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New phosphines with self-assembling 6-pyridinone moities were prepared, characterized, and examined in the hydroformylation of diverse olefins. Testing various known and novel ligands in the presence of [Rh(acac)(CO) 2 ] under industrially relevant conditions, the hydroformylation of 1-octene proceeds best with 6,6'-(phenylphosphanediyl)bis(pyridin-2(1 H )-one) (DPONP). Control experiments and modelling studies indicate dimerization of this ligand at higher temperatures (>100 °C). The optimal catalyst system is able to conserve high product linearity (>90%) for a broad range of olefins at industrially-employed temperatures at low ligand loading.

Herein we present a new strategy for the oxidative synthesis of formamides from various types of amines and bioderived formyl sources (DHA, GLA and GLCA) and molecular oxygen (O 2 ) as oxidant on g-C 3 N 4 supported Cu catalysts. Combined characterization data from EPR, XAFS, XRD and XPS revealed the formation of single CuN 4 sites on supported Cu phen /C 3 N 4 catalysts. EPR spin trapping experiments disclosed ⋅OOH radicals as reactive oxygen species and ⋅NR 1 R 2 radicals being responsible for the initial C-C bond cleavage. Control experiments and DFT calculations showed that the successive C-C bond cleavage in DHA proceeds via a reaction mechanism co-mediated by ⋅NR 1 R 2 and ⋅OOH radicals based on the well-equilibrated Cu II and Cu I cycle. Our catalyst has much higher activity (TOF) than those based on noble metals., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The nature of the support can fundamentally affect the function of a heterogeneous catalyst. For the novel type of isolated metal atom catalysts, sometimes referred to as single-atom catalysts, systematic correlations are still rare. Here, we report a general finding that Pd on nitride supports (non-metal and metal nitride) features a higher oxidation state compared to that on oxide supports (non-metal and metal oxide). Through thorough oxidation state investigations by X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), CO-DRIFTS, and density functional theory (DFT) coupled with Bader charge analysis, it is found that Pd atoms prefer to interact with surface hydroxyl group to form a Pd(OH) x species on oxide supports, while on nitride supports, Pd atoms incorporate into the surface structure in the form of Pd-N bonds. Moreover, a correlation was built between the formal oxidation state and computational Bader charge, based on the periodic trend in electronegativity., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Selective cleavage and subsequent functionalization of C-C single bonds present a fundamental challenge in synthetic organic chemistry. Traditionally, the activation of C-C single bonds has been achieved using stoichiometric transition-metal complexes. Recently, examples of catalytic processes were developed in which use is made of precious metals. However, the use of inexpensive and Earth-abundant group IV metals for catalytic C-C single-bond cleavage is largely underdeveloped. Herein, the zirconium-catalyzed C-C single-bond cleavage and subsequent hydroboration reactions is realized using Cp 2 ZrCl 2 as a catalytic system. A series of structures of various γ-boronated amines are readily obtained, which are otherwise difficult to obtain. Mechanistic studies disclose the formation of a N-Zr IV species, and then a β-carbon elimination route is responsible for C-C single bond activation. Besides zirconium, hafnium exhibits a similar performance for this transformation., (© 2024. The Author(s).)

The use of bis(NHC) manganese(I) complexes 3 as catalysts for the hydrogenation of esters was investigated. For that purpose, a series of complexes has been synthesized via an improved two step procedure utilizing bis(NHC)-BEt 3 adducts. By applying complexes 3 with KHBEt 3 as additive, various aromatic and aliphatic esters were hydrogenated successfully at mild temperatures and low catalyst loadings, highlighting the efficiency of the novel catalytic system. The versatility of the developed catalytic system was further demonstrated by the hydrogenation of other substrate classes like ketones, nitriles, N-heteroarenes and alkenes. Mechanistic experiments and DFT calculations indicate an inner sphere mechanism with the loss of one CO ligand and reveal the role of BEt 3 as cocatalyst., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Manganese-catalyzed hydrogenation reactions have aroused widespread interest in recent years. Among the catalytic systems described, especially PNP- and NNP-Mn pincer catalysts have been reported for the hydrogenation of aldehydes, ketones, nitriles, aldimines and esters. Furthermore, NNP-Mn pincer compounds are efficient catalysts for the hydrogenolysis of less reactive amides, ureas, carbonates, and carbamates. Herein, the synthesis and application of specific imidazolylaminophosphine ligands and the corresponding Mn pincer complexes are described. These new catalysts have been characterized and studied by a combination of experimental and theoretical investigations, and their catalytic activities have been tested in several hydrogenation reactions with good to excellent performance. Especially, the reduction of N-heterocycles can be performed under very mild conditions., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The isomerism of dimethyl 2,2'-(7,8-dichloro-1H-benzo[b][1,4]diazepine-2,4-(3H,5H)diylidene)diacetate (1a) and dimethyl 2,2'-(7,8-dichloro-3-methyl-1H-benzo[b][1,4]diazepine-2,4-(3H,5H)diylidene)diacetate (1b) was investigated by 1 H, 13 C and 15 N nuclear magnetic resonance (NMR) spectroscopy. In CDCl 3 solution, inversion of the diazepine ring was observed, whereas in (D 6 )DMSO and (D 7 )DMF solution, besides the ring inversion, a partial cleavage of one chelate ring appeared connected with (E/Z) isomerization about one of the exocyclic C=C bonds. Gibbs free energies (ΔG) and free activation energies (ΔG ≠ ) were calculated based on B3PW91-SCRF/ZVP DFT computations. Agreement between NMR data and density functional theory (DFT) computations was found., (© 2022 John Wiley & Sons, Ltd.)

