N2 Functionalization via Molybdenum-Nitride Complex: Stepwise BH Bond Additions.

Reactivity of (triphosphine)MoIV-nitrido complex generated by N2 splitting, toward boranes is reported. The simple adduct Mo≡N→BH3 is observed with BH3.SMe2 while 1,2 addition is evidenced with 9-BBN leading to H-Mo=NBR2. A second addition of BH3.SMe2 is facile and forms an unprecedented complex featuring two bridging H between two B and the Mo centers. Addition of PMe3 or BH3.SMe2 promotes reductive elimination and N-H bond formation. The full sequence of functionalization at Mo≡N obtained after N2 splitting is therefore evidenced in this work.

Taming the Lewis Superacid Al(ORF)3 (RF=C(CF3 )3 ): DFT Guided Identification of the "Stable yet Reactive" Adduct SiPr2 →Al(ORF)3 ; Its Use as ORF- Abstractor from a "Ni-ORF" complex.

A DFT study of several L→Al(ORF )3 (L=Lewis bases) adducts allowed the identification of (i Pr2 S)→Al(ORF )3 1-Si Pr2 as a "stable yet reactive" adduct. 1-Si Pr2 was shown to act as a masked Lewis superacid able to release Al(ORF )3 under mild conditions. It could be used to abstract a ORF- ligand from (bipyMe2 )Ni(ORF )2 (bipyMe2 : 6,6'-dimethyl-2,2'-dipyridyl) and generate the nickel alkoxide complex [(bipyMe2 )Ni(ORF )(i Pr2 S)]+ [(RF O)3 Al-F-Al(ORF )3 ]- 5. Ligand exchange of i Pr2 S by Ph3 P yielded [(bipyMe2 )Ni(ORF )(PPh3 )]+ [(RF O)3 Al-F-Al(ORF )3 ]- 6.

Assessing Combinations of B(C6 F5 )3 and N2 -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(C6 F5 )3 . The stable adducts were assessed for frustrated Lewis pair-type heterolytic E-H bond splitting of hydrosilanes (E=Si) and HB(C6 F5 )2 . Whereas Si-H bond activation was achieved, HB(C6 F5 )2 was shown to substitute B(C6 F5 )3 in a quantitative or equilibrated fashion, depending on the nature of the nitrido complex. No B-H bond splitting was observed. Thermodynamics of these reactions, computed by DFT, are in agreement with the experimental outcomes.

One Ligand to Bind them All: S~C~S2- Carbon- and Sulfur-Based Gem-Dianion as Structuring Ligand for Iron Polymetallic Assemblies.

Numerous synthetic models of the FeMo-co cluster of nitrogenases have been proposed to find the simplest structure with relevant reactivity. Indeed, such structures are able to perform multi-electrons reduction processes, such as the conversion of N2 to ammonia, and of CO2 into methane and alkenes. The most challenging parameter to imitate is indeed the central carbide ligand, which is believed to maintain the integrity of iron sulfide assembly during the course of catalytic cycles. The study proposes the use of bis(diphenylthiophosphinoyl)methanediide (SCS)2- as an ideal platform for the synthesis of bi- and tetra-metallic iron complexes, in which the iron-carbon interaction is maintained upon structural diversification and redox state changes.

Ammonia Synthesis at Room Temperature and Atmospheric Pressure from N2 : A Boron-Radical Approach.

Ammonia, NH3 , is an essential molecule, being part of fertilizers. It is currently synthesized via the Haber-Bosch process, from the very stable dinitrogen molecule, N2 and dihydrogen, H2 . This process requires high temperatures and pressures, thereby generating ca 1.6 % of the global CO2 emissions. Alternative strategies are needed to realize the functionalization of N2 to NH3 under mild conditions. Here, we show that boron-centered radicals provide a means of activating N2 at room temperature and atmospheric pressure whilst allowing a radical process to occur, leading to the production of borylamines. Subsequent hydrolysis released NH4 + , the acidic form of NH3 . EPR spectroscopy supported the intermediacy of radicals in the process, corroborated by DFT calculations, which rationalized the mechanism of the N2 functionalization by R2 B radicals.

Molecular Electrochemical Reductive Splitting of Dinitrogen with a Molybdenum Complex.

