Iridium catalysis addition with

Since iridium(I) readily undergoes oxidative addition with H2, studying hydrogenation catalysis with iridinm... 

It is interesting to note that, when operating at approximately 5% water content, and with good reaction rates, it is possible to save about 30% of the energy costs of the process when compared to the Monsanto process. In addition, the current price of rhodium is 20-fold that of iridium. Even with annual unit capacity productions as large as 500 000 tons, it is still possible to improve catalysis and to achieve significantly better performances. 

Catalysis of hydrosilylation by dimeric or by monomeric rhodium (and iridium) siloxide complexes occurs via preliminary oxidative addition of siUcon hydride followed by elimination of disiloxane (detected by GC/MS) to generate the square planar 16e hydride complex with an already coordinated molecule of alkene (Scheme 7.7). 

Two classes of promoter have been identified for iridium catalysed carbonylation (i) transition metal carbonyls or halocarbonyls (ri) simple group 12 and 13 iodides. Increased rates of catalysis are achieved on addition of 1-10 mole equivalents (per Ir) of the promoter. An example from each class was chosen for spectroscopic study. An Inis promoter provides a relatively simple system since the main group metal does not tend to form carbonyl complexes which can interfere with the observation of iridium species by IR. In situ HP IR studies showed that an indium promoter (Inl3 Ir = 2 1) did not greatly affect the iridium speciation, with [MeIr(CO)2l3] being converted into [Ir(CO)2l4] as the batch reaction progressed, as in the absence of promoter. 

In addition to transfer hydrogenation reactions, arene ruthenium complexes also display excellent activity in the catalytic hydrogenation of olefins and alkynes including asymmetric reduction [40]. Remarkably, this process occurs under milder conditions, than required for catalysis with the dissociation of arene-metal bond. Lately, arene iridium complexes have also been found to be effective hydrogenation catalysts [41 ]. It is noteworthy that iridium can also promotes addition to the carbon-nitrogen double bond. 

In addition to iridium and cobalt catalysis, and following the work initiated by Cavell et al. [138] on the alkylation of azolium salts, nickel-catalyzed alkylations of various heteroarenes (i.e., indoles [139], benzimidazoles [139], benzothiazoles [139], benzoxazoles [139], 1,3,4-oxadiazoles [140]) with olefins have been reported (Scheme 19.95 and Scheme 19.96). These reactions proved complementary to other methods because they proceeded with the Markovnikov regioselectivity with respect to the olefin. 

Pincer-ligated metal complexes have displayed extraordinarily rich chemistry and have found widespread use in catalysis. Pincer complexes of numerous transition metals have been synthesized, but the most well-studied probably involve Ru, Rh, Ir, and Pd [1-7], Our group has largely focused on pincer-iridium complexes, which have shown a strong tendency toward the activation of C-H bonds. These complexes have been found to effect the oxidative addition of a variety of C-H bonds including those with sp - and sp-hybridized carbon [8-10], Most notable, however, has been the activation of C(sp )-H bonds, leading to alkane dehydrogenation [6, 7],... 

---