Iridium electronic properties

An iridium(I) complex with the l,2-bis(tcrt-butylmethylphosphino)ethane (4) and tetrakis(3,5-bis(trifluoromethyl)phenyl)borate as the counter anion catalyzes the hydrogenation of several acyclic aromatic Ai-arylimines under atmospheric hydrogen pressure at room temperature, giving the desired chiral amines with high-to-excellent enantioselectivities (up to 99%, Fig. 6) [19]. The authors also tested (S )-BINAP (Fig. 1) and (/ )-Ph-PHOX (PHOX = 2-[2-(diphenylphosphino) phenyl]-4,5-dihydrooxazole) hgands with lower enantioselectivities [19]. Both steric and electronic properties of the ligand and the combination with the BArF anion are in the base of the efficacy of this catalytic system. On the other hand, attempted hydrogenations of Ai-(2,2,2-trifluoro-l-phenylethylidene)aniline and M-(l,2,2-trimethyl-propylidene)aniline under the same conditions resulted in... 

Tetrahedral perchlorate ion, [C104] , is an uncommon ligand.1 The molecular perchlorato complexes of iridium and rhodium2 described here are thus of inherent interest as such, but their principal importance lies in their versatile reactivity. These compounds undergo addition, substitution, and addition-substitution reactions with many molecules and ions.3 In particular, the latter conversions lead to a remarkable number of cationic d8 complexes of these metals, which offer themselves as a unique series for a study of the electronic properties of a variety of molecules as ligands (L).3 Not less significant are the substitution reactions in which the perchlorate ligand is replaced by other unusual anions.4... 

The rhodium complexes are more resistant towards oxidative addition than their iridium counterparts and this is believed to be linked to steric crowding, especially when employing bulky tertiary phosphine ligands. Work by Wilkinson explored several aspects of the steric and electronic properties of the rhodium(i) analogues, but definite crystal structural confirmation of the reaction... 

Supported iridium clusters on oxides were intensively investigated [267] because they form rather stable metal frames such as Ir4. Despite the substantial work on such samples, questions remained due to limitations of EXAFS spectroscopy widely used for the characterization and the lack of other experimental techniques suitable for investigating metal species dispersed in porous solids. To clarify how the interaction with a zeolite framework can modify the structural and electronic properties of small supported metal particles, we carried out a scalar relativistic DKH DF study of the interaction between fr4 clusters and a zeolite fragment, using a cluster model of a faujasite six-ring [268]. 

Polysilanes are also applicable as matrix materials in phosphorescent OLEDs. Mixtures of polysilanes and triplet emitters are sufficient to effect an energy transfer from polysilane triplet states to emitter triplet states, thus amplifying the luminescence of the device. It has been shown that if polysilanes have electrophosphorescent side chains consisting of triplet emitters, the energy transfer from polysilane to emitter is most effective [124]. Thus the beneficial electronic properties of polysilanes are perfectly combined with the spectroscopic properties of transition metal based triplet emitters. The compounds described are derivatives of polymethylphenylsi-lanes, (Fig. 24) which are covalently attached to triplet emitters with iridium as metal centre. The polymers were applied in OLEDs with an ITO/active layer/Ca/Ag layer sequence. The active layer contained a fraction of 70% by weight of the... 

The Iridium-catalyzed borylation reaction was found to he suitable for arenes possessing various functional groups such as OMe, halides, COOMe, CN, CF3, and benzyhc C-H bonds. Because the borylation reaction is not electrophihc aromatic substitution, the electronic property of the substituents has httle influence on regioselectivity. The reactions of monosubstituted arenes result in a mixture of meta- and para-products in statistical ratios (ca. 2 1) in most cases. Regioisomerically pure products were obtained in... 

It is a matter of historical interest that Mossbauer spectroscopy has its deepest root in the 129.4 keV transition line of lr, for which R.L. Mossbauer established recoilless nuclear resonance absorption for the first time while he was working on his thesis under Prof. Maier-Leibnitz at Heidelberg [267]. But this nuclear transition is, by far, not the easiest one among the four iridium Mossbauer transitions to use for solid-state applications the 129 keV excited state is rather short-lived (fi/2 = 90 ps) and consequently the line width is very broad. The 73 keV transition line of lr with the lowest transition energy and the narrowest natural line width (0.60 mm s ) fulfills best the practical requirements and therefore is, of all four iridium transitions, most often (in about 90% of all reports published on Ir Mossbauer spectroscopy) used in studying electronic stractures, bond properties, and magnetism. 

In order to explain the changing optical properties of AIROFs several models were proposed. The UPS investigations of the valence band of the emersed film support band theory models by Gottesfeld [94] and by Mozota and Conway [79, 88]. The assumption of nonstoichiometry and electron hopping in the model proposed by Burke et al. [87] is not necessary. Recent electroreflectance measurements on anodic iridium oxide films performed by Gutierrez et al. [95] showed a shift of optical absorption bands to lower photon energies with increasing anodic electrode potentials, which is probably due to a shift of the Fermi level with respect to the t2g band [67]. 

It is important to note that the strong electron-donating properties of diphenylphosphinoferrocene are able to stabilize the central iridium atom in the unusual 0 and —I oxidation states. 

In order to vary the electronic situation at the carbene carbon atom a number of carbo- and heterocycle-annulated imidazolin-2-ylidenes like the benzobis(imida-zolin-2-ylidenes) [58-60] and the singly or doubly pyrido-annulated A -heterocyclic carbenes [61-63] have been prepared and studied. Additional carbenes derived from a five-membered heterocycle like triazolin-5-ylidenes 10 [36], which reveals properties similar to the imidazolin-2-ylidenes 5 and thiazolin-2-ylidene 11 [37] exhibiting characteristic properties comparable to the saturated imidazolidin-2ylidenes 7 have also been prepared. Bertrand reported the 1,2,4-triazolium dication 12 [64]. Although all attempts to isolate the free dicarbene species from this dication have failed so far, silver complexes [65] as well as homo- and heterobimetallic iridium and rhodium complexes of the triazolin-3,5-diylidene have been prepared [66]. The 1,2,4-triazolium salts and the thiazolium salts have been used successfully as precatalysts for inter- [67] and intramolecular benzoin condensations [68]. 

The iridium-catalysed hydrosilylation of alkynes in the presence of 4,4, 5,5,-tetra-methylbiphosphinine (tmbp) has been explored and shown to proceed effectively to afford /S-( >vinylsilanes with high selectivity in moderate to high yields, whereas a similar hydrosilylation in the absence of tmbp produced /i-(Z)-vinyl si lanes. This stereoselectivity reversal is believed to be a function of the electron-withdrawing properties of tmbp coordinated to iridium.111... 

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