Jacques E. Guerchais

Comparison of the properties of the 1,1,2,4,5,5-hexacyano-3-aza-penta-1,4-dienide[(NC)2CC(CN)NC(CN)C(CN)2] unit as anion and as ligand. Crystal structures of (Et4N)(C10N7) and [{Ag(C10N7)}∞]

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.

Electrochemically-induced isomerization of {(η5-C5H5)Mo(CO)2(μ-SR)}2 (R Me, t-Bu, Ph) complexes. 1H NMR and electrochemical studies. Sythesis and X-ray crystal structure of {(η5-C5H5)Mo(CO)2(μ-S-t-Bu)}2(BF4)2

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.

Réactions d'insertion du cyanoacétylène et du dicyanoacétylène dans les deux liaisons métalhydrogène des dihydrures [(C5H5)2MH2] (M Mo ou W)

Abstract Only alkyne or alkene insertion reactions into one MH bond of [(C 5 H 5 ) 2 MH 2 ] (M  Mo or W) have been reported up to now. The insertion of alkynes with low steric hindrance, cyanoacetylene (HCCCN) and dicyanoacetylene (NCCCCN) into both MH of [(C 5 H 5 ) 2 MH 2 ] bonds are described in this paper. The first, as well as the second insertion of the same alkyne (either HCCCN or NCCCCN) is stereoselective. The (C 5 H 5 ) 2 M(H)AAH or (C 5 H 5 ) 2 M(AAH) 2 complexes are formed. In the case of mixed diinsertion complexes, ([(C 5 H 5 ) 2 M(σ-C 3 H 2 N)(σ-C 4 HN 2 )]) containing both cyanoacetylene and dicyanoacetylene, the geometry of the final products depends on the order of addition of the reactants. Thus, the insertion of (HCCCN) into [(C 5 H 5 ) 2 MH(σ- trans -C(CN)CHCN)] is stereoselective, while in the reaction of (NCCCCN) with [(C 5 H 5 ) 2 MH(σ-C(CN)CH 2 ] two stereoisomers [(C 5 H 5 ) 2 M(σ- trans - and - cis -C(CN)CHCN)(σ-C(CN)CH 2 )] are formed. Insertions of cyanoacetylene and dicyanoacetylene into a MH bond of (C 5 H 5 ) 2 M(H)AAH complexes (AA  HCCCF 3 , CH 3 O 2 CCCCO 2 CH 3 , NCCHCHCN, CH 3 O 2 CCHCHCO 2 CH 3 ) are also reported. The stereochemistry of the various complexes is proposed on the basis of 1 H and 13 C NMR spectra, and the mechanisms of the various insertion reactions are discussed.

Chimie organométallique du niobium VIII. Etude détaillée de la réaction d'acétyléniques perfluorés avec (η5C5H5)2NbH3: Mise en evídence de la coupure de liaison C-F, de la formation de liaison Nb-F et de la reduction du niobium. Structure cristalline d'un dérivé niobiacyclopentadiène

Abstract Hexafluorobutyne (CF3CCCF3 = Hfb) reacts with Cp2NbH3 (Cp = η5-C5H5) affording five new complexes I–V, whose structures have been studied by mass, Ir, ESR and NMR spectroscopy. The X-ray study of II shows the presence of a planar NbC4 ring Nb—C(1): 2.25(5); C(1)—C(2): 1.31(7); C(2)—C(3): 1.53(8); C(3)—(4): 1.34(7); C(4)—Nb: 2.23(5) A. With trifluoropropyne (CF3CCH = tfp), only the analog of III, i.e. Cp2NbFf(tfpH), has been isolated.

Organic chemistry of dinuclear metal centres. Part 12. Synthesis, X-ray crystal structure, and reactivity of the di-µ-alkylidene complex [Ru2(CO)2(µ-CHMe)(µ-CMe2)(η-C5H5)2]: alkylidene linking

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.

Niobium organometallic chemistry : V. Crystal and molecular structure of bis(η5-cyclopentadienyl)peroxochloroniobium(V) [(η5-C5H5)2Nb(OO)Cl]

Abstract The structure of bis(η5-cyclopentadienyl)peroxochoroniobium(V) has been determined from diffractometer data by X-ray methods; a = 17.81, b = 6.343, c= 26.156 A,β = 138.28°, space group P21/c, Mo-Kα radiation, 3706 indepen reflections with I > 2σ(I), final R = 0.036. Each Nb atom is η5 bonded to two C5H5 rings. The two oxygen atoms (OO = 1.47, NbO = 1.97 and 2.00 A) and the chlorine atom (NbCl = 2.483 A) are in the plane (within ±0.02 A) which bisects the (η5-C5H5)Nb bent sandwich system.

