Natalia V. Belkova

Coordination and organometallic chemistry of relevance to the rhodium-based catalyst for ethylene hydroamination.

The RhCl(3)·3H(2)O/PPh(3)/nBu(4)PI catalytic system for the hydroamination of ethylene by aniline is shown to be thermally stable by a recycle experiment and by a kinetic profile study. The hypothesis of the reduction under catalytic conditions to a Rh(I) species is supported by the observation of a high catalytic activity for complex [RhI(PPh(3))(2)](2). New solution equilibrium studies on [RhX(PPh(3))(2)](2) (X = Cl, I) in the presence of ligands of relevance to the catalytic reaction (PPh(3), C(2)H(4), PhNH(2), X(-), and the model Et(2)NH amine) are reported. Complex [RhCl(PPh(3))(2)](2) shows broadening of the (31)P NMR signal upon addition of PhNH(2), indicating rapid equilibrium with a less thermodynamically stable adduct. The reaction with Et(2)NH gives extensive conversion into cis-RhCl(PPh(3))(2)(NHEt(2)), which is however in equilibrium with the starting material and free Et(2)NH. Excess NHEt(2) yields a H-bonded adduct cis-RhCl(PPh(3))(2)(Et(2)NH)···NHEt(2), in equilibrium with the precursors, as shown by IR spectroscopy. The iodide analogue [RhI(PPh(3))(2)](2) shows less pronounced reactions (no change with PhNH(2), less extensive addition of Et(2)NH with formation of cis-RhI(PPh(3))(2)(NHEt(2)), less extensive reaction of the latter with additional Et(2)NH to yield cis-RhI(PPh(3))(2)(Et(2)NH)···NHEt(2). The two [RhX(PPh(3))(2)](2) compounds do not show any evidence for addition of the corresponding X(-) to yield a putative [RhX(2)(PPh(3))(2)](-) adduct. The product of C(2)H(4) addition to [RhI(PPh(3))(2)](2), trans-RhI(PPh(3))(2)(C(2)H(4)), has been characterized in solution. Treatment of the RhCl(3)·3H(2)O/PPh(3)/nBu(4)PI/PhNH(2) mixture under catalytic conditions yields mostly [RhCl(PPh(3))(2)](2), and no significant halide exchange, demonstrating that the promoting effect of iodide must take place at the level of high energy catalytic intermediates. The equilibria have also been investigated at the computational level by DFT with treatment at the full QM level including solvation effects. The calculations confirm that the bridge splitting reaction is slightly less favorable for the iodido derivative. Overall, the study confirms the active role of rhodium(I) species in ethylene hydroamination catalyzed by RhCl(3)·3H(2)O/PPh(3)/nBu(4)PI and suggest that the catalyst resting state is [RhCl(PPh(3))(2)](2) or its C(2)H(4) adduct, RhCl(PPh(3))(2)(C(2)H(4)), under high ethylene pressure.

Iridium and rhodium complexes with the planar chiral thioether ligands in asymmetric hydrogenation of ketones and imines

Rhodium complexes with the planar chiral phosphinoferrocenyl thioether ligands [Rh(P,SR)(diene)X] (R = Me, But, Ph, Bn, diene is cyclooctadiene (COD) or norbornadiene (NBD), X = Cl, BF4) catalyze hydrogenation of ketones, imines, and heteroaromatic compounds; in the case of acetophenone, the enantioselectivity reached 60% ee. Similar iridium complexes demonstrate a good activity in the hydrogenation of imines, the maximal enantioselectivity in the case of N-phenyl-N-(1-phenylethylidene)amine was about 40% ee.

Dihydrogen bonding formed by (hydrido)[hydrotris(pyrazolyl)borato]ruthenium. The effect of ligands on the proton-accepting ability of ruthenium complexes

Reactions of [1,2-bis(diphenylphosphino)ethane](hydrido)[hydrotris(pyrazolyl)borato]-ruthenium with proton donors were studied by IR and 1H NMR spectroscopy in CH2Cl2 over a wide temperature range. Dihydrogen bonding to CF3CH2OH was detected; its spectral and thermodynamic parameters (ΔH° =–3.3±0.2 kcal mol–1, ΔS° =–6.7±0.6 cal mol–1 K–1) were determined. The basicity factor Ej of the hydride ligand is 0.81. The H⋯H distance in the dihydrogen-bonded complex (2.05 Å) was estimated from the changes in the spin-lattice relaxation time T1min of the hydride resonance. Comparison of the results obtained with the literature data revealed a correlation between the length and enthalpy of formation of the dihydrogen bond as well as a correlation between the basicity of the hydride ligand and the tendency of the fragment [MLn] toward stabilization and oxidative addition of H2.

Hydrogen bonds, coordination isomerism, and catalytic dehydrogenation of alcohols with the bifunctional iridium pincer complex ^{{{\left( {HOC{H_2}} \right)}_2}}\left( {P{C_{s{p^3}}}P} \right)IrHCl

The reaction of iridium(iii) hydride complex 1 based on the pincer dibenzobarrelene ligand (HOCH2)2(PCsp3P)documentclass[12pt]{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} usepackage{upgreek} setlength{oddsidemargin}{-69pt} begin{document}

First Investigation of Non‐Classical Dihydrogen Bonding between an Early Transition‐Metal Hydride and Alcohols: IR, NMR, and DFT Approach

^{{{left( {HOC{H_2}} right)}_2}}left( {P{C_{s{p^3}}}P} right)

Hydrogen Bonding and Proton Transfer to the Trihydride Complex [Cp*MoH3(dppe)]: IR, NMR, and Theoretical Investigations

end{document} with pyridine proceeds stepwise to show different reactivities of the starting fac-isomers 1A and 1B. The kinetic product of the reaction is mer-complex 2 with a trans disposition of the pyridine and hydride ligands. Isomerization into the thermodynamic product 2′ containing pyridine in the cis-position with regard to hydride proceeds slowly. The estimation of activation parameters (ΔH≠ and ΔS≠) shows that the change in the geometry of fac-complexes upon coordination of pyridine occurs through an associative transition state, while isomerization of the mer-complexes is a dissociative process. The isomers of complex 1 and its pyridine-containing derivatives 2 and 2′ are shown to exhibit different reactivities in the formation of dihydrogen bond and the catalytic dehydrogenation of PriOH under model conditions.