Chemistry of Group 13 Lewis acids
Branch, Catherine Steiner
Barron, Andrew R.
Doctor of Philosophy
Reaction of 9-fluorenone with a Group 13 Lewis acid, MX3 (M = B, Al, Ga; X = Cl, Br), yields a Lewis acid-base adduct, MX3(9-fluorenone) n. Bond dissociation energies for MX3(9-fluorenone) in solution have been determined. BDE and other thermodynamic values are good indicators of the strength of a Lewis acid-base interaction. Correlating these values with various spectroscopic data should lead to a simple test of Lewis acidity. Hydrogen/deuterium exchange between naphthalene and C6D 6 is catalyzed by Hg(C6D6)2(GaCl 4)2 and occurs by electrophilic substitution. In this regard, we have studied the kinetics of H/D exchange, using 1H NMR. There are two distinct first order regimes, separated by a non-first order regime. In the first regime, Hg(C6D6)2(GaCl 4)2 deuterates free naphthalene. As the reaction progresses, a ligand exchange occurs between C6D6 and naphthalene, resulting in the protonation of C6D6 by Hg(C10 H8)2(GaCl4)2. This ligand exchange has been confirmed by 13C CPMAS NMR of Hg(C10 H8)2(GaCl4)2, as well as by DFT calculations, UV-visible spectroscopy, and MS. The rates of not only H/D exchange, but also the rate of ligand exchange has been determined. Reaction of M(tBu)3 with anthranilic, salicylic, and ortho-toluic acids yields [(tBu) 2M(mu-O2CC6H4-2-NH2)] 2, M = Al, Ga; [(tBu)2Ga(mu-O2CC 6H4-2-OH)]2, and [(tBu)2Ga(mu-O 2CC6H4-2-Me)]2, respectively. Reaction of anthranilic acid with two equivalents of Al(tBu)3 allows for the isolation of (tBu)2Al(mu-O 2CC6H4-2-NH2)Al(tBu) 3. Based on this compound's isolation and its conversion to [( tBu)2Al(mu-O2CC6H4-2NH 2)]2 during physical grinding, a proposal that the formation of [(tBu)2M(mu-O2CC6H 4-2-X)]2 occurs via a chelate species can be made. Additionally, intra-molecular hydrogen bonding, found in the anthranilate and salicylate ligands, remains present in the Group 13 compounds but is not enhanced.