The anion derived from B(C 6 F 5 ) 3 has been detected by EPR, and the boron and fluorine hyperfine splitting constants have been determined. Treatment of B(C 6 F 5 ) 3 with the reductant Cp* 2 Co in THF at -50 °C rapidly results in a dark blue (λ max ) 603 nm) paramagnetic solution containing the anion radical. The halflife for disappearance of λ max , about 10 min at room temperature, is consistent with that of the EPR signal.

The reaction of trimethylaluminum with the hexameric tert-butylalumoxane, [( t Bu)Al-(µ 3 -O)] 6 , has been investigated. Reaction of [( t Bu)Al(µ 3 -O)] 6 with 1 equiv of AlMe 3 results in the formation of two isomers (A and B) of the hybrid tert-butylmethylalumoxane, [Al 7 (µ 3 -O) 6 -( t Bu) 6 Me 3 ]. The structures of compounds A and B, as determined by NMR spectroscopy and mass spectrometry, consist of [Al 6 (µ 3 -O) 6 ( t Bu) 5 Me] alumoxane cages, formed via tert-butyl/ methyl exchange, in which one of the edges of the Al 6 O 6 cage is complexed to the ( t Bu)-AlMe 2 formed during alkyl exchange. The difference between the isomers results from the geometric relationship of the cage Al-Me group and the opened edge. The activity of [Al 7 -(µ 3 -O) 6 ( t Bu) 6 Me 3 ], for the [Me 2 C(Cp)(Flu)]ZrBz 2 -catalyzed polymerization of 1,5-hexadiene, is significantly increased in comparison to [( t Bu)Al(µ 3 -O)] 6 . The effect of additional equivalents of AlMe 3 on the cocatalytic activity of [Al 7 (µ 3 -O) 6 ( t Bu) 6 Me 3 ] suggests that a maximum activity is obtained at a [( t Bu)Al(µ 3 -O)] 6 to AlMe 3 ratio of 1:6. Under conditions of equal Al:Zr ratio the [( t Bu)Al(µ 3 -O)] 6 (AlMe 3 ) 6 system has a higher activity than a representative sample of commercial methylalumoxane (MAO). 1 H NMR suggests that the reaction of [( t Bu)Al-(µ 3 -O)] 6 with 6 equiv of AlMe 3 yields ( t Bu)AlMe 2 as the only tert-butyl-containing species and a proposed AlMe 3 "free" form of MAO. Whereas the activity of [Al 7 (µ 3 -O) 6 ( t Bu) 6 Me 3 ] and MAO shows slight inhibition by the addition of Al( i Bu) 3 , the activity of the [( t Bu)Al(µ 3 -O)] 6 / (AlMe 3 ) 6 system is unaffected. The reaction of Cp 2 Zr(CD 3 ) 2 with [Al 7 (µ 3 -O) 6 ( t Bu) 6 Me 3 ] demonstrates that methyl exchange does not occur between a metallocene and the alkyls of the alumoxane cage, but does occur with the complexed ( t Bu)AlMe 2 .

The reaction of AlCl 3 with 3 equiv of the tert-amyl Grignard reagent (Me 2 EtC)MgCl yields the monomeric trialkyl compound Al(CMe 2 Et) 3 (1). Reaction of compound 1 with MeCN and [PPN]Cl yields the Lewis acid-base complexes Al(CMe 2 Et) 3 (MeCN) (2) and [PPN][AlCl-(CMe 2 Et) 3 ] (3), respectively. The hydrolysis of Al(CMe 2 Et) 3 in hexane results in the formation of the trimeric hydroxide [(Me 2 EtC) 2 Al(µ-OH)] 3 (4), which is converted to the dimer [(Me 2 EtC) 2 Al(µ-OH)] 2 (5) upon heating. The reaction of Al(CMe 2 Et) 3 with H 2 S at room temperature yields the cubane compound [(Me 2 EtC)Al(µ 3 -S)] 4 (6). If the reaction is carried out at 0 °C, then the hexamer [(Me 2 EtC)Al(µ 3 -S)] 6 (7) may be isolated along with compound 6. The selenide analog of 6, [(Me 2 EtC)Al(µ 3 -Se)] 4 (8), is prepared directly from the reaction of compound 1 with H 2 Se, while the telluride analog, [(Me 2 EtC)Al(µ 3 -Te)] 4 (9), is prepared by the direct reaction of compound 1 with tellurium metal. The gallium cubane compounds [(Me 2 EtC)Ga(µ 3 -E)] 4 , (E ) S (10), Se (11), Te ( 12)) have been prepared from the reaction of Ga(CMe 2 Et) 3 with the appropriate element. The tert-amyl compounds are compared to their tert-butyl analogs, and the isolation of compound 7 is used as a precedent to prepare [( t Bu)Al(µ 3 -S)] 6 (13). A structural analysis is made of the M 4 E 4 cubane cores (M ) Al, Ga, In; E ) S, Se, Te), and a new topological method is proposed to predict the intracage bond angles in group 13 cage compounds, [(R)M(µ 3 -X)] n . The molecular structures of compounds 3, 6, 8, and 10-12 have been determined by X-ray crystallography, and a discussion of the crystallographic problems associated with the tert-amyl group is presented.

The reaction of Al(tBu)3 with carboxylic acids, RCO2H, yields the dimeric di-tert-butylaluminum carboxylates [(tBu)2Al(μ-O2CR)]2, where R = tBu (1), CCl3 (2), Ph (3), CH2Ph (4), CHPh2 (5), CPh3 (6), C(H)=C(H)Ph (7), CH2OCH3 (8), CH2OCH2CH2OCH3 (9), and CH2(OCH2CH2)2OCH3 (10), which have been characterized by 1H and 13C NMR and IR spectroscopy and mass spectrometry. The molecular structures of compounds 1, 3, 4, and 9 have been determined by X-ray crystallography, the first structural determinations for any such compounds. The carboxylate groups act as bidentate bridging ligands consistent with spectroscopic characterization. Ab initio calculations on the model compounds H2Al(λ2-O2CH), eclipsed-H2Al[OC(O)H], staggered-H2Al[OC(O)H], [H2Al(μ-O2CH)]2, and [H3Al{OC(O)H}]- indicate that the observed carboxylate-bridged dimer is thermodynamically favored over the hypothetical chelating monomer. The Al2O4C2 cyclic core in compound 1 is flat while those in compounds 3, 4, and 9 adopts chairlike conformations. The extent of the puckering of the core in [(tBu)2Al(μ-O2CR)]2 is dependent on the steric bulk of the carboxylate substituent, R. The dimeric compounds, [(tBu)2Al(μ-O2CR)]2, are satisfactory as simplistic structural models for the carboxylate groups bound to the boehmite-like core of carboxylate alumoxanes, [Al(O) x (OH) y (O2CR) z ] n , as prepared from the reaction of boehmite with a carboxylic acid. Ab initio calculations on the model anion [(H5Al)2(μ-O2CH)]5- indicate that the optimum Al···Al distance for the carboxylate ligand bridging two six-coordinate aluminum centers constrained on a surface is 3.2−3.8 Å. The carboxylate ligand is therefore near perfectly suited to bind to the (100) surface of boehmite, Al···Al = 3.70 Å, and hence stabilize the boehmite-like core in carboxylate alumoxanes.