EFFICIENT SUBSTITUTIONAL PHOTOCHEMISTRY OF A 3RD-ROW TRANSITION-METALBETA-P-DIKETONATE COMPLEX

Ultraviolet irradiation of Pt(acac)(2) (acac(-) is the anion of acetyl acetone) in nonaqueous solvents results in competing photochemical pro cesses whose relative importance depends upon the solution environment . In CH3CN containing a strong protonic acid, the complex undergoes cl ean, irreversible substitution of an acac(-) ligand by solvent to yiel d Pt(acac)(CH3CN)(2)(+) and free H(acac), The quantum yield for this p rocess is high (similar to 0.3) and independent of the irradiation wav elength, presence of dissolved oxygen, incident light intensity, acid concentration ((1-50) x 10(-3) M), and temperature. The primary photoc hemical step has been identified as heterolytic cleavage of a Pt-O bon d to yield an intermediate, I-1, formulated as a Pt(II) complex contai ning; a monodentate O-bonded acac(-) ligand and a coordinated solvent molecule. Protonation of this monodentate ligand labilizes the remaini ng bond to the metal and facilitates loss of H(acac). In nonacidified CH3CN, I-1 undergoes rechelation of the dangling acac(-) ligand to reg enerate Pl(acac)(2) in competition with secondary photolysis to form a complicated mixture oi products. Photolysis in CH2Cl2 and CH3OH resul ts in inefficient redox decomposition of Pt(acac)(2) to yield Pt metal and free H(acac). The role of solvent in determining the relative imp ortance of photosubstitution vr; photoredox decomposition is discussed . In addition, the mechanism by which Pt(acac)(2) functions as a photo initiator for the anionic polymerization of a 2-cyanoacrylate is recon sidered in light of the present study.