Ce(IV) Complexes with Donor-Functionalized Alkoxide Ligands: Improved Precursors for Chemical Vapor Deposition of CeO₂

Abstract

Thin films of ceria (CeO(2)) have many applications, and their synthesis by liquid-injection MOCVD (metal-organic chemical vapor deposition) or ALD (atomic layer deposition) requires volatile precursor compounds. Here we report the synthesis of a series of homoleptic and heteroleptic Ce(IV) complexes with donor-functionalized alkoxide ligands mmp (1-methoxy-2-methylpropan-2-olate), dmap (1-(dimethylamino)propan-2-olate), and dmop (2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)propan-2-olate) and their potential as precursors for MOCVD and ALD of CeO(2). New complexes were synthesized by alcohol exchange reactions with [Ce(OBu(t))(4)]. [Ce(mmp)(4)] and [Ce(dmap)(4)] were both found to be excellent precursors for liquid-injection MOCVD of CeO(2), depositing high purity thin films with very low carbon contamination, and both have a large temperature window for diffusion controlled growth (350-600 °C for [Ce(mmp)(4)]; 300-600 °C for [Ce(dmap)(4)]). [Ce(mmp)(4)] is also an excellent precursor for liquid-injection ALD of CeO(2) using H(2)O as oxygen source and demonstrates self-limiting growth from 150 to 350 °C. [Ce(dmap)(4)] has lower thermal stability than [Ce(mmp)(4)] and does not show self-limiting growth in ALD. Heteroleptic complexes show a tendency to undergo ligand redistribution reactions to form mixtures in solution and are unsuitable as precursors for liquid-injection CVD.

Synthesis and Characterization of Cerium(IV) Metallocenes

“…Soluble cerium(IV) complexes are also important precursors for the preparation of ceria nanoparticles [14] and this has increased the demand for well-characterized precursors for the development of this area. Ce(IV) alkoxides are well suited for this purpose and reports of Ce(IV) alkoxides exist where these have exhibited utility as precursors in CVD applications [15] and in ring-opening polymerization of lactide [16]. The synthesis of Ce(IV) organometallic complexes, however, is limited by the lack of available starting materials and this has constrained the growth and development of traditional organometallic chemistry and reactivity using this high-oxidation state lanthanide [17].…”

Effective and Reversible Carbon Dioxide Insertion into Cerium Pyrazolates

“…[23] Other homoleptic Ce IV complexes, [Ce-(L) 4 ] (with L as a donor-functionalized alkoxy ligand engaged in a 5-membered chelate to cerium), also have similar Ce À O bond lengths as those in 2, thus highlighting a common chelating coordination motif. [24,25] Seemingly, no delocalization occurs across the O=CÀO fragment, which exhibits average CÀO bond lengths of 1.207 (terminal) and 1.291 (bridging). Support for the localization of the CÀO double bond came from DRIFTS measurements of 2·toluene and 2·thf, which showed the presence of a strong absorption band at ñ = 1732 and 1718 cm À1 , respectively, for the CO stretching of the C À O double bond as well as a strong absorption band at ñ = 1336 cm À1 for the CO stretching of the C À O single bond.…”

Synthesis, Structure, and Reactivity of a Tetranuclear Cerium(IV) Oxo Cluster Supported by the Kläui Tripodal Ligand [Co(η5‐C5H5){P(O)(OEt)2}3]−

“…Selected bond lengths and angles are collected in Table 1. [17] and [Ce IV 2 (m-O)(dmop) 4 (mmp) 2 ]( dmop = 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)propan-2-ol;m mp = 1-methoxy-2-methylpropan-2-ol)) [2.106 ], [18] but shortert han those for the m 4 -oxo ligands [av. The geometry Scheme2.Synthesis and reactivity of cluster 1.…”