Solid and Crystalline State-specific Photoreaction of Organocobalt complexes with small molecules

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We have previously found solid state-specific and unidirectional photoisomerizations and chiral-crystal-lattice-controlled (β→α and γ→β→α) photoisomerizations of (ω-substituted alkyl)bis-(dimethylglyoximato)cobalt(III) complexes (ω=β or γ) which occur only in the solid-state and crystalline- state (enantioselectivities:〜91%ee). The reactions have many excellent characteristics, but some disadvantages exist as well. To improve these disadvantages and also to explore novel reactions, especially intermolecular reactions, it was considered essential to modify the peripheral position on in-plane ligands.Thus, we examined the photoreactions of (ω-substituted alkyl)cobaloxime complexes having in-plane ligands modified with bulky substituents (R = phenyl or furyl) which resulted in higher enantioselectivities (〜85%ee in the photoisomerization of β-methoxycarbonylethyl complexes) as well as in higher reaction rates. When substituent X is a group to stabilize the radical at the carbon bonded to … More X and also to destabilize the Co-C bond of α-alkyl complex (X=Ph, OPh etc.) sterically and/or electronically, a unique (solid-state-specific) dioxygenation reaction took place efficiently only after (ω→α) isomerization. (When the substituent is a group to stabilize both the Co-C bond and the alkyl radical, isomerization occurred to give α-substituted alkyl complex which is considerably difficult to convert into the dioxygen-insertion product). Based on the X-ray structural studies, the reaction rate was found to be primarily controlled by the volume and shape of the reaction cavity surrounding a reactive group. The dioxygen-insertion reaction proceeded enantioselectively (-74%ee) in cases of chiral amine-coordinated (3-phenylpropyl)cobaloximes (X = Ph), in spite of the intermolecular radical reaction.The occurrence of asymmetric induction in isomerization and the succeeding oxygenation, both of which proceed through radical intermediates, can be said to be one of the most noteworthy characteristics of solid and crystalline-state reactions. Less