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We report on an additive-free Mn(I)-catalyzed dehydrogenative silylation of terminal alkenes. The most active precatalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic process is initiated by migratory insertion of a CO ligand into the Mn–alkyl bond to yield an acyl intermediate which undergoes rapid Si–H bond cleavage of the silane HSiR3 forming the active 16e– Mn(I) silyl catalyst [Mn(dippe)(CO)2(SiR3)] together with liberated butanal. A broad variety of aromatic and aliphatic alkenes was efficiently and selectively converted into E-vinylsilanes and allylsilanes, respectively, at room temperature. Mechanistic insights are provided based on experimental data and DFT calculations revealing that two parallel reaction pathways are operative: an acceptorless reaction pathway involving dihydrogen release and a pathway requiring an alkene as sacrificial hydrogen acceptor.

In the present work we have prepared and fully characterized several Fe(0) complexes of the type [Fe(PNP)(CO)2] treating Fe(II) complexes [Fe(PNP)(Cl)2] with KC8 in the presence of carbon monoxide. While complexes [Fe(PNPNMe‐iPr)(CO)2], [Fe(PNPNEt‐iPr)(CO)2] adopt a trigonal bipyramidal geometry, the bulkier and more electron rich [Fe(PNPNH‐tBu)(CO)2] is closer to a square pyramidal geometry. Mössbauer spectra showed isomer shifts very close to 0 and similar to those reported for Fe(I) systems. Quadrupole splitting values range between 2.2 and 2.7 mm s−1 both in experiments and DFT calculations, while those of Fe(I) complexes are much smaller (∼0.6 mm s−1).

For the first time, an efficient manganese-catalyzed dimerization of terminal alkynes to afford 1,3-enynes is described. This reaction is atom economic, implementing an inexpensive, earth abundant non-precious metal catalyst. The pre-catalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic process is initiated by migratory insertion of a CO ligand into the Mn-alkyl bond to yield an acyl intermediate which undergoes rapid C-H bond cleavage of the alkyne forming an active Mn(I) acetylide catalyst [Mn(dippe)(CO)2(C≡CPh)(η2-HC≡CPh)] together with liberated butanal. A range of aromatic and aliphatic terminal alkynes were efficiently and selectively converted into head-to-head Z-1,3-enynes and head-to-tail gem-1,3-enynes, respectively, in good to excellent yields. Moreover, cross-coupling of aromatic and aliphatic alkynes yields selectively head-to-tail gem-1,3-enynes. In all cases, the reactions were performed at 70 °C with a catalyst loading of 1-2 mol %. A mechanism based on DFT calculations is presented.

In this paper, several Mn(I) complexes were applied as catalysts for the homogeneous hydrogenation of ketones. The most active precatalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe) (CO)3(CH2CH2CH3)]. The reaction proceeds at room temperature under base-free conditions with a catalyst loading of 3 mol % and a hydrogen pressure of 10 bar. A temperature-dependent selectivity for the reduction of α,β-unsaturated carbonyls was observed. At room temperature, the carbonyl group was selectively hydrogenated, while the C=C bond stayed intact. At 60 °C, fully saturated systems were obtained. A plausible mechanism based on DFT calculations which involves an inner-sphere hydride transfer is proposed.

The catalytic reduction of carbon dioxide is a process of growing interest for the use of this simple and abundant molecule as a renewable building block in C1-chemical synthesis and for hydrogen storage. The well-defined, bench-stable alkylcarbonyl Mn(I) bis(phosphine) complex fac-[Mn(CH2CH2CH3)(dippe)(CO)3] [dippe = 1,2-bis(diisopropylphosphino)ethane] was tested as an efficient and selective non-precious-metal precatalyst for the hydrogenation of CO2 to formate under mild conditions (75 bar total pressure, 80 °C), in the presence of a Lewis acid co-catalyst (LiOTf) and a base (DBU). Mechanistic insight into the catalytic reaction is provided by means of density functional theory (DFT) calculations.

The synthesis, characterization, and catalytic activity of low-spin {CoNO}8 pincer complexes of the type [Co(PCP)(NO)(H)] are described. These compounds are obtained either by reacting [Co(PCP)(κ2-BH4)] with NO and Et3N or, alternatively, by reacting [Co(PCP)(NO)]+ with boranes, such as NH3·BH3 in solution. The five-coordinate, diamagnetic Co(III) complex [Co(PCPNMe-iPr)(NO)(H)] was found to be the active species in the hydroboration of alkenes with anti-Markovnikov selectivity. A range of aromatic and aliphatic alkenes were efficiently converted with pinacolborane (HBpin) under mild conditions in good to excellent yield. Mechanistic insight into the catalytic reaction is provided by means of isotope labeling, NMR spectroscopy, and APCI/ESI-MS as well as DFT calculations.

A new Ru

A new Ru3(CO)12-catalyzed directed alkenylation of 2-carboxaldimine-heterocyclopentadienes has been accomplished. This process allows to couple furan, pyrrole, indole and thiophene 2-carboxaldimines with electron-poor alkenes such as acrylates, vinylsulfones, and styrenes. This regio- and chemoselective oxidative C–H coupling does not require the presence of an additional sacrificial oxidant. Density functional theory (DFT) calculations allowed to propose a mechanism and unveiled the nature of the H2 acceptor.

