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Jean Fischer

Publications and source records attributed to Jean Fischer.

9 recordsLinked to original sources
PubMed2002

Expression of the prohelicity of bis-cyclomanganated 2,3-diphenylquinoxaline through reactions with diaryldiazomethanes.

The reactions of bis-cyclomanganated 2,3-diphenylquinoxaline with diazodiphenylmethane and 9-diazofluorene allowed the formation of a new oligomeric and dinuclear manganospiralene and the ready preparation of a pentacyclic helix comprising two (eta 5-fluorenyl)Mn(CO)3 fragments, whose helicity can be locked upon one-dimensional linear coordination to silver cation.

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PubMed1999

Four-Coordinate, Low-Spin (S = 0) and Six-Coordinate, High-Spin (S = 1) Nickel(II) Complexes of Tetraphenylporphyrins with beta-Pyrrole Electron-Withdrawing Substituents: Porphyrin-Core Expansion and Conformation.

To examine the porphyrin-core expansion and the conformational variations induced by a change in the coordination sphere of nickel(II) from four-coordinate, low-spin (S = 0) to six-coordinate, high-spin (S = 1), several nickel(II) derivatives of tetraphenylporphyrins, substituted in their beta-pyrrole positions with electron-withdrawing groups, were isolated and studied by X-ray crystallography. The four-coordinate nickel(II) complex studied, Ni(TPP(Br)(4)(CN)(4)) (1), is a derivative of the antipodal beta-pyrrole brominated and cyanated macrocycle, 2,3,12,13-tetrabromo-7,8,17,18-tetracyano-5,10,15,20-tetraphenylporphyrin. One of the six-coordinate species is the bis-pyridine nickel(II) adduct, Ni(TPP(Br)(4)(CN)(4))(py)(2) (2), of this antipodal beta-pyrrole brominated and cyanated ring, whereas the second six-coordinate complex is the bis-1-methylimidazole nickel(II) adduct, Ni(TPP(CN)(4))(1-MeIm)(2) (3), of the antipodal tetracyanated macrocycle, 7,8,17,18-tetracyano-5,10,15,20-tetraphenylporphyrin. This study confirms that, upon conversion of a four-coordinate, low-spin nickel(II) derivative of a beta-pyrrole-substituted tetraphenylporphyrin into a six-coordinate, high-spin complex, a radial expansion of the porphyrin core also takes place. This radial expansion flattens the porphyrin core, inducing more planarity in the conformations of the six-coordinate nickel(II) porphyrin species. The X-ray structure of 1 reveals an average Ni-N(p) bond distance of 1.920(2) Å, similar to that present in tetragonal Ni(OEP) [(Ni-N(p))(av) = 1.929(3) Å], the ruffled low-spin nickel(II) (S = 0) porphyrin derivative, and many other low-spin nickel(II) complexes of distorted porphyrins. The conformation of the macrocycle present in 1 is severely saddle-shaped with a small ruffling and a minor doming. The structures of 2 and 3 indicate a clear expansion of the porphyrin cores with two sets of (Ni-N(p))(av) bond lengths of 2.040(2) and 2.073(2) Å in 2 and 2.037(2) and 2.068(2) Å in 3, which differ significantly from the average Ni-N(p) distance occurring in 1. Relative to the conformation of the porphyrin ring present in 1, the high-spin complex 2 is less saddle-shaped, but more ruffled. In 3, in which only two opposite pyrrole rings of the porphyrin are substituted by cyano groups, the macrocycle adopts a slightly waved conformation. Crystal data: Ni(TPP(Br)(4)(CN)(4)).2.5(1,2-Cl(2)C(2)H(4)), [1.2.5(1,2-Cl(2)C(2)H(4))], triclinic, space group P&onemacr;, a = 13.741(1) Å, b = 14.029(2) Å, c = 15.201(2) Å, alpha = 89.037(9) degrees, beta = 70.829(8) degrees, gamma = 67.607(8) degrees, V = 2539.4(5) Å(3), T = 20 degrees C, Z = 2, R(F)() = 0.047 and R(wF) = 0.067 based on 5341 reflections with I > 3sigma(I); Ni(TPP(Br)(4)(CN)(4))(py)(2).2.5(1,2-Cl(2)C(2)H(4)), [2.2.5(1,2-Cl(2)C(2)H(4))], triclinic, space group P&onemacr;, a = 11.9472(9) Å, b = 14.3651(7) Å, c = 19.556(1) Å, alpha = 87.049(5) degrees, beta = 73.181(6) degrees, gamma = 70.613(5) degrees, V = 3026.8(4) Å(3), T = 173 K, Z = 2, R(F)() = 0.036, R(wF) = 0.041 based on 6846 reflections with I > 3sigma(I); Ni(TPP(CN)(4))(1-MeIm)(2).2CH(2)Cl(2), [3.2(CH(2)Cl(2))], monoclinic, space group C2/c, a = 26.804(8) Å, b = 10.948(3) Å, c = 19.453(5) Å, beta = 113.13(2) degrees, V = 5251.5 Å(3), T = 20 degrees C, Z = 4, R(F)() = 0.047, R(wF) = 0.067 based on 4384 reflections with I > 3sigma(I).

