The cationic nine-coordinate pentahydrido complex [MoH5(depe)2]BPh4 (1·BPh4, depe  =  1,2-(diethylphosphino)ethane) is, to the best of our knowledge, the first early transition metal polyhydride shown to efficiently catalyze the hydrogenation of a diverse set of unactivated alkenes. Preliminary mechanistic investigation by Density Functional Theory (DFT) calculations indicates that turnover relies on the ability of this 18-electron, d° complex to undergo thermally facile H2 reductive elimination, which opens coordination sites and supplies the metal center the necessary electrons to engage in the reduction of the substrate. According to the computations, ethylene hydrogenation catalysis by 1·BPh4 follows a sequence of migratory insertion prior to H2 oxidative addition. These findings demonstrate that high-coordinate early transition metal polyhydrides are not mere structural curiosities but can act as genuine hydrogenation catalysts. The unique reactivity of 1·BPh4 provides a foundation for new design concepts in base-metal homogeneous catalysis, beyond the current focus on late 3d metals.

The transition metal-mediated activation of element-hydrogen bonds is an important goal for the preparation of commodity chemical compounds and novel materials. Here a facile route to the activation of germanium-hydrogen bonds, based on the spontaneous elimination of dihydrogen, is reported. This represents a mechanistic divergence from the established methods for Ge─H bond cleavage. The novel complexes [Ru(η5-C5H5)(OTf)(PPh3)2] and [{Ru(η5-C5H5)(dppe)}2(μ-N2)]OTf2 are central to the success of this route. These crystalline species may be prepared in high yield and are highly effective sources of the 16-electron [Ru(η5-C5H5)(P)2]+ fragment. Both complexes react with GeH2Ph2 to eliminate H2 and afford [Ru(η5-C5H5)(GePh2OTf)(P)2] [(P)2 = 2 PPh3, dppe], which is best described as a triflate-stabilized metallogermylenium complex. Different species are observed on initial treatment of [Ru(η5-C5H5)(OTf)(PPh3)2] or [{Ru(η5-C5H5)(dppe)}2(μ-N2)]OTf2 with GeH2Ph2. In the dppe case, a σ-germane complex is identified, which is proposed to undergo spontaneous elimination of H2: a key step in the double Ge─H bond activation, promoted by the sterically demanding half-sandwich ruthenium complexes. This represents a distinct pathway for Ge─H bond activation when compared to the established routes, such as deprotonation by a basic hydrocarbyl ligand or oxidative addition, leading the way to new pathways to functionalize organogermanium compounds.

[2,1]-Azaboranaphthalenes represent unique boron–nitrogen (BN) isosteres of naphthalenes, attracting interest for the development of molecules with enhanced therapeutic potency. The existing synthetic strategies are generally two-component reactions with harsh conditions. Here we report an organocatalysed three-component modular synthesis of ring-fused BN isosteres and BN-2,1-azaboranaphthalenes following ring expansion of unstrained cyclic ketones (n = 4–8) via Wolff-type rearrangement. The strategy used 2-formylarylboronic acid as a C–B surrogate and TMSN3 as an exogenous single nitrogen source, allowing the de novo rapid synthesis of BN isosteres by forging C–C, C–N and B–N bonds under a single operation. The developed method proved to be compatible with a broad substrate scope (58 examples), including cyclic ketones and diverse heterocycles, which afforded 1C ring-expanded [2,1]-azaborines.The reaction was also effective with acyclic ketones, yielding BN naphthalene isosteres. Control experiments and density functional theory study dictate the plausible reaction pathways following [1,2]-C–C/C–H shift, analogous to Wolff rearrangement. [2,1]-Azaboranaphthalenes represent unique boron–nitrogen (BN) isosteres of naphthalenes. Now a modular approach to the three-component synthesis of BN-2,1-azaboranaphthalene has been developed using TMSN3 as an exogenous nitrogen source. The method proceeds under mild conditions and enables a regioselective incorporation of carbon and nitrogen atoms, showcasing broad potential for the synthesis of BN-based scaffolds.

Coordination of the redox non-innocent and proto-responsive 2,6-bis(pyrazol-3-yl)pyridine (bpp) ligand to Mo(0) precursors in the presence of silver acetate produces hepta-coordinated Mo(ii) complexes in moderate to good yields.

Herein, we report a rare example of organocatalyzed skeletal editing of unstrained rings (n = 4–8) to ring-expansion via Wolff-type rearrangement and through regioselective fixation of carbon and nitrogen atom. Strategy employed 2-formylarylboronic acid as C-B surrogate and TMSN3 as an exogenous single nitrogen source; allowed the de novo rapid synthesis of BN isosteres by forging C-C, C-N and B-N bonds under single operation. The developed method proved to be compatible with wide substrate scope (50 examples) including cyclic ketones and diverse heterocycles afforded 1C ring expanded [1,2]-azaborines. Reaction was also effective to acyclic ketones to give BN naphthalene isosteres. Control experiments and DFT study dictate the plausible reaction pathways following [1,2]-C-C/C-H shift, analogous to Wolff rearrangement.

