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

The reaction of n ‐C 8 H 17 B[N(Me)SiMe 3 ] 2 ( 1 ) with n ‐C 8 H 17 BCl 2 ( 2 a ) yielded, instead of a linear poly(iminoborane), the aminoborane n ‐C 8 H 17 B(Cl)N(Me)SiMe 3 ( 4 ) and after cyclotrimerization the borazine cyclo ‐( n ‐C 8 H 17 BNMe) 3 ( 6 ). Side reactions that result in borazine formation were effectively suppressed if 1,3‐bis(trimethylsilyl)‐1,3,2‐diazaborolidines 7 were employed as co‐monomers in combination with dichloro‐ or dibromoboranes 2 or 8 , respectively. Silicon/boron exchange polycondensation led to oligo(iminoborane)s 11 a , b , ac , d . Alternative synthetic routes to such species involve Sn/B exchange of 1,3‐bis(trimethylstannyl)‐2‐ n ‐octyl‐1,3,2‐diazaborolidine ( 16 ) and n ‐C 8 H 17 BBr 2 ( 8 a ), and the initiated polycondensation of the dormant monomer 14 in the presence of a Brønsted acid (HCl, HOTf, or HNTf 2 ; 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 n ‐octyl boron substituents ( 11 ac ), as well as for a derivative with 4‐ n ‐butylphenyl side groups ( 11 d ). The highest‐molecular‐weight sample obtained was 11 ac . Featuring about 18 catenated BN units, on average, this is the closest approach to a poly(iminoborane) known.