A novel one-pot iridium-catalyzed domino hydroxymethylation of olefins, which relies on using two different ligands at the same time, is reported. DFT computation reveals different activities for the individual hydroformylation and hydrogenation steps in the presence of mono- and bidentate ligands. Whereas bidentate ligands have higher hydrogenation activity, monodentate ligands show higher hydroformylation activity. Accordingly, a catalyst system is introduced that uses dual ligands in the whole domino process. Control experiments show that the overall selectivity is kinetically controlled. Both computation and experiment explain the function of the two optimized ligands during the domino process., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

To understand the metal-support interaction of oxide supported transition metal catalysts, we computed the reaction mechanisms of dry and steam reforming of methane on a tetragonal ZrO 2 (101) supported Ni catalyst. Based on the limited number of active sites on the surface, an irregular and non-ideal Ni 13 cluster on ZrO 2 (101) is identified as a catalyst. A simple reaction mechanism is proposed, and the first direct dissociation step of CO 2 , CH 4 and H 2 O is the most difficult based on the computed Gibbs free energies and no surface CH X O and CH X OH intermediates are involved, different from that on the flat Ni(111) surface. Analysis of other supported nickel catalysts shows that not only the support but also the size and shape of the metal clusters play an important role in the reaction mechanisms and kinetics.

In catalysis science, the electronic structure of the active site determines the structure-activity relationship of the catalyst to a large extent. Therefore, modulating the electronic structure has become a main route for the rational design of metal-based catalyst materials. In this work, we prepared a LaCoSiH x material that has more electronegativity and a lower workfunction than traditional supported Co-based catalysts. Using CO 2 methanation as a model catalytic reaction, the facile dissociation of CO 2 and CO (a key reaction intermediate) on the surface of the LaCoSiH x catalyst is observed by various experimental methods (e.g., in situ Raman and FTIR) at room temperature. Moreover, theoretical calculation results further show that LaCoSiH x has a much stronger capacity for carbon-oxygen bond activation than the Co surface. The intrinsic mechanism is attributed to the marked electron transfer from catalysts into the antibonding orbital of CO 2 and CO., (© 2021 Wiley-VCH GmbH.)

Propane dehydrogenation (PDH) to propene is an important alternative to oil-based cracking processes, to produce this industrially important platform chemical 1,2 . The commercial PDH technologies utilizing Cr-containing (refs. 3,4 ) or Pt-containing (refs. 5-8 ) catalysts suffer from the toxicity of Cr(VI) compounds or the need to use ecologically harmful chlorine for catalyst regeneration 9 . Here, we introduce a method for preparation of environmentally compatible supported catalysts based on commercial ZnO. This metal oxide and a support (zeolite or common metal oxide) are used as a physical mixture or in the form of two layers with ZnO as the upstream layer. Supported ZnO x species are in situ formed through a reaction of support OH groups with Zn atoms generated from ZnO upon reductive treatment above 550 °C. Using different complementary characterization methods, we identify the decisive role of defective OH groups for the formation of active ZnO x species. For benchmarking purposes, the developed ZnO-silicalite-1 and an analogue of commercial K-CrO x /Al 2 O 3 were tested in the same setup under industrially relevant conditions at close propane conversion over about 400 h on propane stream. The developed catalyst reveals about three times higher propene productivity at similar propene selectivity., (© 2021. The Author(s).)

