Efficient catalytic interconversion between NADH and NAD + accompanied by generation and consumption of hydrogen with a water-soluble iridium complex at ambient pressure and temperature

Abstract

Regioselective hydrogenation of the oxidized form of β-nicotinamide adenine dinucleotide (NAD +) to the reduced form (NADH) with hydrogen (H 2) has successfully been achieved in the presence of a catalytic amount of a [C,N] cyclometalated organoiridium complex [Ir III(Cp)(4- (1H-pyrazol-1-yl-κN 2)benzoic acid-κC 3)(H 2O)] 2 SO 4 [1] 2·SO 4 under an atmospheric pressure of H 2 at room temperature in weakly basic water. The structure of the corresponding benzoate complex Ir III(Cp)(4-(1H-pyrazol-1-yl-κN 2)-benzoate- κC 3)(H 2O) 2 has been revealed by X-ray single-crystal structure analysis. The corresponding iridium hydride complex formed under an atmospheric pressure of H 2 undergoes the 1,4-selective hydrogenation of NAD + to form 1,4-NADH. On the other hand, in weakly acidic water the complex 1 was found to catalyze the hydrogen evolution from NADH to produce NAD + without photoirradiation at room temperature. NAD + exhibited an inhibitory behavior in both catalytic hydrogenation of NAD + with H 2 and H 2 evolution from NADH due to the binding of NAD + to the catalyst. The overall catalytic mechanism of interconversion between NADH and NAD + accompanied by generation and consumption of H 2 was revealed on the basis of the kinetic analysis and detection of the catalytic intermediates. © 2011 American Chemical Society.