Metal-mediated couplings of a diphosphastibolyl ring anion, [1,4,2-P2SbC2But2]−: synthesis and characterisation of novel antimony-containing cage compounds

Abstract

Two equivalents of the diphosphastibolyl ring anion, [1,4,2-P2SbC2But2]– reacted with FeCl3 to produce an antimony-containing cage compound, P4Sb2C4But4, via an oxidative coupling mechanism. This cage underwent an intramolecular rearrangement reaction when treated with [W(CO)5(thf)] (thf = tetrahydrofuran) to produce the complex [{W(CO)5}P4Sb2C4But4], which X-ray crystallography shows to contain a three-membered PPC ‘diphosphirane’ ring. Treatment of cis-[PtCl2(PEt3)2] with 1 equivalent of [1,4,2-P2SbC2But2]– yielded the first example of a complex, trans-[PtCl(PEt3)2(η1-P2SbC2But2)], containing a solely η1-co-ordinated diphosphastibolyl ring. The crystal structure of this compound shows the heterocyclic ring to retain its aromaticity after co-ordination. Treatment of cis-[PtCl2(PEt3)2] with 2 equivalents of [1,4,2-P2SbC2But2]– initiated a ring-coupling reaction at the metal to give the novel cage complex cis-[Pt(PEt3)2(η2-P4Sb2C4But4]. The molecular structure of the cage shows it to contain a highly strained, dianionic ligand, [P4Sb2C4But4]2–, which chelates the platinum through antimony and phosphorus atoms. Unusual features in the 31P-{1H} NMR spectrum of the complex are described.