Aromaticity in Silole Dianions: Structural, Energetic, and Magnetic Aspects

Structural, energetic, and magnetic criteria confirm that the silole dianion (CH) 4 Si 2- ( 7 ) and its alkali-metal ion pairs, e.g. (CH) 4 SiLi - ( 7a ), (CH) 4 SiLi 2 ( 7b ), (CH) 4 SiNa 2 ( 13 ), and (CH) 4 SiK 2 ( 14 ), are highly aromatic. Inverse sandwich structures and strongly delocalized silole rings are prefered by 7b, 13, and 14 . The degree of aromaticity in [η 5 -(CH) 4 Si]Li - ( 7a ) exceeds that of the isoelectronic third-period heterocycles (CH) 4 PLi ( 5a ) and (CH) 4 SLi + ( 6a ) and even approaches that of (CH) 5 Li ( 3a ).