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Issue 1, 2013
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Hydrogen storage and evolution catalysed by metal hydride complexes

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Abstract

The storage and evolution of hydrogen are catalysed by appropriate metal hydride complexes. Hydrogenation of carbon dioxide by hydrogen is catalysed by a [C,N] cyclometalated organoiridium complex, [IrIII(Cp*)(4-(1H-pyrazol-1-yl-κN2)benzoic acid-κC3)(OH2)]2SO4 [Ir–OH2]2SO4, under atmospheric pressure of H2 and CO2 in weakly basic water (pH 7.5) at room temperature. The reverse reaction, i.e., hydrogen evolution from formate, is also catalysed by [Ir–OH2]+ in acidic water (pH 2.8) at room temperature. Thus, interconversion between hydrogen and formic acid in water at ambient temperature and pressure has been achieved by using [Ir–OH2]+ as an efficient catalyst in both directions depending on pH. The Ir complex [Ir–OH2]+ also catalyses regioselective hydrogenation of the oxidised form of β-nicotinamide adenine dinucleotide (NAD+) to produce the 1,4-reduced form (NADH) under atmospheric pressure of H2 at room temperature in weakly basic water. In weakly acidic water, the complex [Ir–OH2]+ also catalyses the reverse reaction, i.e., hydrogen evolution from NADH to produce NAD+ at room temperature. Thus, interconversion between NADH (and H+) and NAD+ (and H2) has also been achieved by using [Ir–OH2]+ as an efficient catalyst and by changing pH. The iridium hydride complex formed by the reduction of [Ir–OH2]+ by H2 and NADH is responsible for the hydrogen evolution. Photoirradiation (λ > 330 nm) of an aqueous solution of the Ir–hydride complex produced by the reduction of [Ir–OH2]+ with alcohols resulted in the quantitative conversion to a unique [C,C] cyclometalated Ir–hydride complex, which can catalyse hydrogen evolution from alcohols in a basic aqueous solution (pH 11.9). The catalytic mechanisms of the hydrogen storage and evolution are discussed by focusing on the reactivity of Ir–hydride complexes.

Graphical abstract: Hydrogen storage and evolution catalysed by metal hydride complexes

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Publication details

The article was received on 09 Aug 2012, accepted on 01 Oct 2012 and first published on 04 Oct 2012


Article type: Perspective
DOI: 10.1039/C2DT31823G
Citation: Dalton Trans., 2013,42, 18-28
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    Hydrogen storage and evolution catalysed by metal hydride complexes

    S. Fukuzumi and T. Suenobu, Dalton Trans., 2013, 42, 18
    DOI: 10.1039/C2DT31823G

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