Loı̈c Toupet

Continuous Symmetry Breaking Induced by Ion Pairing Effect in Heptamethine Cyanine Dyes: Beyond the Cyanine Limit

The association of heptamethine cyanine cation 1(+) with various counterions A (A = Br(-), I(-), PF(6)(-), SbF(6)(-), B(C(6)F(5))(4)(-), TRISPHAT) was realized. The six different ion pairs have been characterized by X-ray diffraction, and their absorption properties were studied in polar (DCM) and apolar (toluene) solvents. A small, hard anion (Br(-)) is able to strongly polarize the polymethine chain, resulting in the stabilization of an asymmetric dipolar-like structure in the crystal and in nondissociating solvents. On the contrary, in more polar solvents or when it is associated with a bulky soft anion (TRISPHAT or B(C(6)F(5))(4)(-)), the same cyanine dye adopts preferentially the ideal polymethine state. The solid-state and solution absorption properties of heptamethine dyes are therefore strongly correlated to the nature of the counterion.

From Hetero- to Homochiral Bis(metallahelicene)s Based on a PtIII−PtIII Bonded Scaffold: Isomerization, Structure, and Chiroptical Properties

Hetero- and homochiral diastereomeric bis(metallahelicene)s have been synthesized. They possess a rare Pt(III)-Pt(III) scaffold bridged by benzoato ligands. It is shown that heterochiral (P,M)-bis(Pt(III)-[6]helicene) can isomerize into the homochiral (P,P)- and (M,M)-bis(Pt(III)-[6]helicene). A theoretical study shows a unique σ-π conjugation between the two π-helices and the σ-Pt(III)-Pt(III) scaffold that impacts the strong chiroptical properties.

Redox-active organometallics: magnetic and electronic couplings through carbon-silicon hybrid molecular connectors.

Treatment of the triflate complex Cp*(dppe)FeOTf [12; Cp* = eta(5)-C(5)(CH(3))(5), dppe = 1,2-bis(diphenylphosphino)ethane, OTf = CF(3)SO(3)] with an excess of HC[triple bond]C-(Si(CH(3))(2))(x)-C[triple bond]CH (x = 2-4) in diethyl ether provides the binuclear bis(vinylidene) derivatives [Cp*(dppe)Fe=C=CH(Si(CH(3))(2))(x)CH=C=Fe(dppe)Cp*][OTf](2) (x = 2, 13; x = 3, 14; x = 4, 15), which were isolated as ochre solids and rapidly characterized by FT-IR, (1)H, (31)P, and (13)C NMR spectroscopies. The complexes 13-15 were reacted with potassium tert-butoxide to afford the bis(alkynediyl) complexes [Cp*(dppe)Fe-C[triple bond]C(Si(CH(3))(2))(x)C[triple bond]C-Fe(dppe)Cp*] (x = 2, 1; x = 3, 2; x = 4, 3), which were isolated as orange powders in yields ranging from 76 to 91%. The IR, cyclic voltammetry, and UV-vis data obtained for 1-3 and the X-ray crystal structures determined for 1 and 3 reveal the importance of the sigma-pi conjugation (hyperconjugation) between the Si-Si sigma bond and the adjacent C[triple bond]C pi-symmetric orbitals in the description of the electronic structure of the ground state of these complexes. When reacted at low temperature with 2 equiv of [(C(5)H(5))(2)Fe]X or AgX [X = BPh(4), B(3,5-(CF(3))(2)C(6)H(3))(4))], compounds 1-3 provide 1[X](2), 2[X](2), and 3[X](2), which can be isolated and stored below -20 degrees C. EPR spectroscopy and magnetization measurements established that the superexchange interaction propagates through the Si-Si bonds (J = -0.97(2) cm(-1) for 3[X](2)). UV-vis-near-IR spectra were obtained with an optically transparent thin-layer electrosynthetic (OTTLE) cell for 1-3[OTf](n) (n = 0-2). A band with a maximum that increases from 6400 cm(-1) (1[OTf]) to 8500 cm(-1) (3[OTf]) observed for the mixed-valence species was ascribed to intervalence charge transfer evidencing photodriven electron transfer through the carbon-silicon hybrid connectors with H(ab) parameters ranging from 64 to 285 cm(-1).

