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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.

The syntheses of various manganese and iron PCP pincer complexes via a solvothermal oxidative addition methodology is described. Upon reacting [Mn2(CO)10] with the ligands (P(C–Br)PCH2-iPr) (1a) and (P(C–Br)PO-iPr) (1b), Mn(I) PCP pincer complexes [Mn(PCPCH2-iPr)(CO)3] (2a) and [Mn(-PCPO-iPr)(CO)3] (2b) were obtained. Protonation of 2a with HBF4·Et2O led to the formation of [Mn(κ3P,CH,P-P(CH)PCH2-iPr)(CO)3]BF4 (3) featuring an η2-Caryl–H agostic bond. The solvothermal reaction of 1a with [Fe2(CO)9] afforded the Fe(II) PCP pincer complex [Fe(PCPCH2-iPr)(CO)2Br] (4). Treatment of 4 with Li[HBEt3] afforded the Fe(I) complex [Fe(PCPCH2-iPr)(CO)2] (5a). When using the sterically more demanding ligands (P(C–Br)PCH2-tBu) (1c) and (P(C–Br)PO-tBu)(1d) striking differences in reactivity were observed. While neither 1c nor 1d showed any reactivity towards [Mn2(CO)10], the reaction with [Fe2(CO)9] and [Fe(CO)5] led to the formation of the Fe(I) complexes [Fe(PCPCH2-tBu)(CO)2] (5b) and [Fe(PCPO-tBu)(CO)2] (5c). X-ray structures of representative complexes are provided.

Boronic acids (BAs) are a promising bioconjugation function to design dynamic materials as they can establish reversible covalent bonds with oxygen/nitrogen nucleophiles that respond to different pH, ROS, carbohydrates and glutathione levels. However, the dynamic nature of these bonds also limits the control over the stability and site-selectivity of the bioconjugation, which ultimately leads to heterogeneous conjugates with poor stability under physiological conditions. Here we disclose a new strategy to install BAs on peptide chains. In this study, a "boron hot spot" based on the 3-hydroxyquinolin-2(1H)-one scaffold was developed and upon installation on a peptide N-terminal cysteine, enables the site-selective formation of iminoboronates with 2-formyl-phenyl boronic acids (Ka of 58128±2 m-1 ). The reaction is selective in the presence of competing lysine ϵ-amino groups, and the resulting iminoboronates, displayed improved stability in buffers solutions and a cleavable profile in the presence of glutathione. Once developed, the methodology was used to prepare cleavable fluorescent conjugates with a laminin fragment, which enabled the validation of the 67LR receptor as a target to deliver cargo to cancer HT29 cells.

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.

The family of recently described salts based on the electron donor CNB-EDT-TTF (5-cyanobenzene-ethylenedithio-tetrathiafulvalene) and different anions A, with general formula (CNB-EDT-TTF)4A, constitutes an unprecedented type of molecular conductor based on a bilayer structure of the donors. The crystal structures of the bilayer conductors (CNB-EDT-TTF)4A with small discrete anions are reviewed and analyzed considering previously reported compounds with different anions (A = I3−, ClO4−, BF4−, ReO4−, PF6− and SbF6−), as well as three new members of this family described here with AsF6−, AuI2−and I2Br−. A common structural feature of this family of compounds is the head-to-head arrangement of the donors, induced by a network of weak CN⋯H–C interactions, which can be described as an effective combination of R22(10) and R24(10) synthons, forming donor bilayers alternating with anionic layers. The magnitude of the interactions associated with R22(10) and R24(10) synthons is estimated to be 4.7 and 10.0 kcal mol−1, respectively. In spite of the common donor bilayer arrangement, a rich diversity of structural variations and polymorphs is observed. These structures are related to different types of donor or anion arrangements, which are analyzed. For all anions a β′′-type packing pattern of the donor molecules arranged in virtually identical bilayers is observed. However, for (CNB-EDT-TTF)4I3, so far a unique exception in this family of compounds, a distinct κ-type packing of the donors, is also obtained as a metastable phase as shown also by DFT calculations that predict the κ-phase above the β′′-phase. Another type of polymorphism is observed in β′′-(CNB-EDT-TTF)4A, compounds with tetrahedral anions, related to the tilting of the donor molecules (either alternating or uniform) in successive bilayers, leading to monoclinic or triclinic unit cells, with doubling of one cell parameter corresponding to the thickness of one bilayer (∼25 A). Finally, the anions, which often appear with fractional site occupation factors, can be ordered in the anionic plane, with different degrees of correlation between successive anion planes as shown in the AsF6.compound. The implications of these structural features in the electronic properties of these compounds are also discussed.

