Synthesis of endoperoxides derived from cyclooctatetraenes via singlet oxygenation

Cyclooctatetraene (1) reacted with photo-generated singlet oxygen to give the endoperoxide 7,8-dioxabicyclo[4.2.2]deca-2,4,9-triene (1a), which was further transformed to the cis-diepoxide 1b by catalytic rearrangement with Co-TTP to the unsaturated cis-diol 1c and the saturated cis-diol 1d by catalytic hydrogenation, to the saturated endoperoxide 1e by reaction with diimide, and to the epoxycyclooclatetraene If by deoxygenation with dimethylphosphine. Similarly, the methoxy-, phenyl- and methyl-substituted cyclooctatetraenes 3-5, respectively, gave the corresponding endoperoxides with the substituents located at the 1-position (3a, 5a), the 2-position (5b) and the 9-position (3b, 4a). Their structures were determined on the basis of their ¹H- and ¹³C-NMR data and by means of chemical transformation to the corresponding syn-diepoxides, i.e. 5,10-dioxatricyclo[7.1.0.0^4,6]deca-2,7-dienes. The formation of the endoperoxides is postulated to involve an electron transfer mechanism to give the radical cation of cyclooctatetraene and the superoxide ion. The latter couples into the homotropylium-type zwitterionic intermediate and subsequent cyclization leads to the endoperoxides.     

Petits cycles—XL: Sur le mecanisme de formation des hydroperoxydes allyliques dans la reaction de l'oxygene singulet avec les vinylcyclopropanes

The different parameters of the dye-sensitized photooxygenation of vinylcyclopropanes are studied. Solvent and isotopic effects measured in the case of 1,1-dicyclopropylethylenes 1–3 and Hammett plots measured in the case of α-cyclopropylstyrenes 5–10 (?= ?1,0) reveal no special reactivity of these olefins with singlet oxygen compared to classical olefins. The results suggest that hydrogen abstraction is not the kinetic step of the process. In contrast a clear regio- and stereo-control has been found in photooxygenation of heterosubstituted vinylcyclopropanes 11–14(methyl enol ether isomers Z, E). This result reinforces the idea of an intermediate in the addition of singlet oxygen to olefins leading to allylic hydroperoxides.     

Structures of the tricyclododecenes prepared by the catalytical intramolecular cyclisation of 1,5,9-cyclododecatriene

The internal cyclisation of 1,5,9-cyclododecatriene, induced by a catalytical amount of Cp₂TiCl₂-LAHδ, leads to a mixture of cis, anti, cis-tricyclo[7.3.0.0^2,6]-7-dodecene (1), cis,syn,trans-tricyclo[7.3.0.0^2,6]-7-dodecene (2), trans,syn-tricyelop[7.3.0.0^2,6]-6-dodecene (3) and 5,6,7,8,9,10-hexahydrobenzocyclooctene (4). The structures of the main products were determined from the spectra of a number of derivatives taking into account symmetry properties and configurational flexibility.     

Aminobis(phenolate)s of imidomolybdenum(VI) and -tungsten(VI)

The reactions of trans-[MoO(ONO^Me)Cl₂] 1 (ONO^Me = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) dianion) and trans-[MoO(ONO^tBu)Cl₂] 2 (ONO^tBu = methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate) dianion) with PhNCO afforded new imido molybdenum complexes trans-[Mo(NPh)(ONO^Me)Cl₂] 3 and trans-[Mo(NPh)(ONO^tBu)Cl₂] 4, respectively. As analogous oxotungsten starting materials did not show similar reactivity, corresponding imido tungsten complexes were prepared by the reaction between [W(NPh)Cl₄] with aminobis(phenol)s. These reactions yielded cis- and trans-isomers of dichloro complexes [W(NPh)(ONO^Me)Cl₂] 5 and [W(NPh)(ONO^tBu)Cl₂] 6, respectively. The molecular structures of 4, cis-6 and trans-6 were verified by X-ray crystallography. Organosubstituted imido tungsten(VI) complex cis-[W(NPh)(ONO^tBu)Me₂] 7 was prepared by the transmetallation reaction of 6 (either cis or trans isomer) with methyl magnesium iodide.     

