Reactivity of secondary metallocene alkyls and the question of dormant sites in catalytic alkene polymerization.
The reactivity of [rac-(C2H4(1-indenyl)2)Zr(n-butyl)][MeB(C6F5)3] (4), [rac-(C2H4(1-indenyl)2)Zr(sec-butyl)][MeB(C6F5)3] (5), and [rac-(C2H4(1-indenyl)2)Zr(polypropenyl)][MeB(C6F5)3] with propene, ethene, and hydrogen was studied by low-temperature (<-40 degrees C) 1H and 13C NMR spectroscopy in toluene solutions. In contrast with previous suggestions that 2 degrees zirconium alkyl species such as 5 are dormant sites, these measurements demonstrate reactivity of 2 degrees zirconium alkyls with propene and ethene comparable to the 1 degrees zirconium alkyl species 4 and [rac-(C2H4(1-indenyl)2)Zr(polypropenyl)][MeB(C6F5)3]. Because 2,1-insertion of propene is an infrequent event, these results preclude significant accumulation of catalyst in the form of 2 degrees zirconium alkyls for this metallocene and counterion. The reactivity of 5 with hydrogen is at least 2 orders of magnitude faster than other 1 degrees zirconium alkyls. Such high reactivity accounts for the puzzlingly high fraction of butyl end groups in prior hydrooligomerization studies and implies that catalyst responsivity to H2 as a molecular weight control agent correlates with the regioselectivity of the catalyst.
Landis
Clark R
CR
Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, USA. landis@chem.wisc.edu
Sillars
Douglass R
DR
Batterton
Jeanine M
JM
D000475:Alkenes / Q000737:chemistry*; D000478:Alkylation; D002384:Catalysis; D009682:Magnetic Resonance Spectroscopy; D009942:Organometallic Compounds / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D013237:Stereoisomerism; D015040:Zirconium / Q000737:chemistry*
D000475:Alkenes; D009942:Organometallic Compounds; D011108:Polymers; C013108:metallocene; D015040:Zirconium