Facial-meridional isomerization of some tris-(.BETA.-diketonato)ruthenium(III) complexes.

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Nine complexes of type [RuII(R–CO–CH–CO–R′)3] were examined; only those with R=–CF3 underwent the facial–meridional isomerization in N,N-dimethylformamide (DMF) at the reflux temperature. Qualitative examination of the occurrence of isomerization of the complex with R=–CF3 and R′=–CH3 in various solvents supports the presence of solvent-assisted bond-rupture mechanisms. This complex did not isomerize photochemically in acetonitrile. The isomerization of four complexes with R=–CF3 and R′=–CH3, –C2H5, –CH-(CH3)2, and –C(CH3)3 in DMF at 70–100 °C followed the reversible first-order kinetics. The equilibrium constants, which were temperature independent, decreased from 4.27 to 1.74 in the order cited above. The enthalpies of activation, ranging from 66.4 kJ mol−1 (R′=–CH(CH3)2) to 96.0 kJ mol−1 (R′=–CH3), depended linearly on the atomic bond populations of the Ru–O bonds calculated by means of a modified extended Hückel method.
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