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PubMed2004

Dissociation of carbanions from acyl iridium compounds: an experimental and computational investigation.

Instead of reductive elimination of aldehyde, or decarbonylation to give a trifluoroalkyl hydride, heating Cp(PMe(3))Ir(H)[C(O)CF(3)] (1) leads to the quantitative formation of Cp(PMe(3))Ir(CO) (2) and CF(3)H. Kinetic experiments, isotope labeling studies, solvent effect studies, and solvent-inclusive DFT calculations support a mechanism that involves initial dissociation of trifluoromethyl anion to give the transient ion-pair intermediate [Cp(PMe(3))Ir(H)(CO)](+)[CF(3)](-). Further evidence for the ability of CF(3)(-) to act as a leaving group came from the investigation of the analogous methyl and chloride derivatives Cp(PMe(3))Ir(Me)[C(O)CF(3)] and Cp(PMe(3))Ir(Cl)[C(O)CF(3)]. Both of these compounds undergo a similar loss of trifluoromethyl anion, generating an iridium carbonyl cation and CF(3)D in CD(3)OD. Three additional acyl hydrides, Cp(PMe(3))Ir(H)[C(O)R(F)] (where R(F) = CF(2)CF(3), CF(2)CF(2)CF(3), or CF(2)(CF(2))(6)CF(3)) undergo R(F)-H elimination to give 2 at a faster rate than CF(3)H elimination from 1. Stereochemical studies using a chiral acyl hydride with a stereocenter at the beta-position reveal that ionization of the carbanion occurs to form a tight ion-pair with high retention of configuration and enantiomeric purity upon proton transfer from iridium.

Journal Article↗
PubMed2005

A simple route to difluorocarbene and perfluoroalkylidene complexes of iridium.

Primary perfluoroalkyl compounds of iridium undergo facile two-electron reduction to afford a simple route to difluorocarbene and perfluoroalkylidene complexes, two of which have been crystallographically characterized. Low-temperature protonation reactions illustrate that the thermodynamic site of protonation depends on the nature of the fluorinated carbene; the difluorocarbene complex undergoes protonation at iridium, while its perfluoroethylidene congener undergoes protonation at carbon.

Journal Article↗
PubMed2006

Iridium-iron-monocarborane clusters from oxidative insertion reactions of [IrCl(CO)(PPh3)2] with ferracarborane anions.

The nine-vertex ferracarborane salt [N(PPh3)2][7,7,7-(CO)3-closo-7,1-FeCB7H8] (1) reacts with an excess of [IrCl(CO)(PPh3)2] in the presence of Tl[PF6] to form, successively, the bimetallic species [7,7,9,9,9-(CO)5-7-PPh3-closo-7,9,1-IrFeCB6H7] (3), in which one {BH}- vertex has formally been subrogated by an {Ir(CO)2(PPh3)} unit, and the trimetallic complex [6,7,9-{Ir(CO)(PPh3)2}-7,9-(mu-H)2-7,9,9-(CO)3-7-PPh3-closo-7,9,1-IrFeCB6H6] (5), which contains an {FeIr2} triangle. The {FeIrCB6} core in 5 resembles that in 3 with, in addition, the Fe...Ir connectivity being spanned by an {Ir(CO)(PPh3)2} fragment and the consequent Fe-Ir and Ir-Ir bonds bridged by hydrido ligands. In contrast to the above, treatment of the 10-vertex diferracarborane salt [N(PPh3)2][6,6,6,10,10,10-(CO)6-closo-6,10, 1-Fe2CB7H8] (2) with the same reagents yields two very different, trimetallic complexes, namely [8,10-{Ir(mu-PPh2)(Ph)(CO)(PPh3)}-8-(mu-H)-6,6,6,10,10-( CO)5-closo-6,10,1-Fe2CB7H7] (6) and [6,7,10-{Fe(CO)3}-6-(mu-H)-6,10,10,10-(CO)4-6-PPh3-closo-6,10,1-IrFeCB7H7] (7). In 6, an exo-polyhedral {IrPh(CO)(PPh3)} moiety is attached to a {closo-6,10,1-Fe2CB7} framework via a PPh2-bridged Fe-Ir bond and a B-HIr agostic-type linkage, the iridium center formally having inserted into one P-Ph bond of a PPh3 unit. Complex 7 contains an {IrFeCB7} cluster core, with an exo-polyhedral {Fe(CO)3} moiety bridging a {BIrFe} triangular face and with an additional Ir-H-Fe bridge. However, this metal atom arrangement reveals that iridium and iron moieties have exchanged exo- and endo-polyhedral sites with respect to the 10-vertex metallacarborane. X-ray diffraction studies upon 3, 5, 6, and 7 confirmed their novel structural features; some preliminary reactivity studies upon these compounds are also reported.

