Oxidative-addition to a four-coordinate tin(II) complex supported by octamethyldibenzotetraaza[14]annulene dianion ligation, [η-Me8taa]Sn: The syntheses and structures of [η-Me8taa]SnI2 and *[η-Me8taa]SnI(THF)**I3*

The four-coordinate tin(II) complex [η⁴-Me₈taa]Sn undergoes oxidative addition of I₂ to give six-coordinate [η⁴-Me₈taa]SnI₂, in which the iodide ligands exhibit a trans arrangment. Abstraction of I⁻ from [η⁴-Me₈taa]SnI₂ is facile, as indicated by the rapid formation of the triiodide derivative *[η⁴-Me₈taa]SnI(THF)**I₃* upon treatment with I₂ in the presence of THF. The molecular structures of [η⁴-Me₈taa]SnI₂ and *[η⁴-Me₈taa]SnI(THF)**I₃* have been determined by X-ray diffraction.     

C---H bond activation by rhodium(I) and the mechanism of the olefin isomerization: new synthesis of β,γ-unsaturated ketones via η- or η-alkylallylrhodium(III) complexes by reductive elimination

Acylrhodium(III)-η³-1-ethylallyl complex (7) was prepared by the reaction of 8-quinolinecarboxaldehyde (3) and 1,4-pentadienerhodium(I) chloride (2) by C---H bond activation, followed by hydrometallation, and double bond migration. Higher concentrations of pyridine as coordinating ligand transforms η³-1-ethylallylrhodium(III) complexes (8a,8b) into η¹-pent-2-enylrhodium(III) complex (11a). Acylrhodium(III)-η³-syn,anti-1,3-dimethylallyl complex (14) was also prepared from 1,3-pentadienerhodium(I) chloride (16) and 3. The reductive elimination of acylrhodium(III)-η¹- and -η³-1-alkylallyl complexes by trimethylphosphite gives various β,γ-unsaturated ketones.     

Synthesis, structure and hydrogenation catalytic activity of [Ru3(μ3,η-ampy)(μ,η:η-PhC=CHPh)(CO)6(PPh3) (Hampy = 2-amino-6-methylpyridine)

The compound [RU₃(μ₃,η²- -ampy)(μ₃η¹:η²-PhC=CHPh)(CO)₆(PPh₃)₂] (1) (ampy = 2-amino-6-methylpyridinate) has been prepared by reaction of [RU₃(η-H)(μ₃,η²- ampy) (μ,η¹:η²-PhC=CHPh)(CO)₇(PPh₃)] with triphenylphosphine at room temperature. However, the reaction of [RU₃(μ-H)(μ₃, η² -ampy)(CO)₇(PPh₃)₂] with diphenylacetylene requires a higher temperature (110°C) and does not give complex 1 but the phenyl derivative [RU₃(μ₃,η²-ampy)(μ,η ¹:η² -PhC=CHPh)(μ,-PPh₂)(Ph)(CO)₅(PPh₃)] (2). The thermolysis of complex 1 (110°C) also gives complex 2 quantitatively. Both 1 and 2 have been characterized by0 X-ray diffraction methods. Complex 1 is a catalyst precursor for the homogeneous hydrogenation of diphenylacetylene to a mixture of cis- and trans -stilbene under mild conditions (80°C, 1 atm. of H₂), although progressive deactivation of the catalytic species is observed. The dihydride [RU₃(μ-H)₂(μ ₃,η²-ampy)(μ,η¹:η²- PhC=CHPh)(CO)₅(PPh₃)₂] (3), which has been characterized spectroscopically, is an intermediate in the catalytic hydrogenation reaction.     

A study of η-allyl(η-cyclopentadienyl)- dicarbonylmanganese salts

New substituted η³-allyl(η⁵-cyclopentadienyl)dicarbonylmanganese cations have been prepared as their tetrafluoroborates. They readily add a wide range of nucleophiles yielding η²-alkene(η⁵-cyclopentadienyl)dicarbonylmanganese complexes. Of the latter, in general only those involving terminal alkenes are sufficiently stable to permit ready isolation; otherwise metal-free alkenes are obtained. Regioselectivity in these additions depends on the nucleophile.     

