Cobalt(II) tri-tert-butoxysilanethiolates:: in search of models for catalytic metal site of liver alcohol dehydrogenase

The reaction of dimeric [Co{SSi((OBu)-Bu-t)(3)}(2)(NH3)](2) (1) with 2-picoline at 0degreesC leads to the formation of a thiolate complex [Co{SSi((OBu)-Bu-t)(3)}(2)(NH3)(2-Pic)] (3), with two different nitrogen ligands in the cobalt(II) coordination sphere. Dissolution of 1 in acetonitrile gives one cobalt(II) thiolate complex with two ammine ligands bonded to metal: [Co{SSi((OBu)-Bu-t)(3)}(2)(NH3)(2)].MeCN (4). A second, unique, aqua-ligated cobalt(II) thiolate - [Co{SSi((OBu)-Bu-t)(3)}(3)(H2O)](-) +HNEt3 (5) - forms when CoCl2 reacts with an excess of ((BuO)-Bu-t)(3)SiSH in the presence of triethylamine in water. The structures of 3,4 and 5 were determined by X-ray structure methods, revealing a distorted tetrahedral arrangement of ligands around cobalt. Under normal conditions, all three complexes are unstable. 3 loses ammonia to give stable [Co{SSi((OBu)-Bu-t)(3)}(2)(2-Pic)] (2). A reverse reaction is also possible. Moreover, 2 is able to capture water, and there is spectral evidence that a complex [Co{SSi((OBu)-Bu-t)(3)}(3)(H2O)(2-Pic)] with a CoNOS2 core, mimicking the cobalt-substituted liver alcohol dehyrogenase active site, is formed in solution. Copyright (C) 2002 John Wiley Sons, Ltd.