R. A. Mariezcurrena

Re(V) complexes with amino acids based on the ‘3+2’ approach

Abstract Five cationic complexes containing the [Re(V)O] 3+ core have been prepared by substitution on the precursor [ReIO 2 (PPh 3 ) 2 ]. Complexes with general formula [ReO(dien-H)(aa)] + have been obtained by reaction of the precursor with 1 equiv. of dien (diethylenetriamine) and one equivalent of an amino acid (glycine, alanine, valine, leucine, proline). Complexes have been characterized by UV–Vis and IR spectrophotometry, elemental analyses, 1 H NMR spectra, HPLC and conductivity measurements. The molecular structures of [ReO(dien-H)(leu)]I·0.5H 2 O and [ReO(dien-H)(pro)]ReO 4 have been determined by means of single-crystal X-ray analyses. Cations consist of a six-coordinated rhenium atom bonded to two trans -oxo groups, one of the [ReO] 3+ core and one from the carboxilate. Four nitrogen atoms make the equatorial plane. Three N belong to the dien ligand and the other one to the amino acid. One of the secondary amine proton of the dien ligand is lost upon coordination. This arrangement corresponds to the so-called ‘3+2’ chelating framework, with the novel NNN/NO atom set. Complexes are not very stable in aqueous solution. However, solutions in MeOH and DMSO are stable enough to be studied by several techniques. The solid state structure seems to be retained in solution.

Osmylation of chiral cis-cyclohexadienediols

A study on the osmylation of a series of chiral cis-cyclohexadienediols is described. Dihydroxylation takes place preferentially on the more electron-rich double bond. For 3-methylcyclohexa-3,5-diene-1,2-diol, 1a, the presence of protecting groups on the diol functionality is crucial in determining the degree of regio- and stereoselectivity of the reaction. X-ray crystal structure data of the major product of the osmylation of diene 1a, a protected (2S)-2-methylconduritol E, is reported. The regioselectivity of the reaction also depends on the method of osmylation used, the stoichiometric procedure being more selective than the catalytic one.

Synthesis, characterization and spectroscopic properties of [CuI(alkylisocyanide)4]BF4 complexes. X-ray crystal structures of [Cu(MIBI)4]BF4 and [Cu(CPI)4]BF4

Abstract Alkylisocyanide complexes of copper(I) with formula [Cu(CNR)4]BF4 [where R = 2-methoxyisobutyl and 2-(carbomethoxy)-2-methylethyl] were synthesized by direct reaction of cuprous chloride with ligand. The stability of solid complexes and their aqueous solutions were tested by HPLC. Comparative studies were carried out on electronic, IR and 1H NMR spectroscopy. Crystal structures of [Cu(MIBI)4]BF4 and [Cu(CPI)4]BF4 were determined from X-ray data and show a tetrahedral arrangement of ligands around the central copper atom in both compounds.

Structural and conformational analysis of Tcv and Rev dioxo complexes. X-ray crystal structure of [TcO2(tn)2]·H2O

Abstract [Tc v O 2 (tn) 2 ]I (tn = trimethylenediamine) was prepared form direct reduction of TcO 4 − with dithionite in presence of the ligand. The crystal structure of [TcO 2 (tn) 2 ]I·H 2 O was determined from X-ray data. It consists on a squashed octahedron with TcO bond legnths of 1.784 and 1.754 A conforming a TcO 2 + core. The amines lie in the equatorial plane, almost perpendicular to the core. Conformational analyses of several analogous trans -M v dioxo complexes (M = Tc, Re) was performed by molecular mechanics and semiempirical calculations. Energy differences between possible conformers are low. Therefore, a mixture of different conformers is expected to be found in solution.

Cationic complexes of Re with dppm (bis(diphenylphosphinomethane)). Crystal structure of [Re(dppm)3]I·CH3OH·CH2Cl2

The reaction of [ReO2(PPh3)2I] with bis-diphenylphosphines (dpp) only produces complexes with general formula [ReO2(dpp)2]+. However, when the ligand used in this work (bis(diphenylphosphinomethane) (dppm)) reacts with the same precursor an interesting Re(I) complex is also afforded. By changing the reaction conditions, trans-[ReVO2(dppm)2]+ and [ReI(dppm)3]I were obtained and characterized. The crystal structure of [Re(dppm)3]I·CH3OH·CH2Cl2 is given. In this compound, the P atoms are arranged in a strongly distorted octahedral coordination polyhedron around the rhenium center. This is the first case of a tris(dppm) complex ever reported.

Two natural products from the algae Laurencia scoparia.

The structures and absolute stereochemistries of two chamigrene-type metabolites (spiro[5.5]undecane derivatives) isolated from the red algae Laurencia scoparia are described. One, a non-sesquiterpene named maĩlione (8-bromo-9-hydroxy-7,7-dimethyl-11-methylenespiro[5.5]undec-1-en-3-one), C(14)H(19)BrO(2), was detected previously in Laurencia cartilaginea, while the other, the sesquiterpene isorigidol (8-bromo-3,7,7-trimethyl-11-methylenespiro[5.5]-undec-1-ene-3,9-diol), C(15)H(23)BrO(2), is a new isomer of rigidol, first isolated from Laurencia rigida. The A rings of these spirocyclic compounds show the same carbon skeleton. However, the relative stereochemistry of the 8-Br and 9-OH substituents is different. While maĩlione displays the usual syn (or cis) relative stereochemistry of the bromohydroxy vicinal group, isorigidol shows an anti (or trans) arrangement. The 8-Br and 9-OH groups are both in equatorial positions in isorigidol, while the 9-OH group is axial in maĩlione, as in most chamigrenes. The absolute configurations of the chiral centers were determined as 6S, 8S and 9R in maĩlione, and 3R, 6S, 8S and 9S in isorigidol.

