Pyrazolylborate-zinc alkoxide complexes. 2. Solvolytic chemistry

The methoxides Tp(Ph,Me)Zn-OMe and Tp(cum,Me)Zn-OMe were tested for their reactivity toward substrates that are hydrolytically cleaved with Tp*Zn-OH complexes. They do not induce the cleavage of nonactivated esters, phosphoesters, lactones, or lactams. They cleave the P-O-P linkage of tetraalkylpyrophosphates, but not the C-O-C linkage of dialkyl pyrocarbonates. Transesterification of esters and phosphoesters occurs when they are activated as p-nitrophenolates. The most facile cleavage occurs for thiolate functions present in dithioesters, thiolactones, and trithiocarbonates. These findings indicate that, while the leaving group properties of the methoxide unit are essential, it is the strength of the resulting zinc-substrate bonds that decides upon the occurrence or nonoccurrence of the cleavage reactions.