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(BIPMTMS)(Cl)(μ-Cl)2Li(THF)2] (1, BIPMTMS=C(PPh2NSiMe3)2) into [U(BIPMTMS)(Cl){CH(Ph)(SiMe3)}] (2), and addition of [Li{CH(SiMe3)(PPh2)}(THF)]/Me2NCH2CH2NMe2 (TMEDA) gave [U{C(SiMe3)(PPh2)}(BIPMTMS)(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)}(BIPMTMS)(Cl)][Li(2,2,2-cryptand)] (4) or [U{C(SiMe3)(PPh2)}(BIPMTMS)(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.