Reactivity of the uranium(iv) carbene complex [U(BIPMTMS)(Cl)(μ-Cl)2Li(THF)2] (BIPMTMS = {C(PPh2NSiMe3)2}) towards carbonyl and heteroallene substrates: metallo-Wittig, adduct formation, C–F bond activation, and [2 + 2]-cycloaddition reactions

Abstract

The reactivity of the uranium(IV) carbene complex [U(BIPM^TMS)(Cl)(μ-Cl)₂Li(THF)₂] (1, BIPM^TMS = {C(PPh₂NSiMe₃)₂}) towards carbonyl and heteroallene substrates is reported. Reaction of 1 with benzophenone proceeds to give the metallo-Wittig terminal alkene product Ph₂CC(PPh₂NSiMe₃)₂ (2); the likely “UOCl₂” byproduct could not be isolated. Addition of the bulky ketone PhCOBu^t to 1 resulted in loss of LiCl, coordination of the ketone, and dimerisation to give [U(BIPM^TMS)(Cl)(μ-Cl){OC(Ph)(Bu^t)}]₂ (3). The reaction of 1 with coumarin resulted in ring opening of the cyclic ester and a metallo-Wittig-type reaction to afford [U{BIPM^TMS[C(O)(CHCHC₆H₄O-2)]-κ³-N,O,O′}(Cl)₂(THF)] (4) where the enolate product remains coordinated to uranium. The reaction of PhCOF with 1 resulted in C–F bond activation and oxidation resulting in isolation of [U(O)₂(Cl)₂(μ-Cl)₂{(μ-LiDME)OC(Ph)C(PPh₂NSiMe₃)(PPh₂NHSiMe₃)}₂] (5) along with [U(Cl)₂(F)₂(py)₄] (6). The reactions of 1 with tert-butylisocyanate or dicyclohexylcarbodiimide resulted in the isolation of the [2 + 2]-cycloaddition products [U{BIPM^TMS[C(NBu^t){OLi(THF)₂(μ-Cl)Li(THF)₃}]-κ⁴-C,N,N′,N′′}(Cl)₃] (7) and [U{BIPM^TMS[C(NCy)₂]-κ⁴-C,N,N′,N′′}(Cl)(μ-Cl)₂Li(THF)₂] (8). Complexes 2–8 have been variously characterised by single crystal X-ray diffraction, multi-nuclear NMR and FTIR spectroscopies, Evans method solution magnetic moments, variable temperature SQUID magnetometry, and elemental analyses.