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.     

Synthesis of soluble bis-terpyridine ligands bearing ethynylene-phenylene spacers

Soluble and rigid terpyridine-based ditopic ligands bearing one to five phenylene/ethynylene modules have been synthesized by way of a stepwise procedure. Each module is attached to the terpyridine unit via an ethynylene fragment and functionalized at the 4-position with an additional ethynylene connector and in the 2,5-positions with two flexible dodecyloxy chains. The synthetic protocol is based on sequential Pd(0)-catalyzed cross-coupling reactions between a terpyridine subunit grafted with the necessary diethynyl/phenyl or ethynylphenyl/bromide appendage. For ditopic ligands displaying an even number of phenyl/ethynylene modules, the final step involves a single cross-coupling reaction between 4'-ethynylene-2,2':6',6' '-terpyridine and the appropriate bromo derivative. In the case of the ligands having an odd number of phenylene/ethynylene fragments, a double cross-coupling reaction between an extended dibromopolyphenylene intermediate and 4'-ethynylene-2,2':6',6' '-terpyridine or 1-(4'-ethynylene-2,2':6',2' '-terpyridine)-4-ethynylene-2,5-didodecyloxy-benzene is required. For ligands I-V, optimal preparative conditions were found with [Pd(0)(PPh(3))(4)] (6 mol %) in n-propylamine at 70 degrees C. Oxidative dimerization of the 1-(4'-ethynylene-2,2':6',2' '-terpyridine)-4-ethynylene-2,5-didodecyloxybenzene derivative in the presence of cupric salts and oxygen gives the corresponding homoditopic ligand II(2)() bearing a central diphenyldiacetylene spacer. Spectroscopic data for the new oligomers are discussed in terms of the extent of pi-electron conjugation. Upon increasing the number of phenylene/ethynylene modules, there is a progressive lowering in energy of absorption and fluorescence transitions.     

The photophysical properties of short, linear arrays of ruthenium(II) tris(2,2′-bipyridine) complexes

A series of linear polynuclear ruthenium(II) tris(2,2′-bipyridine) complexes has been synthesized whereby individual chromophores are separated by 1,4-diethynylenebenzene subunits bearing alkoxy groups for improved solubility. These arrays contain two, three, four or five metal centers. The compounds are reasonably soluble in polar organic solvents and they possess optical absorption spectral properties that are dominated by transitions associated with the polytopic ligand. Weak luminescence is observed for each complex in deoxy genated acetonitrile at room temperature that appears to be characteristic of emission from a metal-to-ligand charge-transfer triplet state. The emission lifetime is essentially independent of temperature, at least over a modest range. There is no indication for interaction between close-lying triplet states and no obvious sign of a low-energy τ, τ^* triplet associated with the polytopic ligand. The photophysical properties suggest that the longer arrays are segmented.     

Synthesis of new molecules containing head,spacer, and label moieties

We describe the synthesis and characterization of novel molecules containing head with precise shape, spacer, and label moieties. The protocol is based on a Pd(0)-catalyzed cross-coupling reaction between ethynylphenyl/bromide to obtain a rigid head followed by the attachment of a flexible spacer possessing two reactive functional groups on the termini. The final step consists of forming a covalent bond between spacer and label. In addition, monosubstituted soluble labels were synthesized in good yields.     

Synthesis of quasi-linear and segmented bis- to penta-2, 2'-bipyridine polytopic ligands built via a convergent approach

Reliable and practical routes for the preparation of segmented oligomeric 2,2'-bipyridine-based ligands possessing rigid and conjugated spacers are presented. The first series of ligands bears a single alkyne function as a bridge and has been built by Pd(0)-catalyzed cross-coupling reactions between ethynylated and bromo-substituted derivatives of 2,2'-bipyridine (bipy). These new ligands provide access to numerous hexameric, octameric, and decameric pyridine-based materials. Optimum conditions were found with [Pd(PPh(3))(4)] (6 mol %) in benzene containing diisopropylamine at 80 degrees C. The second series of soluble ligands was synthesized around a 1,4-diethynyl-2, 5-didodecyloxybenzene bridging unit. The synthesis required a protection/deprotection methodology, as well as a chemioselective palladium-catalyzed Sonogashira-Hagihara cross-coupling protocol to obtain the target multitopic ligands. Within this strategy, the pivotal 15b, 17, and 19b intermediates bearing one or two bipy and phenyl units are required and such entities have been isolated in excellent yield. The products are highly soluble and photostable. In each case, the final step involves a double cross-coupling reaction between the appropriate constituents, with the best preparative conditions involving [Pd(PPh(3))(4)] (6 mol %) in n-propylamine at 70 degrees C. The main advantage of this methodology lies in its synthetic versatility and adaptability for creating multitopic metal-binding scaffolds with a potentially large variety of bridging units and phenyl substituents. Spectroscopic data for the new oligomers show a steady decrease in optical energy with an increasing degree of oligomerization. The different results obtained with these ligands highlight the importance of the rigid 1, 4-diethynylphenyl linker in directing the outcome of the nanosized molecules.     

Approche analytique de la convection forcée des fluides de Bingham dans un tubeAnalytical approach for forced convection of Bingham fluids in a tube

The asymptotic behaviour of laminar forced convection for Bingham fluid in a circular tube subjected to an axially varying wall heat flux is studied analytically. The effect of viscous dissipation is taken into account while the axial heat conduction in the fluid is considered as negligible. The asymptotic temperature profile and the asymptotic Nusselt number are determined for various axial wall heat flux distributions which yield a thermally developed region. The results obtained show a diminution in asymptotic Nusselt number when the Brinkman number and the dimensionless radius of the plug flow region increase. Comparisons with the results in the literature for Newtonian fluids show the validity of the present analysis. To cite this article: R. Khatyr et al., C. R. Mecanique 330 (2002) 69–75.     

Controlling Electronic Communication in Ethynylated-Polypyridine Metal Complexes

By introduction of a naphthalene subunit in the middle of a butadiynylene spacer the triplet lifetime of the ruthenium chromophore in RR is prolongated to 475 ns. By increasing laser intensities the two Ru-terpy terminals are simultaneously promoted to the triplet state, and triplet - triplet annihilation occurs. In contrast, in the mixed Ru/Os complex (RO) the long inherent triplet lifetime of the Os-terpy fragment facilitates reverse triplet energy transfer. terpy=bis(2,2':6',2"-terpyridine).     

New ligands bearing chiral bioactive fragments

[see reaction]. Reliable and practical synthetic routes for the construction of hybrid molecules bearing both a chelating center and a useful biofunction are presented. They comprise the sequential cross-coupling reaction between ethynylated synthons with iodo-substituted L-tyrosine derivatives and provide access to various rationally designed chiral ligands.