Synthesis, structures and electrochemical properties of VIB carbonyl complexes containing bis(4-halopyrazol-1-yl)alkanes

Bis(4-halopyrazol-l-yl)alkanes (1=bis(4-bromopyrazol-l-yl)methane CH2(4-BrP z)(2), 2=bis(3,5-dimethyl-4-bromopyrazor-l-yl)methane CH2(3,5-Me-2-4-BrPz)( 2), 3=bis(4-chloropyrazol-l-yl)methane CH2(4-ClPz)(2), 4=bis(3,5-dimethyl-4 -chloro-pyrazol-l-yl)methane CH2(3,5-Me-2-4-ClPz)(2)) have been synthesized by the reaction of bis(pyrazol-l-yl)methane or bis(3,5-dimethylpyrazol-l-y l)methane with Br-2 or SO2Cl2. These ligands react with M(CO)(6) (M=Cr, Mo, W) to yield bis(4-halopyrazol-l-yl) methane tetracarbonyl chromium(0), mol ybdenum(0) and tungsten(0) complexes in reasonable yield. All new compounds have been characterized by elemental analyses, IR, LH NMR and C-13 NMR in the case of tungsten complexes. The electrochemical properties of these com plexes studied by the cyclic voltammograms indicate that each compound exhi bits one reversible or quasi-reversible couple corresponding to a one-elect ron oxidation. The structure of CH2(3,5-Me-2-4-ClPz)(2)W(CO)(4) determined by X-ray crystallography shows that the six-membered <(W-N-N-C-N-N)over bar > metallacycle adopts a boat form. (C) 1999 Elsevier Science Ltd. All right s reserved.