Volume 55, Issue 2

In context with studies on silicon-containing α-amino acids and peptides, a strategy for the synthesis of the 4-sila-proline skeleton was developed. The synthesis of rac-and (R)-4,4-dimethyl-4-sila-proline ethyl ester [rac-2 and (R)-2] is described. Compounds rac-2 and (R)-2 (≥ 99% ee) were prepared by two-step syntheses, starting from 3,6-diethoxy-2,5-dihydro-pyrazine and (R)-3,6-diethoxy-2-isopropyl-2,5-dihydropyrazine, respectively.

New quaternary niobium cluster chlorides corresponding to the general formula ATi[Nb 6 Cl 18 ] (A = K, Rb, Cs, In, Tl) have been synthesized in sealed quartz tubes at 720 °C, starting from stoichiometric amounts of NbCl 5 , niobium metal, TiCl 3 , and ACl (A = K, Rb, Cs), or In or Tl metals. The structures of RbTi[Nb 6 Cl 18 ] and CsTi[Nb 6 Cl 18 ] were determined using single­ crystal X-ray diffraction. RbTi[Nb 6 Cl 18 ] crystallizes in the rhombohedral crystal system, space group R3̄ (no. 148), Z = 3, with lattice parameters: a = 9.163(4), c = 25.014(14) Å (hexagonal setting). The structure refinement converged to R 1 = 0.044 and wR 2 = 0.058 for all data. In this structure, discrete [Nb 6 Cl 18 ] 4- cluster units are linked by Rb + and Ti 3+ cations, located in a 12-coordinated anticubeoctahedral and octahedral chloride coordination environment, respectively. In contrast, CsTi[Nb 6 Cl 18 ] crystallizes in the trigonal crystal system, space group P3̄1c (no. 163), Z = 2. The lattice parameters were determined to be a = 9.1075(6), c = 17.0017(8) Å. The structure refinement gives the reliability factors R 1 = 0.029 and wR 2 = 0.063 for all data. The structure is built up of discrete octahedral [Nb 6 Cl 18 ] 4- cluster units, linked by Cs + and Ti 3+ cations which are located in a distorted hexagonal antiprismatic and octahedral chloride coordination environment, respectively. The structures of the compounds ATi[Nb 6 Cl 18 ] (A = K, In, Tl) were found to be isotypic with RbTi[Nb 6 Cl 18 ], and their unit cell parameters were refined using X-ray powder diffraction analysis.

Imines of salicylaldehyde and 2,6-diformyl-p-cresol have been used as ligands in palladium (II) complexes. Enantiomerically pure ligands give enantiomerically pure complexes, racemic ligands give racemates and meso-forms. Differences between the respective isomers of the ligands within the complexes and between the diastereomers of the complexes were investigated. Crystal structure analyses established the trans configuration at the metal center.

New intermetallic cerium compounds Ce 2 T 2 Mg (T = Ni, Cu, Pd), C 2 T 2 Cd (T=Pd, Pt, Au), and C 2 T 2 Pb (T = Pt, Au) were prepared by reaction of the elements in sealed tantalum tubes in a high-frequency furnace. Most C 2 T 2 X (X = Mg, Cd, Pb) compounds are stable after annealing at about 1000 K, while Ce 2 Pd 2 Mg is obtained as single phase only after melting and quenching. A thermal treatment at about 1000 K leads to decomposition in CePdMg and CePd. The eight compounds were investigated by X-ray diffraction both as powders and single crystals, and most structures were refined from single crystal data. They adopt an ordered U 3 Si 2 type structure with space group P4/mbm: a = 759.6(1), c = 376.71 (9) pm, wR2 = 0.0562, 294 F 2 values, 12 parameters for Ce 2 Ni 2 Mg, a = 787.41(9), c = 387.23(7) pm, wR2 = 0.0438, 222 F 2 values, 12 parameters for Ce 2 Cu 2 Mg, a = 777.14(8), c = 400.03(7) pm, wR2 = 0.0276, 221 F 2 values, 13 parameters for Ce 2 Pd 2.03 Mg 0.97 , a = 777.90(6), c = 393.28(6) pm, wR2 = 0.0360,317 F 2 values, 12 parameters for Ce 2 Pd 2 Cd, and a = 779.90(7), c = 389.97(7) pm, wR2 = 0.0453, 315 F 2 values, 12 parameters for Ce 2 Pt 2 Cd. Refinement of the occupancy parameters revealed full occupancy for most sites. A mixed palladium/magnesium (97 % Mg / 3 % Pd) occupancy was observed only for the 2a site of Ce 2 Pd 2.0 3Mg 0.97 , indicating a small homogeneity range for this compound. Ce 2 Au 2 Cd (a = 804.93(7), c =393.36(6) pm) and the plumbides Ce 2 Pt 2 Pb (a = 794.63(7), c = 381.50(6) pm) and Ce 2 Au 2 Pb (a = 810.70(7), c = 394.85(7) pm) were characterized through their Guinier powder data. The structures of the Ce 2 T 2 X compounds can be interpreted as an intergrowth of distorted AIB 2 and CsCl related slabs of compositions CeT 2 and CeX. The course of the lattice parameters and chemical bonding within the series of Ce 2 T 2 X compounds are briefly discussed.

