Tetravalent cerium oxo complexes and clusters are of significance because they
are related to the active sites of cerium(IV) oxide catalysts. There is also an
increasing interest in the speciation of the Ce(IV) ion in water due to the possible
involvement of cerium hydroxide/oxide species in cerium-based water oxidation. In
this thesis, water-soluble Ce(IV) oxo and aqua complexes supported by Kläui’s
oxygen tripodal ligand L
OEt- ([Co(η
5-C
5H
5){P(O)(OEt)
2}
3]
-) have been synthesized in
an attempt to model cerium-oxo surfaces and the reactive intermediates of
cerium(IV)-based oxidations. Chloride abstraction of (L
OEt)
2CeCl
2 (1) and
(L
OEt)
2Ce(NO
3)Cl(2) with AgX (X = OTs
-, OTf
-) in wet MeCN afforded the Ce(IV)
aqua complexes [(L
OEt)
2Ce(H
2O)
2](X)
2 (X = OTs
-, OTf
-) and [(L
OEt)
2Ce(NO
3)(H
2O)](X) (X = OTs
-, OTf
-), respectively.
In contrast with the transition metal and actinide analogues, prior to this work
terminal oxo complexes of lanthanide elements remain elusive. In this project, we
have successfully synthesized and structurally characterized the first lanthanide
terminal oxo complex, [(L
OEt)
2Ce(O)(H
2O)]·MeC(O)NH
2 (7·acetamide), by the
reaction of 1 with Ag
2O in wet acetonitrile in the presence of acetamide. 7·acetamide
features a very short Ce-O bond distance [1.857 (3) Å], consistent with a Ce-O
multiple bond. Density functional theory (DFT) calculations suggested that the
co-crystallized acetamide molecule plays a crucial role in stabilizing the Ce(IV) oxo
aqua complex in the solid state. The calculated occupied molecular orbitals which
feature σ and π interactions involving between the Ce 4f/5d and O 2p orbitals are
mostly localized on oxygen. Thus, the Ce-oxo bond in 7·acetamide is best described
as a polarized Ce-O double bond. 7·acetamide exhibits nucleophilic and oxidizing
reactivity. Protonation of 7·acetamide with triflic acid afforded
[(L
OEt)
2Ce(OH
2)
2][OTf], whereas reactions of 7·acetamide with CO
2 and Bu
tNCO
afforded the carbonate complexes [(L
OEt)
2Ce(CO
3)]·MeC(O)NH
2 and [(L
OEt)
2Ce(CO
3)]·2(Bu
tNH)
2CO, respectively. Reactions of 7·acetamide with CO and
SO
2 afforded the Ce(III) μ-carbonate [{(L
OEt)
2Ce}(μ-CO
3){Ce(H
2O)(L
OEt)
2}] and
sulfate [(L
OEt)
2Ce]
2(SO
4) complexes, respectively.
The tetranuclear oxo cluster [(L
OEtCe)
4(μ4-O)(μ-O)
4(μ-OH)
2] (15) has been
prepared by the reaction of (L
OEt)Ce(NO
3)
3 with Et
4NOH. Reaction of 15 with H
2O
2
gave a Ce(IV) peroxo hydroxo cluster [(L
OEtCe)
4(μ4-O)(μ-η
2:η
2-O
2)
4(μ-OH)
2] (18).
Alternatively, 18 could be prepared by the reaction of 15 with PhIO. Chlorination of
15 with HCl afforded (L
OEt)CeCl
3 (19), which can serve as a good precursor to
heterobimetallic Ce(IV) oxo clusters. Treatment of 19 with AgX (X = OTf
-, OTs
-,
ReO
4-) and Ag
2MoO
4 afforded L
OEtCe(OTf)
3, L
OEtCe(OTs)
3 and [{L
OEtCe(ReO
4)
2(H
2O)(μ-ReO
4)}
2], and H
4[(L
OEtCe)
6(μ
6-MoO
6)(μ
3-MoO
4)
8]
respectively.
A stable Re(VI) nitrido complex L
OEtRe(N)(OMe)Cl (26) has been prepared by
the reaction of (
nBu
4N)[Re(N)Cl
4] with NaL
OEt. Oxidation of L
OEtRe(N)(PPh
3)Cl
with [Cp
2Fe][PF
6] afforded [L
OEtRe(N)(PPh
3)(Cl)][PF
6] (27). Reactions of 26 with
CPh
3BF
4 and [Ir(COD)Cl]
2 (COD = 1,5-cyclooctadiene) afforded the imido
[L
OEtRe(NCPh
3)(OMe)(Cl)][BF
4] and μ-nitrido [L
OEtRe(OMe)(Cl)(μ-N)Ir(COD)Cl]
complexes, respectively. Treatment of 27 and [L
OEtRe(N)(PPh
3)Cl] with
[Ir(COD)Cl]
2 afforded [L
OEtRe(PPh
3)(Cl)(μ-N)Ir(COD)Cl][PF
6] and
[L
OEtRe(PPh
3)(Cl)(μ-N)Ir(COD)Cl], respectively. The first heterobimetallic
μ-nitrido complex of Rh
2(OAc)
4 (OAc
- = acetate),
[L
OEtRe(OMe)(Cl)(μ-N)]
2Rh
2(OAc)
4 (30), has been prepared by the reaction of 26
with Rh
2(OAc)
4. 30 features a donor-acceptor type interaction between Re≡N and
the Rh center.
The Pd(IV) complexes [L
OEtPd(Ph)(PPh
3)(Cl)][PF
6] and
[L
OEtPd(ppyBu
t)Cl][PF
6] have been prepared by reactions of (η
2-L
OEt)Pd(PPh
3)Ph and (η
2-L
OEt)Pd(ppyBu
t) (ppyBu
t = 2-(4'-tert-butylphenyl)pyridine) with PhICl
2 and
NH
4PF
6, respectively. The Cu-L
OEt complexes L
OEtCu(NO
3)(H
2O),
L
OEtCu[N(Ph
2PO)
2], [L
OEtCu(H
2O)
2][BF
4], [L
OEtCu(bpy)][BF
4] have been
synthesized and characterized.
The L
OEtRu aqua complexes [L
OEtRu(H
2O)
2(L)][OTs]
2 (L = Bu
tNH
2, pyridine,
imidazole and pyrazole) have been synthesized by the chloride abstraction of
L
OEtRuCl
2(L) with AgOTs in water. Reaction of L
OEtRuCl
2{N(H)C(Me)NHBu
t}
with AgOTs gave the triaqua complex [L
OEtRu(H
2O)
3][OTs]
2.
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