Preparation of Ti(IV) Fluoride <i>N</i>-Heterocyclic Carbene Complexes

1,3,4,5-Tetramethylimidazol-2-ylidene (LMe) and 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (LiPr) readily form complexes of trans-TiF4(LMe)2 (1) and of trans-TiF4(LiPr)2 (4) with TiF4 in THF, respectively. Complex 1 has been used as a precursor for preparing the Ti(IV) fluoride carbene complexes [{TiF2(LMe)(NEt2)}2(μ-F)2] (2) and (TiF4(LMe)2)(NacNacLi) (3) (NacNac = HC(CMeN(2,6-iPr2C6H3))2). Complex 2 was prepared from the reaction of 1−3 equiv of 1 and 1 equiv of Ti(NEt2)4 or by reacting TiF4 with Ti(NEt2)4 and LMe in toluene. Complex 3 has been prepared from 1 and NacNacLi in toluene. Reaction of 1 and AlMe3 in toluene results in ligand transfer and formation of AlMe3(LMe). Complex 4 is unstable in solution at room temperature and degrades with formation of [HLiPr][TiF5(LiPr)] (5). Complexes 1, 2·2CH2Cl2, 4, and 5 were characterized by single crystal X-ray structural analysis, elemental analysis, IR and NMR spectroscopy, and mass spectrometry. The relative basicities of LMe, LiPr, and the donor ligands THF, pyridine, DMSO, and H2O as well as [Cl]− and [F]− toward the Ti(IV) pentafluoride anion were established by NMR and confirmed by density functional theory (DFT) calculations. LMe and LiPr are more basic than the mentioned molecular donors and more basic than chloride, however less basic than fluoride.