The Viability of C5‐Protonated‐ and C4,C5‐Ditopic Carbanionic Abnormal NHCs: A New Dimension in NHC Chemistry

The first C5‐protonated abnormal N‐heterocyclic carbene (aNHC), PhC{N(2,6‐ i Pr 2 C 6 H 3 )} 2 CHC: ( 4 ) is readily accessible by C4‐deprotonation of [ArC{N(2,6‐ i Pr 2 C 6 H 3 )} 2 CHCH]X ( 3 a ‐X) (Ar=Ph, X=Br or I) with a base. The aNHC 4 is stable at 298 K in [D 8 ]THF solution and has been spectroscopically characterized. The facile availability of 4 enables the synthesis of a series of main‐group compounds as well as transition‐metal complexes featuring a new phosphorus‐aNHC hybrid ligand. Double deprotonation of [ArC{N(2,6‐ i Pr 2 C 6 H 3 )} 2 CHCH]X (Ar=Ph, 3 a ‐X (X=Br or I); 4‐Tol, 3 b ‐Br; 4‐DMP, 3 c ‐Br; Tol=MeC 6 H 4 , DMP=Me 2 NC 6 H 4 ) with n BuLi yields the C4,C5‐ditopic carbanionic aNHCs, [ArC{N(2,6‐ i Pr 2 C 6 H 3 )} 2 (C:) 2 ]Li(THF) n (Ar=Ph, 13 a ; 4‐Tol, 13 b ; 4‐DMP, 13 c ), which on treatment with Ph 2 PCl affords cationic vicinal bisphosphine derivatives [ArC{N(2,6‐ i Pr 2 C 6 H 3 )} 2 {C(PPh 2 } 2 ]X (Ar=Ph, 14 a ‐X, X=Br or I; 4‐Tol, 14 b ‐Br; 4‐DMP, 14 c ‐Br).