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-P₂SbC₂Bu^t₂]^– reacted with FeCl₃ to produce an antimony-containing cage compound, P₄Sb₂C₄Bu^t₄, 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}P₄Sb₂C₄Bu^t₄], 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-P₂SbC₂Bu^t₂]^– yielded the first example of a complex, trans-[PtCl(PEt₃)₂(η¹-P₂SbC₂Bu^t₂)], 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-P₂SbC₂Bu^t₂]^– initiated a ring-coupling reaction at the metal to give the novel cage complex cis-[Pt(PEt₃)₂(η²-P₄Sb₂C₄Bu^t₄]. The molecular structure of the cage shows it to contain a highly strained, dianionic ligand, [P₄Sb₂C₄Bu^t₄]^2–, which chelates the platinum through antimony and phosphorus atoms. Unusual features in the ³¹P-{¹H} NMR spectrum of the complex are described.