The selective semihydrogenation of alkynes with the Mn(I) alkyl catalyst fac-[Mn(dippe)(CO)3(CH2CH2CH3)] (dippe = 1,2-bis(di-iso-propylphosphino)ethane) as pre-catalyst is described. Hydrogen gas required for the hydrogenation is generated in situ upon alcoholysis of KBH4 with methanol. A series of aryl-aryl, aryl-alkyl, alkyl-alkyl and terminal alkynes were readily hydrogenated to yield E-alkenes in good to excellent isolated yields. The reaction proceeds at 90°C with catalyst loadings of 0.5 -2 mol%. The implemented protocol tolerates a variety of electron donating and electron withdrawing functional groups including halides, phenols, nitriles, unprotected amines and heterocycles. The reaction can be upscaled to the gram scale. Mechanistic investigations including deuterium labelling studies and DFT calculations were undertaken to provide a reasonable reaction mechanism showing that initially formed Z-isomer undergoes fast isomerization to afford the thermodynamically more stable E-isomer.

A Mn(I)-catalyzed hydroboration of terminal alkenes and the 1,2-diboration of terminal alkynes with pinacolborane (HBPin) is described. In the case of alkenes anti-Markovnikov hydroboration takes place, while in the case of alkynes the reaction proceeds with excellent trans-1,2-selectivity. The most active pre-catalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic process is initiated by migratory insertion of a CO ligand into the Mn-alkyl bond to yield an acyl intermediate which undergoes B-H bond cleavage of HBPin (in the case of alkenes) and rapid C-H bond cleavage (in the case of alkynes) forming the active Mn(I) boryl and acetylide catalysts [Mn(dippe)(CO)2(BPin)] and [Mn(dippe)(CO)2(CCR)], respectively, together with liberated butanal. The diboration is accompanied by dihydrogen liberation. A broad variety of aromatic and aliphatic alkenes and alkynes was efficiently and selectively borylated. Mechanistic insights are provided based on experimental data and DFT calculations revealing that an acceptorless reaction pathway involving dihydrogen release is operating.

We report on an additive-free Mn(I)-catalyzed dehydrogenative silylation of terminal alkenes. The most active pre-catalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic pro-cess is initiated by migratory insertion of a CO ligand into the Mn-alkyl bond to yield an acyl intermediate which un-dergoes rapid Si-H bond cleavage of the silane HSiR3 forming the active 16e- Mn(I) silyl catalyst [Mn(dippe)(CO)2(SiR3)] together with liberated butanal. A broad variety of aromatic and aliphatic alkenes was efficient-ly and selectively converted into E-vinylsilanes and allylsilanes, respectively, at room temperature. Mechanistic insights are provided based on experimental data revealing that two parallel reaction pathways are operative: an acceptorless reaction pathway involving dihydrogen release and a pathway requiring an alkene as sacrificial hydrogen acceptor.

Antibody-drug conjugates (ADCs) are a new class of therapeutics that combine the lethality of potent cytotoxic drugs with the targeting ability of antibodies to selectively deliver drugs to cancer cells. The synthesis of ADCs is challenging, and studies in this area show that their therapeutic effect is highly dependent on the chemistries used to connect both functions. Therefore, the linker evolved in recent years from being a simple chemical spacer to a functional structure that controls the potency and selectivity of ADCs. The linker provides a platform to integrate mechanisms to access synthetic homogeneity, stability in circulation and more importantly the installation of chemical units that release the drug as a response to the disease chemical environment. In this study we show for the first time the synthesis of a reactive-oxygen-species (ROS) responsive ADC (VL-DAB31-SN-38) that is highly selective and cytotoxic to B-cell lymphoma (CLBL-1 cell line, IC50 value of 54.1 nM). The synthesis of this ADC was possible due to the discovery that diazaborines (DABs) are a very effective ROS responsive unit (0.422 and 0.103M-1S-1 with 100 and 10 equiv. of H2O2 respectively), that is also very stable in buffer (over 14 days at different pHs) and in plasma (over 5 days). DFT calculation performed on this system revealed a favourable energetic profile (ΔGR = –74.3 kcal/mol) similar to the oxidation mechanism of aromatic boronic acids. DABs very fast formation rate and modularity enabled the construction of different ROS responsive linkers featuring self-immolative modules, bioorthogonal functions and bioconjugation handles. These structures were used in the site-selective functionalization of a VL antibody and in the construction of the homogeneous ADC. The enclosed ROS-responsive linker technology based on DABs, is expected to become a valuable tool to prepare stimuli responsive therapeutic materials, as ROS is a very important hallmark in several important diseases

A small family of novel modular monofunctional epicinchonidine-1,2,3-triazole compounds was prepared in very good overall yield (3 steps from cinchonidine, 49���87% yield) using simple Cu(I) catalyzed click-chemistry. The objective of this study was to access their hitherto unknown catalytic role in some key organic reactions like: ketimine hydrosilylation, Michael-addition and the Biginelli reaction. This is the first report on the application of cinchonidine derived 1,2,3-triazoles in organocatalysis, and includes catalytic screening and preliminary Density Functional Theory (DFT) mechanistic studies. The new compounds were screened for antimalarial activity against Plasmodium falciparum (W2 strain), exhibiting IC50 values in the range 2.0���6.8 ��M; and cholinesterase inhibition, showing activity against eqBuChE, but their main potential is for tumor anti-proliferation (showing a lowest GI50 of 8.1 ��M). Gratifyingly, all our compounds were non-cytotoxic against the non-tumor healthy cell line, BJ-hTERT and they presented excellent simulated pharmacological properties.

The Michael addition step and the following C5 isomerization in Hayashi's synthesis of Oseltamivir was studied by means of a DFT mechanistic study. These steps are crucial for the viability of the process where the formation of a single stereoisomer is required. The results indicate that the addition reaction is under thermodynamic and not kinetic control and that the key factor determining the reaction stereoselectivity are the stereochemical constraints imposed by all substituents in the cyclohexane ring. The DFT results indicate that cyclohexylthiol should behave similarly to p-toluylthiol, the one actually employed, and tert-butylthiol should increase the ratio between isomers favoring the desired S configuration of the C5 atom. This work shows that DFT studies can be useful in the selection of a reactant to improve stereoselectivity of a chemical step.

