Alfonso Grassi

Gold nanoparticles incarcerated in nanoporous syndiotactic polystyrene matrices as new and efficient catalysts for alcohol oxidations.

The controlled synthesis of gold nanoparticles (AuNPs), incarcerated in a semicrystalline nanoporous polymer matrix that consisted of a syndiotactic polystyrene-co-cis-1,4-polybutadiene multi-block copolymer is described. This catalyst was successfully tested in the oxidation of primary and secondary alcohols, in which we used dioxygen as the oxidant under mild conditions. Accordingly, (±)-1-phenylethanol was oxidised to acetophenone in high yields (96%) in 1 h, at 35 °C, whereas benzyl alcohol was quantitatively oxidised to benzaldehyde with a selectivity of 96% in 6 h. The specific rate constants calculated from the corresponding kinetic plots were among the highest found for polymer-incarcerated AuNPs. Similar values in terms of reactivity and selectivity were found in the oxidation of primary alcohols, such as cinnamyl alcohol and 2-thiophenemethanol, and secondary alcohols, such as indanol and α-tetralol. The remarkable catalytic properties of this system were attributed to the formation, under these reaction conditions, of the nanoporous ε crystalline form of syndiotactic polystyrene, which ensures facile and selective accessibility for the substrates to the gold catalyst incarcerated in the polymer matrix. Moreover, the polymeric crystalline domains produced reversible physical cross-links that resulted in reduced gold leaching and also allowed the recovery and reuse of the catalyst. A comparison of catalytic performance between AuNPs and annealed AuNPs suggested that multiple twinned defective nanoparticles of about 9 nm in diameter constituted the active catalyst in these oxidation reactions.

Novel iron(III) catalyst for the efficient and selective coupling of carbon dioxide and epoxides to form cyclic carbonates

“Re-cycling carbon dioxide with iron”. The synthesis of cyclic organic carbonates in high yield, stereo- and chemo-selectivity was accomplished through the coupling of carbon dioxide and epoxides, catalysed by a novel air-stable and easy-to-handle thioether-triphenolate iron(III) complex.

Syndiotactic-specific polymerization of styrene: catalyst structure and polymerization mechanism

The mechanistic investigation of syndiotactic-specific polymerization of styrene is reviewed, mainly with reference to the research work carried out at the University of Salerno. NMR analysis of the stereochemical structure of s-PS macromolecules, in some cases suitably labelled, provided valuable information concerning the regiochemistry of polyinsertion, the type of addition to the monomer double bond, and the model of stereospecific propagation. Kinetic studies and spectroscopic investigation of the catalytic systems suggested a cationic Ti(III) complex with a strongly π-co-ordinated benzyl-type growing chain as the true active species.

Selective detection of ATP and ADP in aqueous solution by using a fluorescent zinc receptor

We report on the successful use of a new zinc complex for the selective fluorescent detection of ADP and ATP in water. This is achieved by the complementary coordination of the phosphate groups to the metal centre and hydrogen bonding of the adenosine with the coordinated ligand.

Dynamics of Aromatic Molecules Clathrated in Crystalline Syndiotactic Polystyrene: A Solid State 2H NMR Investigation of the Host/Guest Complexes

Syndiotactic polystyrene clathrates hosting benzene-d 6 or toluene-d 8 molecules in the cavities of the δ crystalline form have been prepared and investigated by means of solid state 2 H NMR spectroscopy. Benzene-d 6 molecules were found to be involved in a fast rotation about the C 6 symmetry axis whereas the toluene-d 8 molecules exhibit a fast rotation of the methyl group about the symmetry axis passing through the C 1 and C 4 carbon atoms.

