Dmitry G. Gusev

From Esters to Alcohols and Back with Ruthenium and Osmium Catalysts

There and back again: hydrogenation of esters and the reverse reaction of dehydrogenative coupling of alcohols are efficiently catalyzed by dimeric complexes of Ru and Os under neutral conditions. The Os dimer is an outstanding catalyst for the hydrogenation of alkenoates and triglycerides, and allows production of fatty alcohols from olive oil. This complex converts ethanol into ethyl acetate and hydrogen under reflux.

Replacing Phosphorus with Sulfur for the Efficient Hydrogenation of Esters

Catalyst tune-up: A readily available, air-stable amino-sulfide catalyst, [RuCl(2)(PPh(3)){HN(C(2)H(4)SEt)(2)}], has been developed. This complex displays outstanding efficiency for the hydrogenation of a broad range of substrates with C=X bonds (esters, ketones, imines), as well as for the acceptorless dehydrogenative coupling of ethanol to ethyl acetate.

Chemoselective Hydrogenation of Carbonyl Compounds and Acceptorless Dehydrogenative Coupling of Alcohols

OsHCl(CO)[κ(3)-PyCH2NHC2H4NHPtBu2] is the first efficient catalyst for chemoselective reduction of challenging unsaturated esters to enols and for acceptorless coupling of amines with MeOH and EtOH affording formamides and acetamides. The NMR, ESI-MS, and DFT data indicate a mechanism proceeding in the metal coordination sphere and producing no free organic intermediates.

Preparation of a Dihydrogen Complex of Cobalt

Ammonia borane (AB) is an attractive candidate for the chemical storage of hydrogen. Recently, our research group reported that the complex [(pocop)IrH2] (pocop= k -C6H31,3-[OP(tBu)2]2) has facilitated the rapid release of H2 from AB under mild conditions. While this result is promising, iridium is too expensive for widespread application. Our efforts to extend the catalytic chemistry of [(pocop)IrH2] to Co have led to several intriguing complexes. Direct analogues of the Ir catalyst were obtained, thereby demonstrating the unusual ligation of H2 on a Co center. Herein we report the first cobalt–dihydrogen complex, which was characterized by NMR spectroscopy and studied by means of theoretical calculations. The metalation of pocop–H with Co, achieved with a method similar to procedures developed for Ir or Ni, did not proceed in satisfactory yield. An alternative approach that makes use of an iodinated pocop ligand was pursued, as described for a similar synthesis. Complex 1 was prepared in good yield by activation of the ligand with nBuLi and the addition of CoI2·THF (Scheme 1).

Homogeneous catalytic hydrogenation of long-chain esters by an osmium pincer complex and its potential application in the direct conversion of triglycerides into fatty alcohols

The osmium hydride complexes OsH2(CO)[NH(CH2PiPr2)2] (1) and OsHCl(CO)[NH(CH2PiPr2)2] (2) were evaluated in the catalytic hydrogenation of hexyl octanoate and cis-3-hexenyl hexanoate to alcohols as model substrates for triglycerides. Both complexes achieve full conversion of the saturated ester at 220 °C and 800 psi pressure of hydrogen gas. In the presence of unsaturated substrates, the complexes hydrogenate CC bonds, but are subsequently ineffective in the reduction of the ester moiety. However complex 1 is capable of hydrogenating fully saturated triglycerides (i.e., hardened fats as obtained by separate initial hydrogenation of seed oils using either 1 or 2 or a standard heterogeneous hydrogenation catalyst) giving cetyl and stearyl alcohols as the main products.

2H MAS NMR of strongly dipolar coupled deuterium pairs in transition metal dihydrides : extracting dipolar coupling and quadrupolar tensor orientations from the lineshape of spinning sidebands

A selectively D2 labeled transition metal dihydride, Os(D2)(Cl)2(CO)(PiPr3)2, was synthesized and studied by 2H magic angle spinning (MAS) NMR spectroscopy. It was found that the interference between the quadrupolar and homonuclear dipolar interaction results in a characteristic lineshape of the MAS sidebands. The basic properties of the interference of homonuclear dipolar and quadrupolar coupling on the 2H NMR lineshape were elucidated, using average Hamiltonian theory, and exact simulations of the experiments were achieved by stepwise integration of the equation of motion of the density matrix. These simulations show that it is possible to determine the size of the dipolar interaction and thus the D–D distance from the lineshape of the sidebands.

