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

Reaction of [Ce(NR(2))(3)] (R = SiMe(3)) with LiNO(3) 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)-O(2)NO)(NR(2))(3)] (1) in 38% yield. Photolysis of 1 at 380 nm affords [Li(2,2,2-cryptand)][Ce(O)(NR(2))(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)[(μ(3)-O){Ce(μ-O)(NR(2))(2)}(3)] (3) and [Li(2,2,2-cryptand)][Ce(OSiMe(3))(NR(2))(3)] (4). Their identities were confirmed by X-ray crystallography. Complex 4 can also be prepared via reaction of [Ce(NR(2))(3)] with LiOSiMe(3) 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 NO(2), 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)(OSiMe(3))(NR(2))(3)], followed by 1e(–) reduction to form 4. Alternatively, complex 4 could form directly via ·SiMe(3) abstraction by 2.