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

Abstract Bis(4-halopyrazol-1-yl)alkanes ( 1 =bis(4-bromopyrazol-1-yl)methane CH 2 (4-BrPz) 2 , 2 =bis(3,5-dimethyl-4-bromopyrazol-1-yl)methane CH 2 (3,5-Me 2 -4-BrPz) 2 , 3 =bis(4-chloropyrazol-1-yl)methane CH 2 (4-ClPz) 2 , 4 =bis(3,5-dimethyl-4-chloro-pyrazol-1-yl)methane CH 2 (3,5-Me 2 -4-ClPz) 2 ) have been synthesized by the reaction of bis(pyrazol-1-yl)methane or bis(3,5-dimethylpyrazol-1-yl)methane with Br 2 or SO 2 Cl 2 . These ligands react with M(CO) 6 (M=Cr, Mo, W) to yield bis(4-halopyrazol-1-yl) methane tetracarbonyl chromium(0), molybdenum(0) and tungsten(0) complexes in reasonable yield. All new compounds have been characterized by elemental analyses, IR, 1 H NMR and 13 C NMR in the case of tungsten complexes. The electrochemical properties of these complexes studied by the cyclic voltammograms indicate that each compound exhibits one reversible or quasi-reversible couple corresponding to a one-electron oxidation. The structure of CH 2 (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 metallacycle adopts a boat form.