Iridium-phosphine complexes, reactions

The iridium phosphine complex [IrC PEt,),] 39b can also activate O-H bonds of carboxylic acids. The stoichiometric reaction with a,(o-alkynoic acids RC=C(CH2)2 CO2H (R = Me, Ph) gave cis-hydrido(carboxylato)iridium(III) complexes 92 (Eq. 6.26), and the molecular structure of 92a was determined crystallographically [59]. 

Support-bound transition metal complexes have mainly been prepared as insoluble catalysts. Table 4.1 lists representative examples of such polymer-bound complexes. Polystyrene-bound molybdenum carbonyl complexes have been prepared for the study of ligand substitution reactions and oxidative eliminations [51], Moreover, well-defined molybdenum, rhodium, and iridium phosphine complexes have been prepared on copolymers of PEG and silica [52]. Several reviews have covered the preparation and application of support-bound reagents, including transition metal complexes [53-59]. Examples of the preparation and uses of organomercury and organo-zinc compounds are discussed in Section 4.1. 

In contrast to the studies with the iridium-phosphine complexes, the very reactive complex shown in [10] reacts with alkyl halides as shown in (30), but in the presence of a large excess of LiCI the reaction of Bu"Br yields the chloro-complex under conditions where the corresponding bromo-complex does not exchange. These observations, together with the isolation of the intermediate, /ranj-[Rh(Me)(Et2mgBF2)(NCMe)] BF 4 and the reactivity order with respect to the alkyl group (Me > Et > secondary alkyl > cyclohexyl), supports an Sn2 mechanism (Collman and MacLaury, 1974). 

CPDN 394 is an important intermediate for the synthesis of corannulene 23 it can be prepared by [2-F2-F1] reaction of 1,8-diethynylnaphthalene 395 using Fe(CO)5 upon demetallation procedure (Scheme 6.97) [235]. Later, Shibata reported the iridium complex-catalyzed carbonylative alkyne-alkyne coupling, which provides 394 in high isolated yields without demetallation procedure. The iridium phosphine complexes, [IrCl(CO)2(PPh3)2l enables the catalytic coupling under carbon monoxide at atmospheric pressure or less (Scheme 6.97) [236]. 

In 1996, consumption in the western world was 14.2 tonnes of rhodium and 3.8 tonnes of iridium. Unquestionably the main uses of rhodium (over 90%) are now catalytic, e.g. for the control of exhaust emissions in the car (automobile) industry and, in the form of phosphine complexes, in hydrogenation and hydroformylation reactions where it is frequently more efficient than the more commonly used cobalt catalysts. Iridium is used in the coating of anodes in chloralkali plant and as a catalyst in the production of acetic acid. It also finds small-scale applications in specialist hard alloys. 

The fourth chapter gives a comprehensive review about catalyzed hydroamina-tions of carbon carbon multiple bond systems from the beginning of this century to the state-of-the-art today. As was mentioned above, the direct - and whenever possible stereoselective - addition of amines to unsaturated hydrocarbons is one of the shortest routes to produce (chiral) amines. Provided that a catalyst of sufficient activity and stabihty can be found, this heterofunctionalization reaction could compete with classical substitution chemistry and is of high industrial interest. As the authors J. J. Bmnet and D. Neibecker show in their contribution, almost any transition metal salt has been subjected to this reaction and numerous reaction conditions were tested. However, although considerable progress has been made and enantios-electivites of 95% could be reached, all catalytic systems known to date suffer from low activity (TOP < 500 h ) or/and low stability. The most effective systems are represented by some iridium phosphine or cyclopentadienyl samarium complexes. 

Brunner, Leitner and others have reported the enantioselective transfer hydrogenation of alpha-, beta-unsaturated alkenes of the acrylate type [50]. The catalysts are usually rhodium phosphine-based and the reductant is formic acid or salts. The rates of reduction of alkenes using rhodium and iridium diamine complexes is modest [87]. An example of this reaction is shown in Figure 35.8. Williams has shown the transfer hydrogenation of alkenes such as indene and styrene using IPA [88]. 

The methyl iridium dioxygen complex Ir(CH3)C0(02)[P(p-tolyl)3]2 reacts with added triphenylphosphine to produce triphenylphos-phine oxide (191). That this is a bimolecular reaction was demonstrated both by the complete absence of any oxidation of the tris(para-tolyl)-phosphine and by the lack of any substitution of the bound tris(para-tolyl)phosphine by triphenylphosphine. 

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