Rosa Adam

Low-Temperature Hydrogenation of Carbon Dioxide to Methanol with a Homogeneous Cobalt Catalyst

Herein we describe the first homogeneous non-noble metal catalyst for the hydrogenation of CO2 to methanol. The catalyst is formed in situ from [Co(acac)3 ], Triphos, and HNTf2 and enables the reaction to be performed at 100 °C without a decrease in activity. Kinetic studies suggest an inner-sphere mechanism, and in situ NMR and MS experiments reveal the formation of the active catalyst through slow removal of the acetylacetonate ligands.

Isomorphous replacement of MII ions in MII–GdIII dimers (MII = CuII, MnII, NiII, CoII, ZnII): magnetic studies of the products

Complexes [MIIGdIII{pyCO(OEt)pyC(OH)(OEt)py}3](ClO4)2·EtOH [MII = CuII (1), MnII (2), NiII (3), CoII (4) and ZnII (5)] crystallize in the monoclinic Cc space group and contain one hexacoordinate MII ion and one enneacoordinate GdIII ion, bridged by three {pyCO(OEt)pyC(OH)(OEt)py}− ligands. Magnetic susceptibility measurements indicate a ferromagnetic interaction for 1 and antiferromagnetic interactions for 2–4. Using the Ĥ = −JŜGdIIIŜMII spin Hamiltonian formalism, fits to the magnetic susceptibility data yielded J values of +0.32 cm−1 for 1, −1.7 cm−1 for 2, and −0.22 cm−1 for 3. In complex 4, the orbital contributions of CoII precluded the determination of the magnetic coupling. The complex follows the Curie–Weiss law with θ = −2.07 K (−1.44 cm−1).

A General and Highly Selective Cobalt‐Catalyzed Hydrogenation of N‐Heteroarenes under Mild Reaction Conditions

Herein, a general and efficient method for the homogeneous cobalt-catalyzed hydrogenation of N-heterocycles, under mild reaction conditions, is reported. Key to success is the use of the tetradentate ligand tris(2-(diphenylphosphino)phenyl)phosphine). This non-noble metal catalyst system allows the selective hydrogenation of heteroarenes in the presence of a broad range of other sensitive reducible groups.

A general protocol for the reductive N-methylation of amines using dimethyl carbonate and molecular hydrogen: mechanistic insights and kinetic studies

Herein, we report for the first time a general and selective ruthenium-catalyzed reductive methylation of amines using dimethyl carbonate as a C1 source and molecular hydrogen as a reducing agent. Notably, this methodology allows N-methylated tertiary aromatic and aliphatic amines to be obtained with good to excellent yields using a green, non-toxic and biodegradable carbon source in the presence of an in situ formed Ru/Triphos complex. The catalytic protocol presented here opens the possibility of developing new sustainable processes for the selective synthesis of N-methyl substituted amines using molecular hydrogen. Mechanistic and kinetic studies have been carried out in order to understand the pathways involved in the general reaction mechanism for the N-methylation of aniline.

Selective Hydrogenation of Nitriles to Primary Amines by using a Cobalt Phosphine Catalyst

A general procedure for the catalytic hydrogenation of nitriles to primary amines by using a non-noble metal-based system is presented. Co(acac)3 in combination with tris[2-(dicyclohexylphosphino)ethyl]phosphine efficiently catalyzes the selective hydrogenation of a wide range of (hetero)aromatic and aliphatic nitriles to give the corresponding amines.

Expanding the 3d-4f heterometallic chemistry of the (py)2CO and pyCOpyCOpy ligands: structural, magnetic and Mössbauer spectroscopic studies of two FeII–GdIII co mplexes

