Synthesis, characterization and X-ray crystal structures of chiral ferrocene-containing β-diketones

CCDC 922490, 922491, and 922492 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.International audienceThree new chiral ferrocene-containing β-diketones have been synthesized by reacting 1-ferrocenyl ethanol with the corresponding 1,3-diketone reagent MeCOCH2COR (R = Me, 4-C6H4OMe, Fc; Fc = (η5-C5H5)Fe(η5-C5H4)), using cerium(IV) ammonium nitrate (CAN) mediated C-C bond formation. These compounds identified as 3-(1-ferrocenylethyl)-pentane-2,4-dione (1), 1-(4-methoxyphenyl)-2-(1-ferrocenylethyl)-butane-1,3-dione (2), and 1-ferrocenyl-2-(1-ferrocenylethyl)-butane-1,3-dione (3), have been isolated as air and thermally stable microcrystalline solids in 79, 63 and 44% yields, respectively. Compounds 2 and 3 were formed in 63:37 and 88:12 diastereomeric ratios, respectively. They have been fully characterized by elemental analyses, FT-IR spectra, mass spectrometry, and their complete assignments have been conducted using 2D NMR experiments. In addition, their molecular identity and geometry have been confirmed by single-crystal X-ray diffraction, and both solution and solid state measurements have shown that the three complexes exist solely as their diketo tautomers

Stable divalent germanium, tin and lead amino(ether)-phenolate monomeric complexes: structural features, inclusion heterobimetallic complexes, and ROP catalysis

International audienceStable germanium(ii) and lead(ii) amido complexes {LO(i)}M(N(SiMe3)2) (M = Ge(II), Pb(II)) bearing amino(ether)phenolate ligands are readily available using the proteo-ligands {LO(i)}H of general formula 2-CH2NR2-4,6-tBu2-C6H2OH (i = 1, NR2 = N((CH2)2OCH3)2; i = 2, NR2 = NEt2; i = 3, NR2 = aza-15-crown-5) and M(N(SiMe3)2)2 precursors. The molecular structures of these germylenes and plumbylenes, as well as those of {LO(3)}GeCl, {LO(3)}SnCl and of the congeneric {LO(4)}Sn(II)(N(SiMe3)2) where NR2 = aza-12-crown-4, have been determined crystallographically. All complexes are monomeric, with 3-coordinate metal centres. The phenolate systematically acts as a N^Ophenolate bidentate ligand, with no interactions between the metal and the Oside-arm atoms in these cases (for {LO(1)}(-), {LO(3)}(-) and {LO(4)}(-)) where they could potentially arise. For each family, the lone pair of electrons essentially features ns(2) character, and there is little, if any, hybridization of the valence orbitals. Heterobimetallic complexes {LO(3)}M(N(SiMe3)2)*LiOTf, where the Li(+) cation sits inside the tethered crown-ether, were prepared by reaction of {LO(3)}M(N(SiMe3)2) and LiOTf (M = Ge(II), Sn(II)). The inclusion of Li(+) (featuring a close contact with the triflate anion) in the macrocycle bears no influence on the coordination sphere of the divalent tetrel element. In association with iPrOH, the amido germylenes, stannylenes and plumbylenes catalyse the controlled polymerisation of l- and racemic lactide. The activity increases linearly according to Ge(II) ≪ Sn(II) ≪ Pb(II). The simple germylenes generate very sluggish catalysts, but the activity is significantly boosted if the heterobimetallic complex {LO(3)}Ge(N(SiMe3)2)*LiOTf is used instead. On the other hand, with 10-25 equiv. of iPrOH, the plumbylenes afford highly active binary catalysts, converting 1000 or 5000 equiv. of monomer at 60 °C within 3 or 45 min, respectively, in a controlled fashion

Lobarin from the Sumatran lichen, Stereocaulon halei.

International audienceThe diphenyl ether, lobarin (1) (syn. lobariol carboxylic acid) related to lobaric acid was isolated for the first time as a natural product along with five known compounds from Stereocaulon halei, a fruticose lichen collected in Indonesia. The structure of lobarin was elucidated by spectroscopic data analysis and its most stable conformers were determined by molecular mechanic dynamic calculations. A marked superoxide anion scavenging was found for compound 1 while no cytotoxicity on the B16 murine melanoma and HaCaT human keratinocyte cell lines was observed

Electrochemical synthesis and chemistry of chiral 1-cyanotetrahydroisoquinolines. An approach to the asymmetric syntheses of the alkaloid (-)-crispine a and its natural (+)-antipode.

