Insertion of terminal alkyne into Pt–N bond of the square planar [PtI2(Me2phen)] complex

The reactivity of [PtX2(Me2phen)] complexes (X = Cl, Br, I; Me2phen = 2,9-dimethyl-1,10-phenanthroline) with terminal alkynes has been investigated. Although the dichlorido species [PtCl2(Me2phen)] exhibits negligible reactivity, the bromido and iodido derivatives lead in short time to the formation of five-coordinate Pt(II) complexes of the type [PtX2(Me2phen)(η2-CHuCR)] (X = Br, I; R = Ph, n-Bu), in equilibrium with the starting reagents. Similar to analogous complexes with simple acetylene, the five coordinate species can also undergo dissociation of an halido ligand and formation of the transient square-planar cationic species [PtX(Me2phen)(η2-CHuCR)]+. This latter can further evolve to give an unusual, sparingly soluble square planar product where the former terminal alkyne is converted into a :CvC(H)(R) moiety with the α-carbon bridging the Pt(II) core with one of the two N-donors of coordinated Me2phen. The final product [PtX2{κ2-N,C-(Z)-N̲1–N10–C̲vC(H)(R)}] (N1–N10 = 2,9-dimethyl-1,10-phenanthroline; X = Br, I) contains a Pt–N–C–C–N–C six-membered chelate ring in a square planar Pt(II) coordination environment.