A combined synthetic, mechanistic, and computational study is reported, which provides unique insight into the role of sigma-silane complexes in the catalytic hydrosilylation of nitriles. A novel, highly efficient, highly active, and regioselective catalytic monohydrosilylation of aromatic nitriles with secondary silanes using a ruthenium dihydrogen catalyst is reported along with a novel mechanism for hydrosilylation of nitriles. Investigations into the mechanism of this transformation have revealed the influence of sigma-Si-H complexes in fine-tuning the selectivity of this hydrosilylation reaction. Displacement of the dihydrogen ligand on the ruthenium precatalyst, ruthenium bis-(dihydrogen) complex [RuH2(eta(2)-H-2)(2)(PCy3)(2)], 1, by diphenylsilane leads to the formation of new ruthenium sigma-Si-H complexes, [RuH2(eta(2)-H-2)(eta(2)-HSiHPh2)(PCy3)(2)], 2, and [RuH2(eta(3)-H2SiPh2)(PCy3)(2)], 3. Complex 3 reacts readily with benzonitrile leading to hydrosilylation of the nitrile and coordination of the silylimine formed to the ruthenium as a sigma-H-Si-N-silylimine complex, [RuH2(eta(2)-HSiPh2NCHPh)(PCy3)(2)] (4). This systematic investigation of this reactivity led to the discovery of the first direct evidence of an N-silylimine-coordinated ruthenium complex and its involvement in a catalytic hydrosilylation reaction. This led to the discovery of a catalytic protocol for the efficient and selective coupling of secondary silanes with a range of nitriles using 1 as the catalyst. It is proposed that complexes 3 and 4 are key intermediates on the catalytic reaction coordinate, which leads to hydrosilylation of the nitrile. This is supported by DFT calculations along with the observation that 3 and 4 are catalytically active. The Si-N bond formation was found to proceed via direct attack of the nitrile at the silicon atom in 3. Through carefully chosen structural studies and tests of the new ruthenium complexes, along with DFT calculations, the mechanism of the catalytic hydrosilylation of nitriles has been successfully explained.

A Lewis superacidic bis(borane) C6F4{B(C6F5)2}2 was reacted with tungsten N2-complexes [W(N2)2(R2PCH2CH2PR2)2] (R = Ph or Et), affording zwitterionic boryldiazenido W(ii) complexes trans-[W(L)(R2PCH2CH2PR2)2(N2{B(C6F5)2(C6F4B(C6F5)3})] (L = ø, N2 or THF). These compounds feature only one N-B linkage of the covalent type, as a result of intramolecular boron-to-boron C6F5 transfer. Complex trans-[W(THF)(Et2PCH2CH2PEt2)2(N2{B(C6F5)2C6F4B(C6F5)3})] (5) was shown to split H2, leading to a seven-coordinate complex [W(H)2(Et2PCH2CH2PEt2)2(N2{B(C6F5)2}2C6F4)] (7). Interestingly, hydride storage at the metal triggers backward C6F5 transfer. This reverts the bis(boron) moiety to its bis(borane) state, now doubly binding the distal N, with structural parameters and DFT computations pointing to dative N→B bonding. By comparison with an N2 complex [W(H)2(Et2PCH2CH2PEt2)2(N2{B(C6F5)3}] (10) differing only in the Lewis acid (LA), namely B(C6F5)3, coordinated to the distal N, we demonstrate that two-fold LA coordination imparts strong N2 activation up to the diazene-diide (N22-) state. To the best of our knowledge, this is the first example of a neutral LA coordination that induces reduction of N2.

Low temperature quantum rotation of dihydrogen in RuH 2 (H 2 ) 2 [P(C 5 H 9 ) 3 )] 2 switched to a facile hydride exchange above 150 K.

Breslow intermediates are very often elusive species whose application in frustrated Lewis pair (FLP) chemistry is unprecedented. Described herein is the use of a masked form of an O-borylated Breslow (OBB) intermediate that performs FLP-type activation of the carbonyl function of five different benzaldehyde derivatives with complete diastereoselectivity. The resulting compounds are characterised in solution by NMR spectroscopy (compounds 4-8) and in solid state by X-ray diffraction analysis (compounds 4-6). A combined kinetic and theoretical investigation reveals the associative nature of the rate determining step and suggests that the OBB intermediate part is never released during the whole process.

