Rearrangement of mono- and poly-B-methyl derivatives of 2,4-closo-dicarbaheptaborane, 2,4-C2B5H7

Synthesis of a nitrogen derivative of closo-2,4-dicarbaheptaborane

“…Since /3-cyclodextrin (cycloheptaamylose)3 can be used in enzyme models which under the best circumstances show rate accelerations of enzymatic magnitude,4 and since reactions of substrates bound into the cyclodextrin cavity are frequently very selective with respect to substrate and pathway,5 it was attractive to link the pyridoxal-pyridoxamine coenzymes to /3-cyclodextrin. We report here the first example of such a linked molecule (8). As expected, the combination in this molecule of an enzyme-like binding site with a coenzyme has led to good substrate specificity in transaminations and to some chiral induction.…”

Stereochemical studies on diastereomers of tris(2,3-butanediamine)cobalt(III)

“…A similar conclusion has been reached from *H NMR studies on this and related systems. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]24 The presence of two methyl resonances in NMR spectra of the tris meso complexes has been ascribed to axial and equatorial groups whose conformational interconversions are slow on the NMR time scale;14 however, it has been pointed out that methyl groups which are enantiotopic in the free ligand become diastereotopic arid intrinsically nonequivalent in the chiral tris chelates. 3 Of course, the actual magnitude of the chemical shift nonequivalence observed may be primarily due to stabilization of one chelate conformer over another by lei preference (vide infra)2,4 Thus, we assign the two methine carbon resonances and, as well, the two methyl resonances in the !3C NMR spectra of /ac-[Co(m-bn) 3]3+ to diastereotopic groups in a conformationally fluxional molecule with an effective2 C3 symmetry.…”

“…Very limited 13C NMR spectral data have been previously reported for two [Co((±)-bn)3]3+ isomers. 5 Experimental Section Physical Measurements. Infrared spectral band positions (±3 cm"1) were taken from spectra collected on a Perkin-Elmer Model 621 grating spectrophotometer using KBr pellets.…”

Three-Dimensional Hückel Theory for closo-Carboranes

“…It is geometrically possible for the rearrangements of carborane polyhedra containing 7, 9, and 10 skeletal atoms to take place through double-DSD processes which are also electronically allowed. Isomerizations of both 7- and 10-atom polyhedra have been observed. − ,− The double-DSD framework reorganizations involve two diamonds that share a common edge. In such processes the two edge-switching operations might occur simultaneously, or the second could begin only after the first is complete, or in some intermediate fashion.…”

“…Concerted: Consecutive: Overlapping: Although the three processes lead from the same initial reactant R to the same final product P, the nature of the intervening transition states and intermediates is different in each case. Onak and co-workers have tried to determine the preferred rearrangement process for C 2 B 5 H 7 by observing rearrangements of substituted carboranes. − Following the reasoning of Wales and Stone, the deltahedral structures of R and P should have the lowest energies. To open a square or pivot face requires the expenditure of energy to break a bond.…”