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Issue 12, 2016
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Photochemical pump and NMR probe to monitor the formation and kinetics of hyperpolarized metal dihydrides

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Abstract

On reaction of IrI(CO)(PPh3)21 with para-hydrogen (p-H2), Ir(H)2I(CO)(PPh3)22 is formed which exhibits strongly enhanced 1H NMR signals for its hydride resonances. Complex 2 also shows similar enhancement of its NMR spectra when it is irradiated under p-H2. We report the use of this photochemical reactivity to measure the kinetics of H2 addition by laser-synchronized reactions in conjunction with NMR. The single laser pulse promotes the reductive elimination of H2 from Ir(H)2I(CO)(PPh3)22 in C6D6 solution to form the 16-electron precursor 1, back reaction with p-H2 then reforms 2 in a well-defined nuclear spin-state. The build up of this product can be followed by incrementing a precisely controlled delay (τ), in millisecond steps, between the laser and the NMR pulse. The resulting signal vs. time profile shows a dependence on p-H2 pressure. The plot of kobs against p-H2 pressure is linear and yields the second order rate constant, k2, for H2 addition to 1 of (3.26 ± 0.42) × 102 M−1 s−1. Validation was achieved by transient-UV-vis absorption spectroscopy which gives k2 of (3.06 ± 0.40) × 102 M−1 s−1. Furthermore, irradiation of a C6D6 solution of 2 with multiple laser shots, in conjunction with p-H2 derived hyperpolarization, allows the detection and characterisation of two minor reaction products, 2a and 3, which are produced in such low yields that they are not detected without hyperpolarization. Complex 2a is a configurational isomer of 2, while 3 is formed by substitution of CO by PPh3.

Graphical abstract: Photochemical pump and NMR probe to monitor the formation and kinetics of hyperpolarized metal dihydrides

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Publication details

The article was received on 04 May 2016, accepted on 03 Aug 2016 and first published on 05 Aug 2016


Article type: Edge Article
DOI: 10.1039/C6SC01956K
Citation: Chem. Sci., 2016,7, 7087-7093
  • Open access: Creative Commons BY-NC license
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    Photochemical pump and NMR probe to monitor the formation and kinetics of hyperpolarized metal dihydrides

    B. Procacci, P. M. Aguiar, M. E. Halse, R. N. Perutz and S. B. Duckett, Chem. Sci., 2016, 7, 7087
    DOI: 10.1039/C6SC01956K

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