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An operationally simple, user and eco-friendly synthetic protocol for the synthesis of [Rh(acac)(CO)(NHC)] complexes is described. Insights into the mechanism are provided using operando spectroscopy. The spectroscopic fingerprints of these complexes are correlated to NHCs reported electron-donating descriptor values, highlighting a new strategy to evaluate carbenes' electronic properties. An assessment of these complexes in catalytic applications is also reported, showing promising results in the catalytic hydrogenation of aromatic ketones.

A novel, efficient and facile protocol for the synthesis of a series of [Ru(NHC)(CO3)(p-cymene)] complexes is reported. This family of Ru-NHC complexes was obtained from imidazol(in)ium tetrafluoroborate or imidazolium hydrogen carbonate salts in moderate to excellent yields, employing sustainable weak base. The ruthenium complexes were successfully utilized in the transfer hydrogenation of ketones as highly active multifunctional catalysts.

Amides are among the most important and ubiquitous functional groups in organic chemistry and process development. In this Practical Synthetic Procedure, a protocol for the Suzuki–Miyaura cross-coupling of amides by selective N–C(O) bond activation catalyzed by commercially available, air- and moisture-stable palladium/N-heterocyclic carbene (NHC) complexes is described. The procedure described involves [Pd(IPr)(cin)Cl] [IPr = 2,6-(diisopropylphenyl)imidazol-2-ylidene, cin = cinnamyl] at 0.10 mol% at room temperature and is performed on decagram scale. Furthermore, a procedure for the synthesis of amide starting materials is accomplished via selective N-tert-butoxycarbonylation, which is the preferred method over N-acylation. The present protocol carries advantages of operational simplicity, commercial availability of catalysts, and excellent conversions at low catalyst loadings. The method is generally useful for activation of N–C(O) amide bonds in a broad spectrum of amide precursors. The protocol should facilitate the implementation of amide cross-coupling reactions.

The reaction mechanism leading to the formation of cross-coupling palladium pre-catalysts of the PEPPSI family was investigated. Two intermediates were isolated and proved to be both suitable synthons to the pre-catalysts, with one permitting the design of a novel and greener user-friendly synthetic route. In light of this mechanistic understanding, the traditional one-pot method was shown to be possible using stoichiometric amounts of throw-away ligand, which represents a considerable synthetic improvement over the wasteful "in pyridine" approach.

The integration of a membrane separation protocol with the platinum-catalyzed hydrosilylation of olefins is investigated. The catalytic reaction is first optimized in batch where [Pt(IPr*)(dms)Cl2 ] (IPr*=1,3-bis[2,6-bis(diphenylmethyl)-4-methylphenyl]imidazol-2-ylidene, dms=dimethyl sulfide) demonstrates superior activity compared to the less sterically encumbered [Pt(SIPr)(dms)Cl2 ] (SIPr=1,3-bis(2,6-diisopropylphenyl)imidazolidine) congener. Filtration conditions are identified in membrane screening experiments. Hydrosilylation of 1-octene catalyzed by [Pt(IPr*)(dms)Cl2 ] is conducted in continuous mode and the platinum catalyst is separated efficiently over the commercially available Borsig oNF-2 membrane, all under solvent-free conditions. An advantage of this process is that both reaction and separation are coupled in a single step. Moreover, at the end of the process the intact catalyst was recovered in 80 % yield as an off-white solid without any further purification.

The story of C−C bond formation includes several reactions, and surely Suzuki‐Miyaura is among the most outstanding ones. Herein, a brief historical overview of insights regarding the reaction mechanism is provided. In particular, the formation of the catalytically active species is probably the main concern, thus the preactivation is in competition with, or even assumes the role of the rate determining step (rds) of the overall reaction. Computational chemistry is key in identifying the rds and thus leading to milder conditions on an experimental level by means of predictive catalysis., The complexity of the Pd‐catalyzed Suzuki‐Miyaura C−C bond formation reaction lies in the indivdual steps of the cycle, as well as in the generation of the catalytically active species. An overview of the topic is provided from a historical perspective.

