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

Abstract

Abstract The reactivity of Zn II dialkyl species ZnMe 2 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 Zn II Lewis acidic organocations. CAAC adduct of ZnMe 2 ( 2 ), formed from a 1:1 mixture of 1 and ZnMe 2 , is unstable at room temperature and readily undergoes a CAAC carbene insertion into the Zn−Me bond to produce the ZnX 2 ‐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)ZnC 6 F 5 + ( 7 + ), both isolated as B(C 6 F 5 ) 4 − salts, showing the ability of CAAC for the stabilization of reactive [ZnMe] + and [ZnC 6 F 5 ] + moieties. Due to the lability of the CAAC−ZnMe 2 bond, the formation of bis(CAAC) adduct (CAAC) 2 ZnMe + cation ( 6 + ) was also observed and the corresponding salt [ 6 ][B(C 6 F 5 ) 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 CO 2 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 Zn II organocations.