Synthesis and characterization of sterically hindered tris(pyrazolyl)borate Ni complexes

Addition of KTpPh2 to a solution of NiX2 (X = Cl, Br, NO3, OAc and acac) or NiBr(NO)(PPh3)2 in THF yields the structurally characterized series [NiCl(HpzPh2)TpPh2] (1) and [NiXTpPh2] (X = Br 2, NO 3, NO34, OAc 5 and acac 6) including the first example of a tris(pyrazolyl)borate nickel nitrosyl complex. IR spectroscopy confirms that all the TpPh2 ligands are κ3 coordinated and that the NO ligand in 3 is linearly bound. Electronic spectra are consistent with four- or five-coordinate species in solution. NMR spectroscopic studies indicate that the complexes are paramagnetic, with the exception of 3. This is confirmed by magnetic susceptibility studies, which suggest that complexes 1, 2 and 4–6 are paramagnetic with two unpaired electrons. X-ray crystallographic studies of 5 reveal a distorted trigonal bipyramidal nickel centre with a symmetrically coordinated acetate ligand.