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Issue 12, 2016
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N-heterocyclic carbene induced reductive coupling of phosphorus tribromide. Isolation of a bromine bridged P–P bond and its subsequent reactivity

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Abstract

The room temperature reaction of a 1 : 1 mixture of phosphorus tribromide (PBr3) and the N-heterocyclic carbene 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene (IPr) quantitatively affords the Lewis acid–base adduct (IPr)PBr3 (1). Interestingly, when 1 is heated between 55 and 65 °C for a period of several days, dark red crystals slowly begin to form in the reaction vessel accompanied by the release of bromine. The resulting crystalline sample, [P2(IPr)2Br3]Br ([2]Br), results from the reductive coupling of two equivalents of 1, and contains a cationic moiety with a P–P bond that is bridged by a bromine atom. Anion exchange reactions with Na[BArF4] (BArF4 = B(3,5-{CF3}2C6H3)4) afford [2][BArF4]. Abstraction of two equivalents of bromine allows for the isolation of the unprecedented dicationic species [P2(IPr)2Br2]2+ (3) which was isolated and structurally authenticated as two different [BArF4] salts. Reaction of 2 with mild reductants such as SnBr2 or tetrakis(dimethylamino)ethylene (TDAE) affords [P2(IPr)2Br]+ (4) and the known radical cation [P2(IPr)2+ (5), respectively. These studies show that relatively weak P–Br bonds present in compounds 1–4 can be cleaved in a straightforward manner to afford low oxidation state compounds in high yields.

Graphical abstract: N-heterocyclic carbene induced reductive coupling of phosphorus tribromide. Isolation of a bromine bridged P–P bond and its subsequent reactivity

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Publication details

The article was received on 26 May 2016, accepted on 20 Jul 2016 and first published on 20 Jul 2016


Article type: Edge Article
DOI: 10.1039/C6SC02343F
Citation: Chem. Sci., 2016,7, 6981-6987
  • Open access: Creative Commons BY license
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    N-heterocyclic carbene induced reductive coupling of phosphorus tribromide. Isolation of a bromine bridged P–P bond and its subsequent reactivity

    J. B. Waters, T. A. Everitt, W. K. Myers and J. M. Goicoechea, Chem. Sci., 2016, 7, 6981
    DOI: 10.1039/C6SC02343F

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