A concise and stereospecific synthesis of some cyclitols containing eight-membered rings: cyclooctane-1,2,3,4-tetraoles

A concise and efficient synthesis of cyclooctane-1,2,3,4-tetraoles, new polyhydroxylated eight-membered carbocycles, is described starting from cis,cis-1,3-cyclooctadiene. Cyclooctene endoperoxide obtained by photooxygenation of cis,cis-1,3-cyclooctadiene was the key compound in the synthesis. Reduction of the endoperoxide with zinc or thiourea followed by acetylation of the hydroxyl group and OsO₄/NMO oxidation of the double bond gave (1R(S),2S(R),3R(S),4S(R))-cyclooctane-1,2,3,4-tetraol. Interestingly, epoxidation of cyclooctene-1,4-diol with m-CPBA also afforded trans-epoxy-diol 17. (1R(S),2R(S),3R(S),4S(R))-cyclooctane-1,2,3,4-tetraol was easily obtained by hydrolysis of epoxy-diol 17.     

Synthesis and structure of some cis-and trans-myrtanylstannanes

Enantiomerically pure cis- and trans-myrtanylstannanes cis-MyrSnPh₃ (1), trans-MyrSnPh₃ (2), cis-MyrSnPh₂Cl (3), trans-MyrSnPh₂Cl (4), cis-MyrSnPhCl₂ (5), trans-MyrSnPhCl₂ (6), cis-MyrSnCl₃ (7), trans-MyrSnCl₃ (8) were synthesized and fully characterized by ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. The molecular structures of 1, 3, 6, 7, and [trans-MyrSn(OH)Cl₂ · H₂O]₂ (8a) a hydrolysis product of 8, were determined by X-ray crystallography.     

Stereoisomerism in the representative tetracyclic dispiro ozonide derived from (methylene)dicyclohexanone with the 1,5-diketo arrangement

The conditions and reasons for the stereoselective transformation of the rac form of 2,2′-(methylene)-dicyclohexanone into the meso- or rac-diastereomer of tetracyclic dispiro ozonide (1,2,4-trioxolane) in the reaction with 30% aqueous H₂O₂ in the presence of acid have been determined. A mechanism for the stereoisomerization of ozonides was proposed, and the stereochemistry of diastereomeric ozonides was established by NMR data.     

The photochemical preparation of ozonides by electron-transfer photo-oxygenation of epoxides

9,10-Dicyanoanthracene (DCA) sensitizes the electron-transfer photo-oxygenation of epoxides in oxygen-saturated acetonitrile to form ozonides. Epoxides with oxidation potentials lower than 2 V vs SCE quench the fluorescence of DCA and are converted to the ozonides with DCA alone. Epoxides which do not quench the singlet excited state of DCA are unreactive under these conditions. However, the photo-oxygenation of these epoxides can be effected by addition of biphenyl (BP) as a catalyst or co-sensitizer. Investigations of the stereochemistry of the reactions of cis- and trans-2,3-diaryloxiranes has shown that both isomeric epoxides are converted exclusively to the corresponding cis-ozonides. Co-sensitized photo-oxygenation of cis- and trans-2,3-diphenyloxirane affords only cis-3,5-diphenyl-1,2,4-trioxolane. The same stereochemical course is followed for the electron-transfer photo-oxygenation of more easily oxidized 2,3-dinaphthyloxiranes that do not require BP co-sensitization. The stereochemistry of the naphthyl-substituted ozonides has been unequivocably assigned by an X-ray structure of cis-3,5-bis(2'-naphthyl)-1,2,4-trioxolane. The corresponding trans-ozonide was prepared by ozonation of cis-1,2-bis(2'-naphthyl)ethene and stereochemically identified by Chromatographic resolution using high-performance liquid chromatography with optically active (+)-poly(triphenylmethyl methacrylate) as the stationary phase. These stereochemical results have been interpreted in terms of a mechanism involving addition of singlet oxygen as a dipolarophile to intermediate carbonyl ylides.     