The considerable importance of α-arylated carbonyl compounds, which are widely used as final products or as key intermediates in the pharmaceutical industry, has prompted numerous research groups to develop efficient synthetic strategies for their preparation in recent decades. In this context, the α-arylation of carbonyl compounds catalyzed by transition-metal complexes have been particularly helpful in constructing this motif. As illustrated in this contribution, tremendous advances have taken place using palladium– and nickel–NHC (NHC = N-heterocyclic carbene) complexes as pre-catalysts for the arylation of a wide range of ketones, aldehydes, esters and amides with electron-rich, electron-neutral, electron-poor, and sterically hindered aryl halides or pseudo-halides. Despite significant progress, especially in asymmetric α-arylations promoted by chiral NHC ligands, there are numerous challenges which have and continue to encourage further studies on this topic. Some of these are presented in this report.

A straightforward methodology for the decarboxylative cross-coupling of aryl bromides and phenylpropiolic acid using a Pd(II)-NHC catalyst has been developed. Various aryl bromides have been successfully transformed into the corresponding di-substituted alkynes using environmentally benign conditions (weak base and ethanol as solvent). This efficient catalytic system also proved useful for the copper-free Sonogashira coupling of aryl and alkenyl bromides with various terminal alkynes. The synthetic utility of these methodologies was highlighted in the synthesis of a polyaromatic compound and various fluoroenynes.

The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C.), AstraZeneca (Studenship to C.M.Z) and VLAIO (CO2PERATE) for support of this work. We thank King Saud University (DSF Program) and KAUST (Award No.OSR-2015-CCF-1974-03) for support. A new class of [Au(NHC)(Bpin)] complexes has been synthesized and their unusual reactivity was investigated using computational and experimental methods. The gold-boryl complexes exhibit unexpected high stability and reactivity. Postprint

Summary With the aim of overcoming the well-known limitations of platinum-based antineoplastic drugs, recent efforts have focused on the development of new anticancer agents containing metals other than platinum. Among these agents, organopalladium compounds have received significant recent attention due to their generally high stability under physiological conditions. A significant number of these compounds have shown promising in vitro and in vivo antiproliferative activity toward several cisplatin-sensitive and cisplatin-resistant tumors and have sometimes exhibited a different mechanism of action compared to platinum-based drugs. In this review, recent advances in the field of organopalladium compounds as potential anticancer agents are discussed.

The synthesis and characterization of novel palladium complexes bearing N-heterocyclic carbenes (NHCs) and 1,4,7-triaza-9-phosphatricyclo[5.3.2.1]tridecane (CAP) are reported. These organometallic complexes can be easily obtained using two different synthetic strategies that involve either the substitution of the pyridine ligand from trans-[Pd(NHC)(Py)Cl2] or by simple addition of the CAP ligand to dimeric species [Pd(NHC)Cl2]2. The mixed NHC/CAP complexes were tested as pre-catalysts in the Buchwald–Hartwig aryl amination coupling, showing good catalytic activity, especially in the case of cis-[Pd(IPr)(CAP)Cl2].

Chalcogen-based urea compounds supported by a wide range of N-heterocyclic carbenes are synthesised and fully characterised. Coordination of selenoureas is further explored with Group 11 transition metals to form new copper, gold and silver complexes. Single crystal X-ray analyses unambiguously establish the solid-state coordination of these complexes and show that the geometry of a complex is highly influenced by a combination of electronic properties – mainly π-accepting ability – and steric hindrance of the ligands, as well as the nature of the metal, affording a variety of coordination behaviours. In this report, we investigate these phenomena using several experimental methods.

