Cobalt-Catalyzed Hyperpolarization of Structurally Intact Olefins
Safiyah R. Muhammad, Rianna B. Greer, Steven B. Ramirez, Boyd M. Goodson, Alison R. Fout
Abstract
Signal amplification by reversible exchange (SABRE) is a tool that generates hyperpolarized species via non-hydrogenative interactions between parahydrogen and selected nitrogen-/oxygen-/sulfur-containing substrates, traditionally with an iridium catalyst. The development of this field has allowed for a broadened substrate range amenable to hyperpolarization for applications including magnetic resonance imaging. Herein, we report the utilization of a cobalt-based catalyst for the hyperpolarization of structurally intact olefins via a SABRE-like mechanism. The hyperpolarization of a variety of olefinic substrates is exhibited using NMR spectroscopy and yields signal enhancement values of up to ∼150-fold for 1H resonances at 14.1 T. Transfer of polarization to 13C (nearly 150-fold) and 19F is demonstrated without the use of isotopic labeling or the application of radio-frequency pulse sequences, both with and without the use of microtesla fields. These results demonstrate and provide further insights into the first first-row transition metal catalyst platform capable of facilitating the dramatic signal enhancement of structurally intact substrates not traditionally observed with iridium SABRE chemistry.