High-valent iridium complexes are of interest due to their involvement as reactive intermediates in iridium-catalyzed oxidations. Recent studies have shown that π-donating oxygen-donor ligands can stabilize iridium in high oxidation states. This prompted us to synthesize iridium complexes with chelating oxygen ligands and to investigate their redox chemistry and catalytic activity. In this work, iridium complexes with bidentate imidodiphosphinate ligands have been synthesized and their oxidation chemistry has been studied. Also, heterometallic iridium/ruthenium nitrido complexes supported by oxygen ligands have been synthesized and structurally characterized. Chapter 2 describes the reactions of iridium(III) complexes with the imidodiphosphinate ligand tpip
− ([N(Ph
2PO)
2]
−) with oxidizing agents and ruthenium(VI) nitrido complexes. Oxidative addition of [Ir(L)
2(tpip)] with methyl triflate (MeOTf) afforded [Ir(L)
2(tpip)(CH
3)(H
2O)](OTf) (L = cyclooctene (COE) or 2,6-dimethylphenyl isocyanide), whereas that of [Ir(xylNC)
2(tpip)] with benzyl bromide gave [Ir(xylNC)
2(tpip)(PhCH
2)Br]. Heterometallic Ir/Ru μ-nitrido complexes, including [Ir(L)(tpip)(μ-N)Ru(L
OEt)Cl
2] and [Ir(COE){N(
iPr
2PS)
2}(μ-N)Ru(L
OEt)Cl
2], were synthesized from reactions of [L
OEtRu(N)Cl
2] (L
OEt− = [(η
5-C
5H
5)Co{P(O)(OEt)
2}
3]
−) with [Ir(L)(tpip)] and [Ir(COE){N(
iPr
2PS)
2}], respectively. Ir(tpip) complexes were found to be active catalysts for oxidation of hydrocarbons with PhIO. It is proposed that a high-valent Ir-oxo species is the active species for the Ir-catalyzed oxidation. Chapter 3 describes the synthesis and structures of heterometallic Ir/Hg cyclometalated complexes with Ir−Hg bonds. [IrCl(κ
2-C^N^CH)(COD)HgIr(COD)Cl
2]
2, [Ir(C^N^C)(COD)HgIr(COD)Cl
2] and [Ir(C^N^C)(COD)HgCl] were synthesized from transmetalation of [Ir(COD)Cl]
2 (COD = 1,5-cyclooctadiene) with [Hg(κ
2-C^N^CH)Cl] (H
2C^N^C = 2,6-bis(4-tert-butylphenyl)pyridine) under different conditions. Treatment of [Ir(C^N^C)(COD)HgCl] with PhICl
2 followed by reaction with PCy
3 afforded a mercury-free Ir(C^N^C) complex, [Ir(C^N^C)(COD)Cl], that contains a labile chloride ligand. Reaction of [Ir(PPh
3)
3Cl] with [Hg(κ
2-C^N^CH)Cl] in refluxing tetrahydrofuran led to isolation of [Ir(PPh
3)(κ
2-P,C-PPh
2C
6H
4)
2Cl] that contains two cyclometalated triphenylphosphine ligands. Chapter 4 describes the synthesis of heterometallic Ir/Ru nitrido complexes starting from a cationic Ru(VI) nitrido Schiff base complex, [Ru(N)(salchda)(MeOH)]
+ (H
2salchda = N,N’-bis(salicylidene)-o-cyclohexyldiamine). Treatment of [Ru(N)(salchda)(MeOH)]
+ with [Cp*IrCl
2]
2 (Cp* = pentamethylcyclopentadienyl) and [Ir(TBHPP)(C
8H
13)] (H
2TBHPP = tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)porphyrin) afforded [Cp*IrCl
2(μ-N)Ru(salchda)(PO
2F
2)] and a diamagnetic tetranuclear μ-nitrido and μ-hydroxo complex, [{Ir(TBHPP)(C
8H
13)(μ-N)Ru(salchda)}
2(μ-OH)](PF
6), respectively. X-ray crystallography revealed that these Ir−N−Ru complexes contain Ru−N and Ir−N double bonds, and therefore they can be described as Ru(VI)≡N−Ir(III) or Ru(IV)=N=Ir(V) complexes. Reaction of [Ir(dtbpy)(SiMe
3)Me(CH
2SiMe
3)] (dtbpy = 4,4’-di-tert-butyl-2,2’-bipyridyl) with [L
OEtRu(N)Cl
2] and PhICl
2 afforded the μ-nitrido [(Me)(CH
2SiMe
3)(SiMe
3)Ir(μ-N)Ru(L
OEt)Cl
2] and dichloride [Ir(dtbpy)(SiMe
3)Cl
2] complexes, respectively. Chapter 5 describes the oxidation of [L
OEtRu(
tBuNH
2)Cl
2] with a hydrogen-atom transfer reagent. Treatment of [L
OEtRu(
tBuNH
2)Cl
2] with “magic blue” and 2,6-lutidine produced the Ru(VI) nitrido complex [L
OEtRu(N)Cl
2], presumably via C−N cleavage and butene elimination of a Ru(V) tert-butylimido intermediate. Ru amine complexes with catecholate and perfluoropinacolate have also been synthesized and characterized.
| Date of Award | 2020 |
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| Original language | English |
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| Awarding Institution | - The Hong Kong University of Science and Technology
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