Cyclolinear Oligo‐ and Poly(iminoborane)s: The Missing Link in Inorganic Main‐Group Macromolecular Chemistry.

Abstract: The reaction of <italic>n</italic>‐C₈H₁₇B[N(Me)SiMe₃]₂ (<bold>1</bold>) with <italic>n</italic>‐C₈H₁₇BCl₂ (<bold>2 a</bold>) yielded, instead of a linear poly(iminoborane), the aminoborane <italic>n</italic>‐C₈H₁₇B(Cl)N(Me)SiMe₃ (<bold>4</bold>) and after cyclotrimerization the borazine <italic>cyclo</italic>‐(<italic>n</italic>‐C₈H₁₇BNMe)₃ (<bold>6</bold>). Side reactions that result in borazine formation were effectively suppressed if 1,3‐bis(trimethylsilyl)‐1,3,2‐diazaborolidines <bold>7</bold> were employed as co‐monomers in combination with dichloro‐ or dibromoboranes <bold>2</bold> or <bold>8</bold>, respectively. Silicon/boron exchange polycondensation led to oligo(iminoborane)s <bold>11 a</bold>,<bold>b</bold>,<bold>ac</bold>,<bold>d</bold>. Alternative synthetic routes to such species involve Sn/B exchange of 1,3‐bis(trimethylstannyl)‐2‐<italic>n</italic>‐octyl‐1,3,2‐diazaborolidine (<bold>16</bold>) and <italic>n</italic>‐C₈H₁₇BBr₂ (<bold>8 a</bold>), and the initiated polycondensation of the dormant monomer <bold>14</bold> in the presence of a Brønsted acid (HCl, HOTf, or HNTf₂; Tf=trifluoromethylsulfonyl). Although an attempt to obtain an oligo‐/poly(iminoborane) with phenyl side groups yielded only insoluble material, the incorporation of aryl groups was proven for a derivative with both phenyl and <italic>n</italic>‐octyl boron substituents (<bold>11 ac</bold>), as well as for a derivative with 4‐<italic>n</italic>‐butylphenyl side groups (<bold>11 d</bold>). The highest‐molecular‐weight sample obtained was <bold>11 ac</bold>. Featuring about 18 catenated BN units, on average, this is the closest approach to a poly(iminoborane) known. [ABSTRACT FROM AUTHOR]