Stoichiometric Transformations Research Articles

ChemInform Abstract: Molybdenum‐Catalyzed Reduction of Molecular Dinitrogen into Ammonia under Ambient Reaction Conditions

AbstractReview: 47 refs.

Frustrated Lewis Pairs.

The articulation of the notion of "frustrated Lewis pairs" (FLPs), which emerged from the discovery that H2 can be reversibly activated by combinations of sterically encumbered Lewis acids and bases, has prompted a great deal of recent activity. Perhaps the most remarkable consequence has been the development of FLP catalysts for the hydrogenation of a range of organic substrates. In the past 9 years, the substrate scope has evolved from bulky polar species to include a wide range of unsaturated organic molecules. In addition, effective stereoselective metal-free hydrogenation catalysts have begun to emerge. The mechanism of this activation of H2 has been explored, and the nature and range of Lewis acid/base combinations capable of effecting such activation have also expanded to include a variety of non-metal species. The reactivity of FLPs with a variety of other small molecules, including olefins, alkynes, and a range of element oxides, has also been developed. Although much of this latter chemistry has uncovered unique stoichiometric transformations, metal-free catalytic hydroamination, CO2 reduction chemistry, and applications in polymerization have also been achieved. The concept is also beginning to find applications in bioinorganic and materials chemistry as well as heterogeneous catalysis. This Perspective highlights many of these developments and discusses the relationship between FLPs and established chemistry. Some of the directions and developments that are likely to emerge from FLP chemistry in the future are also presented.

Molybdenum-catalyzed reduction of molecular dinitrogen into ammonia under ambient reaction conditions

Synthesis of transition metal–dinitrogen complexes and stoichiometric transformations of their coordinated dinitrogen into ammonia and hydrazine have so far been well investigated in order to achieve a novel nitrogen fixation under ambient conditions. As an extension of our study, the dimolybdenum–dinitrogen complex bearing PNP pincer ligands has been found to work as an effective catalyst for the formation of ammonia from dinitrogen, where 52 equiv of ammonia are produced based on the catalyst (26 equiv of ammonia are produced based on the molybdenum atom of the catalyst). This is the most effective catalytic reaction system for the formation of ammonia from molecular dinitrogen catalyzed by transition metal–dinitrogen complexes as catalysts under ambient reaction conditions. Herein, we describe recent results concerning the catalytic reaction, including the proposed reaction pathway.

Recent advances in stoichiometric phosphine-mediated organic synthetic reactions

Organic synthetic reactions mediated by tertiary phosphines have attracted much attention in the organic chemistry community in the past two decades. These reactions can be divided into two categories: phosphine-catalyzed and stoichiometric phosphine-mediated transformations. While the phosphine-catalyzed reactions mechanistically rely on the unique properties of tertiary phosphines such as excellent nucleophilicity and good leaving group ability, the stoichiometric transformations are usually driven by nucleophilicity and strong oxyphilicity of tertiary phosphines. Since tertiary phosphines represent an important class of versatile chemical reagents in organic synthesis, stoichiometric phosphine-mediated reactions have recently demonstrated their uniqueness and high efficiency in organic synthesis, particularly with respect to the construction of carbon–carbon and carbon–heteroatom bonds, and therefore have stimulated much research interest. In this review, recent advances in stoichiometric phosphine-mediated reactions primarily including olefinations and annulations are summarized.

Redox-active ligands in catalysis

Odd-electron, redox-active ligands are discussed in the context of catalysis. We focus on ligand-based, non-singlet state intermediates and their participation in catalytic processes and related stoichiometric transformations.

ChemInform Abstract: Tantallaaziridines: From Synthesis to Catalytic Applications

AbstractReview: 76 refs.

ChemInform Abstract: Catalytic Applications of Early/Late Heterobimetallic Complexes

AbstractReview: 100 refs.

Decisive Steps of the Hydrodefluorination of Fluoroaromatics using [Ni(NHC)2

The hydrodefluorination reaction of perfluorinated arenes using [Ni2(iPr2Im)4(COD)] (1; iPr2Im = 1,3-bis(isopropyl)imidazolin-2-ylidene) as a catalyst as well as stoichiometric transformations to elucidate the decisive steps for this reaction are reported. The reaction of hexafluorobenzene with 5 equiv of triphenylsilane in the presence of 5 mol % of 1 affords 1,2,4,5-tetrafluorobenzene after 48 h at 60 °C and 1,4-difluorobenzene after 96 h at 80 °C; the reaction of perfluorotoluene and 5 equiv of Et3SiH for 4 days at 80 °C results in the selective formation of 1-(CF3)-2,3,5,6-C6F4H. Stoichiometric transformations of the complexes cis-[Ni(iPr2Im)2(H)(SiPh3)] and cis-[Ni(iPr2Im)2(H)(SiMePh2)] with hexafluorobenzene at room temperature lead to the formation of trans-[Ni(iPr2Im)2(F)(C6F5)] (2) and trans-[Ni(iPr2Im)2(H)(C6F5)] (4) with elimination of the corresponding silane or fluorosilane. The reactions of the C–F activation products trans-[Ni(iPr2Im)2(F)(C6F5)] (2) and trans-[Ni(iPr2Im)2(F)(4-(CF3)C6F4)] (...

