The intermediates, denoted as I-A, I-B, and I-C display characteristic PASADENA patterns originating from the bound hydrides with decreasing respective signal intensity (Fig. ). The fact that two multiplets are distinguishable allows to conclude that complexes have an asymmetric configuration with one hydrogen being trans to COD double bond 4 so that available Co-L first leads to additional stability and lifetime of PTCs with ACN and then blocks the ligand positions at high concentrations. The 1 H NMR spectra were acquired over a period of around 6 s, covering the time scales of most exchange pathways of substrate and pH 2 . BA would be expected. However, no such splitting was observed, indicating that the charged intermediate is not favored under these conditions. In contrast, 1 H coupled to N for intermediate hydride complexes was observed with the substrate 15 N-ammonia in the mixture of DCM with around 0.2 % water (sample was prepared by extraction of NH 3 /NH 4 OH of 14 M aqueous solution into DCM), and for 15 N-ammonia in methanol, c.f. Figure and Table .