Two Synthetic Tools to Deepen the Understanding of the Influence of Stereochemistry on the Properties of Iridium(III) Heteroleptic Emitters.

Two complementary procedures are presented to prepare -pyridyl-iridium(III) emitters of the class [++] with two orthometalated ligands of the 2-phenylpyridine type () and a third ligand (). They allowed to obtain four emitters of this class and to compare their properties with those of the -pyridyl isomers. The finding starts from IrH(PPr), which reacts with 2-(-tolyl)pyridine to give -[Ir{κ--[CMeH-py]}] with an almost quantitative yield.

Ligand Design and Preparation, Photophysical Properties, and Device Performance of an Encapsulated-Type -Tris(heteroleptic) Iridium(III) Emitter.

The organic molecule 2-(1-phenyl-1-(pyridin-2-yl)ethyl)-6-(3-(1-phenyl-1-(pyridin-2-yl)ethyl)phenyl)pyridine () has been designed, prepared, and employed to synthesize the encapsulated-type -tris(heteroleptic) iridium(III) derivative Ir(κ-'L). Its formation takes place as a result of the coordination of the heterocycles to the iridium center and the -CH bond activation of the phenyl groups. Dimer [Ir(μ-Cl)(η-COD)] is suitable for the preparation of this compound of class [Ir(9h)] (9h = 9-electron donor hexadentate ligand), but Ir(acac) is a more appropriate starting material.

Acetylides for the Preparation of Phosphorescent Iridium(III) Complexes: Iridaoxazoles and Their Transformation into Hydroxycarbenes and -Tetradentate Ligands.

The preparation of three families of phosphorescent iridium(III) emitters, including iridaoxazole derivatives, hydroxycarbene compounds, and -tetradentate containing complexes, has been performed starting from dimers -[Ir(μ-η-C≡CR){κ--(MeCH-py)}] (R = Bu (), Ph ()). Reactions of with benzamide, acetamide, phenylacetamide, and trifluoroacetamide lead to the iridaoxazole derivatives Ir{κ--[C(CHBu)NC()O]}{κ--(MeCH-py)} (R = Ph (), Me (), CHPh (), CF ()) with a disposition of carbons and heteroatoms around the metal center. In 2-methyltetrahydrofuran and dichloromethane, water promotes the C-N rupture of the IrC-N bond of the iridaoxazole ring of to form amidate-iridium(III)-hydroxycarbene derivatives Ir{κ-[NHC()O]}{κ--(MeCH-py)}{═C(CHBu)OH} (R = Me (), CHPh (), CF ()).

Alkynyl Ligands as Building Blocks for the Preparation of Phosphorescent Iridium(III) Emitters: Alternative Synthetic Precursors and Procedures.

Alkynyl ligands stabilize dimers [Ir(μ-X)(3b)] with a cis disposition of the heterocycles of the 3b ligands, in contrast to chloride. Thus, the complexes of this class─[Ir(μ-η-C≡CPh){κ-,-(CH-Isoqui)}] (Isoqui = isoquinoline) and [Ir(μ-η-C≡CR){κ-,-(MeCH-py)}] (R = Ph, Bu)─have been prepared in high yields, starting from the dihydroxo-bridged dimers [Ir(μ-OH){κ-,-(CH-Isoqui)}] and [Ir(μ-OH){κ-,-(MeCH-py)}] and terminal alkynes. Subsequently, the acetylide ligands have been employed as building blocks to prepare the orange and green iridium(III) phosphorescent emitters, Ir{κ-,-[C(CHPh)Npy]}{κ-,-(CH-Isoqui)} and Ir{κ-,-[C(CHR)Npy]}{κ-,-(MeCH-py)} (R = Ph, Bu), respectively, with an octahedral structure of carbon and nitrogen atoms.

-Tris(heteroleptic) Red Phosphorescent Iridium(III) Complexes Bearing a Dianionic ,,','-Tetradentate Ligand.

1-Phenyl-3-(1-phenyl-1-(pyridin-2-yl)ethyl)isoquinoline (HMeL) has been prepared by Pd(-XantPhos)-catalyzed "" to synthesize new phosphorescent red iridium(III) emitters (601-732 nm), including the carbonyl derivative Ir(κ--,'--,'-MeL)Cl(CO) and the acetylacetonate compound Ir(κ--,'--,'-MeL)(acac). The tetradentate 6e-donor ligand (6tt') of these complexes is formed by two different bidentate units, namely, an orthometalated 2-phenylisoquinoline and an orthometalated 2-benzylpyridine. The link between the bidentate units reduces the number of possible stereoisomers of the structures [6tt' + 3b] (3b = bidentate 3e-donor ligand), with respect to a [3b + 3b' + 3b″] emitter containing three free bidentate units, and it permits a noticeable stereocontrol.