International audienceThe stereoselective convergent total syntheses of both enantiomers of the tetrahydroisoquinoline (THIQ) alkaloid crispine A are described. The THIQ precursors (-)-6 (90:10 dr) and (-)-11 (85:15 dr) were prepared from the alkylation-reduction sequence of a common α-amino nitrile (+)-4 derivative that has been conveniently prepared by anodic cyanation. Elaboration of the pyrrolidine ring of the title compound was cleanly achieved by two efficient ring closures methods involving (a) the displacement of a halogen atom and (b) the formation of a cyclic iminium cation to afford (-)-crispine A in 90% and 85% yields, respectively. A crystallization of enantioenriched (-)-crispine A (90:10 er) with 1 equiv of (-)-DBTA afforded the tartrate salt (-)-14 (≥98:2 dr) in 81% yield. The absolute S configuration of (-)-crispine A was simply deduced from examination of the X-ray data of tartrate salt (-)-14. Likewise, the natural (+)-crispine A was prepared in seven workup steps in an overall 30% yield, and reciprocal crystallization with (+)-DBTA afforded the enantiomeric tartrate salt (+)-14 in a ≥98:2 dr. Both enantiomers of crispine A were liberated from their respective DBTA salts in ≥98:2 er's which were determined by proton and carbon NMR spectroscopy, utilizing (R)-(+)-tert-butylphenylphosphinothioic acid (+)-15 as chiral solvating agent

Heteroleptic Tin(II) Initiators for the Ring-Opening (Co)Polymerization of Lactide and Trimethylene Carbonate: Mechanistic Insights from Experiments and Computations.

International audienceThe tin(II) complexes \LOx\Sn(X) (\LOx\-=aminophenolate ancillary) contg. amido (1-4), chloro (5), or lactyl (6) coligands (X) promote the ring-opening polymn. (ROP) of cyclic esters. Complex 6, which models the first insertion of L-lactide, initiates the living ROP of L-LA on its own, but the amido derivs. 1-4 require the addn. of alc. to do so. Upon addn. of one to ten equiv. of iPrOH, precatalysts 1-4 promote the ROP of trimethylene carbonate (TMC); yet, hardly any activity is obsd. if tert-Bu (R)-lactate is used instead of iPrOH. Strong inhibition of the reactivity of TMC is also detected for the simultaneous copolymn. of L-LA and TMC, or for the block copolymn. of TMC after that of L-LA. Exptl. and computational data for the \LOx\Sn(OR) complexes (OR=lactyl or lactidyl) replicating the active species during the tin(II)-mediated ROP of L-LA demonstrate that the formation of a five-membered chelate is largely favored over that of an eight-membered one, and that it constitutes the resting state of the catalyst during this (co)polymn. Comprehensive DFT calcns. show that, out of the four possible monomer insertion sequences during simultaneous copolymn. of L-LA and TMC: 1) TMC then TMC, 2) TMC then L-LA, 3) L-LA then L-LA, and 4) L-LA then TMC, the first three are possible. By contrast, insertion of L-A followed by that of TMC (i.e., insertion sequence 4) is endothermic by +1.1 kcal mol-1, which compares unfavorably with consecutive insertions of two L-Lunits (i.e., insertion sequence 3) (-10.2 kcal mol-1). The copolymn. of L-LA and TMC thus proceeds under thermodn. control. [on SciFinder(R)

Structure vs 119Sn NMR Chemical Shift in Three-Coordinated Tin(II) Complexes: Experimental Data and Predictive DFT Computations

International audienceThe new amido-/alkoxy-tin complexes [Sn(μ-OSiPh3)(OSiPh3)]2 (4), [Sn(μ-OiPr)(OSiPh3)]2 (5), [Sn(μ-OSiPh3)(Cl)]2 (6), [Sn(μ-OiPr)(Cl)]2 (7), [Sn(OSiPh3)(NMe2)]2 (8), and [Sn(OiPr)(NMe2)]2 (9) have been synthesized. The molecular solid-state structures of 4–7 established by XRD analysis show these complexes to exist as μ-O-bridged dimers with three-coordinated tin(II) atoms. Diffusion-ordered NMR spectroscopy (DOSY) measurements demonstrated that the complexes retain their dimeric structure in solution in aromatic solvents. The 119Sn{1H} NMR data for 4–7 and those of the known dimers [Sn(μ-OiPr)(OiPr)]2 (2), [Sn(μ-NMe2)(NMe2)]2 (3), [Sn(μ-OiPr)(N(SiMe3)2)]2 (10), and Lappert’s [Sn(μ-Cl)(N(SiMe3)2)]2 (11) have been recorded in toluene-d8 (using Sn(N(SiMe3)2)2 (1), δ119Sn = +771 ppm, as a reference compound). The resonances, located in the range +138 to −338 ppm, are increasingly shifted toward high fields with substitution according to NMe2 ∼ N(SiMe3)2 < Cl < OtBu ≤ OiPr < OSiPh3. DFT computations have been performed to model the 119Sn NMR chemical shifts in these tin(II) complexes as well as in 10 other heteroleptic, monometallic phenolate-supported stannylenes featuring three-coordinated metal atoms, taking into account the coordination number of the metal atoms. The applied methodology produces computed data that match those recorded experimentally by 119Sn{1H} NMR spectroscopy, hence providing a convenient tool that complements traditional spectroscopic (119Sn NMR, DOSY NMR) and diffraction methods to predict the structural and spectroscopic features of stannylenes

