Zheng Huang

Alkane dehydrogenation has evolved from a fundamental organometallic challenge into a transformative technology for upgrading abundant hydrocarbon feedstocks and modifying complex molecules. This Perspective charts the evolution of modern alkane dehydrogenation, emphasizing the strategic divergence between well-established two-electron pathways and emerging radical-mediated reaction manifolds. For the dehydrogenation of structurally unbiased simple alkanes, research remains centered on noble-metal-based molecular catalysts, represented by pincer–transition-metal systems, where activity and regioselectivity are not only governed by catalysts’ first coordination sphere but also subtly affected by ligands’ scaffold. In contrast, for the dehydrogenation of hydrocarbons with electronically or thermodynamically differentiated C(sp3)–H bonds, a complementary paradigm has emerged in which reactivity is mainly dictated by the intrinsic properties of substrates. The interplay of bond dissociation energies (BDEs) and bond polarity can be harnessed by a diverse array of hydrogen atom transfer (HAT) reagents (or catalysts). We discuss how these two distinct mechanisms dictate the scope of both the dehydrogenation and dehydrogenation-triggered derivatization, which extends beyond small alkane functionalizations to controlled upcycling of macromolecular polyolefins. By analyzing the interplay between thermodynamic constraints, catalyst sustainability, and process integration, we outline a forward-looking roadmap for next-generation catalytic dehydrogenation systems.

A photocatalytic asymmetric protocol for the synthesis of chiral dihydroisoquinolone scaffolds, which are prevalent in natural products and pharmaceuticals, has been developed. Utilizing chiral C₂-symmetric arylthiol as an H atom transfer catalyst, the enantioselective hydroamination-cyclization provides efficient access to a wide range of valuable 4-substituted 3,4-dihydroisoquinolones with moderate to high regio- and enantioselectivity. The synthetic utility of this methodology is demonstrated by the formal synthesis of several bioactive alkaloid intermediates.

We report the development of a class of chiral pincer ruthenium (PCN_Ox)Ru complexes bearing oxazoline-based PCN_Ox ligands for the asymmetric cyclopropanation of olefins with α-diazo carbonyl compounds. These catalysts exhibit high reactivity and stereoselectivity across a broad range of substrates, including monosubstituted, 1,1-disubstituted, and challenging trisubstituted olefins. The present catalyst showed superior performance in the asymmetric intermolecular cyclopropanation of trisubstituted olefins compared to the known (Pheox)Ru catalyst.

Metal carbenes have long been recognized as a pivotal reactive intermediate in organometallic chemistry. Recently catalytic reductive processes with gem-dichloroalkanes have emerged as a promising strategy to generate nonstabilized donor carbenes for alkene cyclopropanation. However, the catalytic cycle remains challenging to study largely due to the inherent instability of metal carbene intermediates. In this study, we elucidated an ECEC mechanism for the (PNN)Co-catalyzed (PNN = bipyridyl phosphine) reductive cyclopropanation of alkenes through an integrated experimental-computational approach combining electroanalytical techniques and density functional theory (DFT) calculations. Initiated by ZnCl₂-assisted one-electron reduction of (PNN)Co^IICl₂ (1) to [(PNN)^•-]Co^IICl (2) featuring a reduced π-radical anion, activation of aryl gem-dichloromethanes by 2 proceeds via outer-sphere electron transfer (OSET) as determined by Hammett linear free-energy relationship (LFER) analysis, producing a cationic benzyl Co(III) species [(PNN)Co^IIICl(benzyl)]⁺ZnCl₃^- (A). Following the first EC, cyclic voltammetry studies, controlled potential electrolysis, and reactivity comparison experiments collectively established the second EC process involving one-electron reduction of A to a cationic Co(II) carbene [(PNN)Co^IICl(carbene)]⁺ZnCl₃^- (C) that is effective for the following carbene transfer. LFER analysis and computational data support the assignment of intermediate C as an electrophilic Co(II) carbene, rationalizing a concerted, nonradical addition pathway for cis-selective alkene cyclopropanation. This work provides a multielectron, multistep mechanistic framework, which could be valuable for developing sustainable catalytic transformations that employ base metals.

A direct deoxygenative alkylation of benzylic and unactivated alkyl alcohols was developed with sulfones as the alkylation reagent, the (PCN)IrHCl complex as the catalyst, and KOtBu as the additive. This protocol offers an efficient approach for the direct conversion of hydroxy groups to alkyl groups without the need for an extra hydrogen source. The utility of this reaction was demonstrated by gram-scale synthesis and derivatization of a bioactive molecule.

The alkyne alkoxycarbonylation to α- or β-substituted acrylates was coupled with the electrocatalytic reduction of CO₂ to CO. The CO-enriched gaseous mixture produced from the electrocatalytic reduction of CO₂ was collected and directly used in the alkyne alkoxycarbonylation. The CO content was found to be critical to the process of carbonylation, and satisfying results were attained by using the gas mixture containing >15 vol % CO. This method offered an efficient but simple CO source from CO₂ electroreduction to the alkoxycarbonylation reaction in two-compartment manner.