Chelating P,N versus P,P Ligands:  Differing Reactivity of Donor-Stabilized Pt(η²-PhC⋮CPh) Complexes Toward Diphenylacetylene

The thermal activation of the η²-diphenylacetylene complex (PN)Pt(η²-PhC⋮CPh) (1) (PN = (diisopropylphosphinodimethylamino)ethane leads to the formation of the platinacyclopenta-2,4-diene compound (PN)Pt(CPh)₄ (3), which can be quantitatively obtained by reaction of 1 with 1 equiv of diphenylacetylene. Two transient intermediates are observed by ³¹P NMR spectroscopy during the course of the latter reaction. These species were independently synthesized and characterized. Hexaphenylbenzene is catalytically generated by reaction of 1 in the presence of excess diphenylacetylene. In contrast, no reaction of diphenylacetylene with (dippe)Pt(η²-PhC⋮CPh) (2) (dippe = bis(diisopropylphosphino)ethane) was observed.