Organometallic derivatives of Ni(II) with poly(pyrazolyl)borate ligands

Abstract

The reaction of the alkyl or aryl derivatives Ni(R)X(PMe 3) 2 (R=CH 2SiMe 3, CH 2CMe 3, C 6H 5; X=Cl, Br) with the potassium salt of the Bp ligand (Bp=dihydrobis(pyrazolyl)borate anion) forms the corresponding compounds BpNi(R)(PMe 3). In contrast, the reaction of the aryl derivatives Ni(C 6H 4- p-X)Br(PMe 3) 2 (X=H, Me, OMe, NMe 2) with the Bp tBu anion (Bp tBu=dihydrobis(3- t-butylpyrazolyl)borate) proceeds with formation of complexes of composition Bp tBuNi(C 6H 4- p-X)(PMe 3) 2, in which the polydentate ligand is bound to the metal through only one pyrazolyl group. The Tp anion leads to only aryl derivatives; the phenyl complex TpNi(C 6H 5)(PMe 3) has been obtained, and the reaction of the alkyl complex Ni(CH 2CMe 2Ph)Cl(PMe 3) 2 with KTp furnishes the aryl TpNi(C 6H 4- o-Bu t)(PMe 3), by means of a rearrangement of the neophyl ligand. The Tp ligand in these complexes is bonded in the η 2 fashion, although an X-ray analysis carried out for TpNi(Ph)(PMe 3) reveals the existence of an important Ni…N interaction with the third pz ring. Upon reaction with the bulky hydrotris(3- t-butylpyrazolyl)borate anion, the aryl derivatives Ni(C 6H 4- p-X)Br(PMe 3) 2 (X=H, Me, OMe, NMe 2) form complexes of composition Tp tBuNi(C 6H 4- p-X)(PMe 3) 2, in which the polydentate ligand is once more bound to the metal through only one pyrazolyl group. These complexes represent the first examples of η 1 coordination of poly(pyrazolyl)borate-type ligands. The acyl and aroyl complexes BpNi(COR)(PMe 3) (R=CH 2SiMe 3, CH 2CMe 3) and TpNi(COPh)(PMe 3) have been obtained by carbonylation of the parent compounds. The aroyls Tp tBuNi(COC 6H 4- p-X)(PMe 3) 2 have also been obtained from the derivatives Ni(COC 6H 4- p-X)Br(PMe 3) 2 although they evolve CO slowly in solution. An X-ray analysis carried out with Tp tBuNi(C 6H 4- p-Me)(PMe 3) 2 confirms the η 1-coordination mode of the Tp tBu ligand, which was deduced from NMR studies.