REACTIONS OF ACETYLENES WITH NOBLE-METAL CARBONYL HALIDES .12. SYNTHESIS, REACTIVITY, AND SOLUTION STRUCTURES BY MULTINUCLEAR NMR-STUDIES OF SIGMA-ALKENYLPLATINUM(II) COMPLEXES - X-RAY STRUCTURE-ANALYSIS OF [PT(C(C6H5)=C(H)C(=O)ME)(CO)CL] AND [PT(C(C6H5)=C(H)C(=NC6H5)ME)(PPH3)2CL]