Synthesis of a terminal Ce(IV) oxo complex by photolysis of a Ce(III) nitrate complex

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(k(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[(mu(3)-O){Ce(mu-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.