Fabrice Guyon

Interplay of Structural Flexibility and Crystal Packing in a Series of Paramagnetic Cyclopentadienyl/Dithiolene Mo and W Complexes: Evidence for Molecular Spin Ladders

The structural flexibility of [Cp2M(dithiolene)] complexes (M=Mo, W; dithiolene=dmit2−, dmid2−, dsit2−; the [CpMo(dmid)] complex is depicted on the right) is manifested in various folding angles of the MS2C2 metallacycle in a series of charge-transfer salts with TCNQF4. The evolution of the electronic structures with the folding angle induces different geometries for the dimeric [{Cp2M(dithiolene)+.}2] entities. The organization of these entities in the solid state reveals one-dimensional intermolecular interactions, as confirmed by the magnetic behavior of these salts, which are characteristic of a spin chain or a rare spin ladder motif (shown on the right).

(Phenylthiomethyl)silanes and (butyltelluromethyl)silanes as novel bifunctional ligands for the construction of dithioether-, ditelluroether- and transition metal /silicon complexes

Abstract The functionalized silanes (PhSCH2)2SiPh2 (1a), (PhSCH2)2Si(vinyl)Me (1b), (PhSCH2)2Si(H)Me (1c) and (PhSCH2)3SiH (1d) have been prepared and co-ordinated as chelating dithioether ligands or via a covalent MSi bond to various transition metal centers. Thus, reaction of 1a with [PtCl2(PhCN)2] affords the dithioether complex cis-[PtCl2{(PhSCH2)2SiPh2}] (3), which exist in solution as mixtures of dl - and meso-invertomers. Treatment of [Re(μ-Br)(CO)3THF]2 with 1a–c yielded the stereochemically rigid chelate complexes fac-[ReBr(CO)3{(PhSCH2)2SiR1R2}] (R1, R2=Ph (4a)), (R1=vinyl, R2=Me (4b)), (R1=H, R2=Me (4c)). Due to the presence of two different substituents R1 and R2 on Si, 4b and 4c are isolated as 50:50 mixtures of diastereomers. The presence of a SiH function in 1c,d can be exploited for SiH activation reactions. Thus, oxidative addition on [Pt(PPh3)2(CH2CH2)] yields the fluxional hydrido silyl complex [Pt(H)(PPh3)2{Si(CH2SPh)2Me}] (5a) and the rigid derivative [Pt(H)(PPh3)2{Si(CH2SPh)3}] (5b). The ditelluroether complexes cis-[PtCl2{(RTeCH2)2SiMe2)] (6a, R=Ph), (6b, R=n-Bu) are obtained by treatment of [PtCl2(PhCN)2] with (PhTeCH2)2SiMe2 (2a) and (n-BuTeCH2)2SiMe2 (2b), respectively. The complex fac-[ReBr(CO)3{(n-BuTeCH2)2SiMe2}] (7) results from the reaction of [Re(μ-Br)(CO)3THF]2 with (2b). The new compounds have been studied by multinuclear NMR techniques, the crystal structures of 3, 4a, 5 and 6b have been determined by X-ray diffraction studies.

Structure, electrochemical and dynamic behavior of bis (pentamethylcyclopentadienyl) titanium (IV) dithiolene complexes

(η5-C5Me5)2Ti(dithiolene) complexes are preapred by reacting (η5-C5Me5)2TiCl2 with the dithiolene ligands dmit2- (1,3-dithiole-2-thione-4,5-dithiolate) or dddt2− (5,6-dihydro-1,4-dithiine-2,3-dithiolate). One reversible reduction wave and irreversible oxidation waves are observed by cyclic voltammetry for each complex at low scan rates. In (η5-C5Me5)2Ti(dddt), the first oxidation system becomes reversible at higher scan rates (η5-C5Me5)2Ti(dmit) crystallizes in the orthorhombic system, space group Pca21 with a = 26.683(6), b = 8.485(1), c = 22.272(6) A, Z = 8, with two independent molecules in the unit cell. The TiS2C2 plane is folded along the SS axis by 38 and 38.3° in each independent molecule, respectively, to be compared with a value of 47° in (η5-C5H5)2Ti(dmit). Extended Huckel calculations show that the steric constraints of the Cp∗ ligands prevail over the metal-dithiolene interactions for explaining the actual geometry of such (η5-C5Me5)2Ti(dithiolene) complexes. The dynamics of fluxional processes involved in the dithiolene ligand folding have been investigated by variable-temperature 1H NMR studies and compared with the data reported for analogous (η5-C5H5)2Ti(dithiolene) complexes.

