PHOTOCHEMICAL-REACTION OF OS3(CO)12 WITH DIPHENYLACETYLENE - SYNTHESIS AND STRUCTURE OF TRICARBONYL-(ETA-4-2,3,4,5-TETRAPHENYLCYCLOPENTA-2,4-DIEN-1-ONE)OSMIUM

Photolysis of OS3(CO)12 in the presence of excess diphenylacetylene gives the title compound (eta4-C4Ph4CO)OS(CO)3 (1C) in moderate yields. Compound 1c represents the hitherto missing member of the iron-triad (eta4-C4Ph4CO)M(CO)3 series. The solid-state structure of 1c was determined and compared to that of the ruthenium analogue. A triad comparison of the spectroscopic features (C-13 NMR and CO stretching frequencies) is presented. The order of the C-13 coordination shifts, inner diene carbons > outer diene carbons, is the reverse of what is typically seen for (eta4-diene) M (CO)3 complexes. This is explained by polarization of the ketonic carbonyl upon coordination. The ''second-row anomaly'' of ruthenium is reflected in the spectroscopic data; accordingly, the ruthenium complex is the most reactive in the triad.