By grafting TaMe5 on Aerosil700, a stable, well-defined, silica-supported tetramethyl tantalum(V) complex, [(≡SiO)TaMe4], is obtained on the silica surface. After thermal treatment at 150 °C, the complex is transformed into two surface tantalum methylidenes, [(≡SiO)2Ta(═CH2)Me] and [(≡SiO)Ta(═CH2)Me2], which are active in alkane metathesis and comparable to the previously reported [(≡SiO)2TaHx]. Here we present the first experimental study to isolate and identify a surface tantalum carbene as the intermediate in alkane metathesis. A systematic experimental study reveals a new reasonable pathway for this reaction.

Synthesis, structure, and olefin metathesis activity of a surface complex [(≡Si-O-)W(═O)(CH)-ImN] (4) (Im = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-iminato) supported on silica by a surface organometallic chemistry (SOMC) approach are reported. The reaction of N-silylated 2-iminoimidazoline with tungsten(VI) oxytetrachloride generated the tungsten oxo imidazolin-2-iminato chloride complex [ImNW(═O)Cl] (2). This was grafted on partially dehydroxylated silica pretreated at 700 °C (SiO) to afford a well-defined monopodal surface complex [(≡Si-O-)W(═O)Cl-ImN] (3). 3 underwent alkylation by ZnMe to produce [(≡Si-O-)W(═O)(CH)-ImN] (4). The alkylated surface complex was thoroughly characterized by solid-state NMR, elemental microanalysis, Raman, FT-IR spectroscopies, and XAS analysis. 4 proved to be an active precatalyst for self-metathesis of terminal olefins such as propylene and 1-hexene.

[WMe6 ] (1) supported on the surface of SiO2 -Al2 O3(500) (2) has been extensively characterized by solid-state NMR spectroscopy, elemental analysis, and gas quantification, which clearly reveal the formation of a mixture of monopodal and bipodal species with the migration of methyl from W to Al. The supported species SiO2 -Al2 O3(500) (2) transformed at 120 °C into two types of carbynic centers, one of which is cationic and the other neutral. These species are very efficient for the metathesis of n-decane. Comparison with already-synthesized neutral bipodal tungsten indicates that the high increase in activity is due to the cationic character of the grafted tungsten.

The silica-supported tungsten oxo-trimethyl complex [(SiO)W(O)Me 3 ] was synthesized using a novel SOMC synthetic approach. By grafting the inexpensive stable compound WOCl 4 on the surface of silica, partially dehydroxylated at 700°C (SiO 2-700 ), a well-defined monopodal surface complex [(SiO)W(O)Cl 3 ] was produced. The supported complex directly methylated with ZnMe 2 and transformed into [(SiO)W(O)Me 3 ], which we fully characterized by microanalysis, IR, mass balance and SS NMR ( 1 H, 13 C, 1 H− 13 C HETCOR, 1 H− 1 H DQ and TQ). [(Si O)W(O)Me 3 ] has two conformational isomers on the surface at room temperature. The conversion of one to the other was observed at 318 K by variable-temperature 13 C CP/MAS and 1 H spin echo MAS solid-state NMR; this was also confirmed by NMR and DFT calculations. [(SiO)W(O)Me 3 ] was found to be active in cyclooctane metathesis and to have a wide distribution range in ring-contracted and ring-expanded products. In addition, [(SiO)W(O)Me 3 ] proved to be highly active for selective transformation of ethylene to propylene compared to other silica-supported organometallic complexes.

Due to their nature, Vehicular Ad hoc NETwork (VANET) is vulnerable to Denial of Service (DoS) attacks, such as jamming attack. The objective of a jammer is to interfere with legitimate wireless communications, and to degrade the overall QoS of the network. In this paper, we propose a model to detect a particular class of Jamming attack, in which the jammer transmits only when valid radio activity is signaled from its radio hardware. This detection model is based upon the measurement of error distribution.