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The crystal structures of the allylic stannanes cyclohex-2-enyl- (1) and cyclohept-2-enyltriphenylstannanes (2) have been determined, and in both, the coordination about tin is tetrahedral, although the enlargement of the zC(13)-Sn-C(19) angle in both 1 (114.4°) and 2 (117.0°) may be in response to a short intramolecular contact between one phenyl ring and the cycloalkene moiety. The Sn-C(phenyl) bond lengths are normal (2.144 ± 0.005 A), but the allyl bond (Sn-C(19) = 2.185 ± 0.005 A) is longer (ca. 0.04-0.05 A) than the normal Sn-C (aliphatic) bond length (2.13 ± 0.01A) and may be associated with a hyperconjugative σC-Sn -πEffect. In 1, the (CH)Sn group formally occupies a quasi-equatorial orientation with a Sn-C(19)-C(20)-C(21) torsion angle of 121° which permits substantial σ-π interaction and may best accommodate other interactions in the crystal. Given the other values of bond and torsion angles, the actual distinction between quasi-axial and quasi-equatorial orientations with respect to double bond interaction with δ is a fine one. The molecular geometry of 2 is a slightly distorted chair arrangement with the (CH)Sn group clearly occupying a quasi-axial position with a Sn-C(19)-C(25)-C(24) torsion angle of 90°, the most favored for σ-π interaction. However, this “outward splaying” of the C-Sn bond is probably also associated with relief of interactions between Sn(CH) and the regions of C(21) and C(23). Solid-state (MAS) C NMR spectra have been recorded of both 1 and 2, and although only one set of signals was observed for each, Sn-C couplings were not located. H and C NMR spectra for 1 and 2 (in solution) have been obtained, and for 1 there is now a preponderance of the conformer with an axially disposed tin group, whereas for 2, the solution conformation is adequately described as a distorted chair arrangement with a quasi-axial Sn(CH) group, as identified in the crystal.

The crystal structures of (C 6 H 11 ) 2 SnCl 2 ( A ) and (C 6 H 11 ) 2 SnBr 2 ( B ) have been determined. The compounds are isomorphous, and the molecules have nearly the same geometry. In both cases the coordination can be regarded as tetrahedral on the basis of the geometrical parameters. The data are critically analysed with that published for analogous compounds.

The cycloaddition of (E)-1,2-bis(benzenesulfonyl)ethylene (2) to 2-acetoxy- and 2-silyloxy-1,3-cyclodienes occurs in high yields and with high steroselectivity. Structure assignment has been based largely on 1H nmr nuclear Overhauser effect (nOe) experiments on the isolated products. The cycloadducts 4a and 4b derived from the 2-oxa substituted cyclopentadienes have been further elaborated to the parent norbornenone, to the respective unsaturated sulfones 5, and to the β-hydroxy substituted sulfone 6. The vinyl sulfones 5 have also been independently synthesized via cycloaddition of benzenesulfonyl acetylene. The sulfones obtained are potentially important starting molecules for the preparation of more complex targets.

An analysis of the preferred conformations and modes of self-association of the N-fluoren-9-methoxycarbonyl derivatives of L-alanine and α-aminoisobutyric acid was performed in solution and in the solid state using infrared absorption, 1H nuclear magnetic resonance, and X-ray diffraction. In a solvent of low polarity (deuterochloroform) non-associated and self-associated species (involving predominantly the hydroxyl and carbonyl groups of the carboxylic acid moiety) simultaneously occur. At high dilution, where self-association is absent, the amount of intramolecularly H-bonded forms, if any, should be extremely small. Z(trans) [Formula: see text]E(cis) isomerism about the amide bond of the secondary urethane moiety was observed only for the less bulky L-alanine derivative. In the solid state all H-bonding donors and acceptors of the L-alanine and α-aminoisobutyric acid derivatives take part to complex schemes of intermolecular H-bonds. In the L-alanine derivative, crystallized as monohydrate, most of the intermolecular H-bonds involve the water molecule. Intramolecular H-bonds are not observed in either compound. The conformation about the secondary urethane CO—NH bond is Z(trans) in both compounds. Both L-alanine and α-aminoisobutyric acid residues are partially folded. The observation of the long C(sp3)—O bond of the fluoren-9-yl-methoxycarbonyl moiety might contribute to explain the unexpected experimental result that this protecting group can be removed by catalytic hydrogenation.

The structure of 1,10-phenanthrolinedichlorodi-n-butyltin has been determined by X-ray analysis. The compound crystallizes in the space group P 2 1 2 1 2 1 with a 10.785(5), b 11.017(5), c 18.163(12) A and Z = 4. It consists of distorted octahedral units of (C 12 H 8 )(C 4 H 9 ) 2 SnCl 2 with trans configuration. The structure and the Mossbauer behaviour are compared with those of similar compounds.