New substituted 5-aryl-2-(N-2,6-diisopropylphenylformimino)-1H-pyrrole ligand precursors reacted with the complex trans-[Ni(o-C6H4Cl)(PPh3)2Cl] to give rise to new mono(2-iminopyrrolyl) nickel(II) complexes with general formula [Ni{κ2N,N′-5-aryl-NC4H2-2-C(H)═N-2,6-iPr2C6H3}(o-C6H4Cl)(PPh3)]. The pyrrole 5-aryl substituent is a phenyl or a bulky anthracen-9-yl ring, the first being also modified by para-substituents with electron-releasing (methoxy) or electron-withdrawing (fluorine) characteristics. The new compounds were fully characterized by NMR spectroscopy, elemental analysis, and two of them by single crystal X-ray diffraction. The complexes were tested as aluminum-free catalysts for the oligo-/polymerization of ethylene, at different reaction conditions, revealing catalytic activity even when tested as single-component catalysts. The addition of a phosphine scavenger, such as [Ni(COD)2], enhances significantly the catalytic activity. The polyethylene products obtained are hyperbranched low-molecula...

The synthesis of cationic mono oxo MoIV PNP pincer complexes of the type [Mo(PNPMe-iPr)(O)X]+ (X = I, Br) from [Mo(PNPMe-iPr)(CO)X2] is described. These compounds are coordinatively unsaturated and feature a strong Mo≡O triple bond. The formation of these complexes proceeds via cationic 14e intermediates [Mo(PNPMe-iPr)(CO)X]+ and requires both molecular oxygen and water. ESI MS measurements with 18O labeled water (H2 18O) and molecular oxygen (18O2) indicates that water plays a crucial role in the formation of the Mo≡O bond. A plausible mechanism based on DFT calculations is provided. The X-ray structure of [Mo(PNPMe-iPr)(O)I]SbF6 is presented.

The four cationic C,C-(NHC-cyanoalkyl)–nickel(II) metallacyclic complexes, [Ni{Me-NHC-CH2CH(CN)}(NCMe)](PF6) (2a), [Ni{Mes-NHC-CH2CH(CN)}(NCMe)](PF6) (2b), [Ni{Mes-NHC-(CH2)2CH(CN)}(NCMe)](PF6) (2c) and [Ni{DiPP-NHC-(CH2)2CH(CN)}(NCMe)](PF6) (2d) were prepared by the removal of the Cp ligand under acidic conditions at 0 °C from the corresponding half-sandwich nickelacycles [NiCp{R-NHC-(CH2)nCH(CN)}] (1a-1d; Cp = η5-C5H5; n = 1 or 2; R-NHC-(CH2)nCH(CN) = 1-R-3-[(CH2)nCH(CN)]-imidazol-2-ylidene). Full characterization of 2a-d by 1H and 13C{1H} NMR spectroscopy in CD3CN and pyridine-d5, ATR-FTIR spectroscopy, mass spectrometry, and CHN microanalyses established the presence of only one acetonitrile ligand per nickel atom in the solid state. A DFT structural study conducted on the cations of the methyl-substituted 5-membered nickelacycle 2a and the mesityl-substituted 6-membered cycle 2c found a small energetic cost (ΔG = 7–12 kcal.mol-1) for the loss of one acetonitrile ligand from the square-planar structures existing in solution, that should be easily amenable upon solvent evaporation (ΔG‡ = 14 kcal.mol-1 in the case of 2c). Two structures with one acetonitrile ligand could be optimized in both cases: (i) a truly T-shaped 14-electron structure with an end-on acetonitrile ligand, and (ii) a masked T-shaped structure stabilized by the π-coordination of the dangling CN group of the metallated alkyl chain, the latter being favoured by 2.4 kcal.mol-1 in the case of the flexible 6-membered ring 2c. Comparison of calculated vibrational frequencies with experimental FTIR spectra ruled out π-coordination of the dangling CN group as a ν(C≡N) band at low frequency was absent. Complexes 2a-d thus probably exist as rare three-coordinate T-shaped 14-electron species in the solid state. Their catalytic activity was studied for the direct arylation of azoles, and 2c proved to be moderately active for the coupling of benzothiazole with aryl iodides. Mechanistic insights suggest that competing processes or a radical process catalysed by nickel particles could follow an initial reduction of 2c by the dimerization of a sacrificial amount of benzothiazole.

International audience; The Murai reaction is a ruthenium-catalyzed transformation leading to alkylated arenes through the CC bond formation between an alkene and an arene bearing a directing group. Discovered in the nineties, this useful C-H activation based coupling has been the object of intense study since its discovery. After having studied the Murai reaction on 2-formylfurans of biomass derivation, we describe here the carbonylative version applied to 2-formylfurans, 2-formylpyrrols and 2-formylthiophenes. This acylation reaction takes place regioselectively at C3 position of the heterocyclopentadienes thanks to the installation of removable imine directing groups. The transformation can be achieved by treating the two reaction partners with a catalytic amount of Ru 3 (CO) 12 , in toluene at 120-150 °C, after CO bubbling, at atmospheric pressure. DFT computations of the full catalytic cycle help in deciphering the mechanism of this transformation, and to rationalize the different behaviors depending on the nature of imine directing groups.

We report the synthesis of the square-planar Cr(II) PCP complex [Cr(POCOP-tBu)(Br)] which is a valuable precursor for novel chromium borohydride PCP pincer complexes in formal oxidation states +I and +II.

We describe here the application of the well-defined bench-stable cationic aminoborane complex as highly efficient pre-catalysts for the semi-hydrogenation of internal alkynes, 1,3-diynes and 1,3-enynes with molecular hydrogen under mild conditions.

