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NMR Studies of the Reaction Path of the o-H-2/p-H-2 Spin Conversion Catalyzed by Vaska's Complex in the Solid State

Matthes, J. and Gründemann, S. and Buntkowsky, G. and Chaudret, B. and Limbach, H. H. (2013):
NMR Studies of the Reaction Path of the o-H-2/p-H-2 Spin Conversion Catalyzed by Vaska's Complex in the Solid State.
44, In: Applied Magnetic Resonance, (1-2), pp. 247-265, [Online-Edition: http://apps.webofknowledge.com/full_record.do?product=WOS&se...],
[Article]

Abstract

We have studied the o/p spin conversion of dihydrogen in contact with frozen solutions of Vaska's complex Ir(CO)Cl(PPh3)(2) (1) in C6D6 and with polycrystalline 1 at 77 K. The main purpose of this study was to elucidate the mechanism of this type of reactions found accidentally previously (Eisenschmid et al JACS 109:8089-8091, 1987 and Eisenberg ACS 24:110-116, 1991). The formation of p-H-2 was followed after thawing of the samples by H-1 nuclear magnetic resonance (NMR) spectroscopy at 298 K, where the oxidative addition of dihydrogen to 1 occurs leading to Vaska's dihydride Ir(CO)ClH2(PPh3)(2) (2) which is known to exhibit para-hydrogen-induced polarization (PHIP). The PHIP signal was shown to be proportional to the concentration of p-H-2 as elucidated from the decrease of the signal of dissolved o-H-2. The reaction was found to be faster for the frozen solution as compared to the polycrystalline powder. Optical microscopy showed that small particles of 1 are separated from the solution during the freezing process, exhibiting a larger surface area as compared to the polycrystalline powder. When a mixture of H-2 and D-2 was exposed to the frozen solutions or to the polycrystalline powder, the formation of HD was observed by H-1 NMR. This finding indicates the presence of a chemical spin conversion involving two dihydrogen molecules. Additional H-1 NMR experiments of dihydrogen in frozen C6D6 at 110 K indicated the formation of larger pores containing gaseous H-2 as well as dihydrogen sites in interstitial sites between benzene molecules. Moreover, in the presence of 1, a signal at -4.5 ppm was observed which was attributed to a dihydrogen in close contact with Ir.

Item Type: Article
Erschienen: 2013
Creators: Matthes, J. and Gründemann, S. and Buntkowsky, G. and Chaudret, B. and Limbach, H. H.
Title: NMR Studies of the Reaction Path of the o-H-2/p-H-2 Spin Conversion Catalyzed by Vaska's Complex in the Solid State
Language: English
Abstract:

We have studied the o/p spin conversion of dihydrogen in contact with frozen solutions of Vaska's complex Ir(CO)Cl(PPh3)(2) (1) in C6D6 and with polycrystalline 1 at 77 K. The main purpose of this study was to elucidate the mechanism of this type of reactions found accidentally previously (Eisenschmid et al JACS 109:8089-8091, 1987 and Eisenberg ACS 24:110-116, 1991). The formation of p-H-2 was followed after thawing of the samples by H-1 nuclear magnetic resonance (NMR) spectroscopy at 298 K, where the oxidative addition of dihydrogen to 1 occurs leading to Vaska's dihydride Ir(CO)ClH2(PPh3)(2) (2) which is known to exhibit para-hydrogen-induced polarization (PHIP). The PHIP signal was shown to be proportional to the concentration of p-H-2 as elucidated from the decrease of the signal of dissolved o-H-2. The reaction was found to be faster for the frozen solution as compared to the polycrystalline powder. Optical microscopy showed that small particles of 1 are separated from the solution during the freezing process, exhibiting a larger surface area as compared to the polycrystalline powder. When a mixture of H-2 and D-2 was exposed to the frozen solutions or to the polycrystalline powder, the formation of HD was observed by H-1 NMR. This finding indicates the presence of a chemical spin conversion involving two dihydrogen molecules. Additional H-1 NMR experiments of dihydrogen in frozen C6D6 at 110 K indicated the formation of larger pores containing gaseous H-2 as well as dihydrogen sites in interstitial sites between benzene molecules. Moreover, in the presence of 1, a signal at -4.5 ppm was observed which was attributed to a dihydrogen in close contact with Ir.

Journal or Publication Title: Applied Magnetic Resonance
Volume: 44
Number: 1-2
Uncontrolled Keywords: hydrogen-induced polarization parahydrogen-induced polarization transition-metal-complexes dihydrogen complexes h-2 nmr mechanism dynamics coherent iridium ligand
Divisions: 07 Department of Chemistry
07 Department of Chemistry > Physical Chemistry
Date Deposited: 27 Oct 2014 20:46
Official URL: http://apps.webofknowledge.com/full_record.do?product=WOS&se...
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074EU Times Cited:2 Cited References Count:38

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