Novel monocyclopentadienyl zirconium and hafnium trialkoxide complexes: Syntheses and catalytic properties for olefin polymerization

Abstract

Monocyclopentadienyl trialkoxy compounds of zirconium and hafnium [CpZr(OR)3 and CpHf(OR)3], which cannot be prepared by earlier methods, are synthesized in situ by reacting bis(cyclopentadienyl) magnesium with zirconium tetraalkoxides [Zr(OR)4] and with hafnium tetraalkoxides [Hf(OR)4], respectively. The generation of CpZr(OR)3 and CpHf(OR)3 compounds involves a highly effective cyclopentadienyl ligand (Cp) transfer reaction from the Cp ligand of bis(cyclopentadienyl) magnesium to Group 4 metal alkoxides. The utilization of CpZr(OR)3 and CpHf(OR)3 compounds as catalyst precursors for mediating α‐olefin polymerizations was carefully investigated. Results show that highly active catalysts can be generated by reacting these mono‐Cp Zr and Hf alkoxides with methylaluminoxane. The resulting active CpZr(OR)3/MAO and CpHf (OR)3/MAO catalysts induce ethylene polymerization and ethylene/propylene copolymerization with high activity (e.g., 1820 kg PE/mole of catalyst‐h). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Facile, aprotic degradation of η-CpZrCl3·dme by ternary sodium/group 14 tert-butoxides: From η-CpZrCl3·dme back to NaCp in two easy steps

“…This oil hardened to a white, waxy solid, which melted at 32 C. The compound has the expectedly simple 1 H NMR spectrum, consisting of singlets at 6.34 (5 H) and 1.24 (27 H), respectively. The peak pattern is identical to that of 4, whose synthesis from the comproportionation of Cp 2 Mg and Zr(O t Bu) 4 recently reported [21]. Unfortunately, the report gave only the NMR spectra and elemental analysis data, but neither the mode of isolation of 4, nor its state of matter was described.…”

“…It is possible that CpZr(O t Bu) 3 is the initial product in all three reactions, and that the three p-donating alkoxide ligands weaken the CpeZr bond sufficiently to cause Cp loss, although mechanistic details are not known at this point. The Group 14 elements, however, must play a crucial role in these reactions, because CpM(O t Bu) 3 , M ¼ Zr, Hf, are effective olefin polymerization pre-catalysts [21] and do not undergo Cp loss in the absence of the Group 14 elements. Moreover, because CpZr(O t Bu) 3 cannot be obtained solely from CpZrCl 3 and NaO t Bu it is clear that the Group 14 elements also play a key role in the transfer of the tertbutoxide groups to zirconium.…”

Multicomponent Mechanochemical Synthesis of Cyclopentadienyl Titanium tert-Butoxy Halides, CpxTiXy(OtBu)4–(x+y) (x, y = 1, 2; X = Cl, Br)

“…28−30 In general, increased electron density on the metal center is associated with weaker Ti−O bond strength. Thus, the Ti−O energy in the Ti (IV) complex Ti(O t Bu) 4 has been placed at 108 kcal mol −1 , whereas in the Ti(III) species Cp 2 TiCl(TEMPO) [TEMPO = (2,2,6,6-tetramethylpiperidine-N-oxyl)], the bond strength is calculated at 17 kcal mol −1 . 30 The ready scission of the Ti(III)−TEMPO bond has been exploited synthetically for the formation of CpTiCl(OR) 2 (R = complexes).…”

“…This is the result of the combinatorial possibilities within the basic metallocene structure, coupled with an extended range of compatible L and L′ ligands. Many applications have been developed for such complexes, mainly in catalysis (e.g., syndiotactic polymerization of styrene, alkyne hydroamination, olefin polymerization, − including copolymerization, e.g., of ethylene/norbornene, , polymerization of lactide monomers and ε-caprolactone − ), but there are also uses in organic synthesis − and for the chemical vapor deposition production of thin-film oxides , and carbides …”