Robust and efficient transfer hydrogenation of carbonyl compounds catalyzed by <i>NN</i>-Mn(I) complexes.

<p>A series of manganese(I) carbonyl complexes bearing structurally related <em>NN</em>- and <em>NNN</em>-chelating ligands have been synthesized and assessed as catalysts for transfer hydrogenation (TH). Notably, the <em>NN</em>-systems based on <em>N</em>-R functionalized 5,6,7,8-tetrahydroquinoline-8-amines, proved the most effective in the manganese-promoted conversion of acetophenone to 1-phenylethanol. In particular, the <em>N</em>-isopropyl derivative, Mn1, when conducted in combination with <em>t</em>-BuONa, was the standout performer mediating not only the reduction of acetophenone but also a range of carbonyl substrates including (hetero)aromatic-, aliphatic- and cycloalkyl-containing ketones and aldehydes with especially high values of TON (up to 17 200; TOF of 3550 h^-1). These findings, obtained through a systematic variation of the <em>N</em>-R group of the <em>NN</em> ligand, are consistent with an outer-sphere mechanism for the hydrogen transfer. As a more general point, this Mn-based catalytic TH protocol offers an attractive and sustainable alternative for producing alcoholic products from carbonyl substrates.</p>