Synthesis of new chloro methyl niobium and tantalum complexes with silyl-cyclopentadienyl ligands: X-ray crystal structure of [Ta{η5-C5H3(SiMe3)2}Cl2Me2]

Ortho-phenylene-bridged aryloxy phosphine ligands and their coordination chemistry with tantalum(V)

The lithium complexes RP(3,5-tBu2C6H2OLi)2(THF)4, where R = Ph or iPr, (R[OPO]Li2)2(THF)4, can be converted quantitatively into the protonated forms, R[OPO]H2, by reaction with Et3NHCl. Reaction of the protonated compounds with KH yields the potassium complexes (Ph[OPO]K2)2(THF)6 and (iPr[OPO]K2)3(THF)3. The reaction of R[OPO]H2 with TaCl5 yields the sparingly soluble tantalum trichloride complexes R[OPO]TaCl3 via elimination of HCl. Reaction of Ph[OPO]H2 with TaMe3Cl2 leads to the monomethyl complex Ph[OPO]TaMeCl2, or the dimethyl halide complex, Ph[OPO]TaMe2Cl, via protonolysis, and the potassium complex (Ph[OPO]K2)2(THF)6 yields the trimethyl complex, Ph[OPO]TaMe3 by a metathesis process.

Novel highly active niobium catalysts for ring opening metathesis polymerization of norbornene

Ring-opening metathesis polymerization (ROMP) of norbornene catalyzed by niobium(V) N,N-dialkylcarbamates Nb(O(2) CNR(2) )(5) , R = Et (1), Me (2) was studied in the presence of methylaluminoxane (MAO) as a cocatalyst. These novel catalytic systems resulted very active in chlorobenzene: 1 in the presence of methylaluminoxane catalyzes the ROMP of norbornene with the highest activity (29 000 kg of polymer/mol of catalyst × hour) never reported up to now for niobium catalysts. The high productivity appears particularly attractive considering that these precursors are rather cheap and easy to synthesize and to handle. Polynorbornenes were characterized by FT-IR and NMR spectroscopies and by DSC calorimetry. A new FT-IR method for the swift determination of the cis/trans content of the polymer is presented.