Synthesis of a terminal Ce(iv) oxo complex by photolysis of a Ce(iii) nitrate complex

摘要

Reaction of [Ce(NR2)3] (R = SiMe3) with LiNO3 in THF, in the presence of 2,2,2-cryptand, results in the formation of the Ce(iii) “ate” complex, [Li(2,2,2-cryptand)][Ce(κ ²-O2NO)(NR2)3] (>1) in 38% yield. Photolysis of >1 at 380 nm affords [Li(2,2,2-cryptand)][Ce(O)(NR2)3] (>2), in 33% isolated yield after reaction work-up. Complex >2 is the first reported example of a Ce(iv) oxo complex where the oxo ligand is not supported by hydrogen bonding or alkali metal coordination. Also formed during photolysis are [Li(2,2,2-cryptand)]2[(μ3-O){Ce(μ-O)(NR2)2}3] (>3) and [Li(2,2,2-cryptand)][Ce(OSiMe3)(NR2)₃] (>4). Their identities were confirmed by X-ray crystallography. Complex >4 can also be prepared via reaction of [Ce(NR₂)₃] with LiOSiMe₃ in THF, in the presence of 2,2,2-cryptand. When synthesized in this fashion, >4 can be isolated in 47% yield. To rationalize the presence of >2, >3, and >4 in the reaction mixture, we propose that photolysis of >1 first generates >2 and NO₂, via homolytic cleavage of the N–O bond in its nitrate co-ligand. Complex >2 then undergoes decomposition via two separate routes: (1) ligand scrambling and oligomerization to form >3; and, (2) abstraction of a trimethylsilyl cation to form a transient Ce(iv) silyloxide, [Ce^IV(OSiMe₃)(NR₂)₃], followed by 1e^– reduction to form >4. Alternatively, complex >4 could form directly via ·SiMe₃ abstraction by >2.