Highly Efficient Direct Aerobic Oxidative Esterification of Cinnamyl Alcohol with Alkyl Alcohols Catalysed by Gold Nanoparticles Incarcerated in a Nanoporous Polymer Matrix: A Tool for Investigating the Role of the Polymer Host

The selective aerobic oxidation of cinnamyl alcohol to cinnamaldehyde, as well as direct oxidative esterification of this alcohol with primary and secondary aliphatic alcohols, were achieved with high chemoselectivity by using gold nanoparticles supported in a nanoporous semicrystalline multi-block copolymer matrix, which consisted of syndiotactic polystyrene-co-cis-1,4-polybutadiene. The cascade reaction that leads to the alkyl cinnamates occurs through two oxidation steps: the selective oxidation of cinnamyl alcohol to cinnamaldehyde, followed by oxidation of the hemiacetal that results from the base-catalysed reaction of cinnamaldehyde with an aliphatic alcohol. The rate constants for the two steps were evaluated in the temperature range 10-45 °C. The cinnamyl alcohol oxidation is faster than the oxidative esterification of cinnamaldehyde with methanol, ethanol, 2-propanol, 1-butanol, 1-hexanol or 1-octanol. The rate constants of the latter reaction are pseudo-zero order with respect to the aliphatic alcohol and decrease as the bulkiness of the alcohol is increased. The activation energy (Ea) for the two oxidation steps was calculated for esterification of cinnamyl alcohol with 1-butanol (Ea = 57.8±11.5 and 62.7±16.7 kJ mol(-1) for the first and second step, respectively). The oxidative esterification of cinnamyl alcohol with 2-phenylethanol follows pseudo-first-order kinetics with respect to 2-phenylethanol and is faster than observed for other alcohols because of fast diffusion of the aromatic alcohol in the crystalline phase of the support. The kinetic investigation allowed us to assess the role of the polymer support in the determination of both high activity and selectivity in the title reaction.

Polymorphism of syndiotactic polypropylene in copolymers of propylene with ethylene and 1-butene

Abstract The structural characterization, by X-ray diffraction and solid-state 13 C n.m.r. CPMAS, of copolymers of propylene with small amounts of ethylene and 1-butene, synthesized with a single centre syndiospecific catalyst, is presented. The effect of the presence of comonomeric units on the polymorphic behaviour of syndiotactic polypropylene is discussed. In the as-prepared samples, the presence of small amounts of ethylene induces the crystallization of conformationally disordered modifications of form II, intermediate between the limit ordered forms II and IV. The conformational disorder is characterized by the presence of long trans-planar sequences, including the ethylene units, and gives rise a structure with kink bands. In copolymers with 1-butene the usual crystallization in form I occurs. In samples of copolymers crystallized from the melt, the usual crystallization of form I is not affected by the presence of any comonomeric units, although disordered modifications of form I are always obtained.

Heteroscorpionate-based Co2+, Zn2+, and Cu2+ complexes: coordination behavior, aerobic oxidation, and hydrogen sulfide detection.

The coordination behavior and reactivity of the phenol-substituted bis(pyrazolyl)methane ligands, (3,5-(t)Bu(2)-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L1-H) and 2-phenol-bis(3,5-Me(2)-pyrazol-1-yl)methane (L2-H) have been investigated in the metal complexes (L1-H)CoCl(2) (1), (L1-H)ZnCl(2) (2), (L3)CuCl(2) (3), (L2)(2)Co(2)Cl(2) (4) (L2-H)ZnCl(2) (5), and (L2-H)CuCl(2)·H(2)O (6). The mononuclear tetrahedral cobalt complex 1 was isolated and fully characterized by X-ray single crystal diffraction and (1)H NMR spectroscopy and relaxometry. The neutral L1-H is κ(2)-coordinated to the metal center whereas the not coordinated hydroxy-phenyl group is involved in extended intermolecular hydrogen bonds. Aerobic oxidation of L1-H was observed in the reaction of this ligand with CuCl(2) to yield the para-quinone derivative L3 (L3 = 2-(t)Bu-6-(bis(3,5-Me(2)-pyrazol-1-yl)methyl)cyclohexa-2,5-diene-1,4-dione). Upon oxidation L3 resulted κ(2)-coordinated to the tetrahedral Cu(II) metal center, affording 3. The reaction of L2-H with CoCl(2)·6H(2)O produced the elimination of 1 equiv of hydrochloric acid and the formation of the binuclear complex 4 in which one cobalt is in an octahedral environment featuring two κ(3)-coordinated deprotonated ligands whereas the second cobalt center is detected in tetrahedral coordination geometry, bound to the octahedral cobalt via two phenoxo bridging moieties. Interestingly L2-H, (3-(t)Bu-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L4-H), or (5-(t)Bu-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L5-H) were not oxidized in the reaction with CuCl(2). The reaction of the ligand L2-H with ZnCl(2) and CuCl(2)·2H(2)O yielded the κ(2)-coordinated tetrahedral complex 5 and the square planar complex 6, respectively. The application of the cobalt complex 1 as molecular dosimeter for H(2)S was explored and compared to that of the zinc analogue 2. Density functional theory (DFT) calculations and NMR experiments to assess the possible mechanisms of H(2)S detection by both 1 and 2 are also described.

