Insertion reactions of small molecules into group 2 metal alkoxides; structural characterization of [Mg9(μ5-CO3)(O2COMe)8(μ3-OMe)8(MeOH)13]•MeOH•C7H8

The SO2 inserted compounds [M(O2SOMe)(2)(MeOH)(2)](infinity) (M = Mg 1; M = Ca 2) were synthesized from the reaction of the corresponding [M(OMe)(2)](infinity) complexes in methanol, followed by recrystallization from either n-hexane or toluene. The reaction of COS or CS2 gas with [M(OMe)(2)](infinity) 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(S2COMe)(2) (MeOH)(x)](n), (x=6, M=Mg 5; x=4, M=Ca 6), respectively. The analogous reaction of[M(OMe)(2)](infinity) (M=Mg, Ca) with CO2 gas gave the mixed methoxide/methylcarbonato compounds [Mg(O-2 COMe)(OMe)(MeOH)(1.5)](n) 7a and [Ca(O2COMe)(OMe)(MeOH)](n), 8. Recrystallization of 7a from a "wet" hydrocarbon solvent mixture led to the crystalline product [Mg-9(CO3)(O2COMe)(8)(OMe)(8) (MeOH)(13)].MeOH.C7H8 7b. The corresponding insertion reaction of CO2 gas with [M(OEt)(2)](infinity,) (M = Mg, Ca) gave the mixed ethoxide/ethylcarbonato compounds [M(O2COEt)(OEt)(EtoH)(2)](n) (M = Mg 9, M = Ca 10). Similarly, the reaction of CO2 gas with [Mg(OR)(2)](infinity) (R = Pr-i, Bu-t) in the parent alcohol. resulted in the [Mg(O2COR)(OR)(ROH)](n), compounds (R = Pr-i 11; R = Bu-t 12). All compounds have been characterized by spectroscopic techniques including NMR (H-1 and C-13) 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 Mg4O4 cubes, with a remote ninth magnesium atom held in position via two bridging methylcarbonato groups and an unusual mu(5)-carbonate ligand. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.