Issue 12, 2016

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

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

Supplementary files

Article information

Article type
Edge Article
Submitted
26 May 2016
Accepted
20 Jul 2016
First published
20 Jul 2016
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2016,7, 6981-6987

Author version available

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

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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