Synthesis and characterization of heptacoordinated molybdenum(II) complexes supported with 2,6-bis(pyrazol-3-yl)pyridine (bpp) ligands.

Functional pincer ligands that engage in metal-ligand cooperativity and/or are capable of redox non-innocence have found a great deal of success in catalysis. These two properties may be found in metal complexes of the 2,6-bis(pyrazol-3-yl)pyridine (bpp) ligands. With this goal in mind, we have attempted the coordination of 2,6-bis(5-trifluoromethylpyrazol-3-yl)pyridine (LCF3) and its Bu analogue 2,6-bis(5--butylpyrazol-3-yl)pyridine (LtBu) to Mo(0) by reactions with mixed phosphine/carbonyl complexes [Mo(CO)(MeCN)(PMePh)] 1-3 (1 ≤ ≤ 3).

Reactivity of metal hydrides with CO: going beyond formate with a high-valent cationic pentahydride Mo(vi) complex.

The cationic molybdenum pentahydride complex [MoH(depe)] (depe = 1,2-bis(diethylphosphino)ethane) is shown to undergo two consecutive reactions with carbon dioxide. In the initial, room-temperature process, classical insertion of CO into a metal-hydride bond is observed, resulting in the formation of the expected formate complex, [MoH(HCOO)(depe)]. Further reactivity is triggered at temperature above 100 °C.

Low-valent group 6 metals/Al(CF) donor-acceptor systems for CO activation and cleavage.

Donor-acceptor systems for CO activation combining a formally zero-valent group 6 metal as the donor with the Lewis acid Al(CF) (AlCF) are reported. They were obtained from AlCF adducts of N-complexes by N-to-CO substitution. One species was capable of C-O cleavage.

Coordination of Al(CF) B(CF) on group 6 end-on dinitrogen complexes: chemical and structural divergences.

The coordination of the Lewis superacid tris(pentafluorophenyl)alane (AlCF) to phosphine-supported, group 6 bis(dinitrogen) complexes [ML(N)] is explored, with M = Cr, Mo or W and L = dppe (1,2-bis(diphenylphosphino)ethane), depe (1,2-bis(diethylphosphino)ethane), dmpe (1,2-bis(dimethylphosphino)ethane) or 2 × PMePh. Akin to tris(pentafluorophenyl)borane (BCF), AlCF can form 1 : 1 adducts by coordination to one distal nitrogen of general formula -[ML(N){(μ-η:η-N)Al(CF)}]. The boron and aluminium adducts are structurally similar, showing a comparable level of N push-pull activation.

Seven-Coordinate Group 6 Metal Hydrides Obtained by H Activation at B(CF) Adducts of N Complexes: Frustrated Lewis Pair-Type Reactivity of The B-N Linkage.

The adducts 2 of general formula trans-[(L)M{RP(CH)PR}{NB(CF)}] (L=ø or N, M=Mo or W, R=Et or Ph), formed from Lewis acid-base pairing of B(CF) to a dinitrogen ligand of zero-valent group 6 bis(phosphine) complexes trans-[M{RP(CH)PR}(N)] are shown to react with dihydrogen to afford hepta-coordinated bis(hydride) complexes [M(H){RP(CH)PR}{NB(CF)}] 3 which feature the rare ability to activate both dinitrogen and dihydrogen at a single metal center, except in the case where M=Mo and R=Ph for which fast precipitation of insoluble [Mo(H)(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane) occurs. The frustrated Lewis pair (FLP)-related reactivity of the B-N linkage in compounds 3 was explored and led to distal N functionalization without involvement of the hydride ligands. It is shown in one example that the resulting bis(hydride) diazenido compounds may also be obtained through a sequence involving first FLP-type N-functionalization followed by oxidative addition of H.

Nitrogen Fixation by Manganese Complexes - Waiting for the Rush?

Manganese is currently experiencing a great deal of attention in homogeneous catalysis as a sustainable alternative to platinum group metals due to its abundance, affordable price and low toxicity. While homogeneous nitrogen fixation employing well-defined transition metal complexes has been an important part of coordination chemistry, manganese derivatives have been only sporadically used in this research area. In this contribution, the authors systematically cover manganese organometallic chemistry related to N activation spanning almost 60 years, identify apparent pitfalls and outline encouraging perspectives for its future development.

Metallomimetic C-F Activation Catalysis by Simple Phosphines.