A series of anionic ruthenium pentahydride complexes with the general formula [M(THF)(x)][RuH5(PCy3)(2)] (M = Li, Na, K) were synthesized. Their characterization by multinuclear NMR, IR, X-ray diffraction, and DFT techniques show that these complexes can adopt different structural features (monomer/dimer, cis/trans phosphines, hydride/dihydrogen ligands) depending on the countercation, the solvent, and/or the temperature. While the X-ray diffraction analyses offer snapshots of three out of five isomeric structures found by DFT, the solution and solid-state NMR analysis proved that these complexes exhibit a highly dynamic behavior. Rapid H-D exchange was found between Ru-H and D-2, which was attributed to the presence of Ru-H center dot center dot center dot center dot center dot M interactions in the absence of crown-ether.

A modular approach has been developed for an efficient synthesis of an aminal group containing a new tetracyclic framework. The strategy has been devised based on selective hydrogen-bond-guided aza-Michael addition of heteroaromatic amines to cyclohexadienone-aldehydes. The reaction is highly atom economic and practical and involves stereoselective construction of four new C-N bonds and four rings. The synthetic utility of the tetracyclic product was explored. The role of a H-bond was explained with the help of experimental and density functional theory (DFT) computation studies.

The understanding of macroalgae functions and processes requires a good understanding of the spatial distribution of the functional diversity of macroalgae. In coral reef environments, this information remains fragmentary. Here, based on 314 species sorted according to a set of 10 functional traits, the functional niches of macroalgae at three remote coral reefs of the Îles Éparses in the Indian Ocean (Europa, Glorioso, and Juan de Nova) are described. For the comparison of intra- and inter-reef functional structures, we characterized both taxonomic and functional beta diversities, and their turnover and nestedness-resultant components. Within the three reefs, we observed strong taxonomic and functional dissimilarities across sampling sites, mainly determined by turnover. Null models highlighted several processes, which structured macroalgal assemblages across sites: a combined effect of environmental variables (geomorphology and wave exposure), limiting similarity and stochastic effects. At the inter-reef scale, the three reefs only shared a small number of species, but the functional beta diversity between Glorioso and Juan de Nova was weak. This suggested that although assemblages were different, fairly similar environmental conditions may have homogenized macroalgae functions through both ecological and evolutionary scale processes. Our results support the idea that macroalgal assemblages can provide similar functional trait portfolios, despite distinct species composition. We stress the need to focus on macroalgae life-history traits for a better understanding of the processes structuring their communities.

This is a first report on the use of the bis(tricyclohexylphosphine)nickel (II) dichloride complex (abbreviated as NiPCy3) into MgH2 based hydrogen storage systems. Different composites were prepared by planetary ball-milling by doping MgH2 with (i) free tricyclohexylphosphine (PCy3) without or with nickel nanoparticles, (ii) different NiPCy3 contents (5 - 20 wt%) and (iii) nickel and iron nanoparticles with/without NiPCy3. The microstructural characterization of these composites before/after dehydrogenation was performed by TGA, XRD, NMR and SEM-EDX. Their hydrogen absorption/desorption kinetics were measured by TPD, DSC and PCT. All MgH2 composites showed much better dehydrogenation properties than the pure ball-milled MgH2. The hydrogen absorption/release kinetics of the Mg/MgH2 system were significantly enhanced by doping with only 5 wt% of NiPCy3 (0.42 wt% Ni); the mixture desorbed H-2 starting at 220 degrees C and absorbed 6.2 wt% of H-2 in 5 min at 200 degrees C under 30 bars of hydrogen. This remarkable storage performance was not preserved upon cycling due to the complex decomposition during the dehydrogenation process. The hydrogen storage properties of NiPCy3-MgH2 were improved and stabilized by the addition of Ni and Fe nanoparticles. The formed system released hydrogen at temperatures below 200 degrees C, absorbed 4 wt% of H-2 in less than 5 min at 100 degrees C, and presented good reversible hydriding/dehydriding cycles. A study of the different storage systems leads to the conclusion that the NiPCy3 complex acts by restricting the crystal size growth of Mg/MgH2, catalyzing the H-2 release, and homogeneously dispersing nickel over the Mg/MgH2 surface. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Photochemical reactions of germane and diphenylgermane with Ru(PP)(2)H-2 (PP = R2PCH2CH2PR2 or DuPhos, R = Ph dppe, R = Et depe, R = Me dmpe) are reported. Reaction with GeH4 generates a mixture of cis and trans isomers of Ru(PP)(2)(GeH3)H except for the DuPhos complex which yields the product only in the cis form. In situ laser photolysis (355 nm) demonstrates that the initial product is the cis isomer that undergoes thermal isomerization to the trans isomer. The complex cis-[Ru(dppe)(2)(GeH3)H] crystallizes selectively, allowing determination of its X-ray structure as a germyl hydride with a long Ru-H center dot center dot center dot Ge separation of 2.64(3) angstrom indicating that no residual interaction between the RuH and Ge is present. DFT calculations are also consistent with full oxidative addition. The structure of cis-[Ru(DuPhos)(2)(GeH3)H] reveals significant distortion from an octahedral geometry. The major species in the crystal (95%) exhibits a structure with a Ru-H center dot center dot center dot Ge distance of 2.42(5) angstrom suggesting negligible interaction between these centers. DFT calculations of the structure are consistent with the experimental determination. The reactions of Ru(PP)(2)H-2 with diphenylgermane yield cis-[Ru(PP)(2)(GePh2H)H] exclusively for PP = dmpe and depe, while the cis isomer is dominant in the case of dppe. A photochemical competition reaction between Ru(dppe)(2)(H)(2) and the two substrates Ph2SiH2 and Ph2GeH2 results in both Si- H and Ge-H oxidative addition activation with a kinetic preference (0.18:1) for the germyl hydride product. Thermal conversion of Ru(dppe)(2)(SiPh2H)H to Ru(dppe)(2)(GePh2H)H is observed on heating.

