Cytisine-like alkaloids from Ormosia hosiei Hemsl. & E.H. Wilson

Four alkaloids named hosieines A-D were isolated from the root and stem of Ormosia hosiei. Their flat structures were established by mass spectrometry and by a combination of NMR experiments. These molecules probably share a common biosynthetic origin with the lupin alkaloids but they differ in the formation of the last ring, being here part of a rare 2-azabicyclo[3.2.1]octane system. Their absolute configuration was determined by X-ray crystallography using CuKα radiation. As has been described for cytisine, they display a remarkable affinity towards neuronal nicotinic acetylcholine α4β2 receptor.

B-H, C-H, and B-C bond activation: the role of two adjacent agostic interactions

Tuning the nature of the linker in a L~BHR phosphinoborane compound led to the isolation of a ruthenium complex stabilized by two adjacent, δ-C-H and ε-B(sp2)-H, agostic interactions. Such a unique coordination mode stabilizes a 14-electron "RuH2P2" fragment through connected σ-bonds of different polarity, and affords selective B-H, C-H, and B-C bond activation as illustrated by reactivity studies with H2 and boranes.

Ruthenium-catalyzed reduction of carbon dioxide to formaldehyde

Functionalization of CO2 is a challenging goal and precedents exist for the generation of HCOOH, CO, CH3OH, and CH4 in mild conditions. In this series, CH2O, a very reactive molecule, remains an elementary C1 building block to be observed. Herein we report the direct observation of free formaldehyde from the borane reduction of CO2 catalyzed by a polyhydride ruthenium complex. Guided by mechanistic studies, we disclose the selective trapping of formaldehyde by in situ condensation with a primary amine into the corresponding imine in very mild conditions. Subsequent hydrolysis into amine and a formalin solution demonstrates for the first time that CO2 can be used as a C1 feedstock to produce formaldehyde.

Nature of Si-H interactions in a series of ruthenium silazane complexes using multinuclear solid-state NMR and neutron diffraction

Three new N-heterocyclic-silazane compounds, 1a-c, were prepared and employed as bidentate ligands to ruthenium, resulting in a series of [Ru(H){(κ-Si,N-(SiMe2-N-heterocycle)}3] complexes (3a-c) featuring the same RuSi3H motif. Detailed structural characterization of the RuSi3H complexes with X-ray diffraction, and in the case of triazabicyclo complex [Ru(H){κ-Si,N-(SiMe2)(C7H12N3)}3] (3a), neutron diffraction, enabled a reliable description of the molecular geometry. The hydride ligand of (3a) is located closer to two of the silicon atoms than it is to the third. Such a geometry differs from that of the previously reported complex [Ru(H){(κ-Si,N-(SiMe2)N(SiMe2H)(C5H4N)}3] (3d), also characterized by neutron diffraction, where the hydride was found to be equidistant from all three silicon atoms. A DFT study revealed that the symmetric and less regular isomers are essentially degenerate. Information on the dynamics and on the Ru···H···Si interactions was gained from multinuclear solid-state ((1)H wPMLG, (29)Si CP MAS, and 2D (1)H-(29)Si dipolar HETCOR experiments) and solution NMR studies. The corresponding intermediate complexes, [Ru{κ-Si,N-(SiMe2-N-heterocycle)}(η(4)-C8H12)(η(3)-C8H11)] (2a-c), involving a single silazane ligand were isolated and characterized by multinuclear NMR and X-ray diffraction. Protonation of the RuSi3H complexes was also studied. Reaction of 3a with NH4PF6 gave rise to [Ru(H)(η(2)-H -SiMe2)κ-N-(C7H12N3){κ-Si,N-(SiMe2)(C7H12N3)}2](+)[PF6](-)(4aPF6) which was isolated and characterized by NMR spectroscopy, X-ray crystallography, and DFT studies. The nature of the Si-H interactions in this silazane series was analyzed in detail.

Antiferromagnetic Cu–Gd interactions through an oxime bridge

The Cu–Gd oximato bridge, which is responsible for the presence of an antiferromagnetic interaction in a trinuclear Cu–Gd–Cu complex, isostructural to the Cu–Tb–Cu one, contrary to what is observed in the magnetic behavior of phenoxo-bridged Cu–Gd complexes.

Perfluorinated 1H-indazoles and hydrotris(indazol-1-yl)borates. Supramolecular organization and a new synthetic procedure to form scorpionate ligands

The molecular and supramolecular structures of new perfluorinated indazoles and hydrotris(indazolyl)borates reveal various types of intra- and intermolecular interactions and organizations.