An efficient additive-free manganese-catalyzed hydrogenation of alkenes to alkanes with molecular hydrogen is described. This reaction is environmentally benign and atom economic, implementing an inexpensive, earth abundant non-precious metal catalyst. The most efficient pre-catalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic process is initiated by migratory insertion of a CO ligand into the Mn-alkyl bond to yield an acyl intermediate which undergoes rapid hydrogenolysis to form the active 16e Mn(I) hydride catalyst [Mn(dippe)(CO)2(H)]. A range of mono- and disubstituted alkenes were efficiently converted into alkanes in good to excellent yields. The hydrogenation of 1-alkenes and 1,1-disubstituted alkenes proceeds at 25 oC, while 1,2-disubstituted alkenes require a reaction temperature of 60oC. In all cases, a catalyst loading of 2 mol % and a hydrogen pressure of 50 bar was applied. A mechanism based on DFT calculations is presented.

The reactivity of ZnII dialkyl species ZnMe2 with a cyclic(alkyl)(amino)carbene, 1-[2,6-bis(1-methylethyl)phenyl]-3,3,5,5-tetramethyl-2-pyrrolidinylidene (CAAC, 1), was studied and extended to the preparation of robust CAAC-supported ZnII Lewis acidic organocations. CAAC adduct of ZnMe2 (2), formed from a 1:1 mixture of 1 and ZnMe2 , is unstable at room temperature and readily undergoes a CAAC carbene insertion into the Zn-Me bond to produce the ZnX2 -type species (CAAC-Me)ZnMe (3), a reactivity further supported by DFT calculations. Despite its limited stability, adduct 2 was cleanly ionized to robust two-coordinate (CAAC)ZnMe+ cation (5+ ) and derived into (CAAC)ZnC6 F5+ (7+ ), both isolated as B(C6 F5 )4- salts, showing the ability of CAAC for the stabilization of reactive [ZnMe]+ and [ZnC6 F5 ]+ moieties. Due to the lability of the CAAC-ZnMe2 bond, the formation of bis(CAAC) adduct (CAAC)2 ZnMe+ cation (6+ ) was also observed and the corresponding salt [6][B(C6 F5 )4 ] was structurally characterized. As estimated from experimental and calculations data, cations 5+ and 7+ are highly Lewis acidic species and the stronger Lewis acid 7+ effectively mediates alkene, alkyne and CO2 hydrosilylation catalysis. All supporting data hints at Lewis acid type activation-functionalization processes. Despite a lower energy LUMO in 5+ and 7+ , their observed reactivity is comparable to those of N-heterocyclic carbene (NHC) analogues, in line with charge-controlled reactions for carbene-stabilized ZnII organocations.

We report on the first synthesis and structural characterization of the iron based aminoborane complexes. These species are formed upon protonation of a borohydride complex by ammonium salts.

A new metal-free reductive amination protocol using a pinacol-derived chlorohydrosilane/pyridine system for the preparation of aminoalkylphenols is described. This method is selective toward iminiums derived from alkylphenol ketones under an in situ formation of a trialkoxyhydrosilane and activation with a Lewis base, as further indicated by computational studies. This method demonstrated high functional group tolerance affording an array of novel aminoalkylphenols in moderate to high yields with equimolar amounts of reactants and a wide substrate scope. publishedVersion

Several new monophosphorylated 2,6-diaminopyridine ligands bearing PiPr2 and PtBu2 units (PNNH2-iPr, PNNH2-tBu, PNNHMe-iPr, and PNNHEt-iPr) are prepared by treatment of the respective 2,6-diaminopyridines with the chlorophosphines PiPr2Cl and PtBu2Cl in the presence of a base. Treatment of anhydrous FeCl2 with 1 equiv of these afforded the tetracoordinated coordinatively unsaturated 14e− complexes [Fe(κ2 P,N-PNNH2-iPr)Cl2] and [Fe(κ2 P,N-PNNH2-tBu)Cl2], while with PNNHMe-iPr and PNNHEt-iPr a phosphine transfer reaction of a second PN ligand took place to yield the known PNP pincer complexes [Fe(κ3 P,N,P-PNPMe-iPr)Cl2] and [Fe(κ3 P,N,P-PNPEt-iPr)Cl2]. The four-coordinate complexes [Fe(κ2 P,N-PNNH2-iPr)Cl2] and [Fe(κ2 P,N-PNNH2-tBu)Cl2] did not react with CO and the formation of iron PNC pincer complexes was not observed. The reason for the reluctance to add CO was investigated in detail by DFT calculations.

The synthesis and application of [Fe(PNPMe-iPr)(CO)(H)(Br)] and [Fe(PNPMe-iPr)(H)2(CO)] as catalysts for the homogeneous hydrogenation of aldehydes is described. These systems were found to be among the most efficient catalysts for this process reported to date and constitute rare examples of a catalytic process which allows selective reduction of aldehydes in the presence of ketones and other reducible functionalities. In some cases, TONs and TOFs of up to 80000 and 20000 h-1, respectively, were reached. On the basis of stoichiometric experiments and computational studies, a mechanism which proceeds via a trans-dihydride intermediate is proposed. The structure of the hydride complexes was also confirmed by X-ray crystallography.

Gold(I) catalysis of olefin activation is still a rare feature in the repertoire of that metal. Mechanistic studies on the gold(I)-catalyzed cyclopropanation of allyl-substituted sulfonium ylides, including kinetic analysis as well as detailed computational studies, reveal that the reaction proceeds through activation of the alkene moiety. Furthermore, a novel competitive allylic isomerization pathway that interconverts "linear" and "branched" allylic isomers is uncovered. The subtle interplay of cyclopropanation and olefin isomerization results in an intriguing domino process where two independent catalytic transformations combine with near-perfect regio- and stereoselectivities.