Reaction of the cationic complex[Ni(C6Cl5)(CH3CN)L2]+ (L = PPh2Me) with β-dicarbonyls (diketones and ethyl-2-oxo-butanoate) in the presence of NEt3 affords the neutral complexes [Ni(C6Cl5)(β-carbonylenolate)L]. A more convenient synthesis of analogous complexes was found in the reaction of trans-[Ni(Cl)(C6Cl5)L2] (L = PPhMe2, PMe3) and [Tl(β-carbonylenolate)]derivatives. The isolated complexes have been characterized by 1H, 31P and 13C NMR and IR spectroscopies. They exhibit a square planar geometry in which the β-carbonylenolate acts as O,O′-chelating ligand; complexes with unsymmetrically substituted β-ketoenolates give rise in solution to mixtures of geometrical isomers. A single crystal X-ray structure of the ketoester derivative, [Ni(C6Cl5)(CH3C(O)CHC(O)OEt)(PPh2Me)], shows that the isomer bearing the ester carbonyl group trans to the phosphine is the only one present in the solid state. The crystal is monoclinic, space group P21/n, Z = 4 and the cell dimensions are a = 13.332(4), b = 23.799(6), c = 8.674(3) A, β = 97.2(3)°.

The crystal structure of dichloro-S,S′bis(O-methylcysteinato)tin(IV), Cl2Sn{SCH2CH(NH2)-CoOMe}2, has been solved by a three-dimensional Patterson synthesis: the crystals are orthorhombic, space group P212121, with cell parameters a = 16.621(9), b = 9.843(5), c = 10.323(5) A, Z = 4, refined to R = 0.0356 for 1715 observable reflections. The tin is coordinated to two cis-nitrogen and two trans- sulphur atoms from the O-methylcysteinato ligands, and to two cis- chlorine atoms, in an approximately octahedral arrangement. The bond distances in the tin coordination sphere are: SnCl 2.445 A, SnS 2.434 A and 2.446 A, and SnN 2.264 A and 2.309 A. This structure is compared with those of other octahedral cis-Cl2Sn(L2)2 complexes and the results of anti-tumour tests on these derivatives are reported. The lack of anti-tumour activity exhibited by the title compound may be associated with the large (99.4°) cisClSnCl bond angle.

The crystal structure of hexagonal polythiomethylene is described. It has a hexagonal unit cell with a = 5.07 A. and c = 36.52 A. The polymer chains are helicoidal with the axis of the helix parallel to c. In the unit cell are comprised 17 CH2Sunits and 9 turns of the helix. Die Kristallstruktur des hexagonalen Polythiomethylens wird beschrieben. Es hat eine hexagonale Elementarzelle mit a = 5,07 A und c = 36,52 A. Die Ketten liegen in der Form von Helices vor, wobei die Schraubenachse parallel zu c verlauft. Die Elementarzelle enthalt 17 CH2SEinheiten bei 9 Schraubengangen der Helix.

The reaction between N-alkylisocyanoacetamides and arylsulfenyl chlorides affords arylcarbonimidochloridothioates which on treatment with triethylamine undergo ring-closure to give 3-alkyl-2-arylthio-1,3-diazolium-4-olates

The Diels–Alder cycloaddition of activated vinyl sulphoxides (1), that are readily obtained by a self-induced chiral oxidation, proceeds highly diastereoselectively to form the corresponding cycloadducts (4) that can be converted into 2-substituted norbornadienes(5) of high enantiomeric purity.

The structure of the compound Sn(CH3)2Cl2(H2O)2·4C5H4N4 has been determined by single-crystal X-ray diffraction methods. The compound crystallizes in the monoclinic system, space group P21/a, with unit-cell dimensions a= 11.218(4), b= 18.374(5), c= 7.193(3)A, β= 101.9(4)°, and Z= 2. The structure is centrosymmetric at the all-trans Sn(CH3)2Cl2(H2O)2 octahedral units, which are surrounded by four purine molecules hydrogen bonded to the H2O ligands. Each purine also makes hydrogen bonds with purines adjacent to different Sn(CH3)2Cl2(H2O)2 units to form a three-dimensional network. The purine molecules are present in tautomeric pairs: in one isomer a hydrogen atom is attached to the atom N(7) of the imidazole ring, as found in crystals of free purine, and in the other one to the atom N(9). Proton n.m.r. measurements on the system Sn(CH3)2Cl2–purine in acetone show that also in solution direct co-ordination of the base to tin does not occur.