Chlorido(η(6)-N (2)-diphenylphosphanyl-N (1),N (1)-diisopropyl-4-methoxybenz-amidine-κP)(triphenylphosphane-κP)ruthenium(II) trifluoromethansulfonate acetone disolvate

In the title compound, [RuCl(C₁₈H₁₅P)(C₂₆H₃₁N₂OP)](CF₃O₃S)·2C₃H₆O, the Ru^II ion is coordinated in a three-legged piano stool, half-sandwich-type geometry by a chlorido ligand, a tri­phenyl­phosphine and a tethered η⁶-(phenyl-p-O-meth­oxy) κ¹-P N-di­phenyl­phosphino N′-diisopropyl amidine ligand charge-balanced by a trifluormethansulfonate counter-anion. The η⁶-coordination mode of the arene incorporated into the structure was generated in situ after addition of methyl tri­fluoro­methane­sulfonate to the neutral η⁵-arene tethered precursor complex [RuCl(PPh₃)(η⁵:κ¹-OC₆H₄C(NiPr₂)=N-PPh₂)] in di­chloro­methane solution.

Bis(2,2'-bipyridine)[1,9-bis(diphenylphos-phanyl)-1,2,3,4,6,7,8,9-octahydropyrim-ido[1,2-a]pyrimidin-5-ium]ruthenium(II) hexa-fluorido-phosphate dibromide di-chloro-methane disolvate monohydrate

In the cation of the title complex, [Ru(C₃₁H₃₂N₃P₂)(C₁₀H₈N₂)₂](PF₆)(Br)₂·2CH₂Cl₂·H₂O, the ruthenium ion is coordinated in a distorted octa­hedral geometry by two 2,2′-bi­pyridine (bpy) ligands and a chelating cationic N-di­phenyl­phosphino-1,3,4,6,7,8-hexa­hydro-2-pyrimido[1,2-a]pyrimidine [(PPh₂)₂-hpp] ligand. The tricationic charge of the complex is balanced by two bromide and one hexa­fluorido­phosphate counter-anions. The compound crystallized with two mol­ecules of di­chloro­methane (one of which is equally disordered about a Cl atom) and a water mol­ecule. In the crystal, one of the Br anions bridges two water mol­ecules via O—H⋯Br hydrogen bonds, forming a centrosymmetric diamond-shaped R⁴₂(8) motif. The cation and anions and the solvent mol­ecules are linked via C—H⋯F, C—H⋯Br, C—H⋯Cl and C—H⋯O hydrogen bonds, forming a three-dimensional network.

Dichapetalins from Dichapetalum species and their cytotoxic properties

Six dichapetalins named dichapetalins N-S were isolated from Dichapetalum mombuttense, Dichapetalum zenkeri and Dichapetalum leucosia. They were accompanied in the same plants by the known dichapetalins A, B, C, I, L and M. The structures of the compounds were elucidated by 1D and 2D NMR experiments and mass spectrometry. They all possessed the dammarane skeleton substituted at position C-3 by a C6-C2 unit forming a 2-phenylpyran moiety. All contained a lactone ring in the side chain except dichapetalins O, Q and R, in which this ring was replaced by a lactol. Dichapetalin Q and R were also the first dichapetalins bearing a tertiary methyl and a double bond instead of the cyclopropane of the dammaranes. All these compounds were assayed against cancer cell lines HCT116 and WM 266-4 and displayed cytotoxic and anti-proliferative activities in the 10(-6) to 10(-8)M range.

Synthesis of a ruthenium bis(diisopropylamino(isocyano)borane) complex from the activation of an amino(cyano)borane

The reactivity of the amino(cyano)borane (i)Pr(2)NBH(CN) (2) towards [RuH(2)(η(2)-H(2))(2)(PCy(3))(2)] (3) was investigated. Our study reveals that the formation of the bis(isocyanoborane) ruthenium complex [RuH(CN)(CN-BHN(i)Pr(2))(2)(PCy(3))(2)] (6) occurs via the intermediacy of the bis(σ-B-H) ruthenium complex [RuH(CN)(H(2)BN(i)Pr(2))(PCy(3))(2)] (5). This transformation involves BCN linkage isomerisation in 2. The diisopropylaminoborane ligand in 5 can be displaced to ultimately produce the bis(σ-borane) complex [RuH(2)(η(2):η(2)-H(2)BN(i)Pr(2))(PCy(3))(2)] (4) as a by-product.