Ligands dehydrogenation

Theoretical studies of catalytic alkane-dehydrogenation reactions by [(PCP )IrH2], PCP rf-C6H3(CH2P112)2-l, 3 and [cpIr(PH3)(H)]+, suggest that they proceed through similar steps in both cases namely (i) alkane oxidation, (ii) dihydride reductive elimination, (iii) /3-II transfer from alkyl ligand to metal, (iv) elimination of olefin.402 The calculated barriers to steps (i), (ii), and (iv) are more balanced for the PCP system than for cp(PH3). 

Dithiolate ligands are of interest in biological and materials chemistry, and zinc polysulfido complexes can effect the dehydrogenative conversion of alkenes into dithiolates (Scheme 2). 

The chemistry of the multistep reactions of Ti+ with propylene was also examined. Bare Ti+ exhibits an active reactivity toward breaking C-H bonds of the alkene molecules. But, the coordination of ligands on Ti+ was found to dramatically alter its dehydrogenation reactivity. For propylene, the multistep reactions were terminated at the fourth step, whereas the reactions with ethylene molecules were found to proceed far beyond the fourth step. Over 20 ethylene molecules have been... 

In summary a few "generalizations" have been found. First, size selective chemistry is strongly associated with chemisorption that requi res bond-breaking. Second, metal clusters react rapidly with ligands that molecularly chemisorb even when the eventual products involve dissociation of the ligand. Dehydrogenation of Cg-alkanes on small platinum clusters take exception to this. 

Oxidative dehydrogenations of many macrocyclic ligand complexes have now been documented. Typically, these reactions involve conversion of coordinated secondary amines to imine groups. 

By using combinations of hydrogenation and dehydrogenation reactions it has been possible to obtain nickel derivatives of the Curtis macrocycle containing from zero to four imine groups (Curtis, 1968 1974). Related reactions in the presence of a variety of other central metal ions have been described. The electrochemical oxidation of the Cu(ii) complex of the reduced Curtis ligand proceeds initially via a two-electron step to yield the monoimine complex (296) (Olson Vasilevskis, 1971). 

The plausible mechanism of this ruthenium-catalyzed isomerization of allylic alcohols is shown in Scheme 15. This reaction proceeds via dehydrogenation of an allylic alcohol to the corresponding unsaturated carbonyl compound followed by re-addition of the metal hydride to the double bond. This mechanism involves dissociation of one phosphine ligand. Indeed, the replacement of two triphenylphosphines by various bidentate ligands led to a significant decrease in the reactivity.37... 

---