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.

[1‐Me‐1‐closo‐SnB11H11]− as a potential weakly coordinating anion: Synthesis of Rh(PPh3)2(1‐Me‐closo‐SnB11H11) and comparisons with Rh(PR3)2 (1‐H‐closo‐CB11 H11)

“…For [1-H-closo-CB 11 H 11 ] − , the relative electronegativity of carbon and boron means that upper belt vertices, BH(2-6), would be expected to be relatively positively charged, while the lower hemisphere of the cage would be relatively negatively charged. Previous calculations at the DFT level have confirmed this [4,25] [4,25] (Fig. 2).…”

“…"Weakly coordinating" carborane monoanions based upon derivatives of [closo-CB 11 H 12 ] − I find application in catalysis mediated by transition metal cations [1], the isolation of superacids [2], and the generation of coordinatively unsaturated complexes [3] that can have interesting structural features such as [M]· · ·H 3 C intermolecular interactions [4,5]. Given this, these anions are not as widely used as the fluorinated aryl borates, such as [B(C 6 [6], even though they exhibit attractive properties such as being more chemically robust [2].…”

Cationic Brønsted Acids for the Preparation of SnIV Salts: Synthesis and Characterisation of [Ph3Sn(OEt2)][H2N{B(C6F5)3}2],[Sn(NMe2)3(HNMe2)2][B(C6F5)4] and [Me3Sn(HNMe2)2][B(C6F5)4]

“…[a] Wolfson Materials and Catalysis Centre, School of Chemical Sciences and Pharmacy, University of East Anglia, University Plain, Norwich NR4 7TJ, UKcharacterised in the solid state, [20][21][22][23][24][25] stannylium cations stabilised by donor heteroatoms appear to be more readily accessible. [2] For instance, cationic tin species stabilised by a Y,C,Y-chelating pincer-type ligand (where Y is an heteroatom such as oxygen or nitrogen) have been prepared very successfully in the past 15 years.…”

Preparation of undecamethylated and hexamethylated 1‐halocarba‐closo‐dodecaborate anions

“…It is known from calculations of atomic charges in the parent (protiated) and in methylated CB 11 cluster anions [12] and neutral C 2 B 10 clusters [31] that the methyl group withdraws more electron density from the vertex atom than a hydrogen atom does. Relative to the hydrogen standard, methyl on boron or carbon is thus calculated to be an electronwithdrawing substituent, and this agrees with the order of Pauling electronegativites (2.1 for hydrogen and 2.5 for carbon).…”

“…Several such salts of main-group [11,12] and transition [13] metals have been prepared and investigated. The metal cation acts as a strong Lewis acid and interacts with one or more of the methyl groups of the anion.…”