Triphosphole, C 2H 3P 3, is a heterocycle with 3 phosphorus atoms.
Pentaphosphole, P 5H, is a cyclic compound with 5 phosphorus atoms.
Structure and bonding
Unlike the related 5-membered heterocycles pyrrole, thiophene, and furan, the aromaticity of phospholes is diminished, reflecting the reluctance of phosphorus to delocalize its lone pair.[2] The main indication of this difference is the pyramidalization of phosphorus. The absence of aromaticity is also indicated by the reactivity of phospholes.[3] Phospholes undergo different cycloaddition reactions; coordination properties of phospholes are also well studied.[4]
Preparation
The parent phosphole was first described in 1983. It was prepared by low-temperature protonation of lithium phospholide.[5] Pentaphenylphosphole was reported in 1953.[6] One route to phospholes is via the McCormack reaction, involving the addition of a 1,3-diene to a phosphonous chloride (RPCl2) followed by dehydrohalogenation.[7] Phenylphospholes can be prepared via zirconacyclopentadienes by reaction with PhPCl2.[8]
Reactivity
The behavior of the secondary phospholes, those with P−H bond, is dominated by the reactivity of this group.[5] The parent phosphole readily rearranges by migration of H from P to carbon-2, followed by dimerization.
Most phospholes are tertiary, typically P-methyl or P-phenyl. The nonaromaticity of these phospholes is manifested in their reactivity but the P−C bonds remain intact. For example, they undergo Diels–Alder reactions with electrophilicalkynes. They are basic at P, serving as ligands.[5]
2,5-Diphenyl phospholes can be functionalised by deprotonation followed by P-acylation then a 1H, 2H, 3H phospholide equilibrium resulting in a 1:3 shift of the acyl group.[9]
^D. B. Chesnut; L. D. Quin (2007). "The important role of the phosphorus lone pair in phosphole aromaticity". Heteroatom Chemistry. 18: 754. doi:10.1002/hc.20364.
^Philip Hindenberg; Carlos Romero-Nieto (2016). "Phosphaphenalenes: An Evolution of the Phosphorus Heterocycles". Synlett. 27: 2293–2300. doi:10.1055/s-0035-1562506.
^Almaz Zagidullin; Vasily A. Miluykov (2013). "Phospholes – development and recent advances". Mendeleev Communications. 23: 117–130. doi:10.1016/j.mencom.2013.05.001.
^ abcClaude Charrier; Hubert Bonnard; Guillaume De Lauzon; Francois Mathey (1983). "Proton [1,5] shifts in P-unsubstituted 1H-phospholes. Synthesis and chemistry of 2H-phosphole dimers". J. Am. Chem. Soc. 105: 6871–6877. doi:10.1021/ja00361a022.
^A Guide to Organophosphorus Chemistry Louis D. Quin 2000 John Wiley & Sons ISBN0-471-31824-8
^Magali Clochard; Joanna Grundy; Bruno Donnadieu & François Mathey (2005). "A straightforward synthesis of 3-acylphospholes". Organic Letters. 7 (20): 4511–4513. doi:10.1021/ol051816d. PMID16178571.
^Grundy, J. & Mathey, F. (2005). "One-Pot Conversion of Phospholide Ions into β-Functional Phosphinines". Angewandte Chemie International Edition. 44: 1082–1084. doi:10.1002/anie.200462020. PMID15662672.