This thesis consists of two parts. The first part is about transition metal complexes bearing σ−aryl
and σ−hydroxyaryl ligands while the second part concerned with mononuclear and heterobimetallic iridium
porphyrin complexes.
Metal aryl complexes are of interest because of their possible involvements in metal-catalyzed coupling reactions. Compared with other transition metal homoleptic aryl complexes, the chemistry of tetraarylruthenium(IV) has not been well explored. In this work, the oxidation and reductive coupling of rutheninum(IV) tetraaryl complexes have been investigated. The oxidation of [Ru(C
8H
9O)
4] (C
8H
9O = 4-methoxy-2-methylphenyl) with AgBF
4 afforded Ru
V aryl complex [Ru(C
8H
9O)
4](BF
4) that has been characterized by X-ray diffraction. Reaction of [Ru(C
8H
9O)
4] with PhICl
2 or BBr
3 gave a dinuclear η
6-biaryl complex through reductive coupling of the aryl ligands.
Reaction of [Ru(C
8H
9)
4] (C
8H
9 = 2,5-dimethylphenyl) with NO resulted in insertion of NO into the Ru-C bond and formation of a tetrameric [Ru(NO)(C
8H
9){κ
2-O,O′-ON (C
8H
9)NO}]
4 complexes. The aryl ligands in Ru(C
8H
9)
4] can be brominated selectively by using N-Bromosuccinimide (NBS). Tetraarylruthenium(IV) complexes are capable of catalyzing the oxidation of thioethers by PhIO and cyclopropanation of styrene with ethyl diazoacetate (EDA).
While metal complexes with pi-bonded quinonoid ligands are well documented, metallaquionones (quionoid compounds with one oxygen atom replaced with a transition metal) are extremely rare. In this thesis, attempts were made to synthesize metallaquinones by deprotonation of metal transition metal complexes with σ-hydroxylaryl ligands followed by oxidation. The σ-hydroxylaryl complexes [Ru(C
8H
9O)
4], [OsO
2(C
8H
9O)
2], [Rh(C
8H
9O)
3] and [PPh
3(C
8H
9O)Ni(µ
2-OH)]
2 (C
8H
9O = 4-hydroxy-2,6-dimethylphenyl) have been prepared by alkylation of [Ru(acac)
3], [OsO
4], [RhCl
3(THT)
3] and [Ni(PPh
3)
2Cl
2] with protected hydroxyaryl Grignard reagents followed by deprotection. The deprotonation of these complexes with Et
4NOH was studied by NMR and UV/Vis spectroscopy. The pK
a values of
[OsO
2(C
8H
9O)
2] in water were determined to be 7.2 and 9.85. Reaction of 4-bromo-2,6-di-tert-butylphenol with [Pd(PPh
3)
4] resulted in isolation of a phosphaquinone [(C
8H
20O)PPh
3] whereas that with [Pt(PPh
3)
4] or [Ni(PPh
3)
4] yielded a biquinone, 3,3'-5,5'-tetra-tert-butyl-4,4'-diphenoquinone.
Although iridium(III) porphyrin complexes are well documented, iridium porphyrins with oxidation states +4 or higher are unknown. In this work, iridium(III) porphyrins of the type [Ir(TPP)(PPh
3)X] (TPP
2- = tetraphenylporphyrin dianion) were synthesized and the effect of axial ligands on the Ir
IV/III redox potential was investigated. Reaction of the Ir(III) alkyl complex [Ir(TPP)(PPh
3)C
8H
13] with NAr
3SbCl
6 (Ar = 4-bromophenyl) gave [Ir(TPP)(PPh
3)Cl]. Chloride abstraction of [Ir(TPP)(PPh
3)Cl] with TlPF
6 in tetrahydrofuran (THF) gave [Ir(TPP)(PPH
3)(THF)][PF
6]. Reaction of [Ir(TPP)(PPh
3)(THF)][PF
6] with PhC≡CH in the presence of CuI afforded a bimetallic alkynyl complex [Ir(TPP)(PPh
3)C
8H
5(CuI)]. Reactions of [Ir(TPP)(PPH
3)(THF)][PF
6] with Li
2S and CsOH gave the hydrosulfido [Ir(TPP)(PPH
3)(SH)] and hydroxo [Ir(TPP)(PPH
3)(OH)] complexes, respectively. Reaction of [Ir(TPP)(PPh
3)(THF)][PF
6] with Na(OOBu
t) gave the alkylperoxo complex [Ir(TPP)(PPh
3)(OOBu
t)] that is capable of oxidizing triphenylphosphine and methyl p-tolyl sulfide
stoichiometrically.
Finally, the first heterometallic nitrido complexes of Ir porphyrins were synthesized and their reaction chemistry was studied. Reactions of [L
OEtRu(N)Cl
2] (L
OEt- = [CpCo{P(O)(OEt)
2}
3]
-) with [Ir(TPP)R] (R = C
8H
13 or C(O)PhCl) gave heterometallic μ-nitrido complexes [R(TPP)Ir(μ-N)RuCl
2(L
OEt)]. Oxidation of [R(TPP)Ir(μ-N)RuCl
2(L
OEt)] with NAr
3SbCl
6 (Ar = 4-bromophenyl) afforded [Cl(TPP)Ir(μ-N)RuCl
2(L
OEt)]. X-ray
diffraction indicated that [Cl(TPP)Ir(μ-N)RuCl
2(L
OEt)] can be described by two resonance forms: Ru
VI≡N-Ir
III ↔
Ru
IV=N=Ir
V. Chloride abstraction of [Cl(TPP)Ir(μ-N)RuCl
2(L
OEt)] with TlPF
6 in THF gave [(TPP)(THF)Ir(N)
RuL
OEtCl
2](PF
6). The redox properties of these nitrido-bridged heterometallic porphyrins complexes have been
investigated using cyclic voltammetry. [(TPP)(THF)Ir(N)RuL
OEtCl
2](PF
6) is capable of catalyzing the
cyclopropanation of styrene with ethyl diazoacetate and the oxidation of styrene with PhIO, possibly via
high-valent μ-nitrido Ir oxo and carbene intermediates, respectively.
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