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PubMed1998

Biphenyl-Strapped Diphenylporphyrins: Synthesis and Spectroscopic Characterization of a Series of Porphyrins with Ether-Linked Straps. Preliminary CO Binding Properties of Their Iron(II) Derivatives.

The synthesis of a series of meso-5,15-diphenylporphyrins strapped by 2,2'-disubstituted biphenyl units (6H(2), 7H(2), 8H(2)) is described. The biphenyl straps used are linked via their 3,3'-positions by CH(2)O groups to ortho-positions of the phenyl rings of the 5,15-diphenylporphyrins. The straps of these porphyrins have their 2,2'-positions occupied by H (6H(2)), Me (7H(2)), and OMe (8H(2)). The electronic spectral properties of these strapped porphyrins are given, and their conformational properties, which have been studied by (1)H NMR spectroscopy, are described. The synthesis and spectroscopic characterization of several iron(II) and iron(III) derivatives of these porphyrins with different axial bases are also presented. The X-ray structure of the chloroiron(III) derivative of the diphenylporphyrin dianion 6 has been determined. Violet crystals of composition 6-FeCl.CH(3)OH.CH(2)Cl(2) have been obtained by slow evaporation of CH(2)Cl(2)/MeOH solutions of 6-FeCl. These crystals belong to the monoclinic system, space group P2(1)/c, with a = 10.164(3) Å, b = 28.977(9) Å, c = 14.283(4) Å, beta = 106.22(2) degrees, and Z = 4. The iron atom of 6-FeCl is five-coordinate, high-spin. The axial chloride ligand lies opposite to the strap. The average Fe-N(p) bond distance is 2.046(6) Å, and the Fe-Cl bond length equals 2.234(2) Å. The porphyrin is slightly domed and ruffled with the iron atom lying at 0.45(1) Å out of the 4N(p) mean-plane and 0.49(1) Å out of the 24-atom core mean-plane of the porphyrin ring. Ferrous carbonyl adducts of these porphyrins have been obtained in various solvents in the presence or absence of nitrogenous bases. Their structures have been studied by (1)H NMR and IR spectroscopy. Two CO stretching vibrations differing by 20 cm(-)(1) occur in the IR spectra of 6-Fe(CO)(B) (B = py, ImH, NMeIm). The possible origin of these two nu(CO) bands is discussed.

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PubMed1996

Effect of a Phosphazene Base on the Diastereoselectivity of Addition of alpha-Sulfonyl Carbanions to Butyraldehyde and Isopropylideneglyceraldehyde.

The effect of tBuP4, a strong and cation-free base, on the yield and diastereoselectivity of additions of thus formed "naked" alpha-sulfonyl carbanions to achiral butyraldehyde and chiral isopropylideneglyceraldehyde was studied. It has been found that with tBuP4 a reasonable yield ( approximately 55%) and a slightly better diastereoselectivity (72% of the anti diastreomer) are obtained with achiral and nonfunctionalized butyraldehyde while with isopropylideneglyceraldehyde the use of tBuP4 allowed us to greatly increase the yields (up to 95-100%) and the diastereoselectivities (83-89% of a single diastereomer over the four possible diastereomers). It was also shown that the extra oxygen atom in the alpha-position plays a determinant role in this effect.