Summary The development of more reactive, general, easily accessible, and readily available Pd(II)–NHC precatalysts remains a key challenge in homogeneous catalysis. In this study, we establish air-stable NHC–Pd(II) chloro-dimers, [Pd(NHC)(μ-Cl)Cl]2, as the most reactive Pd(II)–NHC catalysts developed to date. Most crucially, compared with [Pd(NHC)(allyl)Cl] complexes, replacement of the allyl throw-away ligand with chloride allows for a more facile activation step, while effectively preventing the formation of off-cycle [Pd2(μ-allyl)(μ-Cl)(NHC)2] products. The utility is demonstrated via broad compatibility with amide cross-coupling, Suzuki cross-coupling, and the direct, late-stage functionalization of pharmaceuticals. Computational studies provide key insight into the NHC–Pd(II) chloro-dimer activation pathway. A facile synthesis of NHC–Pd(II) chloro-dimers in one-pot from NHC salts is reported. Considering the tremendous utility of Pd-catalyzed cross-coupling reactions and the overwhelming success of [Pd(NHC)(allyl)Cl] precatalysts, we believe that NHC–Pd(II) chloro-dimers, [Pd(NHC)(μ-Cl)Cl]2, should be considered as go-to precatalysts of choice in cross-coupling processes., Graphical Abstract, Highlights • Highly reactive, air-stable PdII–NHC chloro-dimer catalysts for cross-coupling reactions • Broad substrate scope, excellent functional group tolerance, and chemoselectivity • Rapid one-step catalyst synthesis and facile catalyst activation • DFT studies provide key insights into PdII–NHC chloro-dimer activation pathway, Chemistry; Inorganic Chemistry; Catalysis; Organic Synthesis

Transition-metal-catalyzed cross-coupling reactions represent a most powerful tool for the rapid construction of C-C and C-X bonds available to synthetic chemists. Recently, tremendous progress has been made in the burgeoning area of cross-coupling reactions of amides and esters enabled by regio- and chemoselective acyl C-X (X = N, O) cleavage using well-defined Pd(II)-NHC complexes. The use of N-heterocyclic carbenes as ligands in palladium-catalyzed cross-couplings permits reactions of amides and esters that were previously impossible using palladium or could be achieved only under harsh conditions. These reactions provide an attractive method to synthetic chemists to manipulate the traditionally inert amide and ester bonds with the broad cross-coupling generality inherent to palladium catalysis. Research in the area of cross-coupling of stable acyl electrophiles can be broadly categorized by the type of electrophile undergoing the cross-coupling. Recent studies have shown that cross-coupling of amides by transition-metal catalysis represents one of the most straightforward and wide-ranging ways of manipulating the classically inert amide bonds into generic acyl-metal intermediates that can be systematically exploited in cross-coupling reactions as a new paradigm in organic synthesis. The key to achieving high chemoselectivity of the process is control of amidic resonance (n

The authors gratefully acknowledge the European Commission (EC) for funding through the seventh framework program SYNFLOW, the European Research Council (ERC) (Advanced Investigator Award “FUNCAT” to S. P. N.), The Engineering and Physical Sciences Research Council (EPSRC) and AstraZeneca (Studentship to C. M. Z.). The influence of C4,5-halogenation on palladium N-heterocyclic carbene complexes and their activity in the Suzuki-Miyaura reaction have been investigated. Two [Pd(NHC)(cin)Cl] complexes bearing IPrCl and IPrBr ligands were synthesized. After determining electronic and steric properties of these ligands, their properties were compared to those of [Pd(IPr)(cin)Cl]. The three palladium complexes were studied using DFT calculations to delineate their behaviour in the activation step leading to the putative 12-electron active catalyst. Experimentally, their catalytic activity in the Suzuki-Miyaura reaction involving a wide range of coupling partners (30 entries) at low catalyst loading was studied. Postprint

