Tetsushi Totani

Quadrupole collapse of spin multiplets in the nuclear magnetic resonance of protons bonded to 10B

The collapse of multiplet structures in the nuclear magnetic resonance spectra of protons bonded to boron was investigated using various boron compounds enriched or not enriched with 10B. The extent of collapse increases with increasing field gradient at the boron nuclei in the order of lithium borohydride (sp 3), trimethylaminoborane (sp 3), and n-tri(methyl-d3)-borazine (sp 2) (effect of field gradient). The collapse is stronger for 10BH signals than for 11BH signals, because the quadrupole moment of 10B is greater than that of 11B (effect of the quadrupole moment). With increasing temperature, the collapse decreases because the correlation time of molecular motion decreases (effect of the correlation time of quadrupole perturbation). Various typical line contours for the 10BH septet (a well resolved and equally spaced septet having the highest outermost peaks and the lowest second outermost peaks, a group of poorly resolved seven lines having maxima at both ends of the septet, and a broad flat-topped a...

Infra-red absorptions of N-trideuteroborazole and B-trichloro-N-trideuteroborazole

Abstract The infra-red absorption spectra of N-trideuteroborazole and B-trichloro-N-trideuteroborazole have been recorded across the rock-salt and potassium bromide regions and an assignment of major absorption peaks has been made. Comparison between the frequencies of fundamentals of borazole and N-trideuteroborazole has shown that revisions must be made for a few assignments hitherto accepted.

Preparation, characterization, and properties of 1,1′-azo-o-carbaboranes

1-Amino-1,2-dicarbadodecaborane anions, o-RCB10H10CNH22–(R = H, Me, or Ph), are oxidized by K[MnO4] in liquid NH3 to give 1,1′-azo-o-carbaboranes, RCB10H10CNNCB10H10CR (3), whereas oxidation of HCB10H10CCB10H10CNH24– in the same solvent exclusively affords hydrazobis(o-carbaborane), HCB10H10CCB10H10CNHNHCB10H10CCB10H10CH. The reduction of (3) to the corresponding hydrazocarbaborane, RCB10H10CNHNHCB10H10CR (2), has been successfully achieved. closo-nido-Azocarbaboranes, RCB10H10CNNCB9H10CR–(4), and nido-nido ones, RCB9H10CNNCB9H10CR2–(5), have also been prepared by the degradation of (3) with K[OH]. Their structure and properties are discussed on the basis of spectroscopic data.

Friedel–crafts acetylation products of (η-cyclopentadienyl)[η-(3)-1,2-dicarbaundecaborane(11)]cobalt and their molecular structures

Friedel–Crafts acetylation of [(cp)Co{η-(3)-1,2-B9C2H11}] with aluminium chloride in carbon disulphide results in the formation of [(cp)Co{η-(3)-1,2-B9C2H10Cl}], (I), [(cp)Co{η-(3)-1,2-B9C2H10(8-OCOMe)}], (II), [(cp)Co{η-(3)-1,2-B9C2H10(8-OH)}], (III), and [(cp)Co{η-(3)-1,2-B9C2H10(8-COMe)}], (IV)(cp =η-cyclo-pentadienyl). The complexes have been characterized by i.r., n.m.r., and mass-spectral measurements. X-Ray structure analyses of (II) and (IV) have been made and the substituents are bonded to B(8). Possible mechanisms for the production of these complexes are described.

Preparation and properties of alkyl- and aryl-substituted closo-closo- and closo-nido-hydrazocarbaboranes

closo-closo-1,1′-Azo-o-carbaboranes RCB10H10CNNCB10H10CR react with alkyl- and aryl-lithiums to afford the derivatives RCB10H10CNHNR′CB10H10CR (R = H, Me, or Ph; R′= alkyl or aryl group)(3) along with the hydrazo-carbaboranes RCB10H10CNHNHCB10H10CR (2). Further substitution of these compounds with alkyl halides resulted in the formation of the NN′-disubstituted compound RCB10H10CNR″NR′CB10H10CR (4). The closo-closo compounds (2) and (4) can be converted into the corresponding closo-nido ones in the presence of piperidine base. By means of variable-temperature 1H n.m.r. spectroscopy, the free-energy barriers to conformational interconversion have been estimated [15.5 kcal mol–1 for (3e; R = Me, R′= Et), >22 kcal mol–1 for (4b; R = H, R′= R″= Et), and (4e; R = Me, R′= R″= Et)]. In addition, the existence of interconvertible diastereoisomers has been evidenced for RCB10H10CNMeNMeCB9H10CR–(6a; R = H) and (6b; R = Me) for which the free energies of activation are also estimated.

Preparation of azocarbaboranes: oxidation of 1-amino-o-carbaborane anion in liquid ammonia

1-Amino-o-carbaborane anions, (o-RCB10H10CNH2)2– in liquid NH3 have been found to be oxidized with KMnO4 to give the symmetrically substituted 1-azo-o-carbaboranes, RCB10H10CNNCB10H10CR (R = H, Me, Ph).