Nitrogen reduction under mild conditions (room T and atmospheric P), using a non-fossil source of hydrogen remains a challenge. Molecular metal complexes, notably Mo based, have recently been shown to be active for such nitrogen fixation. We report electrochemical N2 splitting with a MoIII triphosphino complex [(PPP)MoI3 ], at room temperature and a moderately negative potential. A MoIV nitride species was generated, which is confirmed by electrochemistry and NMR studies. The reaction goes through two successive one electron reductions of the starting Mo species, coordination of a N2 molecule, and further splitting to a MoIV nitride complex. Preliminary DFT studies support the formation of a bridging MoI N2 MoI dinitrogen dimer evolving to the Mo nitride via a low energy transition state. This example joins a short list of molecular complexes for N2 electrochemical reductive cleavage. It opens a door to electrochemical proton-coupled electron transfer (PCET) conversion studies of N2 to NH3 .

Cross-Coupling through Ag(I)/Ag(III) Redox Manifold.

In ample variety of transformations, the presence of silver as an additive or co-catalyst is believed to be innocuous for the efficiency of the operating metal catalyst. Even though Ag additives are required often as coupling partners, oxidants or halide scavengers, its role as a catalytically competent species is widely neglected in cross-coupling reactions. Most likely, this is due to the erroneously assumed incapacity of Ag to undergo 2e- redox steps. Definite proof is herein provided for the required elementary steps to accomplish the oxidative trifluoromethylation of arenes through AgI /AgIII redox catalysis (i. e. CEL coupling), namely: i) easy AgI /AgIII 2e- oxidation mediated by air; ii) bpy/phen ligation to AgIII ; iii) boron-to-AgIII aryl transfer; and iv) ulterior reductive elimination of benzotrifluorides from an [aryl-AgIII -CF3 ] fragment. More precisely, an ultimate entry and full characterization of organosilver(III) compounds [K]+ [AgIII (CF3 )4 ]- (K-1), [(bpy)AgIII (CF3 )3 ] (2) and [(phen)AgIII (CF3 )3 ] (3), is described. The utility of 3 in cross-coupling has been showcased unambiguously, and a large variety of arylboron compounds was trifluoromethylated via [AgIII (aryl)(CF3 )3 ]- intermediates. This work breaks with old stereotypes and misconceptions regarding the inability of Ag to undergo cross-coupling by itself.

Synthesis of Monodisperse InP Quantum Dots: Use of an Acid-Free Indium Carboxylate Precursor.

The role of indium carboxylate precursors in the synthesis of monodisperse InP quantum dots was investigated. The reaction between acid-free indium palmitate and tris(trimethylsilyl)phosphine (P(TMS)3) was monitored by using high-temperature 31P NMR, indicating the presence of a single molecular phosphorus species throughout the duration of the reaction. The addition of varying amounts of carboxylic acid and its effects on both the reaction kinetics and the optical properties of InP QDs were studied. In the presence of acid, rapid protonation of P(TMS)3 led to the formation of a mixture of four HxP(TMS)3-x species, resulting in the poorer controlled formation of InP nanocrystals. Upon deposition of a gradated ZnSeS shell on the synthesized InP core, luminescent quantum dots were obtained (QY 67%; PL: FWHM 40 nm).

Aluminum-Hydride-Catalyzed Hydroboration of Carbon Dioxide.

This study describes the first use of a bis(phosphoranyl)methanido aluminum hydride, [ClC(PPh2NMes)2AlH2] (2, Mes = Me3C6H2), for the catalytic hydroboration of CO2. Complex 2 was synthesized by the reaction of a lithium carbenoid [Li(Cl)C(PPh2NMes)2] with 2 equiv of AlH3·NEtMe2 in toluene at -78 °C. 2 (10 mol %) was able to catalyze the reduction of CO2 with HBpin in C6D6 at 110 °C for 2 days to afford a mixture of methoxyborane [MeOBpin] (3a; yield: 78%, TOF: 0.16 h-1) and bis(boryl)oxide [pinBOBpin] (3b). When more potent [BH3·SMe2] was used instead of HBpin, the catalytic reaction was extremely pure, resulting in the formation of trimethyl borate [B(OMe)3] (3e) [catalytic loading: 1 mol % (10 mol %); reaction time: 60 min (5 min); yield: 97.6% (>99%); TOF: 292.8 h-1 (356.4 h-1)] and B2O3 (3f). Mechanistic studies show that the Al-H bond in complex 2 activated CO2 to form [ClC(PPh2NMes)2Al(H){OC(O)H}] (4), which was subsequently reacted with BH3·SMe2 to form 3e and 3f, along with the regeneration of complex 2. Complex 2 also shows good catalytic activity toward the hydroboration of carbonyl, nitrile, and alkyne derivatives.

