Alessandro Sassi

Cis addition of dimethylamine to the coordinated nitriles of cis- and trans-[PtCl2(NCMe)2]. X-ray structure of the amidine complex cis-[PtCl2{E-N(H)C(NMe2)Me}2]·CH2Cl2

Abstract The reaction of cis-[PtCl2(NCMe)2] with a 5-fold excess of Me2NH in CH2Cl2 at −10°C affords in high yield the bis-amidine complex cis-[PtCl2{E-N(H)C(NMe2)Me}2] (E,E-2), where both the amidine ligands assume the E configuration. E,E-2 was characterized by X-ray structure analysis, NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). The corresponding reactions of trans-[PtCl2(NCMe)2] with Me2NH gave the bis-amidine complex trans-[PtCl2{E-N(H)C(NMe2)Me}2] (E,E-3) and the mono-amidine derivative trans-[PtCl2{E-N(H)C(NMe2)Me}(NCMe)] (E-4).

Electrospray mass spectrometry of Pt(II) amidine complexes of the type cis- and trans-[PtCl2{NHC(R)NR′R″}2] and trans-[PtCl2(RCN){NHC(R)NR′R″}]

The ESI mass spectrometric behaviour of a series of Pt(II) amidine complexes of the type cis- and trans-[PtCl2{NHC(R)NR′R″}2] (R=Me, Ph; R′=H, R″=Me, Et, But, Pri; R′=R″=Me, Et) and trans-[PtCl2(RCN){NHC(R)NR′R″] (R=Me, Ph; R′=R″=Me, Et) is reported. The bis-amidine complexes have been prepared by nucleophilic attack of primary and secondary amines on acetonitrile and benzonitrile ligands coordinated to Pt(II) substrates, while the mono-amidine complexes are obtained by reaction of secondary amines with trans-[PtCl2(RCN){NHC(R)NR′R″}] (R=Me, Ph; R′=R″=Me, Et). The protonated molecular ions or cationized ions are usually observed. The fragmentation processes are extremely reduced and in any case related to the original structure. As a general feature, cis and trans compounds give rise to different ESI spectra. Additions of Na+ and/or K+ are observed. From these data, ESI mass spectrometry, due to the soft ionisation, furtherly proposes as an efficient method for the characterisation of metal complexes in solution.

Surface modification of poly(ethylene-co-acrylic acid) with amino-functionalized silica nanoparticles

In this work we studied the possibility to achieve a hybrid-surface through the modification, via a facile wet chemical process, of the surface of films of poly(ethylene-co-acrylic acid) (EAA) with amino-modified silica nanoparticles. Films of EAA were preliminarily activated by the introduction of –COCl groups on their surface. Silica nanoparticles were thereafter covalently bound on the polymeric surface as confirmed by FTIR, ATR-FTIR, XPS, NMR and SEM determinations. The nanoparticles formed a multilayer on the film surface and covered almost uniformly the whole film surface. Direct measurements of superficial amino groups by titration allowed us to detect a concentration of about 18 nmol cm−2. The presence of this uniform layer of nanoparticles bearing polar groups strongly changed the wettability of the material as confirmed by static contact angle measurements that passed from 87° of the neat EAA to about 30° of the amino-functionalized silica nanoparticles modified material.

Catalytic Activity of Dicationic Platinum(II) and Rhodium(II) Complexes towards 9-Diazofluorene

Abstract 9-Diazofluorene (DAF) is catalytically decomposed at 25°C in CH 2 Cl 2 in the presence of 1 mol% of the dicationic platinum(II) complex cis -[Pt(PPh 3 ) 2 (CH 3 CN) 2 ][BF 4 ] 2 ( 1 ) to give the olefin product 9,9 ′ -bifluorenylidene in high yield. Furthermore, DAF undergoes an insertion reaction into the O–H bond of methanol at 25°C in CH 2 Cl 2 /MeOH (DAF/MeOH molar ratio 1/20) in the presence of 1 mol% of 1 to give 9-methoxyfluorene in excellent yield. With neutral or cationic dirhodium(II) complexes as catalysts the same reaction yields further products, suggesting the existence of different parallel reaction pathways.

Characterisation of Solute Mobility in Hypercross-Linked Resins in Solvents of Different Polarity: Two Promising Supports for Catalysis

Two hypercross-linked resins stemming from a gel-type poly-chloromethylated styrene-divinylbenzene resin (GT) in beaded form are investigated with a combination of spectroscopic techniques (EPR and time-domain (TD)-NMR spectroscopy) to evaluate their use as supports for the development of operationally flexible heterogeneous metal catalysts, suitable to be employed in liquid and gas phase. The first resin (HGT) is the direct product of the hypercross-linking reaction, whereas the second one (HGS) is the sulphonated analogue of HGT obtained by exchanging approximately 3 wt % of the chloromethyl groups with sulphonic groups. HGT and HGS absorb both polar and apolar solvents in the permanent nanoporosity created by the hypercross-linking, and NMR data highlight that the pore size is not affected by the different properties of the investigated liquid media. The EPR analysis of the dry resins reveals that during the hypercross-linking process paramagnetic species are formed in the HGT beads, which persist in the sulphonated resin. The mobility of solutes inside the polymers framework was investigated with EPR spectroscopy upon soaking the resins with solutions of two spin probes (2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL)) in THF, toluene, n-heptane and water. The EPR spectra show that, depending on the solvent, the two resins can act as sorbents, able to trap the solutes in the polymer framework, or as simple supports that allow free diffusion of the solutes. Our results suggest that HGT and HGS are promising supporting materials for metal catalysts, provided one chooses carefully the solvent to be employed for the catalysed reaction as this choice strongly affects the mobility of the substrates and, thus their effective reactivity.

