Silyl‐Phosphino‐Carbene Complexes of Uranium(IV)

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(PPh 2 NSiMe 3 ) 2 ) into [U(BIPM TMS )(Cl){CH(Ph)(SiMe 3 )}] ( 2 ), and addition of [Li{CH(SiMe 3 )(PPh 2 )}(THF)]/Me 2 NCH 2 CH 2 NMe 2 (TMEDA) gave [U{C(SiMe 3 )(PPh 2 )}(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(SiMe 3 )(PPh 2 )}(BIPM TMS )(Cl)][Li(2,2,2‐cryptand)] ( 4 ) or [U{C(SiMe 3 )(PPh 2 )}(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.