A Stable Crystalline N‐Heterocyclic Carbene with a 1,1’‐Ferrocenylene Backbone and BenzylicN‐Substituents

Abstract

AbstractTwo ferrocene‐based NHCs of the type fc[(NR)2C:] (1R; fc=1,1’‐ferrocenylene) containing benzylicN‐substituents were synthesised from the corresponding formamidinium compounds1RH[BF4] by reaction with LiN(SiMe3)2. In the case of R=CH2Ph (Bn), the carbene was characterised through trapping reactions with sulfur and selenium, which afforded fc[(NBn)2CS] (1BnS) and fc[(NBn)2CSe] (1BnSe), respectively. A thermally stable carbene was obtained with R=CH2Mes (Bn*). Its reaction with sulfur and selenium afforded fc[(NBn*)2CS] (1Bn*S) and fc[(NBn*)2CSe] (1Bn*Se), respectively. Its reaction with [Rh(μ‐Cl)(COD)]2(COD=cycloocta‐1,5‐diene), followed by substitution of the COD ligand by CO, furnishedcis‐[RhCl(CO)2(1Bn*)]. In combination with IR data ofcis‐[RhCl(CO)2(1Bn*)], NMR data of1Bn*H[BF4],1Bn*and1Bn*Se indicate that1Bn*is substantially more nucleophilic and more electrophilic than conventional Arduengo carbenes, exhibiting an ambiphilicity similar to that of CAACs. The crystal structures of the formamidinium salts1RHX (X=[BF4], R=Bn, Bn*; X=Cl, R=Bn*), of the carbene1Bn*and its AuIcomplex [AuCl(1Bn*)] as well as of the sulfur and selenium derivatives1RE (E=S, Se; R=Bn, Bn*), the RhIcomplexescis‐[RhCl(CO)2(1R)] (R=Bn, Bn*) and the CuIcomplex [CuBr(1Bn)] were determined by single‐crystal X‐ray diffraction (XRD). In addition, the crystals structures of the diimine fc(N=CHMes)2and the diamine fc(NHBn*)2were also determined by XRD.