21 Cyclic Boron Compounds VI. A BN Substituted Cyclobutadiene Analog. Synthesis Structure, Stereochemistry, and Mechanism of Formation
Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on December 11, 2014 | http://pubs.acs.org Publication Date: January 1, 1964 | doi: 10.1021/ba-1964-0042.ch021
MICHAEL F. LAPPERT and M A N O J Department Manchester,
of Chemistry, England
Faculty
K.
MAJUMDAR
of Technology,
University
of
Manchester,
The first example of a cyclic 3-coordinate boron-nitrogen ring compound (the dimeric borazyne, isoelectronic with a cyclobutadiene de rivative), 1, 3-di-tert - butyl-2, 4-di- tert butylamino-1, 3-diaza-2, 4-boretane, has been obtained and characterized. Physical measure ments ( H nuclear magnetic resonance and in frared spectral and mass spectrometric data) confirm the structure and provide information on the bonding. Cis/trans isomerism, due to restricted rotation about two bonds, is demon strated. A proposal for the mechanism of elim ination-cyclization reactions, leading to diazaboretanes, borazines, or borazocines is made, which involves diborylamines as intermediates, isolable only under sterically favorable condi tions. 1
A f the borazynes (XB=NY) and their oligomers, only the cyclic t r i mers (the borazines) (12,15) and recently the tetramers (the bora zocines) (18) have been well characterized; polymeric, presumably linear, derivatives have also been described (5, 7, 8). We now report the preparation of a cyclic dimer, systematically named l,3-di-ter£butyl-2,4-di-teri-butylamino-1, 3-diaza-2, 4-boretane (V). [A pre liminary account of this work has been published (10)]· Reactions leading to its formation are indicated in the reaction scheme shown below; the yields in each step were high. Compounds II to VI, which have been characterized (see Tables I and Π), represent novel classes of boron compounds ; an example of a bisborylamine is known (13) and tris-ter£-butylaminoborane (I) has been obtained pre viously (1). Ter£-Butylaminochlorophenylborane (VI) is not related to the main reactions: It was prepared Ph.BCl
2
+ PH.B(NHBuS _
2 Ph. B(C1). NHBu*
2
in an effort, which proved unsuccessful, to obtain successively Cl.fPhjB.NBu^BÎPhJ.NHBut, Bu* NH. (Ph)B. NBu*. Β (Ph). NHBu*, and (PhB.NBu ), . 1
2
208
In Boron-Nitrogen Chemistry; Niedenzu, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1964.
27
LAPPERT AND
MAJUMDOR
Table I. . . B.P. Compound
20
^20 ^
c
74-78/10.0
&
209
Analog
Characterization of New BN Compounds /Mm. (M.P.),