Spin Delocalization in Electron-Rich Iron(III) Piano-Stool -Acetylides. An Experimental (NMR) and Theoretical (DFT) Investigation

International audienceSeveral paramagnetic electron-rich Fe(III) mononuclear arylacetylide complexes of formula [(2-dppe)(5-C5Me5)Fe(CC-Ar)]+ in which Ar represents a functional aryl group were studied by means of multinuclear NMR. All signals detected for the various nuclei were assigned. Hyperfine coupling constants for selected nuclei of the arylacetylide ligand were derived from 1H or 19F NMR contact shifts. These NMR data are diagnostic of a metal-centered unpaired electron partly residing in a molecular orbital on the arylacetylide ligand, in line with DFT computations. We show here that the 1H NMR paramagnetic shifts of the ortho (H1) and meta (H2) arylacetylide protons convey decisive information on the charge distribution in the aryl ring. Estimates of the relaxation rates of the unpaired electron were also derived from half-widths of the 1H NMR signals. Finally, line-broadening studies of Fe(II)/Fe(III) mixtures allowed extracting the self-exchange rates for several redox couples among these complexes. The self-exchange rates appear slightly substituent dependent and are apparently larger for compounds with electron-withdrawing substituents on the aryl ring. Reorganization energies of ca. 4000 cm-1 could be derived for these outer-sphere electron-transfer processes

[(η5-​C5Me5)​Ru]​+ fragments ligated to polyaromatic hydrocarbons: an experimental and computational approach to pathways for haptotropic migration

International audienceLigand exchange reactions between [Cp*Ru(NCMe)3][PF6], where Cp* represents η(5)-C5Me5, and the polycyclic aromatic hydrocarbons (PAHs) pyrene, acenaphthylene and fluoranthene afforded the known [Cp*Ru(η(6)-pyrene)][PF6] (1) and the new mixed sandwiches [Cp*Ru(η(6)-acenaphthylene)][PF6] (2) and [Cp*Ru(η(6)-fluoranthene)][PF6] (3), respectively, isolated in quantitative yields (94-100%). Complex 3 is formed as a mixture of two isomers: 3A as the major product where the [Cp*Ru(+)] moiety is coordinated to the naphthalene fragment of fluoranthene, and 3B with the coordination of the arenophile to the peripheral benzene ring, in a 90/10 spectroscopic ratio. The composition and identity of the complexes were deduced by elemental analysis, (1)H and (13)C multidimensional NMR spectroscopy, and mass spectrometry. Compounds 1A, 3A and 2A have been characterized using X-ray structural investigations. That showed that the [Cp*Ru(+)] unit is η(6)-attached to one of the two naphthalene rings in each complex. Heating 1 and 3 at 90 °C in CD3NO2 solutions or heating 3 at 120 °C in the solid phase did not provide any evidence for thermally induced intramolecular inter-ring haptotropic rearrangements. These rearrangements were modelled by DFT calculations which indicated rather high activation energies

Topological dependence of the magnetic exchange coupling in arylethynyl-bridged organometallic diradicals containing [(eta(2)-dppe)(eta(5)-C(5)Me(5))Fe(III)](+) fragments.

International audienceWe have investigated the spin distribution and determined the magnetic exchange coupling J(ab) (defined according to the following Hamiltonian: H(spin) = -2J(ab)S(a).S(b)) for three arylethynyl-bridged organoiron(III) diradicals containing [(eta(2)-dppe)(eta(5)-C(5)Me(5))Fe(III)](+) fragments. Considering the distance separating the Fe(III) centers (>or=11 A), remarkably large intramolecular magnetic interactions between unpaired spins were found for two of them. Thus, an antiferromagnetic coupling (J(ab)) of ca. -190 cm(-1) was experimentally determined for the binuclear Fe(III) species featuring a 1,4-diethynylbenzene bridge 1[PF(6)](2), while a ferromagnetic interaction of over +150 cm(-1) was evidenced for its 1,3-substitued analogue 2[PF(6)](2). We also show that a much weaker interaction (0 > J(ab) >or= -1 cm(-1)) takes place in the 4,4'-biphenyl analogue of 1[PF(6)](2) (3[PF(6)](2)), evidencing that insertion of an additional 1,4-phenylene unit in the bridge severely disrupts the magnetic communication in these diradicals. With the help of NMR and density functional theory, the magnetic properties of these compounds were rationalized and compared to those of the corresponding mononuclear Fe(III) relatives 4[PF(6)] and 5[PF(6)]. Finally, it is shown that, for all of these dinuclear Fe(III) complexes, the structural changes between singlet and triplet spin isomers remain very small regarding the carbon-rich bridge. Thus, even for a strongly coupled diradical such as 1[PF(6)](2), a dominant diradicaloid character dominates the valence-bond description of the singlet state unpaired electrons