A direct and selective synthesis of α,β-unsaturated piperidones by a new palladium-catalyzed cascade carbonylation is described. In the presented protocol, easily available propargylic alcohols react with aliphatic amines to provide a broad variety of interesting heterocycles. Key to the success of this transformation is a remarkable catalytic cleavage of the present carbon-carbon triple bond by using a specific catalyst with 2-diphenylphosphinopyridine as ligand and appropriate reaction conditions. Mechanistic studies and control experiments revealed branched unsaturated acid 11 as crucial intermediate., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The dicarbonylation of 1,3-butadiene to adipic acid derivatives offers the potential for a more cost-efficient and environmentally benign industrial process. However, the complex reaction network of regioisomeric carbonylation and isomerization pathways, make a selective and direct transformation particularly difficult. Here, we report surprising solvent effects on this palladium-catalysed process in the presence of 1,2-bis-di-tert-butylphosphin-oxylene (dtbpx) ligands, which allow adipate diester formation from 1,3-butadiene, carbon monoxide, and methanol with 97 % selectivity and 100 % atom-economy under scalable conditions. Under optimal conditions a variety of di- and triesters from 1,2- and 1,3-dienes can be obtained in good to excellent yields., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A series of hydroxy-functionalized phosphonium salts were studied as bifunctional catalysts for the conversion of CO 2 with epoxides under mild and solvent-free conditions. The reaction in the presence of a phenol-based phosphonium iodide proceeded via a first order rection kinetic with respect to the substrate. Notably, in contrast to the aliphatic analogue, the phenol-based catalyst showed no product inhibition. The temperature dependence of the reaction rate was investigated, and the activation energy for the model reaction was determined from an Arrhenius-plot (E a =39.6 kJ mol -1 ). The substrate scope was also evaluated. Under the optimized reaction conditions, 20 terminal epoxides were converted at room temperature to the corresponding cyclic carbonates, which were isolated in yields up to 99 %. The reaction is easily scalable and was performed on a scale up to 50 g substrate. Moreover, this method was applied in the synthesis of the antitussive agent dropropizine starting from epichlorohydrin and phenylpiperazine. Furthermore, DFT calculations were performed to rationalize the mechanism and the high efficiency of the phenol-based phosphonium iodide catalyst. The calculation confirmed the activation of the epoxide via hydrogen bonding for the iodide salt, which facilitates the ring-opening step. Notably, the effective Gibbs energy barrier regarding this step is 97 kJ mol -1 for the bromide and 72 kJ mol -1 for the iodide salt, which explains the difference in activity., (© 2020 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

A chemo-, regio-, and stereoselective mono-hydroamidation of (un)symmetrical 1,3-diynes is described. Key for the success of this novel transformation is the utilization of an advanced palladium catalyst system with the specific ligand Neolephos. The synthetic value of this general approach to synthetically useful α-alkynyl-α, β-unsaturated amides is showcased by diversification of several structurally complex molecules and marketed drugs. Control experiments and density-functional theory (M06L-SMD) computations also suggest the crucial role of the substrate in controlling the regioselectivity of unsymmetrical 1,3-diynes., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

The first general and regioselective Pd-catalyzed cyclocarbonylation to give α-methylene-β-lactones is reported. Key to the success for this process is the use of a specific sterically demanding phosphine ligand based on N-arylated imidazole (L11) in the presence of Pd(MeCN) 2 Cl 2 as pre-catalyst. A variety of easily available alkynols provide under additive-free conditions the corresponding α-methylene-β-lactones in moderate to good yields with excellent regio- and diastereoselectivity. The applicability of this novel methodology is showcased by the direct carbonylation of biologically active molecules including natural products., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

A general and atom-economical synthesis of 1,1-diborylalkanes from alkenes and a borane without the need for an additional H 2 acceptor is reported for the first time. The key to our success is the use of an earth-abundant zirconium-based catalyst, which allows a balance of self-contradictory reactivities (dehydrogenative boration and hydroboration) to be achieved. Our method avoids using an excess amount of another alkene as an H 2 acceptor, which was required in other reported systems. Furthermore, substrates such as simple long-chain aliphatic alkenes that did not react before also underwent 1,1-diboration in our system. Significantly, the unprecedented 1,1-diboration of internal alkenes enabled the preparation of 1,1-diborylalkanes., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Reduction of carbonyl moieties to the corresponding alcohol using simply hydrazine hydrate has been considerably unfeasible until now due to the well-known condensation reaction. However, herein, we report that using an excess of 20-fold equivalents, the reduction proceeds in excellent yields. 1 H NMR study of the reaction and density functional theory (DFT) calculations indicate that the final fate of the hemiaminal intermediate is crucial to obtain the alcohol or the hydrazone.

The development of base metal catalysts for industrially relevant amination and hydrogenation reactions by applying abundant and atom economical reagents continues to be important for the cost-effective and sustainable synthesis of amines which represent highly essential chemicals. In particular, the synthesis of primary amines is of central importance because these compounds serve as key precursors and central intermediates to produce value-added fine and bulk chemicals as well as pharmaceuticals, agrochemicals and materials. Here we report a Ni-triphos complex as the first Ni-based homogeneous catalyst for both reductive amination of carbonyl compounds with ammonia and hydrogenation of nitroarenes to prepare all kinds of primary amines. Remarkably, this Ni-complex enabled the synthesis of functionalized and structurally diverse benzylic, heterocyclic and aliphatic linear and branched primary amines as well as aromatic primary amines starting from inexpensive and easily accessible carbonyl compounds (aldehydes and ketones) and nitroarenes using ammonia and molecular hydrogen. This Ni-catalyzed reductive amination methodology has been applied for the amination of more complex pharmaceuticals and steroid derivatives. Detailed DFT computations have been performed for the Ni-triphos based reductive amination reaction, and they revealed that the overall reaction has an inner-sphere mechanism with H 2 metathesis as the rate-determining step., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

The development of earth abundant 3d metal-based catalysts continues to be an important goal of chemical research. In particular, the design of base metal complexes for reductive amination to produce primary amines remains as challenging. Here, we report the combination of cobalt and linear-triphos (bis(2-diphenylphosphinoethyl)phenylphosphine) as the molecularly-defined non-noble metal catalyst for the synthesis of linear and branched benzylic, heterocyclic and aliphatic primary amines from carbonyl compounds, gaseous ammonia and hydrogen in good to excellent yields. Noteworthy, this cobalt catalyst exhibits high selectivity and as a result the -NH 2 moiety is introduced in functionalized and structurally diverse molecules. An inner-sphere mechanism on the basis of the mono-cationic [triphos-CoH] + complex as active catalyst is proposed and supported with density functional theory computation on the doublet state potential free energy surface and H 2 metathesis is found as the rate-determining step.