A convenient synthesis of Fe(CO)2(η-S2CNMe2)2 and Fe(η-S2CNMe2)2 from the monodentate dithiocarbamato derivative, [(η-C5H5)(CO)3W(η-SCSNMe2)] and Fe2(CO)9

A high yield synthesis of the carbonyl dithiocarbamato derivative Fe(CO)₂(η²-S₂CNMe₂)₂ and Fe(η²-S₂CNMe₂)₂ by photolysis with visible light of solutions containing Fe₂(CO)₉ or Fe₃(CO)₁₂ and [(η⁵-C₅H₅)(CO)₃W(η¹-SCSNMe₂)] is reported.     

Synthesis and crystal structure of the complex [MoW(OEt)(μ-CH2){μ-C(C6H4Me-4)C(Me)O}(η-C7H7)(η-C2B9H10Me)]

The complex [MoW(μ-CC₆H₄Me-4)(CO)₂(η⁷-C₇H₇)(η⁵-C₂B₉H₁₀Me)] reacts with diazomethane in Et₂O containing EtOH to afford the dimetal compound [MoW(OEt)(μ-CH₂){μ-C(C₆H₄Me-4)C(Me)O}(η⁷-C₇H₇)(η⁵-C₂B₉H₁₀Me)]. The structure of this product was established by X-ray diffraction. The Mo---W bond [2.778(4) Å] is bridged by a CH₂ group [μ-C---Mo 2.14(3), μ-C---W 2.02(3) Å] and by a C(C₆H₄Me-4)C(Me)O fragment [Mo---O 2.11(3), W---O 2.18(2), Mo---C(C₆H₄Me-4) 2.41(3), W---C(C₆H₄Me-4) 2.09(3), Mo---C(Me) 2.26(3) Å]. The molybdenum atom is η⁷-coordinated by the C₇H₇ ring and the tungsten atom is η⁵-coordinated by the open pentagonal face of the nido-icosahedral C₂B₉H₁₀Me cage. The tungsten atom also carries a terminally bound OEt group [W---O 1.88(3) Å]. The ¹H and ¹³C-{¹H} NMR data for the dimetal compound are reported and discussed.     

Übergangsmetallketen-verbindungen : XXIX. Cyclopropylsubstituierte η- und η-Ketenylverbindungen des Wolframs; Elektronenstruktur und Bindungsverhältnisse in Carbonyl(η-cyclopentadienyl)(η-cyclopropylketenyl) (trimethylphosphin)wolfram

Synthesis and spectroscopic data of carbonyl(η⁵-cyclopentadienyl)(η²-cyclopropylketenyl) (trimethylphosphine)tungsten and dicarbonyl(η⁵-cyclopentadienyl)(η¹-cyclopropylketenyl) (trimethylphosphine)tungsten are reported. The electronic structure of, and types of bonding in carbonyl(η⁵-cyclopentadienyl)(η²-cyclopropylketenyl) (trimethylphosphine)tungsten are described.     

Bis(η-pentamethylcyclopentadienyl)-and(ηcyclopentadienyl) (η-pentamethylcyclopentadienyl)-platinium dications: Pt(IV) metallocenes

Reaction of [Pt₂(η⁵-C₅Me₅)₂(η-Br)₃]³⁺(Br⁻)₃ with C₅R₅H (R = H,Me) in the presence of AgBF₄ gives the first platinocenium dications, [Pt(η⁵-C₅Me₅)(η⁵-C₅R₅)]²⁺(BF₄⁻ )₂. On electrochemical reduction, [pt(η⁵-C₅Me₅)₂]²⁺ yields [Pt(η⁴-C₅Me₅H)(η²-C₅Me₅)]+ BF₄⁻. kw]Cyclopentadienyl; Metallocenes; Platinum; Electrochemistry     

Wasserstoff-wanderungen in organometall-verbindungen: Die thermisch induzierte isomerisierung des (η-cyclopentadienyl)(η-1,1-dimethylallyl)(η-isopren)-zirconiums

Treatment of CpZrCl₃ with 3-methylbutenyl-Grignard reagent yields thermally labile tris(1,1-dimethylallyl) ZrCp (6), which is slowly decomposed (5d) at −15°C to give (η-cyclopentadienyl)(η³-1,1-dimethylallyl)(η⁴-isoprene)zirconium (7), which is thermally unstable; with a half-live of 43 h at 20°C it rearranges to the η₃-1,2-dimethylallyl isomer and an (isoprene) zirconium hydride is proposed as the intermediate for this hydrogen-migration reaction.     

