Assembly of Functionalized Organic Fragments via Reductive Activation and (Cross)-Coupling of C₂H₄, CO, CO₂ and/or H₂...

Reactions of 1,2-dimagnesioethane compound [{K(^TCHPNON)Mg}₂(μ-C₂H₄)] (^TCHPNON = 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 N₂, viz. [{K(^TCHPNON)Mg}₂(μ-N₂)], with CO and CO₂ 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(^TCHPNON)Mg}₂(μ-O₂C₄H₄)], which when exposed to THF gave adduct [{K(^TCHPNON)Mg}₂(μ-O₂C₄H₄)(THF)]. Treating [{K(^TCHPNON)Mg}₂(μ-C₂H₄)] with CO₂ led to the insertion of CO₂ into both Mg─C bonds and all Mg─N bonds, yielding a magnesium succinate complex, [{K(^TCHPNON-C₂O₄)Mg}₂(μ-O₄C₄H₄)], in which the diamide ligands have been converted to xanthene bridged dicarbamates. The reaction of [{K(^TCHPNON)Mg}₂(μ-N₂)] with CO₂, proceeded via reductive coupling of the heterocumulene to give the oxalate dianion, in addition to the insertion of CO₂ into all Mg─N bonds of the magnesium-dinitrogen complex, forming dimeric [{K(^TCHPNON-C₂O₄)Mg}₂(μ-O₄C₂)]₂. When treated with THF this yields monomeric [{K(THF)(^TCHPNON-C₂O₄)Mg(THF)}₂(μ-O₄C₂)]. Related chemistry results from the reaction of a dianionic magnesium(I) compound with CO₂. In contrast, C─C bond formation was not observed in the reaction of [{K(^TCHPNON)Mg}₂(μ-N₂)] with a CO₂ analog, i.e., the carbodiimide CyNCNCy (Cy = cyclohexyl). Instead, H abstraction by a proposed radical intermediate gave polymeric formamidinate complex [K(^TCHPNON)Mg{(CyN)₂CH}]_∞. Reaction of CO₂ with the magnesium hydride complex [{K(^TCHPNON)Mg(μ-H)}₂] gave the unusual trimeric magnesium formate complex [{K(^TCHPNON-CO₂)Mg}(μ-O₂CH)]₃ in which CO₂ has inserted into only one Mg─N bond of each ^TCHPNON ligand. This study highlights the capacity of [{K(^TCHPNON)Mg}₂(μ-N₂)] to act as a masked dimagnesium(I) diradical in reductive coupling or cross-coupling of the simple gaseous reagents, C₂H₄, CO, CO₂ and H₂, to give value-added organic fragments.