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Philippe Turek

Publications and source records attributed to Philippe Turek.

7 recordsLinked to original sources
PubMed2006

Built-in axial base binding on phenanthroline-strapped zinc(II) and iron(III) porphyrins.

In addition to the need for functional models of cytochrome c oxidase, structural models are still required for a better understanding of the small reorganizations occurring during the catalytic cycle. An efficient synthetic approach has been designed to prepare several phenanthroline-strapped porphyrins, two of them bearing two pendant imidazoles. These built-in bases are both potentially able to act as axial bases for the metalloporphyrin and as complementary ligands for copper if necessary. Diamagnetic zinc(II) was used to demonstrate that the distal/proximal selectivity demonstrated by exogenic bases binding studies can be extended to the coordination of iron(III). Combination of EPR and paramagnetic 1H NMR shows that the imidazole binding on the zinc species can be further extended to the iron(III) species in dilute conditions.

Copper↗
PubMed2006

C7 and C9 carbon-rich bridges in diruthenium systems: synthesis, spectroscopic, and theoretical investigations of different oxidation States.

Two methodologies of C-C bond formation to achieve organometallic complexes with 7 or 9 conjugated carbon atoms are described. A C7 annelated trans-[Cl(dppe)2Ru=C=C=C-CH=C(CH2)-C[triple bond]C-Ru(dppe)2Cl][X] (X = PF6, OTf) complex is obtained from the diyne trans-[Cl(dppe)2Ru-(C[triple bond]C)2-R] (R = H, SiMe3) in the presence of [FeCp2][PF6] or HOTf, and C7 or C9 complexes trans-[Cl(dppe)2Ru-(C[triple bond]C)n-C(CH3)=C(R1)-C(R2)=C=C=Ru(dppe)2Cl][X] (n = 1, 2; R1 = Me, Ph, R2 = H, Me; X = BF4, OTf) are formed in the presence of a polyyne trans-[Cl(dppe)2Ru-(C[triple bond]C)n-R] (n = 2, 3; R = H, SiMe3) with a ruthenium allenylidene trans-[Cl(dppe)2Ru=C=C=C(CH2R1)R2][X]. These reactions proceed under mild conditions and involve cumulenic intermediates [M+]=(C=)nCHR (n = 3, 5), including a hexapentaenylidene. A combination of chemical, electrochemical, spectroscopic (UV-vis, IR, NIR, EPR), and theoretical (DFT) techniques is used to show the influence of the nature and conformation of the bridge on the properties of the complexes and to give a picture of the electron delocalization in the reduced and oxidized states. These studies demonstrate that the C7 bridging ligand spanning the metal centers by almost 12 angstroms is implicated in both redox processes and serves as a molecular wire to convey the unpaired electron with no tendency for spin localization on one of the halves of the molecules. The reactivity of the C7 complexes toward protonation and deprotonation led to original bis(acetylides), vinylidene-allenylidene, or carbyne-vinylidene species such as trans-[Cl(dppe)2Ru[triple bond]C-CH=C(CH3)-CH=C(CH3)-HC=C=Ru(dppe)2Cl][BF4]3.

Carbon↗
PubMed2005

Towards a better understanding of magnetic interactions within m-phenylene alpha-nitronyl nitroxide and imino nitroxide based radicals, part III: Magnetic exchange in a series of triradicals and tetraradicals based on the phenyl acetylene and biphenyl coupling units.

The present work completes and extends our previous reports on the determination of the magnetic ground state and on the strength of the through bond exchange coupling within series of biradicals. This knowledge was subsequently exploited for the analysis of the magnetic interactions in their crystals. We report here the studies of series of triradicals incorporating alpha-nitronyl nitroxides (NN) or alpha-imino nitroxides (IN) as terminal radical fragments connected through a m-phenylene coupling unit in one case and a phenyl acetylene unit in other case. Tetraradical derivatives have also been studied. The studies of isolated molecules (EPR in solution and DFT calculations) allow the assessment of the magnetic interactions through the magnetic coupling unit. All triradical derivatives are found to exhibit a quartet ground state, whereas a singlet ground state is determined for the tetraradical. This last result reinforces previous findings that the singlet ground state is favoured in related biradicals involving similar m-phenylene couplers. Moreover, the through bond magnetic exchange coupling for the ortho-meta connectivity could be demonstrated as being ferromagnetic, thus ascertaining our previous hypotheses. The magnetic properties of the triradicals and tetraradicals in their solid state have been rationalized by using a previously proposed methodology, allowing to identify the most relevant magnetic pathways.

Journal Article↗
PubMed2004

Strong exchange interactions between two radicals attached to nonaromatic spacers deduced from magnetic, EPR, NMR, and electron density measurements.

