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The reaction of trimethylaluminum with the hexameric tert-butylalumoxane, [(tBu)Al(μ3-O)]6, has been investigated. Reaction of [(tBu)Al(μ3-O)]6 with 1 equiv of AlMe3 results in the formation of two isomers (A and B) of the hybrid tert-butylmethylalumoxane, [Al7(μ3-O)6(tBu)6Me3]. The structures of compounds A and B, as determined by NMR spectroscopy and mass spectrometry, consist of [Al6(μ3-O)6(tBu)5Me] alumoxane cages, formed via tert-butyl/methyl exchange, in which one of the edges of the Al6O6 cage is complexed to the (tBu)AlMe2 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 [Al7(μ3-O)6(tBu)6Me3], for the [Me2C(Cp)(Flu)]ZrBz2-catalyzed polymerization of 1,5-hexadiene, is significantly increased in comparison to [(tBu)Al(μ3-O)]6. The effect of additional equivalents of AlMe3 on the cocatalytic activity of [Al7(μ3-O)6(tBu)6Me3] suggests that a maximum activity is obtained at a [(tBu)Al(μ3...

Reaction of M(tBu)3 (M = Al, Ga) with neol-H2 (2,2-dimethylpropane-1,3-diol) yields [M2(tBu)4(neol-H)2], M = Al (1) and Ga (2), respectively. Use of an equimolar mixture of Al(tBu)3 and Ga(tBu)3 allows for the formation of [AlGa(tBu)4(neol-H)2] (3). Compounds 1 and 2 may be considered as bifunctional (two OH groups), tetradentate (4O) ligands as highlighted by their reactivity with Group 13 hydrides and alkyls. Reaction of compound 1 with AlH3(NMe3), AlH2Cl(NMe3) and AlMe3 yields the tri-aluminium compounds, [Al3(tBu)4(X)(neol)2] with X = H (4), X = Cl (5), Me (6), respectively. Similarly, compound 2 reacts with Ga(tBu)3 to yield the tri-gallium compound, [Ga3(tBu)5(neol)2] (7). The mixed metal complexes, [Ga2Al(tBu)4(X)(neol)2], where X = H (8), Me (9) and tBu (10), are formed by the reaction of compound 2 with AlH3(NMe3), AlMe3, and Al(tBu)3, respectively. The solid state conformation of the neol backbone and the 1H NMR chemical shift of the neol's CH2 protons, in compounds 4–10, are both dependent on the steric bulk of the substituent of the central metal. Thermolysis of compound 2 in toluene results in the formation of [Ga3(tBu)4(CH2Ph)(neol)2] (11), while the reaction of 2 with LiOH in Et2O and hexane yields [Ga3Li4(tBu)6(neol)3(OH)(THF)] (12) and [Ga2Li(tBu)4(OH)2(neol-H)] (13), respectively. The molecular structures of compounds 1, 2, 4–13 and [Ga3Cl5(OSiMe2OSiMe2O)2] (14) have been determined by X-ray crystallography.

Dialkylaluminium compounds with bi-functional ligands, [E(CH2)xNR2]– (x = 2, 3; E = S, NR′) have been prepared, and compared to those that contain [O(CH2)xNR2]–, in order to investigate the effect of the anionic termini on the structure of the aluminium compounds, [R2Al{E(CH2)xNR′2}]n. The reaction of R2NCH2CH2SH·HCl with Li[Al(tBu)3Me], formed in situ from Al(tBu)3 with MeLi, yields (tBu)2Al(SCH2CH2NR2), R = Me 1 and Et 2. Reaction of Al(tBu)3 with HN(Me)CH2CH2NMe2 and HN(Me)CH2CH2CH2NMe2 ultimately yields (tBu)2Al[N(Me)CH2CH2NMe2] 3 and (tBu)2Al[N(Me)CH2CH2CH2NMe2] 4, respectively. Reaction of HAl(iBu)2 with HN(Me)CH2CH2NMe2 yields [(iBu)2Al{µ-N(Me)CH2CH2NMe2}]2 5, while [H2Al{µ-N(R)CH2CH2NMe2}]2, R = Me 6 and Et 7, are formed from the reaction of AlH3(NMe3) with HN(R)CH2CH2NMe2. The molecular structures of compounds 1, 2, 6 and 7 have been determined by X-ray crystallography. Compounds 1–4 are monomeric with five (1–3) and six (4) membered chelate heterocyclic rings. Compound 5 exists as a monomer/dimer equilibrium in solution, in contrast, compounds 6 and 7 exist as bridged dimers. The formation of monomeric chelate structures for compounds 1 and 2, rather than the bridged dimers found for the alkoxide analogs is due to the relative ligand base strength. However, the formation of monomers in the case of compounds 3 and 4 is found to be due to a combination of the steric bulk of the aluminium alkyl and the geometry at the potentially bridging amide group. These results demonstrate a remote geometric control over the degree of association.