Journal Article↗
PubMed2006

Stable single-layer light-emitting electrochemical cell using 4,7-diphenyl-1,10-phenanthroline-bis(2-phenylpyridine)iridium(III) hexafluorophosphate.

A significant improvement in the stability of a light emitting electrochemical cell was achieved by utilizing a novel iridium(III) complex: 4,7-diphenyl-1,10-phenanthroline-bis(2-phenylpyridine)iridium(III) hexafluorophosphate. The enhanced device stability is correlated by means of DFT studies to be related to a more efficient shielding of the reactive LUMO of the complex.

Journal Article↗
PubMed2006

Potential solution processible phosphorescent iridium complexes toward applications in doped light-emitting diodes: rapid syntheses and optical and morphological characterizations.

A series of carbazol-9-yl end-capped red-emitting heteroleptic iridium complexes was readily synthesized using post Suzuki coupling. The appealing solubility, photoluminescent characteristics, and morphological stability enabled the current heteroleptic iridium complexes to be highly desirable phosphorescent dopant emitters in doped light-emitting diodes for the purpose of resisting molecular aggregations in the doped emitting layers.

Journal Article↗
PubMed2005

Effects of adsorbates on supported platinum and iridium clusters: Characterization in reactive atmospheres and during alkene hydrogenation catalysis by X-ray absorption spectroscopy.

MgO-, SiO2-, and gamma-Al2O3-supported platinum clusters and particles (with average diameters ranging from 11 to 45 A) and zeolite-supported Ir4 clusters (approximately 6 A in diameter) were characterized by extended X-ray absorption fine structure spectroscopy in the presence of H2, O2, ethene, propene, and ethane, as well as under conditions of alkene hydrogenation catalysis. The results indicate that under various atmospheres, the presence of adsorbates affects the smaller platinum clusters (11 A) on gamma-Al2O3 more substantially than the larger platinum particles (i.e., those greater than approximately 21 A in average diameter) on MgO or SiO2. When Pt/gamma-Al2O3 was exposed to H2, the platinum morphology did not change, although the Pt-Pt bond distance increased. In contrast, when the same sample was exposed to O2, complete oxidative fragmentation took place. This processes was reversed following subsequent treatment with H2. Exposure to alkenes changed both the morphology and electron density (as indicated by X-ray absorption near-edge spectra) of the gamma-Al2O3-supported platinum clusters. Under conditions of alkene hydrogenation catalysis at room temperature, the electronic properties and the structure of the platinum clusters were found to depend on the reactant composition and the nature of molecules involved in the reaction process. The effects of the reactant gases on the smaller iridium clusters (Ir4) were substantially less pronounced, apparently as a consequence of the extremely small number of atoms in each iridium cluster.

Journal Article↗
PubMed2000

Trifluoromethyl-substituted indenyl rhodium and iridium complexes are highly selective catalysts for directed hydroboration reactions

Rhodium and iridium catalysts containing trifluoromethyl-substituted indenyl ligands (Ind'MCod, Ind' = C9H7, (1-CF3)C9H6, (2-CF3)C9H6, (1,3-CF3)2C9H5) have been developed for the directed hydroboration of 4-(benzyloxy)cyclohexene to cis-3-(benzyloxy)cyclohexanol. Compared to unsubstituted complexes, trifluoromethyl substitution yields a 3-10% increase in selectivity which is attributed to the strong electron-withdrawing effect of the trifluoromethyl group. Rhodium complexes give selectivities of 74-84%, and iridium complexes give high levels of selectivity (93-98%).

