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 cis-pyridyl-iridium(III) emitters of the class [3b+3b+3b'] with two orthometalated ligands of the 2-phenylpyridine type (3b) and a third ligand (3b'). They allowed to obtain four emitters of this class and to compare their properties with those of the trans-pyridyl isomers. The finding starts from IrH5(PiPr3)2, which reacts with 2-(p-tolyl)pyridine to give fac-[Ir{κ2-C,N-[C6MeH3-py]}3] with an almost quantitative yield. Stirring the latter in the appropriate amount of a saturated solution of HCl in toluene results in the cis-pyridyl adduct IrCl{κ2-C,N-[C6MeH3-py]}2{κ1-Cl-[Cl-H-py-C6MeH4]} stabilized with p-tolylpyridinium chloride, which can also be transformed into dimer cis-[Ir(µ-OH){κ2-C,N-[C6MeH3-py]}2]2. Adduct IrCl{κ2-C,N-[C6MeH3-py]}2{κ1-Cl-[Cl-H-py-C6MeH4]} directly generates cis-[Ir{κ2-C,N-[C6MeH3-py]}2{κ2-C,N-[C6H4-Isoqui]}] and cis-[Ir{κ2-C,N-[C6MeH3-py]}2{κ2-C,N-[C6H4-py]}] by transmetalation from Li[2-(isoquinolin-1-yl)-C6H4] and Li[py-2-C6H4]. Dimer cis-[Ir(µ-OH){κ2-C,N-[C6MeH3-py]}2]2 is also a useful starting complex when the precursor molecule of 3b' has a fairly acidic hydrogen atom, suitable for removal by hydroxide groups. Thus, its reactions with 2-picolinic acid and acetylacetone (Hacac) lead to cis-Ir{κ2-C,N-[C6MeH3-py]}2{κ2-O,N-[OC(O)-py]} and cis-Ir{κ2-C,N-[C6MeH3-py]}2{κ2-O,O-[acac]}. The stereochemistry of the emitter does not significantly influence the emission wavelengths. On the contrary, its efficiency is highly dependent on and associated with the stability of the isomer. The more stable isomer shows a higher quantum yield and color purity.

Acetylides for the Preparation of Phosphorescent Iridium(III) Complexes: Iridaoxazoles and Their Transformation into Hydroxycarbenes and N,C(sp3),C(sp2),O-Tetradentate Ligands.

The preparation of three families of phosphorescent iridium(III) emitters, including iridaoxazole derivatives, hydroxycarbene compounds, and N,C(sp3),C(sp2),O-tetradentate containing complexes, has been performed starting from dimers cis-[Ir(µ2-η2-C≡CR){κ2-C,N-(MeC6H3-py)}2]2 (R = tBu (1a), Ph (1b)). Reactions of 1a with benzamide, acetamide, phenylacetamide, and trifluoroacetamide lead to the iridaoxazole derivatives Ir{κ2-C,O-[C(CH2tBu)NC(R)O]}{κ2-C,N-(MeC6H3-py)}2 (R = Ph (2), Me (3), CH2Ph (4), CF3 (5)) with a fac 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 3-5 to form amidate-iridium(III)-hydroxycarbene derivatives Ir{κ1-N-[NHC(R)O]}{κ2-C,N-(MeC6H3-py)}2{═C(CH2tBu)OH} (R = Me (6), CH2Ph (7), CF3 (8)). In contrast to 1a, dimer 1b reacts with benzamide and acetamide to give Ir{κ4-N,C,C',O-[py-MeC6H3-C(CH2-C6H4)NHC(R)O]}{κ2-C,N-(MeC6H3-py)}(R = Ph (9), Me (10)), which bear a N,C(sp3),C(sp2),O-tetradentate ligand resulting from a triple coupling (an alkynyl ligand, an amide, and a coordinated aryl group) and a C-H bond activation at the metal coordination sphere. Complexes 2-4 and 6-10 are emissive upon photoexcitation, in orange (2-4), green (6-8), and yellow (9 and 10) regions, with quantum yields between low and moderate (0.01-0.50) and short lifetimes (0.2-9.0 µs).

Alternative Conceptual Approach to the Design of Bifunctional Catalysts: An Osmium Germylene System for the Dehydrogenation of Formic Acid.