Reaction of Al(tBu)3 with (tBu)3Al[O(H)CH2CH2CH2NMe2] yielded the Lewis acid–base complex [(tBu)2Al{µ-OCH2CH2CH2N(Me)2Al(tBu)3}]2 1. Compound 1 is also formed directly when 2 equivalents of Al(tBu)3 reacts with 1 equivalent of [(tBu)2Al(µ-OCH2CH2CH2NMe2)]2. In contrast, the reaction of 2 equivalents of Al(tBu)3 with 1 equivalent of [Me2Al(µ-OCH2CH2NMe2)]2 yielded Me2Al(µ-OCH2CH2NMe2)Al(tBu)3 2. The molecular structure of compound 2 shows the AlMe2 moiety chelate bound to the anionic bidentate ligand, while the Al(tBu)3 unit is bonded to the anionic terminus of the ligand. The formation of compound 1 is proposed to occur via the tert-butyl analog of compound 2, i.e., (tBu)2Al(µ-OCH2CH2CH2NMe2)Al(tBu)3, which is unstable due to significant tBu· · ·tBu inter-ligand interactions. The implications of the differences in products is discussed with respect to the extent of intra-molecular Al· · ·N coordination in compounds of the general formula [R2Al{µ-O(CH2)nNMe2}]2.

Reaction of [(tBu)2Ga(μ-Cl)]2 with Li(o-C6H4NMe2) yields [ ( t Bu ) 2 Ga (o- C 6 H 4 NMe 2 )] 2 (1). The atmospheric oxidation/hydrolysis of 1 results in the isolation of ( t Bu ) 2 Ga (o- C 6 H 4 Me 2 ] (2). The structure of compound 2 (as determined by X-ray crystallography) consists of a gallium dimer in which one of the ortho-(dimethylamino)phenyl ligands is oxidized and the other exhibits strong intramolecular O3·N hydrogen bonding ( ΔG ‡ = 57.3 kJ mol −1 ) to the hydroxide bridge. A pathway for the formation of 2 is proposed. Reaction of compound 1 with OPPh3 results in the formation of the Lewis acid-base complex [ ( t Bu ) 2 Ga (o- C 6 H 4 NMe 2 )(OPPh3) (3), whose structure has been confirmed by X-ray crystallography.

To develop an understanding of the factors that control the strength of the Lewis acid−base interactions in five-coordinate compounds of aluminum, dimeric dialkylaluminum compounds [R2Al{μ-O(CH2)nER‘x}]2 (n = 2, 3; ER‘x = OR‘, SR‘, NR‘2) have been prepared from AlR3 and the appropriate substituted alcohol, thiol, or amine: [R2Al(μ-OCH2CH2OMe)]2, R = tBu (1), iBu (2), and Et (3); [R2Al(μ-OCH2CH2OnBu)]2, R = tBu (4) and Me (5); [R2Al(μ-OCH2CH2CH2OMe)]2, R = tBu (6) and Me (7); (tBu)2Al(μ-OnBu)(μ-OCH2CH2OMe)Al(tBu)2 (11); [R2Al(μ-OCH2CH2SMe)]2, R = tBu (12), iBu (13), Et (14), and Me (15); [R2Al(μ-OCH2CH2CH2SMe)]2, R = tBu (16) and Me (17); [R2Al(μ-OCH2CH2NMe2)]2, R = tBu (18), iBu (19), Et (20), and H (21); [(tBu)2Al(μ-OCH2CH2NH2)]2 (22); [(tBu)2Al(μ-OCH2CH2CH2NH2)]2 (23). The molecular structures of compounds 1, 2, 6, 7, 12, 13, 16, 18−22, and [Me2Al(μ-OCH2CH2NMe2)]2 have been determined by X-ray crystallography. The solution structures have been probed by 13C NMR spectroscopy using the alkoxide derivativ...

Reaction of Al(Bu t ) 3 with between 1 and 2 equivalents of HOCH 2 CH 2 CH 2 NMe 2 allows for the isolation of the Lewis acid–base complex, (Bu t ) 3 Al[O(H)CH 2 CH 2 CH 2 NMe 2 ] 1, which undergoes alkane elimination above 45 °C to yield [(Bu t ) 2 Al(µ-OCH 2 CH 2 CH 2 NMe 2 )] 2 2. Compound 2 is also formed directly when 2 equivalents of Al(Bu t ) 3 react with 1 equivalent of HOCH 2 CH 2 CH 2 NMe 2 . The molecular structure of 1 shows an Al–O bond distance comparable to that found in the bridging alkoxide compounds 2 and [(Bu t ) 2 Al(µ-OPr n )] 2 3, suggesting that the Al–O · · · H unit may be considered analogous to a bridging alkoxide unit, Al(µ-OR)Al, as a consequence of a significant contribution from the zwitterionic alkoxide - /ammonium + form made possible by a strong intraligand hydrogen bond. The kinetics of the conversion of 1 into 2 have been studied. A large activation energy and positive deuterium isotope effect are consistent with breaking of the hydrogen bond during the transition state. The reaction of (Bu t ) 3 Al(NMe 3 ) 4 with ethanol yields [(Bu t ) 2 Al(µ-OEt)] 2 5. The reaction of Al(Bu t ) 3 with HN(Me)(CH 2 ) n NMe 2 (n = 3 or 2) yields the stable Lewis acid–base adducts (Bu t ) 3 Al[NH(Me)CH 2 CH 2 CH 2 NMe 2 ] 6 and (Bu t ) 3 Al[NH(Me)CH 2 CH 2 NMe 2 ] 7, respectively. The molecular structures of compounds 1–3, 6 and 7 have been confirmed by X-ray crystallography. The implications of the structures and stabilities of compounds 1, 6 and 7 are discussed with respect to the protonolysis reaction of aluminium alkyls with Bronsted acids (HX) and a new intermolecular elimination mechanism is proposed.