Divergent catalysis is an emerging field whereby access to structurally diverse compounds from a common precursor is achieved through controlled reaction pathways. Herein we present an unusual example of π-acid catalyst dependent selectivity in the cycloisomerization of alkene-tethered sulfonium ylides. Computational mechanistic studies revealed how the ability of palladium to cycle through oxidation states largely controls the selectivity.

In the present study a complete series of seven-coordinate neutral halocarbonyl Mo(II) complexes of the type [Mo(PNPMe-Ph)(CO)2X2] (X = I, Br, Cl, F), featuring the new PNP pincer ligand N,N′-bis(diphenylphosphino)-N,N′-methyl-2,6-diaminopyridine (PNPMe-Ph), were prepared and fully characterized. The synthesis of these complexes was accomplished by different methodologies depending on the halide ligands. For X = I and Br, [Mo(PNPMe-Ph)(CO)2I2] and [Mo(PNPMe-Ph)(CO)2Br2] were obtained by reacting [Mo(PNPMe-Ph)(CO)3] with stoichiometric amounts of I2 and Br2, respectively. Alternatively, these complexes were obtained upon treatment of [MoX2(CO)3(CH3CN)2] (X = I, Br) with 1 equiv. of PNPMe-Ph. On the other hand, in the case of X = Cl, [Mo(PNPMe-Ph)(CO)2Cl2] was afforded by the reaction of [Mo(CO)4(μ-Cl)Cl]2 with 1 equiv. of PNPMe-Ph. The equivalent procedure also worked for X = Br. Finally, addition of 1 equiv. of 1-fluoro-2,4,6-trimethylpyridinium tetrafluoroborate to [Mo(PNPMe-Ph)(CO)3] yielded the analogous fluorine complex [Mo(PNPMe-Ph)(CO)2F2]. The modification of the ligand scaffold by introducing a Me group instead of H changed the properties of the PNP-Ph ligand significantly. While in the present case exclusively neutral seven-coordinate complexes of the type [Mo(PNPMe-Ph)(CO)2X2] were obtained, with the parent PNP-Ph ligand, i.e., featuring NH spacers, cationic seven-coordinate complexes of the type [Mo(PNP-Ph)(CO)3X]X were afforded. DFT calculations indicated that the reactions are under thermodynamic control. The structures of representative complexes were determined by X-ray single crystal analyses., Graphical abstract A complete series of seven-coordinate neutral halocarbonyl Mo(II) complexes of the type [Mo(PNPMe-Ph)(CO)2X2] (X = I, Br, Cl, F) were prepared by three different methodologies and fully characterized., Highlights • A complete series of seven-coordinate halocarbonyl complexes are described. • Modification of the PNP ligand scaffold changes properties significantly. • Fragmentation of complexes is investigated by means of ESI-MS. • Structures of complexes were determined by X-ray single crystal analyses.

Several ferrocene camphor compounds of the general formula FcCONHR, where Fc ¼ ferrocenyl and R isN(C 10 H 13 NSO 2 )(2), N(C 10 H 14 O) (3), N(C 10 H 16 )(4) or NLiCO(C 10 H 14 O) (6), were synthesized by the reactionof FcCONHNH 2 (1) with the respective camphor derivatives. In the resulting compounds, the ferroceneand camphor units are connected via a hydrazone link formed through condensation of the terminal NH 2 group in 1 and the carbonyl group of the camphor derivative. The characterization of the complexes isbased mostly on analytical data and on NMR and IR spectra. Additional insight into the structuralcharacteristics of complex (E)-FcCONHN(C 10 H 14 O) (3) was obtained from variable temperature and 2DNMR measurements while computational calculations were used to assign the bands in IR spectra ofFcCONHN(C 10 H 13 NSO 2 ) isomers. X-ray diffraction analysis has shown that the molecules of (E)-FcCONHN(C 10 H 13 NSO 2 ) associate into symmetric dimers in the solid state via Ne /O hydrogen bondsbetween the hydrazone moieties. 2013 Elsevier B.V. All rights reserved.

Mn(i) PNP pincer hydride complexes were shown for the first time to catalyse the hydrogenation of CO2 to formate reaching quantitative yields and high TONs., The catalytic reduction of carbon dioxide is of great interest for its potential as a hydrogen storage method and to use carbon dioxide as C-1 feedstock. In an effort to replace expensive noble metal-based catalysts with efficient and cheap earth-abundant counterparts, we report the first example of Mn(i)-catalysed hydrogenation of CO2 to HCOOH. The hydride Mn(i) catalyst [Mn(PNPNH-iPr)(H)(CO)2] showed higher stability and activity than its Fe(ii) analogue. TONs up to 10 000 and quantitative yields were obtained after 24 h using DBU as the base at 80 °C and 80 bar total pressure. At catalyst loadings as low as 0.002 mol%, TONs greater than 30 000 could be achieved in the presence of LiOTf as the co-catalyst, which are among the highest activities reported for base-metal catalysed CO2 hydrogenations to date.

International audience; Discrete two-coordinate ZnII organocations of the type (NHC)Zn−R+ are reported, thanks to NHC stabilization. In preliminary reactivity studies, such entities, which are direct cationic analogues of long-known ZnR2 species, act as effective and tunable π-Lewis acid catalysts in alkene, alkyne, and CO2 hydrosilylation.

