Reaction Chemistry of the <i>syn</i>-[Mo<sub>2</sub>O<sub>2</sub>(μ-S)<sub>2</sub>(S<sub>2</sub>)(DMF)<sub>3</sub>] Complex with Cyanide and Catalytic Thiocyanate Formation
Sigrídur G. Suman, Johanna M. Gretarsdóttir, Paul E. Penwell, Jón Pétur Gunnarsson, Sindri Frostason, Sigríður Jónsdóttir, Krishna K. Damodaran, A.S. Hirschon
Abstract
Removal of cyanide as nontoxic thiocyanate under physiological conditions may serve as a catalytic detoxification route in vivo. Aqueous catalytic reaction conditions were explored where at the conditions employed the reaction proceeded to exhaustion in 1 h. The complex, syn-[Mo2O2(μ-S)2(S2)(DMF)3] 1, participates in a ligand exchange reaction of the dimethylformamide ligands and cyanide. Simultaneous sulfur abstraction reaction from the terminal disulfide group forms thiocyanate and terminal sulfido ligand. Respective reaction rates for the two reactions appear competitive where different products were isolated solely based on change of reaction temperature. The approach to determine the number of cyanide ligands participating in the ligand exchange reaction by varying the stoichiometry and reaction temperature led to identification and isolation of tetranuclear complexes 2 and 5 and dinuclear complexes 3, 4, and 6. A synthesized and fully characterized thiocyanate analog of 6 (7) supports spectroscopic characterization of 6. The tetranuclear anion, [Mo4O4(μ-S)6(CN)4]4–, 2, was crystallized from a reaction at ambient temperature. The dinuclear anion, [Mo2O2(μ-S)2(S)(CN)3]3–, 3, was crystallized from similar reaction conditions at lower temperature. The reaction yield of thiocyanate obtained at pH of 7.4 and at 9.2 as a function of time, for several ratios of cyanide, favors the sulfur abstraction reaction at elevated pH. The sulfur abstraction reaction is the first step in a proposed mechanism of the reaction of cyanide and thiosulfate to form thiocyanate and sulfite by 1.