A nitronyl-nitroxide (NIT) biradical D-NIT2 linked by a single double bond has been engineered and investigated in the solid state by a combination of X-ray diffraction, magnetic susceptibility measurement, EPR, as well as solid-state (1)H and (13)C NMR spectroscopies, and experimental electron density distribution. All techniques reveal that a double bond is a very efficient coupling unit for exchange interactions between two radical moieties. Using a Bleaney-Bowers model dimer (H = -JS(1)S(2)), a singlet-triplet energy gap of J = -460 K was found with the singlet state being the ground state. This very strong intramolecular interaction was confirmed by EPR measurements in CH(2)Cl(2) solution (6 10(-4) M) or dispersed in a polymer matrix at low concentration. In keeping with these unusual interactions, solid-state NMR signals of the biradical were found to be considerably less shifted than those found for related monoradicals. Temperature-dependent solid-state (13)C NMR spectra of D-NIT2 confirmed the very strong intramolecular coupling constant (J = -504 K). The electron density distribution of D-NIT2 was measured by high resolution X-ray diffraction, which also revealed that this biradical is an ideally conjugated system. The in-depth characterization includes the deformation maps and the observed electron density ellipticities, which exhibit a pronounced sigma-pi character of the O-N-C=C-N-O cores in keeping with an efficient electronic delocalization along the alkene spacer.

Journal Article↗
PubMed2003

Spin exchange interaction through phenylene-ethynylene bridge in diradicals based on iminonitroxide and nitronylnitroxide radical derivatives. 1. Experimental investigation of the through-bond spin exchange coupling.

A series of bis-iminonitroxide diradical derivatives of different lengths and geometry have been prepared that incorporate a conjugated phenylene-ethynylene bridge as a rigid spacer. This paper describes the synthesis of these new components and their main characterizations. An unexpected singlet ground state and substituent effects on the singlet-triplet gap have been found for substituted "m-phenylene"-based diradicals. The effects of the pi-conjugation on the intramolecular through-bond spin coupling have been investigated by changing the length of the spacer within linear derivatives. The EPR studies demonstrate the intramolecular magnetic coupling between the radical spins within all compounds. This result is very attractive and unusual, given the large distance between the radicals from 15 A in the dimer to 36 A in the pentamer.

Journal Article↗
PubMed2003

Aminomethyl-bipyridine bearing two flexible nitronyl-nitroxide arms: a new podand for complexation of transition metals in a facial or meridional conformation.

Transition metal complexes of 6-aminomethyl-bis[methyl-2-(4,5-dihydro-4,4,5,5- tetramethylimidazolinyl-3-oxide-l-oxy)]-2,2'-bipyridine, bpyN(NIT)(2), 1, have been synthesized and characterized by FAB-MS, UV-vis, FT-IR, and EPR spectroscopies, elemental analysis, and susceptibility measurements. Single-crystal X-ray diffraction studies have been performed on all compounds giving the following crystal data: bpyN(NIT)(2), 1, triclinic, P(-)1, Z = 2, a = 10.7224(4) A, b = 11.0995(4) A, c = 13.1134(3) A, alpha = 114.101(9) degrees, beta = 97.476(9) degrees, gamma = 99.667(9) degrees; ZnbpyN(NIT)(2), 2, hexagonal, P3(2), Z = 3, a = 15.4545(3) A, b = 15.4545(3) A, c = 13.5594(3) A; NibpyN(NIT)(2), 3, hexagonal, P3(2), Z = 3, a = 15.2867(1) A, b = 15.2867(1) A, c = 13.7160(1) A; CubpyN(NIT)(2), 4, triclinic, P(-)l, Z = 2, a = 11.8640(4) A, b = 13.2023(4) A, c = 13.2661(5) A, alpha = 90.539(9) degrees, beta = 104.983(9) degrees, gamma = 113.252(9) degrees. The two radicals of the free ligand 1 are almost perpendicular to one another in the solid state, favoring a weak ferromagnetic interaction (J/k(B) = 8.8 K). The complexes obtained by wrapping the ligand around a single metal center gave rise to two different coordination schemes where the two radicals of 1 adopt a ON(3)O meridional (with Ni and Zn) or a ON(3)O facial conformation (with Cu), which strongly affects the magnetic and electronic properties (O accounts for the coordinated oxygen atoms of the nitroxide radicals and N(3) accounts for the tertiary amine). For 2, a model of a dimer has been used giving rise to a weak antiferromagnetic interaction between the radicals (J/k(B) = -5.3 K). For 3, a very strong intramolecular antiferromagnetic coupling has been found and estimated at J/k(B) = -230 K and J'/k(B) = -110 K between the nickel and each radical using an asymmetric model of a trimer. For 4, an unusual magnetic behavior is observed, dominated by antiferromagnetic interactions with a residual plateau at chiT = 0.63 emu.K.mol(-)(1). Molecular modeling at the CASSCF level is in keeping with an antiferromagnetic coupling of the radical bound with the Cu(II) in the equatorial position. The combined structural, electronic, and magnetic characteristics suggest that the use of a flexible molecule provide an additional approach for fine-tuning magnetic interactions.

Journal Article↗