Stereoselective synthesis of 3-amino-4-substituted-2-azetidinones via [2+2] cycloadditions of tricarbonyl(ηarene)chromium(0)complexed imines

The stereoselective [2+2] cycloaddition reaction between the chiral tricarbonyl(η⁶arene) chromium(0) complexed imines 1 and 6 and phthalimidoketene affords tricarbonyl (η⁶arene)chromium(0) complexed 3-phthalimido-2-azetidinones 3, 7 and 8, both in racemic and enantiopure form. Decomplexation and the cleavage of the phthalimido group give 3-amino-4-substituted-2-azetidinones 5 and 10. Some insights into the stereochemical outcome of the [2+2] cycloaddition process are discussed.     

Vibrational spectroscopic detection of H-bonded β- and γ-turns in cyclic peptides and glycopeptides

The conformation of N-glycoproteins and N-glycopeptides has been the subject of many spectroscopic studies over the past decades. However, except for some preliminary data, no detailed study on the vibrational spectroscopy of glycosylated peptides has been published until recently.

This paper reports FTIR spectroscopic properties in DMSO and TFE of the N-glycosylated cyclic peptides cyclo[Gly-Pro-Xxx(GlcNAc)-Gly-δ-Ava] 3a and 3b in comparison with data on the non-glycosylated parent peptides cyclo(Gly-Pro-Xxx-Gly-δ-Ava) 2a and 2b [a, Xxx = Asn; b, Xxx = Gln; δ-Ava = NH-(CH₂)₄-CO] and N-acetyl 2-acetamido-2-deoxy-β- -gluco pyranosylamine (GlcNAc-NHAc, 4). The assignment of amide I band frequencies to conformation is based on ROESY experiments and determination of the temperature coefficients in DMSO-d₆ solution. (For the synthesis and NMR characterization of 2a and 3a see Ref. [19].)

Cyclic peptides are expected to adopt folded (β- and/or γ-turn) conformations which may be fixed by intramolecular H-bonding(s). A comparison of the temperature coefficients of the NH protons and amide I band frequencies and intensities suggests that in DMSO there is no significant difference in the backbone conformation and H-bond system of the N-glycosylated models and their parent cyclic peptides. The common feature of the backbone conformation of models 2 and 3 is the predominance of a 1 ← 4 (C₁₀) H-bonded type II β-turn encompassing Pro-Xxx or Pro-Xxx(GlcNAc), respectively. The ROESY connectivities in the Asn(GlcNAc) model (3a) have not been found to reflect intramolecular H-bondings between the peptide and the sugar.

The unique feature of the FTIR spectra in DMSO of the cyclic models is the lack or weakness of low-frequency (< 1640 cm⁻¹) amide I component bands. In TFE the amide I region of the FTIR spectra shows an increased number of components below 1650 cm⁻¹ reflecting a mixture of open and H-bonded β- and γ-turn conformers.

Because of its destabilizing effect upon γ-turns and other weakly H-bonded structures, DMSO decreases the number of backbone conformers. DMSO also destroys side-chain-backbone H-bondings of type C₇, C₆ or C₈. Possible ‘glyco’ C₇ H-bondings in GlcNAc-NHAc (4) or in glycopeptides 3a and 3b cannot resist the effect of DMSO either.

The FTIR data in TFE of models 2–4 suggest that the acceptor amide group of strong C₇ H-bondings in peptides and glycopeptides absorbs at 1630 ± 5 cm⁻¹ and that of bifurcated H-bondings between 1600–1620 cm⁻¹.     

Synthese en serie dedoublee d''un precurseur tricyclique du nor-18 methyl-8β-oestradiol

A diastereoisomeric mixture of cis- and trans-(10aR)- 7-hydroxy-10a-methyl-1-oxo-1,2,3,4,4a,9,10,10a-phenanthrene was synthesised from 2-methyl-1,3-cyclohexanedione. The enantiomers were separated at an early stage in the synthesis via a cyclohexane-carboxylic acid intermediate and no racemisation or inversion occurred at any step. The products are precursors of 8β-methyl 18-nor estradiol and of 8β-méthyl 18-nor 9β-estradiol respectively.     

