HERVE Alexandre

No summary available.

Treatment of the metallacycle [UN*2(N,C)] [N* = N(SiMe3)2. N,C = CH2SiMe2N(SiMe3)] with [HNEt3][BPh4], [HNEt3]Cl, and [pyH][OTf] (OTf = OSO2CF3) gave the cationic compound [UN*3][BPh4] (1) and the neutral complexes [UN*3X] [X = Cl (3), OTf (4)], respectively. The dinuclear complex [UN*(?-N,C)(?-OTf)2] (5) and its tetrahydrofuran (THF) adduct [UN*(N,C)(THF)(?-OTf)2] (6) were obtained by thermal decomposition of 4. The successive addition of NEt4CN or KCN to 1 led to the formation of the cyanido-bridged dinuclear compound [(UN*3)2(?-CN)][BPh4] (7) and the mononuclear mono- and bis(cyanide) complexes [UN*3(CN)] (2) and [M][UN*3(CN)2] [M = NEt4 (8), K(THF)4 (9)], while crystals of [K(18-crown-6)][UN*3(CN)2] (10) were obtained by the oxidation of [K(18-crown-6)][UN*3(CN)] with pyridine N-oxide. The THF adduct of 1, [UN*3(THF)][BPh4], and complexes 2?7, 9 and 10 were characterized by their X-ray crystal structure. In contrast to their UIII analogues [NMe4][UN*3(CN)] and [K(18-crown-6)]2[UN*3(CN)2] in which the CN anions are coordinated to the metal center via the C atom, complexes 2 and 9 exhibit the isocyanide U?NC coordination mode of the cyanide ligand. This UIII/UIV differentiation has been analyzed using density functional theory calculations. The observed preferential coordinations are well explained considering the electronic structures of the different species and metal?ligand bonding energies. A comparison of the different quantum descriptors, i.e., bond orders, NPA/QTAIM data, and energy decomposition analysis, has allowed highlighting of the subtle balance between covalent, ionic, and steric factors that govern the U?CN/NC bonding.

No summary available.

Reactions of [MN*3] (M = Ce, U. N* = N(SiMe3)2) and NR4CN (R = Me, Et, or (n)Bu) or KCN in the presence of 18-crown-6 afforded the series of cyanido-bridged dinuclear compounds [NEt4][(MN*3)2(μ-CN)] (M = Ce, 2a, and U, 2b), [K(18-crown-6)(THF)2][(CeN*3)2(μ-CN)] (2'a), and [K(18-crown-6)][(UN*3)2(μ-CN)] (2'b), and the mononuclear mono-, bis-, and tris(cyanide) complexes [NEt4][MN*3(CN)] (M = Ce, 1a(Et), and U, 1b(Et)), [NMe4][MN*3(CN)] (M = Ce, 1a(Me), and U, 1b(Me)), [K(18-crown-6)][MN*3(CN)] (M = Ce, 1'a, and U, 1'b), [N(n)Bu4]2[MN*3(CN)2] (M = Ce, 3a, and U, 3b), [K(18-crown-6)]2[MN*3(CN)2] (M = Ce, 3'a, and U, 3'b), and [N(n)Bu4]2[MN*2(CN)3] (M = Ce, 4a, and U, 4b). The mono- and bis(cyanide) complexes were found to be in equilibrium. The formation constant of 3'b (K3'b) from 1'b at 10 °C in THF is equal to 5(1) × 10(-3), and -ΔH3'b = 104(2) kJ mol(-1) and -ΔS3'b = 330(5) J mol(-1) K(-1). The bis(cyanide) compound 3a or 3b was slowly transformed in solution into an equimolar mixture of the mono- and tris(cyanide) derivatives with elimination of N(n)Bu4N*. The crystal structures of 1a(Me), 1b(Me), 1'a·toluene, 1'b·toluene, 2'a, 2'b, 3a, 3'a, 3'b, 3'a·2benzene, 3'b·2benzene, 4a·0.5THF, and 4b·Et2O were determined. Crystals of the bis(cyanide) uranium complexes 3'b and 3'b·2benzene are isomorphous with those of the cerium counterparts 3'a and 3'a·2benzene, but they are not isostructural since the data revealed distinct coordination modes of the CN group, through the C or N atom to the U or Ce metal center, respectively. This differentiation has been analyzed using density functional theory calculations. The observed preferential coordination of the cyanide and isocyanide ions toward uranium or cerium in the bis(cyanide) complexes is corroborated by the consideration of the binding energies of these groups to the metals and by the comparison of DFT optimized geometries with the crystal structures. The better affinity of the cyanide ligand toward U(III) over Ce(III) metal center is related to the better energy matching between the 6d/5f uranium orbitals and the cyanide ligand ones, leading to a non-negligible covalent character of the bonding.

