The sterically crowded aluminum diphenolate (2,6-Mes 2 C 6 H 3 O) 2 AlEt (2; Mes =2,4,6-Me 3 C 6 H 2 −) was converted into the ionic species [(2,6-Mes 2 C 6 H 3 O) 2 Al] + [CHB 11 Cl 11 ] − (6) by ethide abstraction with the silylium salt [Et 3 Si][CHB 11 Cl 11 ] or by a combination of β-hydride abstraction and concomitant ethylene elimination with the trityl salt [Ph 3 C][CHB 11 Cl 11 ]. Compound 6 consists of solvent-separated ions, and the cation features very short Al•••C contacts involving the flanking mesityl groups, leading to an overall distorted-tetrahedral coordination geometry around the aluminum center. Analogous reactions with the diphenolate (2,6-tBu 2 -4-MeC 6 H 2 O) 2 AlEt ( 1) led to tert-butyl transfer to the benzene solvent to afford tert-butylbenzene as the main product. A 1:1 mixture of the triphenolate (2,6-Ph 2 C 6 H 3 O) 3 Al and tri-tert-butylphosphine forms a frustrated Lewis pair, which reacts with CO 2 at room temperature to give the compound (2,6-Ph 2 C 6 H 3 O) 3 AlOC(O)Pt-Bu 3 (8). The high Lewis acidity of 6 catalyzes the scrambling of the subsituents of Et 3 SiH at room temperature to give Et 4 Si, Et 2 SiH 2 , and EtSiH 3 and also the reduction of CO 2 to d 5 -toluene (C 6 D 5 CH 3 ) and CH 4 at 82 °C in d 6 -benzene solution.

Fully chlorinated carborate and dodecaborate cages such as [CHBCl] and [MeNBCl] are prominent examples of valuable and chemically rather inert weakly coordinating anions. While both anions can be obtained by chlorination of the precursors [CHB] and [HNBH] with SOCl followed by methylation for the synthesis of [MeNBCl], best results were found using photochemical chlorination with SOCl for [CHB] and thermal chlorination with SOCl for [HNBH]. The hexachlorinated anion [n-PrNBHCl] was formed readily within 30 min by chlorination of [n-PrNBH], but attempts to synthesize isopropyl-substituted ammonio-dodecaborates with a higher chlorination number resulted in the formation of mixtures and partial decomposition. The silver and trityl salts of the anions [CHBCl], [MeNBCl], and [n-PrNBHCl] as well as the contact ion-pair [EtAl][MeNBCl] were also prepared, and the compounds [Ag(NCMe)][MeNBCl], [EtAl][MeNBCl], and [EtN][i-PrNBHCl] were also characterized by X-ray crystallography.

Ethide abstraction from Et3M (M = Al and Ga), (2,6-Ph2C6H3)­AlEt2, 1, and (2,6-Dipp2C6H3)­GaEt2, 2 (Dipp = 2,6-iPr2C6H3), using the silylium ion [Et3Si]­[CHB11Cl11] afforded crystalline ion-like compounds [Et2M]­[CHB11Cl11] (M = Al, 3; Ga, 5) and [(2,6-Ph2C6H3)­AlEt]­[CHB11Cl11], 4, and the likely solvent-separated ion pair [(2,6-Dipp2C6H3)­GaEt]­[CHB11Cl11], 6. Crystalline compounds 3–5 feature cation···anion contacts in the solid state, and their solubility in low polarity benzene indicates that these contacts are maintained in solution. All compounds catalyze the reduction of CO2 with Et3SiH, but the activity of the gallium compound 5 is significantly lower due to its polymeric structure and the lower Lewis acidity of gallium. Whereas the reduction products from the reactions catalyzed by compounds 3–5 are mostly methane and toluene (from Friedel–Crafts alkylation of the benzene solvent), catalysis by 6 led mostly to Et3SiOCH3.

No abstract

This study attempts to use [3H]a-endosulfan to examine directly the binding site(s) for cyclodienes, lindane and toxaphene (collectively referred to as the polychlorocycloalkane or PCCA insecticides) in the 4-aminobutyric acid (GABA)-gated chloride channel. C3H] a-Endosulfan was prepared by reduction of hexachloronorbornenedicarboxylic anhydride with sodium borotritide, then coupling the labelled alcohol with thionyl chloride followed by HPLC purification (35 Ci mmol-', > 99% radiochemical purity). This new candidate radioligand readily partitions into lipid membranes and undergoes indiscriminate adsorption to surfaces resulting in high levels of non-specific binding. This makes it very difficult to differentiate the small portion of specific binding at the site relevant to toxic action. This problem was partially circumvented by incubating C3H] aendosulfan (0.1 nM) with house-fly head membranes (0.2 mg protein) for 70 min at 22°C giving 23 (*4)% specific binding (40 fmol mg-' protein) determined as the difference between the radioligand alone and on preincubation for 15 min with unlabelled a-endosulfan (final concentration 100 nM). This procedure is not appropriate for determination of saturation isotherms and standard binding kinetics. However, the effectiveness of 16 PCCAs (also at 100 nM final concentration) in blocking the specific binding of C3H] a-endosulfan is generally consistent with their relative potencies as inhibitors of 4-[3H]propyl-l-(4-ethynylphenyl)-2,6,7trioxabicyclo[2.2.2] octane (C3H]EB0B) binding suggesting that the binding site for both [3H]a-endosulfan and the PCCAs is part of the GABA-gated chloride channel. Insecticidal channel blockers of other types (e.g. picrotoxinin, trioxabicyclooctanes, a dithiane, and phenylpyrazoles) and GABA are poor inhibitors of C3H] a-endosulfan binding relative to their potencies as inhibitors of C3H]EBOB binding. It therefore appears that the PCCAs compete directly for the C3H]aendosulfan site, whereas the other channel blockers bind with different inhibition kinetics or at a site more closely coupled to the EBOB than the a-endosulfan binding domain.