Synthesis and structural characterization of the first stable cycloheptatrienyl metal complexes bearing a CF3 moiety. DFT investigations of structures, energetics, NBO charges, and frontier MOs of W-CF3 and Mo-CF3 with η7-C7H7 and η5-C5H5

Abstract

Thermally stable cycloheptatrienyl metal complexes bearing the trifluoromethyl moiety are reported for the first time. While the syntheses, properties and structural characterizations of transition metal complexes of the type [(η5–C5H5)MLnCF3] are well known in organometallic chemistry, analogous chemistry of the elusive [(η7–C7H7)MLnCF3] complexes was just recently disclosed by the syntheses of Mo complexes such as [(η7–C7H7)Mo(CO)(PMe3)CF3] (I). Nevertheless, complex I and similar complexes were found to be of extreme thermal instability, indicative in the fact that their purification and isolations require low temperature chromatography. Advancing past the stability hindrance, we report herein the syntheses of the W complexes [(η7-C7H7)W(CO)2CF3] (II), and [(η7–C7H7)W(CO)(PMe3)CF3] (III), which are found to be indefinitely thermally stable, a fact that allowed the study of complex II by X-ray crystallography. In addition, the first DFT studies on I-III, as well as their η5–C5H5 analogues, were performed both in the gas phase and with the implicit diethyl ether effects included, the structures, energetics, NBO charges, and frontier MOs were investigated. For the η7-C7H7-complexes, the metal change from Mo to W was shown to significantly increase the singlet–triplet energy difference, whereas for the η5-C5H5-complexes the metal change essentially has no effect on this difference, which is in line with the experimental findings. Comparison of the calculated structure of complex II with its X-ray structure showed quite reasonable agreement with the experimental data. The negative NBO charges on W in the C5H5-complexes were calculated to be significantly lower than in the C7H7-complexes, which again is completely in line with the stability profile of the complex.