The structure of Sn(CH3)2Br2·C4H6N2S [C4H6N2S = 1 -methyl-2(3H)-imidazolinethione] consists of trigonal-bipyramidal molecules held together in pairs by two N–H ⋯ Br hydrogen bonds. The ligand is bonded to the metal through the sulphur atom. The bromine atoms occupy apical positions with a greater Sn–Br bond length for the hydrogen-bonded atom. The mass spectra of Sn(CH3)2Br2·C4H6N2S and Sn(CH3)2Cl2·C4H6N2S show a much lower tendency for the bromine complex to form ions containing the deprotonated ligand through elimination of hydrogen halide.

Deprotonation of indene–tricarbonylchromium with KH in tetrahydrofuran at –40 °C gives the η6-tricarbonylchromium–indenyl anion which reacts with [Rh(CI)COD]2(COD = cyclo-octa-1,5-diene) to form [η6-Cr(CO)3-indenyl-η3-rhodium-η4- COD]; the same bimetallic complex is obtained by reaction of the rhodium dimer with the isomeric η5-indenyl-tricarbonylchromium anion.

Me 2 Sn(NCS) 2 (OH 2 ) 2 . 18-crown-6 cristallise dans P2 1 /n avec Z=2; affinement jusqu'a R=0,058

The structure of the title compound has been determined by X-ray analysis using direct methods. The compound crystallizes in the space group Pna21 with a= 13.874, b= 13.822, c= 9.914 A, Z= 4, and R= 0.029 for 1 648 independent reflections. It consists of discrete [(MeHN)2CS]22+ and TeCl62– ions. The co-ordination of the Te atom is distorted octahedral with the Te–Cl distances ranging from 2.420 to 2.740 A.

From the reaction mixture of benzyloxycarbonyl chloride and a-aminoisobutyric acid three crystalline compounds were isolated and characterized by chromatographic and spectroscopic techniques and Xray diffraction. Two of them are polymorphic forms of the N-protected amino acid, which differ in the orientation of the phenyl ring relative to the urethane moiety and in the packing modes of the molecules, including the intermolecular hydrogen- bonding arrangements. The third compound is the N-protected dipeptide, the formation of which is not unexpected in the synthesis of the N- benzyloxycarbonyl amino acid derivative. The crystal structure of the symmetric carboxylic anhydride from the N-protected amino acid, a reasonable reactive intermediate in the formation of the N-protected dipeptide, is also described.

Acetoacetamides add quantitatively to cyanogen in aprotic media at ambient conditions in the presence of [M(acac)2](M = Cu or Ni; acac = acetylacetonate) complexes to give selectively 1 : 1 addition compounds. Products are amidic cyanoenaminones which can be converted thermally both in solution and in solid state into pyrrolinic cycloisomers. A variety of physicochemical methods including X-ray analysis, thermal analysis, 13C n.m.r. and 1H n.m.r. has been employed for characterizing the new compounds and monitoring the isomerization reactions.

The crystal structures of 1-aminocyclohexane-1-carboxylic acid (H-Acc6-OH) and six derivatives (including dipeptides) have been determined. The derivatives are Boc-Acc6-OH, Boc-(Acc6)2-OH, Boc-L-Met-Acc6-OMe, ClCH2CO-Acc6-OH, p-BrC6H4CO-Acc6-OH oxazolone, and the symmetrical anhydride from Z-Acc6-OH, [(Z-Acc6)2O]. The cyclohexane rings in all the structures adopt an almost perfect chair conformation. The amino group occupies the axial position in six structures; the free amino acid is the only example where the carbonyl group occupies an axial position. The values determined for the torsion angles about the N–Cα(φ) and Cα–CO (ψ) bonds correspond to folded, potentially helical conformations for the Acc6 residue.

The macrocyclic complex (2,3:9,10-dibenzo- 5,7,1 2,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca- 2,4,6,9,11,13-hexaenato(2−)- k4N)nickel(II), [Ni(Bzo2Me4[14]hexaenatoN4)] reacts with cyanogen under mild conditions to give addition-insertion to the methine CH group. The two resulting complexes are characterized by one or two cyanoimino methyl C(NH)CN substituents, from which HCN can be easily released to give the corresponding cyano derivatives. The mono cyano complex [Ni(Bzo2(CN)Me4 [14]hexaenatoN4)] crystallizes in the monoclinic system (space group P21/n) and has a saddle-shaped structure, in which the benzene and β-diiminato groups are tilted in opposite directions, with respect to the plane defined by the four nitrogen and the nickel atoms (CN bond distance 1.141(14) A).

