Research On Reactions Of Haloboranes With Electron-rich 1,4-Bis(Trimethylsilyl)-1,4-diaza-2,5-cycl Ohexadiene Derivatives

Low-valent boron species are novel compounds that have attracted the attention of the main group chemists.It is meaningful to explore new methods to synthesize low-valent boron species.1,4-Bis?trimethylsilyl?-1,4-diaza-2,5-cyclohexadienes and its derivatives?1,2 and 3?are electron-rich ligands which have a strong reduction ability to early transition metal compounds.Both of them have a one electron reduction trend to high-valent metal compounds and aromatization effect on low-valent metal center.In this paper,the reduction ability of 1,4-bis?trimethylsilyl?-1,4-diaza-2,5-cyclohexadienes and its derivatives to trivalent boron halides was studied.One equivalent amount and two equivalent amounts of borane halides?4,5,6 and 7?were used to react with 1,4-bis?trimethylsilyl?-1,4-diaza-2,5-cyclohexadienes and its derivatives?1,2 and 3?.The results of X-ray single crystal diffraction experiments show that the compounds 8-12,17-19,23-25 obtained by the reaction between 1,4-bis?trimethylsilyl?-1,4-diaza-2,5-cyclohexadienes and its derivatives with borane halides are not low-valent boron species,but unexpected olefin products compounds 20-22 by symmetry forbidden 1,3-hydrogen shift.The B=N rotational barrier of 19?>71.56 k J/mol?,23?58.79 k J/mol?and 25?58.65 k J/mol?was determined by variable-temperature 1H NMR spectroscopy,thus reflecting different degrees of B=N double bond character in the corresponding compounds.In addition,this paper also test the reactivity of compound 11,it can get EPR signal compound 15 with coupled hyperfine splitting by reaction with excessive c AACs,and get boron-boron bond?compound 16?by reaction with IPrAuBr₃ in t BuNC atmosphere.