title: Metal cation-methyl interactions in CB11Me12(-) salts of Me3Ge+, Me3Sn+, and Me3Pb+.
abstract: Oxidation of Me(6)M(2) (M = Ge, Sn) and Me(4)Pb with the CB(11)Me(12)(*) radical in alkane solvents produced the insoluble salts Me(3)M(+)CB(11)Me(12)(-), characterized by CP-MAS NMR and EXAFS. The cations interact with methyl groups of CB(11)Me(12)(-) with coordination strength increasing from Pb to Ge. Density functional theory (DFT) calculations for the isolated ion pairs, Me(3)M(+)CB(11)Me(12)(-) (M = Ge, Sn), revealed three isomers with the cation above methyl 2, 7, or 12, and not above a BB edge or a BBB triangle. The interaction has a considerable covalent component, with the cation attempting to perform a backside S(E)2 substitution on the methyl carbon. In a fourth less favorable isomer the cation is near methyl 1, inclined toward methyl 2, and interacts with hydrogens. DFT atomic charge distributions and plots of the electrostatic potential on the surface of spheres centered at the CB(11)H(12)(-) and CB(11)Me(12)(-) icosahedra display the effects of uneven charge distribution within the anion and contradict the common belief that the negative charge of the cage anion is concentrated primarily on the cage boron atoms 7-12; in CB(11)Me(12)(-), roughly half is on the cage carbon and the rest on methyls 7-12.
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA.
authors.forename: Ilya
authors.initials: I
authors.lastname: Zharov
authors.forename: Tsu-Chien
authors.initials: TC
authors.lastname: Weng
authors.forename: Anita M
authors.initials: AM
authors.lastname: Orendt
authors.forename: Dewey H
authors.initials: DH
authors.lastname: Barich
authors.forename: James
authors.initials: J
authors.lastname: Penner-Hahn
authors.forename: David M
authors.initials: DM
authors.lastname: Grant
authors.forename: Zdenek
authors.initials: Z
authors.lastname: Havlas
authors.forename: Josef
authors.initials: J
authors.lastname: Michl
mesh_terms: D001896:Boron Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D005583:Fourier Analysis; D005857:Germanium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D013057:Spectrum Analysis / Q000379:methods; D055672:Static Electricity; D013756:Tetraethyl Lead / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry*; D014298:Trimethyltin Compounds / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D001896:Boron Compounds; D002412:Cations; D014298:Trimethyltin Compounds; D005857:Germanium; C119788:dodecaborate; D013756:Tetraethyl Lead; C039474:trimethyllead