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Four furanoditerpenoids were isolated from roots of Croton jatrophoides (Euphorbiaceae) collected in Tanzania. In addition to the known compounds penduliflaworosin and teucvin (mallotucin A), a new teucvin isomer, which was named isoteucvin, and a furanoditerpenoid with a new skeleton, for which the name jatrophoidin was adopted, were isolated. Their structures were elucidated by spectroscopic methods such as ESI-MS and NMR, including 1H-, 13C-, and two-dimensional NMR. The crystal structures of isoteucvin and jatrophoidin were solved using single-crystal X-ray diffraction, by which we also established the absolute configuration of jatrophoidin. The refined crystal structure of isoteucvin has the same (absolute) configuration as jatrophoidin, although the X-ray diffraction data of isoteucvin were not conclusive with respect to the absolute configuration. [ABSTRACT FROM AUTHOR]

A new family of bidentate phosphine ligands based on the biscarbazole backbone has been synthesized and applied in the ruthenium- and rhodium-catalyzed asymmetric hydrogenations of methyl acetoacetate and dimethyl itaconate. The nitrogen atoms in these BICAP ligands allow facile introduction of substituents providing structurally similar, but electronically different ligands, which were used to fine-tune these reactions to 98% and 55% ee, respectively.

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The synthesis and resolution of a novel chiral C2-symmetric bicarbazolediol (BICOL), is reported. The key step in the synthesis is the copper(II)-catalysed oxidative phenol coupling of 3-hydroxycarbazole. Menthyl chloroformate is used as resolving agent for the separation of the two enantiomers of BICOL. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

The structures of neutral and ionic 4-cyanophenylpalladium(ii) and methylpalladium(ii) complexes containing bidentate phosphine ligands were investigated in solution and in the solid state. Diphosphine ligands with a xanthene and a ferrocene backbone were used. New bis(dialkylphosphino) substituted Xantphos ligands were synthesised. 1H NMR and 31P NMR spectroscopy, conductivity measurements, UV-Vis spectroscopy, and X-ray crystallography were used to elucidate the structures of the complexes. Subtle changes of the phosphine ligands govern the coordination mode of the ligand. A variety of bidentate cis-, and trans-coordination and terdentate P–O–P, P–S–P and P–Fe–P coordination modes of the ligands were observed.

Donor−acceptor compounds containing a phenylenediamine electron donor and a naphthalene, a cyanobenzene, or a cyanonaphthalene acceptor were studied. The two chromophores are connected by three different bridging units, consisting of CH2 groups linked to a semiflexible piperidine or piperazine ring or to a rigid 2,5-diazabicyclo[2.2.1]heptane group. All donor−acceptor compounds show photoinduced charge separation, resulting in the formation of a compact charge-transfer (CCT) state in nonpolar solvents. The conformational change needed to arrive at this species is impossible in a nonpolar polymer matrix and also in methylcyclohexane at low temperature. In the cases of the piperidine- and piperazine-bridged donor−acceptor compounds, evidence for the involvement of an extended charge-transfer (ECT) species as a precursor of the CCT species was obtained from time-resolved fluorescence measurements. In contrast to harpooning systems studied previously, the energy differences between the species in the present case are so small that their interconversions are reversible within the excited state lifetimes.

Eight monodentate phosphites (2–9) based on the calix[4]arene backbone were synthesised following two synthetic routes. Out of six conformations only three were actually formed under the applied reaction conditions. X-Ray analysis of two conformers (4 and 5) provided insight into the 3-dimensional structure of two of these conformations. The three conformations were characterised by ¹H, ¹³C and ³¹P NMR spectroscopy. NMR experiments showed that several of the phosphites are flexible showing fluxional behaviour of the molecular backbone in solution, but no interconversion between the different conformers was observed. The conformation of the product in the phosphite synthesis is determined at the point where the phosphorus atom is linked to two hydroxyl groups of the calix[4]arene (phosphorus amidite). Such an intermediate phosphorus amidite (12) was isolated in the synthesis of 4 and 5. Phosphites 3–6, 8 and 9 were tested in rhodium-catalysed hydroformylation. Differences in rate can be correlated to the conformation of the ligand.

Compounds of the type M(N∩N-κN)(nq)2 and M2(μ²-N∩N)(μ²-pbq)2, in which nq = 1,4-naphthoquinone, pbq = 1,4-benzoquinone, and N∩N is a monodentate or bridging ligand of the α-diimine type, were obtained from reactions of Pd(dba)2 in toluene with the 3,3'-annelated-2,2'-bipyridines: 4,5-diazafluoren-9-one (dafo) and 4,5-diazafluorene (dafe) in the presence of the appropriate p-quinone. In the corresponding reactions with 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 2,2'-bipyrimidine (bpym), N,N'-dicyclohexyl-1,4-diaza-1,3-butadiene (chex-dab), bis[N-(o,o'-diisopropyl)phenylimino]acenaphthene (o,o'-iPr2-bian) and 5,6-dihydro-1,10-phenanthroline (dh-phen) only complexes of the type M(N∩N-κ²N)(Q) were formed (Q = nq, pbq). The structures of the complexes have been established by NMR in solution and by X-ray diffraction in the solid state; crystal structures of Pd(bpy-κ²N)(η²-pbq) (1) Pd(dafo-κN)(η²-nq)2 (14) and Pd2(μ²-dafo)(μ²,η²:η²-pbq)2 (16) have been determined. Of the ligands, dafo and dafe are the only ones apt to form complexes containing a monodentate or bridging N∩N ligand. This behaviour is ascribed to the geometrical constraints of dafo and dafe; the annelation by one carbon atom at the 3,3'-positions in these ligands causes an increase in bite angle from approximately 77° to 82°.

