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A cationic nickel complex of the bis(8-quinolyl)(3,5-di-tert-butylphenoxy)phosphine (NPN) ligand, [(NPN)NiCl]+, is a precursor to efficient catalysts for the hydrosilation of alkenes with a variety of hydrosilanes under mild conditions and low catalyst loadings. DFT studies reveal the presence of two coupled catalytic cycles based on [(NPN)NiH]+ and [(NPN)NiSiR3]+ active species, with the latter being more efficient for producing the product. The preferred silyl-based catalysis is not due to a more facile insertion of alkene into the Ni-Si (vs. Ni-H) bond, but by consistent and efficient conversions of the hydride to the silyl complex.

In this manuscript a general photocatalytic approach for the synthesis of alkyl‐substituted gem‐difluoroalkenes using readily available oxime esters and 1‐bromo‐1,1‐difluoroprop‐2‐ene (BDFP) has been established. This strategy involving a radical bromo elimination provides access to a large variety of value‐added fluorinated molecules. The mild reaction conditions are compatible with many functional groups including complex natural products or drug molecules. Experimental and theoretical mechanistic investigations indicate that the efficiency of the process relies on the crucial role of imine radical, which is formed after photoexcitation via energy transfert (EnT) and decarboxylation of the oxime ester. Indeed, the imine radical would either behave as a bromine radical scavenger or an XAT promoter in this reaction. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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(C6F5)3. The stable adducts were assessed for frustrated Lewis pair‐type heterolytic E−H bond splitting of hydrosilanes (E=Si) and HB(C6F5)2. Whereas Si−H bond activation was achieved, HB(C6F5)2 was shown to substitute B(C6F5)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. [ABSTRACT FROM AUTHOR]

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 R2B radicals. [ABSTRACT FROM AUTHOR]

The scope of the four-step mechanism for [d.sup.0] complexes and the factors that favor the olefin metathesis reaction are evaluated by studying the influence of the metal (Mo, W and Re), the imido vs. the alkylidyne and the X and Y spectator ligands. The results have shown that the Re complexes are less efficient than the Mo and W catalysts, except when Re is unsymmetrically substituted.

Density functional calculations with the B3PW91 functional have been carried out on the TpRh(CNMe) species [Tp = HB[(pyrazolyl).sub.3]] as a model for Tp'Rh(CNC[H.sub.2]C[Me.sub.3]) [Tp' = HB[(3,5-dimethylpyrazolyl) .sub.3]] in interaction with propane. Two [sigma] complexes have been found as minima coordinated through either a methyl or a methylene C-H bond, the former being more stable. The approach of the alkane to TpRh(CNMe) has been studied. Although no transition state could be located, study of this path reveals the key importance of the partial decoordination of one pyrazole ring. The full coordination of the alkane can only be achieved when the metal is essentially in a square pyramid coordination with one of the three pyrazole groups only weakly interacting with Rh. The main reaction of the methyl [sigma] complex is oxidative addition, leading to the n-propyl hydride complex. In contrast, two reactions are found for the methylene Cr complex: (i) oxidative addition to give the isopropyl complex and (ii) exchange between the secondary and primary C-H bonds to convert the methylene complex of propane into a methyl complex of propane. This latter reaction has a much lower barrier than the oxidative addition at the methylene C-H bond. The results account well for most of the experimental results obtained from kinetic studies. Steric factors are found to control the energy barriers between these various processes, disfavoring any process that brings the central carbon into close proximity to Rh. density functional theory | hydrocarbon activation | rhodium | selectivity

Protonation of the ortho-metalated ruthenium complexes RuH([H.sub.2])(X)[([P.sup.i][Pr.sub.3]).sub.2] [X = 2-phenylpyridine (ph-py) (1), benzoquinoline (bq)(2)] and RuH(CO)(ph-py)[([P.sup.i][Pr.sub.3]).sub.2] (3) with [[H(O[Et.sub.2]).sub.2]].sup.+][[B[Ar'.sub.4]].sup.-](B[Ar'.sub.4] = [(3,5-[[(C[F.sub.3]).sub.2][C.sub.6][H.sub.3]).sub.4]B]) under [H.sub.2] atmosphere yields the corresponding cationic hydrido dihydrogen ruthenium complexes [RuH([H.sub.2])(H-X)[([P.sup.i][Pr.sub.3]).sub.2]][BAr'4] [X = phenylpyridine (ph-py)(1-H); benzoquinoline (bq)(2-H)] and the carbonyl complex [RuH(CO)(H-phpy)([P.sup.i][Pr.sub.3]) .sub.2][B[Ar'.sub.4]] (3-H). The complexes accommodate an agostic C-H interaction characterized by NMR and in the case of 1-H by x-ray diffraction. Fluxional processes involve the hydride and dihydrogen ligands in 1-H and 2-H and the rotation of the phenyl ring displaying the agostic interaction in 1-H and 3-H. NMR studies (lineshape analysis of the temperature-dependent NMR spectra) and density functional theory calculations are used to understand these processes. Under vacuum, one equivalent of dihydrogen can be removed from 1-H and 2-H leading to the formation of the corresponding cationic orthometalated complexes [[Ru([H.sub.2])(THF)(X)([P.sup.i][Pr.sub.3]).sub.2]].sup.+] [X = ph-py (1-THF), bq (2-THF)]. The reaction is fully reversible. Density functional theory calculations and NMR data give information about the reversible mechanism of C-H activation in these ortho-metalated ruthenium complexes. Our study highlights the subtle interplay between key ligands such as hydrides, [sigma]-dihydrogen, and agostic bonds, in C-H activation processes. C-H activation | density functional theory | hydrogen transfer | NMR | sigma bonds

