Investigation of a possible solvent cage effect in the reduction of 4-aminocyclohexanone by a hydroxycyclopentadienyl ruthenium hydride

No solvent cage effect could be found in the reduction of 4-aminocyclohexanone 3 by Shvo's hydroxycyclopentadienyl ruthenium hydride 2. No preference was observed in the complex formation from trapping by aminoalcohol product 4 over external trapping by aminoketone 3 or by Shvo hydride 2. A solvent cage effect has previously been proposed to support an outer-sphere mechanism in the reduction of imines by 2; this was based on the observation that there was >90% preference for complexation of the newly formed amine over an external amine. Since alcohols form stronger hydrogen bonds than amines a larger cage effect would be expected in the present study. The lack of a cage effect in the present reduction suggests that the previous results from imine reduction require an additional explanation (other than a solvent cage effect).