Ion mobility mass spectrometry uncovers regioselectivity in the carboxylate-assisted C-H activation of palladium N-heterocyclic carbene complexes.

Carboxylate-assisted Pd-catalyzed C-H bond activation constitutes a mild and versatile synthetic tool to efficiently and selectively cleave inert C-H bonds. Herein, we demonstrate a simple method to experimentally evaluate both reactivity and selectivity in such systems using mass spectrometry (MS) methods. The N-heterocyclic carbene (NHC) cations [(NHC)PdX], bearing as X ligand bases commonly used to promote the C-H activation (carboxylates and bicarbonate), are generated in the gas-phase by ESI-MS.

Introducing Ion Mobility Mass Spectrometry to Identify Site-Selective C-H Bond Activation in N-Heterocyclic Carbene Metal Complexes.

The activation of C-H bonds in a selective manner still constitutes a major challenge from a synthetic point of view; thus, it remains an active area of fundamental and applied research. Herein, we introduce ion mobility spectrometry mass spectrometry-based (IM-MS) approaches to uncover site-selective C-H bond activation in a series of metal complexes of general formula [(NHC)LMCl] (NHC = N-heterocyclic carbene; L = pentamethylcyclopentadiene (Cp*) or -cymene; M = Pd, Ru, and Ir). The C-H bond activation at the N-bound groups of the NHC ligand is promoted upon collision induced dissociation (CID).