The reaction of the hexahydride OsH6(PiPr3)2 with a P,Ge,P-germylene-diphosphine affords an osmium tetrahydride derivative bearing a Ge,P-chelate, which arises from the hydrogenolysis of a P-C(sp3) bond. This Os(IV)-Ge(II) compound is a pioneering example of a bifunctional catalyst based on the coordination of a σ-donor acid, which is active in the dehydrogenation of formic acid to H2 and CO2. The kinetics of the dehydrogenation, the characterization of the resting state of the catalysis, and DFT calculations point out that the hydrogen formation (the fast stage) exclusively occurs on the coordination sphere of the basic metal center, whereas both the metal center and the σ-donor Lewis acid cooperatively participate in the CO2 release (the rate-determining step). During the process, the formate group pivots around the germanium to approach its hydrogen atom to the osmium center, which allows its transfer to the metal and the CO2 release.

Preparation and Photophysical Properties of Bis(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 0.5 equiv of the dimer [Ir(µ-Cl)(η2-COE)2]2 (COE = cyclooctene) with 1.0 equiv of Hg(dpyb)Cl leads to the iridium(III) derivative IrCl2{κ3-N,C,N-(dpyb)}(η2-COE) (3), which reacts with 2-(1H-imidazol-2-yl)-6-phenylpyridine (HNImpyC6H5) and 2-(1H-benzimidazol-2-yl)-6-phenylpyridine (HNBzimpyC6H5) in the presence of Na2CO3 to give Ir{κ3-C,N,N-(NImpyC6H4)}{κ3-N,C,N-(dpyb)} (4) and Ir{κ3-C,N,N-(NBzimpyC6H4)}{κ3-N,C,N-(dpyb)} (5), respectively. Similar reactions of the Williams's dimer [IrCl(µ-Cl){κ3-N,C,N-(dpyMeb)}]2 with HNImpyC6H5 and HNBzimpyC6H5 in the presence of Na2CO3 afford the dimethylated counterparts Ir{κ3-C,N,N-(NImpyC6H4)}{κ3-N,C,N-(dpyMeb)} (6) and Ir{κ3-C,N,N-(NBzimpyC6H4)}{κ3-N,C,N-(dpyMeb)} (7), whereas 2-(6-phenylpyridine-2-yl)-1H-indole (HIndpyC6H5) initially gives IrH{κ2-N,N-(IndpyC6H5)}{κ3-N,C,N-(dpyMeb)} (8) and subsequently Ir{κ3-C,N,N-(IndpyC6H4)}{κ3-N,C,N-(dpyMeb)} (9). Complexes 4-7 are phosphorescent green emitters (λem 490-550 nm), whereas 9 is greenish yellow emissive (λem 547-624 nm). They display lifetimes in the range 0.5-9.7 µs and quantum yields in both doped poly(methyl)methacrylate films and in 2-methyltetrahydrofuran at room temperature depending upon the ligands: 0.5-0.7 for 6 and 7, about 0.4 for 4 and 5, and 0.3-0.2 for 9.

Synthesis of Polysubstituted Iodoarenes Enabled by Iterative Iodine-Directed para and ortho C-H Functionalization.

Among halogenated aromatics, iodoarenes are unique in their ability to produce the bench-stable halogen(III) form. Earlier, such iodine(III) centers were shown to enable C-H functionalization ortho to iodine via halogen-centered rearrangement. The broader implications of this phenomenon are explored by testing the extent of an unusual iodane-directed para C-H benzylation, as well as by developing an efficient C-H coupling with sulfonyl-substituted allylic silanes. Through the combination of the one-shot nature of the coupling event and the iodine retention, multisubstituted arenes can be prepared by sequentially engaging up to three aromatic C-H sites. This type of iodine-based iterative synthesis will serve as a tool for the formation of value-added aromatic cores.

The Coming of Age in Iodane-Guided ortho-C-H Propargylation: From Insight to Synthetic Potential.

As early as 1991 Ochiai et al. reported that an acid-activated form of phenyliodine diacetate, PhI(OAc)2 , undergoes a reaction with propargyl-silanes, germanes and stannanes to give the ortho-propargyl iodobenzene. This formal C-H alkylation was proposed to take place through an unusual (even to date) iodonio-based [3,3] rearrangement of an intermediate allenylsilane. Although this mechanistic principle has been invoked in related iodane-directed C-H coupling reaction, some underlying principles have remained unaddressed, and the reaction rarely employed. Herein, DFT evidence for a mechanism best described as iodine-guided electrophilic aromatic substitution is presented. Using a newly optimized reaction protocol that significantly reduces the undesired reduction process, the potency of the method is showcased through the synthesis of >40 structurally diverse ortho-iodo propargyl (or allenyl) arenes.

Acid Activation in Phenyliodine Dicarboxylates: Direct Observation, Structures, and Implications.