A combined experimental and density functional theory (DFT) study of the reactions of the titanium imido methyl cation [[Ti([N.sup.1])Bu)([Me.sub.3][9]ane[N.sub.3])Me].sup.}[4.sup.} with Al[Me.sub.3] and Zn[Me.sub.2] is presented. These studies have helped in understanding the molecular and electronic structures and energetic aspects of Al[Me.sub.3] and Zn[Me.sub.2] adducts of group 4 monomethyl cations.

Density functional theory is used to calculate H-C and M-C bond dissociation enthalpies for evaluating the feasibility of correlating relative M-C bond enthalpies. The calculations provide an independent demonstration that M-C bond enthalpies are most sensitive to substituent than C-H bond enthalpies.

The trans-bis[2-(2-chloroethyl)pyridine]palladium chloride was prepared and structurally characterized by X-ray spectroscopy and computational study. The reaction of the palladium complex with quinuclidine in CH(sub 3)CN, at 25 degree Celsius, leads to competing elimination and displacement reactions with formation of vinylpyridine and chloroethylpyridine in the ratio of 1.5:1.

The strong counterion effects in the reaction of 2-pyridylmethyl imidazolium salts with IrH5(PPh3)(sub 2) to give chelating NHC(super 13-18) complexes, where NHCs are bound to either at C2 or at C5 depending on the anion, are described. The results indicate that the relative energetics of the normal versus the abnormal forms is strongly affected by choice of anion and hence big anion effects are observed.

The EXAFS measurements have been interpreted as the cation (dppe)Pd[H2-CC(H)CMe(sub 2)](super +) has different structures in the solid phase and in THF solution. This structural alteration was suggested to play a role in governing the regioselectivity of the nucleophilic addition to the allyl carbons.

A novel catalytic reaction which combines, in one step, two molecules of alkynes and one of carboxylic acid to give only one diene isomer, thus with high stereoselectivity and atom economy is demonstrated. The unique catalytic formation of (1E,3E)-1,4-disubstituted-1,3-dienes is highly regioselectivity in the head-to-head coupling of alkynes and stereoselective in the concomitant formation of the three C--C, C--H, and C--O bonds.

Research has been conducted on the ligand electronic parameters which predict the donor powers of the cationic, neutral and negatively charged ligands. The use of the quantum chemical methods in calculating these parameters is described and the results indicate that the calculated parameters correlate with the Tolman and Lever parameters and with Hammett constants.

A two-dimensional dynamical parametrized model was developed to investigate the M-(H2) interaction in transition-metal molecular hydrogen complexes. The parameters were adjusted to reproduce the observed inelastic neutron scattering transitions through a least-squares fits process. The vibrational levels were obtained by solving the nuclear Schrodinger equation in a discrete variable representation. From this process, structural information such as the barrier to rotation of the H2 ligand and the H-H distance were obtained.

Research was conducted to examine the thermodynamic and kinetic aspects of the reactions of a partially fluorinated benzene (1,4-difluorobenzene) to give 16-electron OsII and 18-electron RhIII complexes, respectively. The objective was to determine why only the C-H activation product is observed. Calculations reveal that the C-F oxidative addition is thermodynamically preferred. Results demonstrate that the inertness of the C-F bond has a kinetic origin.

A study of a variety of adducts of the type where L'=H2 and the consequences of varying L' on exchange coupling among three hydrides found that the rotation angle produces the largest tunneling effect but the internuclear distance between the exchanging hydrogens cannot be neglected. Results indicate that quantum exchange coupling is larger in Cl than in the case of I. Additional ligand L raises the value of the coupling by decreasing the activation energy for quantum exchange between pairs.

An economical source of hydrogen forms a metal hydride under wild conditions when the hydrogen is split heterolytically. The splitting is categorized by the presence of molecular H2 to be Bronsted-acidic. Coordinated H2 is known to quickly dissociate, disallowing the intracellular molecular rearrangement in d octahedra. Hydrogen binds with five-coordinate substructures, varying in equilibrium constants. The varying lengths of the bonding H2 are caused by a reduction in the strength of the sigma bond. The reducing power of the bonding fragments also vary.

The synthesis and characterization of Cu2Cl2(C5H8), Cu4Br2Cl2(C7H8)4 and Cu4Br4(C7H8)4 are presented. Cu2Cl2(C5H8) is prepared from the reaction of copper(I) chloride and ethyl vinyl chloride with 1,4-pentadiene. Cu4Br2Cl2(C7H8)4 is generated from the reaction of copper(I) chloride with copper(I) bromide, while Cu4Br4(C7H8)4 is prepared from copper(I) bromide in norbornadiene. The first complex has cubane cores bridged by 1,4-pentadiene ligands to form an infinite ribbon. The second and third complexes are isostructural with Cu4Cl4(C7H8)8.

Transition metal polyhydride complexes have clearly played a significant part in the application of theoretical techniques to transition metal chemistry. H-containing transition metal systems have shown an extremely wide range of chemical properties.