Pasquale Piraino

Epoxy–silica polymers as restoration materials

Abstract The epoxy monomer 3-glycidoxypropyltrimethoxysilane reacts, under non-hydrolytic conditions, with the primary amine (3-aminopropyl)triethoxysilane in 2:1 (1), 5:1 (2) and 10:1 (3) molar ratios leading to epoxy–silica materials which were characterized by TGA, DSC, Raman, and NMR investigations. The epoxy ring opening and the hydrolysis reactions of the Si(OR)3 groups were examined by means of 13C NMR before gelation occurs. The identification of the different types of silicate substructures present in the solids 1, 2 and 3 was accomplished by 29Si CP-MAS NMR spectroscopy which also provides a quantitative measure of the degree of condensation through the relative abundance of T0 [RSi(OR)3], T1 [RSi(OR)2OSi], T2 [RSi(OR)(OSi)2] and T3 [RSi(OSi)3] silicon nuclei. The combined results of the Raman and 29Si CP-MAS investigations clearly show that all the mixtures, especially the higher ratio ones, are characterized by a high degree of cross-linking; in addition, for 2 and 3, residual epoxy fragments are still present in the solid structure. The absence of residual enthalpy curing peaks in the calorimetric analysis indicates that the volatiles are simply released from all the samples. The thermogravimetric analysis shows that, among all the mixtures, 1 is featured by different structural properties which cause a higher degradation temperature and a longer decomposition time. To evaluate the effect of different experimental conditions on the properties of the final products, the reactions were also performed in the presence of small amounts of KOH and of a stoichiometric amount of water to effect hydrolysis of Si(OR)3 groups.

A new application of ionic liquids: hydrophobic properties of tetraalkylammonium-based poly(ionic liquid)s

The potential of using poly(ionic liquid)s as a new family of hydrorepellent materials has been explored. Free-radical polymerization of a series of ionic liquids based on the polymerizable cation [2-(methacryloyloxy)ethyl]trimethylammonium and on the hydrophobic anions bis(trifluoromethylsulfonyl)imide, nonafluoro-1-butanesulfonate and dodecylbenzenesulfonate led to the corresponding poly(ionic liquid)s that were characterized by TGA and DSC analysis, SEM, MALDI-TOF and XPS spectroscopy. Contact angle investigations show that the nature of the surface of the poly(ionic liquid)s based on the nonafluoro-1-butanesulfonate and dodecylbenzenesulfonate anions are featured by remarkable hydrophobic properties with advancing contact angles (θadv) lying in the range 113–118°, while to the polymer poly[2-(methacryloyloxy)ethyl]trimethylammonium bis(trifluoromethylsulfonyl)imide is associated poor hydrorepellent activity (θadv = 76°). The tensiometric measurements also experience receding contact angles (θrec) lying in the range 16–20° and a consequent high hysteresis suggesting that, on the outermost layers of the polymers, very high and very low-energy surface portions are present.

Epoxy-silica polymers as restoration materials. Part II

Abstract Room temperature reaction of the epoxy resin poly(bisphenolA- co -epichlorohydrin), glycidyl end-capped with the coupling agent (3-aminopropyl)triethoxysilane, in 1:2 ( 1 ), 1:1 ( 2 ) and 2:1 ( 3 ) molar ratios, leads, after curing for three months at room temperature, to glassy, transparent, crack-free solids which were investigated by SEM, TGA, DSC, NIR and Raman spectroscopy. SEM investigations show substantially a great homogeneity over the entire area with absence of cracks, veins and/or fissures and without formations of clusters and/or aggregates. The conversion of oxirane rings, as found by Raman spectroscopy, decreases by increasing the epoxy/amine ratio, with conversion percentages ranging from 95.3 to 81.3%. As a common feature, the presence in 1 , 2 and 3 of Si–O–Si linkages increases the polymer degradation temperature and thermal oxidative stability relative to the parent epoxy resin by shifting the weight loss to higher temperatures. Differently from mixtures 2 and 3 , which show the T g at 90 °C, the mixture 1 does not exhibit any detectable glass transition.

