Iridium complexes with -

Scheme 8.18 Hydrogenations of olefins with iridium complexes containing dithio-ether ligands with a pyrrolidine backbone.

Scheme 8.22 Hydrogenation of acetamidoacrylic acid with iridium complexes containing dithioether ligands.

During recent years, substantial progress has been made in the hydrogenation of unfunctionalized alkenes. With iridium complexes derived from chiral phos-phino-oxazolines and related ligands, excellent enantioselectivities and high TON/TOF values can now be obtained for a wide range of unfunctionalized olefins. Most substrates studied to date have at least one aryl substituent at the... 

W Zhu, Y Mo, M Yuan, W Yang, and Y Cao, Highly efficient electrophosphorescent devices based on conjugated polymers doped with iridium complexes, Appl. Phys. Lett., 80 2045-2047, 2002. 

X Gong, JC Ostrowski, GC Bazan, D Moses, and AJ Heeger, Red electrophosphorescent from polymer doped with iridium complex, Appl. Phys. Lett., 81 3711-3713, 2002. 

Initial studies with iridium complexes derived from chiral phosphinooxazolines (PHOX ligands) and (E)- ,2-diphenyl-1-propene as substrate gave encouraging results (Scheme 1) [5, 15]. With 4 mol% of catalyst (X = PFs ) at 10-50 bar hydrogen pressure, up to 98% ee could be obtained. However, the turnover numbers were disappointingly low. 

Cycloisomerization represents another approach for the construction of cyclic compounds from acyclic substrates, with iridium complexes functioning as efficient catalysts. The reaction of enynes has been widely studied for example, Chatani et al. reported the transformation of 1,6-enynes into 1-vinylcyclopentenes using [lrCl(CO)3]n (Scheme 11.26) [39]. In contrast, when 1,6-enynes were submitted in the presence of [lrCl(cod)]2 and AcOH, cyclopentanes with two exo-olefin moieties were obtained (Scheme 11.27) [39]. Interestingly, however, when the Ir-DPPF complex was used, the geometry of olefinic moiety in the product was opposite (Scheme 11.28) [17]. The Ir-catalyzed cycloisomerization was efficiently utilized in a tandem reaction along with a Cu(l)-catalyzed three-component coupling, Diels-Alder reaction, and dehydrogenation for the synthesis of polycyclic pyrroles [40]. 

Another chemical approach to the chemical conversion of methane involves organometallic reactions.85-89 Interesting work with iridium complexes and other transition metal insertion reactions (rhodium, osmium, rhenium, etc.) were carried out. Even iron organometallics were studied. These reactions take place in the coordination spheres of the metal complexes, but so far the reactions are stoichiometric and noncatalytic.77 In terms of synthetic hydrocarbon chemistry, these conversions are thus not yet practical, but eventually it is expected that catalytic reactions will be achieved. 

The main methods of reducing ketones to alcohols are (a) use of complex metal hydrides (b) use of alkali metals in alcohols or liquid ammonia or amines 221 (c) catalytic hydrogenation 14,217 (d) Meerwein-Ponndorf reduction.169,249 The reduction of organic compounds by complex metal hydrides, first reported in 1947,174 is a widely used technique. This chapter reviews first the main metal hydride reagents, their reactivities towards various functional groups and the conditions under which they are used to reduce ketones. The reduction of ketones by hydrides is then discussed under the headings of mechanism and stereochemistry, reduction of unsaturated ketones, and stereochemistry and selectivity of reduction of steroidal ketones. Finally reductions with the mixed hydride reagent of lithium aluminum hydride and aluminum chloride, with diborane and with iridium complexes, are briefly described. 

This chapter will not deal with iridium complexes in which the coordination chemistry of the iridium-carbon bond is implicated inasmuch as Leigh and Richards have very recently (1982) provided an excellent detailed review on such compounds organoiridium2 and iridium carbonyl3 complexes were also previously reviewed. Iridium complex chemistry has been reviewed (1980) along with rhodium,4 and in annual reviews.3 Additionally, iridium complexes have been treated in Comprehensive Inorganic Chemistry .6... 

Since those initial reports, there have been a number of reports of C-H activation with iridium complexes, induced both thermally andphotochemically. Werner has demonstrated a number of iridium systems with bulky ligands that are capable of adding C-H bonds. [Ir(COD)(PMe3)3]Cl (11) will react with aromatic C-H bonds thermally to yield octahedral iridium(III) complexes of the form mer-(Me3P)3lr(H)(Ar)(Cl) (103).i >i3 ... 

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