Role of the reaction intermediates in determining PHIP (parahydrogen induced polarization) effect in the hydrogenation of acetylene dicarboxylic acid with the complex [Rh (dppb)]+ (dppb: 1,4-bis(diphenylphosphino)butane)

Abstract

Articles you may be interested inThis study deals with the parahydrogenation of the symmetric substrate acetylene dicarboxylic acid catalyzed by a Rh(I) complex bearing the chelating diphosphine dppb (1,4-bis(diphenylphosphino)butane). The two magnetically equivalent protons of the product yield a hyperpolarized emission signal in the 1 H-NMR spectrum. Their polarization intensity varies upon changing the reaction solvent from methanol to acetone. A detailed analysis of the hydrogenation pathway is carried out by means of density functional theory calculations to assess the structure of hydrogenation intermediates and their stability in the two solvents. The observed polarization effects have been accounted on the basis of the obtained structures. Insights into the lifetime of a short-lived reaction intermediate are also obtained. © 2014 AIP Publishing LLC.

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“… The addition of parahydrogen to the unsaturated precursor should occur in a pairwise manner. Pairwise addition implies that two hydrogen atoms from the same H 2 molecule are included in the product molecule together as a pair, thus preserving spin correlation between the two proton spins. The characteristic nuclear spin relaxation time for para ‐H 2 ‐nascent protons should be longer than the time needed to complete the pairwise hydrogenation process. The magnetic equivalence of the two correlated nuclear spins should be broken during the hydrogenation or in the product of the hydrogenation reaction …”

“…The magnetic equivalence of the two correlated nuclear spins should be broken during the hydrogenation or in the product of the hydrogenation reaction …”