Reactions of di-2-pyridyl sulfide with the palladium(II) and platinum(II) diene or methoxydiene complexes. Dynamic behaviour of the cationic compounds. Crystal structure of Pd(di-2-pyridyl sulfide)Cl2

Abstract The complexes [M(dps)Cl2] (MPdII (1); PtII (2)) and the labile compounds [M(MeOdiene)(dps)Cl] (MPdII, MeOdieneCH3OC8H12 (3) or CH3OC10H12 (4); MPtII, MeOdieneCH3OC8H12 (5) or CH3OC10H12 (6)) have been synthesized by reaction of dps (dps=di-2-pyridyl sulfide) with [M(diene)Cl2] (diene=cycloocta-1,5-diene or dicyclopentadiene) and the appropriate chloro-bridged methoxydiene complexes, respectively. The last reactions required drastic conditions. Also the reactions of dps with the solvento species [M(diene)(acetone)2]X2 and [M(MeOdiene)(acetone)2]X (X=BF4, PF6, ClO4) have been studied and the compounds [M(MeOdiene)(dps)]X (MPdII, MeOdieneCH3OC8H12 (7) or CH3OC10H12 (8); MPtII, MeOdieneCH3OC8H12 (9) or CH3OC10H12 (10)) were prepared. The structure of 1 has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P21/n, with Z=4 in a unit cell of dimensions a=9.933(4), b=14.802(5), c=8.465(3) A, β=101.94(2)°. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full- matrix least-squares on the basis of 2163 observed reflections to R and R′ values of 0.0277 and 0.0348, respectively. In the square planar coordination around the Pd atom the dps molecule acts as a chelate ligand through the two pyridinic N atoms and adopts a N,N-inside conformation. The six-membered chelate ring shows a boat conformation with the Pd and S atoms out of the plane through the other four atoms on the same side. Although dissociation in the usual solvents prevents full characterization of 3–6 IR spectra suggest that the dps acts as monodentate ligand. The 1H NMR spectra, at variable temperature, and 13C NMR spectra of 7–10 show that the cationic complexes in solution undergo at least two dynamic processes; a ligand site exchange and a boat to boat inversion of the chelate dps ring. The ligand site exchange is fast, in the NMR time scale, at room temperature for palladium complexes and at higher temperature for the platinum complexes and makes equivalent the pyridine rings of dps. This process is interpreted in terms of formation of stereochemically non-rigid five- coordinate intermediates. The boat to boat inversion is fast at room temperature at least for platinum complexes. At low temperature the latter process is absent or occurs at markedly reduced rate for palladium complexes while the slow ligand site exchange results in equilibria between two conformers.

Crystal structure of [Pd(μ3-2-propenyl)(dps)][Pd(μ3-2-propenyl)Cl2]. NMR evidence of binuclear μ3-allyl palladium(II) species with bridging dps

Abstract The reactions of di-2-pyridyl sulfide (dps) with (μ3-allyl)palladium chloride dimers gave the ionic compounds [Pd(μ3-allyl)(dps)][Pd(μ3-allyl)Cl2] (allyl=2-propenyl (1), 2-methyl-2-propenyl (2), 2-butenyl (3)). The structure of 1 has been determined by X-ray diffraction methods. Crystals are triclinic, space groupP 1 , with Z=2 in a unit cell of dimensions a=8.840(1), b=8.928(1), c=12.317(2) A, α= 98.82(1), β=90.46(1), γ=95.46(1)°. The structure has been solved from diffractometer data by direct and Fourier methods and refined by full-matrix least-squares on the basis of 3855 observed relections to R and Rw values of 0.0269 and 0.0339, respectively. Compound 1 consists of discrete complex ion pairs, containing allyl groups coordinated to both the cationic and anionic palladium centres. In the cationic portion the dps acts as a chelate ligand and adopts an N,N inside conformation. The six-membered chelate ring shows a boat conformation. The cation and anion are connected by a short Pd2…Cl2 interaction (3.073(1) A) which determines pseudo-five-coordination for the cation. At low temperature the 1H NMR spectra in CD3OD of 1 and 2 confirm the presence of the cation and the anion while in CDCl3 they also indicate the presence of a binuclear species with bridging dps. The 1H NMR spectra, at variable temperature, show that 1, 2 and 3 in solution undergo dynamic processes. In CDCl3, a lower energy process makes the π-allyl groups equivalent at room temperature, a higher energy process determines the magnetic equivalence of syn and anti π-allyl protons at high temperature.