Iron-catalysed transformation of molecular dinitrogen into silylamine under ambient conditions

Although stoichiometric transformations using transition metal-N(2) complexes have been well investigated towards the goal of nitrogen fixation under mild reaction conditions, only a few examples of the catalytic transformations of N(2) using transition metal-N(2) complexes as catalysts have been reported. In almost all the catalytic systems, the use of Mo is essential to realize the catalytic transformation of N(2), where Mo-N(2) complexes are considered to work as effective catalysts. Here we show the first successful example of the Fe-catalysed transformation of N(2) into N(SiMe(3))(3) under ambient conditions, in which iron complexes such as iron pentacarbonyl [Fe(CO)(5)] and ferrocenes have been found to work as effective catalysts. A plausible reaction pathway is proposed, where Fe(II)-N(2) complex bearing two Me(3)Si groups as ancillary ligands has an important role as a key reactive intermediate, with the aid of density-functional-theory calculations.

Tantallaaziridines: from synthesis to catalytic applications

Tantallaaziridines are a class of organometallic compounds containing three-membered rings that include a tantalum, carbon and nitrogen atom. Closely related complexes containing the related iminoacyl ligand can be used as starting materials for tantallaaziridine synthesis. Tantallaaziridines can also be synthesized by reduction of imines or β-hydrogen abstraction of amides to give stable, isolable complexes. Tantallaaziridines possess a reactive Ta-C bond that can undergo stoichiometric transformations with unsaturated organic molecules to give new organometallic products. Upon quenching of such reactions with aqueous workup, selectively substituted small molecule amines can be prepared. Tantallaaziridines have also been proposed as catalytic intermediates in the direct α-alkylation of amines, hydroaminoalkylation, by exploiting the β-hydrogen abstraction route to regenerate the catalytically active species. Recent progress and remaining challenges in the field will be discussed.

Catalytic Applications of Early/Late Heterobimetallic Complexes

Transition metal complexes that combine electronically different metals are most readily designed by combining an early transition metal and a late transition metal, typically via a bridging ligand framework. These so-called “early/late” heterobimetallic complexes have recently proven active in a number of catalytic transformations that are not accessible with analogous monometallic complexes. This review discusses recent contributions to catalytic and stoichiometric transformations of early/late heterobimetallic complexes.

Stable Mononuclear Organometallic Pd(III) Complexes and Their C−C Bond Formation Reactivity

Organometallic Pd(III) complexes have been implicated as intermediates in a number of catalytic and stoichiometric transformations. While a few dinuclear organometallic Pd(III) complexes have been characterized, no mononuclear organometallic Pd(III) complexes have been isolated to date. Reported herein is the synthesis and characterization of a series of Pd(III) complexes supported by the tetradentate ligand N,N'-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane (N4). Chemical or electrochemical oxidation of the Pd(II) complexes (N4)Pd(II)(R)(X) (R = Me, X = Cl: 1; R = Ph, X = Cl: 2; R = X = Me: 3) generates [(N4)Pd(III)MeCl](+) (1(+)), [(N4)Pd(III)PhCl](+) (2(+)), and [(N4)Pd(III)Me(2)](+) (3(+)). These stable Pd(III) complexes were isolated and characterized by X-ray diffraction, cyclic voltammetry, UV-vis, EPR, magnetic moment measurements, and DFT to confirm the presence of paramagnetic d(7) Pd(III) centers. Moreover, these Pd(III) complexes undergo light-induced C-C bond formation to give the corresponding homocoupled products ethane or biphenyl. Particularly remarkable is the observation for the first time of ethane formation from monomethyl Pd complexes.

