Trigonal Planar <i>Bis</i> (carbene)Cu(I) Complexes Enable Divergent H ₂ Activation with H ₂ O for Accelerated Olefin Hydrogenation

Abstract

Abstract CuH‐catalyzed olefin hydrogenation is rare compared to those of carbonyl‐derived substrates. Olefin insertion into Cu–H to form Cu‐alkyl is ubiquitous; however, subsequent H 2 activation remains unknown to our knowledge. Herein, we investigated the transformations of β‐H elimination, H 2 cleavage, and catalytic olefin hydrogenation in a series of linear and trigonal planar Cu(I)‐alkyl complexes supported by monodentate N ‐heterocyclic carbene and bidentate naphthyridine‐ bis (carbene) ligands, respectively. Contrary to unreactive linear species, trigonal planar variants promote β‐H elimination, hydrogenolysis, and catalytic hydrogenation of unactivated alkenes at mild temperatures and H 2 pressure. The rare isolation of a naphthyridine‐ bis (carbene)CuH monomer further affirms two predominant competing pathways for H 2 cleavage of metal–ligand cooperativity at Cu(I)‐alkyl or internal electrophilic substitution at Cu(I)‐OH. Employing either isolated or in situ generated Cu(I)‐OH complex, via protonolysis of alkyl precatalyst by adventitious water, significantly accelerated catalysis compared to that operating primarily by the metal–ligand cooperativity pathway. DFT calculations and energy decomposition analysis on the disparate β‐H elimination reactivity between linear and trigonal planar tert‐butyl complexes and the mechanism of H 2 activation at a hydroxide complex, indicate that coordination geometry at Cu(I) and properties of the naphthyridine‐ bis (carbene) ligand are integral to the transformations reported here.