(179a) Trends of Heteroatom and Metal Identities in C–X Hydrogenolysis

Selective hydrogenolysis of organic molecules with heteroatoms plays a large role in hydrogen-treating molecules from biomass (O, N removal), petroleum (S removal), wastewater (Cl removal), and pharmaceuticals (O, N, Cl removal). Kinetic and density functional theory (DFT) studies have shown that hydrogenolysis of saturated C–C bonds occurs via unsaturated CH*–CH* intermediates on various Pt-group metals.¹ Kinetic and DFT studies of 1-propanol and 1-butanol on Ir, Pt, Ru, and Cu directly contrasted C–O hydrogenolysis, C–C hydrogenolysis, and decarbonylation.² Decarbonylation was favored on all Pt-group metals, followed by C–O hydrogenolysis with C–C hydrogenolysis occurring at the lowest rate, except on Cu, where C–O hydrogenolysis was favored over competing C–C activation reactions.² Our recent study of saturated CH₃XH_n molecules (X = C, N, O, S, Cl) on group 8–11 transition metals have shown that when cleaving, the heteroatom and metal identities affect the predicted level of unsaturation of the transition state.³ Free energy barriers indicate that C–X activations on group 8–10 transition metals typically occur after removing two H atoms regardless of heteroatom identity, whereas hydrogenolysis on group 11 transition metals occurs via more saturated intermediates.³ Metal identity determines dehydrogenation of –NH₂ prior to C–N activation. Dehydrogenation of –OH was rare while dehydrogenation of –SH was universal.³ We have since extended prior study to assess the mechanisms that activate Ph–X in substituted aromatic species. In addition to varying heteroatom identity, we vary hydrogenation of the ring moiety by systematically adding and subtracting H atoms. In general, understanding the mechanisms of heteroatom removal from simple organic molecules furthers fundamental insight into hydrogenolysis of more complex organic molecules.

References:

1. J Catal., 2014, 311, 350–356
2. Am. Chem. Soc., 2015, 137, 11984–11995
3. ACS Catal., 2020, 10, 5086–5100