Eduardo Peris

Bio: Eduardo Peris is an academic researcher from James I University. The author has contributed to research in topics: Carbene & Catalysis. The author has an hindex of 65, co-authored 236 publications receiving 14182 citations. Previous affiliations of Eduardo Peris include Paul Sabatier University & Yale University.

Complexes with poly(N-heterocyclic carbene) ligands: structural features and catalytic applications.

Abstract: ion of the chloride ligands, compound 2 was further reacted with MeMgCl, yielding the bimetallic compound 3 in which the biscarbene ligand is bridging two Cr(II) atoms, also bridged by two methyl ligands. Recent studies by Arnold and co-workers showed that the incorporation of an anionic functional group (alkoxide, amido, or amino) in an NHC unit allows the preparation of tridentate ligands capable of coordinating to d0 early transition metals such as yttrium, titanium, and zirconium.87 The lithium aminodicarbene chloride complex 5 reacts with Y[N(SiMe3)2]3 affording the yttrium(III) complex 6 (Scheme 10). Hexacoordinated titanium (7) and zirconium (8) complexes were synthesized by reaction of 4 with M(NEt2)4 (M ) Ti, Zr) (Scheme 10). Complexes 7 and 8 constituted the first examples of group 3 and 4 metal complexes with monoanionic biscarbene ligands. Another interesting example of early transition metal NHC-based complexes was described by Smith and coworkers.88 By the reaction shown in Scheme 11, the tris(NHC)borate 989,90 afforded a tricarbonyl complex of Mn(I) with a tripodal tris-NHC ligand, 10. The analysis of the ν(CO) bands on the IR spectrum of this complex showed that 9 is the most electron-donating tripodal ligand compared with all others that have been bound to the same Mntricarbonyl fragment. Compound 10 is air-sensitive and is easily oxidized to a homoleptic Mn(IV) complex (11, Scheme 11), which is the first example of a Mn(IV)-NHC complex reported to-date. 4.2. Catalytic Applications Although many catalytic applications of late transition metal complexes bearing poly-NHC ligands have been described, those of early transition metals are restricted to a few examples. In 2003, Gibson and co-workers reported Cr(III)-based ethylene oligomerization precatalysts that incorporate a CNC-pincer carbene ligand.91,92 More recently, McGuinness shed some light on the mechanism of the reaction with the mentioned pincer complexes in combination with MAO.93 The Cr(II) and Cr(III) complexes described by Theopold were tested for polymerization of ethylene with a MAO cocatalyst, showing low activities and a broad weight distribution of the polymers.85 In particular, Cr(II) compounds such as 2 (Scheme 9) were unreactive to ethylene when exposed to MAO, showing that the more Lewis acidic Cr(III) performs better in this reaction. The authors pointed out the ease with which the Cr(III) complexes are reduced to Cr(II), arguing that very strong σ-donating but soft NHC ligands may have a stronger affinity for the softer Cr(II) rather than the harder Cr(III). Thus, they concluded that this ligand system may be better suited for lower oxidation state chromium chemistry and that, due to the inactivity of the Cr(II) compounds tested, it would not lead to successful results in ethylene polymerization. 5. Poly-NHC Ligands in Complexes of Group 8 Metals

Smart N-Heterocyclic Carbene Ligands in Catalysis

Abstract: It is well-recognized that N-heterocyclic carbene (NHC) ligands have provided a new dimension to the design of homogeneous catalysts. Part of the success of this type of ligands resides in the limitless access to a variety of topologies with tuned electronic properties, but also in the ability of a family of NHCs that are able to adapt their properties to the specific requirements of individual catalytic transformations. The term “smart” is used here to refer to switchable, multifunctional, adaptable, or tunable ligands and, in general, to all those ligands that are able to modify their steric or electronic properties to fulfill the requirements of a defined catalytic reaction. The purpose of this review is to comprehensively describe all types of smart NHC ligands by focusing attention on the catalytically relevant ligand-based reactivity.

N-heterocyclic carbenes: a new concept in organometallic catalysis.

