Cyclic(Alkyl)(Amino)Carbene (CAAC)‐Supported Zn Alkyls: Synthesis, Structure and Reactivity in Hydrosilylation Catalysis - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Chemistry - A European Journal Année : 2019

Cyclic(Alkyl)(Amino)Carbene (CAAC)‐Supported Zn Alkyls: Synthesis, Structure and Reactivity in Hydrosilylation Catalysis

Résumé

The reactivity of ZnII dialkyl species ZnMe2 with a cyclic(alkyl)(amino)carbene, 1-[2,6-bis(1-methylethyl)phenyl]-3,3,5,5-tetramethyl-2-pyrrolidinylidene (CAAC, 1), was studied and extended to the preparation of robust CAAC-supported ZnII Lewis acidic organocations. CAAC adduct of ZnMe2 (2), formed from a 1:1 mixture of 1 and ZnMe2, is unstable at room temperature and readily undergoes a CAAC carbene insertion into the Zn−Me bond to produce the ZnX2-type species (CAAC-Me)ZnMe (3), a reactivity further supported by DFT calculations. Despite its limited stability, adduct 2 was cleanly ionized to robust two-coordinate (CAAC)ZnMe+ cation (5+) and derived into (CAAC)ZnC6F5+ (7+), both isolated as B(C6F5)4− salts, showing the ability of CAAC for the stabilization of reactive [ZnMe]+ and [ZnC6F5]+ moieties. Due to the lability of the CAAC−ZnMe2 bond, the formation of bis(CAAC) adduct (CAAC)2ZnMe+ cation (6+) was also observed and the corresponding salt [6][B(C6F5)4] was structurally characterized. As estimated from experimental and calculations data, cations 5+ and 7+ are highly Lewis acidic species and the stronger Lewis acid 7+ effectively mediates alkene, alkyne and CO2 hydrosilylation catalysis. All supporting data hints at Lewis acid type activation–functionalization processes. Despite a lower energy LUMO in 5+ and 7+, their observed reactivity is comparable to those of N-heterocyclic carbene (NHC) analogues, in line with charge-controlled reactions for carbene-stabilized ZnII organocations.
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hal-02324087 , version 1 (04-02-2022)

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Jean‐charles Bruyere, David Specklin, Christophe Gourlaouen, Rosita Lapenta, Luis Veiros, et al.. Cyclic(Alkyl)(Amino)Carbene (CAAC)‐Supported Zn Alkyls: Synthesis, Structure and Reactivity in Hydrosilylation Catalysis. Chemistry - A European Journal, 2019, 25 (34), pp.8061-8069. ⟨10.1002/chem.201900961⟩. ⟨hal-02324087⟩
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