If the chemistry of cyanide complexes of d metals has been a highly studied discipline for many years, it is however little developed with f metals and in particular with actinides. The cyanide ion, which is an extremely coordinating ligand, bidentate and capable of stabilizing both the high and low oxidation states of the metal centers, seems particularly well suited to uranium. Its use with the f-elements offers, in addition to attractive synthetic perspectives that have already overturned some commonly accepted ideas, a definite interest in obtaining compounds with interesting physicochemical properties. This PhD concerns the development of the chemistry of cyanide complexes of the f elements (Ce, U, Th) in the two series of precursors [Mf(N*)₃]ʲ˖ (j = 0, 1) and [An(Cot)₂] (N* = -N(SiMe₃)₂ . Cot = C₈H₈²-). The first chapter deals with the reactivity of trivalent [Mf(N*)₃] complexes (Mf = Ce, U) with cyanide ion. The syntheses and crystal structures of the mono- and polycyanide complexes [Mf(N*)₃(CN)][M] [Mf(N*)₃(CN)₂][M]₂ and [Mf(N*)₂(CN)₃][M]₂, and of the bimetallic complexes [{Mf(N*)₃}₂(µ-CN)][M] (M = NR₄, K(18-C-6)) are presented. Depending on the ion considered, Ce³˖ or U³˖, the structural characterizations show a different coordination mode of the cyanide ligand. For example, bis-cyanide complexes reveal coordination of cerium by the nitrogen atom (Ce-NC) and uranium by the carbon atom (U-CN). The isocyanide coordination mode is extremely rare with the transition metals d and f. Cyanide complexes of U(IV) presented in Chapter 2 were also obtained from the new tris-amide precursor [U(N*)₃][BPh₄]. The bimetallic species [{U(N*)₃}₂(µ-CN)][BPh₄] and especially the neutral [U(N*)₃(CN)] and anionic [U(N*)₃(CN)₂][M] terminal cyanide derivatives [M] (M = NEt₄, K) were isolated. These monometallic species exhibit the U-NC isocyanide ligation mode, in contrast to other previously known uranium cyanide complexes. Theoretical DFT studies explain the origin of these different coordination modes of the cyanide ligand towards Ce³˖ and U³˖ ions by the involvement of the 5f orbitals and the distinct hardnesses (according to Pearson) of the metal centers. These calculations are in agreement with experiment and highlight the slightly greater energy stability of the Ce³˖-NC , U³˖-CN and U⁴˖-NC bonded compounds. The contribution of cyanide to the chemistry of actinocenes [An(Cot)₂] (An = U, Th), mythical sandwich compounds considered until recently as species without any coordination chemistry, is evident with the preparation of a new class of compounds with bent geometries. While the mono-cyanide complex [U(Cot)₂(CN)][NEt₄] is the only bent compound characterized with uranium, [Th(Cot)₂] exhibits a much more varied chemistry that is the subject of the third chapter. Thorocene thus reacts with CN-, N₃-, and H- ions to give the anionic complexes [Th(Cot)₂(X)][M] (X = CN-, N₃-, and M = Na(18-C-6) and NBu₄), dianionic [Th(Cot)₂(CN)₂][NBu₄]₂ and bimetallic [{Th(Cot)₂}₂(μ-X)][M] (X = CN-, H- and M = Na(18-C-6) and NBu₄]. The structures of the [An(Cot)₂(CN)][NR₄]₂ analogues are notably different (monomer for U and polymer for Th). Cyanide-terminated complexes are interesting molecular building blocks for the elaboration of polynuclear systems and materials that, due to the particular physicochemical properties of the f-elements, are particularly attractive for applications in the field of molecular magnetism and/or luminescence.

(Cot)2Th (1) was found to react with Na*CN (Cot = η8-C8H8. Na* = Na(18-crown-6)) or the ammonium salts NR4CN (R = Et, nBu) in pyridine to give a variety of anionic products, depending on the (Cot)2Th:MCN ratio and the nature of M+ (Na*+ or NR4+). When it was treated with 1 mol equiv of NR4CN (R = Et, nBu) or Na*CN, (Cot)2Th (1) was transformed into the anionic monocyanide derivative [Th(Cot)2(CN)]− (2−) with a bent geometry and crystallized either as a binuclear complex with a Th−CN−Na ligation mode in [(Cot)2Th(μ-CN)][Na*] (2[Na*]) or as a 1D coordination polymer in [(Cot)2Th(μ-CN)][NEt4]∞ (2[NEt4]) due to the presence of Th−CN−Th bridges. The structure of 2[NEt4] is remarkable because it is different from that of [(Cot)2U(CN)][NEt4], where the cyanide is terminal, and because it evidences two available coordination sites on the bent-thorocene fragment, suggesting that the anionic species [(Cot)2Th(μ-CN)Th(Cot)2]− (4) and [(Cot)2Th(CN)2]2− (5) could be obtained. In the presence of 0.5 mol equiv of NnBu4CN in pyridine, 1 was indeed transformed into the binuclear complex [(Cot)2Th2(CN)][NnBu4] (4[NnBu4]), which was characterized by X-ray diffraction, as well as its analogue [(Cot)2Th2(μ-CN)][Na*(py)2]·2py (4[Na*(py)2]·2py) obtained under similar conditions. Crystallization of [(Cot)2Th(CN)][NnBu4] (2[NnBu4]) did not afford a polymeric compound analogous to 2[NEt4] but gave crystals of 4[NnBu4] and of the trinuclear compound [(Cot)2Th(μ-CN)2Th(Cot)2][NnBu4]2·py (3[NnBu4]2·py). Thorocene 1 rapidly reacted with 2 mol equiv of NnBu4CN to give the dianionic complex [(Cot)2Th(CN)2][NnBu4]2 (5[NnBu4]2). However, with an excess of NEt4CN, only the monocyanide compound 2[NEt4] could be obtained from 1, likely as the result of distinct solubilities. The reactions reported here illustrate the chemical potential of thorocene which, in contrast to (Cot)2U, can easily trap strongly coordinating anions and evidence that [Th(CN)]q− species such as 2− may be useful building blocks for the formation of polymetallic derivatives and clusters. Crystal structures show that compounds 2−5 exhibit an unusual bent-thorocene moiety, a long-sought and rare geometry for bis(cyclooctatetraenyl) complexes.

