Reactions of Dihydrogen

In the reactions above we have not explicitly touched upon the reactions of dihydrogen and transition metal complexes. Here the reactions that involve the activation of dihydrogen will be summarised, because they are very common in homogeneous catalysis and because a comparison of the various mechanisms involved may be useful. Three reactions are usually distinguished for hydrogen ... 

The catalases catalyze the disproportionation reaction of dihydrogen peroxide according to the following equation (Eq. 5) [5] ... 

The catalytic cycle starts with the dissociation of one ligand P which is replaced e.g. by a solvent molecule. An oxidative addition reaction of dihydrogen... 

The two most important mechanisms involve the reaction of an alkene with dihydrido complexes or, the reverse of this, the reaction of dihydrogen with an alkene complex. The third process, known as the alkyl route, is of limited applicability and may give rise to substantial quantities of by-products. 

Oxidative addition reactions of dihydrogen , iodine ", alkyl halides and Hg(CN)2 to carbonyl, olefin or phosphine substituted derivatives of rhodium(I) and iridium(I) have been described. In order to determine the effect on the rate of the reaction, the kinetics of the oxidative addition of Hg(CN)2 to Rh(dik)(P(OPh)3)2 has been studied . A second-order rate law coupled to large negative values of the activation entropy suggest an associative mechanism which probably proceeds via a cyclic three-centred transition state (equation 58). Analogous results were obtained with Ir(dik)(cod) . ... 

Reaction of dihydrogen complex 4 with phenylethyne gives vinylidene 5 as shown. No other reagents are required for this reaction. Propose a pathway from 4 to 5. [Hint The first step probably involves elimination of HC1.]10S... 

Some substances can act as a Bronsted-Lowry acid in one reaction and a Bronsted-Lowry base in another. Consider the following net ionic equations for the reaction of dihydrogen phosphate ion with either the acid hydrochloric acid or the strong base hydroxide. 

The remainder of this chapter presents the reactions of nonpolar reagents with a range of metals. The reactions of dihydrogen are presented first the reactions of silanes are presented second because they often react like dihydrogen. The additions of C-H bonds are presented third examples of intramolecular additions of C-H bonds are presented before intermolecular examples. This chapter closes with a discussion of the oxidative addition of C-C bonds. 

Fu X, Wayland BB (2004) Equilibrium thermodynamic studies in water reactions of dihydrogen with rhodium(lll) porphyrins relevant to Rh-Rh, Rh-H, and Rh-OH bond energetics. J Am Chem Soc 126(8) 2623-2631... 

Such a stoichiometric branching reaction is endothermic, its A//=+79 kJ/mol. In the chain reaction of dihydrogen with fluorine branching proceeds through three successive stages (see below) according to the empirical equation... 

As simple prototype examples, let us first consider two elementary gas-phase reactions that were previously encountered in Problem 4.1, both leading to production of formaldehyde (H2CO, product species Pj). The first involves bimolecular reaction of dihydrogen and carbon monoxide (H2- CO, reactant species Rn), namely. 

Complexes 3.2 and 2.59 were mentioned earlier. The former was isolated as a solid from the reaction of dihydrogen with 2.58. The latter, as mentioned earlier, is a precatalyst for hydroformylation, and was also made using Wilkinson s complex. 

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