Ir­(NHC) (NHC, N-heterocyclic carbene)-catalyzed dehydrogenative coupling of sustainable ethylene glycol and various bioalcohols can produce industrially valuable α-hydroxy acids (AHAs). This study is the first to report the sustainable synthesis of higher C n AHAs, in addition to glycolic acid (C2 AHA) and lactic acid (C3 AHA). This catalytic system can be recycled to the seventh cycle while maintaining good yields. A reaction mechanism, including facile dehydrogenation of each alcohol and fast cross-coupling of dehydrogenated aldehydes forming products, was proposed based on 18O- and 2H-labeling experiments and electron spray ionization-mass spectrometry (ESI-MS) and NMR spectral analyses.

Novel tri-N-heterocyclic carbene (triNHC)-coordinated iridium catalysts (Ir­(triNHC)) were employed for generating clean hydrogen and useful C n acids from biomass-derived alcohols. The high efficiency and fast rate of hydrogen production (maximum turnover frequency = 13,080 h–1 and 485 L of H2/g-cat·h) from sustainable ethylene glycol were elucidated by the increased electron-richness of Ir­(triNHC) complexes where three NHC ligands were coordinated to an iridium­(I) ion. Elaborated mechanistic studies support the proposed reaction mechanisms forming H2 and C n acids. This Ir­(triNHC)-catalyzed process converting sustainable alcohols to useful fuels and chemicals is a promising carbon-neutral process.

The iridium(Ir) (triNHC = tri-N-heterocyclic carbene)-catalyzed transfer hydrogenation of glycerol carbonate (GC) is described in the absence of additional hydride sources. The described reduction provides a sustainable route to produce industrially-valuable formate and lactate with high turnover numbers (TONs). The bimetallic Ir(I) involving triNHC carbene ligands exhibits high TONs, and the reaction mechanism, including the bimetallic Ir(triNHC) catalyst, is proposed based on mechanistic studies.