The authors acknowledge FAPERJ for providing research grants and financial support. MB thanks the School of Chemistry and EaStCHEM for support and for access to a computer cluster maintained by Dr H. Früchtl. JWMC acknowledges CNPq for a research grant. The experimental work was supported via our membership of the UK Catalysis Hub consortium funded by EPSRC (grants EP/K014706/2, EP/K014668/1, EP/K014854/1 and EP/K014714/1). SPN gratefully acknowledges the European Commission for support in the form of an ERC Advanced Researcher grant (227817-FUNCAT). A new mechanism is proposed for the Ni-catalysed carboxylation of organoboronates with CO2. DFT investigations at the PBE0-D3 level have shown that direct CO2 addition to the catalysts [Ni(NHC)(Allyl)Cl] (1NHC, NHC = IMe, IPr, SIPr and IPr*) is kinetically disfavored and formation of the Aresta-type intermediate is unlikely to occur. According to the mechanism proposed here, the carboxylation process starts with addition of the borate species to 1NHC, followed by transmetalation, CO2 cycloaddition and carboxylation. The rate-determining step was identified as being the transmetalation process, with computed relative free energy barriers of 34.8, 36.8 and 33.5 kcal mol-1 for 1IPr, 1SIPr and 1IPr*, respectively Postprint

ADS thanks the Royal Society for a Wolfson Research Merit Award. We also thank the EPSRC UK National Mass Spectrometry Facility at Swansea University. SPN thanks King Abdullah University of Science and Technology (Award No. SR-2015-CCF-1974-03) and King Saud University for support. During an investigation into the potential union of Lewis basic isothiourea organocatalysis and gold catalysis, the formation of gold‐isothiourea complexes was observed. These novel gold complexes were formed in high yield and were found to be air‐ and moisture stable. A series of neutral and cationic chiral gold(I) and gold(III) complexes bearing enantiopure isothiourea ligands was therefore synthesized and fully characterized. The steric and electronic properties of the isothiourea ligands was assessed through calculation of their percent buried volume and the synthesis and analysis of novel iridium(I)‐isothiourea carbonyl complexes. The novel gold(I)‐ and gold(III)‐isothiourea complexes have been applied in preliminary catalytic and biological studies, and display promising preliminary levels of catalytic activity and potency towards cancerous cell lines and clinically‐relevant enzymes. Postprint

A palladium N-heterocyclic carbene catalyzed methodology for the synthesis of substituted, N-unprotected indoles and azaindoles is reported. The protocol permits access to various, highly substituted members of these classes of compounds. Although two possible reaction pathways (deprotonative and Heck-like) can be proposed, control experiments, supported by computational studies, point toward a deprotonative mechanism being operative.

A generalized approach to the optimization and implementation of Buchwald-Hartwig reactions in flow is reported, through the combination of three key factors: a highly active palladium catalyst; a universal approach for continuous work-up and purification, and a methodology for catalyst recycling and reuse. The palladium N-heterocyclic carbene (NHC) pre-catalyst [Pd(IPr*)(cin)Cl] 4 (IPr* = 1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene; cin = η3-cinnamyl) is an excellent choice for continuous Buchwald-Hartwig reactions, due to its inherent high activity and stability. In preparation for running this reaction in flow (published concurrently), a detailed study has been carried out into its water stability, ultimately allowing the recycling of the catalyst in the organic phase up to 3 times in batch mode. A “right-first-time” work-up methodology has also been developed, resulting in a universal protocol that allows the selective extraction of the Buchwald-Hartwig product into the aqueous stream as a salt, while retaining the aryl bromide starting material in the organic stream with the catalyst, thus negating the requirement for further purification. It is therefore envisaged that this approach will particularly amenable to exploitation in the Pharmaceutical industry. An optimized, scalable synthesis of [Pd(IPr*)(cin)Cl] is also reported on multi-hundred gram scale.

The first turnover event of an olefin metathesis reaction using a new family of homogenous Ru-based catalysts bearing modified indenylidene ligands has been investigated, using methoxyethylene as a substrate. The study is carried out by means of density functional theory (DFT). The indenylidene ligands are decorated with ortho-methyl and isopropyl groups at both ortho positions of their phenyl ring. DFT results highlight the more sterically demanding indenylidenes have to undergo a more exothermic first phosphine dissociation step. Overall, the study emphasises advantages of increased steric hindrance in promoting the phosphine release, and the relative stability of the corresponding metallacycle over classical ylidene ligands. Mayer bond orders and steric maps provide structural reasons for these effects, whereas NICS aromaticity and conceptual DFT confirm that the electronic parameters do not play a significant role.