First lanthanide dipolar complexes for second-order nonlinear optics

New push-pull NLO-phores based on lanthanide complexes (Ln = La, Gd, Dy, Yb) featuring an annelated dibutylaminophenyl functionalised terpyridyl ligand have been synthesised and shown to exhibit large first-order hyperpolarizability.

Novel chiral molecular tweezer from (+)-usnic acid.

A new chiral molecular tweezer was synthesized with (1R,2R)-1,2-diaminocyclohexane as spacer and two molecules of (+)-usnic acid as pincers. The ability of this molecular tweezer to bind 2,4,7-trinitrofluorenone was studied. A charge-transfer complex was formed in which TNF was sandwiched between the two usnic acid units with pi-pi-stacked aromatic interactions.

An efficient route to per-O-acetylated hexofuranoses

Anomeric mixtures of per-O-acetylated D-galacto-, D-gluco- and D-manno-furanose derivatives were prepared via the corresponding n-octyl hexofuranosides under mild acetolysis conditions. The crystal X-ray data of 1,2,3,5,6penta-O-acetyl-a-D-mannofuranose corroborate the proposed structures.

Buta-1,2,3-trienylidene, acylvinylidene and acylalkynyl ruthenium complexes via activation of alkynes with RuCl2(dppe)2. X-ray structure of trans-[Ru(CCHCOCH2Ph)(Cl)(dppe)2]O3SCF3

The activation of several functional alkynes HCC–CC–Ph ( a ), HCCCOCHPh 2 ( b ) and HCC–CHOH–CHPh 2 ( c ) with the precursor [RuCl(dppe) 2 ]PF 6 [RuCl(dppe) 2 ={Ru}], in situ generated from RuCl 2 (dppe) 2 /NaPF 6 , has been performed. It selectively produces the buta-1,2,3-trienylidene {Ru}CCCCHR] + PF 6 − intermediates ( I ) from a , and acylvinylidene complexes {Ru}CCH–COR] + PF 6 − [R=CH 2 Ph (3) and R=CHPh 2 (5) ] from a and b and {Ru}CCH–CHCPh 2 ] + PF 6 − (10) from c . The deprotonation of 3 , 5 and 10 , respectively, affords acylalkynyl derivatives {Ru}–CC–CO–R] 4 , 6 and {Ru}–CC–CHCPh 2 ] 11 . The X-ray diffraction study of trans -[(Cl)(dppe) 2 RuCCHCOCH 2 Ph]O 3 SCF 3 3 , obtained by reaction of {Ru}–CC–CCPh] with CF 3 SO 3 H and water, has been carried out. Crystal data are: a 13.362(4), b 23.669(4), c 42.218(6) A, orthorhombic space group Pbca , Z =8. The structure shows Ru–C(1) (1.77(1) A) and C(1)–C(2) (1.36(2) A) bond distances.

Synthesis and reactivity of E,Z butadiene-iron tricarbonyl complexes

Abstract The synthesis, structure and thermal stability of the E,Z butadiene-iron tricarbonyl complex 1 is reported. This complex reacts with organometallic nucleophiles in a stereoselective synthesis of functionalized E,Z dienes.

Organometallic Additions to β-substituted N-Boc-β-aminoaldehydes: a New Synthesis of Enantiomerically Pure 1,3-disubstituted N-Boc-1,3-aminoalcohols

Abstract 1,2-addition of organolithium and organomagnesium derivatives to β-substituted (N-Boc)-β-aminoaldehydes gave access to enantiomerically pure, 1,3-disubstituted, 1,3-aminoalcohols. A diastereoselective version of this addition was also investigated and Gilman cuprates were found to add onto aldehydes 1a–b with notable diastereoselectivity (up to 70% de) in favour of the anti isomer. The absolute configuration of each obtained 1,3-aminoalcohol was determined.

Intramolecular cyclization of ω-primary amino electrophilic olefins to functionalized pyrrolidines and piperidines

The intramolecular 1,4-Michael type addition of in situ chemoselectively generated primary amines bearing an electrophilic double bond in the ω position leads to functionalized pyrrolidines and piperidines under very mild conditions.