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N-Heterocyclic carbene adducts of the heavier group 15 tribromides. Normal to abnormal isomerism and bromide ion abstraction

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Abstract

The reactivity of the heavier group 15 tribromides, SbBr3 and BiBr3, towards 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene (IPr) is described. These reactions quantitatively afford Lewis acid–base adducts, (IPr)EBr3 (E = Sb 1; Bi 2), which readily react with AlBr3 yielding cationic species [(IPr)EBr2]+ (E = Sb 3; Bi 4). Under thermal treatment, the N-heterocyclic carbene ligands in 1 and 2 will readily isomerise to afford the abnormally-bonded (or mesoionic) complexes (aIPr)EBr3 (E = Sb 5; Bi 6). As with 1 and 2, bromide abstraction from such compounds readily affords the cationic complexes [(aIPr)EBr2]+ (E = Sb 7; Bi 8). Finally, in an effort to elucidate the isomerisation process which allows for the conversion of 1 and 2 to the abnormally bonded systems (compounds 5 and 6), compound 1 was reacted with a further equivalent of IPr to afford the cationic species [(aIPr)2SbBr2]+ (9). This strongly suggests that the normal to abnormal isomerisation of the N-heterocylic carbene ligands in compounds 1 and 2 is mediated by the presence of free IPr. Compound [9]Br can be used to access the dicationic species [(aIPr)2SbBr]2+ (10), which we have identified spectroscopically. Single crystal X-ray structures and spectroscopic data for all compounds are discussed.

Graphical abstract: N-Heterocyclic carbene adducts of the heavier group 15 tribromides. Normal to abnormal isomerism and bromide ion abstraction

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Publication details

The article was received on 05 Jul 2017, accepted on 24 Jul 2017 and first published on 25 Jul 2017


Article type: Paper
DOI: 10.1039/C7DT02431B
Citation: Dalton Trans., 2017, Advance Article
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    N-Heterocyclic carbene adducts of the heavier group 15 tribromides. Normal to abnormal isomerism and bromide ion abstraction

    J. B. Waters, Q. Chen, T. A. Everitt and J. M. Goicoechea, Dalton Trans., 2017, Advance Article , DOI: 10.1039/C7DT02431B

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