The influence of beta-diketones on the induction times for hydrolysis of zirconium(IV) alkoxides

The influence of low ligand/Zr mole ratios (rho = 0-0.1) of acetylacetone o n the hydrolysis of Zr(OPrn)(4) has been examined by investigating its effe ct on the induction time (t(i)) before precipitation commences in the syste m. A remarkable feature of the data is the large increase in the induction time (reduction in hydrolysis/condensation rate) caused by addition of acet ylacetone. This occurs even though only a maximum of one in eighty Zr-OR bo nds have reacted with ligand and are no longer available for hydrolysis or further condensation. The effects on t(i) of five other beta-diketones havi ng varying steric properties (trifluoroacetylacetone, hexafluoroacetylaceto ne, benzoylacetone, dibenzoylmethane and dipivaloylmethane) are compared wi th that of acetylacetone, under similar concentration conditions, with rho = 0.1. Each shows a greater effect than acetylacetone, the largest change b eing caused by dibenzoylmethane which, under the conditions used, increases the induction time by a factor of 26 relative to acetylacetone. A mechanis m rationalising the origin of the effect is discussed.