Tuning Coordination in s‐Block Carbazol‐9‐yl Complexes

1,3,6,8‐Tetra‐ tert ‐butylcarbazol‐9‐yl and 1,8‐diaryl‐3,6‐di( tert ‐butyl)carbazol‐9‐yl ligands have been utilized in the synthesis of potassium and magnesium complexes. The potassium complexes (1,3,6,8‐ t Bu 4 carb)K(THF) 4 ( 1 ; carb=C 12 H 4 N), [(1,8‐Xyl 2 ‐3,6‐ t Bu 2 carb)K(THF)] 2 ( 2 ; Xyl=3,5‐Me 2 C 6 H 3 ) and (1,8‐Mes 2 ‐3,6‐ t Bu 2 carb)K(THF) 2 ( 3 ; Mes=2,4,6‐Me 3 C 6 H 2 ) were reacted with MgI 2 to give the Hauser bases 1,3,6,8‐ t Bu 4 carbMgI(THF) 2 ( 4 ) and 1,8‐Ar 2 ‐3,6‐ t Bu 2 carbMgI(THF) (Ar=Xyl 5 , Ar=Mes 6 ). Structural investigations of the potassium and magnesium derivatives highlight significant differences in the coordination motifs, which depend on the nature of the 1‐ and 8‐substituents: 1,8‐di( tert ‐butyl)‐substituted ligands gave π‐type compounds ( 1 and 4 ), in which the carbazolyl ligand acts as a multi‐hapto donor, with the metal cations positioned below the coordination plane in a half‐sandwich conformation, whereas the use of 1,8‐diaryl substituted ligands gave σ‐type complexes ( 2 and 6 ). Space‐filling diagrams and percent buried volume calculations indicated that aryl‐substituted carbazolyl ligands offer a steric cleft better suited to stabilization of low‐coordinate magnesium complexes.