Intrinsic reactivity of a uranium metallacyclopropene toward unsaturated organic molecules

Abstract

The uranium metallacyclopropene (η⁵-C₅Me₅)₂U[η²-C₂(SiMe₃)₂] (1) reacts with various small unsaturated organic molecules. For example, replacement of bis(trimethylsilyl)acetylene occurs when complex 1 is exposed to alkynes, conjugated alkenes, nitriles and quinones. Reaction of 1 with internal phenyl(alkyl)acetylene PhCCMe selectively yields the C_s symmetric uranium metallacyclopentadiene (η⁵-C₅Me₅)₂U[η²-C(Ph)C(Me)–C(Ph)C(Me)] (6) after the loss of bis(trimethylsilyl)acetylene, while treatment of 1 with phenyl(silyl)acetylenes (PhCCR, R = SiHMe₂, SiMe₃) gives the corresponding C_2v symmetric isomers (η⁵-C₅Me₅)₂U[η²-C(R)C(Ph)–C(Ph)C(R)] (R = SiHMe₂ (7), SiMe₃ (8)). Furthermore, while no deprotonation occurs between complex 1 and pyridine derivatives, cyclohexanone can be inserted into the uranium metallacyclopropene moiety of 1 to yield the five-membered, heterocyclic complex (η⁵-C₅Me₅)₂U[OC(CH₂)₅(C₂(SiMe₃)₂)] (14) in quantitative conversion. Density functional theory (DFT) studies have been performed to complement the experimental studies.