Selective synthesis, characterization, and configurational flexibility of the coordinatively unsaturated metal center of half-sandwich type complexes with the less-hindered hydrotris(3, 5-dimethyl-4-X-1-pyrazolyl)borate ligands [TpMe2,XMII(κ2-O,O′-L)] (M = Ni, Co; L = NO3, OAc; X = Me, H, Br)

The selective synthesis of half-sandwich type complexes of Ni(II) and Co(II) with the less-hindered hydrotris(3,5-dimethyl-4-X-1-pyrazolyl)borate [X = Me (Tp(Me3); a series), H (Tp(Me2); b series), and Br (Tp(Me2,Br); c series)] ligands, [Tp(Me2.X)M(II)(kappa(2)-O,O'-L)] [L = NO3 (2), OAc (3)], has been achieved by dropwise addition of a THF solution of NaTp(Me2,X) to an excess amount of ML2 dissolved in MeOH. The solid state structures of the nitrato complexes 2 have been characterized by X-ray crystallography as their solvated form, 2.solv. (solv. = MeCN, MeOH), in which the metal centers have the six-coordinated octahedral geometry. Solvates are readily dissociated from the metal center upon dissolution in noncoordinationg solvents, such as CH2Cl2 and toluene, as well as drying of a solid sample to give the non-solvated five-coordinated species 2. The crystal structure of the non-solvated Tp(Me2)Ni derivative 3b(Ni) consists of a highly distorted trigonal bipyramidal nickel center.