CHEMICAL INTERCONVERSIONS IN THE SYSTEM TP-ASTERISK-ZN CO2/ALCOHOL [TP-ASTERISK EQUALS SUBSTITUTED TRIS(PYRAZOLYL)BORATE]/

The zinc hydroxide complexes TpZn-OH with Tp(Cum,Me) = tris (3-cumeny l-5-methylpyrazolyl)borate and Tp(tBu,Me) = tris(3-tert-butyl-5-methyl pyrazolyl)borate can be converted to the alkyl carbonate complexes Tp Zn-OCOOR by reaction with dialkyl dicarbonates or with alcohol and CO2 . An alternative formation reaction is the treatment of the pyrazolyl berate with zinc perchlorate and potassium carbonate in alcohol. The i nterconversion between Tp(Cum,Me) Zn-OH and Tp(Cum,Me)Zn-OCOOMe in met hanol-containing solution can be repeatedly performed in both directio ns by bubbling either CO2 or N-2 through the solution. The alkyl carbo nate complexes show a variable sensitivity towards hydrolytic destruct ion with reformation of the hydroxide complexes. The complex:es Tp(tBu ,Me)Zn-OCOOR (R = Me, Et) release CO2 under high vacuum to form the al koxide complexes Tp(tBu,Me)-Zn-OR, which could not be obtained pure du e to their extreme water sensitivity. Indirect evidence for their exis tence 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 hy droxide complexes catalyse the formation of diethyl carbonate from eth anol and CO2.