From single-site tantalum complexes to nanoparticles of Ta N and TaO N supported on silica: elucidation of synthesis chemistry by dynamic nuclear polarization surface enhanced NMR spectroscopy and X-ray absorption spectroscopy.

Air-stable catalysts consisting of tantalum nitride nanoparticles represented as a mixture of Ta N and TaO N with diameters in the range of 0.5 to 3 nm supported on highly dehydroxylated silica were synthesized from TaMe (Me = methyl) and dimeric Ta(OMe) with guidance by the principles of surface organometallic chemistry (SOMC). Characterization of the supported precursors and the supported nanoparticles formed from them was carried out by IR, NMR, UV-Vis, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopies complemented with XRD and high-resolution TEM, with dynamic nuclear polarization surface enhanced NMR spectroscopy being especially helpful by providing enhanced intensities of the signals of H, C, Si, and N at their natural abundances.

Synthesis and characterization of a homogeneous and silica supported homoleptic cationic tungsten(vi) methyl complex: application in olefin metathesis.

A method for the synthesis of a homogeneous cationic tungsten(vi)pentamethyl complex [(WMe)(CF)BMe] from neutral tungstenhexamethyl (WMe) and a silica supported cationic tungstentetramethyl complex [([triple bond, length as m-dash]Si-O-)WMe (CF)BMe] from a neutral silica supported tungstenpentamethyl complex [([triple bond, length as m-dash]Si-O-)WMe] is described. In both cases a direct demethylation using the B(CF) reagent was used. The aforesaid complexes were characterized by liquid or solid state NMR spectroscopy.

Controlling the hydrogenolysis of silica-supported tungsten pentamethyl leads to a class of highly electron deficient partially alkylated metal hydrides.

The well-defined single-site silica-supported tungsten complex [([triple bond, length as m-dash]Si-O-)W(Me)], , is an excellent precatalyst for alkane metathesis. The unique structure of allows the synthesis of unprecedented tungsten hydrido methyl surface complexes a controlled hydrogenolysis. Specifically, in the presence of molecular hydrogen, is quickly transformed at -78 °C into a partially alkylated tungsten hydride, , as characterized by H solid-state NMR and IR spectroscopies.

Simple addition of silica to an alkane solution of a Wilkinson WMe6 or Schrock W alkylidyne complex gives an active complex for saturated and unsaturated hydrocarbon metathesis.

The addition of partially dehydroxylated silica (PDS) to a solution of the Wilkinson WMe6 as well as the Schrock W neopentylidyne tris neopentyl complex catalyzes linear or cyclic alkanes to produce respectively a distribution of linear alkanes from methane up to triacontane or a mixture of cyclic and macrocyclic hydrocarbons. This single catalytic system transforms also linear α-olefins into higher and lower homologues via an isomerization/metathesis mechanism (ISOMET). This complex is also efficient towards functionalized olefins.