Triplet Photosensitized -Hydrogen Induced Polarization.

Despite its enormous utility in structural characterization, nuclear magnetic resonance (NMR) spectroscopy is inherently limited by low spin polarization. One method to address the low polarization is -hydrogen (-H) induced polarization (PHIP) which uses the singlet spin isomer of H to generate disparate nuclear spin populations to amplify the associated NMR signals. PHIP often relies on thermal catalysis or, more infrequently, UV-activated catalytic hydrogenation. Light-activated hydrogenation enables direct and timed control over the hyperpolarization of target substrates, critical for identifying short-lived intermediates. Here, we use an established Ir(III) triplet photosensitizer () to visible light sensitize the triplet ligand-field states in the d-transition metal dihydride Ru(CO)(PPh)(H) (). Excitation inside a 9.4 T NMR spectrometer with the and a 420 nm blue LED, under 3 atm of -H, successfully photosensitized hyperpolarization in and in a range of unsaturated substrates at and below room temperature, up to 1630-fold. In otherwise identical experimental conditions without light activation, no polarization was realized in or the substrates evaluated. We believe triplet-sensitized PHIP (Trip-PHIP) represents a facile experimental means for probing triplet sensitized light activation in transition metal catalysts possessing low-lying triplet ligand-field states, providing mechanistic insight of potentially tremendous value in chemical catalysis.