Reactions of [MN*3] (M = Ce, U. N* = N(SiMe3)2) and NR4CN (R = Me, Et, or nBu) or KCN in the presence of 18-crown-6 afforded the series of cyanido-bridged dinuclear compounds [NEt4][(MN*3)2(?-CN)] (M = Ce, 2a, and U, 2b), [K(18-crown-6)(THF)2][(CeN*3)2(?-CN)] (2?a), and [K(18-crown-6)][(UN*3)2(?-CN)] (2?b), and the mononuclear mono-, bis-, and tris(cyanide) complexes [NEt4][MN*3(CN)] (M = Ce, 1aEt, and U, 1bEt), [NMe4][MN*3(CN)] (M = Ce, 1aMe, and U, 1bMe), [K(18-crown-6)][MN*3(CN)] (M = Ce, 1?a, and U, 1?b), [NnBu4]2[MN*3(CN)2] (M = Ce, 3a, and U, 3b), [K(18-crown-6)]2[MN*3(CN)2] (M = Ce, 3?a, and U, 3?b), and [NnBu4]2[MN*2(CN)3] (M = Ce, 4a, and U, 4b). The mono- and bis(cyanide) complexes were found to be in equilibrium. The formation constant of 3?b (K3?b) from 1?b at 10 °C in THF is equal to 5(1) ? 10?3, and ??H3?b = 104(2) kJ mol?1 and ??S3?b = 330(5) J mol?1 K?1. The bis(cyanide) compound 3a or 3b was slowly transformed in solution into an equimolar mixture of the mono- and tris(cyanide) derivatives with elimination of NnBu4N*. The crystal structures of 1aMe, 1bMe, 1?a·toluene, 1?b·toluene, 2?a, 2?b, 3a, 3?a, 3?b, 3?a·2benzene, 3?b·2benzene, 4a·0.5THF, and 4b·Et2O were determined. Crystals of the bis(cyanide) uranium complexes 3?b and 3?b·2benzene are isomorphous with those of the cerium counterparts 3?a and 3?a·2benzene, but they are not isostructural since the data revealed distinct coordination modes of the CN group, through the C or N atom to the U or Ce metal center, respectively. This differentiation has been analyzed using density functional theory calculations. The observed preferential coordination of the cyanide and isocyanide ions toward uranium or cerium in the bis(cyanide) complexes is corroborated by the consideration of the binding energies of these groups to the metals and by the comparison of DFT optimized geometries with the crystal structures. The better affinity of the cyanide ligand toward UIII over CeIII metal center is related to the better energy matching between the 6d/5f uranium orbitals and the cyanide ligand ones, leading to a non-negligible covalent character of the bonding.

No summary available.

Oenological strains show a significant diversity in their nitrogen requirements, which translates into differences in fermentative capacity. At present, the mechanisms involved in the variability of fermentation profiles, following a nitrogen depletion in the environment, are not known. The identification of these mechanisms would be an asset in the understanding of the phenomena leading to problematic fermentations and in fermentation restarts. In order to identify these mechanisms, we coupled a classical physiological and genomic approach with a genetic approach involving the search for QTLs based on the fermentative efficiency under nitrogen deficiency conditions. We characterized this difference in nitrogen requirement between strains as a variability in the ability to perceive nitrogen deficiency and to develop a quiescence program that reduces energy flow and increases a stress state. These energy shifts then translate into differences in fermentative capacity. The QTL approach allowed us to detect 23 regions of the genome potentially involved in the maintenance of fermentative capacity. After analysis, we identified 4 genes whose allelic variations are responsible for phenotypic variations between strains. The use of these genes could allow the design of genetic markers, exploited for the selection of strains with good fermentative capacities. Data from this QTL approach suggest a close correlation between differences in stress response by strains and the involvement of nitrogen perception and signaling mechanisms. Finally, our work offers a new hypothesis, pointing to the TOR pathway as the mechanism responsible for the variation in fermentative capacities between strains.

Reaction of the linear thorocene with NC−, N3− and H− led to the bent derivatives [(Cot)2Th(X)]− (X = CN, N3) and the bimetallic [{(Cot)2Th}2(μ-H)]−, whereas only [(Cot)2U(CN)]− could be formed from (Cot)2U.