Mechanism of Alkyne Insertion of a Cationic Zirconocene Aryl Complex

J. Am. Chem. Soc., 129 (43), 12952 -12953, 2007. 10.1021/ja0760067 S0002-7863(07)06006-4
Web Release Date: October 4, 2007

Mechanism of Alkyne Insertion of a Cationic Zirconocene Aryl Complex

Orson L. Sydora, Stefan M. Kilyanek, and Richard F. Jordan*

Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois, 60637

rfjordan@uchicago.edu

Received August 9, 2007

Abstract:

The reaction of Cp₂Zr(4-F-o-tolyl)(CD₂Cl₂)⁺ (A) with 2-butyne at -85 C in CD₂Cl₂ proceeds by reversible formation of the alkyne complex Cp₂Zr(4-F-o-tolyl)(2-butyne)⁺ (C), followed by rate limiting insertion to produce Cp₂Zr{CMe=CMe(4-F-o-tolyl)}⁺ (D). Analysis of this system by pre-equilibrium kinetics (-85 C) gives K_eq = 1.4(1) M^-1 for 2-butyne coordination to A and k_insert = 6.3(8) × 10^-4 s^-1 and = 13.5(4) kcal/mol for the insertion step. Stabilization of C by an agostic interaction and steric crowding in the transition state contribute to the high insertion barrier.

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