The electrochemical conversion of N 2 at ambient conditions using renewably generated electricity is an attractive approach for sustainable ammonia (NH 3 ) production. Considering the chemical inertness of N 2 , rational design of efficient and stable catalysts is required. Therefore, in this work, it is demonstrated that a C-doped TiO 2 /C (C-Ti x O y /C) material derived from the metal-organic framework (MOF) MIL-125(Ti) can achieve a high Faradaic efficiency (FE) of 17.8 %, which even surpasses most of the established noble metal-based catalysts. On the basis of the experimental results and theoretical calculations, the remarkable properties of the catalysts can be attributed to the doping of carbon atoms into oxygen vacancies (OVs) and the formation of Ti-C bonds in C-Ti x O y . This binding motive is found to be energetically more favorable for N 2 activation compared to the non-substituted OVs in TiO 2 . This work elucidates that electrochemical N 2 reduction reaction (NRR) performance can be largely improved by creating catalytically active centers through rational substitution of anions into metal oxides., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Determining the locations and distributions of Al substitution in zeolite-based catalysts and catalysis is always very challenging. Despite advanced experimental characterization techniques and improved theoretical models, this issue is not reasonably solved and this is because the locations and distributions of Al substitution in zeolites are more kinetically than thermodynamically controlled. In this work, we computed one Al substitution in the orthorhombic form of MFI (HZSM-5) which contains 12 distinct tetrahedral (T) centers on the basis of a periodic slab model containing 96 T centers including van der Waals dispersion correction (GGA-PBE-D3). For all 12 T centers, there are 48 acidic sites and each site can be considered for the adsorption of probe molecules. Thermodynamically, the energy span of the twelve most stable acidic sites is less than 15 kJ mol-1, and such a small energy difference enables all adjustable possibilities for the locations and distributions of Al substitution under suitable conditions. Excellent agreement between experiment and theory in the adsorption enthalpies of pyridine, methylamine, dimethylamine and trimethylamine shows that the location of Al substitution is most likely at T1, T3, T5, T7 and T11, while much less likely at the often used T12 site. These results provide the basis for identifying Al substitution in new synthesized HZSM-5 catalysts and for studying the acidic site-dependent catalytic activity of HZSM-5 in cracking and hydrogenation reactions.

Triphosphiranes are three-membered phosphorus cycles and their fundamental reactivity has been studied in recent decades. We recently developed a high-yielding, selective synthesis for various aryl-substituted triphosphiranes. Variation of the reaction conditions in combination with theoretical studies helped to rationalize the formation of these homoleptic phosphorus ring systems and highly reactive intermediates could be isolated. In addition we showed that a titanocene synthon [Cp 2 Ti(btmsa)] facilitates the selective conversion of these triphosphiranes into titanocene diphosphene complexes. This unexpected reactivity mode was further studied theoretically and experimental evidence is presented for the proposed reaction mechanism., (This journal is © The Royal Society of Chemistry 2019.)

The well-defined iron PNP pincer complex catalyst [Fe(H)(BH 4 )(CO)(HN{CH 2 CH 2 P(iPr) 2 } 2 ] was used for the catalytic dehydrogenation of secondary alcohols to give the corresponding ketones. Using acetone as inexpensive hydrogen acceptor enables the oxidation with good to excellent yields. DFT computations indicate an outer-sphere mechanism and support the importance of an acceptor to achieve this transformation under milder conditions., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Catalytic chemistry that involves the activation and transformation of main group substrates is relatively undeveloped and current examples are generally mediated by expensive transition metal species. Herein, we describe the use of inexpensive and readily available tBuOK as a catalyst for P-P and P-E (E = O, S, or N) bond formation. Catalytic quantities of tBuOK in the presence of imine, azobenzene hydrogen acceptors, or a stoichiometric amount of tBuOK with hydrazobenzene, allow efficient homodehydrocoupling of phosphines under mild conditions (e.g. 25 °C and < 5 min). Further studies demonstrate that the hydrogen acceptors play an intimate mechanistic role. We also show that our tBuOK catalysed methodology is general for the heterodehydrocoupling of phosphines with alcohols, thiols and amines to generate a range of potentially useful products containing P-O, P-S, or P-N bonds.

