title: Calix[4]arenes of aluminum and gallium with benzimidazolyl ligands: steric control of the conformation via substitution on the ligand.
abstract: Complexes [bzimAlR(2)](4) [bzim = benzimidazolate; R = Et (2), (i)Bu (3)], [mbzimAlR(2)](4) [mbzim = 2-methylbenzimidazolate; R = Et (6), (i)Bu (7)], [dmbzimAlR(2)](4) [dmbzim = 5,6-dimethylbenzimidazolate; R = Me (9), Et (10), (i)Bu (11)], and [tmbzimAlR(2)](4) [tmbzim = 2,5,6-trimethylbenzimidazolate; R = Me (12), Et (13), (i)Bu (14)] have been prepared via alkane elimination and coordinative self-assembly upon the reaction of benzimidazole ligands with aluminum alkyls in benzene, toluene, or xylene. Characterization of the complexes was achieved by spectroscopic methods, microanalysis, and X-ray crystallography of 2, 7, 10, 11, 13, and 14. The complexes reported herein and the aluminum and gallium analogues 1, 4, 5, and 8 reported in a previous paper (1)  are predominantly tetranuclear aggregates related to calix[4]arenes in which the benzimidazolyl ligands bind two metal atoms in a η(1):η(1) fashion. X-ray crystallography demonstrates that modulation of the conformation adopted by these metallacalix[4]arenes is achieved by proper substitution on the C atom at the 2 position of the benzimidazolyl ligand. An H substituent for 1, 2, 4, 10, and 11 favors a chair conformation with a small cavity and approximate C(2h) symmetry, while a CH(3) substituent for 5, 7, 8, 13, and 14 introduces enough repulsion to switch the conformation to a 1,3-alternate or double cone with a concomitant larger cavity and approximate C(2v) symmetry.
authors.affiliation: Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Avenida Universidad 1001, Colonia Chamilpa, Cuernavaca, Morelos 62209, Mexico.
authors.forename: Ernesto
authors.initials: E
authors.lastname: Rufino-Felipe
authors.forename: Miguel-Ángel
authors.initials: MÁ
authors.lastname: Muñoz-Hernández
authors.forename: Hugo F
authors.initials: HF
authors.lastname: Saucedo-Azpeitia
authors.forename: Sara A
authors.initials: SA
authors.lastname: Cortes-Llamas
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D001562:Benzimidazoles / Q000737:chemistry*; D047250:Calixarenes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005708:Gallium / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*
chemical_list: D001562:Benzimidazoles; D008024:Ligands; D009942:Organometallic Compounds; D010636:Phenols; C121325:calix(4)arene; D047250:Calixarenes; D005708:Gallium; D000535:Aluminum