Delivering metallomimetic reactivity from simple p-block compounds is highly desirable in the search to replace expensive, scarce precious metals by cheap and abundant elements in catalysis. This contribution demonstrates that metallomimetic catalysis, involving facile redox cycling between the P(III) and P(V) oxidation states, is possible using only simple, cheap, and readily available trialkylphosphines without the need to enforce unusual geometries at phosphorus or use external oxidizing/reducing agents. Hydrodefluorination and aminodefluorination of a range of fluoroarenes was realized with good to very good yields under mild conditions.

Biomimetic catalysis of nitrite reductase enzyme using copper complexes in chemical and electrochemical reduction of nitrite.

Copper nitrite reductase mimetics were synthesized using three new tridentate ligands sharing the same ,, motif of coordination. The ligands were based on L-proline modifications, attaching a pyridine and a triazole to the pyrrolidine ring, and differ by a pendant group (R = phenyl, -butyl and -propan-1-ol). All complexes coordinate nitrite, as evidenced by cyclic voltammetry, UV-Vis, FTIR and electron paramagnetic resonance (EPR) spectroscopies.

An Experimental and Computational Investigation Rules Out Direct Nucleophilic Addition on the N Ligand in Manganese Dinitrogen Complex [Cp(CO) Mn(N )].

We have re-examined the reactivity of the manganese dinitrogen complex [Cp(CO) Mn(N )] (1, Cp=η -cyclopentadienyl, C H ) with phenylithium (PhLi). By combining experiment and density functional theory (DFT), we have found that, unlike previously reported, the direct nucleophilic attack of the carbanion onto coordinated dinitrogen does not occur. Instead, PhLi reacts with one of the CO ligands to provide an anionic acylcarbonyl dinitrogen metallate [Cp(CO)(N )MnCOPh]Li (3) that is stable only below -40 °C.

Assessing Combinations of B(C F ) and N -Derived Molybdenum Nitrido Complexes for Heterolytic Bond Activation.

Two different dinitrogen-derived molybdenum nitrido complexes varying by their geometry, ligand spheres and oxidations states were shown to engage their N ligand in dative bonding with the strong Lewis acid B(C F ) . The stable adducts were assessed for frustrated Lewis pair-type heterolytic E-H bond splitting of hydrosilanes (E=Si) and HB(C F ) . Whereas Si-H bond activation was achieved, HB(C F ) was shown to substitute B(C F ) in a quantitative or equilibrated fashion, depending on the nature of the nitrido complex.

Dinitrogen-derived (diarylboryl)diazenido complexes with differing coordination to the thallium cation.

To prepare N-derived cationic boryldiazenido-tungsten complexes as models of semimetallic metal-borinium frustrated Lewis pairs activating N, we have attempted halide abstraction from -(diarylboryl)diazenido-halo-tungsten complexes. Reactions with Tl led to adducts in which coordination of the cation differs depending on the boryldiazenide substituents and the ancillary ligand. Chloride scavenging was not observed.

Borane-catalysed dinitrogen borylation by 1,3-B-H bond addition.

The borylation of ligated dinitrogen by 1,3-B-H bond addition over a W-N[triple bond, length as m-dash]N unit using various hydroboranes has been examined. In a previous study, we have shown that Piers' borane (1) reacted with the tungsten dinitrogen complex 2 to afford a boryldiazenido-hydrido-tungsten species. The ease and mildness of this reaction have encouraged us to extend its scope, with the working hypothesis that 1 could potentially catalyse the 1,3-B-H bond addition of other hydroboranes.

Synthesis, Characterization, and Comparative Theoretical Investigation of Dinitrogen-Bridged Group 6-Gold Heterobimetallic Complexes.

We have prepared and characterized a series of unprecedented group 6-group 11, N-bridged, heterobimetallic [ML(η-N)(μ-η:η-N)Au(NHC)] complexes (M = Mo, W, L = diphosphine) by treatment of -[ML(N)] with a cationic gold(I) complex [Au(NHC)]. The adducts are very labile in solution and in the solid, especially in the case of molybdenum, and decomposition pathways are likely initiated by electron transfers from the zerovalent group 6 atom to gold. Spectroscopic and structural parameters point to the fact that the gold adducts are very similar to Lewis pairs formed out of strong main-group Lewis acids (LA) and low-valent, end-on dinitrogen complexes, with a bent M-N-N-Au motif.