The use of the ITent-based series of Pd-N-heterocyclic carbenes precatalysts (Tent= Tentacular) enables the Buchwald–Hartwig amine arylation reaction in apolar alkane solvents. The use of such solvents is rare because of their poor solvation properties. Nonetheless, they could be of interest for industrial applications, as they can be disposed of in an energetically favorable manner and may potentially simplify product isolation. The excellent solubility of the precatalysts permitted the desired products to be obtained in yields ranging from 75 to 96 %, even with deactivated and functionalized coupling partners.

Three new Au(I) complexes of the formula [Au(NHC)(NTf2)] (NHC = N-heterocyclic carbene) bearing bulky and flexible ligands have been synthesised. The ligands studied are IPent, IHept and INon which belong to the ‘ITent’ (‘Tent’ for ‘tentacular’) family of NHC derivatives. The effect of these ligands in gold-promoted transformations has been investigated.

A nickel-catalyzed methodology for the α-arylation of ketones has been applied to the synthesis of an industrially relevant intermediate. The optimization of the reaction shows the important influence of subtle changes in reaction conditions, and leads to an improved procedure employing only a small excess of the substrate and a relatively low catalyst loading.

We gratefully acknowledge the EC for funding through the seventh framework program SYNFLOW, the ERC (Advanced Investigator Award ‘FUNCAT’ to SPN) and the EPSRC. S.P.N. is a Royal Society Wolfson Research Merit Award holder.

The authors thank the ERC (Advanced Researcher award-FUNCAT), 7th Framework Program NMP2-LA-2010-246461 (SYNFLOW), the EPSRC and King Saud University for funding. A general methodology for the α-arylation of ketones using a nickel catalyst has been developed. The new well-defined [Ni(IPr*)(cin)Cl] (1c) pre-catalyst showed great efficiency for this transformation, allowing the coupling of a wide range of ketones, including acetophenone derivatives, with various functionalised aryl chlorides. This cinnamyl-based Ni(NHC) complex has demonstrated a different behaviour to previously reported NHC-Ni catalysts. Preliminary mechanistic studies suggest a Ni0/NiII catalytic cycle to be at play. Postprint

In this work, a flexible and efficient flow microreactor has been developed for the synthesis of an aromatic amine via a Buchwald–Hartwig reaction, a key bond-forming reaction in the synthesis of a wide range of naturally-occurring and pharmaceutically active targets. The microreactor, coupled with a highly active palladium N-heterocyclic carbene (NHC) catalyst, enabled the full conversion of the reagents within twenty minutes, even at very low catalyst concentrations. In addition to the classical two-feed design, a novel, more flexible four-feed flow system was developed with a configuration optimised to avoid clogging, which is one of the main problems in microreactors and in continuous flow reactive systems in general. We report the effect of flow rate, temperature and catalyst loading on conversion degree. In particular, a slight increase in temperature allowed faster conversion even at low catalyst loadings, likely due to the highly efficient heat transfer provided by the confined microreactor geometry.

The authors thank the ERC (Advanced Researcher award-FUNCAT), the EPSRC (grant no EP/J011053/1) and King Saud University for funding. SPN is a Royal Society Wolfson Research Merit Award holder. The first nickel catalyzed deprotonative cross coupling between C(sp3)-H bonds and aryl chlorides is reported, allowing the challenging arylation of benzylimines in the absence of directing group or stoichiometric metal activation. This methodology represents a convenient access to the (diarylmethyl)amine moiety, which is widespread in pharmaceutically relevant compounds. Publisher PDF

The ERC (Advanced Researcher Award FUNCAT to SPN), the EPSRC and Sasol (Stipend to BJT) are gratefully acknowledged for support. Herein we report robust methods for the preparation and full characterisation of a range of Ir(I) and Rh(I) fluoride and bifluoride complexes using N-heterocyclic carbenes (NHCs) as ancillary ligands. The processes that link the fluoride and the bifluoride species are investigated and reports of the first Ir–bifluoride and Ir(I)–NHC and Rh(I)–NHC trifluoromethyl complexes are revealed. Postprint

