In this work, we used SABRE and studied the activation of an Ir-based N-heterocyclic carbene complex, [Ir(IMes)(COD)Cl], with hydrogen in various solvents using benchtop 1 H NMR spectroscopy. Ir-complexes of neutral configurations were found in dichloromethane (DCM), charged Ir-conformers -in methanol (MeOH), a mix of netural and charged configurations were identified in acetonitrile (ACN) or in multi-phase systems (e.g., DCM/water mixtures). This understanding allowed us to develop a protocol for achieving stable and reproducible molar polarization of acetonitrile, capable of generating hyperpolarizationenhanced signals on naturally-abundant [ 15 N]-ACN molecules. This SABRE-based solvent polarization methodology can find particular utility in various fundamental physics experiments since the need for a robust methodology to prepare large volumes of highly polarized molecules remains acute. In this paper: first, chemical transformations accompanying activation of PTCs in a hydrogen atmosphere during SABRE with acetonitrile were elucidated; then, dilution experiments with the stabilizing co-ligand (Co-L) benzylamine were carried out to validate the presented assignments; finally, the results of this work and those from systems shown in the literature are analyzed, and a generalized finding regarding the neutral and charged activation pathways are presented.