Journal Article↗
PubMed2004

Utility of the iridium complex of the pybox ligand in regio- and enantioselective allylic substitution.

The viability of the iridium complex of pybox as chiral catalyst in allylic substitutions and the enantioselective synthesis of branched products was studied. Among several chiral ligands evaluated, the iridium complex of pybox having a phenyl group catalyzed the reaction with high activity to form the branched amines with good enantioselectivities when hydroxylamine, amine, and aniline were employed as a nucleophile. The allylic substitution with oximes proceeded smoothly to give the branched oxime ethers with good enantioselectivities. [reaction: see text]

Journal Article↗
PubMed2003

Head-to-tail dimerization of acrylates catalyzed by iridium complexes.

Head-to-tail dimerizations of acrylates and vinyl ketone were successfully performed by the use of iridium complexes in good yields. An iridium hydride complex generated in situ from [IrCl(cod)]2 and alcohols in the presence of Na2CO3 and (MeO)3P was found to be an active species promoting the head-to-tail dimerization of acrylates. Thus, butyl acrylate afforded the corresponding head-to-tail dimer in 86% yield.

Journal Article↗
PubMed2006

The role of halogenated carborane monoanions in olefin hydrogenation catalysed by cationic iridium phosphine complexes.

Iridium hydridophosphine complexes of general formula [Ir(PR3)2H2(anion)](PR3= PPh3, PMe2Ph; anion =[1-closo-CB(11)H(6)Cl(6)]-, [1-closo-CB(11)H(6)I(6)]-, [BAr(F)4]-) have been prepared by hydrogenation of cyclooctadiene precursor complexes. Solid-state structures of selected examples of these complexes reveal intimate contacts between the carborane anion and cation, with the anion binding through two lower-hemisphere halogen ligands. In CD2Cl2 solution the very weakly coordinating anions [1-closo-CB(11)H(6)Cl(6)]- and [BAr(F)4]- are suggested to favour the formation of solvent complexes such as [Ir(PR3)2H2(solvent)n][anion], while the [1-closo-CB(11)H(6)I(6)]- anion forms a tightly bound complex with the cationic iridium fragment. Calculated DeltaG values for anion reorganisation in d8-toluene reflect this difference in interaction between the anions and cation. With the bulky anion [1-closo-CB(11)Me(5)I(6)]- different complexes are formed: Ir(PPh3)H2(1-closo-HCB(11)Me(5)I(6)) and [(PPh3)3Ir(H2)H2][1-closo-HCB(11)Me(5)I(6)] which have been characterised spectroscopically. Diffusion measurements in CD2Cl2 are also consistent with larger, solvent coordinated, complexes for the more weakly coordinating anions and a tighter interaction between anion and cation for [1-closo-CB(11)H(6)I(6)]-. All the complexes show some ion-paring in solution. Comparison with data previously reported for the [1-closo-CB(11)H(6)Br(6)]- anion shows that this anion--as expected--fits between [1-closo-CB(11)H(6)Cl(6)]- and [1-closo-CB(11)H(6)I(6)]- in terms of coordinating ability. Although not coordinating, the large [1-closo-CB(11)H(6)Cl(6)]- and [BAr(F)4)]- anions do provide some stabilisation towards the metal centre, as decomposition to the hydride bridged dimer [Ir2(PPh3)4H5]+ is retarded. This is in contrast to the [PF6]- salt where decomposition is immediate. As expected, complexes with the smaller phosphine PMe2Ph form tighter interactions with the carborane anions. These observations on the interaction between anion and cation in solution are reflected in benchmark hydrogenation studies that show a significant attenuation in rate of hydrogenation of cyclohexane on using the [1-closo-CB(11)H(6)I(6)]- anion or complexes with the PMe2Ph phosphine. We also comment on the reusability of the catalysts and their tolerance to water and oxygen impurities. Overall the catalyst with the [1-closo-CB(11)H(6)Br(6)]- anion shows the best combination of rate of hydrogenation, reusability and tolerance to impurities.

