Arene Complexes of β-Diketiminato Supported Organoscandium Cations: Mechanism of Arene Exchange and Alkyne Insertion in Solvent Separated Ion Pairs
✍ Scribed by Paul G. Hayes; Warren E. Piers; Masood Parvez
- Publisher
- John Wiley and Sons
- Year
- 2007
- Tongue
- English
- Weight
- 229 KB
- Volume
- 13
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
A family of isolable solvent separated organoscandium methyl cations stabilized by β‐diketiminato ligands (Ar)NC(CH~3~)CHC(CH~3~)N(Ar) (Ar=2,6‐__i__Pr‐C~6~H~3~, L^Me^) has been prepared by reaction of L^Me^ScR~2~ with [CPh~3~][B(C~6~F~5~)~4~] in the presence of an arene solvent. Arenes such as bromobenzene, benzene, toluene, para‐xylene and mesitylene bind the scandium center in an η^6^‐bonding mode, yielding cations 1 a–e. Their solution and solid‐state structures have been explored using multinuclear NMR spectroscopy and X‐ray crystallography. Mechanistic studies on arene exchange reactions and the insertion of diphenylacetylene indicate that these processes occur via arene intermediates of lower hapticity, followed by binding of the incoming reagent. Which of the two steps is rate limiting depends on the arene being displaced and/or the nature of the incoming substrate. The experiments present a unified view of these mechanisms, which have relevance to propagation processes in olefin polymerizations mediated by such cations.