Unusual Reactivity of Tris(pyrazolyl)borate Zirconium Benzyl Complexes

2005-07-06T00:00:00Z (GMT) by Han Lee Richard F. Jordan
The synthesis and reactivity of [Tp*Zr(CH<sub>2</sub>Ph)<sub>2</sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (<b>2</b>, Tp* = HB(3,5-Me<sub>2</sub>pz)<sub>3</sub>, pz = pyrazolyl) have been explored to probe the possible role of Tp‘MR<sub>2</sub><sup>+</sup> species in group 4 metal Tp‘MCl<sub>3</sub>/MAO olefin polymerization catalysts (Tp‘ = generic tris(pyrazolyl)borate). The reaction of Tp*Zr(CH<sub>2</sub>Ph)<sub>3</sub> (<b>1</b>) with [Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] in CD<sub>2</sub>Cl<sub>2</sub> at −60 °C yields <b>2</b>. <b>2</b> rearranges rapidly to [{(PhCH<sub>2</sub>)(H)B(μ-Me<sub>2</sub>pz)<sub>2</sub>}Zr(η<sup>2</sup>-Me<sub>2</sub>pz)(CH<sub>2</sub>Ph)][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (<b>3</b>) at 0 °C. Both <b>2</b> and <b>3</b> are highly active for ethylene polymerization and alkyne insertion. Reaction of <b>2</b> with excess 2-butyne yields the double insertion product [Tp*Zr(CH<sub>2</sub>Ph)(CMeCMeCMeCMeCH<sub>2</sub>Ph)][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (<b>4</b>). Reaction of <b>3</b> with excess 2-butyne yields [{(PhCH<sub>2</sub>)(H)B(μ-Me<sub>2</sub>pz)<sub>2</sub>}Zr(Cp*)(η<sup>2</sup>-Me<sub>2</sub>pz)][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (<b>6</b>, Cp* = C<sub>5</sub>Me<sub>5</sub>) via three successive 2-butyne insertions, intramolecular insertion, chain walking, and β-Cp* elimination.