Insertion reactions of small molecules into group 2 metal alkoxides; structural characterization of [Mg 9( μ5−CO 3)(O 2COMe) 8( μ3−OMe) 8(MeOH) 13] · MeOH · C 7H 8

Abstract

The SO 2 inserted compounds [M(O 2SOMe) 2(MeOH) 2] ∞ (M = Mg 1; M = Ca 2) were synthesized from the reaction of the corresponding [M(OMe) 2] ∞ complexes in methanol, followed by recrystallization from either n-hexane or toluene. The reaction of COS or CS 2 gas with [M(OMe) 2] ∞ in methanol, yielded the inserted products [M({OCS}OMe) 2(MeOH) x ] n ( x = 2, M = Mg 3, x = 3, n = 2, M = Ca 4) and [M(S 2COMe) 2(MeOH) x ] n ( x = 6, M = Mg 5; x = 4, M = Ca 6), respectively. The analogous reaction of [M(OMe) 2] ∞ (M = Mg, Ca) with CO 2 gas gave the mixed methoxide/methylcarbonato compounds [Mg(O 2COMe(OMe)(MeOH) 1.5] n 7a and [Ca(O 2COMe)(OMe)(MeOH)] n 8. Recrystallization of 7a from a “wet” hydrocarbon solvent mixture led to the crystalline product [Mg 9(CO 3)(O 2COMe) 8(OMe) 8 (MeOH) 13]·MeOH·C 7H 8 7b. The corresponding insertion reaction of CO 2 gas with [M(OEt) 2] ∞ M = Cg, Ca) gave the mixed ethoxide/ethylcarbonato compounds [M(O 2COEt)(OEt)(EtOH) 2] n (M = Mg 9; M = Ca10). Similarly, the reaction of CO 2 gas with [Mg(OR) 2] ∞ (R = Pr i, Bu t) in the parent alcohol, resulted in the [Mg(O 2COR)(OR)(ROH)] n compounds (R = Pr i 11; R = Bu t 12). All compounds have been characterized by spectroscopic techniques including NMR ( 1H and 13C) and IR spectroscopy, and in selected cases by TGA/DSC. Complex 7b was unambiguously characterized by single crystal X-ray diffraction. It was established that 7b is a nonameric complex comprising of two Mg 4O 4 cubes, with a remote ninth magnesium atom held in position via two bridging methylcarbonato groups and an unusual μ 5-carbonate ligand.