o Sergi

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.

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.

Platinum(II) complexes of N,N′-di-nbutyldithiooxamide showing a peculiar +NH···Cl− interaction. The crystal and molecular structure of bis-di-nbutyldithiooxamidato-platinum(II)

Abstract N,N′-di-butyldithiooxamide, nbu2-DTO, reacts in chloroform with neutral complexes of the type cis-PtL2Cl2. When L=bz2S or 1 2 COD the tight contact ion pair {Pt(H2-nbu2-DTO)22+,(Cl−)2} (1) is obtained for any metal to ligand ratio. When L is Me2SO the ion pair {(Me2SO)ClPt(H2-nbu2-DTO+,(Cl−)} (2) separates in the solid state on adding the ligand to platinum in a 1:1 ratio. This monochelate complex, however, is unstable in chloroformic solution where a symmetrization equilibrium with the corresponding bis-chelate ion pair 1 and the dichloroplatinum starting material can be found. Compound 1 by reaction with pyridine, dipyridine, phenanthroline or similar nitrogen Lewis bases loses one or both HCl molecules so giving {Pt(H-nbu2-DTO)(H2-nbu2-DTO)+,(Cl−)} (3) or [Pt(H-nbu2-DTO)2] (4), depending on the base concentration. Dissolution of 1 in a basic solvent (DMF, alcohols) leads to the formation of the neutral species 4, which is also formed when a chloroformic solution of 1 undergoes a double phase reaction with the −OH group of HOH, AlOH or SiOH. Compound 4 crystallizes in the monoclinic space group P21/c, with a=10.572(2), b=10.748(1), c=12.165(2) A, β=93.37(2)°, V=1379.9(4) A3, Z=2 and Dcalc=1.58 g cm−3; the structure was refined to R=0.033 and Rw=0.038. The [Pt(H-nbu2-DTO)2] complex has imposed square-planar geometry about the Pt atom, two thioamide S atoms of the nbu2-DTO molecule acting as a chelating ligand. The two crystallographically independent values for the PtS bond distance are: PtS(1)=2.297(3) A and PtS(2)=2.284(2) A, the bond angles are very close to 90°. The deprotonated complex [Pt(H-nbu2-DTO)2] (4) restores the ion pair by a double phase reaction with aqueous HCl, while none of the oxoacids is able to give {Pt(H2-nbu2-DTO)22+,(Ox−)2} (Ox−=oxoanion). As a consequence, the + NH···Cl− hydrogen interaction in {Pt(H2-nbu2-DTO)22+,(Cl−)2} is thought to be crucial in stabilizing the tight ion pair.

Ligand effects on oxidative addition reactions of d8 metal complexes. Preparation and oxidation addition reactions of complexes of the type trans-[Rh(CO)L2Cl] (L = S(C2H5)2, Se(C2H5)2 Te(C2H5)2)

Abstract The preparation and properties of the new complexes trans -[Rh(CO)L 2 Cl], where L = S(C 2 H 5 ) 2 , Se(C 2 H 5 ) 2 , Te(C 2 H 5 ) 2 are described. These halocarbonylrhodium(I) derivatives very readily undergo oxidative addition. The reactions of these new compounds with Cl 2 , Br 2 , I 2 , HCl, CH 3 I, C 6 H 5 SO 2 CI are described, and their behaviour is compared with that of the analogous compounds containing ligands with Group V donor elements. The complexes [Rh(CO)(CH 3 )L 2 ClI] have been shown to undergo CO insertion into the RhCH 3 bond. The versatility of the new complexes for various oxidative additions is attributed to a balance of σ and π factors, the former being dominant in the case of the ligands considered.

New σ-bonded aryl derivatives of palladium(II)

Abstract A new series of organopalladium complexes of the type trans-[PdL2RX] (L = SeEt2, TeEt2; R = aryl group; X = halogen) containing σ-bonded organic substituents has been obtained from trans-[PdL2X2] complexes and the appropriate Grignard reagents. Analogous aryl derivatives could not be obtained from trans-PdL2X2] complexes (L = SEt2 or SPh2). The properties of the new compounds are reported and discussed. Their stabilities vary with the size of the neutral ligand and the position of bustitution on the benzene ring.