cis-Bis(7-methylnaphth-1-yl)bis(triphenylphosphan)platin(II)

From the reaction of cis-dichlorobis(triphenylphosphane)platinum(II) with the lithium compound obtained as the bromination product of 2-methylnaphthalene cis-bis(7-methylnaphth-1-yl)bis(triphenylphosphane)platinum(II) (6), has been isolated. The unexpected formation of 6 has been explained.     

Synthesis, characterization, and coordination chemistry of two new tartaric acid-derived bis(phosphite) ligands

The syntheses of two chiral bis(phosphite) ligands with tartaric acid-derived backbones: 1 (from dimethyl tartrate) and 2 (from dipyrollidene tartramide), three complexes of 1: cis-Mo(CO)₄(1), cis-PtCl₂(1), and cis-PdCl₂(1) and two complexes of 2: cis-Mo(CO)₄(2) and cis-PdCl₂(2) are described. Each ligand and complex has been fully characterized by ¹H, ¹³C, and ³¹P NMR spectroscopy, and the coordination ³¹P NMR chemical shifts have been compared to those observed for complexes of related ligands. The X-ray crystal structures of each of the metal complexes have also been determined. The X-ray crystal structures indicate that the conformation of the seven-membered chelate ring varies depending on the substituents on the tartrate backbone. However, the conformations of the seven-membered rings do not change when the metal center is changed or when the coordination environment around the metal center is changed.     

Organoplatinum(II) complexes with phosphite ligands

The phosphite complexes cis-[PtMe₂L(SMe₂)] in which L = P(OⁱPr)₃, 1a, or L = P(OPh)₃, 1b, were synthesized by the reaction of cis,cis-[Me₂Pt(μ-SMe₂)₂PtMe₂] with 2 equiv. of L. If 4 equiv. of L was used the bis-phosphite complexes cis-[PtMe₂L₂] in which L = P(OⁱPr)₃, 2a, or L = P(OPh)₃, 2b, were obtained. The reaction of cis-[Pt(p-MeC₆H₄)₂(SMe₂)₂] with 2 equiv. of L gave the aryl bis-phosphite complexes cis-[Pt(p-MeC₆H₄)₂L₂] in which L = P(OⁱPr)₃, 2a′, or L = P(OPh)₃, 2b′. Use of 1 equiv. of L in the latter reaction gave the bis-phosphite complex along with the starting complex in a 1:1 ratio.The complexes failed to react with MeI. The reaction of cis,cis-[Me₂Pt(μ-SMe₂)₂PtMe₂] with 2 equiv. of the phosphine PPh₃ gave cis-[PtMe₂(PPh₃)₂] and cis-[PtMe₂(PPh₃)(SMe₂)] along with unreacted starting material. Reaction of cis-[PtMe₂L(SMe₂)], 1a and 1b with the bidentate phosphine ligand bis(diphenylphosphino)methane, dppm = Ph₂PCH₂PPh₂, gave [PtMe₂(dppm)], 8, along with cis-[PtMe₂L₂], 2. The reaction of cis-[PtMe₂L(SMe₂)] with 1/2 equiv. of the bidentate N-donor ligand NN = 4,4′-bipyridine yielded the binuclear complexes [PtMe₂L(μ-NN)PtMe₂L] in which L = P(OⁱPr)₃, 3a, or L = P(OPh)₃, 3b.The complexes were fully characterized using multinuclear NMR (¹H, ¹³C, ³¹P, and ¹⁹⁵Pt) spectroscopy.     

