Responsive Iron Neighboring Group Participation in Amino-Substituent-Stabilized [3]Ferrocenophane α-Carbenium Ions: A Combined Theoretical and Experimental Study

Treatment of the dimethylamino-[3]ferrocenophane 1a with B(C 6 F 5 ) 3 results in hydride abstraction at the −CH(NMe 2 ) moiety in α-position to the ferrocene nucleus to yield the corresponding cation 4a . The X-ray crystal structure analysis of the salt 4a ·[HO{B(C 6 F 5 ) 3 } 2 - ] has revealed a residual Fe−C α interaction even in this case of a strongly substituent-stabilized α-ferrocenyl carbenium ion. A DFT calculation of a series of derivatives containing nitrogen substituents of a decreasing ability for carbenium ion stabilization ( 4a, −NMe 2; 4b, −pyrrolyl; 4c, −triazolyl) revealed a markedly increased Fe−C interaction with decreasing C + stabilization by the hetarene substituents.