With borazine

In contrast to borazine, the three corresponding excited singlet states of benzene have a much wider spread of absorbing wavelengths and exhibit easily distinguished vibrational fine structure. Many photolysis experiments have been performed using laser lines tuned to selective excite a particular vibrational level of a particular excited state of benzene. Such experiments are more difficult with borazine. The triplet states of benzene have been located experimentally and quantum yields for fluorescence and phosphorescence at various wavelengths and pressure conditions have been determined. 

The photolysis reaction of borazine with a second reagent can be classified on the basis of two types of bimolecular processes. In process A, borazine is the photochemical recent, and the products are formed by bimolecular exchange reactions between an excited borazine molecule and the second recent The preparation of a large number of B-substituted borazines is linked to this type of process (Table 3). In process B, the photochemical recent is a species other than borazine, as for example in the reaction of ammonia with borazine. 

Regents which are active upon irradiation with benzene are olefins and dienes None of these react photochemically with borazine. Recently, the photolysis of benzene at X = 184.9 run with D2 has been shown to produce a small amount of CgHsD (4> = 0.01) This is contrast to the very efficient deuteration at the boron site of borazine (4 = 0.90). Hexafluoroacetone as the absorbing species reacts with borazine to produce a B-alkoxyborazine substitution product. Reaction of this reagent with benzene, on the other hand, involves the CF3 radicals and the products are addition rather than substitution products ss)... 

Table 4. Electronic transitions to the excited states of N-trimethylborazine (compared with borazine) (eV)...

Table 5. The theoretical and exp imental vertical ionization potentials of N trimethyiborazine compared with borazine (eV)...

Borazinium ion undergoes reaction with borazine to form a protonated isomer of diborazinyl. 

Polymers are formed, together with borazines, from iminoboranes RBNR with a-unbranched alkyl groups. By absolute control of the temperature, the stabilization would presumably be directed toward the borazine. Loss of thermal control will cause a loss of kinetic control, so that hot iminoborane molecules will trimerize or polymerize rather unspecifically. 

By analogy with borazines, the initial interest in the analogous unsaturated boron-phosphorus rings focused on the fundamental issue of the extent of... 

Photochemical insertion into a B—H bond occurs with borazine 267). The CF3 substituted product 234b arises from radical decomposition of the HFA molecule. 

Syntheses of Si-B-C-N polymers in which borazine units are directly attached to polysilazanes were investigated in detail by Sneddon et al." " The principle was to join borazine or its derivatives to oligomeric or polymeric silazanes by dehydrocoupling or dehydrosilylative (elimination of HSiRj) coupling reactions. For example, hydridopolysilazane was treated with borazine at temperatures... 

Isoelectronic with borazine is boroxine, H3B3O3. It can be produced by the explosive oxidation of or B5H9. Boroxine is planar but has even less ir de-localization than borazine. It is also less stable, decomposing at room temperature to diborane and boron oxide. 

Whereas the reaction of hydrogen halides with borazines typically results in addition across the B—N bond to form the coordinately saturated trihalo rings, it has been observed that treatment of (HNBCOj with acetic acid (or acetic anhydride) effects a similar addition, along with chlorine replacement, but with a concomitant reduction in ring size to the dimer ... 

Scheme 7.4 Polyphosphazenes with borazine, organosilicon, or transition metal organometallic side groups.

The gas-phase reactivity of selected ionic species with borazine and borazine-derived ions with selected neutral molecules has been studied by FT-ICR and ab initio calculations. Evidence for an electrophilic substitution on the borazine ring was found in the alkylation by gaseous Me2F+, Me2CH+, and MesC that led to neutral substitution products, as a result of an N-alkylation. Further studies on the protonation, all lation, and nitration of neutral borazine have been compared with the corresponding reactions of benzene, and it was shown that the cyclic B3N3H5+ reacts similarly to the phenylium cation CeHs. In this sense, borazine shows a remarkable similarity to benzene. 

Publications dealing with borazines have concerned the syntheses of amido-borazines/ amidinoborazines/ and macrocyclic polyborazines. ... 

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