Geminal Dianions Stabilized by Main Group Elements.

This review is dedicated to the chemistry of stable and isolable species that bear two lone pairs at the same C center, i.e., geminal dianions, stabilized by main group elements. Three cases can thus be considered: the geminal-dilithio derivative, for which the two substituents at C are neutral, the yldiide derivatives, for which one substituent is neutral while the other is charged, and finally the geminal bisylides, for which the two substituents are positively charged. In this review, the syntheses and electronic structures of the geminal dianions are presented, followed by the studies dedicated to their reactivity toward organic substrates and finally to their coordination chemistry and applications.

Conversion of Dinitrogen into Nitrile: Cross-Metathesis of N2 -Derived Molybdenum Nitride with Alkynes.

The direct synthesis of nitrile from N2 under mild conditions is of great importance and has attracted much interest. Herein, we report a direct conversion of N2 into nitrile via a nitrile-alkyne cross-metathesis (NACM) process involving a N2 -derived Mo nitride. Treatment of the Mo nitride with alkyne in the presence of KOTf afforded an alkyne-coordinated nitride, which was then transformed into MoV carbyne and the corresponding nitrile upon 1 e- oxidation. Both aryl- and alkyl-substituted alkynes underwent this process smoothly. Experiments and DFT calculations have proved that the oxidation state of the Mo center plays a crucial role. This method does not rely on the nucleophilicity of the N2 -derived metal nitride, offering a novel strategy for N2 fixation chemistry.

Catalytic Reduction of N2 to Borylamine at a Molybdenum Complex.

Catalytic formation of borylamines from atmospheric N2 is achieved for the first time using a series of homogenous (triphosphine)Mo complexes. Stepwise functionalization of the (triphosphine)Mo-nitrido complex with chloroborane led to the synthesis of the imido complex. Electrochemical characterization of the (PPP)Mo-nitrido and (PPP)Mo-borylimido complexes showed that the latter is much more easily reduced.

Pyridyl-Functionalized 1-Phosphabarrelene: Synthesis, Coordination Chemistry and Photochemical di-π-Methane Rearrangement.

The [4+2] cycloaddition of 2-(2'-pyridyl)-4,6-diphenyl-λ3 -phosphinine with the highly reactive dienophile hexafluoro-2-butyne has been studied and the first pyridyl-functionalized 1-phosphabarrelene was obtained and structurally characterized. Although monodentate CF3 -1-phosphabarrelenes show only a poor coordination ability, the chelating nature of the novel P,N-hybrid ligand gives access to various transition-metal complexes. Upon irradiation with UV light, the pyridyl-functionalized 1-phosphabarrelene undergoes a rather selective di-π-methane rearrangement in the coordination sphere of the metal center, leading to the formation of a complex based on a hitherto unknown pyridyl-functionalized 5-phosphasemibullvalene derivative. DFT calculations provide first insights into the mechanism of this reaction.

Phosphinine-Based Ligands in Gold-Catalyzed Reactions.

A series of substituted phosphinines, 1-phosphabarrelenes and 5-phosphasemibullvalenes were synthesized and evaluated for their potential application as ligands in homogeneous catalytic reactions. While their buried volume (%Vbur ) was calculated to get insight into the steric properties, [LNi(CO)3 ] complexes were prepared in order to determine the corresponding Tolman electronic parameter. ETS-NOCV (extended-transition-state natural orbital for chemical valence) calculations on [LAuCl] complexes further allowed an estimation of the σ- and π-contributions to the L-M interaction. AuI coordination compounds of selected examples were prepared and characterized by single crystal X-ray diffraction. Finally, the three classes of PIII compounds were successfully used in the AuI -catalyzed cycloisomerization of N-2-propyn-1-ylbenzamide, showing very good activities and selectivities, which are comparable with the reported data of cationic phosphorus-based gold catalysts.

