Roger Pichon

Structure of the exopolysaccharide of Vibrio diabolicus isolated from a deep-sea hydrothermal vent.

The structure of the exopolysaccharide produced under laboratory conditions by Vibrio diabolicus, a bacterium recovered from a deep-sea hydrothermal vent, has been investigated using sugar and methylation analysis and NMR spectroscopy. The polysaccharide consists of a linear tetrasaccharide repeating unit with the following structure. -->3)-beta-D-Glcp Nac-(1-->4)-beta-D-Glcp A-(1-->4)-beta-D-Glcp A-(1-->4)-alpha-D-Galp NAc-(1-->

Complete 1H and 13C spectral assignment of floridoside.

Floridoside (2-O-alpha-D-galactopyranosylglycerol) was extracted from the red marine alga Rhodymenia palmata, and purified by ion-exchange chromatography: 1D and 2D NMR spectroscopy experiments were used to unambiguously assign the complete 1H and 13C spectra.

Synthesis of electron donor–acceptor polyunsaturated methylenepyran Fischer type carbene complexes: dynamic 1H-NMR study and solvatochromic properties

Condensation of α and γ methylenepyran aldehydes with the Fischer carbene complexes (CO)5MC(OCH3)Me (M=Cr, W) or (CO)5WC(OCH3)CHCH–CH3 in the presence of ClSiMe3/NEt3 yield donor acceptor complexes, in which the electron donating group is connected to the organometallic accepting group by a conjugated ethylenic spacer. 1H- and 13C-NMR studies, suggest that the carbene fragment and the unsaturated chain lie in the same plan, allowing a mesomeric interaction between the oxygen atom of the heterocycle and the metal via the spacer. The positive solvatochromism of the molecules obtained is reported.

Electrochemical, spectrochemical characterization and crystal structure of (1,4,8,11-tetrazacyclotetradecane)(acetylcetonate) cobalt(III) complexes

Two Co III -cyclam-acac complexes have been synthesized and isolated (acac −0 = acetylacetonate ion): [Co III (cyclam)(acac)](acac) 2 and [Co III (cyclam)(acac)](BF 4 ) 2 . Fast atom bombardment mass spectrometry has been used to characterize [Co III (cyclam)(acac)](BF 4 ) 2 Electrochemistry, spectrophotometry and IR spectroscopy helped to clear-up the role of acac − . The acetylacetonato ligand is in the Co III coordination sphere of [Co III (cyclam)(acac)](BF 4 ) 2 . In [Co III (cyclam)(acac)](acac) 2 , acac − is a ligand for the metal ion and also a counter-ion for the cationic complex, identical in both compounds. The various protons [Co III (cyclam)(acac)](BF 4 ) 2 have been identified using 1 H NMR (1D, 2D, COSY-DQF). 13 C NMR reveals that a symmetry element exists in the complex; the α carbons of cyclam have been identified using an inverse 1 H- 13 C correlation (HMQC). An X-ray crystallographic study ascertained the probable structure deduced from these methods. Co III is six coordinated, the octahedron being slightly distorted: two of the four N atoms of the tetraazamacrocycle occupy adjacent positions of the equatorial plane, the O atom of acacetylacetonate the two others.

Characterization of N‐methyl‐L‐methionine sulfoxide and isethionic acid from the red alga Grateloupia doryphora

Isethionic acid (2‐hydroxyethane sulfonic acid) and N‐methyl‐L‐methionine sulfoxide (4‐methane sulfinyl‐2‐methylamino butyric acid) were isolated from the red alga Grateloupia doryphora (Cryptonemiales) collected from Brittany (France); they were identified as major organic solutes together with floridoside (α‐D‐galacto‐pyranosyl‐(1–2)‐glycerol). The presence of isethionic acid has recently been reported in certain red algae, however, the occurrence of N‐methyl‐L‐methionine sulfoxide is still very rare. This report deals with the first isolation of isethionic acid and N‐methyl‐L‐methionine sulfoxide from G. doryphora and their subsequent NMR characterization.

95Mo and 199Hg NMR studies on complexes containing molybdenum-mercury bonds and substituted-cyclopentadienyl ligands: [(C5H5-nRn)(CO)3Mo]xHgX2-x (R = Me, n = 0, 1, 4, 5; R = Ph, n = 4; X = Cl, Br, I; x = 1, 2)

Abstract NMR data for 95Mo and 199Hg nuclei have been obtained for di- and tri-metallic complexes containing molybdenum-mercury bonds and substituted-cyclopentadienyl ligands [(C5H5-nRn)(CO)3Mo]xHgX2-x; R = Me, n = 0, 1, 4, 5; R = Ph, n = 4; X = Cl, Br, I; x = 1, 2. The 95Mo chemical shifts vary markedly with the substituent on the C5 ring, with the shielding decreasing in the order C5H5 > C5H4Me > C5HMe4 > C5Me5 > C5HPh4, but for a given cyclopentadienyl ligand they are little affected by changes in the X ligands. In contrast, the 199Hg shifts are only slightly affected by ring substitution, except in the case of C5HPh4 (which it is suggested may give rise to intramolecular mercury-phenyl interactions), but are strongly influenced by the ligands X. Some aspects of the chemistry of the complexes studied are considered.

