The formation of C–N bonds is an undeniably valuable goal in chemical synthesis. Research in our group focuses on the discovery of novel C–N bond-forming methods using catalysts based on Earth-abundant and nontoxic first-row transition metals like iron and manganese. Our approach to reaction development takes advantage of stoichiometric investigation of proposed catalytic intermediates to gain fundamental insights into the targeted catalytic transformations. We recently discovered a novel alkyne carboamination process in the reaction of an isolable iron imide complex with a terminal alkyne substrate. Stoichiometric studies identified a catalyst-deactivating hydrogen atom transfer process that can be suppressed in the presence of a Lewis basic additive. This vital information allowed us to render the process catalytic in iron. In addition to their own synthetic utility, the alkynyl enamine products of carboamination serve as precursors to 2,4-disubstituted pyrroles via copper-catalyzed cyclization. Another project targets the manganese-catalyzed C–H amination of hydrocarbon substrates using hydroxylamine and oxime partners as sources of both the nitrogen group and the oxidant. The manganese oximate precursor to an active oxo species can be prepared by protonolysis of the manganese hydroxide. Oxidation of the oximate complex in the presence of a hydrocarbon substrate leads to C–H functionalization, presumably via a hydrogen atom abstraction/cage escape pathway related to the desired C–N bond-forming chemistry.

C–N bond formation using earth-abundant transition metal catalysts: New methods for iron-catalyzed carboamination and manganese-catalyzed C–H amination

ACS Spring Meeting 2021

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