Jacques E. Guerchais

Abstract: Upon treatment with methyl-lithium followed by HBF4·OEt2 a carbon monoxide ligand of the µ-alkylidene complex [Ru2(CO)2(µ-CO)(µ-CMe2)(η-C5H5)2](1) is converted into µ-ethylidyne, giving [Ru2(CO)2(µ-CMe)(µ-CMe2)(η-C5H5)2]+(2). This is deprotonated readily by water to form the µ-vinylidene complex [Ru2(CO)2(µ-CCH2)(µ-CMe2)(η-C5H5)2](3), which quantitatively regenerates (2) with HBF4·OEt2. Addition of NaBH4 to (2) results in hydride attack on µ-CMe to yield the di-µ-alkylidene complex [Ru2(CO)2(µ-CHMe)(µ-CMe2)(η-C5H5)2](4) as cis and trans isomers. The structure of the trans isomer has been established by X-ray diffraction. Crystals are triclinic, space group P, with Z= 2 in a unit cell for which a= 8.474(2), b= 7.802(3), c= 12.989(5)A, α= 99.42(3), β= 96.96(3), and γ= 107.73(3)°. The structure was solved by heavy-atom methods and refined to R 0.026 (R′ 0.031) for 4 092 independent intensities. A ruthenium–ruthenium single bond of 2.701(1)A is symmetrically bridged by ethylidene [mean Ru–C 2.079(3)] and isopropylidene [mean Ru–C 2.107(3)A] ligands to form an approximately planar Ru2C2 ring with a non-bonding Me2C··CHMe distance of 3.20 A. Upon thermolysis the alkylidenes link to evolve Me2CCHMe, Me2CHCHCH2, and Et(Me)CCH2. The absence of C4 and C6 hydrocarbons indicates that the alkylidene coupling occurs intramolecularly, and the electronic and stereochemical requirements of this process are discussed. Unlike mono-µ-alkylidene complexes, [Ru2(CO)2(µ-CO)(µ-CR2)(η-C5H5)2], the cis and trans forms. of (4) do not interconvert thermally below 145 °C, but u.v. irradiation effects a slow trans to cis isomerisation. U.v. irradiation of (4) in the presence of dimethyl acetylenedicarboxylate promotes ethylidene–alkyne linking to form [Ru2(CO)(µ-CMe2){µ-C(CO2Me)C(CO2Me)CHMe}(η-C5H5)2], but with ethyne both of the alkylidenes are lost and the ruthenium–ruthenium double-bonded complex [Ru2(µ-CO)(µ-C2H2)(η-C5H5)2] is produced.

Abstract: The previously reported compounds, Et 4 N(C 10 N 7 ), 1 , and [{Ag(C 10 N 7 )} ∞ ], 2 , have been structurally characterized by X-ray diffraction. The C 10 N 7 unit acts in 1 as a monoanion and in 2 as a sophisticated bridging ligand (via the nitrogen atoms of its four external cyanogroups) leading to a structure with two crystallographically distinct silver cations. The first one has an usual pseudo-tetrahedral coordination, the second one presents an unexpected square planar coordination which is discussed. The geometry of the organic fragment is only slightly modified upon coordination: in both cases, the C 10 N 7 unit is essentially planar with central CN bond lengths of 1.317(4) and 1.334(4) A in 1 , 1.33(1) and 1.34(1) A in 2 and CNC angles of 128.3(3) in 1 and 129.2(9)° in 2 . In benzonitrile solutions, the C 10 N 7 anion shows two one electron diffusion-controlled reversible reduction rocesses, the first one leading to the radical species [(C 10 N 7 )] 2− characterized by ESR.

Abstract: [Mo(C 22 H 22 N 4 )] 2 PF 6 •CH 2 Cl 2 cristallise dans le systeme monoclinique avec le groupe d'espace C2/c. Affinement de la structure jusqu'a 0,054

Abstract: The first example of geometrical isomerization of thiolato-bridged dimolybdenum complexes induced by the transfer of two electrons at the same potential is reported. Variable temperature 1H NMR (R  Me, Ph) studies and an X-ray crystal structure determination for the dication (R  t-Bu) allowed the isomers to be identified. Comparisons of the cyclic voltammetry of the compounds {(η5-C5H5)MO(CO)2(μ-SR)}2 (R  Me, t-Bu, Ph) suggest that steric factors are responsible for the preferred trans geometry of the neutral complexes. The compound {(η5-C5H5)(CO)2 Mo(μ-S-t-Bu) 2 M o(CO)2 (η5-C5H5)}(BF4)2. CH3CN has been characterized by X-ray diffraction. The crystals are orthorhombic, space group P212121, with four molecules in a unit cell of dimensions a 10.598(3), b 13.489(3), c 21.801(3) A. The structure was refined to R = 0.60.

Abstract: Metallophthalocyanines and their derivatives appear as promising electrocatalysts for a great variety of electrochemical reactions. The factor that control the activity of these chelates are not fully understood but parameters such as redox potentials of the metal and electronic structure appear to be crucial.

Abstract: The reaction chemistry of nitriles, RCN, where R is usually an organyl group, with transition metal complexes is reviewed. The review surveys data published during the period 1977-early 1994 on new reaction processes such as insertion into metal-hydrogen and -carbon bonds, coupling between one nitrile and an unsaturated metal fragment or between two nitriles, reduction to amines, attack by protic and aprotic nucleophiles and electrophilic attack as well as some catalytic transformations, which result from the ability of nitriles to coordinate to transition metal centres with a consequent change in the electrophilicity or nucleophilicity of the coordinated ligand.

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Abstract: A spectroscopic and structural investigation of binuclear silver(I) complexes supported by aliphatic phosphine ligands, namely [Ag(PCy3)(O2CCF3)]2 (1), [Ag2(μ-dcpm)2]X2 (X = CF3SO3, 2; PF6, 3; dcpm = bis(dicyclohexylphosphino)methane), and [Ag2(μ-dcpm)(μ-O2CCF3)2] (4), is described. X-ray structural analyses of 1−4 reveal Ag−Ag separations of 3.095(1), 2.948 (av), 2.923 (av), and 2.8892(9) A, respectively. Due to the optical transparency of the phosphine ligands, the UV−vis absorption band at 261 nm in CH3CN for 2 and 3 is assigned to a 4dσ* → 5pσ transition originating from Ag(I)−Ag(I) interactions. The argentophilic nature of this band is verified by the resonance Raman spectrum of 2 with 273.9 nm excitation, where virtually all of the Raman intensity appears in the Ag−Ag stretch fundamental (80 cm-1) and overtone bands. Complexes 2 and 3 exhibit photoluminescence in the solid state at room temperature.