Silyl-Phosphino-Carbene Complexes of Uranium(IV)

Abstract

Unprecedented silyl-phosphino-carbene complexes of uranium(IV) are presented, where before all covalent actinide-carbon double bonds were stabilised by phosphorus(V) substituents or restricted to matrix isolation experiments. Conversion of [U(BIPM^TMS )(Cl)(μ-Cl)₂ Li(THF)₂ ] (1, BIPM^TMS =C(PPh₂ NSiMe₃ )₂ ) into [U(BIPM^TMS )(Cl){CH(Ph)(SiMe₃ )}] (2), and addition of [Li{CH(SiMe₃ )(PPh₂ )}(THF)]/Me₂ NCH₂ CH₂ NMe₂ (TMEDA) gave [U{C(SiMe₃ )(PPh₂ )}(BIPM^TMS )(μ-Cl)Li(TMEDA)(μ-TMEDA)_0.5 ]₂ (3) by α-hydrogen abstraction. Addition of 2,2,2-cryptand or two equivalents of 4-N,N-dimethylaminopyridine (DMAP) to 3 gave [U{C(SiMe₃ )(PPh₂ )}(BIPM^TMS )(Cl)][Li(2,2,2-cryptand)] (4) or [U{C(SiMe₃ )(PPh₂ )}(BIPM^TMS )(DMAP)₂ ] (5). The characterisation data for 3-5 suggest that whilst there is evidence for 3-centre P-C-U π-bonding character, the U=C double bond component is dominant in each case. These U=C bonds are the closest to a true uranium alkylidene yet outside of matrix isolation experiments.

Keywords: alkylidenes; carbenes; metal-ligand multiple bonding; phosphines; uranium.