Steric Effects in Aluminum Compounds Containing Monoanionic Potentially Bidentate Ligands: Toward a Quantitative Measure of Steric Bulk

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...