Synthesis, characterization, and C-H activation reactions of novel organometallic O-donor ligated Rh(III) complexes

The synthesis and characterization of the O-donor ligated, air and water stable organometallic complexes trans- (2), and cis-(hfac-O,O)₂Rh(CH₃)(py) (3), trans-(hfac-O,O)₂Rh(C₆H₅)(py) (4), cis-(hfac-O,O)₂Rh(C₆H₅)(py) (5), and cis-(hfac-O,O)₂Rh(Mes)(py) (6) (where hfac-O,O = κ²-O,O-1,1,1,5,5,5-hexafluoroacetylacetonato) are reported. These compounds are analogues to the O-donor iridium complexes that are active catalysts for the hydroarylation and C-H activation reactions as well as the bis-acetylacetonato rhodium complexes, which we recently reported. The trans-complex 2 undergoes a quantitative trans to cis isomerization in cyclohexane to form 3, which activates C-H bonds in both benzene and mesitylene to form compounds 5 and 6, respectively. All of these compounds are air and water stable and do not lead to decomposition products. Complex 5 promotes hydroarylation of styrene by benzene to generate dihydrostilbene.     

trans-chloro(N,N-dimethyl-d-phenylglycine)-(3-methyl-1-phenylpent-1-ene)platinum(II) complexes. HPLC separation and identification of all the diastereomers

The diastereomeric trans-chloro(N,N-dimethyl-d-phenylglycine)(3-methyl-1-phenylpent-1-ene)platinum(II) complexes, derived by coordination of the enantiomeric and geometric isomers of 3-methyl-1-phenylpent-1-ene (2), were separated by HPLC. Four trans- and two cis-olefin complexes were recognized in the chromatogram. The configuration of all chiral centers of the olefin in the six complexes were assigned. Under the conditions of preparation, the pairs of diastereomers 1R,2R,3S/1S,2S,3S and 1S,2S,3R/1R,2R,3R were formed in a ratio > 1 for the trans-isomer, whereas the cis-isomer gave the 1R,2S,3S and 1S,2R,3R epimers only. The complexes do not epimerize on standing at room temperature in solution; similar behaviour of the corresponding complexes of trans-stilbene (4C) indicates that the conjugated aromatic double bond is coordinated more strongly than those aliphatic and cycloaliphatic olefins.The efficient HPLC separation of the diasteromeric complexes 2C, permits the enantiomeric analysis of 2, as well as the preparative resolution of the olefin.     

Efficient and regioselective chromium(0)-catalyzed reaction of 2-substituted furans with diazo compounds: stereoselective synthesis of (2E,4Z)-2-aryl-hexadienedioic acid diesters

Pentacarbonyl(η²-cis-cyclooctene)chromium(0) (1) catalyzes efficiently reactions of diazo compounds with electron-rich furans. The reaction of 2-methoxyfuran (2) with alkyl α-diazoarylacetate (3a-g) furnishes the (2E,4Z)-2-aryl-hexadienedioic acid diesters (4a-g) in excellent yields. These reactions are highly regioselective. The cyclopropanation intermediates formed from 1 and diazo compounds 3a-g always arise from a carbene addition to the less substituted CC bond of 2. The resulting cyclopropanation product undergoes a ring opening reaction to form the corresponding (2E,4Z)-2-aryl-hexadienedioic acid diesters (4a-g). The pentacarbonylchromium(0)-catalyzed reactions of 2-alkylfuran (5a-b) with ethyl α-diazophenylacetate (3a) and 9-diazo-9H-fluorene (3h) produce the 1(E),3(E)-butadienes (6a-d) in very good yields.     

cis-Palladium(II) complexes of derivatives of di-(2-pyridyl)methane: Study of the influence of the bridge group in the coordination mode

