Conjugated Bis‐Guanidines (CBGs) as β ‐Diketimine Analogues: Synthesis, Characterization of CBGs/Their Lithium Salts and CBG Li Catalyzed Addition of B−H and TMSCN to Carbonyls

Herein, we report a range of conjugated bis‐guanidines (CBGs) L [L={(ArHN)(ArHN)C=N−C=(NAr)(NHAr)}; Ar=2, 6‐Me 2 ‐ C 6 H 3 , ( 1 ), 2, 4, 6‐Me 3 −C 6 H 2 , ( 2 ), 2, 6‐Et 2 −C 6 H 3 , ( 3 ), 2, 6‐ i Pr 2 −C 6 H 3 , ( 4 )]. These compounds can be easily accessed by the reaction between N,N′ ‐diaryl carbodiimide, and aq. ammonia in acetonitrile. Deprotonation of 1 with n ‐BuLi in a 1 : 1 ratio in THF resulted in the formation of four coordinate lithium complex, [ 1 Li ⋅ (THF) 2 ] ( 5 ), while at the same reaction conditions, ligands 3 and 4 gave three coordinate lithium complexes, [ 3 Li⋅THF] ( 6 ) and [ 4Li ⋅THF] ( 7 ), respectively. However, both compounds 1 and 4 upon deprotonation with n ‐BuLi in diethyl ether allowed [ 1 Li⋅Et 2 O] ( 8 ) and [ 4 Li⋅Et 2 O] ( 9 ), respectively, while compounds 1 and 3 in toluene afforded un‐solvated lithium complexes [ 1 Li] ( 10 ) and [ 3 Li] ( 11 ), respectively. Significantly, a reaction between compound 4 and n ‐BuLi in a 1 : 1 ratio in toluene yielded sandwich lithium complex [ 4 Li] ( 12 ). All new CBGs 1 – 4 and lithium salts of CBG, 5 , 8 , and 12 were characterized by single‐crystal X‐ray structural analysis. The compounds 5 – 12 were characterized by multinuclear magnetic resonance spectroscopy. Moreover, we have investigated the catalytic application of lithium salts of CBGs for the addition of B−H and TMSCN to carbonyls.