TY - JOUR

T1 - Manipulating stereoselectivity of parahydrogen addition to acetylene to unravel interconversion of ethylene nuclear spin isomers

AU - Sviyazov, Sergey V.

AU - Babenko, Simon V.

AU - Skovpin, Ivan V.

AU - Kovtunova, Larisa M.

AU - Chukanov, Nikita V.

AU - Stakheev, Alexander Yu

AU - Burueva, Dudari B.

AU - Koptyug, Igor V.

N1 - (grant №23-23-00394)

PY - 2024/2/6

Y1 - 2024/2/6

N2 - Symmetric molecules exist as distinct nuclear spin isomers (NSIMs). A deeper understanding of their properties, including interconversion of different NSIMs, requires efficient techniques for NSIM enrichment. In this work, selective hydrogenation of acetylene with parahydrogen (p-H2) was used to achieve the enrichment of ethylene NSIMs and to study their equilibration processes. The effect of the stereoselectivity of H2 addition to acetylene on the imbalance of ethylene NSIMs was experimentally demonstrated by using three different heterogeneous catalysts (an immobilized Ir complex and two supported Pd catalysts). The interconversion of NSIMs with time during ethylene storage was studied using NMR spectroscopy by reacting ethylene with bromine water, which rendered the p-H2-derived protons in the produced 2-bromoethan(2H)ol (BrEtOD) magnetically inequivalent, thereby revealing the non-equilibrium nuclear spin order of ethylene. A thorough analysis of the shape and transformation of the 1H NMR spectra of hyperpolarized BrEtOD allowed us to reveal the initial distribution of produced ethylene NSIMs and their equilibration processes. Comparison of the results obtained with three different catalysts was key to properly attributing the derived characteristic time constants to different ethylene NSIM interconversion processes: ∼3-6 s for interconversion between NSIMs with the same inversion symmetry (i.e., within g or u manifolds) and ∼1700-2200 s between NSIMs with different inversion symmetries (i.e., between g and u manifolds).

AB - Symmetric molecules exist as distinct nuclear spin isomers (NSIMs). A deeper understanding of their properties, including interconversion of different NSIMs, requires efficient techniques for NSIM enrichment. In this work, selective hydrogenation of acetylene with parahydrogen (p-H2) was used to achieve the enrichment of ethylene NSIMs and to study their equilibration processes. The effect of the stereoselectivity of H2 addition to acetylene on the imbalance of ethylene NSIMs was experimentally demonstrated by using three different heterogeneous catalysts (an immobilized Ir complex and two supported Pd catalysts). The interconversion of NSIMs with time during ethylene storage was studied using NMR spectroscopy by reacting ethylene with bromine water, which rendered the p-H2-derived protons in the produced 2-bromoethan(2H)ol (BrEtOD) magnetically inequivalent, thereby revealing the non-equilibrium nuclear spin order of ethylene. A thorough analysis of the shape and transformation of the 1H NMR spectra of hyperpolarized BrEtOD allowed us to reveal the initial distribution of produced ethylene NSIMs and their equilibration processes. Comparison of the results obtained with three different catalysts was key to properly attributing the derived characteristic time constants to different ethylene NSIM interconversion processes: ∼3-6 s for interconversion between NSIMs with the same inversion symmetry (i.e., within g or u manifolds) and ∼1700-2200 s between NSIMs with different inversion symmetries (i.e., between g and u manifolds).

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85186148360&origin=inward&txGid=137ccf19af65295af8c88345741d051a

UR - https://www.mendeley.com/catalogue/50c35f9b-d2d2-3890-a91d-9a44f45742e3/

U2 - 10.1039/d3cp04983c

DO - 10.1039/d3cp04983c

M3 - Article

C2 - 38375632

VL - 26

SP - 7821

EP - 7829

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 9

ER -