Abstract: N-Heterocyclic carbenes have become universal ligands in organometallic and inorganic coordination chemistry. They not only bind to any transition metal, be it in low or high oxidation states, but also to main group elements such as beryllium, sulfur, and iodine. Because of their specific coordination chemistry, N-heterocyclic carbenes both stabilize and activate metal centers in quite different key catalytic steps of organic syntheses, for example, C-H activation, C-C, C-H, C-O, and C-N bond formation. There is now ample evidence that in the new generation of organometallic catalysts the established ligand class of organophosphanes will be supplemented and, in part, replaced by N-heterocyclic carbenes. Over the past few years, this chemistry has been the field of vivid scientific competition, and yielded previously unexpected successes in key areas of homogeneous catalysis. From the work in numerous academic laboratories and in industry, a revolutionary turning point in oraganometallic catalysis is emerging.

An overview of N-heterocyclic carbenes

Abstract: The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of organic compounds for investigation. From these beginnings as academic curiosities, N-heterocyclic carbenes today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. Here we provide a concise overview of N-heterocyclic carbenes in modern chemistry, summarizing their general properties and uses and highlighting how these features are being exploited in a selection of pioneering recent studies.

Carboxylate-assisted transition-metal-catalyzed C-H bond functionalizations: mechanism and scope.

Abstract: The site-selective formation of carbon-carbon bonds through direct functionalizations of otherwise unreactive carbon-hydrogen bonds constitutes an economically attractive strategy for an overall streamlining of sustainable syntheses. In recent decades, intensive research efforts have led to the development of various reaction conditions for challenging C-H bond functionalizations, among which transition-metal-catalyzed transformations arguably constitute thus far the most valuable tool. For instance, the use of inter alia palladium, ruthenium, rhodium, copper, or iron complexes set the stage for chemo-, site-, diastereo-, and/or enantioselective C-H bond functionalizations. Key to success was generally a detailed mechanistic understanding of the elementary C-H bond metalation step, which depending on the nature of the metal fragment can proceed via several distinct reaction pathways. Traditionally, three different modes of action were primarily considered for CH bond metalations, namely, (i) oxidative addition with electronrich late transition metals, (ii) σ-bond metathesis with early transition metals, and (iii) electrophilic activation with electrondeficient late transition metals (Scheme 1). However, more recent mechanistic studies indicated the existence of a continuum of electrophilic, ambiphilic, and nucleophilic interactions. Within this continuum, detailed experimental and computational analysis provided strong evidence for novel C-H bond metalationmechanisms relying on the assistance of a bifunctional ligand bearing an additional Lewis-basic heteroatom, such as that found in (heteroatom-substituted) secondary phosphine oxides or most prominently carboxylates (Scheme 1, iv). This novel insight into the nature of stoichiometric metalations has served as stimulus for the development of novel transformations based on cocatalytic amounts of carboxylates, which significantly broadened the scope of C-H bond functionalizations in recent years, with most remarkable progress being made in palladiumor ruthenium-catalyzed direct arylations and direct alkylations. These carboxylate-assisted C-H bond transformations were mostly proposed to proceed via a mechanism in which metalation takes place via a concerted base-assisted deprotonation. To mechanistically differentiate these intramolecular metalations new acronyms have recently been introduced into the literature, such as CMD (concerted metalationdeprotonation), IES (internal electrophilic substitution), or AMLA (ambiphilic metal ligand activation), which describe related mechanisms and will be used below where appropriate. This review summarizes the development and scope of carboxylates as cocatalysts in transition-metal-catalyzed C-H functionalizations until autumn 2010. Moreover, experimental and computational studies on stoichiometric metalation reactions being of relevance to the mechanism of these catalytic processes are discussed as well. Mechanistically related C-H bond cleavage reactions with ruthenium or iridium complexes bearing monodentate ligands are, however, only covered with respect to their working mode, and transformations with stoichiometric amounts of simple acetate bases are solely included when their mechanism was suggested to proceed by acetate-assisted metalation.

Recent advances in catalytic hydrogenation of carbon dioxide

Abstract: Owing to the increasing emissions of carbon dioxide (CO2), human life and the ecological environment have been affected by global warming and climate changes. To mitigate the concentration of CO2 in the atmosphere various strategies have been implemented such as separation, storage, and utilization of CO2. Although it has been explored for many years, hydrogenation reaction, an important representative among chemical conversions of CO2, offers challenging opportunities for sustainable development in energy and the environment. Indeed, the hydrogenation of CO2 not only reduces the increasing CO2 buildup but also produces fuels and chemicals. In this critical review we discuss recent developments in this area, with emphases on catalytic reactivity, reactor innovation, and reaction mechanism. We also provide an overview regarding the challenges and opportunities for future research in the field (319 references).