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Issue 27, 2019
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Expansion of the scope of alkylboryl-bridged N → B-ladder boranes: new substituents and alternative substrates

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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 9H-borabicyclo[3.3.1]-nonane (9H-BBN), dimesitylborane (Mes2B-H), or Piers’ borane ((C6F5)2B-H, BPF-H) furnished new π-extended boranes capable of forming intramolecular six- or seven-membered N → B-heterocycles (tBuBBN, SiBPF), and, in the case of Mes2BH, formation of a sterically crowded styrylborane (SiBMes2) incapable of intramolecular N → B-coordination was observed. All the boranes listed above except BMe2 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) and B(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.

Graphical abstract: Expansion of the scope of alkylboryl-bridged N → B-ladder boranes: new substituents and alternative substrates

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Publication details

The article was received on 11 Apr 2019, accepted on 09 Jun 2019 and first published on 10 Jun 2019


Article type: Paper
DOI: 10.1039/C9DT01555H
Dalton Trans., 2019,48, 10298-10312

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    Expansion of the scope of alkylboryl-bridged N → B-ladder boranes: new substituents and alternative substrates

    F. Pammer, J. Schepper, J. Glöckler, Y. Sun and A. Orthaber, Dalton Trans., 2019, 48, 10298
    DOI: 10.1039/C9DT01555H

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