Assembly of Functionalized Organic Fragments via Reductive Activation and (Cross)-Coupling of CH, CO, CO and/or H Using a Magnesium-Dinitrogen Complex.

Reactions of 1,2-dimagnesioethane compound [{K(NON)Mg}(μ-CH)] (NON = 4,5-bis(2,4,6-tricyclohexylanilido)-2,7-diethyl-9,9-dimethyl-xanthene), formed by the two-electron reduction of ethene with a dimagnesium/dipotassium complex of reduced N, viz. [{K(NON)Mg}(μ-N)], with CO and CO have been explored. In the case of the reaction with CO, cross-coupling of the reduced ethene fragment with two molecules of CO gave a heterobimetallic complex of the parent cyclobutenediolate dianion, [{K(NON)Mg}(μ-OCH)], which when exposed to THF gave adduct [{K(NON)Mg}(μ-OCH)(THF)]. Treating [{K(NON)Mg}(μ-CH)] with CO led to the insertion of CO into both Mg─C bonds and all Mg─N bonds, yielding a magnesium succinate complex, [{K(NON-CO)Mg}(μ-OCH)], in which the diamide ligands have been converted to xanthene bridged dicarbamates. The reaction of [{K(NON)Mg}(μ-N)] with CO, proceeded via reductive coupling of the heterocumulene to give the oxalate dianion, in addition to the insertion of CO into all Mg─N bonds of the magnesium-dinitrogen complex, forming dimeric [{K(NON-CO)Mg}(μ-OC)]. When treated with THF this yields monomeric [{K(THF)(NON-CO)Mg(THF)}(μ-OC)]. Related chemistry results from the reaction of a dianionic magnesium(I) compound with CO. In contrast, C─C bond formation was not observed in the reaction of [{K(NON)Mg}(μ-N)] with a CO analog, i.e., the carbodiimide CyNCNCy (Cy = cyclohexyl). Instead, H abstraction by a proposed radical intermediate gave polymeric formamidinate complex [K(NON)Mg{(CyN)CH}]. Reaction of CO with the magnesium hydride complex [{K(NON)Mg(μ-H)}] gave the unusual trimeric magnesium formate complex [{K(NON-CO)Mg}(μ-OCH)] in which CO has inserted into only one Mg─N bond of each NON ligand. This study highlights the capacity of [{K(NON)Mg}(μ-N)] to act as a masked dimagnesium(I) diradical in reductive coupling or cross-coupling of the simple gaseous reagents, CH, CO, CO and H, to give value-added organic fragments.