Borazine, 2,4,6-trichloro

B-trichloro-N-triphenylborazine, mp 290-292°C, was obtained in 86 yield following the procedure of Groszos and StafieJ (6). This material was then transformed into B-triamino-N-triphenyl-borazine in 67 yield using the method of Toeniskoetter and Hall (2)- B-trianilinoborazine and the novel B-tris[di(trimethylsilyl)-amlno]borazlne (mp, 131.5-132°C characterized by GC/MS, molecular ion 558 amu, and elemental analysis) were synthesized in 76 and 71 yields, respectively, by interaction of aniline and hexamethyl-disllazane with chloroborazine in the presence of triethylamine. 

The synthesis of B-trichloro-N-tris(trimethylsilyl)borazine was much more complicated than that of the other borazines. The overall scheme is given below ... 

The pyrolysis of bis(trimethylsilyl)aminodichloroborane to B-trichloro-N-tris(trimethylsilyl)borazine, contrary to literature (in. did not take place in boiling xylene. Temperatures above 150 C were necessary for trimethylchlorosilane elimination. The highest yield of the relatively pure product was around 20%. The transformation of the B-trichloro-N-tris(trimethylsilylJborazine to B-triamino-N-tris(trimethylsilyl)borazine proceeded readily using liquid ammonia. 

The trichloro derivative having a chlorine atom bound to each of the boron atoms is known as B-trichloroborazine. Borazine can be prepared by several different methods, one of which is the reduction of the trichloro compound ... 

Boron-bonded p -borazine complexes of transition metals have been prepared by two different approaches (a) nucleophilic substitution of B,fi, fi"-trichloro-borazine with an anionic metal carbonyl reagent and (b) oxidative addition of a B-Br bond of 5,5, B"-tribromoborazine to a zerovalent group 10 complex (see examples in Scheme 9.2). 

Substitution reactions of B-trichloro - N- trialkyl (or triaryl)borazines and alchohols, phenols, or excess amine yield the corresponding borazines (100,94). 

IV-Trimethoxyborazines are available from reaction of dichloroboranes and O-methyl-IV,IV-bis(trimethylsilyl)hydroxylamine (eq. 31). The B-trichloro-borazines undergo substitution reactions at the B atoms to give B-tri(Z -butoxy)- or B-tri(/< butyl)-IV-trimethoxyborazines (101)... 

Recently, a method has been described which eliminates the long reflux time needed for completion of the Brown-Laubengayer reaction. Only 2—3 hours refluxing are required for the formation of 2,4,6-trichloro-borazine from the interaction of NH4CI with the acetonitrile-trichloro-borane adduct 44>. The yield is about 60%. No mechanism has been proposed, but it is known that in other B—N ring syntheses (cf. Sections II.2.4. and II.7) the use of trihaloborane complexes is an essential feature. 

B,B, 5"-Trichloroborazine is readily reduced with alkali metal hydroborates to yield borazine, (HBNH)3. The boron-bonded chlorine can be replaced by fluorine through the action of metal fluorides upon the trichloroborazine. With amines, the latter reacts to yield B,B, B"-triaminoborazines. The substitution of chlorine in iV-substituted B,B, B"-trichloro-borazines by organic groups is most easily achieved by the Grignard method but has also been effected by the use of organolithium compounds. 

The monomer tri-isocyanto-trimethyl-borazine (TITMB) was synthesized from trichloro-trimethyl-borazine (TCTMB) according to the method reported in the literature [12]. The Intermediate TCTMB was synthesized via a modification of the procedure of Brown and Laubengayer [13]. Methyl-amine hydrochloride and excess of BCI3 were refluxed in chlorobenzene for 6h and then maintained for 16h at 80°C. The reaction mixture was filtered warm, vacuum dried and subsequently sublimed under reduced pressure. A slight increase in yield (12%) of pure TCTMB was achieved. 

Hexaphenyldisilane allowed to react with 1 5 Na,K-alloy in anhydrous ether under Ng, excess alloy removed by amalgamation, the resulting green ethereal triphenylsilyl-K added to an ethereal suspension of B-trichloro-N-trimethyl-borazine, and the product isolated when the green color has disappeared B-tris(triphenylsilyl)-N-trimethylborazine. Y 78%.—This is the first prepn. of compounds containing boron-silicon bonds. F. e. s. A. H. Gowley, H. H. Sisler, and G. E. Ryschkewitsch, Am. Soc. 82, 501 (1960). 

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