In order to improve the hydrogenation/dehydrogenation properties of the Mg/MgH2 system, the nickel hydride complex NiHCl(P(C6H11)(3))(2) has been added in different amounts to MgH2 by planetary ball milling. The hydrogen storage properties of the formed composites were studied by different thermal analyses methods (temperature programmed desorption, calorimetric and pressure-composition-temperature analyses). The optimal amount of the nickel complex precursor was found to be of 20 wt%. It allows to homogeneously disperse 1.8 wt% of nickel active species at the surface of the Mg/MgH2 particles. After the decomposition of the complex during MgH2 dehydrogenation, the formed composite is stable upon cycling at low temperature. It can release hydrogen at 200 degrees C and absorb 6.3 wt % of H-2 at 100 degrees C in less than 1 h. The significantly enhanced H-2 storage properties are due to the impact of the highly dispersed nickel on both the kinetics and thermodynamics of the Mg/MgH2 system. The hydrogenation and dehydrogenation enthalpies were found to be of -65 and 63 kJ/mol H-2 respectively (+/- 75 kJ/mol H-2 for pure Mg/MgH2) and the calculated apparent activation energies of the hydrogen uptake and release processes are of 22 and 127 kJ/mol H-2 respectively (88 and 176 kJ/mol H-2 for pure Mg/MgH2). The change in the thermodynamics observed in the formed composite is likely to be due to the formation of a Mg0.992Ni0.008 phase during dehydrogenation/hydrogenation cycling. The impact of another hydride nickel precursor in which chloride has been replaced by a borohydride ligand, namely NiH(BH4)(P(C6H11)(3))(2), is also reported. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Two known and two new ortho-phenyl phosphonium-sulfonate compounds have been synthesized and analyzed in solution and in the solid state. When the phosphonium moiety bears alkyl substituents, two rotamers are in equilibrium in solution. These two rotamers have been entirely characterized and are shown to differ by the spatial arrangement of the phosphonium proton relative to the sulfonate moiety. The phosphonium proton chemical shift and the 1JPH coupling constant are characteristic values for each rotamer. The kinetic and thermodynamic constants have been determined by means of NMR and DFT studies.

The reactivities of tris(benzyldimethylsilyl)-phosphine [P(o-C6H4-CH2SiMe2H)(3)] (1) and tris(benzyldiphenylsilyl)phosphine [P (o-C6H4-CH2SiPh2H)(3)] (6) toward the same platinum precursor [Pt(PPh3)(3)] are strikingly different. The reaction with 1 renders the trans disilyl platinum(II) complex [Pt{P(o-C6H4-CH2SiMe2)(2) (o-C6H4CHSiMe2)}PPh3] (2) in which the ligand coordinates in a tridentate fashion while a new Si-C bond is formed from the third Si moiety. The most prominent feature is an anagostic interaction that is established at the apical position. In contrast, the reaction of [Pt(PPh3)(3)] with 6 yields the hexacoordinated hydrido trisilyl platinum(IV) complex [PtH{P(o-C6H4- CH2SiPh2)(3)}PPh3] (7). We have studied the effect of the variation of the monodentate ligand in 2 by simple substitution reactions. We found a systematic variation of the chemical shift of the anagostic hydrogen in the H-1 nuclear magnetic resonance spectrum of the corresponding PMe3, P(OPh)(3), and CO complexes that can in principle be ascribed to a varying degree of the pi acceptor character of the ancillary ligand. However, theoretical calculations at the density functional theory level show only slight changes in the frontier orbitals in line with predominantly closed-shell electrostatic interactions.

Addition of ruthenium precursor complexes to the Mg/MgH2 system for improved desorption and absorption properties.