Photochemistry of η 5 cylclopentadienylcobalt) tricarbonyl, tris(η 5-cyclopentadienylcobalt monocarbonyl) and tetra(η 5-cyclopentadienylcobalt) dicarbonyl*

Abstract

The photolysis of η 5 -C 5H 5Co(CO) 2 (XIII) has been found to produce a new, reactive binuclear complex (η 5 -C 5H 5) 2(CO) 3 as a primary photoproduct; this material has been assigned structure XVII. The material is very liable thermally and decomposes in solution at ambient temperature, releasing a molecule of XIII and forming trinuclear complex (η 5 -C 5H 5CoCO) 3 (XVIII). This molecule is also thermally unstable, and once again decomposes (130°C) with extrusion of XIII, leading in this case to tetranuclear complex (η 5 -C 5H 5) 4Co 4(CO) 2 (XIX). It is produced that the driving force or cluster complex decomposition arises from the expulsion of a molecule of relatively stable mononuclear metal carbonyl, leaving behind a coordinately unsaturated intermediate which (in the absence of other reagents) oligomerizes to form a higher, coordinatively saturated cluster. This suggests that in the presence of organic ligands, such decompositions might give rise to active catalysts; in agreement with this idea primarily studies have shown that complexes XVII and XVIII catalyze acetylene trimerization reactions at temperatures much lower than that required factor catalysis by XIII.