Pyrazolyl- and Hydrocarbyl-Bridged Binuclear Complexes of Nickel

The binuclear nickel complex Ni2Br2(PMe3)3(μ2-η3:η1-CH2-o-C6H4) (1) reacts with pyrazolyllithium (LiPz) to give the μ-pyrazolyl μ-hydrocarbyl compound Ni2(PMe3)2Br(μ2-η3:η1-CH2-o-C6H4)(μ2-Pz) (2). X-ray studies show a short Ni−Ni distance (2.710(2) A) which suggests the existence of some bonding interaction. The bromide ligand of compound 2 can be replaced by anionic (N3-, 2,5-dimethylpyrrolide) or neutral (PMe3, Me2PCH2CH2PMe2) ligands. Other related complexes containing methyl or tert-butyl substituents on the 3-position or on the 3- and 5-positions of the pyrazolate ligand can be obtained using the corresponding pyrazolylthallium derivatives. The monosubstituted pyrazole complexes exist in solution as equilibrium mixtures of two isomers which differ in the relative position of the pyrazolate substituent. However, only one isomer has been isolated in the solid state.