Alkoxohydridoaluminates. I 27Al NMR Characteristics of (C4 H9)4N+ AlH4-n(OR)n - in Benzene

Abstract

The 27Al NMR spectra of (C4H9)4N+AlH4-n(OR)n - prepared in the reaction of (C4H9)4NAlH4 with ROH (R = CH3, C2H5, i-C3H7, t-C4H9, n-C5H11, n-C9H19, cyclo-C6U11, C6H5, CH3OCH2CH2) in benzene show - in contrast to the Li+ and Na+ salts - a distinct H-splitting, which has allowed to ascertain: 1) the presence of all members (n = 0-4) in solution, 2) the Al chemical shift and AI -H coupling constant of all individual classes, namely (n = 0): 101.6 ppm, quintet 174 Hz; (n = 1): 114-123 ppm, quartet 184-193 Hz; (n = 2): 103-112 ppm, triplet 197-219 Hz; (n = 3): 75-91 ppm, doublet 218-237 Hz; (n = 4): 51-73 ppm, singlet, 3) increased shielding in the order: CH3 < n-R = i-R = sec-R < C6H11 ⪡ C6H5 < t-C4H9. The anomalous "sagging" pattern of the curve: δ27Al vs. number of OR groups, is interpreted on the basis of significant differences among Al and H and OR in electronegativity.