N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds

Abstract

The N-lithioborazine LiH2N3B3Me3, 1, reacts with organoboron halides not only to the respective borazinyl organylboranes but also by Me/halogen exchange. (Me2N)2B-H2N3B3Me3 was obtained from 1 and (Me2N)2BCl. A new ten-membered B6N4 ring system, 5, results on treatment of Cl(Me2N)B-B(NMe2)Cl with 1. The B-N-borazinyl borazines 6 - 8 can be prepared from 1 and B-monohalo borazines. The synthesis of 2,4,6-trimethylborazinyl-aluminum and -titanium compounds is achieved only with mononuclear monohalides of Al(III) and Ti(IV). The 2,4,6-trimethylborazinyl- bis(piperidino)alane 9 and the tris(2,6-diisopropylphenoxo)-2,4,6-trimethylborazinyltitanium 10 were characterized by X-ray structure analysis. The distortion of the borazine ring by B and N substitution is discussed. In case of the N-substituted borazines YH2N3B3Me3 the B-N bonds of the YNB2 units are elongated, e. g. for Y = PBr2 or (RO)3Ti, while N lithiation leads to a shortening of these B-N bond. These changes of bond lengths are also reflected by changes in the B1-N2 and B3-N3 bond lengths which become shorter in the presence of electron-withdrawing groups, but longer in case of Li substitution. Also, the bond angles B1-N2-B2 and B2-N3-B3 are affected by an increase of up to 128°.