Iridium N-heterocyclic carbene complexes as efficient catalysts for magnetization transfer from para-hydrogen

TY - JOUR

T1 - Iridium N-heterocyclic carbene complexes as efficient catalysts for magnetization transfer from para-hydrogen

AU - Cowley, M.J.

AU - Adams, Ralph W.

AU - Atkinson, Kevin

AU - Cockett, Martin Charles Roy

AU - Duckett, Simon

AU - Green, Gary George Reginald

AU - Lohman, J.A.B.

AU - Kerssebaum, R

AU - Kilgour, D

AU - Mewis, Ryan Edward

PY - 2011/4/27

Y1 - 2011/4/27

N2 - While the characterization of materials by NMR is hugely important in the physical and biological sciences, it also plays a vital role in medical imaging. This success is all the more impressive because of the inherently low sensitivity of the method. We establish here that [Ir(H)(2)(IMes)(py)(3)]Cl undergoes both pyridine (py) loss as well as the reductive elimination of H(2). These reversible processes bring para-H(2) and py into contact in a magnetically coupled environment, delivering an 8100-fold increase in (1)H NMR signal strength relative to non-hyperpolarized py at 3 T. An apparatus that facilitates signal averaging has been built to demonstrate that the efficiency of this process is controlled by the strength of the magnetic field experienced by the complex during the magnetization transfer step. Thermodynamic and kinetic data combined with DFT calculations reveal the involvement of [Ir(H)(2)(eta(2)-H(2))(IMes)(py)(2)](+), an unlikely yet key intermediate in the reaction. Deuterium labeling yields an additional 60% improvement in signal, an observation that offers insight into strategies for optimizing this approach.

AB - While the characterization of materials by NMR is hugely important in the physical and biological sciences, it also plays a vital role in medical imaging. This success is all the more impressive because of the inherently low sensitivity of the method. We establish here that [Ir(H)(2)(IMes)(py)(3)]Cl undergoes both pyridine (py) loss as well as the reductive elimination of H(2). These reversible processes bring para-H(2) and py into contact in a magnetically coupled environment, delivering an 8100-fold increase in (1)H NMR signal strength relative to non-hyperpolarized py at 3 T. An apparatus that facilitates signal averaging has been built to demonstrate that the efficiency of this process is controlled by the strength of the magnetic field experienced by the complex during the magnetization transfer step. Thermodynamic and kinetic data combined with DFT calculations reveal the involvement of [Ir(H)(2)(eta(2)-H(2))(IMes)(py)(2)](+), an unlikely yet key intermediate in the reaction. Deuterium labeling yields an additional 60% improvement in signal, an observation that offers insight into strategies for optimizing this approach.

UR - http://www.scopus.com/inward/record.url?scp=79955001732&partnerID=8YFLogxK

U2 - 10.1021/ja200299u

DO - 10.1021/ja200299u

M3 - Article

SN - 0002-7863

VL - 133

SP - 6134

EP - 6137

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

IS - 16

ER -