The classical metallocenes, ferrocene and ruthenocene, dissolve readily in neat ethyl 2-cyanoacrylate (CA) monomer. The electronic spectra of the resulting solutions display a near-ultraviolet absorption band assigned as a charge-transfer-to-solvent (metallocene → CA) transition. Irradiation into this band causes the one-electron oxidation of the metallocene to the corresponding metallocenium cation accompanied by reduction of CA to its radical anion. Addition of the latter species to CA initiates the anionic polymerization of the electrophilic monomer. The progress of photoinitiated polymerization was monitored in real time by attenuated total reflectance infrared spectroscopy.

No abstract

Ultraviolet irradiation of Pt(acac)2 (acac- is the anion of acetylacetone) in nonaqueous solvents results in competing photochemical processes whose relative importance depends upon the solution environment. In CH3CN containing a strong protonic acid, the complex undergoes clean, irreversible substitution of an acac- ligand by solvent to yield Pt(acac)(CH3CN)2 + and free H(acac). The quantum yield for this process is high (∼0.3) and independent of the irradiation wavelength, presence of dissolved oxygen, incident light intensity, acid concentration ((1−50) × 10-3 M), and temperature. The primary photochemical step has been identified as heterolytic cleavage of a Pt−O bond to yield an intermediate, I 1 , formulated as a Pt(II) complex containing a monodentate O-bonded acac- ligand and a coordinated solvent molecule. Protonation of this monodentate ligand labilizes the remaining bond to the metal and facilitates loss of H(acac). In nonacidified CH3CN, I 1 undergoes rechelation of the dangling acac- ligand to regenerate Pt(acac)2 in competition with secondary photolysis to form a complicated mixture of products. Photolysis in CH2Cl2 and CH3OH results in inefficient redox decomposition of Pt(acac)2 to yield Pt metal and free H(acac). The role of solvent in determining the relative importance of photosubstitution vs photoredox decomposition is discussed. In addition, the mechanism by which Pt(acac)2 functions as a photoinitiator for the anionic polymerization of a 2-cyanoacrylate is reconsidered in light of the present study.