Insertion of Unsaturated C-C Bonds into the O-H Bond of an Iridium(III)-Hydroxo Complex: Formation of Phosphorescent Emitters with an Asymmetrical β-Diketonate Ligand.

A synthetic methodology to prepare iridium(III) emitters of the class [3b+3b+3b'] with two -metalated 1-phenylisoquinolines and an asymmetrical β-diketonate has been discovered. The abstraction of the chloride ligands of the dimer [Ir(μ-Cl){κ-,-(CH-isoqui)}] (, CH-isoqui = 1-phenylisoquinoline) with AgBF in acetone and the subsequent addition of water to the resulting solution affords the water solvate mononuclear complex [Ir{κ-,-(CH-isoqui)}(HO)]BF (), which reacts with KOH to give the dihydroxo-bridged dimer [Ir(μ-OH){κ-,-(CH-isoqui)}] (). Treatment of the latter with dimethyl acetylenedicarboxylate leads to Ir{κ-,-(CH-isoqui)}{κ-,-[OC(COCH)CHC(OCH)O]} (), as a result of the -addition of the O-H bond of a mononuclear [Ir(OH){κ-,-(CH-isoqui)}] fragment to the C-C triple bond of the alkyne and the coordination of one of the carboxylate substituents to the metal center.

Phosphorescent Iridium(III) Complexes with a Dianionic C,C',N,N'-Tetradentate Ligand.

To prepare new phosphorescent iridium(III) emitters, 2-phenyl-6-(1-phenyl-1-(pyridin-2-yl)ethyl)pyridine (HL) has been designed and its reactions with [Ir(μ-Cl)(η-COD)] (, COD = 1,5-cyclooctadiene) have been studied. The products obtained depend on the refluxing temperature of the solvent. Thus, complexes Ir(κ-'-L)Cl(CO) (), [Ir(η-COD)(κ-HL)][IrCl(η-COD)] (), and [Ir(μ-Cl)(κL)] () have been formed in 2-ethoxyethanol, propan-2-ol, and 1-phenylethanol, respectively.

Preparation and Photophysical Properties of (tridentate) Iridium(III) Emitters: Pincer Coordination of 2,6-Di(2-pyridyl)phenyl.

The way to prepare molecular emitters [5t + 4t'] of iridium(III) with a 5t ligand derived from the abstraction of the hydrogen atom at position 2 of the aryl group of 1,3-di(2-pyridyl)benzene (dpybH) is shown. In addition, the photophysical properties of the new emitters are compared with those of their counterparts resulting from the deprotonation of 1,3-di(2-pyridyl)-4,6-dimethylbenzene (dpyMebH), at the same position, which are also synthesized. Treatment of 0.

Preparation of Tris-Heteroleptic Iridium(III) Complexes Containing a Cyclometalated Aryl-N-Heterocyclic Carbene Ligand.

A new class of phosphorescent tris-heteroleptic iridium(III) complexes has been discovered. The addition of PhMeImAgI (PhMeIm = 1-phenyl-3-methylimidazolylidene) to the dimer [Ir(μ-Cl)(COD)] (1; COD = 1,5-cyclooctadiene) affords IrCl(COD)(PhMeIm) (2), which reacts with 1-phenylisoquinoline, 2-phenylpyridine, and 2-(2,4-difluorophenyl)pyridine to give the respective dimers [Ir(μ-Cl){κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}] (3), [Ir(μ-Cl){κ- C, C-(CH-ImMe)}{κ- C, N-(CH-py)}] (4), and [Ir(μ-Cl){κ- C, C-(CH-ImMe)}{κ- C, N-(CFH-py)}] (5), as a result of the N-heterocyclic carbene (NHC)- and N-heterocycle-supported o-CH bond activation of the aryl substituents and the hydrogenation of a C-C double bond of the coordinated diene. In solution, these dimers exist as a mixture of isomers a (Im trans to N) and b (Im trans to Cl), which lie in a dynamic equilibrium.

Preparation of Phosphorescent Iridium(III) Complexes with a Dianionic C,C,C,C-Tetradentate Ligand.

