Base‐Free Cationic 14‐Electron Titanium and Zirconium Alkyls: In situ Generation, Solution Structures, and Olefin Polymerization Activity

Abstract

6] Addition of crown ether has been reported to increase the reactivity of the silyl anion by forming a crown ether-sodium ion complex; A. Sekiguchi, T. Yatabe, C. Kabuto, H. Sakurai, Angew. Chem. f O 1 (1989) 778; Angew. Chem. Int. Ed. Engl. 28 (1989) 757; M. FuJino, H. Isaka, J. Chem. SOC., Chem. Commun. 1989,466. 171 A single crystal with dimensions of 0.5 x 0.2 x 0.2 mm, obtained from ethanol was used for the X-ray analysis. Lattice constants were determined by the least-squares method with an angular setting of 25 reflections within the range 11 < 6 < 13". Intensity data were obtained on a Enraf-Nonius CAD4 diffractometer equipped with graphite monochromatized Mo,, radiation and using thew-28 scan technique (26 < 50"). Duringdata collection three standards, measured every 120 min, indicated a total loss in intensity of 18.4%. A h e a r decay correction was applied. Of 3158 independent reflections measured, only 2298 were considered as observed on the basis of the criterion I > 3.0 o(1). All intensities were corrected for Lorentz and polarization effects but not for absorption. Crystal data for 1: M , = 483.19; orthorhombic; P,,,; a = 15.037(3), b = 9.029(3), c = 23.231(5) A; V = 3154.3 A3; 2 = 4; = 1.02 g ~m -~; p (Mo~.) = 3.0 cm-I. The structure of 1 was solved by direct methods and refined by full-matrix least-squares methods. The final refinements with anisotropic temperature factors for the non-hydrogen atoms lowered Rand R, values to 0.059 and 0.072, respectively.

Kinetic and mechanistic aspects of metallocene polymerisation catalysts

“…It is now well recognised that the active species is a cationic complex, or more precisely an ion pair, [L 2 M-R + Á Á ÁX À ] [15,27]. Such species can be generated from group 4 metallocene dichlorides and MAO, or from metallocene dialkyls and cation generating agent such as B(C 6 F 5 ) 3 , HNMe 2 Ph þ BðC 6 F 5 Þ À 4 or CPh þ 3 BðC 6 F 5 Þ À 4 [15,19,21,28].…”

“…This dissociative model has been favoured in the past [15,[19][20][21][25][26][27][28][29] since it allows a convenient explanation of the observed polymer stereochemistry by considering only the ligands of the cationic metallocene complex. However, anion dissociation must be questioned since in non-polar solvents charge separation is energetically expensive.…”

Control of symmetry in active cationic ansa-zirconocene species: catalyst preparation, characterization and ethylene–norbornene copolymerization

“…When 3 was treated with B(C 6 F 5 ) 3 the species 3b was formed; structural differences were observed by 1 H, 13 C NMR and 19 F NMR spectroscopy. All complexes 1, 2 and 3 exhibited C 2v molecular symmetry in solution, as determined by NMR spectroscopy and were strictly speaking ion pairs in which the anion is located outside the metal coordination sphere [17] as in complexes 1, 2 and 3. It is proposed that the species {[H 2 C(Me 2 C 5 H 2 ) 2 ]-Zr(CH 2 Ph)} + {(CH 2 Ph)B(C 6 F 5 ) 4 } À (2b) exists as an ion pair in toluene with one benzyl group bound to boron in the anion, assigned by 1 H NMR spectroscopy (Fig.…”

Gas-Phase Oxidation of Reactive Organometallic Ions

“…The final reactive system that we studied involved the ion [Cp2Zr(µ-Me)2AlMe2] + (m/z 307) which can be conveniently generated in situ from Cp2ZrMe2, excess AlMe3 and [Ph3C][B(C6F5)4] in fluorobenzene solution. 28,29 As discussed elsewhere, the appearance of the mass spectrum of this ion is sensitive to cone voltage (in-source fragmentation via collision-induced dissociation), and loss of 72 Da (Me3Al) in the gas phase via CID, either in source or the collision cell is facile. 4,14 The resulting (gas phase) 14 electron ion [Cp2ZrMe] + (m/z 235) is known to be exceptionally reactive towards a variety of gaseous species [30][31][32][33] but its reaction with O2 or water has not been systematically studied.…”