Time-resolved laser spectroscopy and CIDNP experiments have been used to study the excitedstate interactions between photoinitiators and thioxanthones used as photosensitizers. The thioxanthones are shown to interact with a-morpholino-substituted acetophenone photoinitiators bearing various substituents on the benzoyl moiety. These interactions are discussed in terms of electron and energy transfer, the balance of which is dependent on the nature of the thioxanthone and the polarity of the medium.

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SummuryThe I3C-NMR. spectra of the series of complexes q6-naphthalene. CrL, (L=CO (l), PF, (2), PF20Me (6), P(OMe), (3), CloH8 ( = 3 L ) (4) and PMe, ( 5 ) ) are reported. Definite assignments of the I3C-NMR. resonances were made through the synthesis of [2,3,6, 7-2H,]-naphthalene complexes. The coordinated ring 13C-resonances are found to undergo a smooth transition to higher field with increasing donor character of the coligands L. A correlation of the coordination shifts with the reactivity of the coordinated naphthalene is proposed. In complexes containing strong acceptor ligands the naphthalene is activated to attack by nucleophiles. Sequential treatment of complexes 1-4, 6 and [CloH8FeC~H5]+ [PF6]-(7) with stabilized carbanions and I2 or Ce (1V)-salt yields a-substituted naphthalenes in the case of 1, 2, 6 and 7 but not in the case of 3 and 4. Treatment of 3 with an excess of HBF, results not in the expected metal protonation but in a novel ligand transformation to yield 6.Introduction. -When an arene is coordinated to Cr (CO),, profound changes in its reactivity occur [2] [3]: ring and benzylic H-atoms exhibit enhanced acidity, and typical arene reactions such as electrophilic aromatic substitutions are quenched. In contrast to this, the ring C-atoms are activated toward attack by nucleophiles [ 2 ] . These changes in reactivity are manifestations of the forceful electron withdrawing nature of the Cr(C0)3 component, and of the ability of this group to stabilize charged intermediates. The Umpotung of the arene in these complexes, combined with their stability and straightforward synthesis make them increasingly attractive for organic synthesis.Arene reactivity in metal complexes is affected by the nature of the metal and the electron density on the metal. Even within an oxidation state the latter can vary substantially depending on the donor/acceptor properties of the coligands. It has been demonstrated that the activating influence brought about by the Cr(CO), group is modified by the replacement of even one carbonyl group by another ligand. Alkylation at the benzylic position of alkyl arenes coordinated to