Poly(lactide-co-ε-caprolactone) copolymers prepared using bis-thioetherphenolate group 4 metal complexes: synthesis, characterization and morphology

Titanium and zirconium complexes 1–3 (1 = (t-BuOS)2Ti(O-i-Pr)2; 2 = (t-BuOS)2Zr(O-t-Bu)2; 3 = (CumOS)2Zr(O-t-Bu)2) supported by two phenolate bidentate ligands (t-BuOS-H = 4,6-di-tert-butyl-2-phenylsulfanylphenol and CumOS-H = 4,6-di-cumyl-2-phenylsulfanylphenol) promoted the copolymerization of L-lactide with e-caprolactone. The reactivity displayed by the two monomers during the copolymerization experiments and the microstructure disclosed by 13C NMR analysis indicated a gradient distribution of the two monomers along the polymer chain. Copolymers with high e-caprolactone content showed a large scale formation of crystalline spherulites prone to perfection of the crystallinity upon thermal annealing at 50 °C. Differently L-lactide rich copolymers revealed a thin film morphology consisting of small rigid domains of L-lactide segments of about 15 nm embedded in a soft matrix of the counterpart. Copolymers with comparable mole fractions of the two monomers were entirely amorphous.

Olefin polymerisation promoted by monodicarbollide complexes of group 4 metals

The behavior of (C2B9H11)M(NEt2)2(NHEt2) [M=Ti (1), Zr (2)] mono-dicarbollide complexes in olefin and styrene polymerisation has been investigated. Compounds 1 and 2, when activated by MAO (Al/M=100 to 1000), polymerise ethylene with good activity. Surprisingly, 2 can also be activated with small amounts of triisobutylaluminum (TIBA, Al/Zr=3 to 40). The ethylene polymerisation activity of the 2/TIBA catalyst (50°C, 5 atm, toluene–chlorobenzene) is greater than that reported for the CpZrX3/MAO catalysts but lower by about one or two orders of magnitude than zirconocene–MAO systems (e.g. Cp2ZrCl2/MAO, rac-(ethylene-bis-1-idenyl)ZrCl2/MAO). The GPC (gel permeation chromatography) curve of the polyethylene sample obtained with 2/TIBA catalyst (50°C, 5 atm, toluene–chlorobenzene) is bimodal indicating that at least two species are active in this system and one is more active than the other. The 2/MAO system (50°C, 5 atm, toluene–chlorobenzene) slowly polymerises propylene to atactic polymer. Under the same experimental conditions 1-pentene does not polymerise at all. Compounds 1 and 2, activated with MAO, produce syndiotactic polystyrene (sPS) with very low activity. Attempts to copolymerise styrene with ethylene by the 1/MAO and 2/MAO systems afforded a mixture of the two homopolymers.