Among the known liquid organic hydrogen carriers, formic acid attracts increasing interest in the context of safe and reversible storage of hydrogen. Here, the first molecularly defined cobalt pincer complex is disclosed for the dehydrogenation of formic acid in aqueous medium under mild conditions. Crucial for catalytic activity is the use of the specific complex 3. Compared to related ruthenium and manganese complexes 7 and 8, this optimal cobalt complex showed improved performance. DFT computations support an innocent non-classical bifunctional outer-sphere mechanism on the triplet state potential energy surface., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Lithiumcyclopentadienide, previously identified to be an endless polymer in the ligand-free solid state, was investigated by 13 C- and 6 Li-CP/MAS NMR spectra, and by B3LYP-GIAO theoretical calculations. By spectra simulation, the axially symmetric 13 C-shift tensor components were identified to be δ 11  = δ 22  = 151.5 ppm, δ 33  = 15.5 ppm. The 6 Li-tensor components are δ 11  = δ 22  = +1.0 ppm, δ 33  = -43.0 ppm. This extremely high field component is due to cumulative ring current effects. B3LYP-GIAO/TZVP calculations on the tensor principal components agree remarkably well with the measurements. A new and very simple method of preparing air-sensitive compounds for solid-state NMR analyses is described. Graphical abstract Shielding tensor main components from slow-speed solid state NMR spectra.

With the development of theoretical and computational chemistry, as well as high-performance computing, molecular simulation can now be used not only as a tool to explain the experimental results but also as a means for discovery or prediction. Quantum chemical nanoreactor is such a method which can automatically explore the chemical process based only on the basic mechanics without prior knowledge of the reactions. Here, we present a new method which combines the semiempirical quantum mechanical density functional tight-binding (DFTB) method with the nanoreactor molecular dynamic (NMD) method, and we simulated the reaction process of graphene synthesis via detonation at different oxygen/acetylene mole ratios. The formation of graphene is initiated by the breaking of acetylene (C 2 H 2 ) molecules by collision into pieces such as H atoms, ethynyl (HC≡C•), and vinylidene (H 2 C═C:) radicals. It is followed by the formation of long straight carbon chains coupled with a few branched carbon chains, which then turned into  a 2-D framework made of carbon rings. Trace oxygen could modulate the size of the rings during graphene formation and promote the formation of regular graphene with fused six-membered rings as we see, but the addition of high oxygen content makes more C-containing species oxidized to small oxide molecules instead of polymerization. The calculation speed of the DFTB nanoreactor is greatly improved compared to the ab initio nanoreactor, which makes it a valuable option to simulate chemical processes of large sizes and long time scales and to help us uncover the "unknown unknowns".

The synthesis of an unusual 1-metalla-2,3-cyclobutadiene complex [ rac -(ebthi)Ti(Me 3 SiC 3 SiMe 3 )] ( rac -ebthi = rac -1,2-ethylene-1,1'-bis(η 5 -tetrahydroindenyl)), a formal metallacyclic analogue of a non-existent four-membered 1,2-cyclobutadiene, is described. By variation of the cyclopentadienyl ligand of the titanocene precursor it was possible to stabilise this highly exotic compound which selectively reacts with ketones and aldehydes to yield enynes by oxygen transfer to titanium. Analysis of the bonding and electronic structure of the metallacycle shows that the complex is best described as an unusual antiferromagnetically coupled biradicaloid system, possessing a formal Ti(iii) centre coordinated with a monoanionic radical ligand.

UB3LYP computation including dispersion and toluene solvation has been carried to elucidate the mechanisms of alkene hydrogenation catalyzed by bis(imino)pyridine iron dinitrogen complex ( iPr PDI)Fe(N 2 ) 2 , which has low stability towards N 2 dissociation. The coordinatively unsaturated complexes, ( iPr PDI)Fe(N 2 ) and ( iPr PDI)Fe(1-C 4 H 8 ), favor open-shell singlet ground states. On the basis of our computations, we propose a new mechanism of 1-butene coordination and hydrogenation after N 2 dissociation. The hydrogenation of 1-butene undergoes a concerted open-shell singlet transition state involving H 2 dissociation, C-H bond formation and C=C bond elongation, as well as the subsequent C-H reductive elimination. In the whole alkene hydrogenation, the H-H bond cleavage is the rate-determining step. Graphical abstract The alkene hydrogenation catalyzed by redox-active pyridine(diimine)-chelate iron complex follows the open-shell singlet state path.

Phenazine radical cations (PhRCs) were used for the first time as efficient metal-free catalysts for the oxidative homo- and cross-coupling of a variety of different amines. A series of functional PhRCs were prepared, characterized with X-ray diffraction, and their radical character was investigated with DFT calculations. They were tested as catalysts under neat conditions with low oxygen pressure to prepare homo- and cross-coupled aliphatic and aromatic imines in high yields. Although all synthesized phenazines were catalytically active, the highest reaction rates and the best selectivity were achieved using the 5,10-dihydro-5,10-dimethylphenazine radical cation. By means of fluorescence, UV-vis and EPR spectroscopy, a mechanism of the oxidative amine coupling, catalyzed by PhRCs, is proposed.