Effect of t-BuS vs. n-BuS on the topology, Cu⋯Cu distances and luminescence properties of 2D Cu4I4/RS(CH2)4SR metal–organic frameworks

CuI reacts with RS(CH2)4SR (R = n-Bu (L1); t-Bu (L2)) to afford the 2D coordination polymers [Cu4I4{μ-RS(CH2)4SR}2]n (R = n-Bu (1); t-Bu (2)). Their grid networks exhibit nodal Cu4(μ3-I)4 clusters interconnected by dithioethers with mean Cu⋯Cu distances of 2.7265(10) and 2.911(2) A for 1 and 2, respectively. This difference translates in a blue shift of the solid state emission bands and a decrease in emission lifetimes when trading R = n-Bu to the bulky t-Bu.

Syntheses, structures, and photophysical properties of mono- and dinuclear sulfur-rich gold(I) complexes.

The dinuclear gold complexes [{Au(PPh 3)} 2(mu- dmid)] ( 1) ( dmid = 1,3-dithiole-2-one-4,5-dithiolate) and [{Au(PPh 3)} 2(mu- dddt)] ( 2) ( dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) were synthesized and characterized by X-ray crystallography. Both complexes exhibit intramolecular aurophilic interactions with Au...Au distances of 3.1984(10) A for 1 and 3.1295(11) A for 2. A self-assembly reaction between 4,5-bis(2-hydroxyethylthio)-1,3-dithiole-2-thione ( (HOCH 2 CH 2 ) 2 dmit) and [AuCl(tht)] affords the complex [AuCl{ (HOCH 2 CH 2 ) 2 dmit}] 2 ( 4), which possesses an antiparallel dimeric arrangement resulting from a short aurophilic contact of 3.078(6) A. This motif is extended into two dimensions due to intra- and intermolecular hydrogen bonds via the hydroxyethyl groups, giving rise to a supramolecular network. Three compounds were investigated for their rich photophysical properties at 298 and 77 K in 2-MeTHF and in the solid state; [Au 2(mu- dmid)(PPh 3) 2] ( 1), [Au 2(mu- dddt)(PPh 3) 2] ( 2), and [AuCl{( HOCH 2 CH 2 ) 2 dmit}] ( 4). 1 exhibits relatively long-lived LMCT (ligand-to-metal charge transfer) emissions at 298 K in solution (370 nm; tau e approximately 17 ns, where M is a single gold not interacting with the other gold atom; i.e., the fluxional C-SAuPPh 3 units are away from each other) and in the solid state (410 nm; tau e approximately 70 mus). At 77 K, a new emission band is observed at 685 nm (tau e = 132 mus) and assigned to a LMCT emission where M is representative for two gold atoms interacting together consistent with the presence of Au...Au contacts as found in the crystal structure. In solution at 77 K, the LMCT emission is also red-shifted to 550 nm (tau e approximately 139 mus). It is believed to be associated to a given rotamer. 2 also exhibits LMCT emissions at 380 nm at 298 K in solution and at 470 nm in the solid state. 4 exhibits X/MLCT emission (halide/metal to ligand charge transfer) where M is a dimer in the solid state with obvious Au...Au interactions, resulting in red-shifted emission band, and is a monomer in solution in the 10 (-5) M concentration (i.e., no Au...Au interactions) resulting in blue-shifted luminescence. Both fluorescence and phosphorescence are observed for 4.

Syntheses and electrochemical behaviour of novel dithiolatoniobium-(IV) and -(V) complexes with two η5-cyclopentadienyl rings

Abstract Novel niobium(IV) complexes with two cyclopentadienyl rings and dmit, dmio or dddt were synthesized, and their voltammometric behaviour was investigated in acetonitrile and dichloromethane. These complexes in acetonitrile solution exhibited a reversible one-electron oxidation and a reversible one-electron reduction step, corresponding to niobium(V) and niobium(III) respectively, without any complicating side- or subsequent reactions. Among the three niobium(IV) complexes, the reduction potential of the complex with dddt was notably less negative than those of the complexes with dmit or dmio. This fact allows the preparation of the charge-transfer complexes with TCNQ. The niobium(V) dmit and dmio complexes with two cyclopentadienyl rings were also isolated as iodide salts by the oxidation of the corresponding niobium(IV) complex. These Nb V complexes gave two one-electron reduction steps whose potentials were identical to those of Nb IV and Nb III for niobium(IV) dmit and dmio complexes.