Stabile Bis(η-alkin)MCl2-komplexe; Darstellung und reaktivität

The synthesis and reactivity of {(η⁵-C₅H₄SiMe₃)₂Ti(CCSiMe₃)₂} MCl₂ (M = Fe: 3a; M = Co: 3b; M = Ni: 3c) is described. The complexes 3 are accessible by the reaction of (η⁵-C₅H₄SiMe₃) ₂Ti(CSiMe₃)₂ (1) with equimolar amounts of MCl₂ (2) (M = Fe, Co, Ni). 3a reacts with the organic chelat ligands 2,2′-dipyridyl (dipy) (4a) or 1,10-phenanthroline (phen) (4b) in THF at 25°C to afford in quantitative yields (η⁵-C₅H₄SiMe₃)₂Ti(CSiMe₃)₂ (1) and [Fe(dipy)₂]Cl₂ (5a) or [Fe(phen)₂]Cl₂ (5b). 1/n[Cu^IHal]_n (6) or 1/n[Ag^IHal]_n (7) (Hal = Cl, Br) react with {(η⁵ -C₅H₄SiMe₃)₂Ti(CCSiMe₃)₂}FeCl₂ (3a), by replacement of the FeCl₂ building block in 3a, to yield the compounds {(η⁵-C₅H₄SiMe₃)₂Ti(C CSiMe₃)₂}Cu^IHal (8) or {(η⁵-C₅H₄SiMe₃)₂Ti(CSiMe₃)₂}Ag^IHal (9) (Hal = Cl, Br), respectively. In 8 and 9 each of the two Me₃SiCC-units is η²-coordinated to monomeric Cu^I Hal or Ag^IHal moieties. Compounds 8 and 9 can also be synthesized by the reaction of (η⁵-C₅H₄SiMe₃)₂ Ti(CSiMe₃)₂ (1) with 1/n[Cu^IHal]_n (6) or 1/n [Ag^IHal]_n (7) in excellent yields. All new compounds have been characterized by analytical and spectroscopic data (IR, ¹H-NMR, MS). The magnetic moments of compounds 3 were measured.     

Small angle X-ray scattering from lamellar phase for β-3,7-dimethyloctylglucoside/water system: comparison with β-n-alkylglucosides

Small angle X-ray scattering (SAXS) is measured for the lamellar phase in aqueous systems of 1-o-β-3,7-dimethyoctyl-D-glucopyranoside (β-Glc(Ger)), which has recently been prepared by us, 1-o-β-decyl-D-glucopyranoside (β-GlcC₁₀), and 1-o-β-octyl-D-glucopyranoside (β-GlcC₈). The repeat distance d obtained from the position of the diffraction peak does not follow the swelling law d = 2δ_hc/_hc, where δ_hc and _hc are the thickness and the volume fraction of the hydrophobic layer, respectively. This may result from the fact that δ_hc increases and, equivalently, the surface area per surfactant molecule (a_s) decreases with increasing concentration. So we calculate δ_hc and a_s from the observed d value at each concentration using the above swelling law. The half-thickness δ_hc increases in the order β-GlcC₈ < β-Glc(Ger) < β-GlcC₁₀ at a fixed concentration. On the other hand, the data on a_s for β-GlcC₁₀ and β-GlcC₈ lie on the same line and the data for β-Glc(Ger) lies above this line. These results suggest that the cross-sectional area of the geranyl chain is larger than that of the glucose headgroup. Existence of water filled defects in bilayer sheets is also discussed based on the SAXS pattern and the concentration dependence of d.     

π-Olefin-Iridium-Komplexe : XXI. Synthese und Kristallstrukturen heterobinuclearer Komplexe mit wannenförmiger, synfacial gebundener η: η-Benzolbrücke

CpIr(η⁴-C₆H₆) (2) has been obtained in high yield by a four-step synthesis. Thermal reaction of 2 with CpCO(C₂H₄)₂ and photochemical reaction of 2 with CpRh(C₂H₄)₂ or CpRh(C₂H₄)₂ give the compounds μ-(η³: η³-C₆H₆)CoIrCp₂ (3), μ-(η³: η³-C₆H₆)RhIrCp₂ (4), and μ-(η³: η³-C₆H₆)(RhCp)(IrCp) (5), respectively. The X-ray crystallography data of 3 and 4 reveal a boat-shaped conformation of the synfacially bridging benzene ligand with a rather long Co---Ir bond distance in 3 and a relatively short Rh---Ir bond length in 4 which are caused by almost constant folding angles of the benzene unit. The dynamic behaviour of the benzene bridge was investigated by NMR spectrometry.     