Journal Article↗
PubMed2005

Origin of brittle cleavage in iridium.

Iridium is unique among the face-centered cubic metals in that it undergoes brittle cleavage after a period of plastic deformation under tensile stress. Atomistic simulation using a quantum-mechanically derived bond-order potential shows that in iridium, two core structures for the screw dislocation are possible: a glissile planar core and a metastable nonplanar core. Transformation between the two core structures is athermal and leads to exceptionally high rates of cross slip during plastic deformation. Associated with this athermal cross slip is an exponential increase in the dislocation density and strong work hardening from which brittle cleavage is a natural consequence.

Journal Article↗
PubMed1976

Combination teletherapy and iridium implantation in the treatment of locally advanced breast cancer.

Combined teletherapy and interstitial iridium 192 implantation can control locally advanced breast cancer in a consistent fashion without causing significant morbidity. Moreover, in the absence of clinically evident distant metastases, patients who undergo this treatment can survive comfortably for long periods of time. Among 11 patients followed for at least 1 1/2 years, nine are alive without evidence of disease, one is living with distant metastases, and one patient is dead. There has been no local recurrence in the 18 patients included in this report.

Adult↗
PubMed1984

Radiotherapy of high bile duct carcinoma using intra-catheter iridium 192 wire.

The authors developed an original procedure of endo-curietherapy of high bile duct carcinoma. An iridium 192 wire is inserted into either a percutaneous transhepatic catheter or a surgically implanted external diversion catheter. The delivered dose varies between 10 and 60 Gy at 1 cm from the wire. Four of the seven patients analyzed also received external irradiation. There were no systemic or local complications. All patients experienced symptomatic relief and four are alive with no evidence of disease. This well-tolerated procedure permits symptomatic palliation without excessive side effects for the patient. In some cases, a curative effect can be expected.

Adenocarcinoma↗
PubMed1985

Iridium afterloading curietherapy in the treatment of pediatric malignancies. The Institut Gustave Roussy experience.

Between 1972 and 1980, 58 children with malignant tumors underwent iridium 192 (192Ir) curietherapy at the Institut Gustave Roussy. Data from only 45 of them were reviewed (bilateral retinoblastoma and salvage procedures were excluded). The pathologic diagnosis was rhabdomyosarcoma in 75% of cases, yolk sac tumor in 13% of cases, malignant mesenchymoma in two cases, clear cell carcinoma in two cases, and undifferentiated sarcoma in one case. The two major sites were pelvis-perineum (64.5%) and head and neck (31%). The treatment was essentially based on a combination of chemotherapy, which was adapted to the histologic type of the tumor, and curietherapy. Partial surgery was carried out in certain cases, either before chemotherapy for diagnostic purposes, or after chemotherapy to remove infiltrative residual tumor. External beam radiotherapy was used in a few cases in lymph node irradiation. The radioactive material was 192Ir, using afterloading techniques, either intracavitary or interstitially or both. The tumor dose, calculated by computerized dosimetry, was 60 to 65 Gy delivered over 5 to 7 days in the majority of cases. Two patients were lost to follow-up. Thirty-five patients (78%) are alive with no evidence of disease after a mean follow-up period of 5 years. Eight patients died, one of complications related to chemotherapy and seven of the evolution of their disease. The late-complication rate, studied in 33 patients with a minimum follow-up period of 3 years, is 18% (6/33). Curietherapy seems to be a preferable conservative treatment in children with localized and accessible malignant tumors.

Adolescent↗
PubMed1992

Temporary iridium-192 implant in the management of carcinoma of the prostate.

