Cerium oxo clusters are of interest because of their relevance to active sites of ceria-containing materials that have found applications in heterogeneous catalysis and organic synthesis. In an attempt to model the reactions catalyzed by ceria-containing materials, in this thesis the reactions of a tetranuclear Ce
IV oxo cluster compound containing the Kläui tripodal ligand [Co(η
5-C
5H
5){P(O)(OEt)
2}
3]
- (L
OEt-), [Ce
4(L
OEt)
4O
7H
2] (1), with CO
2, NO, SO
2 and Brønsted acids have been studied.
The treatment of 1 with CO
2 and NO led to isolation of [Ce(L
OEt)
2(CO
3)] and [Ce(L
OEt)(NO
3)
3], respectively. The protonation of 1 with ROH (R = 2,4,6-trichlorophenyl) and Ph
3SiOH yielded [Ce(L
OEt)(OSiPh
3)
3] (2) and [Ce(L
OEt)(OR)
3] (3),
respectively. The reaction of 1 in the solid state with SO
2 yie...[
Read more ]
Cerium oxo clusters are of interest because of their relevance to active sites of ceria-containing materials that have found applications in heterogeneous catalysis and organic synthesis. In an attempt to model the reactions catalyzed by ceria-containing materials, in this thesis the reactions of a tetranuclear Ce
IV oxo cluster compound containing the Kläui tripodal ligand [Co(η
5-C
5H
5){P(O)(OEt)
2}
3]
- (L
OEt-), [Ce
4(L
OEt)
4O
7H
2] (1), with CO
2, NO, SO
2 and Brønsted acids have been studied.
The treatment of 1 with CO
2 and NO led to isolation of [Ce(L
OEt)
2(CO
3)] and [Ce(L
OEt)(NO
3)
3], respectively. The protonation of 1 with ROH (R = 2,4,6-trichlorophenyl) and Ph
3SiOH yielded [Ce(L
OEt)(OSiPh
3)
3] (2) and [Ce(L
OEt)(OR)
3] (3),
respectively. The reaction of 1 in the solid state with SO
2 yielded the Ce(III) sulfato cluster
[(L
OEtCe
III)
6(μ-SO
4)
4(μ
4-SO
4)
2(H
2O)
4] (4). The chloride ligands in [Ce(L
OEt)Cl
3] are labile and can be
abstracted by silver(I) salts. The treatment of [Ce(L
OEt)Cl
3] with CF
3COOAg yielded the dimer [L
OEtCe(CF
3COO)(μ-CF
3COO)(μ-OH)]
2 (5). The
electrochemistry of the Ce-L
OEt complexes has been studied by using cyclic voltammetry. The correlation between Ce-O(L
OEt) bond distances
and the Ce(IV/III) redox potentials for the Ce-L
OEt complexes has been investigated. The crystal structures of complexes 2 – 5 have been
determined.
In an attempt to model the active sites of vanadium oxide species on ceria, we sought to synthesize molecular vanadium/cerium oxo clusters
and explore their catalytic activity. Treatment of [Ce(L
OEt)Cl
3] with Ag
3VO
4 yielded H
2(CeL
OEt)
4V
4(O)
4(μ
3-O)
12(μ
4-O)] (6), which features
a unique {Ce
4V
4O
13} oxometallic core. Cluster 6 is a highly efficient catalyst for oxidation of organic sulfides with tert-butyl
hydroperoxide, with total turnover numbers of up to 87,800. Cluster 6 can also catalyze oxdation of benzyl alcohol to benzaldehyde. It is
believed that the Ce(IV)/Ce(III) redox cycle plays a role in the Ce/V-catalyzed oxidation. Treatment of [L
OEtCeCl
3] with Ag
2WO
4 yielded the
Ce/W oxo cluster H
4[(L
OEtCe)
6W
4(μ
2-O)
3(μ
3-O)
9(μ
4-O)(μ
2-Cl)
9Cl
3] (7).
The catalytic oxidation of hydrocarbons with Ru-L
OEt complexes in aqueous media has been investigated. Water-soluble [L
OEtRu
III(H
2O)
2L][OTs]
2 (L = tert-butylamine, pyridine and H
2O) can catalyze C-H oxidation by tert-butyl hydroperoxide in aqueous medium with good
performance and low catalyst loadings (0.1 mol%) under mild conditions. Different substrates including alkybenzenes, aliphatic alkanes and
olefins were tested and their oxidation mechanisms were proposed. The Ru-catalyzed oxidation was completely quenched by radical scavengers such as BHT [BHT= 2,6-bis(1,1-dimethylethyl)-4-methylphenol)] suggesting that a radical pathway is involved. Water-soluble Ru(II)-L
OEt complexes have been synthesized by Zn reduction of the Ru(III) precursors [L
OEtRu(L)(H
2O)
2]
2+ ( L = amine) in water under argon and characterized by NMR spectroscopy.
Post a Comment