Some new σ-bonded aryl—platinum complexes

Abstract The preparations are described of some new complexes trans -[PtL 2 RX] and cis - and trans -[PtL 2 R 2 ] (where L = S(C 2 H 5 ) 2 or Se(C 2 H 5 ) 2 , R = phenyl, o -tolyl or mesityl and X = halogen). The trans -[PtL 2 (mesityl) 2 ] complexes are the first σ-bonded demesityl derivatives of Pt II . The factors determining the stability of these complexes and the IR stretching frequencies v (PtCl) and v (PtC) are discussed.

Activation of thiocyanogen and selenocyanogen by low oxidation state transition metal complexes

Abstract Thiocyanogen and selenocyanogen react with Ru(CO) 3 (PPh 3 ) 2 to give respectively the complexes Ru(CO) 2 (PPh 3 ) 2 (NCS) 2 and Ru(CO) 2 (PPh 3 ) 2 (NCSe) 2 . (M—NCS and M—SCN represent N - and S -thiocyanato groups, M—NCSe and M—SeCN represent N - and Se -selenocyanato groups respectively, while M—CNS indicates the bridging coordination mode of thiocyanate.) Only the thiocyanogen reacts with Ru 3 (CO) 12 giving [Ru(CO) 2 (CNS) 2 ] n , which dissolves in hot coordinating solvents, such as pyridine, to form Ru(CO) 2 (py) 2 (NCS) 2 . Selenocyanogen is less effective than thiocyanogen in the oxidative addition reactions with rhodium(I) and iridium(I) complexes; in fact selenocyanogen does not react with Rh(CO)(PPh 3 ) 2 Cl while with Ir(CO)(PPh 3 ) 2 Cl the former gives Ir(CO)(PPh 3 ) 2 (SeCN) 2 Cl by an equilibrium reaction. The coordination number of the metal and the charge on the complex do not change the bonding mode of the thiocyanate and selenocyanate groups in the iridium(III) complexes; in the Ir(PPh 3 ) 2 ClX 2 and [Ir(Ph 2 PC 2 H 4 PPh 2 ) 2 X 2 ] + (X = SCN and SeCN) complexes the pseudohalogens are S- and Se-bonded. The complexes trans -M(PPh 3 ) 2 (SeCN) 2 (M = Pd, Pt) have been obtained by reacting M(PPh 3 ) 4 with selenocyanogen.

Insertion of sulphur dioxide into platinum—carbon σ-bonds

Abstract Insertion reactions of sulphur dioxide with PtC σ-bonded complexes are described. These occur at about 50° in a Carius tube. The complexes obtained are of the S -sulphinate type, as indicated by their IR spectra. The S -sulphinate group shows a medium trans -effect. A comparison between carbon monoxide and sulphur dioxide insertions shows that the sulphur dioxide reactions are faster, probably because of the greater electrophilicity of sulphur dioxide.

Mechanism of formation of palladium(II)—allyl complexes. The reaction of PdCl2−4 with allyl ether

Abstract A kinetic study of the reaction bctween PdCl2−4 and allyl ether in aqueous methanolic solutions is described. The rate law has the form: A mechanism is proposed which involves a rate-determining nucleophilic attack of the OH− coordinated to palladium(II) on the coordinated olefinic double bond of the allyl ether.

Bridge splitting reactions on μ-dichlorobis[tetracarbonylrhenium(I)] with ligands having group VI donor atoms

Abstract Bridge splitting reactions on μ-dichlorobis[tetracarbonylrhenium(I)] with L ligands bearing oxygen, sulphur, selenium and tellurium as donor atoms give compounds of the type Re(CO) 4 LCl and Re(CO) 3 L 2 Cl. The stereochemistries of these new compounds have been established from their IR spectra in the CO stretching region. The ν(CO) frequencies indicate that the order of bond strengths is ReSe > ReTe ∼ ReS > ReO.