Pyridine, complexes, with iridium

Fig. 7.63 Mossbauer spectra of some hexacoordinated ammine and pyridine complexes of trivalent iridium taken at 4.2 K with a source of Os in Os metal. The stick spectra indicate the positions and relative intensities of the individual resonance lines (from [285])...

Ruthenium complexes mediate the hydroamination of ethylene with pyridine.589 The reaction, however, is not catalytic, because of strong complexation of the amine to metal sites. Iridium complexes with chiral diphosphine ligands and a small amount of fluoride cocatalyst are effective in inducing asymmetric alkene hydroamination reaction of norbomene with aniline [the best enantiomeric excess (ee) values exceed 90%].590 Strained methylenecyclopropanes react with ring opening to yield isomeric allylic enamines 591... 

Imidazolium ligands, in Rh complexes, 7, 126 Imidazolium salts iridium binding, 7, 349 in silver(I) carbene synthesis, 2, 206 Imidazol-2-ylidene carbenes, with tungsten carbonyls, 5, 678 (Imidazol-2-ylidene)gold(I) complexes, preparation, 2, 289 Imidazopyridine, in trinuclear Ru and Os clusters, 6, 727 Imidazo[l,2-a]-pyridines, iodo-substituted, in Grignard reagent preparation, 9, 37—38 Imido alkyl complexes, with tantalum, 5, 118—120 Imido-amido half-sandwich compounds, with tantalum, 5,183 /13-Imido clusters, with trinuclear Ru clusters, 6, 733 Imido complexes with bis-Gp Ti, 4, 579 with monoalkyl Ti(IV), 4, 336 with mono-Gp Ti(IV), 4, 419 with Ru half-sandwiches, 6, 519—520 with tantalum, 5, 110 with titanium(IV) dialkyls, 4, 352 with titanocenes, 4, 566 with tungsten... 

In another example, the cyclometalated iridium complex [Ir(ppy)2(4-vinylpyridine)Cl] has been attached via hydrosilation see Hydrosilation) to hydride-terminated poly(dimethylsiloxane) to produce a luminescent material. Evaluation of this material as a luminescent oxygen sensor revealed significantly improved sensitivity over dispersions of the original vinyl pyridine complex in poly(dimethylsiloxane). The luminescent material was blended with polystyrene to give a new sensor that exhibited increased sensitivity and maintained short response times to rapid changes in air pressure. 

The complexes of iridium(IV), fewer in number than those of iridium(III), often contain pyridine as a ligand. An impure substance with the reported composition Ir(C6H6N)2Cl4, prepared by the action of pyridine on an iridium (IV) chloride solution, was described first by Renz and later by Gutbier and Hoyermann. Since the composition was based entirely on iridium content without any allusion to isomerism and since the color was inconsistent with his findings, Delepine concluded that the product was not a pure substance. 

In a manner similar to platinum ones, rhodium—carbene complexes have been recently tested in the hydrosilylation of alkenes and alkynes (3). Especially, rhodium complexes with N-heterocyclic carbene (NHC) ligands have attracted considerable attention. Their performance is comparable with that of phosphine complexes. The following exemplary ligands were used 1,3-imidazoylidene chelate bis(imidazolinum-carbene) phosphine-functionalized NHC alkylammonium-imidazolium chloride salts NHC pincer complexes, pyridine-functionalized N-heterocyclic carbenes (also with iridium), and bis(dichloroimidazolylidene) (also with iridium). 

Some metal-pyridine complexes have promise as anticancer treatments. Cationic iridium (III) complexes with pyridine-based ligands have been shown to localize in the endoplasmic reticulum resulting in stress-induced apoptosis. This effect, useful as a potential cancer treatment, can be tuned by changing the size of the ligands (13JMC3636). 

Iridium(IV), d, salts of halides, hydroxide, sulfide, se-lenide, and telluride have been reported. The commercial product H2[IrCl6] 6H2O is water soluble and acts as a catalyst. Ir02 is prepared from the hexahydroxo complex. Iridium(IV) does not form many complexes, but the six-coordinate halides (excluding the iodo species), and some amine and pyridine complexes are known. Compounds with phosphorus, arsenic, and sulfur donor atoms are not stable these ligands reduce iridium(IV) to the iridium(in) state. 

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