Reaction monitoring using SABRE-hyperpolarized benchtop (1 T) NMR spectroscopy

TY - JOUR

T1 - Reaction monitoring using SABRE-hyperpolarized benchtop (1 T) NMR spectroscopy

AU - Semenova, Olga

AU - Richardson, Peter Michael

AU - Parrott, Andrew

AU - Nordon, Alison

AU - Halse, Meghan Eileen

AU - Duckett, Simon

N1 - © 2019 American Chemical Society.

PY - 2019/5/21

Y1 - 2019/5/21

N2 - The conversion of [IrCl(COD)(IMes)] (COD = cis,cis-1,5-cyclooctadiene, IMes = 1,3-bis(2,4,6-trimethyl-phenyl)imidazole-2-ylidene) in the presence of an excess of p-H2 and a substrate (4-aminopyridine (4-AP) or 4-methylpyridine (4-MP)) into [Ir(H)2(IMes)(substrate)3]Cl is monitored by 1H NMR spectroscopy using a benchtop (1 T) spectrometer in conjunction with the parahydrogen (p-H2) based hyperpolarization technique signal amplification by reversible exchange (SABRE). A series of single-shot 1H NMR measurements are used to monitor the chemical changes that take place in solution through the lifetime of the hyperpolarized response. Non-hyperpolarized high-field 1H NMR control measurements were also undertaken to confirm that the observed time dependent changes relate directly to the underlying chemical evolution. The formation of [Ir(H)2(IMes)(substrate)3]Cl is further linked to the hydrogen isotope exchange reaction (HIE) which leads to the incorporation of deuterium into the ortho positions of 4-AP, where the source of deuterium is the solvent, methanol-d4. Comparable reaction monitoring results are achieved at both high-field (9.4 T) and low-field (1 T). It is notable, that the low sensitivity of the benchtop (1 T) NMR enables the use of protio solvents, which is harnessed here to separate the effects of catalyst formation and substrate deuteration. Collectively, these methods illustrate how low-cost low-field NMR measurements provide unique insight into a complex catalytic process through a combination of hyperpolarization and relaxation data.

AB - The conversion of [IrCl(COD)(IMes)] (COD = cis,cis-1,5-cyclooctadiene, IMes = 1,3-bis(2,4,6-trimethyl-phenyl)imidazole-2-ylidene) in the presence of an excess of p-H2 and a substrate (4-aminopyridine (4-AP) or 4-methylpyridine (4-MP)) into [Ir(H)2(IMes)(substrate)3]Cl is monitored by 1H NMR spectroscopy using a benchtop (1 T) spectrometer in conjunction with the parahydrogen (p-H2) based hyperpolarization technique signal amplification by reversible exchange (SABRE). A series of single-shot 1H NMR measurements are used to monitor the chemical changes that take place in solution through the lifetime of the hyperpolarized response. Non-hyperpolarized high-field 1H NMR control measurements were also undertaken to confirm that the observed time dependent changes relate directly to the underlying chemical evolution. The formation of [Ir(H)2(IMes)(substrate)3]Cl is further linked to the hydrogen isotope exchange reaction (HIE) which leads to the incorporation of deuterium into the ortho positions of 4-AP, where the source of deuterium is the solvent, methanol-d4. Comparable reaction monitoring results are achieved at both high-field (9.4 T) and low-field (1 T). It is notable, that the low sensitivity of the benchtop (1 T) NMR enables the use of protio solvents, which is harnessed here to separate the effects of catalyst formation and substrate deuteration. Collectively, these methods illustrate how low-cost low-field NMR measurements provide unique insight into a complex catalytic process through a combination of hyperpolarization and relaxation data.

U2 - 10.1021/acs.analchem.9b00729

DO - 10.1021/acs.analchem.9b00729

M3 - Article

SN - 0003-2700

VL - 91

SP - 6695

EP - 6701

JO - Analytical Chemistry

JF - Analytical Chemistry

IS - 10

M1 - 9b00729

ER -