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’= t Bu) by reaction with ketones MeC(O)R’ in the presence of NaCN/HOAc or to the diimine fc(N=CPh 2 ) 2 ( 3 ) by condensation with Ph 2 CO. Treatment of 2 a – c or 3 with MeLi furnished fc(NHR) 2 ( 4 a : R= t Bu, 4 b : R=CMe 2 Ph, 4 c : R=CMe 2 t Bu, 4 d : R=CMePh 2 ) after aqueous work‐up. The formylative cyclisation of 4 a – d to fc[(NR) 2 CH][BF 4 ] ( 5 H[BF 4 ]) was possible only for R=CMe 3 ( a ) and CMe 2 Ph ( b ). The reaction of these formamidinium compounds with NaN(SiMe 3 ) 2 afforded the N‐heterocyclic carbenes fc{[N(CMe 3 )] 2 C:} ( 5 a ) and fc{[N(CMe 2 Ph)] 2 C:} ( 5 b ). 5 a was converted to the thiourea derivative 5 a S 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=CMe 3 , 6 b : R=CMe 2 Ph). 6 a was transformed to fc{[N(CMe 3 )][N(CPh 3 )]CH}[BF 4 ] ( 5e H[BF 4 ]) with Ph 3 C[BF 4 ].