H2 Activation by Heterolytic Addition

The real nature of the catalytic cycle is less documented but the H ligand appears to react very much as H  

Formally, no change in the oxidation state of Ru occurs. Although hydrogenolysis of Ru(II)-alkyl to give the alkane (rate determining step) could also occur via heterolytic cleavage of H2, it more probably occurs via an oxidative addition—reductive elimination sequence. 

Actually, RuCl2(PPli3)3 is one of the most active homogeneous catalyst for the hydrogenation of terminal olefins (they are hydrogenated at a rate about 10 times that of the corresponding internal ones). It is also very efficient for the reduction of —NO2 to — NH2 and aldehydes to alcohols. Nitriles, esters or hahdes remain unaffected. 

Another system where heterolytic cleavage has been evidenced is based on anionic Pt complexes. The commercially available H2PtCl2 and SnCl2 2 H2O react in methanol to form deep red solutions that contain species such as (A). 

The anionic hydrido species (B) is then believed to coordinate an olefin which is then inserted into the Pt—H bond. Presumably, protonolysis promotes the cleavage of the metal—alkyl bond. 

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