Reactivity of the uranium(IV) carbene complex [U(BIPM(TMS))(Cl)(μ-Cl)₂Li(THF)₂] (BIPM(TMS) = {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 Ph2C=C(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)]-κ(3)-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}]-κ(4)-C,N,N',N''}(Cl)3] (7) and [U{BIPM(TMS)[C(NCy)2]-κ(4)-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.