Iridium derivatives

The reason for preferential axial site occupancy by mono-dentate ligands is probably related to results of recent CNDO calculations on [Co CO) ] (15) which show that the axial carbonyls are least involved in back-bonding. Extrapolation to Rh - and Ir -derivatives seems reasonable and finds some support from n.m.r. measurements, which show that the n.m.r. chemical shift of the axial carbonyl is always at higher field than the radial carbonyl in both rhodium (16) and iridium derivatives. (12)... 

Ir4(CO)ii(PPh3)149 The structures of the di- and tri-substituted iridium derivative are shown in Fig. 14. In all cases, the phosphines are around the basal plane. However, whereas the two phosphines are in relative trans-positions in the di-substituted compound, in the tris-derivative two of the phosphines are obliged to occupy relative c/s-position and, as a result, are involved in more steric interaction. 

Over the last years, one of the most studied DCR has been the asymmetric version of the cycloaddition of nitrones with alkenes. This reaction leads to the construction of up to three contiguous asymmetric carbon centers (Scheme 4). The resulting five-membered isoxazolidine derivatives may be converted into amino alcohols, alkaloids, or p-lactams. Several chiral metal complexes have been used as catalysts for this process [13-15, 18-22]. However, the employment of iridium derivatives is very scarce. 

The above-mentioned complexes are the sole iridium derivatives applied to DCR, and the cycloaddition of nitrones to enals or methacrylonitrile, the unique process studied. We think that iridium-based catalysts are underrepresented in 1,3-dipolar cycloaddition chemistry. For example, no iridium (1) systems have been developed to this end. It can be anticipated that the (bidentate ligand)lr(l) fragment could be active (and stereoselective if chiral bidentate ligands are used) in DCR such as those involving azomethine ylides. 

Recently, Kaska and coworkers ]37] reported a rigid PCP pincer system based on an anthracene backbone (29) (Scheme 13.17). The iridium derivative of this... 

Ma et al. (4) prepared organic light-emitting devices (OLED) where the organic layer consisted of an iridium derivative having two or three bidentate ligands, (VII), which showed improved stability and efficiency when incorporated into an OLED. 

Crabtree and Chianese have extended the scope of Hoveyda s ligand by making the imidazolium salt 39 in two steps from l,l/-diamino-2,2/-binaphthyl (Fig. 10) [80]. They prepared neutral rhodium and iridium complexes with that ligand precursor and applied these complexes in the asymmetric hydrosilylation of acetophenone. Moderate enantioselectivities were obtained with the iridium derivative (up to 60% ee) whilst the rhodium catalysts only gave low enantioselectivities. 

Iridium-containing copolymers have been prepared by postreacting fluorene-or biphenyl copolymers with a cyclic bidentate ligand iridium derivatives. These block copolymers demonstrate exceptionally high luminescent efficiency. 

Aluminium-pyrazol-5-one derivatives, (I), prepared by Kathirgamanathan [1] were effective as white light emitters and used in organic electroluminescent devices. Bis(2-phenylimidazo[l,2-a]pyridinato-N,C)iridium derivatives, (II), prepared by Lussier [2] were effective as phosphorescent emission agents. 

Iridium is a third-row d-block metal and is the heaviest element in group 9. It is a hard, lustrous, silvery metal, discovered by Tennant in 1803 the name iridium derives from the Latin iris (rainbow). The element occurs as a native platinum alloy and in osmiridium (a native alloy of osmium, 15-40%, and iridium, 50-80%). Selected physical and chemical properties of Ir are given in Table 1. It is considered both as a platinum metal and as a precious metal. At room temperature, Ir is particularly resistant to corrosion. 

Other rhodium and iridium derivatives show spectra with a similar band pattern, with the iridium compounds having the broader and more structured d-band in line with greater ligand field splittings for the heavier metal. 

Stable metal (Ir, Ru, Os, Au)-carbene complexes of such pyridinium and related ylides have been isolated, including an iridium derivative by direct preparation from pyridine. )... 

Current-voltage characteristics of an OPD which consists of ITO (150nm)/PFO with iridium derivatives (30rtm)/CuPc (30rtm)/Au (30nm) under dark and violet light by Xe arc lamp (X=380nm) irradiation. Three kinds of devices are shown for PFO, PFO with FIrpic, and PFO with (btp)2lr(acac). Closed and open symbols show photocurrent in dark and illuminated conditions, respectively. 

Several types of reaction of Ir4(CO)i2 have been investigated. The iridium derivative Iri (C0)i2f unlike its cobalt and rhodium analogs Mi (C0)i2 (M = Co... 

Pra(CX))(PHi2R)2(n C6o)] (R = C 5CH20QH4CH2-) revealed that the pendant arms of the pho hine ligands fomied a cradle around the C60 poiticMis of adjacent mcdecules, giving an infinite chain stnicture. The crystal structures of the di-iridium derivatives ( fr(CX))a(PMe )2)2(Qi)l (n = 60 and 70) have been reported -. ... 

Labeling of one of the proteins of the SOS ribosome was quantitatively achieved by reaction of 31 in solution. Qystals of the reconstituted ribosome particle were found to be isomorphous with those of the native particle [68]. In order to enable reliable assignments of the various components of the small ribosomal subunit T30S, this particle was labeled with 31. A 7.2 A MIR map was constructed from sets of X-ray diffraction data recorded for the native and derivatized ribosome subunit crystals and one major and one minor binding site were located. This iridium derivative was thus helpful to construct a medium-resolution MIR map for a biological particle [69]. 

Thus, as is the case for the st pincer derivatives with nickel, Moulton and Shaw also reported the first PCP pincer rhodium and iridium derivatives and studied their reactivity toward carbon monoxide [4]. Hence, the (PCP) rhodium derivative (38) affords complex (40), as a product of the decomposition of the unstable hydrido chloro carbonyl intermediate (39) via a hydrodechlorination process, although this compound is obtained impure. To favor the hydrodechlorination process, an alternative route was attempted employing EtONa as base. This approach afforded exclusively compound (40) (Scheme 2.21). It is noteworthy that analogous reactions with the iridium analogous to complex (38) only afford impure samples of the carbonyl species analogous to complex (40). 

Evidence for the desulfurization of thiophene by cobaltocene or Cp Co(C2H4)2 was obtained when a dimethylthio-phene adduct of iridium was treated with these organocobalt compounds (Scheme 56)." The proposed mechanism is analogous to the one proposed earlier when the same iridium derivative was treated with iron carbonyl compounds. This type of desulfurization reactivity is consistent with the Involvement of rf- or ring-opened thiophenes in hydrodesulfuration (HDS), as proposed earlier." ... 

---