The reactions of the aromatic ketones benzophenone and 9-fluorenone with trivalent [LnL3] complexes [Ln = Ce, Pr; L = N(SiMe3)2, C5H5 (Cp)] produce highly colored solutions in toluene. Characterization of these complexes by X-ray diffraction revealed them to be monoadducts of the form [LnL3(ketone)]. The crystallographically determined C–O bonds of these complexes are longer than those of the free ketones. Significant ligand-to-metal charge transfer is also indicated by the ν(C=O) vibration of the coordinated ketone, which appears at lower wavelength. Solution-based 1H NMR spectroscopy showed paramagnetic spectra of complexes Ln[N(SiMe3)2]3(ketone) and Ln(C5H5)3(ketone), which further supports this finding.