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(η(2)-CH≡CH)(Me2phen)], that evolve to four-coordinate alkenyl complexes of the type [PtX(η(1)-E-CH=CHX)(Me2phen)]. The alkenyl complexes, in the presence of excess acetylene, establish an equilibrium with the five-coordinate alkyne-alkenyl species [PtX(η(1)-E-CH=CHX)(η(2)-CH≡CH)(Me2phen)] (X = Br, I). The π-bonded acetylene can be exchanged with free olefins or C≡O, affording the new alkene-alkenyl or carbonyl-alkenyl complexes [PtX(η(1)-E-CH=CHX)(η(2)-olefin)(Me2phen)] and [PtX(η(1)-E-CH=CHX)(C≡O)(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(η(1)-E-CH[double bond, length as m-dash]CHBr)(η(2)-CH2=CH2)(Me2phen)].

The reactivity of [PtX(Mephen)] complexes (X = Cl, Br, I; Mephen = 2,9-dimethyl-1,10-phenanthroline) with terminal alkynes has been investigated. Although the dichlorido species [PtCl(Mephen)] exhibits negligible reactivity, the bromido and iodido derivatives lead in short time to the formation of five-coordinate Pt(ii) complexes of the type [PtX(Mephen)(η-CH[triple bond, length as m-dash]CR)] (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(Mephen)(η-CH[triple bond, length as m-dash]CR)]. This latter can further evolve to give an unusual, sparingly soluble square planar product where the former terminal alkyne is converted into a :C[double bond, length as m-dash]C(H)(R) moiety with the α-carbon bridging the Pt(ii) core with one of the two N-donors of coordinated Mephen. The final product [PtX{κ-N,C-(Z)-N[combining low line]1-N10-C[combining low line][double bond, length as m-dash]C(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.