Fast Motions of an Iridium Dihydride Complex in an Aqueous Medium Revealed by NMR Relaxometry with High Resolution

The correlation times in iridium dihydride catalytic complex [Ir(IMes)(Pyeq)2(Pyax)H2]Cl were studied in water, where it remains stable for days. T1 relaxation times of individual protons were measured across magnetic fields using NMR with fast field cycling. Above 4 Tesla, T1 time increased, indicating a transition from the fast (ωτc < 1) to slow motion (ωτc > 1) regime. Fitting the experimental data to a local magnetic field fluctuation model provided the site-specific rotational correlation times with an average of 280 ps for the whole molecule.