A Stable Crystalline N-Heterocyclic Carbene with a 1,1 '-Ferrocenylene Backbone and Benzylic N-Substituents

Two ferrocene-based NHCs of the type fc[(NR)(2)C:] (1(R); fc-1,1'-ferrocenylene) containing benzylic N-substituents were synthesised from the corresponding formamidinium compounds 1(R)H-[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)(2)CS] (1(Bn)S) and fc[(NBn)(2)CSe] (1(Bn)Se), respectively. A thermally stable carbene was obtained with R=CH(2)Mes (Bn*). Its reaction with sulfur and selenium afforded fc[(NBn*)(2)CS] (1(Bn)*S) and fc[(NBn*)(2)CSe] (1(Bn)*Se), respectively. Its reaction with [Rh(mu-Cl)(COD)](2) (COD = cycloocta-1,5-diene), followed by substitution of the COD ligand by CO, furnished cis-[RhCl(CO)(2)(1(Bn))]. In combination with IR data of cis-[RhCl(CO)(2)(1(Bn)*)], NMR data of 1(Bn)*H[BF4], 1(Bn)* and 1(Bn)*Se indicate that 1(Bn)* 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 salts 1(R)HX (X= [BF4], R-Bn, Bn*; X= Cl, R=Bn*), of the carbene 1(Bn)* and its Au' complex [AuCl(1(Bn)*)] as well as of the sulfur and selenium derivatives 1(R)E (E=S, Se; R=Bn, Bn*), the Rh' complexes cis-[RhCl(CO)(2)(1(R)] (R = Bn, Bn*) and the Cu' complex [CuBr(1(Bn))] were determined by single-crystal X-ray diffraction (XRD). In addition, the crystals structures of the diimine fc(N=CHMes)(2) and the diamine fc(NHBn*)(2) were also determined by XRD.