Insertion of alkynes into Pt–X bonds of square planar [PtX2(N^N)] (X = Cl, Br, I) complexes

Abstract

The reactivity with acetylene of [PtX₂(Me₂phen)] (X = Cl, Br, I) complexes has been investigated. Whereas the chlorido species [PtCl₂(Me₂phen)] exhibits negligible reactivity at short reaction times, the bromido and iodido species [PtBr₂(Me₂phen)] and [PtI₂(Me₂phen)] lead initially to formation of Pt(II) five-coordinate complexes, [PtX₂(η²-CHCH)(Me₂phen)], that evolve to four-coordinate alkenyl complexes of the type [PtX(η¹-E-CHCHX)(Me₂phen)]. The alkenyl complexes, in the presence of excess acetylene, establish an equilibrium with the five-coordinate alkyne–alkenyl species [PtX(η¹-E-CHCHX)(η²-CHCH)(Me₂phen)] (X = Br, I). The π-bonded acetylene can be exchanged with free olefins or CO, affording the new alkene–alkenyl or carbonyl–alkenyl complexes [PtX(η¹-E-CHCHX)(η²-olefin)(Me₂phen)] and [PtX(η¹-E-CHCHX)(CO)(Me₂phen)]. The five-coordinate geometry of the alkyne–alkenyl and alkene–alkenyl complexes was assessed from NMR data and is fully consistent with that of a previously determined X-ray structure of [PtBr(η¹-E-CHCHBr)(η²-CH₂CH₂)(Me₂phen)].