Chemistry of a binuclear cadmium(II) hydroxide complex:: Formation from water, CO2 reactivity, and comparison to a zinc analog

Treatment of the bmnpa (N,N-bis-2-(methylthio)ethyl-M((6-neopentylamino-2-pyridyl)methyl)amine) ligand with equimolar amounts of Cd(ClO4)(2).5H(2)O and Me4NCH.5H(2)O in CH3CN yielded the binuclear cadmium hydroxide complex [((bmnpa)Cd)(2)(mu-OH)(2)](ClO4)(2).CH3CN (1). Complex 1 may also be prepared (a) by treatment of a CH3CN solution of (bmnpa)Cd(ClO4)(2) (2) with 1 equiv of n-BuLi, followed by treatment with water or (b) from 2 in the presence of 1 equiv each of water and NEt3. The hydroxide derivative 1 is not produced from 2 and water in the absence of an added base. Complex 1 possesses a binuclear structure in the solid state with hydrogen-bonding and CH/pi interactions involving the bmnpa ligand. The overall structural features of 1 differ from the halide derivative [((bmnpa)Cd)(2)(mu-Cl)(2)](ClO4)(2) (3), particularly in that the Cd-2(mu-OH)(2) core of 1 is symmetric whereas the Cd-2(mu-Cl)(2) core of 3 is asymmetric. In acetonitrile solution, I behaves as a 1:2 electrolyte and retains a binuclear structure and secondary hydrogen-bonding and CH/pi interactions, whereas 3 is a 1:1 electrolyte, indicating formation of a mononuclear [(bmnpa)CdCl]ClO4 species in solution. Treatment of 1 with CO2 in anhydrous CH3CN yields the bridging carbonate complex [((bmnpa)Cd)(2)(mu-CO3)](ClO4)(2)-CH3CN (4). Treatment of a chemically similar zinc hydroxide complex, [((benpa)Zn)(2)(mu-OH)(2)](ClO4)(2) (benpa = N,N-bis-2-(ethylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl)-amine, with CO2 also results in the formation of a carbonate derivative, [((benpa)Zn)(2)(mu-CO3)] (ClO4)(2) (5), albeit the coordination mode of the bridging carbonate moiety is different, Treatment of 4 with added water results in no reaction, whereas 5 under identical conditions will undergo reaction to yield the zinc hydroxide complex [((benpa)Zn)(2)(mu-OH)(2)](ClO4)(2).