The development of efficient and low-cost catalytic systems is important for the replacement of the robust noble metal complexes. A highly efficient, stable, phosphine-free, and easy-tosynthesize iron catalyst system for the reduction of CO 2 , hydrogenocarbonate, and carbonate in pure water is reported. In the presence of the bifunctional cyclopentadienone iron tricarbonyl Fe4a− d, the hydrogenation of carbonic derivatives proceeds in good yields with good catalyst productivity. Turnover numbers (TON) of up to 3343, 4234, and 40 for the hydrogenation of CO 2 , hydrogenocarbonate, and carbonate, respectively, to formate in pure water were achieved. For the CO 2 hydrogenation, a base was required, and triethanolamine emerged as the best one. DFT calculations rationalized the mechanism as well as the better performance of triethanolamine as a base.

A transition-metal frustrated Lewis pair approach has been envisaged to enhance the catalytic activity of tricarbonyl phosphine-free iron complexes in reduction of amines. A new cyclopentadienyl iron­(II) tricarbonyl complex has been isolated, fully characterized, and applied in hydrogenation. This phosphine-free iron complex is the first Earth-abundant metal complex that is able to catalyze chemoselective reductive alkylation of various functionalized amines with functionalized aldehydes. Such selectivity and functionality tolerance (alkenes, esters, ketones, acetals, unprotected hydroxyl groups, and phosphines) have been demonstrated also for the first time at room temperature with an Earth-abundant metal complex. This alkylation reaction was also performed without any preliminary condensation and generated only water as a byproduct. The resulting amines provided rapid access to potential building blocks, metal ligands, or drugs. Density functional theory calculations highlighted first that the formation of the 16 electron species, via the activation of the tricarbonyl complex Fe3, was facilitated and, second, that the hydrogen cleavage did not follow the same pathway as bond breaking, usually described with the known cyclopentadienone iron tricarbonyl complexes (Fe1 and Fe4). These calculations highlighted that the new complex Fe3 does not behave as a bifunctional catalyst, in contrast to its former congeners.