Reactions of di- and poly-nuclear complexes 13. Synthesis, structure and fluxional behaviour of hydrido- and thiolato- or selenato-bridged complexes [Mo2Cp2(μ-H)(μ-ER)(CO)4] (E S, R Me, tBu, Bz, or Ph; E Se, R Ph)

Abstract Oxidative addition of thiols or selenoles across the Mo2 centre of [Mo2Cp2(CO)4] gives complexes with bridging thiolate or selenate and hydride ligands [Mo2Cp2(μ-H)(μ-ER)(CO)4](E  S, R  Me (4), tBu (5), Bz (6), Ph (7); E  Se, R  Ph (8)). The complex 4 is also formed on reaction of [Mo2Cp2(μ-SMe)2(CO)4] with vanadocene [VCp2] with the possible involvement of a thioaldehyde, hydride derivative of the vanadocene. Crystals of 4 are monoclinic, space group C2/c, with a = 17.225 (1), b = 8.418 (1) c = 22.960 (2) A , β = 90.346 (5)°, R = 0.023 for 4213 observed reflections. In the solid state, molecules of 4 contain a planar Mo2(μ-H)(μ-S) core and the Cp ligands are cis with respect to the MoMo bond, the two CpMo(CO)2 unites being related by an approximate plane of symmetry which contains the bridging H and S donor atoms and which is normal to the MoMo bond. The fluxional nature of complexes 4–8 in solution is shown from variable-temperature 1H and 13C NMR spectra to arise from cis-trans isomerisation.

Préparation des complexes [(C5Me4H)2MX2] (M Ti, Zr; X Cl, alkyl, aryl, CO). Etude par RMN dynamique de la gêne stérique à la rotation des groupements aryle liés au métal

Abstract The new ligand C 5 Me 4 H reacts with [TiCl 3 ] or [ZrCl 4 ] to afford the dichlor complexes [(C 5 Me 4 H) 2 MCl 2 ] (M  Ti, Zr) and the trichloro complex [(C 5 Me 4 H)-TiCl 3 ]. Treatment of these complexes with RLi, or their reduction under CO, gives the derivatives [(C 5 Me 4 H) 1 )MR 2 ] (R  CH 3 , C 6 H 5 , p -C 6 H 4 CH 3 , CO). The preparation of the new series of compounds, [(C 5 Me 4 H)(C 5 H 5 )TiR 2 ], is also described. The electronic effects of the C 5 Me 4 H ligand resemble closely those of C 5 Me 5 . The coalescence of the 1 H and 13 C NMR aromatic signals indicates that rotation of the aromatic nucleus around the metal-carbon bond is restricted owing to the large size of the C 5 Me 4 H ligand in the aryl complexes. The activation parameters of this rotation have been determined for [(C 5 Me 4 H) 2 Ti( p -C 6 H 4 CH 3 ) 2 ].

Carbonfluorine bond activation by iron(I). CF bond cleavage induced by addition of phosphines or thiols to a perfluorovinyldiiron complex

Abstract The reaction of phosphines PXYH (X  Y  Ph, i-Pr; X  Ph, Y  H) or ethanethiol with the perfluorovinyl compound [{Fe(CO)3}2{μ-C(SMe)(CF3)CCF2}] (1) proceeds with cleavage of one CF bond and gives rise to unusual ligand transformations. The multicenter processes involved lead to new diiron complexes [{Fe(CO)3}2{μ-C(SMe)(CF3)C(PXY)CF}] (X  Y  Ph, 2a; X  Y-i-Pr, 2b; X  Ph, Y  H, 2c) and [{Fe(CO)3}2{μ-C(SMe)(CF3)C(SEt)CF}] (3). Mechanisms for these reactions are proposed. The fluxional behavior of 2a and 3 has been investigated by variable-temperature 13C NMR spectroscopy. The molecular structure of 2a has been established by a single-crystal X-ray diffraction study. The Fe2(CO)6 core contains an FeFe bond of 2.633(1)A bridged by the six-electron donor C(SMe)(CF3)C(PPh2)CF ligand. 2a crystallizes in the triclinic space group P 1 with a = 9.019(2), b = 9.550(2), c = 18.583(3) A , α = 101.06(2), β = 92.53(2), γ = 116.48(2)°, R = 0.0419 for 3984 reflections.

New synthesis of μ-allenylidene complexes from dimolybdenum carbenium ions crystal structure of [Mo(η5-C5H5)(CO)22(μ, η2-CCC6H10)]

Abstract A selective abstraction of the acetylenic proton of cationic allynyl complexes [MoCp(CO)22(μ-η2,η3-HCCCR1R2)][BF4](Cpη5-C5H5) by using the acetylide LiCCC(CH3)CH2 gives rise to allenylidene complexes [Cp2Mo2(CO)4(μ,η2-CCCR1R2)] R2 = C6H5 (6c). Compounds 3b and 4b exist as two isomers while for 6c the formation reaction is stereoselective. The crystal structure of [Cp2Mo2(CO)4(μ,η2-CCC6H10)] (1b) has been determined.