Synthesis, Electrochemical, and Computational Studies of Organocerium(III) Complexes with Ce–Aryl Sigma Bonds

A set of organolanthanide(III) complexes
featuring Ce(III)–Caryl σ-bonds have been
synthesized and characterized.
The syntheses follow salt metathesis reactions of the salts: ortho-lithiated oxazoline (Li-ortho-oxa)
(L1) and Li2-biphenyl (L2) with
the corresponding metallocene precursors: 1-Ln ([(C5Me5)2LnKCl2(THF)]n) Ln = La and Ce, 2-La, ([(C5Me4SiMe3)2LaKCl2(THF)]n) and 2-Ce ([((C5Me4SiMe3)2CeKCl2)(Et2O)0.5]n). Electrochemical
studies were performed for the organolanthanide(III) complexes. Reversible
Ce(III)/Ce(IV) redox couples were observed for (C5Me5)2Ce(κ2-ortho-oxa) (3-Ce) and [Li(DME)3][(C5Me5)2Ce(biphen)] (5-Ce) complexes.
However, complex (C5Me4(SiMe3))2Ce(κ2-ortho-oxa) (4-Ce) showed an irreversible Ce(III/IV) oxidation wave. A
DFT-computed redox potential for 3-Ce showed good agreement
with experiment. For 5-Ce, calculations indicated that
the redox potential may be influenced strongly by speciation changes
associated with the Li(DME)3+ cation becoming
outer-sphere. Bonding analysis suggests strong bond polarization in
the title complexes (3-Ce and 5-Ce) with
weights of 7–8% from Ce in the Ce−Caryl donation-bond
orbitals. Attempts to isolate Ce(IV) species from these complexes
resulted into the decomposition of the products into unidentified
Ce(III) species, indicating that the bulky and electron-donating cyclopentadienide
derivatives, ortho-oxazolide ligand, and/or the biphenylide
ligand do not effectively stabilize the organocerium(IV) complexes
against decomposition under the conditions employed.