Heterolytic cleavage of dihydrogen

Dihydrogen is said to be heterolytically cleaved when it is dissociated into a proton and a metal bonded hydride. It has been the topic of much study and discussion, and the evidence for its occurrence has been growing steadily [54,55]. In the ideal case the heterolytic splitting is catalyzed by the metal ion and a base which assists in the abstraction of the proton. In this reaction there is no formal change in the oxidation state of the metal. The mechanism has been proposed for Ru(II) complexes which can react with dihydrogen according to  

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Scheme 10.2 Heterolytic cleavage of dihydrogen on platinum SPO complex.

The hydrogenase enzymes (1) catalyse the heterolytic cleavage of dihydrogen into protons and electrons,... 

SCHEME 4 SPO platinum catalysts. Top row stoichiometric hydroformylation with 1 middle row, catalyst 4 and hydrogen bond switching in 6 bottom row heterolytic cleavage of dihydrogen (69-71). (For a color version of this figure, the reader is referred to the Web version of this chapter.)... 

Figure 14 Proposed mechanism of heterolytic cleavage of dihydrogen...

Scheme 1. Steps in the heterolytic cleavage of dihydrogen on Ru(II) starting with the complex trans-Ru(0S02CF3)(CN)(dppe)2.

Heterolytic Cleavage of Dihydrogen by Ruthenium and Molybdenum Complexes... 

Recent studies using 2D ESEEM spectroscopy [28] has provided evidence that a conserved histidine amino acid residue (His-371) is close to the active site and is thus a good candidate for a base that may be required in the heterolytic cleavage of dihydrogen. 

Computational studies on the [NiFe] active site have been performed by a number of workers [198-214]. Theory supports high-spin nickel [189] and suggests that the sulfur atoms of the terminal cysteine ligands act as bases in the heterolytic cleavage of dihydrogen. 

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