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PubMed1996

Thermal Coupling Reactions of 1-Phenyl-3,4-dimethylphosphole within the Coordination Sphere of Palladium(II).

The thermolyses of dihalobis(1-phenyl-3,4-dimethylphosphole)palladium(II) complexes [(DMPP)(2)PdX(2), X = Cl, Br, I] were investigated in 1,1,2,2-tetrachloroethane solutions at 145 degrees C and in the crystalline state at 140 degrees C. For cis-(DMPP)(2) PdCl(2) and cis- or trans-(DMPP)(2) PdBr(2) four types of products were formed: (1) [4 + 2] cycloaddition products, (2) [2 + 2] cycloaddition products, (3) compounds that result from 1,5-hydrogen migration from a methyl group on one phosphole to the beta-carbon of an adjacent phosphole (exo-methylene), and (4) products that result from an intermolecular [4 + 2] coupling of two phospholes followed sequentially by phosphinidene elimination and intramolecular [4 + 2] cycloaddition to another phosphole to give diphosphatetracyclotetradecatrienes (DPTCT). trans-(DMPP)(2)PdBr(2) undergoes thermal isomerization to cis-(DMPP)(2)PdBr(2) in the solid state, and cis- and trans-(DMPP)(2)PdBr(2) give the same products in both their solid- and solution-state thermolyses. In contrast, trans-(DMPP)(2) PdI(2) neither isomerizes to the cis-isomer nor undergoes any of the phosphole coupling reactions in either the solution or solid state. The crystal structures of trans-(DMPP)(2)PdX(2) (X = Br, I), {(DMPP)(2)[2 + 2]}PdBr(2), {(DMPP)(2)(exo-methylene)}PdBr(2), and (DPTCT)PdCl(2) were determined. They crystallize in the monoclinic P2(1)/c, triclinic P&onemacr;, monoclinic P2(1)/c, monoclinic P2(1)/n, and orthorhombic P2(1)2(1)2(1) space groups in units cells of the following dimensions: a = 10.158 (3) Å, b = 14.876 (4) Å, c = 16.829 (5) Å, beta = 104.25(2) degrees, rho(calc) = 1.732 g/cm(3), Z = 4; a = 9.025(1) Å, b = 11.023(1) Å, c = 13.833 (1) Å, alpha = 101.15(1) degrees, beta = 98.82(1) degrees, gamma = 105.30(1) degrees, rho(calc) = 1.886 g/cm(3), Z = 2; a = 13.090 (2) Å, b = 17.637 (2) Å, c = 21.834 (2) Å, beta = 100.51 (1) degrees, rho(calc) = 1.738 g/cm(3), Z = 4, a = 10.721 (1) Å, b = 16.929 (1) Å, c = 14.675(1) Å, beta = 97.86 (1) degrees, rho(calc) = 1.663 g/cm(3), Z = 4; and a = 15.532 (3) Å, b = 19.401 (4) Å, c = 9.910 (2) Å, rho(calc) = 1.490 g/cm(3), Z = 2, respectively. Least-squares refinements converged at final values of R(F) of 0.041, 0.0354, 0.0624, 0.0533, and 0.035 for 2770, 2672, 2729, 2159, and 2525 independent observed reflections, respectively. Kinetic studies suggest that the reaction mechanisms are the same in both the solid and solution states and that the reaction mechanisms are substantially different from those previously reported for the thermolyses of the analogous cis-(DMPP)(2)PtX(2) complexes.

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PubMed1996

Influence of the Sulfinyl Group on the Chemoselectivity and pi-Facial Selectivity of Diels-Alder Reactions of (S)-2-(p-Tolylsulfinyl)-1,4-benzoquinone.

Diels-Alder reactions of (S)-2-(p-tolylsulfinyl)-1,4-benzoquinone (1a) with cyclic (cyclopentadiene and cyclohexadiene) and acyclic dienes (1-[(trimethylsilyl)oxy]-1,3-butadiene and trans-piperylene) under different thermal and Lewis acid conditions are reported. Chemoselectivity (reactions on C(2)-C(3) versus C(5)-C(6) double bonds) is mainly related to the cyclic (on C(5)-C(6)) or acyclic (on C(2)-C(3)) structure of the diene. The high pi-facial selectivity observed could be controlled by choosing adequate experimental conditions.

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