The authors thank the ERC (Advanced Researcher award-FUNCAT), 7th Framework Program NMP2-LA-2010–246461 (SYNFLOW) and King Saud University for funding. A general catalytic protocol for the a-arylation of aryl ketones has been developed. It involves the use of a preformed, bench-stable Pd–N-heterocyclic carbene precatalyst bearing IHept as an ancillary ligand, and allows the coupling of various functionalized coupling partners at very low catalyst loading. Careful choice of the solvent/base system was crucial to obtain optimum catalyst performance. The pre-catalyst was also successfully tested in the synthesis of an industrially relevant compound. Postprint

Reaction of three equivalents of MesCNO (Mes = 2,4,6-trimethylphenyl) with one equivalent of [Pd(IPr)(P(p-tolyl)3)] in toluene yields the solid complex [Pd(IPr)(NCMes)(κ2-O–N C-Mes(–N–C( O)Mes))]. Three major steps are proposed to be involved in the reaction based on spectroscopic studies as well as literature precedents for related cycloadditions: i. oxidation of the coordinated phosphine ligand to phosphine oxide ii. oxygen atom transfer forming a C O bond from the N–O bond of MesCNO, and iii. cycloaddition of a final MesCNO ligand to yield product. Addition of two equivalents of NO at low temperature to the in situ generated peroxide complex [Pd(IPr)2(η2-O2)] generates the N-bonded complex trans-[Pd(IPr)2(NO2)2] in keeping with a literature precedent reported for similar complexes. Insight into the energetics of this reaction are probed by DFT calculations using the truncated ligand complex [Pd(IMe)2]. The computed enthalpy of binding of two moles of NO2 to form [Pd(IMe)2(NO2)2] is −112 kcal/mol indicating that its preparation from [Pd(IMe)2], N2 and 2O2 is thermodynamically favorable by −96 kcal/mol. Crystal structures of [Pd(IPr)(NCMes)(κ2-O–N C-Mes(–N–C( O)Mes))] and trans-[Pd(IPr)2(NO2)2] are reported.

The decomposition of formic acid into H2 and CO2 was successfully performed using a ruthenium hydride catalyst, without any concomitant CO evolution. The reaction mechanism is investigated by means of density functional theory calculations (DFT). The generated H2 was further exploited in a fuel cell to produce electricity. The catalytic hydrogenation of conjugated olefins, using this dihydrogen generation procedure, is also reported.

Conspectus One of the most important challenges in catalyst design is the synthesis of stable promoters without compromising their activity. For this reason, it is important to understand the factors leading to decomposition of such catalysts, especially if side-products negatively affect the activity and selectivity of the starting complex. In this context, the understanding of termination and decomposition processes in olefin metathesis is receiving significant attention from the scientific community. For example, the decomposition of ruthenium olefin metathesis precatalysts in alcohol solutions can occur during either the catalyst synthesis or the metathesis process, and such decomposition has been found to be common for Grubbs-type precatalysts. These decomposition products are usually hydridocarbonyl complexes, which are well-known to be active in several transformations such as hydrogenation, terminal alkene isomerization, and C–H activation chemistry. The reactivity of these side products can be unwanted, and it is therefore important to understand how to avoid them and maybe also important to keep an open mind and think of ways to use these in other catalytic reactions. A showcase of these decomposition studies is reported in this Account. These reports analyze the stability of ruthenium phenylindenylidene complexes, highly active olefin metathesis precatalysts, in basic alcohol solutions. Several different decomposition processes can occur under these conditions depending on the starting complex and the alcohol used. These indenylidene-bearing metathesis complexes display a completely different behavior compared with that of other metathesis precatalysts and show an alternative competitive alcoholysis pathway, where rather than forming the expected hydrido carbonyl complexes, the indenylidene fragment is transformed into a η1-indenyl, which then rearranges to its η5-indenyl form. In particular, [RuCl(η5-(3-phenylindenylidene)(PPh3)2] has been found to be extremely active in numerous transformations (at least 20) as well as compatible with a broad range of reaction conditions, rendering it a versatile catalytic tool. It should be stated that the η5-phenyl indenyl ligand shows enhanced catalytic activity over related half-sandwich ruthenium complexes. The analogous half-sandwich (cyclopentadienyl and indenyl) ruthenium complexes show lower activity in transfer hydrogenation and allylic alcohol isomerization reactions. In addition, this catalyst allows access to new phenylindenyl ruthenium complexes, which can be achieved in a very straightforward manner and have been successfully used in catalysis. This Account provides an overview of how mechanistic insights into decomposition and stability of a well-known family of ruthenium metathesis precatalysts has resulted in a series of novel and versatile ruthenium complexes with unexpected reactivity.

