DESIGN OF TRANSITION-METAL COMPLEXES WITH HIGH QUANTUM YIELDS FOR LIGAND SUBSTITUTION - EFFICIENT PHOTOCHEMICAL CHELATE RING-CLOSURE IN CYCLOPENTADIENYLMANGANESE TRICARBONYL DERIVATIVES

The quantum yields for photosubstitution of (eta(5)-C(5)H(4)R)Mn(CO)(3 ) (R = H, COCH3, COCH2-OCH3, COCH2SCH3, CO(CH2)(2)SCH3, CH2CO2CH3, (CH 2)(2)CO2CH3)) in heptane for 337 nm irradiation are 0.67, 0.82, 0.64, 1.00, 0.82, 0.80, and 1.05, respectively. The yields of ring-closed pr oducts were determined for the sulfur-containing complexes while the y ields of substitution with dispersed ligands were determined for the r emaining complexes since the ring-closed products were not stable. In contrast to a previous study for cyclopentadienyl-manganese complexes the quantum yields were found to change with the structure of a substi tuent. The results for R = COCH2SCH3 and (CH2)(2)CO2CH3 are apparently the first bona fide examples of unit quantum yields for organometalli c complexes in solution. It is proposed that after CO dissociation tha t selected ring substituents can trap the metal center before CO can r ecombine with the metal.