Jean-Yves Salaün

The Key Role of the Intermolecular π−π Interactions in the Presence of Spin Crossover in Neutral [Fe(abpt)2A2] Complexes (A = Terminal Monoanion N Ligand)

New iron(II) complexes of formulas [Fe(abpt) 2(tcm) 2] ( 1), [Fe(abpt) 2(tcnome) 2] ( 2), and [Fe(abpt) 2(tcnoet) 2] ( 3) (abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole, tcm (-) = [C(CN) 3] (-) = tricyanomethanide anion; tcnome (-) = [(NC) 2CC(OCH 3)C(CN) 2] (-) = 1,1,3,3-tetracyano-2-methoxypropenide anion; tcnoet (-) = [(NC) 2CC(OC 2H 5)C(CN) 2] (-) = 1,1,3,3-tetracyano-2-ethoxypropenide anion) have been synthesized and characterized by infrared spectroscopy, magnetic properties and by variable-temperature single-crystal X-ray diffraction. The crystal structure determinations of 1 and 2 reveal in both cases centrosymmetric discrete iron(II) monomeric structures in which two abpt chelating ligands stand in the equatorial plane and two terminal polynitrile ligands complete the distorted octahedral environment in trans positions. For 3, the crystallographic studies revealed two polymorphs, 3- A and 3- B, exhibiting similar discrete molecular structures to those found for 1 and 2 but with different molecular arrangements. In agreement with the variable-temperature single-crystal X-ray diffraction, the magnetic susceptibility measurements, performed in the temperature range 2-400 K, showed a spin-crossover phenomenon above room temperature for complexes 1, 3- A, and 3- B with a T 1/2 of 336, 377, and 383 K, respectively, while complex 2 remains in the high-spin ground state ( S = 2) in the whole temperature range. To understand further the magnetic behaviors of 1, 3-A, and 3-B, single-crystal X-ray diffraction measurements were performed at high temperatures. The crystal structures of both polymorphs could not be obtained above 400 K because the crystals decomposed. However, single-crystal X-ray data have been collected for compound 1, which reaches the full high-spin state at lower temperatures. Its crystal structure, solved at 400 K, showed a strong modification of the iron coordination sphere (average Fe-N = 2.157(3) A vs 1.986(3) A at 293 K). In agreement with the magnetic properties. Such structural behavior is a signature of the spin-state transition from low-spin (LS) to high-spin (HS). On the basis of the intermolecular pi stacking observed for the series described in this paper and for related complexes involving similar discrete structures, we have shown that complexes displaying frontal pi stacking present spin transition such as 1, 3-A, and 3-B and those involving sideways pi stacking such as complex 2 remain in the HS state.

A silver-based metal–organic framework material as a ‘reservoir’ of bactericidal metal ions

The silver-based MOF material Ag3(3-phosphonobenzoate) was evaluated as a bactericidal material. A sustainable release of Ag+, which was quantified by cathodic stripping voltammetry, was responsible for bactericidal activity against the 6 bacterial strains tested.

Magnetic bistability and thermochromism in a molecular Cu(II) chain.

An original magnetic bistability and a thermochromic transition are observed in a new Cu(II) molecular chain. Thermal structural studies reveal changes in the Cu(II) coordination sphere, driven by a more pronounced Jahn-Teller effect at low temperature. These distortions provoke a gradual color change. The structural study at 10 K shows a dimerization of the molecular chain, in agreement with the abrupt magnetic transition observed at 30 K.

COMPLEXATION ON RHODIUM OF BIDENTATE AND POTENTIALLY HEMILABILE PHOSPHOROUS LIGANDS

Abstract Various bifunctional potentially hemilabile ligands bearing phosphorous groups have been prepared and their coordination to rhodium has been studied. Their effect on the hydroformylation of styrene has been assessed.

