TY - JOUR

T1 - Parahydrogen Allows Ultrasensitive Indirect NMR Detection of Catalytic Hydrogen Complexes

AU - Kiryutin, Alexey S.

AU - Sauer, Grit

AU - Yurkovskaya, Alexandra V.

AU - Limbach, Hans Heinrich

AU - Ivanov, Konstantin L.

AU - Buntkowsky, Gerd

PY - 2017/5/11

Y1 - 2017/5/11

N2 - The 1H NMR signal of dissolved molecular hydrogen enriched in parahydrogen (p-H2) exhibits in the presence of an organometallic hydrogenation catalyst an unusual, partially negative line shape (PNL). It results from a strongly enhanced two-spin order connected to the population of the T0 level of orthohydrogen (o-H2). This two-spin order is made visible by a slow asymmetric exchange process between free hydrogen and a transient catalyst-hydrogen complex. By Only Parahydrogen Spectroscopy (OPSY) it is possible to selectively detect the two-spin order and suppress the signal from the thermal o-H2. The intensity of the PNL can be strongly affected by the PArtially NEgative Line (PANEL) experiment, which irradiates a long narrow-band radio frequency (RF) pulse. When the RF is in resonance with the chemical shift values of the hydrogen bound to the elusive catalyst or of the free hydrogen, a strong intensity reduction of the PNL is observed. Numerical simulations of the experiments performed at 500 and 700 MHz proton frequency show that the indirect detection has at least 3 orders of magnitude higher sensitivity than the normal NMR experiment. A theoretical model, including reversible binding and S - T0 evolution, is developed, which reproduces the NMR line shape, the nutation angle dependence and the dependence on the frequency of the irradiation field of the PNL and permits the determination of the proton chemical shift values and the sign of the scalar coupling in the transient NMR invisible complex where singlet-triplet conversion take place.

AB - The 1H NMR signal of dissolved molecular hydrogen enriched in parahydrogen (p-H2) exhibits in the presence of an organometallic hydrogenation catalyst an unusual, partially negative line shape (PNL). It results from a strongly enhanced two-spin order connected to the population of the T0 level of orthohydrogen (o-H2). This two-spin order is made visible by a slow asymmetric exchange process between free hydrogen and a transient catalyst-hydrogen complex. By Only Parahydrogen Spectroscopy (OPSY) it is possible to selectively detect the two-spin order and suppress the signal from the thermal o-H2. The intensity of the PNL can be strongly affected by the PArtially NEgative Line (PANEL) experiment, which irradiates a long narrow-band radio frequency (RF) pulse. When the RF is in resonance with the chemical shift values of the hydrogen bound to the elusive catalyst or of the free hydrogen, a strong intensity reduction of the PNL is observed. Numerical simulations of the experiments performed at 500 and 700 MHz proton frequency show that the indirect detection has at least 3 orders of magnitude higher sensitivity than the normal NMR experiment. A theoretical model, including reversible binding and S - T0 evolution, is developed, which reproduces the NMR line shape, the nutation angle dependence and the dependence on the frequency of the irradiation field of the PNL and permits the determination of the proton chemical shift values and the sign of the scalar coupling in the transient NMR invisible complex where singlet-triplet conversion take place.

KW - HOMOGENEOUS HYDROGENATION

KW - INDUCED POLARIZATION

KW - RHODIUM

KW - DIHYDROGEN

KW - OLEFINS

KW - ACETYLENES

KW - CONVERSION

KW - KINETICS

KW - IRIDIUM

KW - STATES

UR - http://www.scopus.com/inward/record.url?scp=85020453812&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcc.7b01056

DO - 10.1021/acs.jpcc.7b01056

M3 - Article

AN - SCOPUS:85020453812

VL - 121

SP - 9879

EP - 9888

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 18

ER -