Palladium(II) complexes containing di-(2-pyridyl)-N-methylimine (1), di-(2-pyridyl)methanol (2) and di-(2-pyridyl)methyl-N,N-diethyldithiocarbamate (4) ligands were synthesized and characterized by ¹H and ¹³C NMR in solution, IR and X-ray single crystal diffraction. Crystal structures of cis-dichloro[di-(2-pyridyl)-N-methylimine]palladium(II) (5), cis-dichloro[di-(2-pyridyl)methanol]palladium(II) (6) and cis-dichloro[di-(2-pyridyl)methyl-N,N-diethyldithiocarbamate]palladium(II) (7) showed a bidentate coordination mode of the di-(2-pyridyl)methane derivatives 1, 2 and 4. In these complexes is observed the formation of a five-membered chelate ring with the iminic ligand 1 and six-membered chelate rings with the pyridinic ligands 2 and 4. In all complexes the palladium atom displays a distorted square planar geometry.     

Cs2Ba(O3)4 · 2 NH3, das erste ionische Erdalkaliozonid

Cs₂Ba(O₃)₄ · 2 NH₃, the First Ionic Alkaline Earth Metal Ozonide Cs₂Ba(O₃)₄ · 2 NH₃ is the first ionic ozonide containing an alkaline earth metal cation. Its synthesis has been achieved via partial cation exchange of CsO₃ dissolved in liquid ammonia. According to a single crystal X‐ray structure determination (Pnnm; a = 6.312(2) Å, b = 12.975(3) Å, c = 8.045(2) Å; Z = 2; R₁ = 4.6%; 848 independent reflections) ozonide anions, cesium cations and ammonia molecules form a CsCl‐type arrangement, where Cs⁺ and NH₃ occupy one half of the cation sites, each. Ba²⁺ is coordinated by four ozonide groups and two ammonia molecules. Because of a short hydrogen bond to one of the terminal oxygen atoms, the respective O–O‐distance in the ozonide ion is longer than the other. The shortest intermolecular O–O‐distance ever observed in ionic ozonides has been found in this compound, which can be taken as a first clue for the radical ozonide anion to dimerize like the isoelectronic SO₂^– does.     

Polymerization of phenylacetylene by novel Rh (I)-, Ir (I)- and Ru (IV) 1,3-R2-3,4,5,6-tetrahydropyrimidin-2-ylidenes (R = mesityl, 2-propyl): Influence of structure on activity and polymer structure

The preparation of novel Rh (I) and Ir (I) complexes, i.e. [Rh(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD)]⁺[PF₆]⁻ (1), Rh(CF₃SO₃)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (2) and Ir(CF₃CO₂)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (3) (COD = 1,5-cyclooctadiene), is described. Compounds 1 and 3 were structurally characterized by X-ray diffraction. In 1, the N-heterocyclic carbene acts as a bidentate ligand with the carbene coordinating to the Rh(I) center and an arene group acting as a homoazallyl ligand. The catalytic activity of complexes 1–3 in the polymerization of phenylacetylene was studied and compared to that of RhCl(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (4), Rh(CF₃COO)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (5), [Rh(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD)]⁺[BF₄]⁻ (6), IrCl(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (7), IrCl(1,3-diisopropyl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (8), IrBr(1,3-di-2-propylimidazolin-2-ylidene)(COD) (9), RuCl₂(PCy₃)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(CH–C₆H₅) (10), RuCl₂(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(CH-2-(2-PrO)-5-NO₂-C₆H₃) (11), Ru(CO₂CF₃)₂(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(CH-2-(2-PrO)-5-NO₂-C₆H₃) (12). Compounds 1–6 were active in the polymerization of phenylacetylene. cis-Poly(phenylacetylene) (PPA) was obtained with the rhodium-based catalysts 1, 2, 4–6, trans-PPA was obtained with the Ir-based catalysts 3 and 8. In addition, compounds 1 and 6 were found to produce highly stereoregular PPA with a cis-content of 100% in the presence of water. Finally, the Ru-based metathesis initiator 12 allowed for the synthesis of trans-PPA, representing the first example of a ruthenium complex being active in the polymerization of a terminal alkyne.     