Surface functionalization with phosphazene substrates. Part I: Silica and Si-(100) surface functionalization with cyclophosphazenes partially substitued with trialkoxysilane derivatives and 4-cyanophenol as a marker molecule

In this paper we report the utilization of phosphazene substrates for the surface functionalization of silicon-based materials (e.g., silica gel beads and crystalline silicon(100) wafers) and for the preparation of monoliths by means of a sol-gel technique. We used multifunctional cyclophosphazenes to prepare trimers substituted with equimolecular amounts of γ-aminopropyltriethoxysilane and 4-cyanophenol. The first substituent was used to attach the phosphazene materials to the surface of the silicon-based substrates by reaction of the triethoxysilane functions with the free hydroxylic groups present on the surface of the silica gel particles or of the crystalline silicon wafers. Furthermore, the second substituent, i.e., 4-cyanophenol, was exploited as an internal marker, because of the presence of a peculiar band at 2230 cm−1 in its IR spectrum, to reveal the presence of the cyclophosphazene on the surface of the functionalized substrates. This approach is completely general and can be used very easily to induce specific modifications on the surface of different materials by carefully selecting the substituent groups inserted in the cyclophosphazene substrate.

Surface functionalization with phosphazene substrates, Part IV: Silica and Si(100) surface functionalization using cyclophosphazenes partially substituted with trialkoxysilane derivatives and PEG-750 monomethylether, 2,2,3,3-tetrafluoropropanol and 4-hydroxyazobenzene

This paper deals with the possibility of functionalizing the surface of silicon-based materials by exploiting cyclophosphazenes containing suitable substituent groups. Thus, phosphazene trimers were prepared, containing about 50% of the reactive sites substituted by γ-aminopropyltriethoxy silane (APTES), while the residual positions in the cycle contain poly(ethylene glycol) monomethylether (MW approx. 750; PEG-750-ME), tetrafluoropropanol (TFP) and 4-hydroxyazobenzene (AzB). Using these novel materials we succeeded in surface functionalizing SiO2 beads in the coating of silicon wafers or sodalime slides and in the preparation of cyclophosphazene-based monoliths in the presence of hydrolyzed TEOS by sol–gel technique. The whole series of products has been characterized by standard spectroscopic (IR, UV-Vis, 1H-, 13C-, 29Si- and 31P-NMR, both in solution and in solid state) and thermal (DSC and DMTA) techniques. This approach to the surface functionalization of silicon-based materials containing carefully selected substituents is completely general and can be used to attach to the hydroxylated surfaces practically any type of nucleophile that can be supported on the cyclophosphazene ring.

Metal substituted ketenes: first 13C and 31P CP/MAS NMR determinations

Abstract Cross-polarization, combined with magic-angle spinning, has been employed to obtain high-resolution solid-state 13C and 31P NMR spectra of a series of solid, peculiar ketenes, also known as η1-ketenyl derivatives, bearing as substituents a PPh3 moiety and a coordinatively unsaturated Pt(II) fragment. Solid-state NMR data found for trans-[PtCl2(η2-C2H4){η1-C(PPh3)CO}], trans-[PtCl2{η1-C(PPh3)CO}2], Ph3PCCO, trans-[PtCl2(η2-C2H4){η1-CH(PPh3)COMe}], trans-[PtCl2{η1-CH(PPh3)COMe}2] and Ph3PCHCOMe, are compared with NMR values obtained in solution. The general utility of the CP/MAS NMR technique in the study of unstable or insoluble complexes is discussed.

Hydroxylated Cyclophosphazene/Silica Hybrid Materials: Synthesis and Characterization

The synthesis of new hybrid materials that are prepared by the sol-gel technique is presented. The synthesis involves the reaction of a free hydroxylic group-containing cyclophosphazene, hexakis(4-hydroxyphenoxy)cyclophosphazene, and a hydrolyzed tetraethoxysilane under acid catalysis. Evidence for the formation of genuine chemical bonds between the hydroxylated cyclophosphazene and the three-dimensional silica network is presented. The formation of these bonds was confirmed by spectroscopic techniques (FTIR, 31P, 29Si, and 13C NMR both in solution and in the solid state and X-Ray Diffraction analysis). The results are supported by thermal characterization of the materials based on Differential Thermal Analysis (DTA) and Thermogravimetric Analysis (TGA) determinations.

Surface Modification of Plasma-Treated Polyamide-6 with Fluorinated Alcohols and Azobenzene Compounds using Chlorinated Phosphazenes as Coupling Agents

A three-step procedure for surface functionalization of polyamide-6 plates is presented. The substrate was first treated with cold, low pressure Ar plasma to generate surface OH groups, which were successively reacted with chlorophosphazenes to ensure grafting of these molecules. Substitution of the residual chlorines of the phosphazenes with fluorinated alcohols and 4-hydroxyazobenzene yielded the final surface modification. Characterization was performed by contact angle, XPS and UV-Vis techniques.