A crystal-state structural analysis of Boc-Pro-Leu-Gly-NH2(2a) hemihydrate and two conformationally restricted analogues that incorporate a γ- or δ-lactam modification at the –Leu-Gly– sequence, (3) and (4) respectively, has been performed by X-ray diffraction. In all three compounds the conformation of the tertiary amide group of the Nα-protecting urethane moiety is cis and the prolyl residue is semi-extended. The basic conformational feature of the published structure of H-Pro-Leu-Gly-NH2(1), the ten-membered ring type-II β-bend structure at the C-terminus, is preserved in the Nα-t-butyloxycarbonyl derivative (2a). However, the γ- and δ-lactam modifications induce drastic changes in the backbone torsion angles of the –Leu-Gly– sequence, eventually promoting the onset of extended conformations.

Imines (1) cycloadd to cyclopentadiene and Indene to afford substituted tetrahydroquinolines with high diastereoisomeric (corresponding to enantiomeric) selectivity when (–)-8-phenylmenthol is used as a chiral auxiliary. Solvent polarity and temperature greatly affect the diastereoisomeric ratios.

Traces of water induce OH substitution of one of the CN groups in 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ), during complexation of DDQ with amidopyridines, while simple hydrolysis of DDQ leads to the corresponding ammonium salt.

The x-ray diffraction analysis of the N-benzyloxycarbonyl homo-tripeptide from α-amino-isobutyric acid has shown the occurrence of an incipient 310-helix characterized by one type-III (or type-III′) β-bend followed by one oxy-analog of the same type of β-bend. This represents the first unequivocal observation of the latter conformation, where the O—H group of the COOH moiety present at the C-terminus of the peptide main chain plays the role of the hydrogen-bonding donor. These results have been compared with those of the same peptide in its monohydrate form and of its methyl ester derivative, the x-ray diffraction structures of which are also described here.

The crystal structure of rubidium pentabromodistannate(II) (RbSn2Br5) is determined. The crystals are tetragonal and contain four formula units in a cell of dimensions α = 8.442(2) A, and c = 14.754(3) A with Dc = 4.54 g cm−3, and Dm = 4.44 g cm−3. The structure was solved in the space group I 4 mcm . Unlike NaSn2F5, which contains discrete [Sn2F5]− ions, the structure is a layered lattice consisting of two-dimensional polymeric (Sn2Br5)n−n layer units separated by Rb ions. The Sn and bridging Br atoms lie in planes perpendicular to the c-axis at c = 0 and c = 1 2 . Each Sn atom is surrounded by two bridging Br atoms, at 3.105(1) A, in the plane of the polymer network and by two terminal Br atoms, at 2.755(3) A, symmetrically above and below the network plane. The bridging Br atoms are surrounded by four equatorial Sn atoms and by two axial Rb atoms in the direction of the c-axis at 3.688(1) A. The positions of the non-bonding orbitals on the Sn(II) atoms suggest that the lone pairs could be partly delocalized within the polymeric network. The 119Sn Mossbauer data for RbSn2Br5 are interpreted in the light of its structural data.

Reaction of the cationic complex[Ni(C6Cl5)(CH3CN)L2]+ (L = PPh2Me) with β-dicarbonyls (diketones and ethyl-2-oxo-butanoate) in the presence of NEt3 affords the neutral complexes [Ni(C6Cl5)(β-carbonylenolate)L]. A more convenient synthesis of analogous complexes was found in the reaction of trans-[Ni(Cl)(C6Cl5)L2] (L = PPhMe2, PMe3) and [Tl(β-carbonylenolate)]derivatives. The isolated complexes have been characterized by 1H, 31P and 13C NMR and IR spectroscopies. They exhibit a square planar geometry in which the β-carbonylenolate acts as O,O′-chelating ligand; complexes with unsymmetrically substituted β-ketoenolates give rise in solution to mixtures of geometrical isomers. A single crystal X-ray structure of the ketoester derivative, [Ni(C6Cl5)(CH3C(O)CHC(O)OEt)(PPh2Me)], shows that the isomer bearing the ester carbonyl group trans to the phosphine is the only one present in the solid state. The crystal is monoclinic, space group P21/n, Z = 4 and the cell dimensions are a = 13.332(4), b = 23.799(6), c = 8.674(3) A, β = 97.2(3)°.

C 16 N 40 N 2 ReCL 6 cristallise dans C2/c avec affinement jusqu'a 0,052. C 6 H 20 N 2 ReCl 6 cristallise dans P2 1 /n avec affinement jusqu'a 0,029. C 2 H 10 N 2 ReCl 6 cristallise dans P1 avec affinement jusqu'a 0,055