R. M. Claramunt

Rhodium(I) complexes with bis(pyrazolyl)methane ligands. Crystal structure of [Rh(COD)(CH2(Pz)2)]ClO4·12 C2H4Cl2

The synthesis and properties of neutral and cationic complexes of general formulae [{RhCl(diolefin)}2(CH2(pz)2)], [Rh(CO)2 (CH2(pz)2)][RhCl2(CO)2], (Rh(diolefin)(CH2(pz)2)]ClO2, [{Rh(diolefin)(PPh3)}2(CH2(pz)2)](ClO4)2, [Rh(CO)2(CH2(pz)2)]ClO4 and [Rh(CO)(CH2(pz)2)(PPh3)]ClO4 are described. The NMR spectra of [Rh(COD)(CH2(pz)2)]ClO4 complexes are discussed. X-ray structural analysis of [Rh(COD)(CH2(Pz)2)]ClO4 · 12C2H4Cl2 is presented; the final R factor is 0.061 for 2436 observed data, recorded with Cu-Kα, not corrected for absorption and with the sample inside a capillary. The Rh atom presents a distorted square planar coordination in a mononuclear arrangement. The COD ring has a twisted boat conformation, and the two halves of the CH2(Pz)2 moiety, which are quite similar to one another, form an angle of 47.2(4)°.

An 1H and 13C NMR spectroscopic study of the structure of potassium and thallium salts of tris- and tetrakis-(pyrazol-1-yl) borates in solution. Some 13C11B and 13C205Tl residual coupling constants

Abstract The 1 H and 13 C NMR spectra of 18 tris- and tetrakis-pyrazolylborates in the form of potassium or thallium salts have been recorded. Four of these compounds are new. The results are discussed with regard to two main aspects: coupling constants with 205 Tl and positional isomerism of the pyrazole substituents. Most borates are symmetric compounds (all the pyrazole rings being identical isomers) corresponding to less hindered structures (all 3-aryl, 3-i-propyl-4-bromo, 3-t-butyl-5-methyl or 3-t-butyl-5-i-propyl pyrazoles). Only one derivative, potassium hydrotris(2,4,6-trimethylphenylpyrazol-1-yl)borate 5 , does not fit this pattern, being either a 3/3/3/ or a 3/3/5 isomer.

Structure of 3(5)-methyl-4-nitropyrazole in the solid state: tautomerism, crystallography and the problem of desmotropy

The first example of desmotropy in azoles has been found concerning 3-methyl-4-nitropyrazole and its tautomer, 5-methyl-4-nitropyrazole: the crystal and molecular stucture of both tautomers has been determined by X-ray analysis, 13C CPMAS NMR spectroscopy has been used for studying the isomerization processes in the solid state.

Rhodium(I) complexes with pyridazine, 4,6-dimethyl-pyrimidine, 4,6-bis(3,5-dimethylpyrazol-1-yl)pyrimidine, 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine and 3-(3,5-dimethylpyrazol-1-yl)-6-chloropyridazine

Abstract The synthesis and properties of rhodium(I) complexes of formulae [“RhCl(diolefin)” 2 (L)] (or [Rh(Cl(diolefin)(L)]), and [Rh(diolefin)(L)] n (ClO 4 ) n are reported. These complexes react with carbon monoxide to yield the related carbonyl derivatives. Ligands used were pyridazine, 4,6-dimethyl-pyrimidine, 4,6-bis(3,5-dimethylpyrazol-1-yl)pyrimidine, 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine and 3-(3,5-dimethyl-pyrazol-1-yl)-6-chloropyridazine. Related iridium(I) and gold(I) compounds are also reported.

Rhodium(I) complexes with the polydentate ligand 3,5-bis(4-methylpyrazol-1-yl)-4-methylpyrazole

Abstract The behaviour towards RhI of a new ligand containing three linked pyrazoles (HLL) has been studied. Depending on which diolefin, COD or TFB, is used, mono or dinuclear complexes are obtained. The structures of the four complexes, [RHCl(COD)(H LL )], [{RhCl(TFB]}2(μ-H LL )], [Rh(LL)(COD)] and [{Rh(TFB)}2(μ-LL)BF4, have been established by 1H and 13C NMR spectroscopy. In most cases, the NMR spectra reveal fluxional processes involving not only the RhI metal but also the N-H proton and the diolefin.

4-(1H-1,2,4-Triazol-1-yl)phenol

The secondary structure of the title compound, C 8 H 7 N 3 O, consists of O-H…N hydrogen-bonding catemers, similar to those of the parent 1,2,4-triazole, where the molecules are linked by N-H…N bonds. Chains related by translation are linked by C-H(triazole)…O/N interactions to give a tertiary structure of corrugated sheets parallel to the ac plane. The quaternary structure is due to C-H(Ph)…O contacts and to the stacking of triazole rings from centrosymmetrically related sheets.

Regioselective adamantylation of N-unsubstituted pyrazole derivatives

Abstract Reaction of NH-pyrazoles with 1-bromoadamantane in a high pressure stainless steel autoclave (250 ml, maximum working pressure of 200 atm) gives regioselectively 1-adamantyl or 4-adamantylpyrazoles depending on the temperature.

Conformation of 5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene: an experimental and theoretical NMR study

Hybrid abinitio calculations (GIAO/B3LYP/6-31G*) together with new DNMR experiments (1H and 13C) have been used to clarify the problem of the conformation of 5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene. The carbon-13 chemical shifts have been assigned unambiguously to the chair C and twist-boat TB conformations. Lineshape analysis of the 1H NMR spectra has been carried out at several temperatures using an estimated set of Karplus-type vicinal coupling constants.

Photophysics of the 2-(2′-hydroxyphenyl)perimidines: Photostability studies

Abstract Photophysical characterization of perimidine 1 , 1-methylperimidine 2 , 2-phenylperimidine 3 , 1-methyl-2-phenylperimidine 4 , 2-(2′-hydroxyphenyl)perimidine 5 , 1-methyl-2-(2′-hydroxyphenyl)perimidine 6 , 2-(2′-methoxyphenyl)perimidine 7 and 1-methyl-2-(2′-methoxyphenyl)perimidine 8 has been achieved. All derivatives exhibit a high photostability against the UV light with small photochemical quantum yields o r in the range of 10 −5 –10 −6 , implying that non-radiative processes different from the excited state intramolecular proton transfer (ESIPT) mechanism are responsible for their photophysics.

Host-guest chemistry. 2. Amine inclusion compounds of 2-[o-(triphenylphosphoranylidenamino)benzyliden]amino-1H-2,3-dihydroindazol-3-one. X-ray structure of its 1∶1∶1 inclusion complex with isopropylamine and water

The crystal and molecular structure is reported for the inclusion compound 2-[o-(triphenylphosphoranylidenamino)benzyliden]amino-1H-2,3-dihydroindazol-3-one/isopropylamine/water3b. The crystal structure consists of discrete dimeric salt-like aggregates joined together by strong N+−H...−O−C hydrogen bonds between pairs of centrosymmetrically-related indazolonate anions and isopropylammonium cations. Six other inclusion compounds have been prepared and characterized by NMR [with propylamine (3a), withtert-butylamine (3c), withsec-butylamine (3d), withtert-pentylamine (3e), with 1-methylbutylamine (3f) and withiso-pentylamine (3g)]. Two different arrangements are found, both with the host being in the anionic form. The guests are either: (i) one protonated amine and one water molecule (3b and3f); or (ii) one protonated amine and the corresponding neutral amine (3a, 3c, 3d, 3e and3g).