A comparative study of a series of halocarbonyl Mo(ii) and W(ii) complexes featuring PNP pincer ligands based on a 2,6-diaminopyridine scaffold is presented., This work presents a comparative study of a series of halocarbonyl Mo(ii) and W(ii) complexes of the types [M(PNP)(CO)3X]X and [M(PNP)(CO)2X2] (M = Mo, W; X = I, Br), featuring PNP pincer ligands based on a 2,6-diaminopyridine scaffold. The complexes were prepared and fully characterized. The syntheses of these complexes were accomplished by treatment of [M(PNP)(CO)3] with stoichiometric amounts of I2 and Br2, respectively. The modification of the 2,6-diaminopyridine scaffold by introducing NMe and NPh instead of NH spacers with concomitant modification of the phosphine moieties changed the steric and electronic properties of the PNP ligand significantly. While in the case of NH linkers exclusively cationic seven-coordinate complexes of the type [M(PNP)(CO)3X]+ were obtained with NMe and NPh spacers neutral seven-coordinate complexes of the type [M(PNP)(CO)2X2] were afforded. In the case of the latter, when the reaction is performed in the presence of CO also [M(PNP)(CO)3X]+ complexes are formed which slowly lose CO to give [M(PNP)(CO)2X2]. The halocarbonyl tungsten chemistry parallels that of molybdenum. The only exception is molybdenum in conjunction with the PNPMe-iPr ligand, where the coordinatively unsaturated complex [Mo(PNPMe-iPr)(CO)X2] is formed. DFT mechanistic studies reveal that the seven-coordinate complexes should be the thermodynamic as well as the kinetic products. Since [Mo(PNPMe-iPr)(CO)X2] is the observed product it suggests that the reaction follows an alternative path. Structures of representative complexes were determined by X-ray single crystal analyses.

The axial coordination of N-heterocyclic carbene ligands onto dirhodium(II) complexes was examined, together with its role in the intramolecular C-H insertion reactions of alpha-diazoacetamides. The formation of a decarbonylated product occurs by a free-carbene mechanism in which the structures of the catalyst and the acetamide play a decisive role.. - Fundacao para a Ciencia a Tecnologia [POCI 2010]; FEDER [PTDC/QUI/66695/2006, PTDC/QUI/66015/2006, SFH/BPD/46589/2008, SFRH/BD/30619/2006]. - We thank to Fundacao para a Ciencia a Tecnologia (POCI 2010) and FEDER (PTDC/QUI/66695/2006, PTDC/QUI/66015/2006, SFH/BPD/46589/2008 and SFRH/BD/30619/2006) for their financial support, and the Portuguese NMR Network (IST-UTL Center) for providing access to the NMR facility.

The reaction of two commercially available compounds, phenanthrenequinone and 2,6dialkylaniline (alkyl = Me, iPr), catalyzed by formic acid, in refluxing methanol, gave rise exclusively to 10-(2,6-dialkyl-phenylimino)-10H-phenanthren-9-one compounds (alkyl = Me (1), iPr (2)). In refluxing toluene, and when diisopropylaniline is employed, the heterocyclic compound 7-isopropyl-3,3-dimethyl-10'H-spiro(indoline-2,9'-phenanthren)-10'-one (3) was unexpectedly prepared as the major reaction product, in the presence of catalytic amounts of various Bronsted acids. DFT calculations indicate that the conversion of 2 into 3 involves a sigmatropic rearrangement as rate limiting step with a high energy barrier (25-28 kcal/mol), in agreement with the requirement of high reaction temperatures.

Light from a mercury vapor high-pressure lamp was used to induce the photolytic decomposition of alpha-diazo acetamides in hexane and in nonconventional media such as water or a film. The corresponding beta- and/or gamma-lactams were obtained in reasonable yields and in some cases with good diastereoselectivities with no need to use a metallic catalyst. Experimental studies on chiral substrates demonstrated the occurrence of insertion with retention of configuration.

Cleavage of the [Ir(η 4 -COD)Cl] 2 dimer in the presence of the corresponding imidazolium salts and the strong base t BuO − leads to the formation of Ir(I) derivatives of N -heterocyclic carbenes. When halide is replaced by NaCp, a mixture of [Ir(η 4 -COD)(NHC R )(η 1 -Cp)] and [Ir(η 2 -COD)(NHC R )(η 5 -Cp)] is obtained. The latter is favored for R = Cy, while the former predominates for R = Me. Conversely, [Ir(η 4 -COD)(NHC R )(η 1 -Ind)] is the only product of the reaction with NaInd, despite the R substituent. DFT/B3LYP calculations confirmed that the η 1 coordination mode of the ring gives rise to the most stable structures, namely square planar complexes of 5d 8 Ir(I). The energy of the 18 electron species containing η 2 -COD and η 5 -Ind or Cp is higher by 13 and 5 kcal mol −1 , respectively. The fluxional behaviour of indenyl, detected by NMR in the solutions of [Ir(η 4 -COD)(NHC R )(η 1 -Ind)], is associated to the low energy of the η 3 -Ind species required in the conversion process, and is not easily observed in the cyclopentadienyl derivatives, where a similar intermediate is disfavored.

