Synthesis and Reactivity of Catecholate Complexes Containing Quadruply Bonded Metal Ions

Quadruply bonded metal complexes of rhenium and molybdenum have been prepared with tetrachlorocatechol. Structural characterization on the [Re2(Cl4Cat)4]2- anion has shown that it consists of distorted square-planar Re(Cl4Cat)2 units linked by a short (2.2067 Å) quadruple Re−Re bond. The addition of tetrachlorocatechol to molybdenum acetate was used to prepare the isoelectronic molybdenum analogue “[Mo2(Cl4Cat)4]4−”. This complex was found to be far more reactive than the rhenium dimer. A dimer containing a Mo−Mo double bond, [(Cl4Cat)2Mo(μ-O)(μ-OCH3)Mo(Cl4Cat)2]3−, was obtained as the methanolysis product of the complex formed initially, and the oxomolybdenum(V) monomer [MoO(Cl4Cat)2]− was formed under more oxidative conditions. Both complexes are oxygen-sensitive, giving [MoO2(Cl4Cat)2]2− as the final air-stable complex product.