Recently, the rhodium(III)-complex [Cp*RhCl(2)](2) 1 has provided exciting opportunities for the efficient synthesis of aromatic heterocycles based on a rhodium-catalyzed C-H bond functionalization event. In the present report, the use of complexes 1 and its dicationic analogue [Cp*Rh(MeCN)(3)][SbF(6)](2) 2 have been employed in the formation of indoles via the oxidative annulation of acetanilides with internal alkynes. The optimized reaction conditions allow for molecular oxygen to be used as the terminal oxidant in this process, and the reaction may be carried out under mild temperatures (60 °C). These conditions have resulted in an expanded compatibility of the reaction to include a range of new internal alkynes bearing synthetically useful functional groups in moderate to excellent yields. The applicability of the method is exemplified in an efficient synthesis of paullone 3, a tetracyclic indole derivative with established biological activity. A mechanistic investigation of the reaction, employing deuterium labeling experiments and kinetic analysis, has provided insight into issues of reactivity for both coupling partners as well as aided in the development of conditions for improved regioselectivity with respect to meta-substituted acetanilides. This reaction class has also been extended to include the synthesis of pyrroles. Catalyst 2 efficiently couples substituted enamides with internal alkynes at room temperature to form trisubstituted pyrroles in good to excellent yields. The high functional group compatibility of this reaction enables the elaboration of the pyrrole products into a variety of differentially substituted pyrroles.

Ammonia is an abundant and inexpensive nitrogen source that represents an ideal reagent for amine synthesis. Despite its tremendous potential to provide more direct and economical routes to nitrogen-containing molecules, the use of ammonia in transition-metal-catalyzed reactions has only very recently begun to be realized.[1] The copper-or palladium-catalyzed cross-coupling of aryl halides and amines is a well-established and important method for the synthesis of arylamines in both academic and industrial settings, [2] and recent advances in catalyst design have enabled the use of ammonia as a coupling partner to generate primary arylamines. [3][4][5][6][7] Despite the success of these initial reports, a number of serious limitations regarding the scope and utility of metal-catalyzed cross-couplings of aryl halides and ammonia still exist and must be addressed before this method can be considered a viable alternative to more traditional aniline syntheses. In the case of copper, high loadings of metal and ligand are typically required (10-50 mol %) and less reactive but more economically attractive aryl chlorides, [8] or more readily accessible pseudohalides derived from phenols, are poor reaction partners.[3] Limitations regarding the palladium-catalyzed cross-coupling of ammonia [4][5][6][7] include the coupling of electron-rich, sterically unbiased aryl chlorides as well as the selective coupling of ammonia in the presence of additional amine functionality (chemoselectivity).[9] In addition, currently known systems require catalyst loading of 0.5-5 mol % of palladium as well as elevated temperatures (70-120 8C) to maintain reasonable activity for even simple aryl chloride substrates. The slow rate of oxidative addition of electron-rich aryl chlorides, combined with a lower tendency for such species lacking ortho-substitution to undergo reductive elimination [10] from the requisite [L n Pd(Ar)amido] species, can provide a rationale for the difficulties posed by such reaction partners and the elevated reaction temperatures required for catalyst turnover. Herein, we report the preparation of a suitably designed P,N-ligand that addresses several of the above-described challenges in ammonia cross-coupling, including highly chemoselective transformations and the first report of aryl chloride and aryl tosylate coupling with ammonia at room temperature.Recently, we initiated a research program employing P,Nligands as alternatives to more traditional archetypes in C À N coupling reactions. We envisioned that easily prepared and tunable ligands of this type might provide a useful middle ground in Buchwald-Hartwig aminations between strongly chelating bisphosphanes [2a] and biarylmonophosphanes [2b] that feature only weak secondary metal-ligand interactions.We have found L1 (Me-DalPhos) to be a broadly useful ligand for the palladium-catalyzed cross-coupling of aryl chlorides and amines (including ammonia); however, modestly electron-rich substrates lacking ortho-substitution gave very poor results, requiring harsh re...

