A Phototunable Dinuclear Catalyst

The bisbarium complex of azobis(berizo-18-crown-6) ether 28 exhibits catalytic properties that can be reversibly activated-deactivated by light-induced changes in molecular geometry [32]. The azobenzene unit is a well-known photochromic [33], often used in the construction of molecular switches [34]. 

The bis-barium complex of pure trans-28 (0.10 mM) increases the rate of ethano-lysisof29 (65/35 EtOH/MeCN, 1 mM Me4NOEt, 25 °C) by 230-fold. The corresponding figures for quasi-trans-28-Ba2 and quasi-cis-28-Ba2 are 420- and 1280-fold, respectively. Thus, the behavior of trans and ds isomeric catalysts based on azobenzene closely parallels the behavior of the corresponding stilbene derivatives 26 and 27, in that in both cases the ds form is a superior catalyst in the cleavage of anilide 29. 

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