A new synthetic protocol that combines the advantages offered by eco-friendly solvent-free reactions and sequential transformations is reported. This strategy offers straightforward access to benzo[c]chromenes and benzo[b]furans from commercially available starting materials. This two-step, one-pot strategy consists of an Au-catalyzed hydrophenoxylation process followed by Pd-catalyzed C-H activation or Mizoroki-Heck reactions. The selectivity of the process towards C-H activation or Mizoroki-Heck reaction can be easily tuned.

A synthetic protocol making use of a well-defined cationic ruthenium complex 2 enabling the racemization of enantiomerically pure secondary alcohols in the presence of a weak base (K2CO3) is described. The compatibility of 2 with Candida Antarctica lipase B (Novozym 435) allows the development of an efficient dynamic kinetic resolution of sec-alcohols in the absence of an additional strong base. This procedure involves the first example of a dynamic kinetic resolution of alcohols in the presence of a cationic ruthenium catalyst. In addition, we describe the conversion of ketones to the enantioenriched acetates in a one-pot reaction, probing the versatility of complex 2.

NHC-derived selenoureas, which are useful for the quantification of NHC electronic properties, are deployed as ligands for Au(I). Surprisingly, while some compounds led to the expected [AuCl(SeUr)] species, selenoureas derived from more π-accepting NHCs unexpectedly furnished crystals of the corresponding [Au(SeUr)2][AuCl2] species, in which ligand rearrangement had occurred.

Enthalpies of ligand substitution for [Mo(η 5 -C 5 H 5 )(CO) 2 (NO)] producing [Mo(η 5 -C 5 H 5 )Mo(CO)(L)(NO)] have been measured by solution calorimetry at 30 °C in THF for L = P(OMe) 3 2 2 Ph 3 (SIPr = 1,3-bis(2,6-bis(diisopropylphenyl)imidazolinylidene; IPr = 1,3-bis(2,6-bis(diisopropylphenyl)-imidazol-2-ylidene)). The accepting metal fragment [Mo(η 5 -C 5 H 5 )(CO)(NO)] has a vacant site containing strongly π-accepting carbonyl and nitrosyl ligands and this is shown to influence the stability of the product complex. Infrared studies of both ν CO and ν NO show that metal-to-ligand backbonding increases in the order P(OMe) 3 3 5 -C 5 H 5 )(CO)(IPr)(NO)] and [Mo(η 5 -C 5 H 5 )(CO)(SIPr)(NO)] are reported.

The effect of methoxy functionalization of three N-heterocyclic carbene ligands was assessed using a variety of methods. The steric environment of each carbene has been assessed in various coordination environments. The electronic properties, specifically the electron-donating character and π-accepting ability, have been evaluated using nickel and iridium complexes and selenium adducts, respectively. Comparisons with the parent systems have been made with respect to both electronic and steric properties. The carbenes IPrOMe, SIPrOMe, and IPr*OMe have been found to be more electron donating than the parent systems IPr, SIPr, and IPr* and only slightly less π accepting, yet they exhibit similar steric properties.