The bonding of pyrrolyl ligands (pyr′) in group-4 metal complexes, [M(pyr′)Cl 3 ], is studied by means of DFT/B3LYP calculations with a VDZP basis set. Two metals (M = Ti, Hf) and two pyrrolyl ligands are addressed, pyr′ = pyrrolyl (pyr), and 2,5-dimethylpyrrolyl (dmp). The study allowed the characterization of the π-pyr′ complexes with a η 5 coordination of this ligand, the σ complexes with the pyr′ bonding established by the nitrogen lone pair, and the transition states for the interconversion between the two isomers. A comparative analysis of the pyr′ bonding to the metal in all the species is provided, as well as a detailed study of the mechanism for the interconversion between the two pyr′ coordination modes. This is a slippage process without significant folding of the pyr′ ring and the activation energies obtained ( E a –1 ) suggest the possible fluxionality between the two coordination modes, in solution. Calculated pyr′–M bond enthalpies show an increase in the bond strength going down the group, allowing a rationalization of the differences in stability of the two coordination modes observed for the various metals and, consequently, of the associated ring slippage process. To cite this article: A.R. Dias et al., C. R. Chimie 8 (2005) . Resume Les liaisons des ligands pyrrolyl dans les complexes metalliques du groupe 4, [M(pyr′)Cl 3 ], ont ete etudiees a l'aide de calculs de fonctionnelle de densite DFT/B3LYP avec une base VDZP. Les deux metaux (M = Ti, Hf) et deux ligands pyrroles pyr′ = pyrrolyl (pyr), et 2,5-dimethylpyrrolyl (dmp) ont ete etudies. L'etude a permis la caracterisation des complexes π-pyr′ avec une coordination η 5 du ligand, des complexes σ avec liaison pyr′ par la paire azote unique et de l'etat de transition pour l'interconversion entre ces deux isomeres. Une analyse comparative de la liaison pyr′–metal dans toutes les especes est donnee, ainsi qu'une etude detaillee du mecanisme de l'interconversion entre les deux modes de coordinaiton des pyr′. Il s'agit d'un processus de glissement sans effet sur le cycle pyr′ ; les energies d'activation ( E a –1 ) amenent a envisager une possible fluxionalite entre les deux modes de coordination en solution. Les enthalpies des liaisons pyr′–M calculees montre une augmentation de la force des liaisons a mesure que l'on descend dans la colonne, ce qui permet de rationaliser les differences de stabilite entre les deux modes de coordination observes pour des metaux varies et, par consequent, le processus de glissement de cycles associe. Pour citer cet article : A.R. Dias et al., C. R. Chimie 8 (2005) .

Metal–η 5 -cyclopentadienyl (M–Cp) and metal–η 5 -pyrrolyl (M–pyr) bond dissociation enthalpies in group 4 complexes were determined from DFT/B3LYP calculations with a VTZP basis set. Thermochemical cycles involving calculated enthalpies of ligand exchange reactions and experimental values of ligand electron affinities and M–Cl bond dissociation enthalpies were applied to [M(η 5 -X)Cl 3 ] piano stool complexes (M = Ti, Zr, Hf; X = pyr, Cp), allowing a comparative study of those metal–ligand bond strengths. The results indicate that both ligands establish weaker bonds with Ti than with the heavier elements, Zr and Hf. Very similar bond dissociation enthalpies were obtained for pyrrolyl and cyclopentadienyl (within 1 kcal mol −1 ), suggesting that the well known difference in reactivity between those families of complexes should derive from kinetic rather than thermodynamic causes.

The 15e square-planar complexes [Co(PCPMe-iPr)Cl] (2a) and [Co(PCP-tBu)Cl] (2b), respectively, react readily with NaBH4 to afford complexes [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Co(PCP-tBu)(η2-BH4)] (4b) in high yields, as confirmed by IR spectroscopy, X-ray crystallography, and elemental analysis. The borohydride ligand is symmetrically bound to the cobalt center in η2-fashion. These compounds are paramagnetic with effective magnetic moments of 2.0(1) and 2.1(1) μB consistent with a d7 low-spin system corresponding to one unpaired electron. None of these complexes reacted with CO2 to give formate complexes. For structural and reactivity comparisons, we prepared the analogous Ni(II) borohydride complex [Ni(PCPMe-iPr)(η2-BH4)] (5) via two different synthetic routes. One utilizes [Ni(PCPMe-iPr)Cl] (3) and NaBH4, the second one makes use of the hydride complex [Ni(PCPMe-iPr)H] (6) and BH3·THF. In both cases, 5 is obtained in high yields. In contrast to 4a and 4b, the borohydride ligand is asymmetrically bound to the nickel center but still in an η2-mode. [Ni(PCPMe-iPr)(η2-BH4)] (5) loses readily BH3 at elevated temperatures in the presence of NEt3 to form 6. Complexes 5 and 6 are both diamagnetic and were characterized by a combination of 1H, 13C{1H}, and 31P{1H} NMR, IR spectroscopy, and elemental analysis. Additionally, the structure of these compounds was established by X-ray crystallography. Complexes 5 and 6 react with CO2 to give the formate complex [Ni(PCPMe-iPr)(OC(C=O)H] (7). The extrusion of BH3 from [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) with the aid of NH3 to yield the respective hydride complexes [Co(PCPMe-iPr)H] and [Ni(PCPMe-iPr)H] (6) and BH3NH3 was investigated by DFT calculations showing that formation of the Ni hydride is thermodynamically favorable, whereas the formation of the Co(II) hydride, in agreement with the experiment, is unfavorable. The electronic structures and the bonding of the borohydride ligand in [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) were established by DFT computations.

Three new mononuclear oxovanadium(IV) complexes [VO(acac)(R-BIAN)]Cl (BIAN = 1,2-bis{(R-phenyl)imino} acenaphthene, R = H, 1; CH3, 2; Cl, 3) were prepared and characterized. They promoted the catalytic oxidation of olefins such as cyclohexene, cis-cyclooctene, and styrene with both tbhp (tert-butylhydroperoxide) and H2O2, and of enantiopure olefins (S(-)- and R(+)-pinene, and S(-)- and R(+)-limonene) selectively to their epoxides, with tbhp as the oxidant. The TOFs for styrene epoxidation promoted by complex 3 with H2O2 (290 mol mol(-1)V h(-1)) and for cis-cyclooctene epoxidation by 2 with tbhp (248 mol mol(V)(-1) h(-1)) are particularly good. Conversions reached 90% for several systems with tbhp, and were lower with H2O2. A preference for the internal C=C bond, rather than the terminal one, was found for limonene. Kinetic data indicate an associative process as the first step of the reaction and complex [VO(acac)(H-BIAN)](+) (1(+)) was isolated in an FTICR cell after adding tbhp to 1. EPR studies provide evidence for the presence of a V(IV) species in solution, until at least 48 hours after the addition of tbhp and cis-cyclooctene, and cyclic voltammetry studies revealed an oxidation potential above 1 V for complex 1. DFT calculations suggest that a [VO(H-BIAN)(MeOO)](+) complex is the likely active V(IV) species in the catalytic cycle from which two competitive mechanisms for the reaction proceed, an outer sphere path with an external attack of the olefin at the coordinated peroxide, and an inner sphere mechanism starting with a complex with the olefin coordinated to vanadium.

