Rhodium: Inorganic &amp; Coordination Chemistry

Jardine, F. H.

doi:10.1002/0470862106.ia206

Cited by 4 publications

(4 citation statements)

References 10 publications

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“…The outstanding feature of pyalk is the combination of high donor strength and oxidative resistance needed to stabilize high oxidation states. Ligands that excel in one of these areas often underperform in the other: − an electron-rich ligand may be a good donor but is often easily oxidized, while electron-poor ligands can be very resistant to oxidation but are often poor donors. Examples of the first type include thiolates, amides, imides, nitrides, and alkyls: these can support high oxidation states but are easily destroyed by ligand oxidation. ,, Examples of the second type include fluoride, phosphate, nitrate, etc.…”

Section: Design Principlesmentioning

confidence: 99%

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A Pyridine Alkoxide Chelate Ligand That Promotes Both Unusually High Oxidation States and Water-Oxidation Catalysis

et al. 2017

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Water-oxidation catalysis is a critical bottleneck in the direct generation of solar fuels by artificial photosynthesis. Catalytic oxidation of difficult substrates such as water requires harsh conditions, so the ligand must be designed both to stabilize high oxidation states of the metal center and to strenuously resist ligand degradation. Typical ligand choices either lack sufficient electron donor power or fail to stand up to the oxidizing conditions. Our research on Ir-based water-oxidation catalysts (WOCs) has led us to identify a ligand, 2-(2'-pyridyl)-2-propanoate or "pyalk", that fulfills these requirements. Work with a family of Cp*Ir(chelate)Cl complexes had indicated that the pyalk-containing precursor gave the most robust WOC, which was still molecular in nature but lost the Cp* fragment by oxidative degradation. In trying to characterize the resulting active "blue solution" WOC, we were able to identify a diiridium(IV)-mono-μ-oxo core but were stymied by the extensive geometrical isomerism and coordinative variability. By moving to a family of monomeric complexes [Ir(pyalk)] and [Ir(pyalk)Cl], we were able to better understand the original WOC and identify the special properties of the ligand. In this Account, we cover some results using the pyalk ligand and indicate the main features that make it particularly suitable as a ligand for oxidation catalysis. The alkoxide group of pyalk allows for proton-coupled electron transfer (PCET) and its strong σ- and π-donor power strongly favors attainment of exceptionally high oxidation states. The aromatic pyridine ring with its methyl-protected benzylic position provides strong binding and degradation resistance during catalytic turnover. Furthermore, the ligand has two additional benefits: broad solubility in aqueous and nonaqueous solvents and an anisotropic ligand field that enhances the geometry-dependent redox properties of its complexes. After discussion of the general properties, we highlight the specific complexes studied in more detail. In the iridium work, the isolated mononuclear complexes showed easily accessible Ir(III/IV) redox couples, in some cases with the Ir(IV) state being indefinitely stable in water. We were able to rationalize the unusual geometry-dependent redox properties of the various isomers on the basis of ligand-field effects. Even more striking was the isolation and full characterization of a stable Rh(IV) state, for which prior examples were very reactive and poorly characterized. Importantly, we were able to convert monomeric Ir complexes to [Cl(pyalk)Ir-O-IrCl(pyalk)] derivatives that help model the "blue solution" properties and provide groundwork for rational synthesis of active, well-defined WOCs. More recent work has moved toward the study of first-row transition metal complexes. Manganese-based studies have highlighted the importance of the chelate effect for labile metals, leading to the synthesis of pincer-type pyalk derivatives. Beyond water oxidation, we believe the pyalk ligand and its derivatives will also prove use...

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Section: Design Principlesmentioning

confidence: 99%

“…The products themselves are so oxidizing that they are unstable in water. For example, the Pt-group metals form hexavalent fluorides on reaction with fluorine, but these complexes readily decompose on exposure to water or organic solvents and cannot be regenerated under catalytically relevant conditions …”

Section: Design Principlesmentioning

confidence: 99%

A Pyridine Alkoxide Chelate Ligand That Promotes Both Unusually High Oxidation States and Water-Oxidation Catalysis

et al. 2017

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“…Interest in high oxidation state transition-metal complexes has grown considerably in recent years in connection with oxidation catalysis . While there are a number of well-established Ir(IV) complexes, the highest oxidation state commonly encountered for rhodium is Rh(III). , Among the very few Rh(IV) species known, [RhX 6 ] 2– (X = Cl, F) is unstable in water, which has limited its characterization . There are also a number of poorly characterized solid-state Rh(IV) oxide species as well as several formally Rh(IV) dinuclear organometallic compounds .…”

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confidence: 99%

A Stable Coordination Complex of Rh(IV) in an N,O-Donor Environment

et al. 2015

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We describe facial and meridional isomers of [Rh(III)(pyalk)3], as well as meridional [Rh(IV)(pyalk)3](+) {pyalk =2-(2-pyridyl)-2-propanoate}, the first coordination complex in an N,O-donor environment to show a clean, reversible Rh(III/IV) redox couple and to have a stable Rh(IV) form, which we characterize by EPR and UV-visible spectroscopy as well as X-ray crystallography. The unprecedented stability of the Rh(IV) species is ascribed to the exceptional donor strength of the ligands, their oxidation resistance, and the meridional coordination geometry.

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“…Moreover, the labilizing trans effect of chloride is greater than that of the aqua ligand, leading among others to a fac-[RhCl 3 (H 2 O) 3 ] configuration possessing all aqua ligands in positions opposite to those of the chloride ligands. 14 Because of the characteristics of the pyridocarbazole and the tridentate ligand used, additional effects can be exploited to distinguish the stereoisomers. For example, the two possible diastereomers Λ-(R)-Rh1 and Λ-(R)-Rh2 can be distinguished easily by correlating their 1 H NMR spectra.…”

Section: ■ Introductionmentioning

confidence: 99%

Correlation between the Stereochemistry and Bioactivity in Octahedral Rhodium Prolinato Complexes

et al. 2015

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Controlling the relative and absolute configuration of octahedral metal complexes constitutes a key challenge that needs to be overcome in order to fully exploit the structural properties of octahedral metal complexes for applications in the fields of catalysis, materials sciences, and life sciences. Herein, we describe the application of a proline-based chiral tridentate ligand to decisively control the coordination mode of an octahedral rhodium(III) complex. We demonstrate the mirror-like relationship of synthesized enantiomers and differences between diastereomers. Further, we demonstrate, using the established pyridocarbazole pharmacophore ligand as part of the organometallic complexes, the importance of the relative and absolute stereochemistry at the metal toward chiral environments like protein kinases. Protein kinase profiling and inhibition data confirm that the proline-based enantiopure rhodium(III) complexes, despite having all of the same constitution, differ strongly in their selectivity properties despite their unmistakably mutual origin. Moreover, two exemplary compounds have been shown to induce different toxic effects in an ex vivo rat liver model.

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Rhodium: Inorganic & Coordination Chemistry

Abstract: The element and its binary compounds are discussed, including specific discussions of the range of available oxidation states. Complexes of Rhodium(I), (II), and (III) receive attention, together with a discussion of nitrosyl complexes.

Cited by 4 publications

References 10 publications

A Pyridine Alkoxide Chelate Ligand That Promotes Both Unusually High Oxidation States and Water-Oxidation Catalysis

A Pyridine Alkoxide Chelate Ligand That Promotes Both Unusually High Oxidation States and Water-Oxidation Catalysis

A Stable Coordination Complex of Rh(IV) in an N,O-Donor Environment

Correlation between the Stereochemistry and Bioactivity in Octahedral Rhodium Prolinato Complexes

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