Complex [Fe(II)Gd(III){pyCO(OEt)pyCOH(OEt)py}(3)](ClO(4))(2) (1) crystallizes in the Cc space group and contains one hexacoordinate ferrous ion and one enneacoordinate Gd(III) ion. Complex [Fe(2)(II)Gd(III){pyCO(OEt)py}(4)(NO(3))(H(2)O)][Gd(NO(3))(5)](0.5)(ClO(4)) (2) crystallizes in the C2/c space group and contains two hexacoordinate ferrous ions and one octacoordinate Gd(III) ion. Both complexes have been prepared by the metal-assisted ethanolysis of ligands di-2,6-(2-pyridylcarbonyl)pyridine (pyCOpyCOpy, dpcp) and di-2-pyridyl ketone ((py)(2)CO, dpk), which exhibit similar structures. Mössbauer spectroscopic studies of 2 revealed the presence of two quadrupole-split doublets of equal intensities, each assigned to a ferrous site. These doublets exhibit similar isomer shifts (δ(1) = 1.14 mm s(-1), δ(2) = 1.11 mm s(-1)) but quite different quadrupole splittings (ΔE(Q1) = 3.55 mm s(-1), ΔE(Q2) = 2.74 mm s(-1)). Magnetic studies revealed weak ferromagnetic Fe(II)-Gd(III) interactions for both complexes (J(FeGd) = +0.68 cm(-1), D(Fe) = 12.0 cm(-1) for 1 and J(FeGd) = +0.03 cm(-1), J(FeFe) = -1.73 cm(-1) for 2, according to the -JS(i)S(j) spin-Hamiltonian formalism).

A Mild and Base-Free Protocol for the Ruthenium-Catalyzed Hydrogenation of Aliphatic and Aromatic Nitriles with Tridentate Phosphine Ligands

A novel protocol for the general hydrogenation of nitriles in the absence of basic additives is described. The system is based on the combination of [Ru(cod)(methylallyl)2] (cod=cyclooctadiene) and L2. A variety of aromatic and aliphatic nitriles is hydrogenated under mild conditions (50 °C and 15 bar H2) with this system. Kinetic studies revealed higher activity in the case of aromatic nitriles compared with aliphatic ones.

Esters, Including Triglycerides, and Hydrogen as Feedstocks for the Ruthenium-Catalyzed Direct N-Alkylation of Amines.

Triglycerides are used for the direct N-alkylation of amines with molecular hydrogen for the first time. A broad range of interesting and industrially relevant secondary and tertiary amines are obtained in the presence of an in situ formed Ru/Triphos complex. Notably, plant oil can be efficiently applied in this single-step process. Moreover, a variety of other methyl esters can be used as N-alkylation agents in the presence of hydrogen for the synthesis of more advanced building blocks.

Triazolopyridyl ketones as a novel class of antileishmanial agents. DNA binding and BSA interaction.

A new series of triazolopyridyl pyridyl ketones has been synthetized by regioselective lithiation of the corresponding [1,2,3]triazolo[1,5-a]pyridine at 7 position followed by reaction with different electrophiles. The in vitro antileishmanial activity of these compounds was evaluated against Leishmaniainfantum, Leishmaniabraziliensis, Leishmaniaguyanensis and Leishmaniaamazonensis. Compounds 6 and 7 were found to be the most active leishmanicidal agents. Both of them showed activities at micromolar concentration against cultured promastigotes of Leishmania spp. (IC₅₀=99.8-26.8 μM), without cytotoxicity on J774 macrophage cells. These two compounds were also tested in vivo in a murine model of acute infection by L. infantum. The triazolopyridine derivative 6 was effective against both spleen and liver parasites forms, while 7 was inactive against liver parasites. Mechanistic aspects of the antileishmanial activity were investigated by means of DNA binding studies (UV-titration and viscosimetry). Results have revealed that these active ligands are able to interact strongly with DNA [Kb=1.14 × 10(5)M(-1) (6) and 3.26 × 10(5)M(-1) (7)]. Moreover, a DNA groove binding has been proposed for both 6 and 7. To provide more insight on the mode of action of compounds 6 and 7 under biological conditions, their interaction with bovine serum albumin (BSA) was monitored by fluorescence titrations and UV-visible spectroscopy. The quenching constants and binding parameters were determined. Triazolopyridine ketones 6 and 7 have exhibited significant affinity towards BSA [Kb=2.5 × 10(4)M(-1) (6) and 1.9 × 10(4)M(-1) (7)]. Finally, to identify the binding location of compounds 6 and 7 on the BSA, competitive binding experiments were carried out, using warfarin, a characteristic marker for site I, and ibuprofen as one for site II. Results derived from these studies have indicated that both compounds interact at BSA site I and, to a lesser extent, at site II.

Cobalt-catalysed transfer hydrogenation of quinolines and related heterocycles using formic acid under mild conditions

Herein, we report the first example of homogeneous non-noble metal-catalyzed transfer hydrogenation of N-heteroarenes. The combination of Co(BF4)2·6H2O with tris(2-(diphenylphosphino)phenyl)phosphine L1 is able to selectively reduce quinolines in the presence of other sensitive functional groups, under mild conditions, using formic acid as a hydrogen source.