The bench-stable cationic bis(σ-B–H) aminoborane complex [Fe(PNPNMe-iPr)(H)(η2-H2B = NMe2)]+ (2) efficiently catalyzes the semihydrogenation of internal alkynes, 1,3-diynes and 1,3-enynes. Moreover, selective incorporation of deuterium was achieved in the case of 1,3-diynes and 1,3-enynes. The catalytic reaction takes place under mild conditions (25 °C, 4–5 bar H2 or D2) in 1 h, and alkenes were obtained with high Z-selectivity for a broad scope of substrates. Mechanistic insight into the catalytic reaction, explaining also the stereo- and chemoselectivity, is provided by means of DFT calculations. Intermediates featuring a bisdihydrogen moiety [Fe(PNPNMe-iPr)(η2-H2)2]+ are found to play a key role. Experimental support for such species was unequivocally provided by the fact that [Fe(PNPNMe-iPr)(H)(η2-H2)2]+ (3) exhibited the same catalytic activity as 2. The novel cationic bisdihydrogen complex 3 was obtained by protonolysis of [Fe(PNPNMe-iPr)(H)(η2-AlH4)]2 (1) with an excess of nonafluoro-tert-butyl alc...

An efficient additive-free manganese-catalyzed hydrogenation of alkenes to alkanes with molecular hydrogen is described. This reaction is atom economic, implementing an inexpensive, earth-abundant ...

Herein, we report on the first synthesis and structural characterization of the iron based aminoborane complexes [Fe(PNP)(H)(η2 :η2 -H2 B=NR2 )]+ (R=H, Me). These species are formed upon protonation of the borohydride complex [Fe(PNP)(H)(η2 -BH4 )] by ammonium salts [NH2 R2 ]+ (R=H, Me). For R=Me, the reaction proceeds via the cationic dinuclear intermediate [{Fe(PNP)(H)}2 (μ2 ,η2 :η2 -BH4 )]+ . A mechanism for the reaction is proposed based on DFT calculations that also indicate the final aminoborane complex as the thermodynamic product. All complexes were characterized by NMR spectroscopy, HRMS, and X-ray crystallography.

The synthesis and characterization of air-stable cationic mono nitrosonium Fe(I) PNP pincer complexes of the type [Fe(PNP)(NO)Cl]+ are described. These complexes are obtained via direct nitroslyation of [Fe(PNP)Cl2] with nitric oxide at ambient pressure. On the basis of magnetic and EPR measurements as well as DFT calculations, these compounds were found to adopt a low-spin d7 configuration and feature a nearly linear bound NO ligand suggesting FeINO+ rather than FeIINO• character. X-ray structures of all nitrosonium Fe(I) PNP complexes are presented. Preliminary investigations reveal that [Fe(PNPNH- iPr)(NO)(Cl)]+ efficiently catalyzes the conversion of primary alcohols and aromatic and benzylic amines to yield mono N-alkylated amines in good isolated yields.

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.

