Mauro Bassetti

Network assembly of gold nanoparticles linked through fluorenyl dithiol bridges

Gold nanoparticles stabilized by two novel bifunctional fluorenyl thiols, generated in situ from 9,9-didodecyl-2,7-bis(acetylthio)fluorene (1) and 9,9-didodecyl-2,7-bis(acetylthiophenylethynyl)fluorene (2), exhibit bridged structures which self-assemble in parallel lines. The size, shape and structure of the AuNPs have been determined by means of dynamic light scattering (DLS), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). AuNPs modified with fluorenyl thiol derivatives show diameters in the range of 3–7 nm. The linkage between the nanoparticles can be envisaged with the formation of dyads supported by TEM analysis and XPS measurements. Remarkably, investigation by scanning electron microscopy of the AuNP films revealed an ordered distribution of well-separated individual nanoparticles to form a 2D network. The formation of interconnected networks between AuNPs with different distances, depending on the nature of the thiol linkers (1) or (2), and the photoluminescence properties open perspectives for applications in optical devices and electronics.

One-step synthesis of low molecular weight poly(p- phenyleneethynylenevinylene)s via polyaddition of aromatic diynes by catalysis of the [Ru(p-cymene)Cl2]2/AcOH system

pi-Conjugated low molecular weight polymers characterized by regio- and stereoregular alternation of phenylene and ( E)-1-en-3-yne moieties have been synthesized by polyaddition of 1,4-diethynylbenzene or of 2,5-diethynyl-1,4-alkoxybenzene monomers, employing the commercially available di-micro-chlorobis[( p-cymene)chlororuthenium(II)] complex as the metal catalyst source, under homogeneous, atom-economical, amine- and phosphine-free conditions. Bulk materials of poly( p-phenyleneethynylenevinylene) derivatives are obtained with yields larger than 80%, from which polymers readily soluble in chlorinated solvents and in tetrahydrofuran are extracted in 60-75% yields. The polymers with average degrees of polymerization in the range n AV = 4-8 display optical properties in solution similar to those of the higher molecular weights analogues.

The migratory insertion of carbon monoxide in pentamethylcyclopentadienyliridium (III) complexes. Structural effects on reactivity and mechanism for rhodium and iridium systems

The reactions of complex (C5Me5)Ir(Cl) (CO) (Me) (1a) with cyclohexylisocyanide and phosphines (L=CyNC, PHPh2, PMePh2, PMe2Ph) give the products of alkyl migratory insertion (C5Me5Ir(Cl) (COMe) (L), in toluence or tetrahydrofuran at 323 K or higher temperature. The phenyl analogue (C5Me5)Ir(Cl)(CO)(Ph) or the iodide complexes (C5Me5)Ir(I) (CO) (R) (R=Me, Ph_are not reactive under the same conditions. The reaction of (C5Me5)Ir(Cl)(CO)(Me) with PMePh2 and PMe2Ph in acetonitrile yields the chloride substitution product [(C5Me5)Ir(CO)(L)(Me)]+Cl−. Kinetic measurements for the reactions of (C5Me5)Ir(Cl)(CO)(Me) in toluene are first order in the iridium complex and exhibit a saturation dependence on the incoming donors L. Analysis of the data suggests a two-step process involving (i) rapid formation of a molecular complex [(C5Me5)Ir(Cl)(CO)(Me), (L)], in which the structure of 1a is unperturbed within the limits of spectroscopic analysis, and (ii) rate determining methyl migration. The reaction parameters are K for the pre-equilibrium step (K = 1.5 (CyNC), 7.3 (PHPh2), 7.1 (PMePh2) dm3 mol−1 at 323 K) and k2 for the slow carbonue5f8carbon bond formation (k2 (105) = 6.9 (CyNC), 1.2 (PHPh2), 1.0 (PMePh2) s−1 at 323 K). The activation parameters for the methyl migration step in the reaction with PMePh2 obtained between 308 and 338 K, are ΔH≠ = 106±16 kJ mol−1 and ΔS≠ = − 14±5 J K−1 mol−1. The reaction of 1a with PMePh2 proceeds at similar rates in tetrahydrofuran (K = 3.7 dm3 mol−1, k2 (105) = 1.2 s−1, 323 K). The crystal structure of (C5Me5)Ir(Cl)(COMe) (PMe2Ph) has been determined by X-ray diffraction. C20H29ClOPIr: Mr = 544.1, monoclinic, P21/n, a = 8.084 (2), b = 9.030(2), c = 28.715 (3) A, β = 91.41 (3)°, Z = 4, Dc = 1.71 g cm−3, V = 2095.5 A3, room temperatyre, Mo Kα, γ = 0.71069, μ = 65.55 cm−1, F(000) = 1044, R = 0.037 for 2453 independent observed reflections. The complex shows a deformed tetrahedral coordination assuming the η5-C5Me5 molecular fragment as a single coordination site. The iridium-chlorine bond is staggered with respect to two adjacent C(ring)-methyl bonds, while the Irue5f8P and the Irue5f8COMe bonds are eclipsed with respect to C(ring)-methyl bonds.