Calculated Hydride and Fluoride Affinities of a Series of Carbenium and Silylium Cations in the Gas Phase and in C6H5Cl Solution

We report the hydride and fluoride affinities for a group of silylium and carbenium cations. With comparable substituents on the central atom, the silylium cations have the higher fluoride affinity, whereas the carbenium ions have the higher hydride affinity. In the first approximation, the hydride and the fluoride affinities vary in parallel with changes in substitution, but the deviations from linear correspondence of hydride and fluoride affinities are more pronounced for carbenium ions. The hydride and fluoride affinities of silylium cations are very similar, whereas for carbenium ions, the hydride affinities are 35-60 kcal  mol(-1) higher than fluoride affinities. These results are placed in the context of studies of hydrodefluorination of aliphatic C-F bonds enabled by silylium carborane catalysts [C. Douvris, O. V. Ozerov, Science 2008, 321, 1188]. The abstraction of fluoride from perfluoroalkanes by a trialkylsilylium cation is neither thermodynamically favorable nor kinetically accessible and, if at all possible, will require a much more fluorophilic silylium cation.

Triple C–H activation of 1,5-bis(di-tert-butylphosphino)-2-(S)-dimethylaminopentane on ruthenium gives a chiral carbene complex

This communication reports the preparation of a novel trans-chelating diphosphine, 1,5-bis(di-tert-butylphosphino)-2-(S)-dimethylaminopentane, that undergoes triple C-H activation in reaction with [RuCl2(p-cymene)]2 to give a chiral square-pyramidal 16-electron carbene complex of ruthenium.

Cationic, Neutral, and Anionic Hydrides of Iridium with PSiP Pincers

This work describes synthetic routes from the known precursor [IrClH{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (1) to new hydride and polyhydride derivatives. Substituting the chloride ligand with triflate leads to the five-coordinate complex [IrH{κO-O3S(CF3)}{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (2), which can undergo reversible coordination of water (H2O) or dihydrogen (H2) to generate respectively the cationic derivative [IrH{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}(OH2)2](CF3SO3) (3) or the neutral trans-hydride-dihydrogen [IrH{κO-O3S(CF3)}{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}(η2-H2)] (6) in equilibrium. The use of acetonitrile or carbon monoxide (CO) excess instead of water produces stable analogues of 3 (complexes 4 or 5, respectively). The reaction between 1 and NaBH4 affords the tetrahydroborate derivative [IrH{κ2H-H2BH2}{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (7), which can be protonated with triflic acid to form 2 or with HBF4 to give the dinuclear cationic derivative [(μ:κ2H,κ2H-BH4)[IrH{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}]2](BF4) (8). The reactions of 7 with alcohols afford either the dihydride-carbonyl [IrH2{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}(CO)] (9) or the known tetrahydride [IrH4{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (10), depending on the ease of alcohol decarbonylation. NMR observations and density functional theory calculations on the fluxional behavior of 10 indicate that the spatial contour of the mer PSiP framework conditions hydride-ligand exchanges. Complex 10 reacts with NaH in tetrahydrofuran to form the anionic trihydride [IrH3{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}]Na (11), which exists as a mixture of fac and mer isomers in equilibrium.

Gold(I) Metallo-Tweezers for the Recognition of Functionalized Polycyclic Aromatic Hydrocarbons by Combined π-π Stacking and H-Bonding

Two gold(I)-based metallo-tweezers with bis(Au-NHC) pincers and a carbazole connector have been obtained and used for the recognition of polycyclic aromatic hydrocarbons (PAHs). In the case of the tweezer with pyrene-NHC ligands, the presence of the pyrene fragment and the N-H bond in the carbazole linker enable the receptor to show significant enhanced binding abilities toward PAHs functionalized with H-bonding groups, through combined π-π stacking and H-bonding.