Cadmium metal was oxidized in the presence of N-methylisatin N(4)-cyclohexyl-thiosemicarbazone (HMeIs 4 Chex) in an acetonitrile solution, which produced a complex of the formula [Cd(MeIs 4 Chex) 2 ]. The two MeIs 4 Chex ligands are at an angle close to 90° from each other, and there is hydrogen bonding to two adjacent molecules by the anionic ligands remaining NH groups. The complex crystallizes in the monoclinic space group P2 1 /c with a = 11.820(4), b = 11.491(4), c = 27.834(4) Å, β = 106.82(2)°, V = 3618.7(17) Å 3 and Z = 4.

Difluorobromomethyl-triphenylphosphonium bromide [(C 6 H 5 ) 3 PCF 2 Br] + Br - (1) has been prepared by the reaction of triphenylphosphine with dibromodifluoro-methane in acetonitrile or methylene chloride. The colorless crystals are monoclinic, space group P 2 1 /n, Z=4, a = 1067.1(2), b = 1488,5(2), c = 1178,2(2) pm, β = 95,67(3)°. The lattice contains Br - anions and [(C 6 H 5 ) 3 PCF 2 Br] + cations with a Br-Br distance of 322,33(11) pm.. For the title compound the results of AM 1, PM 3 ,and MNDO calculations are in good agreement with corresponding values determined by the X-ray analysis only in the case of PM 3. The yellow-red [(C 6 H 5 ) 3 PCF 2 Br] + Br 3 - (2) has been obtained by treating 1 with equimolar quantities of elemental bromine in methylene chloride solution.

The stoichiometric reaction of N-(2-hydroxyethyl)-1,2-ethylenediamine-N,N,N′-triacetic acid [H 3 hedta = (HOCH 2 CH 2 )(HO 2 CCH 2 )NC 2 H 4 N(CH 2 CO 2 H) 2 )] and copper(II) hydroxy-carbonate in water yields crystalline samples of poly-{(N-(2-hydroxyethyl)-N′-carboxymethyl-1,2-ethylenediamine-N,N′-diacetato)copper(II) hydrate}, {[Cu(Hhedta)] · H 2 O} n (I)-The compound was studied by TG analysis (with FT-IR study of the evolved gases), IR, electronic and ESR spectra, magnetic susceptibility data and single crystal X-ray diffraction methods. It crystallises in the orthorhombic system, space group Fdd2 (a = 21.906(2), b = 36.602(4), c = 6.928(1) Å, Z = 16, and final R 1 = 0.029 for 1554 independent reflections). The Cu(II) atom exhibits a very distorted octahedral coordination (type 4+1 + 1). The Hhedta ligand plays a N,N′,O,O′O″-pentadentate chelating role as well as a O,O′-carboxylate bridging one and has a free N-carboxymethyl arm. The bridging carboxylate group of the Hhedta ligand leads to polymeric chains {[Cu(Hhedta)] · H 2 O}n parallel the c axis. A hydrogen bonding network involves all O-H polar bonds (non-ionised carboxylic and alcoholic hydroxyl groups and water molecules). The structure reveals the preferred formation of a copper(II)-(N-2-hydroxyethyl-amino) or copper(II)-(ethanolamino) versus a copper(II)-(N-carboxymethylamino) chelate ring.

The crystal structures of cis-(n-Bu 4 N) 2 [ReBr 4 (NCS) 2 ] (1) (triclinic, space group P1̄, a = 11.475(6), b = 20.096(16), c = 22.144(11) Å, α = 110.56(6), β = 92.97(5), γ = 99.77(7)°, Z = 4), cis-(n-Bu 4 N) 2 [ReBr 4 (NCS) 2 ] (2) (triclinic, space group P1̄, a = 11.527(3), b = 20.237(7), c = 22.07(2) Å, α = 110.05(4), β = 93.86(6), γ = 99.49(4)°, Z = 4) and cis-{n- Bu 4 N) 2 [ReBr 4 (NCS)(NCSe)] (3) (triclinic, space group P1̄, a = 11.488(2), b = 20.164(6), c = 22.158(5) Å, α = 110.44(2), β = 93.34(2), γ = 99.626(18)°. Z = 4) have been determined by single crystal X-ray diffraction analysis. Based on these molecular parameters the low temperature (10 K) IR and Raman spectra of the (n-Bu 4 N) salts have been assigned by normal coordinate analysis. The valence force constants are f d (ReN) = 1.70 (1), 1.70 (2) and 1.72 (3), f d (ReBr) = 1.36 (1), 1.30 (2) and 1.36 mdyn/Å (3).

Bis(diphenylphosphanyl)amine (1), the disulfide 1S and diselenide 1Se were selected to show the efficient application of the INEPT-HEED pulse sequence for measuring coupling constants 1 J( 31 P. 15 N) and isotope induced chemical shifts 1 ⊿ 14/15 N( 31 P), both at natural abundance of 15 N, from 31 P NMR spectra. The sign of 1 J( 31 P, 15 N) (> 0) in all three compounds was determined by selective heteronuclear ] 1 H{ 31 P} double resonance experiments.

