Insertion of alkynes into Pt-X bonds of square planar PtX_2(N^N) (X = Cl, Br, I) complexes

摘要

The reactivity with acetylene of PtX_2(Me_2phen) (X = Cl, Br, I) complexes has been investigated. Whereas the chlorido species PtCl_2(Me_2phen) exhibits negligible reactivity at short reaction times, the bromido and iodido species PtBr_2(Me_2phen) and PtI_2(Me_2phen) lead initially to formation of Pt(II) five-coordinate complexes, PtX_2(η~2-CHuCH)(Me_2phen), that evolve to four-coordinate alkenyl complexes of the type PtX(η1-E-CHvCHX)(Me_2phen). The alkenyl complexes, in the presence of excess acetylene, establish an equilibrium with the five-coordinate alkyne-alkenyl species PtX(η~1-E-CHvCHX)(η~2-CHuCH)(Me_2phen) (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(η~1-E-CHvCHX)(η~2-olefin)(Me_2phen) and PtX(η~1-E-CHvCHX)(CuO)(Me_2phen). 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(η~1-E-CHvCHBr)(η~2-CH_2vCH_2)(Me_2phen).