Due to the complexity of heterogeneous catalysts, identification of active sites and the ways for their experimental design are not inherently straightforward but important for tailored catalyst preparation. The present study reveals the active sites for efficient C-H bond activation in C 1 -C 4 alkanes over ZrO 2 free of any metals or metal oxides usually catalysing this reaction. Quantum chemical calculations suggest that two Zr cations located at an oxygen vacancy are responsible for the homolytic C-H bond dissociation. This pathway differs from that reported for other metal oxides used for alkane activation, where metal cation and neighbouring lattice oxygen form the active site. The concentration of anion vacancies in ZrO 2 can be controlled through adjusting the crystallite size. Accordingly designed ZrO 2 shows industrially relevant activity and durability in non-oxidative propane dehydrogenation and performs superior to state-of-the-art catalysts possessing Pt, CrO x , GaO x or VO x species.

Generally, a homogeneous catalyst exhibits good activity and defined active sites but it is difficult to recycle. Meanwhile, a heterogeneous catalyst can easily be reused but its active site is difficult to reveal. It is interesting to bridge the gap between homogeneous and heterogeneous catalysis via controllable construction of a heterogeneous catalyst containing defined active sites. Here, we report that a molecularly defined, single-active site heterogeneous catalyst has been designed and prepared via the oxidative polymerization of maleimide derivatives. These polymaleimide derivatives can be active catalysts for the selective oxidation of heterocyclic compounds to quinoline and indole via the recycling of -C=O and -C-OH groups, which was confirmed by tracing the reaction with GC-MS using maleimide as the catalyst and by FT-IR analysis with polymaleimide as the catalyst. These results might promote the development of heterogeneous catalysts with molecularly defined single active sites exhibiting a comparable activity to homogeneous catalysts.

The reaction of the allene precursor Li 2 (Me 3 SiC 3 SiMe 3 ) with [Cp 2 ZrCl 2 ] (Cp=cyclopentadienyl) was examined. The selective formation of hitherto unknown linear, allene-bridged dizirconocene complexes [(Cp 2 ZrCl) 2 {-μ-(Me 3 Si)C 3 (SiMe 3 )-}] and [(Cp 2 Zr) 2 {-μ-(Me 3 Si)C 3 (SiMe 3 )-} 2 ] was observed. Upon σ coordination of the allenediyl unit to {Cp 2 Zr}, pyrophoric Li 2 (Me 3 SiC 3 SiMe 3 ) is tamed stepwise to yield a surprisingly robust 1,5-dizirconacyclooctatetra-2,3,6,7-ene with cumulated double bonds. This complex is unexpectedly inert against moisture, air, water and acetone. Surprisingly, it degrades under MS conditions to give the highly strained 1-zirconacyclobuta-2,3-diene. All compounds isolated have been fully characterised and the molecular structures are discussed. The stability and reactivity of these complexes are rationalised by DFT computations., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

[Fe(PNP)(CO)HCl] (PNP=di-(2-diisopropylphosphanyl-ethyl)amine), activated in situ with KOtBu, is a highly active catalyst for the isomerization of allylic alcohols to ketones without an external hydrogen supply. High reaction rates were obtained at 80 °C, but the catalyst is also sufficiently active at room temperature with most substrates. The reaction follows a self-hydrogen-borrowing mechanism, as verified by DFT calculations. An alternative isomerization through alkene insertion and β-hydride elimination could be excluded on the basis of a much higher barrier. In alcoholic solvents, the ketone product is further reduced to the saturated alcohol., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Commercially available Ru-MACHO TM -BH is an active catalyst for the hydrogenation of several functional groups and for the dehydrogenation of alcohols. Herein, we report on the new application of this catalyst to the base-free transfer hydrogenation of carbonyl compounds. Ru-MACHO TM -BH proved to be highly active and selective in this transformation, even with α,β-unsaturated carbonyl compounds as substrates. The corresponding aliphatic, aromatic and allylic alcohols were obtained in excellent yields with catalyst loadings as low as 0.1-0.5 mol % at mild temperatures after very short reaction times. This protocol tolerates iPrOH and EtOH as hydrogen sources. Additionally, scale up to multi-gram amounts was performed without any loss of activity or selectivity. An outer-sphere mechanism has been proposed and the computed kinetics and thermodynamics of crotonaldehyde and 1-phenyl-but-2-en-one are in perfect agreement with the experiment., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Mechanistic studies of the catalyst [Pd 2 (dba) 3 /1,1'-bis( tert -butyl(pyridin-2-yl)phosphanyl)ferrocene, L2 ] for olefin alkoxycarbonylation reactions are described. X-ray crystallography reveals the coordination of the pyridyl nitrogen atom in L2 to the palladium center of the catalytic intermediates. DFT calculations on the elementary steps of the industrially relevant carbonylation of ethylene (the Lucite α-process) indicate that the protonated pyridyl moiety is formed immediately, which facilitates the formation of the active palladium hydride complex. The insertion of ethylene and CO into this intermediate leads to the corresponding palladium acyl species, which is kinetically reversible. Notably, this key species is stabilized by the hemilabile coordination of the pyridyl nitrogen atom in L2 . The rate-determining alcoholysis of the acyl palladium complex is substantially facilitated by metal-ligand cooperation. Specifically, the deprotonation of the alcohol by the built-in base of the ligand allows a facile intramolecular nucleophilic attack on the acyl palladium species concertedly. Kinetic measurements support this mechanistic proposal and show that the rate of the carbonylation step is zero-order dependent on ethylene and CO. Comparing CH 3 OD and CH 3 OH as nucleophiles suggests the involvement of (de)protonation in the rate-determining step.