The controversy about the treatment of carcinoma of the prostate has increased in the last decade, with most urologists favoring radical prostatectomy rather than primary irradiation. Several reports of persistent tumors in 50% to 90% of patients after external irradiation and permanent iodine-125 implantation of the prostate have been disturbing. From July 1977 to December 1985, 200 patients with adenocarcinoma of the prostate were treated by combining bilateral pelvic lymphadenectomy and temporary interstitial iridium-192 implantation of the prostate, followed by external irradiation. Seventy-four (36%) patients underwent biopsies of the prostate 4 months to 2 years after completion of the irradiation. Only 12 (16%) patients had persistent tumors. Complications were minimized subsequently by dose modifications.

Adenocarcinoma↗
PubMed2000

Six-year recurrence free survival after intraluminal iridium-192 therapy of human bilobar biliary papillomatosis. A case report.

BACKGROUND: Biliary papillomatosis is rare and often fatal. Liver resection or transplantation is recommended but may be impossible due to tumor or patient factors; furthermore, it appears to the authors of this study that no follow-up results after transplantation have been reported in previous studies. METHODS: Bilobar but limited biliary papillomatosis in a man age 54 years was mapped by cholangiopancreatography, cholecystectomy, and operative cholangioscopy. After cholangioscopic electrocoagulation, iridium-192 wires were temporarily inserted into the affected bile ducts, giving a dose of 60 grays at a 3-mm distance. Another percutaneous cholangioscopic electrocoagulation was performed 3 weeks later. RESULTS: The patient has been free of tumor and in good health for 80 months, but he has a long term stenting of a nonneoplastic stricture at the confluence of the bile ducts. CONCLUSIONS: Mechanical tumor reduction and intraluminal brachytherapy could possibly replace transplantation (which up to now has been suggested but not reported) when this life-threatening disease is bilobar, and also possibly replace liver resection for limited tumors in patients who are too frail for surgery.

Bile Duct Neoplasms↗
PubMed2004

Iridium-imine and -amine complexes relevant to the (S)-metolachlor process: structures, exchange kinetics, and C-H activation by Iri causing racemization.

Iridium complexes of DMA-imine [2,6-dimethylphenyl-1'-methyl-2'-methoxyethylimine, 1 a) and (R)-DMA-amine [(1'R)-2,6-dimethylphenyl-1'-methyl-2'-methoxyethylamine, 2 a] that are relevant to the catalytic imine hydrogenation step of the Syngenta (S)-Metolachlor process were synthesized: metathetical exchange of [Ir2Cl2(cod)2] (cod=1,5-cyclooctadiene) with [Ag(1 a)2]BF4 and [Ag((R)-2 a)2]BF4 afforded [Ir(cod)(kappa2- -1 a)]BF4 (11) and [Ir(cod)(kappa2-(R)-2 a)]BF4 ((R)-19)), respectively. These complexes were then used in stopped-flow experiments to study the displacement of amine 2 a from complex 19 by imine 1 a to form the imine complex 11, thus modeling the product/substrate exchange step in the catalytic cycle. The data suggest a two-step associative mechanism characterized by k1=(2.6+/-0.3) x 10(2) M(-1) s(-1) and k2=(4.3+/-0.6) x 10(-2) s(-1) with the respective activation energies EA1=(7.5+/-0.6) kJ mol(-1) and EA2=(37+/-3) kJ mol(-1). Furthermore, complex 11 reacted with H2O to afford the hydrolysis product [Ir(cod)(eta(6-)-2,6-dimethylaniline)]BF4 (12), and with I2 to liberate quantitatively the DMA-iminium salt 14. On the other hand, the chiral amine complex (R)-19 formed the optically inactive eta6-bound compound [Ir(cod)(eta6-rac-2 a)]BF4 (rac-18) upon dissolution in THF at room temperature, presumably via intramolecular C-H activation. This racemization was found to be a two-step event with k'1=9.0 x 10(-4) s(-1) and k2=2.89 x 10(-5) s(-1), featuring an optically active intermediate prior to sp3 C-H activation. Compounds 11, 12, rac-18, and (R)-19 were structurally characterized by single-crystal X-ray analyses.

Acetamides↗