Issue 36, 2017

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

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

Supplementary files

Article information

Article type
Paper
Submitted
05 Jul 2017
Accepted
24 Jul 2017
First published
25 Jul 2017

Dalton Trans., 2017,46, 12053-12066

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, 46, 12053 DOI: 10.1039/C7DT02431B

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