Synthesis and reactivity of silylated tetrathiafulvalenes

Novel organosilylated tetrathiafulvalenes (TTFs) possessing Si-H or Si-Si bonds have been synthesised. The crystal structures of several derivatives have been determined by X-ray diffraction, including that of dimeric (Si2Me4)(TTF)2 (11) incorporating a diatomic SiMe2-SiMe2 linker. Cyclic voltammetry measurements in all cases show two oxidation waves. DFT calculations were performed to rationalize the absence of an electronic communication between the two TTF moieties of 11 through the disilanyl spacer. The reactivity of the Si-H bond has been exploited to prepare the dinuclear complex [{Ru(CO)4}2{mu-(Me2Si)4TTF}] (14), starting from Ru3(CO)12 and TTF(SiMe2H)4 (1). Treatment of 14 with 2 equiv. of PPh3 or dppm results in selective substitution of a CO ligand trans to a SiMe2 group to afford mer-[{Ru(PPh3)(CO)3}2{mu-(Me2Si)4TTF}] (13) and mer-[{Ru(CO)3}2(eta1-dppm){mu-(Me2Si)4TTF}] (16). Attempts to transform the Si-H bonds of some TTF(SiMe2H)n (n = 1, 2) into Si-O functions using stoichiometric amounts of water in the presence of tris(dibenzylideneacetone)dipalladium(0) were unsuccessful. Quantitative cleavage of the C(TTF)-Si bond was observed instead of formation of TTF-based-siloxanes. Essays of catalytic bis-silylation of phenylacetylene with 11 and TTF(SiMe2-SiMe3) (9) in the presence of Pd(OAc)2/1,1,3,3-tetramethylbutylisocyanide failed. Again, cleavage of the C(TTF)-Si bond was noticed.

Synthesis of μ‐C2S44− Cobalt Complexes by Activation of the 1,3,4,6‐tetrathiapentalene‐2,5‐dione, and Electrochemical Study of [(Cp*Co)2(μ‐C2S4)]

The bimetallic complex [Cp(*)Co)2(μ-C2S4)] in which the two metal centres are linked by an ethylenetetrathiolate C2S44− unit, was synthesized in high yield by oxidative addition of 1,3,4,6 tetrathiapentalene-2,5-dione to [Cp(*)Co(CO)2]. The X-ray crystal structure of the intermediate product Cp*Co(dmid) (dmid2− = 4,5-disulfanyl-1,3-dithiol-2-onate) is presented. The electrochemical behaviour of the [(Cp*Co)2(μ-C2S4)] complex was studied in detail in the oxidative range. This study has shown that the nature of the product obtained after oxidation depends on the presence of complexing agent in the solution. The mechanism has been elucidated in a CH2Cl2 solution in the presence of P(OMe)3. In addition, chemical oxidation was conducted with several oxidizing agents (Br2, TCNQF4, and AgBF4). The molecular structure of the tetrathiooxalate bridged complex [(Cp*Co{P(OMe)3})2(μ-C2S4)](BF4)2 was established by an X-ray diffraction study. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Magnetic properties and fluxional behaviour of heteroleptic cyclopentadienyl–dithiolene d1 and d0 niobium complexes

Paramagnetic d1 niobium complexes of general formula [Nb(η-C5H4R)2(dithiolene)][R = SiMe3 or But; dithiolene = C3S52–(4,5-disulfanyl-1,3-dithiole-2-thionate), C3OS42–(4,5-disulfanyl-1,3-dithiol-2-onate) or dddt2–(5,6-dihydro-1,4-dithiine-2,3-dithiolate)] have been prepared and their redox properties studied. The crystal structure determination of [Nb(η-C5H4SiMe3)2(C3S5)] showed that the folding angle of the NbS2C2 plane along the S–S axis is 34(2)°, an intermediate value compared with those of analogous d0(45–50°) and d2(0–10°) complexes, as rationalized by extended-Huckel calculations. The Curie-type temperature dependence of the spin susceptibility of [Nb(cp)2(C3S5)], [Nb(cp)2(C3OS4)] and [Nb(η-C5H4R)2(C3S5)](cp =η-C5H5) demonstrates that the paramagnetic complexes do not interact with each other in the solid state. Cationic d0 complexes were obtained either by chemical oxidation (tetracyanoquinodimethane) of the d1 molecules or from the direct reaction of dddt2– with d0[Nb(η-C5H4R)2Cl2][PF6]. The fluxional behaviour of these d0 complexes has been investigated by temperature-dependent NMR studies and shown to be comparable with that of isoelectronic d0[Ti(cp)2(dithiolene)] complexes.

Two-dimensional polymeric [Hg4(μ2-I)6I2(μ2-C4S6)]n

The title compound, poly[(μ2-2H,5H-1,3-dithiolo[4,5-d][1,3]dithiole-2,5-dithione)hexa-μ2-iodido-diiodidotetramercury(II)], [Hg4I8(C4S6)]n, represents the first example of a coordination polymer assembled by the α,α-C4S6 dithione ligand. The HgII ions are four-coordinated in a distorted tetrahedral geometry, the coordination demand being satisfied either by four bridging iodide ligands or by three iodide ligands (one terminal and two bridging) and a thiocarbonyl S atom. Due to the bridging nature of the dithione ligand, the coordination polymer has a two-dimensional structure, built up of undulated layers parallel to (001). There is an inversion center at the mid-point of the central C=C double bond.