The preparation and photophysical properties of heteroleptic iridium(III) complexes containing a dianionic C,C,C,C-tetradentate ligand and a cyclometalated phenylpyridine group are described. Complex [Ir(μ-OMe)(COD)] (1, COD = 1,5-cyclooctadiene) reacts with 1,1-diphenyl-3,3-butylenediimidazolium iodide ([PhIm(CH)ImPh]I), in the presence NaOBu, to give [Ir(μ-I){κ- C, C, C, C-[CHIm(CH)ImCH]}] (2), which leads to {[Ir{κ- C, C, C, C-[CHIm(CH)ImCH]}](μ-OH)(μ-OMe)} (3) by treatment first with silver trifluoromethanesulfonate (AgOTf) in acetone-dichloromethane and subsequently with KOH in methanol. The reaction of 2 with AgOTf and acetonitrile affords the bis(solvento) complex [Ir{κ- C, C, C, C-[CHIm(CH)ImCH]}(CHCN)]OTf (4).

η -Arene Complexes as Intermediates in the Preparation of Molecular Phosphorescent Iridium(III) Complexes.

Molecular phosphorescent heteroleptic bis-tridentate iridium(III) emitters have been prepared via η -arene intermediates. In the presence of 4.0 mol of AgOTf, the complex [(IrCl{κ -N,C,N-(pyC HMe py)})(μ-Cl)] (1; pyC H Me py=1,3-di(2-pyridyl)-4,6-dimethylbenzene) reacted with 9-(6-phenylpyridin-2-yl)-9H-carbazole (PhpyCzH) and 2-phenoxy-6-phenylpyridine (PhpyOPh) to give [Ir{κ -N,C,N-(pyC HMe py)}{κ -C,N,C'-(C H pyCzH)}]OTf (2) and [Ir{κ -N,C,N-(pyC HMe py)}{κ -C,N,C'-(C H pyOPh)}]OTf (3).

A Capped Octahedral MHC6 Compound of a Platinum Group Metal.

A MHC6 complex of a platinum group metal with a capped octahedral arrangement of donor atoms around the metal center has been characterized. This osmium compound OsH{κ(2) -C,C-(PhBIm-C6 H4 )}3 , which reacts with HBF4 to afford the 14 e(-) species [Os{κ(2) -C,C-(PhBIm-C6 H4 )}(Ph2 BIm)2 ]BF4 stabilized by two agostic interactions, has been obtained by reaction of OsH6 (PiPr3 )2 with N,N'-diphenylbenzimidazolium chloride ([Ph2 BImH]Cl) in the presence of NEt3 . Its formation takes place through the C,C,C-pincer compound OsH2 {κ(3) -C,C,C-(C6 H4 -BIm-C6 H4 )}(PiPr3 )2 , the dihydrogen derivative OsCl{κ(2) -C,C-(PhBIm-C6 H4 )}(η(2) -H2 )(PiPr3 )2 , and the five-coordinate osmium(II) species OsCl{κ(2) -C,C-(PhBIm-C6 H4 )}(PiPr3 )2 .

Designed helical peptides inhibit an intramembrane protease.

gamma-Secretase cleaves the transmembrane domain of the amyloid precursor protein, a process implicated in the pathogenesis of Alzheimer's disease, and this enzyme is a founding member of an emerging class of intramembrane proteases. Modeling and mutagenesis suggest a helical conformation for the substrate transmembrane domain upon initial interaction with the protease. Moreover, biochemical evidence supports the presence of an initial docking site for substrate on gamma-secretase that is distinct from the active site, a property predicted to be generally true of intramembrane proteases.

Synthesis of purine- and pyrimidine-substituted heptadienes. The stereochemistry of cyclization and cyclopolymerization products.

A series of 1,6-heptadienes, substituted in the 4 position with nucleic acid bases 1-6, have been synthesized via Mitsunobu condensations. Guanine, adenine, thymine, and uracil derivatives can be prepared directly by coupling the protected base with 1,6-heptadien-4-ol (7). However, coupling protected cytosine and 7 gives an O-alkylated product.

The search for gamma-secretase and development of inhibitors.

A considerable body of evidence has accumulated in recent years implicating the beta-amyloid protein (Abeta) in the etiology of Alzheimer s disease (AD). The highly hydrophobic Abeta can nucleate and form neurotoxic fibrils that are the principal components of the cerebral plaques characteristic of AD. Abeta is formed from the amyloid-beta precursor protein (APP) through two protease activities.