Fluoride adducts of niobium(V): Activation reactions and alkene polymerizations

Fluoride coordination derivatives of niobium(V) were tested for their activation capabilities with respect to acetone and to olefins. Activation of acetone (formation of mesityloxide) was observed with NbF4(OMe). Several fluoride coordination derivatives of niobium(V) of different nature (neutral or ionic) and nuclearity, i.e. NbF5L [L = Et2O, 4, thf, 5 (thf is tetrahydrofuran), MeOH, 6, EtOH, 7], (NbF4L2)(NbF6) [L = dmf, 8 (dmf is dimethylformamide), dme, 9 (dme is dimethoxyethane)], (NbF4L4)(NbF6) [L = thf, 10, Et2O, 11, MeCN, 12], [S(NMe)3][NbF6], 13, NbF4OMe, 1, NbF4OPh, 3), NbF3(OPh)2, 14, NbF2(OPh)3, 15 and NbF2(OEt)3, 16, promoted the polymerization of ethylene using AlMe3-depleted methylaluminoxane as cocatalyst. Highly linear polyethylene was obtained. Compound 3, upon activation with methylaluminoxane, promoted ring-opening metathesis polymerization (ROMP) of norbornene, affording polymers with a slight excess of trans content.

Examples of activation reactions of acetone and olefin polymerization catalysis based on niobium fluoride derivatives are reported for the first time. In the latter cases, the dependence of the activity on the nature of the catalytic precursors (nuclearity, charge) is discussed.Figure optionsDownload as PowerPoint slideHighlights
► Niobium(V) alkoxides activate acetone with formation of mesityl oxide.
► Fluoride derivatives of niobium(V) have been tested as polymerization catalysts.
► The fluoride complexes have different nature (neutral or ionic) and nuclearity.
► Fluoride complexes are active in the ring-opening metathesis of norbornene.