Reaction of an oxaruthenacycle with DMAD. Stoichiometric transformations of 2,6-xylenol to allylic phenols and benzopyrans via sp3 C–H bond cleavage reaction

Insertion of a dimethyl acetylenedicarboxylate (DMAD) into the Ru-C bond in a cycloruthenated complex Ru[OC(6)H(3)(2-CH(2))(6-Me)-kappa(2)O,C](PMe(3))(4) () has been achieved to give a seven-membered oxaruthenacycle Ru[OC(6)H(3){2-CH(2)C(CO(2)Me)[double bond, length as m-dash]C(CO(2)Me)}(6-Me)-kappa(2)O,C](PMe(3))(3) () in 47% yield. The molecular structure of by X-ray analysis shows an agostic interaction between the ruthenium and one of the benzylic methylene protons. Complex shows fluxional behaviour in solution and the variable temperature NMR studies suggest this fluxionality to be responsible for the turnstile rotation of three PMe(3) ligands and the rotation of the alpha-methoxycarbonyl group. Heating of a toluene solution of at 100 degrees C for 2 h results in the 1,3-H shift reaction in to give a kappa(1)O,eta(3)-C,C',C'' allylic complex Ru[OC(6)H(3){2-CHC(CO(2)Me)CH(CO(2)Me)}(6-Me)-kappa(1)O,eta(3)C,C',C''](PMe(3))(3) () (80-90%), whose molecular structure is revealed by X-ray analysis. Acidolyses of and give 2-[(Z)-2',3'-bis(methoxycarbonyl)allyl]-6-methylphenol () (88%) and 2-[(Z)-2',3'-bis(methoxycarbonyl)propenyl]-6-methylphenol () (47%), respectively, and iodolyses of and produce 2,3-bis(methoxycarbonyl)-8-methyl-4H-benzopyran () (24%) and 2,3-bis(methoxycarbonyl)-8-methyl-2H-benzopyran () (48%), respectively.

New Routes for the Functionalization of P4

New Routes for the Functionalization of P₄

Catalytic and Stoichiometric Transformations by Multimetallic Rare Earth Metal Complexes

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enhanced Reactivity of Cationic Hafnocene Complexes toward σ-Bond Metathesis Reactions. Si−H and Si−C Bond Activations in Stoichiometric and Catalytic Organosilane Conversions

Interest in developing highly active catalysts for processes involving σ-bond metathesis steps led to a study directly comparing neutral, zwitterionic, and cationic derivatives of CpCp*Hf− in reactions with silanes. In stoichiometric transformations, comparisons of the reactivities of CpCp*HfMe2 (1), CpCp*HfMe(OTf) (2), CpCp*HfMe(μ-Me)B(C6F5)3 (3), and [CpCp*HfMe][B(C6F5)4] (4) with organosilanes indicate that the cationic character in the complex influences the activity of the Hf−Me bond toward reactions with Si−H bonds. Enhanced activity in catalytic σ-bond metathesis reactions of PhSiH3 was also observed with zwitterionic hafnium hydride complexes. Neutral CpCp*HfHCl (7) reacts slowly with PhSiH3 to give oligomers, while zwitterionic CpCp*HfH(μ-H)B(C6F5)3 (6) reacts ca. 10 times faster, activating both Si−C and Si−H bonds of PhSiH3, to give redistribution and dehydrocoupling products. A mechanism based on σ-bond metathesis is evidenced by identical experimental rate laws (rate ∝ [catalyst][PhSiH3]2) fo...

Iridium-catalyzed H/D exchange into organic compounds in water.

The air-stable complex Cp(PMe(3))IrCl(2) efficiently catalyzes the exchange of deuterium from D(2)O into both activated and unactivated C-H bonds of organic molecules without added acid or stabilizers. Selectivity is observed in many cases, with activation of primary C-H bonds occurring preferentially. A number of new stoichiometric transformations involving the iridiym catalyst precursor are also presented, including an oxidation-decarbonylation reaction with primary alcohols.

Qualitative analysis of biochemical reaction systems

The qualitative analysis of biochemical reaction systems is presented. A discrete event systems approach is used to represent and analyze bioreaction pathways. The approach is based on Petri nets, which are particularly suited to modeling stoichiometric transformations, i.e. the inter-conversion of metabolites in fixed proportions. The properties and methods for the analysis of Petri nets, along with their interpretation for biochemical systems, are presented. As an example, the combined glycolytic and pentose phosphate pathway of the erythrocyte cell is presented to illustrate the concepts of the methodology.

Molecular solid-gas organometallic chemistry. Catalytic and stoichiometric transformations of ethyne at iridium

Molecular solid-gas organometallic chemistry. Catalytic and stoichiometric transformations of ethyne at iridium

Catalytic and Stoichiometric Transformations with Triphenyl(P,P,P-Triphenylphosphine Imidato-N) Phosphorus Cyanide, [Pnp Cyanide

Abstract Reactions involving anhydrous [PNP]+CN−, 1, are described for a series of nucleophilic displacements. The reagent may be used stoichiometrically with moisture sensitive substrates, and also acts as an efficient phase transfer catalyst.