A series of allyl complexes of the general formula [Cp'Mo(eta(3)-C3H5)(CO)(2)], where Cp' = Cp, CpMe, Cp*, Ind, IndMe, IndMe2, Flu, and three tungsten analogues, has been prepared and characterized by H-1, C-13, and Mo-95 NMR, cyclic voltammetry, and the structure of [IndMo(eta(3)-C3H5)(CO)(2)] was determined by Xray single crystal analysis. Two conformers, corresponding to the two extreme orientations of the allyl ligand (endo and exo), have been identified in solution by H-1 and Mo-95 NMR for all the complexes, except for [FluMo(eta(3)-C3F15)(CO)(2)], which only presents an exo conformation in solution. A Mo-95 NMR investigation also shows the influence of electron donor capability of the Cp' ligands on the Mo-95 chemical shifts of the Mo center. He I and He II photoelectron spectra probe the electron richness of the metal center and the electronic structure of the complexes. Cyclic voltammetry studies show one oxidation process, which is only reversible for the Cp derivatives. DFT calculations provided a reliable way to determine ionization energies, and reflected very well the trends of the other properties, from the Mo-95 NMR chemical shifts, to vibration frequencies, and oxidation potentials. (1) 2015 Elsevier BY. All rights reserved.

The transferability of the IrI bond enthalpies in [Ir(μ-S t Bu)(I) 2 (CO) 2 ] 2 and trans -[Ir(X)(I) 2 (CO)(PPh 3 ) 2 ] (X=F, Cl, Br, I) complexes was investigated by theoretical calculations based on the B3LYP HF/DFT hybrid functional. It was concluded that the IrI bond snap enthalpy, E s (IrI), in [Ir(μ-S t Bu)(I) 2 (CO) 2 ] 2 was 35 kJ mol −1 smaller than in trans -[Ir(X)(I) 2 (CO)(PPh 3 ) 2 ] and, therefore, not transferable between both types of molecules. The relative magnitude of the obtained E s (IrI) values is in agreement with the slightly longer IrI distance and smaller Wiberg index found, on average, for [Ir(μ-S t Bu)(I) 2 (CO) 2 ] 2 . In this case, however, the computed d IrI and WI IrI do not seem to be sensitive indicators of ‘bond strength’, since a variation of 35 kJ mol −1 in the E s (IrI) values leads to changes of only 0.01 A in the bond distances and 0.005 in the Wiberg indexes. The calculations reproduce the experimental IrI mean bond dissociation enthalpies, 〈 DH °〉(IrI), in the binuclear and mononuclear systems with a maximum deviation of ca. 10 kJ mol −1 .

New Cu(I) and Ag(I) binuclear complexes were prepared by reaction of [M(NCCH3)4][PF6] (M = Ag, Cu) with the bidentate phosphine ligands Ph2PNHPPh2 (dppa) and Ph2PCH2PPh2 (dppm). In the reaction of Cu(I) with dppa the phosphine is easily oxidized to give the octahedral species of [Cu(dppaO2)3][PF6], 1. In an inert atmosphere, the binuclear complexes [Cu2(dppa)2(NCCH3)3][PF6]2, 2, [Cu2(dppa)2(NCCH3)4][PF6]2, 3, [Ag2(dppa)2(NCCH3)2][PF6]2, 4, and [Ag2(dppm)2][PF6]2, 5, were formed and structurally characterized by X-ray diffraction (except for 5). The electrochemical studies showed that the most relevant property of the binuclear species was the ease of forming the metal upon reduction. EH and DFT calculations were performed in order to try and understand the structural features of the [M2(dppa)2(NCCH3)x]n+ complexes, including the 0.47 A increase in M⋯M distance upon going from 2 to 3.

We have prepared and structurally characterized a new class of Fe(II) PNP pincer hydride complexes [Fe(PNP-iPr)(H)(CO)(L)]n (L = Br–, CH3CN, pyridine, PMe3, SCN–, CO, BH4–; n = 0, +1) based on the 2,6-diaminopyridine scaffold where the PiPr2 moieties of the PNP ligand are connected to the pyridine ring via NH and/or NMe spacers. Complexes [Fe(PNP-iPr)(H)(CO)(L)]n with labile ligands (L = Br–, CH3CN, BH4–) and NH spacers are efficient catalysts for the hydrogenation of both ketones and aldehydes to alcohols under mild conditions, while those containing inert ligands (L = pyridine, PMe3, SCN–, CO) are catalytically inactive. Interestingly, complex [Fe(PNPMe-iPr)(H)(CO)(Br)], featuring NMe spacers, is an efficient catalyst for the chemoselective hydrogenation of aldehydes. The first type of complexes involves deprotonation of the PNP ligand as well as heterolytic dihydrogen cleavage via metal-alkoxide cooperation, but no reversible aromatization/deprotonation of the PNP ligand. In the case of the N-methylated complex the mechanism remains unclear, but obviously does not allow bifunctional activation of dihydrogen. The experimental results complemented by DFT calculations strongly support an insertion of the C=O bond of the carbonyl compound into the Fe–H bond.