Azatranes and atranes of the group 13 elements

Pinkas, Jiri
Major Professor
John G. Verkade
Committee Member
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This dissertation describes synthesis and reactivity patterns, and the spectral and structural characterization of a series of the group 13 azatranes: (M(RNCH[subscript]2CH[subscript]2)[subscript]3N) [subscript] n (M = B, Al, Ga; R = H, Me, SiMe[subscript]3, SiMe[subscript]2-tert-Bu; n = 1, 2). These azatranes display an oligomeric behavior depending on the nature of the central atom M and the size of the substituents R. Bulky substituents such as SiMe[subscript]3 and SiMe[subscript]2-tert-Bu stabilize monomers with a three-fold molecular symmetry. Single-crystal X-ray diffraction studies on monomeric Al(Me[subscript]3SiNCH[subscript]2CH[subscript]2)[subscript]3N revealed a rare trigonal monopyramidal (TMP) geometry of the aluminum center. The C[subscript]3 propeller-like conformation of these molecules implies the presence of two enantiomers, [delta] and [lambda], whose interconversion (racemization) was observed by variable temperature [superscript]1H NMR spectroscopy in solution for B(Me[subscript]3SiNCH[subscript]2CH[subscript]2)[subscript]3N;Azatranes of Al and Ga possessing smaller equatorial groups form dimers as was shown by multinuclear and two-dimensional NMR spectroscopy experiments. The curious cis configuration of the substituents on the central (M-N)[subscript]2 ring was verified by single-crystal X-ray diffraction studies of three azatranes. The presence of the trans isomer or an interconversion process between the two isomers in solution was ruled out by [superscript]1H and [superscript]13 C NMR spectroscopies in all cases. A series of [superscript]27 Al NMR chemical shifts of monomeric aluminum amides and monomeric and dimeric azaalumatranes containing aluminum ligated exclusively by nitrogens and coordination coordination numbers from three to five displayed a trend toward higher shielding with increasing coordination number;Monomeric and dimeric azaalumatranes and trimethylazaboratrane were found to take part in interesting transmetallation reactions with main-group and transition metal alkoxides and Ga(acac)[subscript]3. By this method, main-group and transition metal azatranes were prepared. Azatranes were also shown to convert to corresponding atranes in a transligation reaction with triethanolamine;The tetrameric nature of alumatrane in solution was substantiated by [superscript]27 Al, [superscript]1 H COSY, and variable temperature [superscript]13 C NMR spectroscopy experiments. The compound displays a complex dynamic behavior including racemization and rotation of the peripheral units.