Excimer fluorescence in β-9,10-dichloroanthracene crystals

The fluorescence of single crystals of β-9,10-dichloroanthracene at 4.2 K consists solely of excimer emission (τ = 95 ± 5 ns). The absence of monomenc emission shows that excimer formation in this crystal is not a thermally activated process. This result is confirmed by excimer-excimer annihilation studies (γ(4.2 K) = 6 × 10⁻¹³, γ(298K) = 3 × 10⁻¹² cm³ s⁻¹).     

Theoretical studies on the aromaticity of η-cyclopentadienyl cobalt dithiolene complexes

Some η⁵-cyclopentadienyl cobalt dithiolene complexes CpCoS₂C₂R₂ have been optimized at B3LYP/6-311++G(d) level. The optimized geometries agree well with experiment. The analyses of nature bond orbital and nucleus-independent chemical shift (NICS) at B3LYP/6-311++G(d) and GIAO-B3LYP/6-311++G(d) levels reveal the aromatic character of the η⁵-cyclopentadienyl cobalt dithiolene complexes. However, their aromaticity is weaker than that of the isolated . There are two reasons for the change of heterocyclic aromaticity of the metal dithiolene in the η⁵-cyclopentadienyl cobalt dithiolene complexes with respect to that of the isolated . The better equalization of bond lengths in the isolated cation is the first reason. The other reason is that the contribution to the NICS from the metallic cobalt atom is much larger in the isolated cation . The planar character of cyclopentadienyl is destroyed slightly in the complexes. At the same time, the size of cyclopentadienyl (Cp) becomes bigger than the isolated Cp⁻¹ and this is caused by the cobalt atom in the pentagon. The π-electron delocalization causes stronger aromaticity of the Cp in the complexes than that of the isolated Cp⁻¹.     

Synthesis and transformation of novel cyclic β-amino acid derivatives from (+)-3-carene

The regio- and stereoselective addition of chlorosulfonyl isocyanate to (+)-3-carene 1 resulted in β-lactam 2, which was converted to N-Boc-β-amino acid 4, β-amino ester 7, and carboxamide derivatives 18 and 20 via N-Boc activation and mild ring opening. The corresponding β-amino ester 7 was transformed to 2-thioxopyrimidin-4-one 11 and 2,4-pyrimidinedione 13. LAH reduction of 5 and 7 resulted in amino alcohols 6 and 8. The reaction of 8 with phenyl isothiocyanate, followed by cyclisation, furnished 1,3-oxazine 15.     

First examples of η- and η --- η-coordination in triphosphorus analogues of ferrocene. Crystal structure of the iron sandwich complex [Fe(η-C5H5) (η-C2R2P3)W (CO)5] (R = Bu)

Syntheses of the novel sandwich compounds [Fe(η⁵-C₅H₅)(η⁵-C₂R₂P₃)] and [Fe(η⁵-C₅H₅)(η⁵-C₂R₂P₃)W(CO)₅], (R = Bu^t), are described. The mode of attachment of the [W(CO)₅] fragment in the latter compound has been determined by NMR and single crystal X-ray diffraction studies.     

Synthesis of 2-hydroxy-6-{[(16R)-β-δ-mannopyransyloxy]heptadecyl}benzoic acid, a fungal metabolite with GABAA ion channel receptor inhibiting properties

An expeditious total synthesis of the physiologically active fungal metabolite 1 is described. The stereoselective formation of its β-δ-mannopyranosidic linkage is achieved in two steps upon reaction of the hexopyranos-2-ulosyl bromide 15 with the glycosyl acceptor 13, followed by reduction of the resulting β-δ-glycos-2-uloside 16. Alcohol 13 was efficiently prepared via a Suzuki reaction of the aryltriflate 11 with the 9-alkyl-9-BBN derivative 10.