The zinc hydroxide complexes Tp*Zn-OH with TpCUmjMe = tris(3-cumenyl-5-methylpyrazolyl)borate and TptBurMe = 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 COz. An alternative formation reaction is the treatment of the pyrazolyl borate with zinc perchlorate and potassium carbonate in alcohol. The interconversion between TpcUmrMeZn-OH and TpCUmrMeZn-OCOOMe in methanol-containing solution can be repeatedly performed in both directions by bubbling either C 0 2 or N2 through the solution. The alkyl carbonate complexes show a variable sensitivity towards hydrolytic destruction with reformation of the hydroxide complexes. The complexes Tp'Ru,MeZn -0COOR (R = Me, Et) release C 0 2 under high vacuum to form the alkoxide complexes TptBurMeZn-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 TpCunl,MeZn--OCOOMe and methyl iodide, forming TpC"nl~MeZn-I and dimethyl ether. The zinc hydroxide complexes catalyse the formation of diethyl carbonate from ethanol and C 0 2 .

No abstract