The synthesis of 16 title compounds and their NMR spectroscopic properties is described. The spectra reveal evidences of the preferred conformation (acetyl group orientation and non-coplanarity) of the aroyl moieties.

Synthesis of 18 1-(2-hydroxyphenyl)-3-α- and -β-naphthylpropan-1,3-diones is described. Their 1 H and 13 C NMR spectra were completely and unambiguously assigned using a combination of both homo- and heteronuclear (gs-COSY ), 1 H -detected heteronuclear one-bond (gs-HMQC ) and long-range (gs-HMBC) correlation experiments. Substituent and conformation effects on the tautomeric equilibria were identified and interpreted in terms of steric and electronic contributions.

Some novel chiral sulfonyl hydantoin derivatives 2a-e and 3 a-e have been prepared. p-Toluenesulfonyl chloride on treatment with L-amino acids in presence of K 2 CO 3 /H 2 O yielded N-(p-toluensulfonyl-)amino acids 1a - e which were cyclized in presence of NH 4 -SCN Ac 2 O to afford 1-(p-toluenesulfonyl)-5-substituted-2-thiohydantoins 2a-e. These compounds were oxidized with HNO 3 to yield 1-(p-toluenesulfonyl)-5-substituted hydantoins 3a-e. The enantiomeric ratios of 3a-e were determined by 1 H NMR spectroscopy using Eu(hfc) 3 . The antidiabetic activity of 3a-d has been determined.

Both title compounds were obtained in stereochemically pure form by refluxing 5,5-dim ethyl-1 ,3-thiazolidine-2,4-dicarboxylic acid (3) with methanolic HCl, followed by a separation of the two diastereomers 4a and 4b on silica gel. The X-ray structure analyses of these stereoisomers confirm the relative configuration to be cis for 4a and trans for 4b with respect to the two carboxymethyl substituents at C(2) and C(4). For both molecules, an envelopetype conformation of the thiazolidine ring was found with C(5)-S(1)-C(2)-N(3) being located in a plane showing a small ring torsion angle of -11.2° and -3.1° for the cis- and the rrafts-epimer, respectively. The trans-configured compound 4b adopts a nearly ideal envelope conformation with C(4) being the flap atom, while the cis-isomer 4a. apparently because of steric interactions of the C(2) and C(4) substituents, shows a twisted envelope conformation.

The inclusion complexes formed from carbon disulfide and p-tert-butylcalix[4]arene ( 1·CS 2 ) or p-tert-butylcalix[6]arene (2·CS 2 ) were investigated by X-ray crystal structure analysis, infrared (IR) and Raman spectroscopy. The complex 1·CS 2 crystallises in the space group P4/n, 2·CS 2 in the space group P2 1 /n. In case of p-tert-butylcalix[4]arene as host the carbon disulfide molecule is included in the cavity. In the crystal structure of p-tert-butylcalix[ 6]arene clathrate, self-complexation of one tert-butyl group in the cavity of another calix[ 6]arene can be observed. Due to inclusion, the symmetry of CS 2 is lowered both in the p-tert- butylcalix[4]arene and p-tert-butylcalix[6]arene case causing significant shifts in the fully assigned infrared and Raman spectra.

1,3-Dipolar cycloaddition reaction of nitrilimines to a variety of 3-aryl-5-arylmethylidene- 3,5-dihydro-2-phenyl-4H-imidazol-4-ones (3) afforded the corresponding 1,3,4,7,8-pentaaryl -1,2,6,8-tetraazaspiro[4.4]-nona-2,6-dien-9-ones (4) and not the regio-isomers 2,3,6,8,9-pentaaryl- 1,3,7,8-tetraazaspiro[4.4]nona-1,6-dien-4-ones (5) in high regioselectivity.

A new triterpenoidal saponin, akebonic acid-3-O-[α-L-rhamnopyranosyl-(1→3)-β-D-glucopyranosyl-( l→3)-α-L-rhamnopyranosyl-(l→2)-β-L-arabinopyranoside], named as guaianin Q (1), was isolated from the n-butanolic extract of the bark of Guaiacum officinale L. The structure of 1 was established with the help of the comparative studies of ID and 2D 1 H - 13 C NMR methods, FABMS, alkaline and acid hydrolyses. In addition to 1, a number of known saponins were also isolated and reported from the same source.

The compounds 4,5-ethylenedithio-1,3-dithiole- 2-thione, 4,5-(methyl) ethylenedithio-1,3-dithiole- 2-thione and 4,5 (dimethyl) ethylenedithio-1,3- dithiole-2-thione were prepared by reaction of 1,3-dithiole-2,4,5-trithione with ethylene, propylene and trans-2-butene, respectively. The preparative and spectroscopic data are identical with those obtained from the corresponding authentic samples.

A diterpenoid, salvipalolide, possessing a new modified abietane skeleton has been isolated from Salvia palaestina. Its structure [12,14-dihy-droxy-7-oxo-2,3-seco-19(4→3)-abeo-4(18), 8,11,13- abietatetraen-2,11-olide] was established by spectroscopic means.