Reactions of ZnR2 Compounds with Dibenzoyl: Characterisation of the Alkyl-Transfer Products and a Striking Product-Inhibition Effect

Izabela Dranka , Marcin Kubisiak , Iwona Justyniak , Michał Lesiuk , Dominik Kubicki , Janusz Lewiński

Abstract

The first systematic theoretical and experimental studies of reaction systems involving ZnR2 (R=Me, Et or tBu) with dibenzoyl (dbz) as a non-innocent ligand revealed that the character of the metal-bonded R group as well as the ratio of the reagents and the reaction temperature significantly modulate the reaction outcome. DFT calculations showed four stable minima for initial complexes formed between ZnR2 and dbz and the most stable structure proved to be the 2:1 adduct; among the 1:1 adducts three structural isomers were found of which the most stable complex had the monodentate coordination mode and the chelate complex with the s-cis conformation of the dbz unit appeared to be the least stable form. Interestingly, the reaction involving ZnMe2 did not lead to any alkylation product, whereas the employment of ZntBu2 resulted in full conversion of dbz to the O-alkylated product [tBuZnPhC(O)C(OtBu)Ph] already at −20 °C. A more complicated system was revealed for the reaction of dbz with ZnEt2. Treatment of a solution of dbz in toluene with one equivalent of ZnEt2 at room temperature afforded a mixture of the O- and C-alkylated products [EtZnPhC(O)C(OEt)Ph] and [EtZnOC(Ph)C(O)(Et)Ph], respectively. The formation of the C-alkylated product was suppressed by decreasing the initial reaction temperature to −20 °C. Moreover, in the case of the dbz/ZnEt2 system monitoring of the dbz conversion over the entire reaction course revealed a product inhibition effect, which highlights possible participation of multiple equilibria of different zinc alkoxide/ZnEt2 aggregates. Diffusion NMR studies indicated that dbz forms an adduct with the O-alkylated product, which is a competent species for executing the inhibition of the alkylation event.
Author Izabela Dranka
Izabela Dranka,,
-
, Marcin Kubisiak ZKChM
Marcin Kubisiak,,
- Department Of Catalysis And Organometallic Chemistry
, Iwona Justyniak
Iwona Justyniak,,
-
, Michał Lesiuk
Michał Lesiuk,,
-
, Dominik Kubicki
Dominik Kubicki,,
-
, Janusz Lewiński ZKChM
Janusz Lewiński,,
- Department Of Catalysis And Organometallic Chemistry
Journal seriesChemistry – A European Journal, ISSN 1521-3765
Issue year2011
Vol17
No45
Pages12713–12721
Keywords in Englishalkoxides, alkylation, ketones, structure–activity relationships, zinc
DOIDOI:10.1002/chem.201101997
URL http://onlinelibrary.wiley.com/doi/10.1002/chem.201101997/abstract
Languageen angielski
File
chej2011_ZnR_dibenzoil.pdf 1.28 MB
Score (nominal)0
Citation count*3 (2015-02-17)
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