Enantio- and Diastereoselective Catalytic Carboalumination of 1-Alkenes and α,ω-Dienes with Cationic Zirconocenes:  Scope and Mechanism

Kevin H. Shaughnessy and Robert M. Waymouth*
Department of Chemistry, Stanford University, Stanford, California 94306
Organometallics, 1998, 17 (26), pp 5728–5745
DOI: 10.1021/om9807811
Publication Date (Web): November 25, 1998
Copyright © 1998 American Chemical Society
*

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

Abstract

Abstract Image

Bis(pentamethylcyclopentadienyl) dimethylzirconium (Cp*2ZrMe2) and bis(1-(−)-neomenthylindenyl) dimethylzirconium ((NMIn)2ZrMe2) upon activation by tris(pentafluorophenyl)borane are efficient catalysts for the carboalumination of a variety of 1-alkenes and nonconjugated dienes. The organoalane products can be oxidized to alcohol products, which are isolated in 50−90% yield. (NMIn)2ZrMe2 carboaluminates 1-alkenes and dienes with moderate (55−65%) enantioselectivities. In contrast, ethylenebis(tetrahydroindenyl) dimethylzirconium ((EBTHI)ZrMe2) and related zirconocenes give low activities and selectivities in the carboalumination reaction. Study of the interaction of zirconocene methyl cations with trimethylaluminum by 1H NMR shows that [(EBTHI)ZrMe][MeB(C6F5)3] forms a stable bis(μ-methyl) aluminum adduct. Zirconocene methyl cations derived from Cp*2ZrMe2 and (NMIn)2ZrMe2 react slowly with large excesses of trimethylaluminum to form weakly bound trimethylaluminum adducts. The difference in trimethylaluminum binding to the cationic zirconocene centers is consistent with the significantly lower activity observed when (EBTHI)ZrMe2 is used as the precatalyst.

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History

  • Published In Issue December 21, 1998
  • Received September 18, 1998

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