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

The reaction of the alkyl or aryl derivatives Ni(R)X(PMe3)(2) (R = CH2SiMe3, CH2CMe3, C6H5; X = Cl, Br) with the potassium salt of the Bp ligand (Bp = dihydrobis(pyrazolyl)borate anion) forms the corresponding compounds BpNi(R)(PMe3). In contrast, the reaction of the aryl derivatives Ni(C6H4-p-X)Br(PMe3)(2) (X=H, Me, OMe, NMe2) with the Bp(tBu) anion (Bp(tBu) = dihydrobis(3-t-butylpyrazolyl)borate) proceeds with formation of complexes of composition Bp(tBu)Ni(C6H4-p-X)(PMe3)(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(C6H5)(PMe3) has been obtained, and the reaction of the alkyl complex Ni(CH2CMe2Ph)Cl(PMe3)(2) with KTp furnishes the aryl TpNi(C6H4-o-Bu-t)(PMe3), by means of a rearrangement of the neophyl ligand. The Tp ligand in these complexes is bonded in the eta(2) fashion, although an X-ray analysis carried out for TpNi(Ph)(PMe3) reveals the existence of an important Ni ... N interaction with the third ps ring. Upon reaction with the bulky hydrotris(3-t-butylpyrazolyl)borate anion, the aryl derivatives Ni(C6H4-p-X)Br(PMe3)(2) (X = H, Me, OMe, NMe2) form complexes of composition Tp(tBu)Ni(C6H4-p-X)(PMe3)(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 eta(1) coordination of poly(pyrazolyl)borate-type ligands. The acyl and aroyl complexes BpNi(COR)(PMe3) (R=CH2SiMe3, CH2CMe3) and TpNi(COPh)(PMe3) have been obtained by carbonylation of the parent compounds. The aroyls Tp(tBu)Ni(COC6H4-p-X)(PMe3)(2) have also been obtained from the derivatives Ni(COC6H4-p-X)Br(PMe3)(2) although they evolve CO slowly in solution. An X-ray analysis carried out with Tp(tBu)Ni(C6H4-p-Me)(PMe3)(2) confirms the eta(1)-coordination mode of the Tp(tBu) ligand, which was deduced from NMR studies. (C) 1998 Elsevier Science S.A.