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‐iPr2C6H3)}2CHC: (4) is readily accessible by C4‐deprotonation of [ArC{N(2,6‐iPr2C6H3)}2CHCH]X (3 a‐X) (Ar=Ph, X=Br or I) with a base. The aNHC 4 is stable at 298 K in [D8]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‐iPr2C6H3)}2CHCH]X (Ar=Ph, 3 a‐X (X=Br or I); 4‐Tol, 3 b‐Br; 4‐DMP, 3 c‐Br; Tol=MeC6H4, DMP=Me2NC6H4) with nBuLi yields the C4,C5‐ditopic carbanionic aNHCs, [ArC{N(2,6‐iPr2C6H3)}2(C:)2]Li(THF)n (Ar=Ph, 13 a; 4‐Tol, 13 b; 4‐DMP, 13 c), which on treatment with Ph2PCl affords cationic vicinal bisphosphine derivatives [ArC{N(2,6‐iPr2C6H3)}2{C(PPh2}2]X (Ar=Ph, 14 a‐X, X=Br or I; 4‐Tol, 14 b‐Br; 4‐DMP, 14 c‐Br). Happy with “H”: Deprotonation of the C2‐arylated 1,3‐imidazolium salt 3‐X affords the C5‐protonated aNHC, (aIPrPh) 4. Double deprotonation of 3‐X yields C4,C5‐ditopic carbanionic aNHC, 13. The facile accessibility of 4 and 13 not only enables easy access to challenging aNHC compounds and phosphorus ligands but also provides a unique platform for the design of new hybrid ligands and heterobimetallic complexes.