Synthesis and structural studies on di-oxovanadium(V) complexes of N(4)-substituted pyrazole based thiosemicarbazones

Three mononuclear cis-dioxovanadium(V) complexes of tridentate thiosemicarbazones derived from 5-methyl-3-formylpyrazole (MPA) and N(4)-methyl/ethyl/dimethyl thiosemicarbazide have been synthesized and characterized. Single crystal X-ray analyses were performed with [VO₂L¹] (1), [VO₂L²] (2) and [VO₂L³] (3), where L¹, L² and L³ denote the [1 + 1] thiosemicarbazone mono-anions derived from MPA and N(4)-substituted methyl/ethyl/dimethyl thiosemicarbazide respectively. In all the complexes the vanadium atom is in a distorted square pyramidal geometry with a N₂SO₂ chromophore. The interesting finding in the work is that in complexes 1 and 2, the thioimine nitrogen unusually participates in coordination whereas in 3 it is the azomethine nitrogen (quite usual) which is involved in the coordination process.     

Synthesis characterization and X-ray crystal structures of cis-1,4-diaminocyclohexane-platinum(II) nucleobase adducts

Platinum complexes of the type [Pt(cis-1,4-DACH)(L)₂]X, where cis-1,4-DACH = cis-1,4-diaminocyclohexane; L = adenine (ade) (1), hypoxanthine (hyp) (2), 9-methylguanine (9-megua) (3), cytosine (cyt) (4), or 1-methylcytosine (1-mecyt) (5); and X = SO₄ or Cl₂ groups, were synthesized and characterized by elemental analysis and by ¹H, ¹³C, and ¹⁹⁵Pt nuclear magnetic resonance spectroscopy. The crystals of [Pt(cis-1,4-DACH)(9-megua)₂]SO₄[9-megua-H]₂SO₄ (3) and [Pt(cis-1,4-DACH)(1-mecyt)₂]Cl₂ · 6H₂O (5) were also subjected to single-crystal X-ray diffraction. The base/PtN4 coordination plane dihedral angles were 74.55° and 85.61° in complex 3 and 78.12° and 81.80° in complex 5. The platinum had distorted square planar geometry in both complexes; the two adjacent corners were occupied by the two nitrogen atoms of cis-1,4-DACH, and the other two corners were occupied by the two N7 atoms of 9-megua in complex 3 and the two N3 atoms of 1-mecyt in complex 5. The cis-1,4-DACH, which has a unique twist-boat configuration, formed a seven-member chelating ring with platinum, which led to considerable strain during bidentate cis-1,4-DACH binding. Cations of both complexes 3 and 5 adopted C₂ molecular symmetry. These adducts were the models for the intrastand cross-links that were relevant to the binding of the Pt(II) antitumor drugs to DNA.     

New emissive fac-tricarbonylchlorobis(ligand)rhenium(I) complexes prepared from pyridine/thiophene hybrid ligands

Stille coupling between tributyl-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)-stannane and 4-bromopyridine resulted in the preparation of the new pyridine/thiophene hybrid ligand 4-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)-pyridine [4-py-EDOT] (1). Reaction of 1, 4-thiophen-2-yl-pyridine (2), or 4-[2,2^′]bithiophenyl-5-yl-pyridine (3) with ClRe(CO)₅ resulted in the isolation of complexes 4-6, ClRe(L)₂(CO)₃, where L=1, 2, or 3 respectively. The solid-state structure of 4 was determined by X-ray crystallography, which clearly shows the fac arrangement of the three CO ligands and the two 4-py-EDOT ligands arranged cis to one another. The metal complexes 4-6 have been characterized by ¹H and ¹³C NMR, ESI or FAB MS, FTIR, UV-Vis, fluorescence, and elemental analysis.