Four paramagnetic 14-electron tetracoordinated Fe(II) complexes of 5-substituted-2-iminopyrrolyl ligands of the type [Fe{κ2N,N′-5-R-NC4H2-2-C(H)N(2,6-iPr2-C6H3)}(Py)Cl], with R = 2,6-Me2-C6H3 (1a), 2,4,6-iPr3-C6H2 (1b), 2,4,6-Ph3-C6H3 (1c) and CPh3 (1d), were synthesized in moderate yields by reacting the respective 5-substituted-2-iminopyrrolyl potassium salts KLa-d with FeCl2(Py)4 in toluene. Complexes 1a–d were characterized by 1H NMR, FTIR spectroscopies, elemental analysis and by the Evans method, the corresponding effective magnetic moments showing a high-spin electronic nature. X-ray diffraction studies on complexes 1a and 1c showed distorted tetrahedral coordination geometries. Complexes 1a–c, activated with K(HBEt3), were efficient catalyst systems for the hydroboration of several terminal alkenes with pinacolborane in good to high yields (50–90%). This system mainly yielded the respective anti-Markovnikov addition products, except when styrenes were used. A screening of the hydroboration of styrene catalyzed by complexes 1a–c activated with K(HBEt3) showed that the selectivity in the Markovnikov product increased with increasing steric bulkiness of the R group, exhibiting selectivities up to 91%. Additionally, the stoichiometric reaction of complex 1b with K(HBEt3) over 30 minutes yielded the mixture of hydride species 2 and 22 (mixture I). On the other hand, when reacting the same components over 16 h, the Fe(I) complex 3 was also identified in the mixture, in addition to 2 + 22 (mixture II). These mixtures were characterized in solution by the Evans method and in the solid state by elemental analysis, 57Fe Mossbauer and FTIR spectroscopies, compounds 22 and 3 being also analyzed by X-ray diffraction. These results suggest that the corresponding catalytic cycle follows the borane oxidative addition route to a Fe(I) species.

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.

Well-defined Mn(I) hydrido carbonyl PNP pincer-type complexes were tested as efficient and selective nonprecious transition metal catalysts for the reduction of CO2 to MeOH in the presence of hydrosilanes. The choice of reaction temperature and type of silanes proved to be pivotal to achieve fast reactions and high selectivity to the methoxysilyl- vs silylformate derivatives in DMSO. The catalytic data are complemented by DFT calculations, highlighting a stepwise CO2 reduction mechanism centered on the Mn catalyst without metal-to-ligand cooperation.

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...

In the present study, Cr(III) complexes of the type trans-[Cr(PCPNEt-iPr)(solvent)Cl2] (solvent = CH3CN, THF), the Cr(0) complex [Cr(κ3P,CH,P-P(CH)PNEt-iPr)(CO)3] which features an η2-Caryl–H agostic bond as well as seven coordinate cationic chloro carbonyl Mo(II) and W(II) complexes of the type [M(PCPNEt-iPr)(CO)3Cl] featuring PCP pincer ligands based on a 1,3-diaminobenzene scaffold were prepared and characterized. The seven coordinate chloro tricarbonyl complexes exhibit fluxional behavior in solution due to rapid CO ligand interconversions. Another interesting aspect is a rapid and reversible addition of one CO ligand across the metal–Cipso bond. The mechanism of the dynamic process of the chloro carbonyl complexes was investigated by means of DFT calculations. The Mo(II) and W(II) tricarbonyl complexes could be reduced to the respective anionic Mo(0) and W(0) complexes [Mo(PCPNEt-iPr)(CO)3]− and [Mo(PCPNEt-iPr)(CO)3]−. These air sensitive compounds are readily protonated by MeOH to form agostic and h...

Nonclassical iron(II) polyhydride complexes supported by PNP-pincer ligands were found to be very active catalysts for the Z-selective hydroboration and head-to-head dimerization of terminal alkynes. Iron(II) bis(acetylide) complexes are identified as catalytically active species in both transformations, which proceed via different reaction pathways, however. These species as well as intermediates relevant for the elucidation of selectivity could be trapped and fully characterized spectroscopically. X-ray structures of key intermediates are presented. Detailed DFT calculations provide a deeper insight into the activation of the precatalysts, and comprehensive catalytic cycles are elucidated. The proposed mechanisms provide a consistent picture of the different reaction pathways and fully explain the stereoselective steps of these transformations.