Frustrated Lewis Pair Chemistry Enables N Borylation by Formal 1,3-Addition of a B-H Bond in the Coordination Sphere of Tungsten.

The first example of a formal 1,3-B-H bond addition across the M-N≡N unit of an end-on dinitrogen complex has been achieved. The use of Piers' borane HB(C F ) was essential to observe this reactivity and it plays a triple role in this transformation: 1) electrophilic N -borylation agent, 2) Lewis acid in a frustrated Lewis pair-type B-H bond activation, and 3) hydride shuttle to the metal center. This chemistry is supported by NMR spectroscopy and solid-state characterization of products and intermediates.

Enhanced Activation of Coordinated Dinitrogen with p-Block Lewis Acids.

This Concept article highlights recent research on Lewis acid adducts of dinitrogen complexes, including our contributions. After a reminder of the early works, it is demonstrated that such kind of species offers a new platform for dinitrogen functionalization as well as valuable models for the understanding of elementary steps of (bio)catalytic cycles. When possible, parallels regarding this mode of activation from the orbital point of view are drawn between the different systems discussed herein.

Group 6 Transition-Metal/Boron Frustrated Lewis Pair Templates Activate N and Allow its Facile Borylation and Silylation.

The reaction of trans-[M(N ) (dppe) ] (M=Mo, 1 , M=W, 1 ) with B(C F ) (2) provides the adducts [(dppe) M=N=N-B(C F ) ] (3) which can be regarded as M/B transition-metal frustrated Lewis pair (TMFLP) templates activating dinitrogen. Easy borylation and silylation of the activated dinitrogen ligands in complexes 3 with a hydroborane and hydrosilane occur by splitting of the B-H and Si-H bonds between the N moiety and the perfluoroaryl borane. This reactivity of 3 is reminiscent of conventional frustrated Lewis pair chemistry and constitutes an unprecedented approach for the functionalization of dinitrogen.

Review on Bioorganometallic Chemistry and New Outcomes in the Synthesis and Substitution of Tetracarbonyl(pyrrolylimine) Complexes of Rhenium with Organophosphorus Ligands.

: After a short review dealing with bioorganometallic chemistry, the synthesis of tetracarbonyl (pyrrolylimine) complexes of rhenium bearing chirality on the pyrrolyl ligands was reported.The reactivity of these compounds towards the substitution of one carbonyl ligand with triphenyl phosphine, tricyclohexyl phosphine and trimethyl phosphite was studied. The rhenium becoming a stereogenic center in that transformation, the resulting tricarbonyl species were obtained as mixtures of diastereomers, with diastereomeric excesses varying from 8 to 84%, according to the reaction conditions and the relative steric hindrances of the pyrrolylimine and the organophosphorus ligands.

Formal SiH4 chemistry using stable and easy-to-handle surrogates.

Monosilane (SiH4) is far less well behaved than its carbon analogue methane (CH4). It is a colourless gas that is industrially relevant as a source of elemental silicon, but its pyrophoric and explosive nature makes its handling and use challenging. Consequently, synthetic applications of SiH4 in academic laboratories are extremely rare and methodologies based on SiH4 are underdeveloped.

Atroposelective [2+2+2] cycloadditions catalyzed by a rhodium(I)-chiral phosphate system.

Enantioselective cationic Rh(I)-catalyzed [2+2+2] cycloaddition reactions between diynes and isocyanates relying on the chiral anion strategy have been devised. In the presence of [Rh(cod)Cl]2, 1,4-bis(diphenylphosphino)butane, and the silver phosphate salt Ag(S)-TRIP as the unique source of chirality, axially chiral pyridones were isolated with ees up to 82%. This approach is novel in the field of chiral anion-mediated asymmetric catalysis since atroposelective transformations have so far remained unprecedented.

Combination of gold catalysis and Selectfluor for the synthesis of fluorinated nitrogen heterocycles.

We herein report the synthesis of 3-fluoro-2-methylene-pyrrolidine (3a) and -piperidine (3b) from 1,5- and 1,6-aminoalkynes, respectively, using a combination of a gold-catalyzed hydroamination reaction followed by electrophilic trapping of an intermediate cyclic enamine by Selectfluor. Careful attention was paid to the elucidation of the mechanism and Selectfluor was suggested to play the double role of promoting the oxidation of gold(I) to a gold(III) active species and also the electrophilic fluorination of the enamine intermediates.