A selection of cobalt(I) and cobalt(II) pincer type complexes with different substitution patterns was tested in the catalytic reduction of carboxylic acid esters to alcohols. The cobalt pincer type complex 4 is suitable for the hydrogenation of aromatic as well as aliphatic and cyclic esters. Mechanistic investigation indicated a metal ligand cooperated reaction pathway., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Green Friedel-Crafts acylation reactions belong to the most desired transformations in organic chemistry. The resulting ketones constitute important intermediates, building blocks, and functional molecules in organic synthesis as well as for the chemical industry. Over the past 60 years, advances in this topic have focused on how to make this reaction more economically and environmentally friendly by using green acylating conditions, such as stoichiometric acylations and catalytic homogeneous and heterogeneous acylations. However, currently well-established methodologies for their synthesis either produce significant amounts of waste or proceed under harsh conditions, limiting applications. Here, we present a new protocol for the straightforward and selective introduction of acyl groups into (hetero)arenes without directing groups by using available olefins with inexpensive CO. In the presence of commercial palladium catalysts, inter- and intramolecular carbonylative C-H functionalizations take place with good regio- and chemoselectivity. Compared to classical Friedel-Crafts chemistry, this novel methodology proceeds under mild reaction conditions. The general applicability of this methodology is demonstrated by the direct carbonylation of industrial feedstocks (ethylene and diisobutene) as well as of natural products (eugenol and safrole). Furthermore, synthetic applications to drug molecules are showcased., Competing Interests: The authors declare no competing financial interest.

Non-metal-catalyzed heterodehydrocoupling of primary and secondary phosphines (R 1 R 2 PH, R 2 = H or R 1 ) with hydrosilanes (R 3 R 4 R 5 SiH, R 4 , R 5 = H or R 3 ) to produce synthetically useful silylphosphines (R 1 R 2 P-SiR 3 R 4 R 5 ) has been achieved using B(C 6 F 5 ) 3 as the catalyst (10 mol %, 100 °C). Kinetic studies demonstrated that the reaction is first-order in hydrosilane and B(C 6 F 5 ) 3 but zero-order in phosphine. Control experiments, DFT calculations, and DOSY NMR studies suggest that a R 1 R 2 HP·B(C 6 F 5 ) 3 adduct is initially formed and undergoes partial dissociation to form an "encounter complex". The latter mediates frustrated Lewis pair type Si-H bond activation of the silane substrates. We also found that B(C 6 F 5 ) 3 catalyzes the homodehydrocoupling of primary phosphines to form cyclic phosphine rings and the first example of a non-metal-catalyzed hydrosilylation of P-P bonds to produce silylphosphines (R 1 R 2 P-SiR 3 R 4 R 5 ). Moreover, the introduction of PhCN to the reactions involving secondary phosphines with hydrosilanes allowed the heterodehydrocoupling reaction to proceed efficiently under much milder conditions (1.0 mol % B(C 6 F 5 ) 3 at 25 °C). Mechanistic studies, as well as DFT calculations, revealed that PhCN plays a key mechanistic role in facilitating the dehydrocoupling reactions rather than simply functioning as H 2 -acceptor.

