Expansion of the scope of alkylboryl-bridged N → B-ladder boranes: new substituents and alternative substrates. Issue 27 (18th June 2019)

• Record Type: Journal Article
• Authors: Pammer, Frank; Schepper, Jonas; Glöckler, Johannes; Sun, Yu; Orthaber, Andreas
• Is Part Of: Dalton transactions. Volume 48:Issue 27(2019)
• Page Start: 10298
• Page End: 10312
• Publication Date: 2019-06-18
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c9dt01555h
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : A series of new boranes capable of forming intramolecular N → B-heterocycles has been prepared and their properties have been studied by electrochemical methods and UV-vis-spectroscopy complemented by DFT calculations. Abstract : A series of new boranes capable of forming intramolecular N → B-heterocycles has been prepared and their properties have been studied by electrochemical methods and UV-vis-spectroscopy complemented by DFT calculations. A dimethylborane (BMe2 ), haloborane derivatives (BBr2, BF2, BI2 ) and mixed cyano/isocyano-borane (B(CN)(NC) ) have been prepared by different techniques. Furthermore, 2′-alkynyl-substituted 2-phenylpyridines bearing terminal tert -butyl- and trimethylsilyl-groups are introduced as a new class of substrates for hydroboration. Successful hydroboration with either 9 H -borabicyclo[3.3.1]-nonane (9 H -BBN), dimesitylborane (Mes2 B-H), or Piers' borane ((C6 F5 )2 B-H, BPF-H) furnished new π-extended boranes capable of forming intramolecular six- or seven-membered N → B-heterocycles ( t BuBBN, SiBPF ), and, in the case of Mes2 BH, formation of a sterically crowded styrylborane (SiBMes2 ) incapable of intramolecular N → B-coordination was observed. All the boranes listed above exceptBMe2 have been structurally characterized, and a study of their electrochemical properties showed that the systematic variation of the substituents on boron allows for the incremental variation of the electron affinity of the phenylpyridine-model system over a total range of >0.7 eV between alkylboranes (BMe2, BBN ) andB(CN)(NC) .B(CN)(NC) shows the strongest N → B-bond (≈175 kJ mol −1 ), and highest electron-affinity observed so far, and is the first example of a borane bearing an isocyano-substituent on boron.