Synthesis and Reactivity of an End-Deck cyclo-P4 Iron Complex.

Reduction of the FeII complex [(Ph PP2Cy )FeCl2 ] (2) generated an electron-rich and unsaturated Fe0 species, which was reacted with white phosphorus. The resulting new complex, [(Ph PP2Cy )Fe(η4 -P4 )] (3), is the first iron cyclo-P4 complex and the only known stable end-deck cyclo-P4 complex outside Group V. Complex 3 features an FeII center, as shown by Mössbauer spectroscopy, associated to a P42- fragment. The distinct reactivity of complex 3 was rationalized by analysis of the molecular orbitals. Reaction of complex 3 with H+ afforded the unstable complex [(Ph PP2Cy )Fe(η4 -P4 )(H)]+ (4), whereas with CuCl and BCF, the complexes [(Ph PP2Cy )Fe(η4 :η1 -P4 )(µ-CuCl)]2 (5) and [(Ph PP2Cy )Fe(η4 :η1 -P4 )B(C6 F5 )3 ] (6) were formed.

Room-Temperature Functionalization of N2 to Borylamine at a Molybdenum Complex.

Intermolecular, stepwise functionalization by BH bonds of a (triphosphine)MoIV -nitrido complex generated by N2 splitting is reported. The imido-hydride and di-hydride-amido MoIV complexes have been isolated and characterized. Addition of PinBH to the [Mo(H)2 (N(BPin)2 )]+ complex at room temperature results in the liberation of borylamines from the metal center.

Mechanistic Investigations of the Synthesis of Size-Tunable Ni Nanoparticles by Reduction of Simple NiII Diamide Precursors.

Herein, we present a detailed study of the conversion of a nickel(II) diamide precursor to size-tunable, monodisperse nickel nanoparticles (NPs). The thermal decomposition of nickel(II) dioleylamide, synthesized either independently or in situ, resulted in the formation of Ni NPs without the coproduction of water. Mechanistic studies were conducted on the stability and reduction pathway of the NiII precursor, and on the consequent particle formation. Variations in the ratio of trioctylphosine (TOP) to nickel allowed size tunability, which resulted in nanoparticles that ranged in size from 4 to 11 nm in diameter. The DFT calculations support a mechanistic pathway that involves nickel reduction by imine formation. This water-free method was extended to the synthesis of water-sensitive M0 NPs (M=Fe, Co).

C-H Bond Trifluoromethylation of Arenes Enabled by a Robust, High-Valent Nickel(IV) Complex.

The robust, high-valent NiIV complex [(Py)2 NiIV F2 (CF3 )2 ] (Py=pyridine) was synthesized and fully characterized by NMR spectroscopy, X-ray diffraction, and elemental analysis. It reacts with aromatic compounds at 25 °C to form the corresponding benzotrifluorides in nearly quantitative yield. The monomeric and dimeric NiIII CF3 complexes 2⋅Py and 2 were identified as key intermediates, and their structures were unambiguously determined by EPR spectroscopy and X-ray diffraction. Preliminary kinetic studies in combination with the isolation of reaction intermediates confirmed that the C-H bond-breaking/C-CF3 bond-forming sequence can occur both at NiIV CF3 and NiIII CF3 centers.

A Nucleophilic Gold(III) Carbene Complex.

The first AuIII carbene complex was prepared by reacting a geminal dianion with a (P,C) cyclometalated AuIII precursor. Its structure and bonding situation have been thoroughly investigated by experimental and computational means. The presence of a high-energy highest occupied molecular orbital (HOMO) centered at the carbene center suggests nucleophilic character for the AuIII carbene complex. This unprecedented feature was confirmed by reactions with two electrophiles (PhNCS and CS2 ), resulting in two types of C=C coupling reactions.

Direct Synthesis of Silylamine from N2 and a Silane: Mediated by a Tridentate Phosphine Molybdenum Fragment.

A homogeneous system which is able to yield silylamine from N2 and bis(silane) in one pot is reported. Mechanistically a {(triphosphine)molybdenum(I)} fragment, generated in situ, splits N2 into the corresponding nitrido complex at room temperature. Then, functionalization of the molybdenum nitrido is achieved by double Si-H addition under mild reaction conditions. Moreover, the bis(silyl)amine product is decoordinated from the metal center.