The effect of fluorinated substituents on some solution properties of metal acetylacetonates

Abstract

The effect of the CF 3 group upon substitution for a CH 3 group is noted in three different solution studies of acetylacetone (AA), trifluoroacetylacetone (TFA), and hexafluoroacetylacetone (HFA) and their corresponding metal complexes. The lability of dimethyl sulfoxide (DMSO) in exchanging from the axial positions of Ni(AA) 2 complexes is dramatically altered by substitution of CF 3 groups with k‡( AA)>k‡( TFA)>k‡( HFA) . The diminution in rate of exchange can be explained by the electron withdrawal of the CF 3 group. A good fit of the rate constants to the Hammett equation is noted. The substitution of a CF 3 group for a CH 3 group causes the bromination of Al(TFA) 3 by N-bromosuccinimide to be about 2800 times slower than Al(AA) 3( k = 6.7 ± 0.5 sec −1 at 25°C). The 13 C and 1 H NMR chemical shifts of AA, TFA and HFA were measured and compared with electron densities for the three compounds calculated by the INDO formalism. The 1H and methine 13C shifts show a linear correlation with electron density. The other 13C chemical shifts can best be explained by assuming that AA is quasi-aromatic and the paramagnetic effect is dominant.