N‐Heterocyclic Carbene and Cyclic (alkyl)(amino)carbene Complexes of Titanium(IV) and Titanium(III)

The reaction of one and two equivalents of the N‐heterocyclic carbene IMes [IMes = 1,3‐bis(2,4,6‐trimethyl‐phenyl)imidazolin‐2‐ylidene] or the cyclic (alkyl)(amino)carbene cAACMe [cAACMe = 1‐(2,6‐diisopropyl‐phenyl)‐3,3,5,5‐tetra‐methylpyrrolidin‐2‐ylidene] with [TiCl4] in n‐hexane results in the formation of mono‐ and bis‐carbene complexes [TiCl4(IMes)] 1, [TiCl4(IMes)2] 2, [TiCl4(cAACMe)] 3, and [TiCl4(cAACMe)2] 4, respectively. For comparison, the titanium(IV) NHC complex [TiCl4(IiPrMe)] 5 (IiPrMe = 1,3‐diisopropyl‐4,5‐dimethyl‐imidazolin‐2‐ylidene) has been synthesized and structurally characterized. The reaction of [TiCl4(IMes)] 1 with PMe3 affords the mixed substituted complex [TiCl4(IMes)(PMe3)] 6. The reactions of [TiCl3(THF)3] with two equivalents of the carbenes IMes and cAACMe in n‐hexane lead to the clean formation of the titanium(III) complexes [TiCl3(IMes)2] 7 and [TiCl3(cAACMe)2] 8. Compounds 1–8 have been completely characterized by elemental analysis, IR and multinuclear NMR spectroscopy and for 2–5, 7 and 8 by X‐ray diffraction. Magnetometry in solution, EPR and UV/Vis spectroscopy and DFT calculations performed on 7 and 8 are indicative of a predominantly metal‐centered d1‐radical in both cases.