| Abstract |
The reactivity of Zn-II dialkyl species ZnMe2 with a cyclic(alkyl)(amino)carbene, 1-[2,6-bis(1-methylethyl)phenyl]-3,3,5,5-tetramethyl-2-pyrrolidinylide ne (CAAC, 1), was studied and extended to the preparation of robust CAAC-supported Zn-II 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)(2)ZnMe+ 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 Zn-II organocations. |
