A Lead-μ-Tetrylide Complex with Osmium(IV) Terminal Components.

A bare lead atom is a σ-donor ligand capable of linearly bonding and stabilizing two units of a classical polyhydride complex, with a high-valent metal center. As a proof of concept, we have prepared and characterized the μ-tetrylide complex (PPr)HOs═Pb═OsH(PPr) in the reaction of OsH(PPr) with Pb{N(SiMe)}. Although the Pb-Os bonds exhibit electrostatic interaction, the main orbital interactions result from two dative σ bonds from the lead atom to the osmium centers.

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.

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 ()).

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

The reaction of the hexahydride OsH(PPr) 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(sp) 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 H and CO. 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 CO release (the rate-determining step).

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)(η-CH)] (M = Rh (), Ir ()) and [M(μ-OH)(η-CH)] (M = Rh (), Ir ()) with 1,3-bis(6'-methyl-2'-pyridylimino)isoindoline (HBMePHI). Complex reacts with HBMePHI, in dichloromethane, to afford equilibrium mixtures of , the mononuclear derivative RhCl(η-CH){κ- -(HBMePHI)} (), and the binuclear species [RhCl(η-CH)]{μ- , -(HBMePHI)} (). Under the same conditions, complex affords the iridium counterparts IrCl(η-CH){κ- -(HBMePHI)} () and [IrCl(η-CH)]{μ- , -(HBMePHI)} ().

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.

Ruthenium-Catalyzed Oxidative Amidation of Alkynes to Amides.

Complex CpRuCl(PPh) 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)(PPh)] which are oxidized to the Ru(η-CO)-ketenes by the N-oxide.

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.

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) , 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.

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 λ iodanes is further enhanced by acids (Lewis or Brønsted). The origin of such activation, however, has remained elusive.

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.