Synthesis and reactivity of formamidinato rhodium(I) complexes

Abstract The syntheses of [Rh(diol)(formamidine)] 2 complexes (diol  cycloocta-1,5-diene (1); diol  norbornadiene (2); formamidine  N , N ′-di- p -tolylformamidine) are reported. These complexes are dimeric and contain the bridging formamidino ligand. They react with CO, dppe and PPh 3 with displacement of the diene ligand to yield the known [Rh(CO) 2 (formamidine)] 2 , [Rh(dppe) 2 ] + and [Rh(PPh 3 ) 2 (formamidine)], respectively; the last complex, in which the formamidine acts as a chelating ligand, was isolated only as the O 2 adduct. With HCl or HBF 4 aqueous 1 and 2 do not form hydrides but instead the formamidino cation [ p -tolyl-NHCHNHtolyl- p ] + and the complexes [Rh(diol)X] 2 (X  Cl, F); a possible scheme for the reaction with HCl is proposed. The [Rh(C 8 H 12 )(formamidine)] 2 complex reacts with heterocumulenes as CS 2 , SO 2 , PhNCS and PhNCO with diene displacement; the only product isolated was [Rh(CS 2 ) 2 (formamidine], to which a polymeric structure is assigned.

Facile cleavage of the ph bond of secondary phospine sulphides by nucleophilic rhodium(I) and iridium(I) metal complexes

Abstract The secondary phosphine sulphide, Ph 2 HPS, reacts with Ir(CO)(PPh 3 ) 2 Cl under mild conditions to give Ir(CO)H(PPh 3 ) 2 (SPPh 2 )Cl (I); the 31 P NMR spectrum indicates that the SPPh 2 group is S-bonded to metal. The same reaction with Rh(CO)(PPh 3 ) 2 Cl gives Rh(CO)(PPh 3 ) 2 (SPPh 2 ), probably by reductive elimination of HCl from a transient intermediate rhodium(III) complex analogous to I. A possible mechanism for these reactions is proposed. The complex I reacts with MeI or EtI to give Ir(CO)H(PPh 3 ) 2 CII.

Self-assembly of [Bu4N][M(qdt)2] [qdt=quinoxaline-2,3-dithiolate; M=Au and Cu] in a 2D network via combination of CH⋯M and CH⋯S interactions

Abstract The compounds [Bu4N][M(qdt)2] (M=Au 1 and M=Cu 2) have been prepared and characterized by X-ray diffraction studies. Complexes 1 and 2 are isomorph and their structure consists of a two-dimensional intermolecular cation–anion network with the [Bu4N] cation acting as a four H-bonded bridging ligand.

Synthesis and dynamic behaviour of rhodium(I) complexes containing the di-2-pyridyl sulphide ligand