The first manganese PCP pincer complex, [Mn(PCPNEt-iPr)(CO)3], was obtained by treating [Mn2(CO)10] and 2-chloro-N1,N3-bis(diisopropylphosphanyl)-N1,N3-diethylbenzene-1,3-diamine (P(C-Cl)PNEt-iPr) in CH3CN under solvothermal conditions in a sealed microwave glass tube for 8 h at 140 °C. Protonation of this complex with HBF4·Et2O leads to the formation of the cationic Mn(I) complex [Mn(κ3P,CH,P-P(CH)PNEt-iPr)(CO)3]BF4, which features an η2-Caryl–H agostic bond. There was no evidence for the formation of a Mn(III) hydride species. The agostic C–H bond is comparatively acidic, and even relatively weak bases, such as NEt3, deprotonate this bond to re-form the starting material [Mn(PCPNEt-iPr)(CO)3]; protonation is fully reversible. Substitution of one CO ligand was achieved upon treatment with NO+, affording the cationic complex [Mn(PCPNEt-iPr)(CO)2(NO)]+, where the two CO ligands are trans to one another.

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.

A novel selenium-containing pyridazinyl-based soft scorpionate ligand (KTnse) was synthesized. It reacts with CoCl2 and NiCl2, yielding the first metallaboratrane complexes with selenium in their donor positions. Further substitution with Ag(OTf) or NaN3 allows isolation of the respective triflate or azide complexes. Reaction with Ag(OTf) leads in the case of nickel to a dinuclear, dicationic complex with a short Ni–Ni distance, while cobalt gave a mononuclear cationic species. Substitution of the chloride by azide yields with both metals the respective azide complexes. All compounds were characterized via single-crystal X-ray diffraction analysis. Density functional theory calculations on the chloride species point to oxidized cobalt(III) and nickel(III) centers.

Herein is described a new modular platform for the construction of cancer-cell-targeting drug conjugates. Tripodal boronate complexes featuring reversible covalent bonds were designed to accommodate a cytotoxic drug (bortezomib), poly(ethylene glycol) (Peg) chains, and folate targeting units. The B-complex core was assembled in one step, proved stable under biocompatible conditions, namely, in human plasma (half-life up to 60 h), and underwent disassembly in the presence of glutathione (GSH). Stimulus-responsive intracellular cargo delivery was confirmed by confocal fluorescence microscopy, and a mechanism for GSH-induced B-complex hydrolysis was proposed on the basis of mass spectrometry and DFT calculations. This platform enabled the modular construction of multivalent conjugates with high selectivity for folate-positive MDA-MB-231 cancer cells and IC50 values in the nanomolar range.

The synthesis, characterization, and catalytic activity of nonclassical iron(II) polyhydride complexes containing tridentate PNP pincer-type ligands is described. These compounds of the general formula [Fe(PNP)(H)2(η2-H2)] exhibit remarkable reactivity toward terminal alkynes. They efficiently promote the catalytic dimerization of aryl acetylenes giving the corresponding conjugated 1,3-enynes in excellent yields with low catalyst loadings. When the reaction is carried out in the presence of pinacolborane, vinyl boronates are obtained. Both reactions take place under mild conditions and are highly chemo-, regio-, and stereoselective with up to 99% Z-selectivity.

Furfural and related compounds are industrially relevant building blocks obtained from lignocellulosic biomass. To enhance the added value of these renewable resources, a Ru-catalyzed hydrofurylation of alkenes, involving a directed C-H activation at C3 of the furan ring, was developed. A thorough experimental study revealed that a bidentate amino-imine directing group enabled the desired coupling. Removal of the directing group occurred during the purification step, directly releasing the C3-functionalized furfurals. Development of the reaction as well as optimization and scope of the method were described. A mechanism was proposed on the basis of DFT calculations.

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.

The bench-stable cationic bis(σ-B-H) aminoborane complex [Fe(PNP

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.

Herein, we report on the first synthesis and structural characterization of the iron based aminoborane complexes [Fe(PNP)(H)(η

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.

The synthesis and characterization of air-stable cationic mono nitrosonium Fe(I) PNP pincer complexes of the type [Fe(PNP)(NO)Cl]