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

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-CHuCH)(Me2phen)], that evolve to four-coordinate alkenyl complexes of the type [PtX(η1-E-CHvCHX)(Me2phen)]. The alkenyl complexes, in the presence of excess acetylene, establish an equilibrium with the five-coordinate alkyne–alkenyl species [PtX(η1-E-CHvCHX)(η2-CHuCH)(Me2phen)] (X = Br, I). The π-bonded acetylene can be exchanged with free olefins or CuO, affording the new alkene–alkenyl or carbonyl–alkenyl complexes [PtX(η1-E-CHvCHX)(η2-olefin)(Me2phen)] and [PtX(η1- E-CHvCHX)(CuO)(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-CHvCHBr)(η2-CH2vCH2)(Me2phen)]