N-tert-Alkyl-Substituted N-Heterocyclic Carbenes with a 1,1’-Ferrocenediyl Backbone

1,1’-Diaminoferrocene (1) was converted to α-aminonitriles fc[NHC(CN)MeR’]₂ (fc=1,1’-ferrocenediyl; 2 a: R’=Me, 2 b: R’=Ph, 2 c: R’=tBu) by reaction with ketones MeC(O)R’ in the presence of NaCN/HOAc or to the diimine fc(N=CPh₂)₂ (3) by condensation with Ph₂CO. Treatment of 2 a–c or 3 with MeLi furnished fc(NHR)₂ (4 a: R=tBu, 4 b: R=CMe₂Ph, 4 c: R=CMe₂tBu, 4 d: R=CMePh₂) after aqueous work-up. The formylative cyclisation of 4 a–d to fc[(NR)₂CH][BF₄] (5H[BF₄]) was possible only for R=CMe₃ (a) and CMe₂Ph (b). The reaction of these formamidinium compounds with NaN(SiMe₃)₂ afforded the N-heterocyclic carbenes fc{[N(CMe₃)]₂C:} (5 a) and fc{[N(CMe₂Ph)]₂C:} (5 b). 5 a was converted to the thiourea derivative 5 aS with elemental sulfur. 5 a and 5 b slowly decompose in solution by alkene elimination, affording the respective formamidine fc(NRCH=N) (6 a: R=CMe₃, 6 b: R=CMe₂Ph). 6 a was transformed to fc{[N(CMe₃)][N(CPh₃)]CH}[BF₄] (5eH[BF₄]) with Ph₃C[BF₄].