Reactivity of cyclopentadienyl and indenyl alkylcarbonyliron(II) complexes. η5 Species as key intermediates in the migratory insertion of carbon monoxide

The reactions of the complexes [Fe(η5-L)(CO)2R](L = C5H5 or C9H7, R = Me or CHMe2) with PR′3(PMe2Ph, PMePh2 and PPh3) have been studied in toluene and tetrahydrofuran (thf) by UV/VIS and IR spectroscopy. The products of alkyl migratory insertion [Fe(η5-C5H5)(CO)(COR)(PR′3)] are formed via an associative mechanism, involving (i) a rapid pre-equilibrium (K) between complex and phosphine and (ii) rate-determining alkyl migration (k2), in analogy to the mechanism previously established for [Fe(η5-C9H7)(CO)2R]. In the intermediate molecular complexes {[Fe(η5-L)(CO)2R], phosphine} the compounds [Fe(η5-C5H5)(CO)2R] bind to phosphine less efficiently than do the indenyl analogues and react one order of magnitude more slowly. Reaction rates are similar in thf and in toluene, in agreement with the proposal that the alkyl migration is not solvent assisted.

Migration of aryl and methyl onto carbonyl in iodorhodium(III) complexes

The complexes [(C5Me5)RhR(CO)I][R = Me, (1a); Ph, (1b); p-MeC6H4, (1c);p-ClC6H4, (1d);p-OHCC6H4(1e);p-NCC6H4, (1f) or p-O2NC6H4, (1g)] were synthesised by the route [(C5Me5)RhMe2(Me2SO)]+ RCHO →[(C5Me5)RhR(CO)Me]; [(C5Me5)RhR(CO)Me]+ I2→[(C5Me5)RhR (CO)I]. The migration reaction, [(C5Me5)RhR(CO)I](1)+ PPh3→[(C5Me5)Rh(COR)(PPh3)I](2), proceeded easily and essentially quantitatively for (1a)–(1d) in a variety of solvents; in a side-reaction, (1e)–(1g) gave the substitution products [(C5Me5)RhR(PPh3)I](3e)–(3g). The reactions of complexes (1a)–(1g) with PPh3 in toluene obeyed second-order kinetics, rate =k3[(1)][PPh3], implying a direct bimolecular attack by the triphenylphosphine on the metal complex. A Hammett plot of kobs. for the reaction of (1b)–(1g) to (2b)–(2g) against σ gave a good linear relationship (ρ=–2.9) indicating that migration is favoured by electron-releasing substituents, R =p-MeC6H4 > Ph > p-ClC6H4 > p-OHCC6H4 > p-NCC6H4≈p-O2NC6H4. Values of ΔG‡, ΔH‡, and ΔS‡ for the reactions of complexes (1a)–(1d) with PPh3 were determined over the temperature range 286–343 K; ΔS‡ was smaller for (1b) than for the others, leading to the phenyl [in (1b)] migrating faster than methyl [in (1a)]. There were only small rate differences for the reactions of (1a) and (1b) between toluene, tetrahydrofuran, and dichloromethane, but they proceeded significantly faster in nitromethane or acetonitrile; for (1b) the migration in these solvents showed a first-order (unimolecular) as well as a second-order (bimolecular) path. Both the second-order rate constant, k3, and the first-order rate constants, k1, were several orders of magnitude larger than for any previously measured unpromoted migration reaction.

An unusual case of bis-methoxymercuration of diphenylethyne: molecular structure of PhC(HgCl)2C(OMe)2Ph

Addition of aqueous KCl to the reaction of diphenylethyne and mercury(II) acetate in methanol induces an unprecedented geminal double mercuration of the triple bond; the X-ray crystal structure of the product shows an unusually short Hg(1)–Hg(2) interatomic distance.

A first example of the faster migration of phenyl over methyl: kinetics of the reaction of triphenylphosphine with organo-carbonyl-iodo-rhodium(III) complexes

The reactions of PPh3 with [C5Me5RhR(CO)l] to yield [C5Me5Rh(COR)(PPh3)l], proceed by a ‘direct attack’ mechanism in less-polar solvents; the migrations are favoured by electron releasing R, but follow organic rearrangements in that phenyl migrates more rapidly than methyl.