Synthesis, Characterization, and Crystal Structure of [ReO(Me4tu)4](PF6)3 (tu = thiourea)

A new ReV oxo complex with tetramethylthiourea, [ReO(Me4tu)4](PF6)3, has been synthesized by reduction of perrhenate with tin(II) chloride in strongly acidic solution in the presence of excess tetramethylthiourea. The complex has been characterized by elemental analysis and electronic and FTIR spectroscopy. The molecular structure of the compound was determined by X-ray diffraction methods. The coordination polyhedron is a regular square pyramid with the substituted thiourea sulfur atoms in the equatorial positions [d(Re–S) = 2.339(3) A] and the oxo ligand located in the summit [d(Re–O) = 1.63(2) A]. Computational methods were employed to analyze the geometric and electronic structures of tetramethylthiourea and thiourea. Quantum mechanical studies suggest steric hindrance as the reason for the stabilization of the ReO3+ center instead of the ReIII one.

Tris(1,10‐phenanthroline)nickel(II) dinitrate thiourea monohydrate

The structure of the first nickel coordination complex with 1,10-phenanthroline (phen) containing thiourea as a cocrystallization molecule is reported. The title compound, [Ni(C 12 H 8 N 2 ) 3 ](NO 3 ) 2 .CH 4 N 2 S.H 2 O, crystallizes in the centrosymmetric space group C2/c. The crystal structure is formed by [Ni(phen) 3 ] 2+ cations, water and thiourea molecules positioned on a twofold axis, with the nitrate anions in general positions. The packing is directed by electrostatic interactions, stacking of phen molecules and hydrogen bonds between the crystallization molecules and the nitrate anions.

A facile synthesis of an oxatricyclic trans-syn-trans-substituted oxepanyl framework

Abstract The regio- and stereochemistry of iodine-promoted transannular ring expansion of cyclic trans -1,2-epoxy-5(E)-ene systems is used to synthesise trans , syn , trans -substituted oxepanyl subunits.

[ReIII(thiourea‐S)6]Cl3 · 4 H2O and [ReIII(N‐methylthiourea‐S)6]Cl3 as Precursors to other ReIII Complexes: a Kinetic Study in Aqueous Media. Crystal Structure of [ReIII(N‐methylthiourea‐S)6](PF6)3 · H2O

Capability of [ReIII(tu-S)6]Cl3, where tu = thiourea, as a precursor to other ReIII complexes by ligand substitution in aqueous medium is studied. For the decomposition of [Re(tu-S)6]Cl3, experiments suggest pseudo first order kinetics and observed rate constants vary from 1.3 × 10–2 to 9.6 × 10–2 min–1 in the pH range 2.80–5.04. Experiments in presence of incoming ligand (ethylendiaminetetraacetic acid or diethylentriaminepentaacetic acid) show that ligand substitution is significantly slower than decomposition of the precursor, even when pH and temperature are modified. Similar results were obtained working with [ReIII(Metu-S)6]Cl3, where Metu = N-methylthiourea. Molecular structure of [ReIII(Metu-S)6](PF6)3 · H2O was determined by single crystal X-ray diffractometry. The coordination polyhedron around the Re ion is a distorted octahedron. The six methylthiourea ligands are bonded to the metal through the sulfur atoms [bond lengths range from 2.409(2) to 2.451(2) A]. [ReIII(thioharnstoff-S)6]Cl3 · 4 H2O und [ReIII(N-methylthioharnstoff-S)6]Cl3 als Vorlaufer fur andere ReIII-Komplexe: Eine kinetische Untersuchung in wasrigem Medium. Die Kristallstruktur von [ReIII(N-methylthioharnstoff-S)6](PF6)3 · H2O Es wird die Eignung von [ReIII(tu-S)6]Cl3 (tu = Thioharnstoff) als Vorlaufer fur andere ReIII-Komplexe durch Ligandenaustausch in wasrigem Medium untersucht. Die Dissoziation von [Re(tu-S)6]Cl3 zeigt im pH-Bereich von 2,80–5,04 eine Kinetik Pseudo-Erster-Ordnung mit einer Geschwindigkeitskonstanten im Bereich von 1,3 × 10–2 bis 9,6 × 10–2 min–1. Experimente im Beisein von Liganden (Ethylendiamin-Tetraessigsaure oder DiethylentriaminPentaessigsaure) zeigen auch bei Variation von Temperatur und pH-Wert eine signifikant langsamere Liganden-Substitution als es der Dissoziation des Vorlaufers entspricht. Ahnliche Ergebnisse werden mit [ReIII(Metu-S)6]Cl3 (Metu = N-Methylthioharnstoff) erzielt. Die Molekulstruktur von [ReIII(Metu-S)6](PF6)3 · H2O wird durch Einkristall-Rontgenstrukturanalyse ermittelt. Das Koordinationspolyeder am Re-Ion ist verzerrt oktaedrisch. Die sechs N-Methylthioharnstoff-Liganden sind uber die Schwefel-Atome an das Rhenium-Atom gebunden [Bindungslangen von 2,409(2) bis 2,451(2) A].