Two new [Ni(allyl)Cl(NHC)] complexes with the bulky yet flexible N-heterocyclic carbene (NHC) ligands IPr* {N,N'-bis[2,6-bis(diphenylmethyl)-4-methylphenyl]imidazole-2-ylidene} and IPr*OMe {N,N'-bis[2,6-bis(diphenylmethyl)-4-methoxyphenyl]imidazol-2-ylidene} are reported. These complexes were employed in the amination and sulfination of aryl halide species and were shown to perform well in these reactions, which typically required less than half as much catalyst as previous state-of-the-art nickel complexes.

[Pd(IPr*OMe)(cin)(Cl)] provides high catalytic activity for Buchwald–Hartwig cross-coupling reactions of sterically demanding aryl chlorides with sterically hindered and deactivated aniline derivatives. This catalyst also proved efficient in Suzuki–Miyaura reactions, thus allowing the preparation of tetra-ortho-substituted biaryls. The Kumada–Corriu coupling has also been investigated using this palladium N-heterocyclic carbene (NHC) catalyst.

Golden delivery: A gold(I)-NHC complex catalyses the protodecarboxylation of various (hetero)aromatic acids. This methodology is simple, highly efficient and combines both the advantages of copper and silver methods with applications to completely deactivated substrates. Moreover, intermediates in this reaction have been isolated and fully characterized and provide fundamental insights into the mechanism of protodecarboxylation with gold.

The direct S-arylation of unactivated arylsulfoxides catalyzed by [Pd(IPr*)(cin)Cl] is described. Several arylmethylsulfoxides were coupled to various aryl halides in moderate to good yields (17 examples, 34–85%). Scope, limitations, and reaction mechanism are discussed.

Ammonia borane dehydrogenation can be catalyzed by a number of organometallic species. [Ir(κ2-ItBu)2][PF6] (ItBu = 1,3-bis(tert-butyl)imidazol-2-ylidene) is the most active catalyst for this proces...

A straightforward catalytic alcohol oxidation procedure using the recently reported complex [RuCl(PPh3)2(3-phenylindenyl)] (1) with KHMDS as cocatalyst, in acetone as the oxidant, is reported. Complex 1 shows remarkable chemoselectivity in oxidizing secondary alcohols to ketones.

The use of the ITent-based series of Pd-N-heterocyclic carbenes precatalysts (Tent= Tentacular) enables the Buchwald–Hartwig amine arylation reaction in apolar alkane solvents. The use of such solvents is rare because of their poor solvation properties. Nonetheless, they could be of interest for industrial applications, as they can be disposed of in an energetically favorable manner and may potentially simplify product isolation. The excellent solubility of the precatalysts permitted the desired products to be obtained in yields ranging from 75 to 96 %, even with deactivated and functionalized coupling partners.

KGaA, Weinheim.Density functional theory calculations have been used to explore the potential of Ru-based complexes with 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (SIMes) ligand backbone (A) being modified in silico by the insertion of a C60 molecule (B and C), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A, B, and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron-withdrawing N-heterocyclic carbene improves the performance of unannulated complex A. The efficiency of complex B is only surpassed by complex A when the backbone of the N-heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic-donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A. Overall, this study indicates that such Ru-based complexes B and C might have the potential to be effective olefin metathesis catalysts A.P. thanks the Spanish MINECO for a project CTQ2014-59832-JIN, and the European Commission for a Career Integration Grant (CIG09-GA-2011-293900)

The use of [Pd(NHC)(cinnamyl)Cl] precatalysts in the direct arylation of heterocycles has been investigated. Among four different precatalysts, [Pd(SIPr)(cinnamyl)Cl] proved to be the most efficient promoter of the reaction. The C–H functionalization of sulfuror nitrogen-containing heterocycles has been achieved at low catalyst loadings. These catalyst charges range from 0.1 to 0.01 mol % palladium. Publisher PDF

The well-defined [Pd(IPr*)(cinnamyl)Cl] complex is reported as one of the best N-heterocyclic carbene (NHC)-based pre-catalysts for the Buchwald–Hartwig amination reaction. This catalytic system displays high efficiency for the coupling of numerous (hetero)aryl chlorides, with a wide range of amines, at room temperature or at extremely low catalyst loading (as low as 0.025 mol%).