe₃)₂]1a(meta) or 1b(para) and the binuclear species trans,trans-[(Me₃P)₂BrNi(µ-σ : σ-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(µ-η³ : σ-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(µ-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(µ-C₆H₄CH₂C₆H₄)NiBr(PMe₃)₂]4a(meta) or 4b(para). A crystal structure determination of complex 2b has been undertaken: monoclinic, space group P2₁/c, with cell dimensions a= 11.241(1), b= 8.866(2), c= 29.323(8)Å, β= 90.22(1)° 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)°.