title: Tuning coordination in s-block carbazol-9-yl complexes.
abstract: 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-tBu4carb)K(THF)4 (1; carb = C12H4N), [(1,8-Xyl2-3,6-tBu2carb)K(THF)]2 (2; Xyl = 3,5-Me2C6H3) and (1,8-Mes2-3,6-tBu2carb)K(THF)2 (3; Mes = 2,4,6-Me3C6H2) were reacted with MgI2 to give the Hauser bases 1,3,6,8-tBu4carbMgI(THF)2 (4) and 1,8-Ar2-3,6-tBu2carbMgI(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.
authors.affiliation: School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD (UK), Fax: (+44) 115-9513555; School of Chemistry, University of Manchester, Manchester M13 9PL (UK).
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Ortu
authors.forename: Graeme J
authors.initials: GJ
authors.lastname: Moxey
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Blake
authors.forename: William
authors.initials: W
authors.lastname: Lewis
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Kays
keywords: N ligands; alkaline earth metals; ligand effects; magnesium; potassium