Ammonia is an abundant and inexpensive nitrogen source that represents an ideal reagent for amine synthesis. Despite its tremendous potential to provide more direct and economical routes to nitrogen-containing molecules, the use of ammonia in transition-metal-catalyzed reactions has only very recently begun to be realized. [1] The copper-or palladium-catalyzed cross-coupling of aryl halides and amines is a well-established and important method for the synthesis of arylamines in both academic and industrial settings, [2] and recent advances in catalyst design have enabled the use of ammonia as a coupling partner to generate primary arylamines. [3][4][5][6][7] Despite the success of these initial reports, a number of serious limitations regarding the scope and utility of metal-catalyzed cross-couplings of aryl halides and ammonia still exist and must be addressed before this method can be considered a viable alternative to more traditional aniline syntheses. In the case of copper, high loadings of metal and ligand are typically required (10-50 mol %) and less reactive but more economically attractive aryl chlorides, [8] or more readily accessible pseudohalides derived from phenols, are poor reaction partners. [3] Limitations regarding the palladium-catalyzed cross-coupling of ammonia [4][5][6][7] include the coupling of electron-rich, sterically unbiased aryl chlorides as well as the selective coupling of ammonia in the presence of additional amine functionality (chemoselectivity). [9] In addition, currently known systems require catalyst loading of 0.5-5 mol % of palladium as well as elevated temperatures (70-120 8C) to maintain reasonable activity for even simple aryl chloride substrates. The slow rate of oxidative addition of electron-rich aryl chlorides, combined with a lower tendency for such species lacking ortho-substitution to undergo reductive elimination [10] from the requisite [L n Pd(Ar)amido] species, can provide a rationale for the difficulties posed by such reaction partners and the elevated reaction temperatures required for catalyst turnover. Herein, we report the preparation of a suitably designed P,N-ligand that addresses several of the above-described challenges in ammonia cross-coupling, including highly chemoselective transformations and the first report of aryl chloride and aryl tosylate coupling with ammonia at room temperature.Recently, we initiated a research program employing P,Nligands as alternatives to more traditional archetypes in C À N coupling reactions. We envisioned that easily prepared and tunable ligands of this type might provide a useful middle ground in Buchwald-Hartwig aminations between strongly chelating bisphosphanes [2a] and biarylmonophosphanes [2b] that feature only weak secondary metal-ligand interactions. We have found L1 (Me-DalPhos) to be a broadly useful ligand for the palladium-catalyzed cross-coupling of aryl chlorides and amines (including ammonia); however, modestly electron-rich substrates lacking ortho-substitution gave very poor results, requiring harsh...

The synthesis of indoles via the metal-catalyzed cross-coupling of ammonia is reported for the first time; the developed protocol also allows for the unprecedented use of methylamine or hydrazine as coupling partners. These Pd/Josiphos-catalyzed reactions proceed under relatively mild conditions for a range of 2-alkynylbromoarenes.

An examination of the [{Pd(cinnamyl)Cl}(2)]/Mor-DalPhos (Mor-DalPhos = di(1-adamantyl)-2-morpholinophenylphosphine) catalyst system in Buchwald-Hartwig aminations employing ammonia was conducted to better understand the catalyst formation process and to guide the development of precatalysts for otherwise challenging room-temperature ammonia monoarylations. The combination of [{Pd(cinnamyl)Cl}(2)] and Mor-DalPhos afforded [(κ(2)-P,N-Mor-DalPhos)Pd(η(1)-cinnamyl)Cl] (2), which, in the presence of a base and chlorobenzene, generated [(κ(2)-P,N-Mor-DalPhos)Pd(Ph)Cl] (1 a). Halide abstraction from 1 a afforded [(κ(3)-P,N,O-Mor-DalPhos)Pd(Ph)]OTf (5), bringing to light a potential stabilizing interaction that is offered by Mor-DalPhos. An examination of [(κ(2)-P,N-Mor-DalPhos)Pd(aryl)Cl] (1 b-f) and related precatalysts for the coupling of ammonia and chlorobenzene at room temperature established the suitability of 1 a in such challenging applications. The scope of reactivity for the use of 1 a (5 mol %) encompassed a range of (hetero)aryl (pseudo)halides (X = Cl, Br, I, OTs) with diverse substituents (alkyl, aryl, ether, thioether, ketone, amine, fluoro, trifluoromethyl, and nitrile), including chemoselective arylations.

No abstract

Photocatalytic processes to convert CO2 to useful products including CO and HCOOH are of particular interest as a means to harvest the power of the sun for sustainable energy applications. Herein, we report the photocatalytic reduction of CO2 using iron-based catalysts and visible light generating varying ratios of synthesis gas.

Catalytic generation of hydrogen from aqueous ethanol solution proceeds in the presence of pincer-type transition metal catalysts. Optimal results are obtained applying a [Ru(H)(Cl)(CO)(iPr2PEtN(H)EtPiPr2)] complex (catalyst TON 80,000) in the presence of water and base. This dehydrogenation reaction provides up to 70% acetic acid in a selective manner. For the first time, it is shown that bioethanol obtained from fermentation processes can be used directly in this protocol without the need for water removal. The produced hydrogen can be directly utilized in proton exchange membrane (PEM) fuel cells, since very low amounts of CO are formed.