The use of the hypervalent iodine reagents in oxidative processes has become a staple in modern organic synthesis. Frequently, the reactivity of λ3 iodanes is further enhanced by acids (Lewis or Brønsted). The origin of such activation, however, has remained elusive. Here, we use the common combination of PhI(OAc)2 with BF3·Et2O as a model to fully explore this activation phenomenon. In addition to the spectroscopic assessment of the dynamic acid-base interaction, for the first time the putative PIDA·BF3 complex has been isolated and its structure determined by X-ray diffraction. Consequences of such activation are discussed from a structural and electronic (DFT) points of views, including the origins of the enhanced reactivity.

NH-Heterocyclic Aryliodonium Salts and their Selective Conversion into N1-Aryl-5-iodoimidazoles.

The synthesis of N-arylimidazoles substituted at the sterically encumbered 5-position is a challenge for modern synthetic approaches. A new family of imidazolyl aryliodonium salts is reported, which serve as a stepping stone on the way to selective formation of N1-aryl-5-iodoimidazoles. Iodine acts as a "universal" placeholder poised for replacement by aryl substituents. These new λ(3) -iodanes are produced by treating the NH-imidazole with ArI(OAc)2 , and are converted to N1-aryl-5-iodoimidazoles by a selective copper-catalyzed aryl migration. The method tolerates a variety of aryl fragments and is also applicable to substituted imidazoles.

Preparation and Degradation of Rhodium and Iridium Diolefin Catalysts for the Acceptorless and Base-Free Dehydrogenation of Secondary Alcohols.

Rhodium and iridium diolefin catalysts for the acceptorless and base-free dehydrogenation of secondary alcohols have been prepared, and their degradation has been investigated, during the study of the reactivity of the dimers [M(µ-Cl)(η4-C8H12)]2 (M = Rh (1), Ir (2)) and [M(µ-OH)(η4-C8H12)]2 (M = Rh (3), Ir (4)) with 1,3-bis(6'-methyl-2'-pyridylimino)isoindoline (HBMePHI). Complex 1 reacts with HBMePHI, in dichloromethane, to afford equilibrium mixtures of 1, the mononuclear derivative RhCl(η4-C8H12){κ1-N py-(HBMePHI)} (5), and the binuclear species [RhCl(η4-C8H12)]2{µ-N py,N py-(HBMePHI)} (6). Under the same conditions, complex 2 affords the iridium counterparts IrCl(η4-C8H12){κ1-N py-(HBMePHI)} (7) and [IrCl(η4-C8H12)]2{µ-N py,N py-(HBMePHI)} (8). In contrast to chloride, one of the hydroxide groups of 3 and 4 promotes the deprotonation of HBMePHI to give [M(η4-C8H12)]2(µ-OH){µ-N py,N iso-(BMePHI)} (M = Rh (9), Ir (10)), which are efficient precatalysts for the acceptorless and base-free dehydrogenation of secondary alcohols. In the presence of KO t Bu, the [BMePHI]- ligand undergoes three different degradations: alcoholysis of an exocyclic isoindoline-N double bond, alcoholysis of a pyridyl-N bond, and opening of the five-membered ring of the isoindoline core.

Ruthenium-Catalyzed Oxidative Amidation of Alkynes to Amides.

Complex CpRuCl(PPh3)2 catalyzes reactions of terminal alkynes with 4-picoline N-oxide and primary and secondary amines to afford the corresponding amides. The reactions occur in chlorinated solvent and aqueous medium, showing applications in peptide chemistry. Stoichiometric studies reveal that the true catalysts of the processes are the vinylidene cations [CpRu(═C═CHR)(PPh3)2]+ which are oxidized to the Ru(η2-CO)-ketenes by the N-oxide. Finally, nucleophilic additions of primary and secondary amines to the free ketenes yield the corresponding amides.

Impact of the introduction of high-affinity specific monoclonal antibodies in the improvement of sensitivity and specificity parameters of UMELISA HBsAg PLUS and UMELISA TSH immunoenzymatic techniques.

Improvement in the sensitivity and specificity of UMELISA techniques as a result of the introduction of monoclonal antibodies superseding the use of polyclonal antibodies was studied. For this purpose, we performed a comparison of the results in the functioning of the screening programs before and after the introduction of monoclonal antibodies. We analyzed some parameters such as sensitivity, specificity and detection limit in the UMELISA HBsAg PLUS and UMELISA TSH techniques. The sensitivity and specificity parameters were evaluated by means of comparison with the commercial assays. The detection limit was calculated as the fluorescence of the calibrator 0 + 2 standard deviations. Since the introduction of MAb obtained for us an increase in the sensitivity, specificity, and positive predictive value was evidenced. On the other hand, the use of the MAb guarantees better stability in the diagnostic kit production process.