RADICAL CATION-RADICAL ANION SALTS : MOLYBDENUM COMPLEXES CONTAINING THE TCNQ.- OR TCNE.- RADICAL ANIONS. X-RAY CRYSTAL STRUCTURE OF MO(ET2NCS2)4(TCNQ )

Abstract The reactions between the molybdenum(IV) complexes [Mo(dtc) 4 ] 1 (dtc = Et 2 NCS 2 for 1a and Me 2 NCS 2 for 1b ) and TCNQ produced the 1 : 1 derivatives [Mo(dtc) 4 ](TCNQ) 2. Subsequent reaction of 2 with TCNQ gave the 1 : 2 complexes 3 [Mo(dtc) 4 ](TCNQ) 2 . Complexes 1 reacted with TCNE under nitrogen to give the 1 : 1 compounds [Mo(dtc) 4 ](TCNE) 4 while under ambient conditions the pentacyanopropenide derivatives [Mo(dtc) 4 ](NC) 2 CC(CN)C(CN) 2 ] 5 were obtained. In solution, cyclic voltammetry and ESR studies revealed the presence for all types of complexes of the molybdenum(V) radical cation [Mo(dtc) 4 ] •− which is associated with the radical anion TCNX •− in 2 (X = Q) and 4 (X = E) and with a 1:1 mixture of neutral and anionic TCNQ species in 3 . Complex 2a has been studied by single crystal X-ray diffraction. The crystal structure consists of monomeric TCNQ •− radical anions and [Mo(dtc) 4 ] •+ cations with a triangular dodecahedral arrangement of S atoms and a point group symmetry which is approximately D 2 d .

Complexes biscyclopentadienyles avec des liaisons metal de transitionmercure ☆: III. Structure de deux phases de (C5H5)2Mo(HgSC2H5)2; etude de la distribution electronique dans les complexes (C5H5)2MoX2 par resonance magnetique nucleaire

Abstract (C5H5)2Mo(HgSC2H5)2 crystallizes in two different forms; a red one (A) which is insoluble in the usual organic solvents, the other one (B) is orange and soluble. Their structures were determined by X-ray diffraction. A: P21/c, a 10.342(5), b 17.757(10), c 10.193(6) A, β 113.39(4)°, Z = 4; B: C2/c, a 31.503(8), b 7.986(3), c 20.843(11) A, β 97.87(3)°, Z = 12. The molecular geometry is nearly the same in the two phases (MoHg: 2.677 A (A) and 2.676 A (B); HgS: 2.43 A (A) and (B): HgMoHg; 70.8° (A) and 73.1° (B); MoHgS: 167.6° (A) and 171.2° (B); C5H5MoC5H5: 140.5° (A) and 137.8° (B), whereas the overall structure is different. “Dimeric units” exist in A. The shortest distances HgS between two different molecules in the “dimeric unit” are equal to 3.17 A. An infinite system of mercurysulfur interactions is shown to exist in the form B(HgS: 3.32–3.33 A). The electronic structure of the (C5H5)2Mo(HgSR)2 compounds is discussed on the basis of 1H, 13C, 199Hg and 95Mo NMR results and compared with the geometrical parameters. A relation between the nature of the X-ligands in the (C5H5)MoX2 complexes (X = O, Cl, S, H, Hg), the C5H5MoC5H5 angle and the 1H(C5H5) chemical shifts is evident.

Niobium organometallic chemistry: XIII. Alkylation of η2-CS2 derivatives and reaction with NaBH4. Evidence for a η2-CH(S)SR ligand☆

Abstract The cationic complexes 2 [Nb(η-C5H5)2(Bu)(η2-C(S)SR]]X are formed from [Nb(η-C5H5)2(Bu)[η2-CS2]] (1) and RX (R = Me, Et, i-Pr, CH2COOEt; X = I. R = CH2C6H5, CH2CH2CH2Cl, CH2CHCH2; X = Br). They react with NaBH4 in THF giving complexes 4. These decompose in solution and give, after column chromatography, neutral complexes 3 of the type [Nb(η-C5H5)2(Bu)[η-CH(S)SR]]. The conversion of 2 into 3, which corresponds to nucleophilic attack by the hydride ion on the CS2 carbon atom, seems to proceed via formation of intermediate derivatives 4 containing a niobium-coordinated BH4 group. Reaction of 1 with diiodomethane as alkylating reagent results in the formation of a dimeric niobium compound containing the NbC(S )SCH2S( S)CN b unit, which reacts further with NaBH4.

Carbon–carbon bond formation through olefin–methylcarbyne linkage at a diruthenium centre: X-ray crystal structure of [Ru2(CO)(µ-CO){µ-η1,η3-C(Me)C(Me)CH2}(η-C5H5)2]

Reaction of [Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2]+ with RCHCH2(R = H or Me) under u.v. radiation provides [Ru2(CO)(µ-CO){µ-η1,η3-C(Me)C(R)-CH2}(η-C5H5)2] which, for RH, may also be obtained by treatment of [Ru2(CO)(C2H4)(µ-CO)2(η-C5H5)2] with MeLi, HBF4 successively; the structure of [Ru2(CO)(µ-CO){µ-η1,η3-C(Me)C(Me)CH2}(η-C5H5)2] has been determined by X-ray diffraction.