From Boron-Containing Fragments

Nearly all fragments in the mass spectra for the complexes investigated showed sets of isotopic peaks, which indicate the presence of boron-containing fragments in these species. As seen from the composition of the ionic fragments, their formation in the gas phase largely occurs with detachment of dioximate fragments from the "parent" molecule or ion ... 

It has recently been shown that carbanions generated from carboranes are able to substitute hydrogen in pyrazines, triazine-iV-oxides, and other )t-deficient systems. This original approach to incorporate boron-containing fragments into heterocyclic molecules proved to be rather effective for the s3tnthesis of new ligands and also compounds which can be used for neutron-capture therapy of cancer (Scheme 43) [82, 83]. 

The most bulky fragmental ions resulted from heterolytic bond rupture and withdrawal of the apical substituent (OH-group) from a boron-containing capping fragment after addition of the proton ... 

In compound 91 the diborahexasiloxane ring system 89 can be identified, which has been expanded to a three-dimensional structure by an additional (R2Si0)20 fragment bridging now, in contrast to compound 90, two boron atoms [127], This cage can be obtained in yields of 45% from tetraphenyldisiloxanediol and boric acid when reacted in a 6 1 stoichiometry. The molecule contains a... 

The reactivity of l-bora-4-phosphacyclohexadienes-2,5 (175) is typical of tertiary phosphines. NMR data bear witness to the absence of a significant interaction between boron and phosphorus and delocalization of the phosphorus lone electron pair. In this respect, they also differ from cyclic compounds containing a P—C—O—B fragment. 

Since the samples contained three isotopic isomers with potential variation in enrichment at each position aU three positions needed to be measured separately for each data point. However because of the nature of the structure of the molecule and the resultant fragmentation patterns, none of the three positions could be measured without interference from one or both of the other two. The use of other derivatives, such as the butyl-boronate or trl- methylsUyl derivatives, did not improve this situation. Thus, corrections for the interfering enrichments needed to be made. Both (70eV) electron Impact Ionization (El) and methane chemical ionization (Cl) were used to take advantage of particular fragments or enhanced signal abundances which occurred in each mode. 

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