Coordination of the alkyl-substituted alkynes Me 3 SiC 2 CH 2 R (1: R=SiMe 3 ; 2: R=N(SiMe 3 ) 2 ) to titanocene centres [Cp' 2 Ti] (Cp'=Cp, Cp*) yields stable alkyne complexes of the type Cp' 2 Ti(η 2 -Me 3 SiC 2 CH 2 R) (3: Cp'=Cp, R=SiMe 3 ; 5: Cp'=Cp, R=N(SiMe 3 ) 2 ; 6: Cp'=Cp*, R=SiMe 3 ) that are not prone to alkyne/allene isomerisation. When reacting alkyne 2 with Cp * 2 TiCl 2 and Mg formation of the complex Cp* 2 Ti(III)(η 3 -Me 3 SiC 2 CH 2 ) (7) which displays a propargylic unit coordinated to the Ti III centre takes place. All complexes were fully characterised, the molecular structures for 5, 6, and 7 are discussed., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The palladium-catalyzed chemoselective carbonylation of bromoaryl triflates is reported. The selective C-Br bond versus C-OTf (OTf=triflate) bond functionalization can be remarkably tuned by the combination of the ligand [4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos) vs. 1,1'-bis(diphenylphosphino)ferrocene (DPPF)] and the solvent (toluene vs. DMSO). The respective ligand and solvent effects are rationalized by DFT calculations. In contrast, the monodentate ligands BuPAd 2 and tBu 3 P prefer the selective C-Br bond activation and are solvent insensitive., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new chiral manganese PNP pincer complex is described. The asymmetric hydrogenation of several prochiral ketones with molecular hydrogen in the presence of this complex proceeds under mild conditions (30-40 °C, 4 h, 30 bar H 2 ). Besides high catalytic activity for aromatic substrates, aliphatic ketones are hydrogenated with remarkable selectivity (e.r. up to 92:8). DFT calculations support an outer sphere hydrogenation mechanism as well as the experimentally determined stereochemistry., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A mixed decamethyltitanocene(III) isonitrile alkynyl complex (7) was synthesized by the sequential introduction of the isonitrile and alkynyl ligands. Direct synthesis results in the formation of the diamagnetic decamethyltitanocene bis(isonitrile) (2) and bis(alkynyl) (3) complexes. Compound 7 undergoes disproportionation at room temperature to give 2 and 3. All complexes were fully characterized by IR, NMR, and EPR spectroscopy, and mass spectrometry. Molecular structures for complexes 2 and 7 are reported. The stability and reactivity of these complexes are rationalized by DFT computations., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The mechanism of coverage dependent CO adsorption and dissociation on the Mo(100) surface was investigated using periodic density functional theory. Structure optimization and frequency calculation were carried out using the GGA-PBE method and a p(3 × 3) supercell model. Energetic data have been obtained using the revised PBE method and the PBE optimized structures. CO adsorption prefers tilted adsorption configuration at the 4-fold hollow sites at low coverage and tilted and atop configurations at high coverage. The computed C-O stretching frequencies of the tilted and atop adsorbed CO molecules agree very well with the experimental results. Starting from the saturation coverage, five binding states have been found: two for molecular (α) CO adsorption and three for dissociative (β) CO adsorption, which are in agreement with the temperature-programmed desorption experiments. In addition, CO prefers dissociation with very low barriers in all coverages as long as free sites are available and is coverage independent; this nicely explains the observed CO dissociation at very low temperatures. All such agreements validate our computational methods and provide the basis of further studies.

For the first time, structurally defined manganese pincer complexes catalyze the dehydrogenation of aqueous methanol to hydrogen and carbon dioxide, which is a transformation of interest with regard to the implementation of a hydrogen and methanol economy. Excellent long-term stability was demonstrated for the Mn-PNPiPr catalyst, as a turnover of more than 20 000 was reached. In addition to methanol, other important hydrogen carriers were also successfully dehydrogenated., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Combining the basin hopping structure searching algorithm and density functional theory, the iron carbide clusters, Fe x C y (x ≤ 8 and y ≤ 8), and clusters with various stoichiometries (Fe 2n C n , Fe 3n C n , Fe n C 2n , Fe n C 3n and Fe n C 4n (n = 1-7), Fe 5n C 2n , and Fe 4n C n (n = 1-5)) are predicted. The stable structures of iron rich carbide clusters are composed of C-C dimers or single C atoms on the surface of the clusters, which are remarkably different from their corresponding bulk structures, where the carbon atoms are atomically distributed in the iron matrix. The most stable carbon rich clusters are highly diverse in topology (bowl, basket, plane, shoe, necklace, etc.) with long carbon chains. The Bader charge analysis shows that the size effect on iron carbide clusters is an electronic tuning. Large carbon-rich clusters appear even under low carbon chemical potentials, whereas small iron-rich clusters are only energetically stable in high carbon chemical potentials, which indicates that changing the carbon chemical potential can tune the morphology (size and stoichiometry) of the iron carbide clusters. These results may help us understand the catalytic activity of iron and iron carbides in reactions such as the Fischer-Tropsch synthesis and the carbon nanotube formation process.

The first manganese-catalyzed hydrogenation of esters to alcohols has been developed. The combination of Mn(CO) 5 Br with [HN(CH 2 CH 2 P(Et) 2 ) 2 ] leads to a mixture of cationic and neutral Mn PNP pincer complexes, which enable the reduction of various ester substrates, including aromatic and aliphatic esters as well as diesters and lactones. Notably, related pincer complexes with isopropyl or cyclohexyl substituents showed very low activity., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Hydroesterification reactions represent a fundamental type of carbonylation reaction and constitute one of the most important industrial applications of homogeneous catalysis. Over the past 70 years, numerous catalyst systems have been developed that allow for highly linear-selective (anti-Markovnikov) reactions and are used in industry to produce linear carboxylates starting from olefins. In contrast, a general catalyst system for Markovnikov-selective alkoxycarbonylation of aliphatic olefins remains unknown. In this paper, we show that a specific palladium catalyst system consisting of PdX 2 /N-phenylpyrrole phosphine (X, halide) catalyses the alkoxycarbonylation of various alkenes to give the branched esters in high selectivity (branched selectivity up to 91%). The observed (and unexpected) selectivity has been rationalized by density functional theory computation that includes a dispersion correction.