Probing the Reactivity of the CeO Multiple Bond in a Cerium(IV) Oxo Complex

The reactivity of
the cerium­(IV) oxo complex [(LOEt)2CeIV(O)­(H2O)]·MeC­(O)­NH2 (1; LOEt– = [CoCp­{P­(O)­(OEt)2}3]−, where Cp = η5-C5H5) toward electrophiles and Brønsted
acids has been investigated. The treatment of 1 with
acetic anhydride afforded the diacetate complex [CeIV(LOEt)2(O2CMe)2] (2). The reaction of 1 with B­(C6F5)3 yielded [CeIV(LOEt)2(Me2CONH2)2]­[B­(C6F5)3(OH)]2 (3), in which
the [B­(C6F5)3(OH)]− anions are H-bonded to the O-bound acetamide ligands. The treatment
of 1 with HCl and HNO3 afforded [CeIV(LOEt)2Cl2] and [CeIV(LOEt)2(NO3)2], respectively.
Protonation of 1 with triflic acid (HOTf) gave the diaqua
complex [CeIV(LOEt)2(H2O)2]­(OTf)2 (4), in which the triflate
anions are H-bonded to the two aqua ligands. The treatment of 1 with phenol afforded the phenoxide complex [CeIV(LOEt)2(OPh)2] (5).
The oxo-bridged bimetallic complex [(LOEt)2(Me2CONH2)­CeIV(O)­NaLOEt] (6) with the Ce–Ooxo and Na–Ooxo distances of 1.953(4) and 2.341(4) Å, respectively,
was obtained from the reaction of 1 with [NaLOEt]. Density functional theory calculations showed that the model complex
[(LOMe)2CeIV(Me2CONH2)­(O)­NaLOMe] (6A; LOMe– = [CoCp­{P­(O)­(OMe)2}3]−) contains a polarized CeO multiple bond. The energy for
dissociation of the {NaLOMe} fragment from 6A in acetonitrile was calculated to be +33.7 kcal/mol, which is higher
than that for dissociation of the H-bonded acetamide from [(LOMe)2CeIV(O)­(H2O)]·MeC­(O)­NH2 (1A) (calculated to be +17.4 kcal/mol). In hexanes
containing trace water, complex 1 decomposed readily
to a mixture of a tetranuclear cerium­(IV) oxo cluster, [CeIV4(LOEt)4(μ4-O)­(μ2-O)4(μ2-OH)2] (7), and a cerium­(III) complex, [CeIII(LOEt)2(H2O)2]­[LOEt] [8(LOEt)], whereas the cerium/sodium oxo complex 6 is stable under the same conditions. The crystal structures
of 3, 4·H2O, 6, and 8(LOEt) have been determined.