The syntheses, structures, and spectroscopic properties are reported for trans,cis and cis,cis isomers of [Ru(I)(Me)(CO)2(α-diimine)] [α-diimine = N,N'-diisopropyl-1,4-diazabutadiene (iPr-DAB), pyridine-2-carbaldehyde N-isopropylimine (iPr-PyCa), 4,4'-dimethyl-2,2'-bipyridine (dmb)] which differ in their photochemical behaviour. The structures of trans,cis- and cis,cis-[Ru(I)(Me)(CO)2(iPr-DAB)] have been determined by a single-crystal X-ray diffraction study. The crystals of both isomers are monoclinic and belong to the same P21/n space group with Z = 4. Refinement converged to R = 0.043 for the trans,cis isomer and to R = 0.065 for the cis,cis isomer. Both complexes have a distorted octahedral geometry, in the cis,cis isomer the methyl ligand is located in an equatorial, the iodide in an axial position. According to the ¹H- and ¹³C-NMR and resonance Raman spectra the imine groups of the iPr-DAB ligand are inequivalent in the cis,cis isomer. The absorption spectra vary with the α-diimine, not so much with the isomeric structure of the complex. Both isomers possess two visible absorption bands, which, according to the resonance Raman spectra, belong to charge transfer transitions from mixed metal-halide orbitals to the α-diimine. The resonance Raman spectra show that this charge transfer excitation is accompanied, for both isomers, with an angular distortion of the methyl ligand. These spectral data show that the difference in photochemical behaviour of the two isomers is not due to a change in the excited state character.

The platinum complex [{PtCl2(C2H4)}2(dpf *) 1 [dpf * 4;= 4;octamethyl-5,5′-di(2-pyridyl)ferrocene] has been obtained by the reaction of dpf * with K[PtCl3(C2H4)]. The reaction of dpf * with [Cu(NCCH3)4]+[BF4]– afforded the copper complexes [Cu(dpf *)]+ [BF4]–2 and [Cu(dpf *)]+[CuCl2]–3 as well as the ferrocenium salt [dpf *]+[BF4]–4, depending on the stoichiometry. The crystal structures of 1–4 have been determined by X-ray diffraction. The dpf * acts as a bridging ligand in the case of 1 and as a trans-chelating ligand in 2 and 3, which contain near-linear two-co-ordinate copper centres. Complex 3 shows a remarkably short, ligand-unsupported CuI · 4;· 4;·  CuI contact [281.0(2) pm]. A cyclovoltammetric study of 2 revealed an unprecedentedly high anodic shift of the half-wave potential of the ferrocene moiety upon co-ordination of Cu+ by dpf *.

Complexes of Pd(tcne) (tcne = tetracyanoethylene) containing bidentate ligands with large bite angles, bis[2-(diphenylphosphino)phenyl] ether (L1), 4,6-bis(diphenylphosphino)-10,10-dimethyl-10H-dibenzo[b ,e][1,4]oxasiline(L2), 4.6-bis(diphenylphosphino)-2,8-dimethylphenoxathiine (L3), 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (L4) and trans-5,6-bis(2-pyridyl)bicyclo[2.2.1]hept-2-ene (L6), were prepared and characterised. The compound 4,6-bis(diphenylphosphino)dibenzo[b,d]furan (L5) did not form chelating palladium complexes, owing to its large natural bite angle of 138°. The crystal structures of L6, [PdL1(tcne)]·2.5CH2Cl2 1, [PdL2(tcne)]·4CH2Cl2 2, [PdL4(tcne)]·2CH2Cl2 4 and [PdL6(tcne)] 5 have been determined. The similarity of electronic effects induced by the free diphosphines was demonstrated by MOPAC calculations. The geometries of the ligands, however, were most accurately predicted by molecular mechanics (MM2) calculations for the diphosphines, and MNDO for L6. The largest P–Pd–P angle in the zerovalent palladium complexes was found to be 104.6°. A further increase in the natural bite angle of the ligand results in elongation of the Pd–P bond length in the complex rather than enlargement of the P–Pd–P bite angle. The ligand L6 assumed a bite angle of 99.5(2)° in complex 5, which is considerably smaller than its calculated value of 117°.

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The crystal structure of the novel cluster [Os3(CO)10(4,4',5,5'-tetramethyl-2,2'-biphosphinine)] reveals an unprecedented coordination mode of the biphosphinine ligand that occupies a doubly-bridging position spanning the open osmium triangle. The cluster is photostable, pointing to a localization of the lowest-energy electronic transition largely on the negatively charged biphosphinine ligand.

The title compound, C11H17N2O3PS2, is a cyclic thio­phos­phoryl pyrimidine derivative exhibiting insecticidal properties. The crystal structure determination gives evidence for the presence of the thione isomer of the compound. The pyrimidine nucleus is planar and its substituents have small deviations from the least‐squares plane. The dioxaphos­phorinane ring adopts a chair conformation. The lack of classical hydrogen bonds and the weak intermolecular interactions lead to a `loose' packing characterized by channels in the structure.

The synthesis of the enantiopure left-hand substructure of solanoeclepin A is described. Key steps include a chromium-mediated coupling of an oxabicyclic aldehyde with a β-ketoester-derived enol triflate to give a lactone, and a ring-closing metathesis reaction to form the seven-membered ring.

The synthesis of a tricyclic substructure of solanoeclepin A is described. The key step involves an intramolecular [2+2] photocycloaddition between a dioxinone and a tetrasubstituted bicyclic alkene providing the strained bicyclo[2.1.1]hexane moiety.

For Abstract see ChemInform Abstract in Full Text.

For Abstract see ChemInform Abstract in Full Text.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.