Chemical Interconversions in the System TP^*Zn/CO₂/Alcohol [Tp^* = Substituted Tris(pyrazolyl)borate]

Abstract

Abstract The zinc hydroxide complexes Tp * Zn–OH with Tp Cum,Me = tris(3‐cumenyl‐5‐methylpyrazolyl)borate and Tp tBu,Me = tris(3‐tert‐butyl‐5‐methylpyrazolyl)borate can be converted to the alkyl carbonate complexes Tp * Zn–OCOOR by reaction with dialkyl dicarbonates or with alcohol and CO 2 . An alternative formation reaction is the treatment of the pyrazolyl borate with zinc perchlorate and potassium carbonate in alcohol. The interconversion between Tp Cum,Me Zn–OH and Tp Cum,Me Zn–OCOOMe in methanol‐containing solution can be repeatedly performed in both directions by bubbling either CO 2 or N 2 through the solution. The alkyl carbonate complexes show a variable sensitivity towards hydrolytic destruction with reformation of the hydroxide complexes. The complexes Tp tBu,Me Zn–OCOOR (R = Me, Et) release CO 2 under high vacuum to form the alkoxide complexes Tp tBu,Me ‐Zn–OR, which could not be obtained pure due to their extreme water sensitivity. Indirect evidence for their existence is also obtained by the reaction between Tp Cum,Me Zn–OCOOMe and methyl iodide, forming Tp Cum,Me Zn–I and dimethyl ether. The Zinc hydroxide complexes catalyse the formation of diethyl carbonate from ethanol and CO 2 .