Reactions of Acetylenes with Noble Metal Carbonyl Halides. Part 12. Synthesis, Reactivity, Solution Structures by Multinuclear NMR studies of -alkenyl Platinum(II) Complexes. X-Ray Structural Analysis of [Pt(C(C6H5)=C(H)-C(=O)-Me)(CO)Cl] and [Pt(C(C6H5)=C(H)-C(=NC6H5)-Me)(PPh3)2Cl]