The complexes [Rh(cod)(dps)]X 1(cod = cycloocta-1,5-diene; dps = di-2-pyridyl sulphide; X = BF4, PF6 or ClO4) has been prepared by reaction of dps and AgX with [{Rh(µ-Cl)(cod)}2]; [Rh(CO)2(dps)]X 2 can be prepared by a similar route but higher yields are obtained by bubbling CO through a CH2Cl2 solution of 1. Triphenyl-phosphine or -arsine easily replaces a molecule of CO in 2 to give [Rh(CO)(PPh3)(dps)]X 3 or [Rh(CO)(AsPh3)(dps)]X 4. These compounds have been characterized by usual spectroscopic techniques which indicate a N, N-inside conformation for the chelate dps ligand. The reaction of [{Rh(µ-Cl)(cod)}2] with dps gives rise to stoichiometry-, concentration-, solvent- and temperature-dependent equilibria in which the starting materials, the binuclear complex [{Rh(cod)Cl}2(µ-dps)]5a, [Rh(cod)(dps)]+, [Rh(cod)Cl2]– and Cl– are involved. Complex 5a and [Rh(cod)(dps)][Rh(cod)Cl2]5b can be isolated as solids whereas [Rh(cod)(dps)]Cl is present only in solution. Conductivity measurements and electronic spectra indicate that the ionic species are stabilized in methanol, whereas in CH2Cl2 the starting materials and binuclear species dominate at low and higher concentration respectively. Proton and 13C NMR spectra, in CD2Cl2 indicate that exchange of the Rh(cod) unit between the starting materials, binuclear and ionic species occurs rapidly in the NMR time-scale at room temperature. When dps is added to 5a or 5b(molar ratio 1:1) the concentration of the binuclear species decreases and an equilibrium occurs between [Rh(cod)(dps)]Cl and [Rh(cod)Cl(dps)] where the dps ligand is monodentate.

Ligating properties of thionitrosoamines: II. Crystal and molecular structure of cis-dichloro-(N-thionitrosodimethylamine)(triphenylarsine)-palladium(II) complex. Synthesis and characterization of neutral binuclear complexes of palladium(II) and cationic complexes of palladium(II) and platinum(II) containing N-thionitrosodimethylamine

Abstract The crystal and molecular structure of Pd(SNNMe2)(AsPh3)Cl2 was determined from single-crystal X-ray diffraction data. In agreement with the structure previously proposed on the basis of IR data, the complex has the cis-configuration with the Me2NNS ligand S-bonded to the metal. It crystallizes in the space group P 1 with a 9.407(2), b 10.540(2), c 12.265(4) A; α 68.1(1), β 78.3(1), γ 86.3(1)° and Z = 2. The structure was refined to R = 0.029 for 2664 diffractometer data with I ≥ 3σ(I. The palladium atom is in a nearly square planar coordination geometry with PdS 2.249(1), PdAs 2.362(1), Pd-Cl(1) 2.313(1), PdCl(2) 2.359(1) A. The very short PdS bond length may indicate a strong σ + π synergistic interaction of the Pd atom with the N-thionitrosodimethylamine ligand. Me2NNS reacts with Pd(PhCN)2Cl2 to give, besides the known cis-Pd(SNNMe2)2Cl2, the complex [μ-Cl)2{Pd(SNNMe2Cl}2] (IIIa), and an unstable compound which is probably [Pd(SNNMe2)4]Cl2. The stable salts [Pd(SNNMe2(BPh4)2 (IVa) and [Pd(SNNMe2)4]HgCl4 (IVd) were obtained from this unstable compound and NaBPh2 or HgCl4. Alternatively the stable salts [Pd(SNNMe2)4](PF6)2 (IVb) and [Pd(SNNMe2)]PdCl4 (IVc) were obtained from Me2NNS and [Pd(diene)(acetone)2](PF6)2 (diene = 1,5-cyclooctadiene, norbornadiene) or Na2PdCl4. Me2NNS reacts with Pt(PhCN)2Cl2 to form an unstable compound probably [Pt(SNNMe2)4]Cl2 which was obtained in the stable form as [Pt(SNNMe2)4]Y2 (Y = BPh4 (Va), PF6 (Vb); Y2 = PtCl4 (Vc)). The complexes [(μ-X)2{Pd(SNNMe2)Cl}2] (X = Cl (IIIa), Br (IIIb), SCN (IIIc), SeCN (IIId)) were prepared by reaction of Pd(PhCN)2Cl2 with Pd(SNNMe2)2X2.