Although tetravalent cerium compounds have been widely used as oxidizing agents in organic synthesis, the coordination chemistry of oxidizing cerium(IV) complexes has not been well explored owing to the high oxidizing power of cerium(IV). In this thesis, cerium(IV) complexes supported by the Kläui's tripodal ligand [CpCo{P(O)(OEt)
2}
3]
-(L
OEt-) have been synthesized and characterized. In particular, cerium(IV) complexes containing pyridine N-oxide, phosphine oxide, and iodosylbenzene ligands have been isolated and their structures and bonding have been analyzed. In addition, cerium complexes with pyrroloquinoline quinone (PQQ) ligand have been synthesized.
Chapter 2 describes the synthesis of Ce(IV) complexes containing group 15 element oxide ligands. Reaction of (L
OEt)
2Ce(BF
4)
2 (2.1) wi...[
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Although tetravalent cerium compounds have been widely used as oxidizing agents in organic synthesis, the coordination chemistry of oxidizing cerium(IV) complexes has not been well explored owing to the high oxidizing power of cerium(IV). In this thesis, cerium(IV) complexes supported by the Kläui's tripodal ligand [CpCo{P(O)(OEt)
2}
3]
-(L
OEt-) have been synthesized and characterized. In particular, cerium(IV) complexes containing pyridine N-oxide, phosphine oxide, and iodosylbenzene ligands have been isolated and their structures and bonding have been analyzed. In addition, cerium complexes with pyrroloquinoline quinone (PQQ) ligand have been synthesized.
Chapter 2 describes the synthesis of Ce(IV) complexes containing group 15 element oxide ligands. Reaction of (L
OEt)
2Ce(BF
4)
2 (2.1) with 4-methylpyridine N-oxide (4-MePyO) afforded a Ce(IV) pyridine N-oxide complex, [(L
OEt)
2Ce(4-MePyO)
2](BF
4)
2 (2.2). Treatment of 2.1 with 2,2'-bipyridyl-1,1'-dioxide (bpyO
2) led to isolation of a Ce(IV) complex containing a chelating pyridine N-oxide ligand, [(L
OEt)
2Ce(bpyO
2)](BF
4)
2 (2.3). Reaction of 2.1 with triphenylphosphine oxide (OPPh
3) and trimethylphosphine oxide (OPMe
3) generated the Ce(IV) mono-phosphine oxide [(L
OEt)
2Ce(OPPh
3)(OH
2)](BF
4)
2 (2.4) and bis-phosphine oxide [(L
OEt)
2Ce(OPMe
3)
2](BF
4)
2 (2.5) complexes respectively. Treatment of 2.1 with triphenylarsine oxide (OAsPh
3) produced [(L
OEt)
2Ce(OAsPh
3)(OH
2)](BF
4)
2 (2.6).
Chapter 3 reports the synthesis of Ce(IV) iodoxybenzene (PhIO
2) complexes. Reaction between 2.1 and excess PhIO led to isolation of the bis(iodoxybenzene) complex [(L
OEt)
2Ce(PhIO
2)
2](BF
4)
2 (3.1). X-ray diffraction revealed that there is a secondary I=O×××I interaction between the two iodoxybenzene ligands in 3.1. Ligand exchange of 3.1 with 2.2 afforded the mono-iodoxybenzene complex [(L
OEt)
2Ce(PhIO
2)(4-MePyO)](BF
4)
2 (3.3). The cyclic voltammograms of complexes 3.1 and 3.3 in dichloromethane displayed irreversible couples at -0.01 V and 0.02 V vs. ferrcoenium/ferrocene that are attributed to the Ce(III/IV) oxidation.
Chapter 4 describes the synthesis of cerium(IV) complexes containing pyrroloquinoline quinone (PQQ) ligand. Treatment of (L
OEt)
2CeCl
2 with Na
2PQQ produced (L
OEt)
2Ce(PQQ) (4.1), which has been characterized by NMR spectroscopy, elemental analysis, mass spectrometry, and infrared spectroscopy. Reaction of 4.1 with Co(OAc)
2 (OAc
- = acetate) led to the isolation of a trinuclear complex, (L
OEt)
5Ce
3(PQQ')
2 (4.2), where PQQ' is a pentacarboxylic ligand derived from oxidative cleavage of the quinone moiety of PQQ. A mechanism for the formation of 4.2 has been proposed.
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