Spectroscopy vertex

In order to characterize the alkali metal salts of the 11-vertex nido-dicarbaborates [C2B9H11]2- in solution, a series of salts were synthesized and studied by NMR spectroscopy and quantum mechanical calculations. Comparison of the theoretical nB, 13C, and H NMR chemical shifts of the isomeric dianions 7,8-, 7,9-, and [2,9-C2B9Hn]Z, and the ion pairs [ap-M-CzBgHn]- and MHP-MC2B9HH] with the observed data indicate that the alkali metal salts M2[C2B9Hn] exist in solution as anionic ion pairs [ap-M-C2B9Hn]- with the metal in apical position (ap) coordinated at the five-membered open face of the cluster.14... 

From the reaction of -butyl nitrite with the macropolyhedral borane [ //-B18H22], an 18-vertex azaborane anti-[9-NB17H2q] was isolated and characterized on the basis of NMR spectroscopy data.119... 

The 11-vertex /0-diphosphaborane [7,9-Ph2- ri/ -7,9-P2B9H9] 35 was synthesized in 20% yield from [B9H12] and PhPCl2 and was characterized by NMR spectroscopy and X-ray crystal structure analysis.141... 

The structure of this compound, inferred from nB NMR spectroscopy (26) is shown in Fig. 19. The metal resides at the high-coordinate vertex, while the 2 polyhedral carbon atoms occupy the two low-coordinate positions in the closed eleven-vertex geometry. The analogous Fe(III) compound was formed using Fe(II) in the polyhedral expansion reaction (24). 

The structure of m cfo-pentaborane(9) is obtained by the removal of a single vertex from [B6H6]2 and is shown in Fig. 11. Since electron- and X-ray diffraction, and microwave spectroscopy have all been used to determine structural parameters, the data are all summarized in Table 3. 

The reaction of XIII with EtOH in CHjCl EtOH, in 1 1 molar ratio, affords the ethoxy-derivative, [8,8-(q2-dppp)-9-(OEt)-nido-RhSB,H,] (XIV) behavior which is seen in the series of related compounds.12,111 This suggests that the boron vertex at the 9-position in Xm, and the related series of compounds, is prone to nucleophilic substitution reactions. XIV was characterized by NMR spectroscopy, mass spectrometry and X-ray diffraction. In contrast to the parent rhodathiaborane IV, and XIII, compound XIV does not feature fluxional behavior, even at 373 K implying, perhaps, AG values greater than 64 kjmol 1 for a possible dynamic process in XIV. The apparent large difference in the activation energy for the substituted versus the unsubstituted species may be due to either electronic or steric effects. The differences in the structures of XIII and XIV are minimal except for the B(9)-B(10) distances which differ by 0.083 A.4b This tends to suggest a role for this bond in the fluxional process although a purely steric influence of the substituent at the 9-position in XIV cannot be ruled out. 

A fascinating recent development in imidotin-cluster chemistry involves the isolation of a series of double cubanes, which contain an Sn7(tt3-NR)8 core. Wright and coworkers have demonstrated that when pyridinyl or pyrimidinyl groups are present on the imido nitrogen centers, the unusual double-cubane clusters 55-60 are obtained (Scheme 2.2.11), rather than the [Sn()a3-NR)]4 cubanes. These clusters are comprised of two interlocked [Sn( a3-NR)]4 cubanes, which share one tin vertex. The central tin center is formally in the +4 oxidation state, so that these double cubanes may be viewed as involving the coordination of two [Sn3()a3-NR)4] anions, such as those present in the clusters 53 and 54, to a central Sn+" cation. The presence of both Sn(II) and Sn(IV) centers was verified by Sn NMR spectroscopy. The deposition of tin metal was observed during the syntheses of 55-60, suggesting that... 

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