Assembly of Functionalized Organic Fragments via Reductive Activation and (Cross)-Coupling of C2H4, CO, CO2 and/or H2 using a Magnesium-Dinitrogen Complex

Reactions of 1,2-dimagnesioethane compound [{K(TCHPNON)Mg}2(-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(-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(-O2C4H4)], which when exposed to THF gave adduct [{K(TCHPNON)Mg}2(-O2C4H4)(THF)]. Treating [{K(TCHPNON)Mg}2(-C2H4)] with CO2 led to insertion of CO2 into both Mg‒C bonds and all Mg‒N bonds of the 1,2-dimagnesioethane species, yielding a magnesium succinate complex, [{K(TCHPNON-C2O4)Mg}2(-O4C4H4)], in which the diamide ligands of the starting material have been converted to xanthene bridged dicarbamates. The reactions can be viewed as involving the “masked-magnesium(I)” induced cross-coupling of ethene with either CO or CO2, to give more complex organic products. Reaction of [{K(TCHPNON)Mg}2(-N2)] with CO2, proceeded via reductive coupling of the heterocumulene to give the oxalate dianion, in addition to insertion of CO2 into all Mg‒N bonds of the magnesium-dinitrogen complex, forming dimeric [{K(TCHPNON-C2O4)Mg}2(-O4C2)]2. When treated with THF this dissociates to monomeric [{K(THF)(TCHPNON-C2O4)Mg(THF)}2(-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(-N2)] with a CO2 analogue, i.e. the carbodiimide CyNCNCy (Cy = cyclohexyl). Instead, H abstraction by a proposed intermediate containing a reduced carbodiimide radical fragment, gave polymeric formamidinate complex [K(TCHPNON)Mg{(CyN)2CH}]∞. Reaction of CO2 with the magnesium hydride complex [{K(TCHPNON)Mg(-H)}2] (formed by activation of H2 with [{K(TCHPNON)Mg}2(-N2)]), gave the unusual trimeric magnesium formate complex [{K(TCHPNON-CO2)Mg}(-O2CH)]3 in which CO2 has inserted into only one Mg‒N bond of each TCHPNON ligand. All of the above-mentioned reactions reveal the capacity of [{K(TCHPNON)Mg}2(-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.