Photochemistry of polyenes. Control by orbital symmetry and ground state conformations

Abstract It is shown that ground state conformations of cyclohexadienes and acyclic hexatrienes play an important role, in addition to orbital symmetry factors, to govern the stereochemistry of the photoisomerization reactions of these compounds. Studying the influence of the wave-length of irradiation allows to attribute to discrete conformations some specific photoreactions (H shift, formation of bicyclo {3.1. 0} hexene). New examples are given, with kinetic data, showing a {4π a + 2π a} stereospecificity for the hexatriene Photo-DIELS-ALDER reaction with a predominent orbital control. The concertedness of the reaction is discussed. Kinetics of Z, E-photoisomerizations around C-C double bonds of hexatrienes are shown, in relation with the ease of terminal compared to central double bonds rotations. Singlet and triplet states have different behaviours in this respect, as well as different wave-lengths of excitation.

Synthesis, reactivity of the [(CO)3(L)Fe(CO2R)2] dialkoxycarbonyl carbonyl iron complexes (L = CO or PPh3; R CH3, C2H5), and an easy access to [(CO)5Fe(CO2Me)]+

Abstract The cis -dialkylcarboxytetracarbonyliron complexes [(CO) 4 Fe(CO 2 R) 2 ] were readily obtained from reaction of oxalyl chloride with the corresponding tetracarbonylcarboxyiron anion [(CO) 4 Fe(CO 2 R)] − (R  Me, 1a ; R  Et, 1b ). 1a underwent a clean ligand exchange with triphenylphosphine to give [Fe(CO) 3 (PPh 3 )(CO 2 Me) 2 ] ( 2 ). Neither 1a nor 2 yielded dimethyl oxalate after thermolysis; rather, a mixture of methanol and methyl carbonate was obtained. The mobility of the alkoxy groups on 1 was shown by several exchange experiments. A clean reaction of the tetrafluoroboric acid ether with 1a gave [(CO) 5 Fe(CO 2 Me)] + which was isolated and characterized by IR, 1 H, and 13 C NMR spectroscopy.

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.

Synthesis of bis-(acyl, carbamoyl or alkoxycarbonyl) iron monomer or dimer complexes by reaction of oxalyl chloride with various tetracarbonyl ferrates: {Fe[C(O)R](CO)4}−

Abstract The reaction of oxalyl chloride with various tetracarbonyl ferrates bearing a carbonylated organic ligand induces the formation of bis substituted monomers Fe[C(O)R] 2 (CO) 4 or dimers {Fe[C(O)R](CO) 4 } 2 and of bis-[μ,η 2 -C(O)R]Fe 2 (CO) 6 bridged dimers. The orientation of the reaction depends on the nature of the organic ligand of the ferrates. Thus carbamoyls or alkoxycarbonyls ferrates bearing mobile R groups are found to induce the formation of bis substituted monomers while bulky alkoxycarbonyl ligands afford non-bridged dimers. Acyls and bulky carbamoyls give rise to dimers bearing bridging acyls or carbamoyls. The mechanisms of formation of these different complexes and the possible thermal interconversions of these compounds are investigated.

Mechanism of formation of the metallacyclic iron carbenes (CO)3)NR2] formed by thermal evolution of bis carbamoyl complexes, characterization of η2-carbamoyl intermediates

Abstract The reaction of oxalyl chloride with carbamoyl ferrates: {Fe[C(O)NR 2 ](CO) 4 } − or alkoxy–amine exchanges from Fe(CO 2 R) 2 (CO) 4 ( 1 ) are found to afford the same metallacyclic carbene complexes: (CO) 3 Fe[C(NR 2 )OC(O )NR 2 ] ( 3 ) instead of the expected bis carbamoyl: Fe[C(O)NR 2 ] 2 (CO) 4 ( 2 ) compounds. Low temperature monitorings and trapping experiments (carried out with phosphines) of the two reactions leading to 3 establish the rapid evolution of 2 into 3 and the easy achievement of η 2 -carbamoyl bonding modes for these iron complexes. It is also shown that the formation of the metallacycle pattern of 3 is obtained by a carbon–oxygen-coupling process performed between the two carbamoyl ligands of [η 1 -C(O)NR 2 ][η 2 -C(O)NR 2 ]Fe(CO) 3 intermediates.

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 ].