Synthesis and Characterization of Cationic Rhodium Peroxo Complexes

Cipot-Wechsler, Judy; Covelli, Danielle; Praetorius, Jeremy M.; Hearns, Nigel G. R.; Zenkina, Olena V.; Keske, Eric C.; Wang, Ruiyao; Kennepohl, Pierre; Crudden, Cathleen M.

doi:10.1021/om300766x

Cited by 23 publications

(31 citation statements)

References 49 publications

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“…Based on literature precedent, the reduction of Rh III to Rh I is expected to shift the rising portion of the K-edge to lower energy by 2-3 eV. 19,20 Indeed, we observe a significant difference in both the position and shape of the K-edge between [Rh III Cp*(phen)Cl] + and Rh I Cp*(phen) ( Figure S20). The Rh K-edge for [Rh III Cp*(phen)Cl] + has an inflection point at 23,226.5 eV, while the Rh K-edge for Rh I Cp*(phen) onsets earlier and has two inflection points at 23,225.6 and 23,231.7 eV ( Figure S21).…”

Section: Electrochemistry and X-ray Absorption Spectroscopy Of Gcc-rhsupporting

confidence: 55%

Strong Electronic Coupling of Molecular Sites to Graphitic Electrodes via Pyrazine Conjugation

et al. 2018

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Glassy carbon electrodes were functionalized with redox-active moieties by condensation of o-phenylenediamine derivatives with o-quinone sites native to graphitic carbon surfaces. Electrochemical and spectroscopic investigations establish that these graphite-conjugated catalysts (GCCs) exhibit strong electronic coupling to the electrode, leading to electron transfer (ET) behavior that diverges fundamentally from that of solution-phase or surface-tethered analogues. We find that (1) ET is not observed between the electrode and a redox-active GCC moiety regardless of applied potential. (2) ET is observed at GCCs only if the interfacial reaction is ion-coupled. (3) Even when ET is observed, the oxidation state of a transition metal GCC site remains unchanged. From these observations, we construct a mechanistic model for GCC sites in which ET behavior is identical to that of catalytically active metal surfaces rather than to that of molecules in solution. These results suggest that GCCs provide a versatile platform for bridging molecular and heterogeneous electrocatalysis.

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Section: Electrochemistry and X-ray Absorption Spectroscopy Of Gcc-rhsupporting

confidence: 55%

Strong Electronic Coupling of Molecular Sites to Graphitic Electrodes via Pyrazine Conjugation

et al. 2018

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“…[2][3][4] Many of the reported compounds are mononuclear complexes of Group 9 transition metals. [5][6][7][8][9][10][11] When the metals are anchored on solid surfaces, the complexity of the structures involving metal-oxygen bonding is typically greater than that in molecular species, because of the multiple metal centers involved, with additional complexity associated with oxide-support surface heterogeneity and interactions and possible surface distortion by ligated oxygen. [12][13][14][15][16][17] An improved understanding of supported structures comprising metal-metal and metal-oxygen bonds is crucial for the prediction of structurefunction relationships and is essential for design of solid noblemetal catalysts.…”

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confidence: 99%

Spectroscopic Characterization of μ-η¹:η¹-Peroxo Ligands Formed by Reaction of Dioxygen with Electron-Rich Iridium Clusters

et al. 2019

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Although oxygen is a common ligand in supported-metal catalysts, its coordination has been challenging to elucidate. Using a well-defined Ir-dimer cluster that incorporates a µ-η 1 :η 1-peroxo ligand, we observe a FT-Raman band at 756 cm-1 assigned to the 16 O-16 O stretch, and a greatly enhanced intensity at 788 cm-1. The frequency of this latter band does not change upon 18 O labeling, suggesting it arises due to a change in symmetry accompanying bridging peroxo-ligand incorporation. We also investigate reaction of oxygen with a silica-supported tetrairidium carbonyl cluster protected with bulky electron-donating phosphine ligands (p-tert-butylcalix[4]arene(OPr)3(OCH2PPh2; Ph = phenyl; Pr = propyl), and observe the same Raman band at 788 cm-1 , which is associated with formation of similar bridging peroxo ligands on the tetrairidum frame. IR spectra recorded as the supported cluster was decarbonylated in sequential exposures to (i) H2, (ii) O2, (iii) H2, and (iv) CO are consistent with two bridging peroxo ligands bonded irreversibly per supported tetrairidium cluster, replacing bridging carbonyl ligands, without altering either the cluster frame or bound phosphine ligands. X-ray absorption near edge and infrared spectra recorded as the cluster reacted with O2 include isosbestic points signifying a stoichiometrically simple reaction, and mass spectra of the effluent gas identify CO2 formed by oxidation of one terminal CO ligand per cluster and H2 (not H2O)-evidence that hydride ligands had been present on the cluster. The results demonstrate that O2 reacts with intact ligated metal polyhedra on supports-an inference that pertains broadly to oxidation catalysis on supported noble metals.

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“…The crystallographic data and spectral features of 4 are consistent with those of related Rh III (η 2 -O 2 ) complexes. 5,34,39,40 The X-ray crystal structure of 4b, which is provided in Figure 3 Inorg. Chem.…”

Section: ■ Resultsmentioning

confidence: 99%

Oxygen Reduction Mechanism of Monometallic Rhodium Hydride Complexes

2015

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The reduction of O2 to H2O mediated by a series of electronically varied rhodium hydride complexes of the form cis,trans-Rh(III)Cl2H(CNAd)(P(4-X-C6H4)3)2 (2) (CNAd = 1-adamantylisocyanide; X = F (2a), Cl (2b), Me (2c), OMe (2d)) was examined through synthetic and kinetic studies. Rhodium(III) hydride 2 reacts with O2 to afford H2O with concomitant generation of trans-Rh(III)Cl3(CNAd)(P(4-X-C6H4)3)2 (3). Kinetic studies of the reaction of the hydride complex 2 with O2 in the presence of HCl revealed a two-term rate law consistent with an HX reductive elimination (HXRE) mechanism, where O2 binds to a rhodium(I) metal center and generates an η(2)-peroxo complex intermediate, trans-Rh(III)Cl(CNAd)(η(2)-O2)(P(4-X-C6H4)3)2 (4), and a hydrogen-atom abstraction (HAA) mechanism, which entails the direct reaction of O2 with the hydride. Experimental data reveal that the rate of reduction of O2 to H2O is enhanced by electron-withdrawing phosphine ligands. Complex 4 was independently prepared by the addition of O2 to trans-Rh(I)Cl(CNAd)(P(4-X-C6H4)3)2 (1). The reactivity of 4 toward HCl reveals that such peroxo complexes are plausible intermediates in the reduction of O2 to H2O. These results show that the given series of electronically varied rhodium(III) hydride complexes facilitate the reduction of O2 to H2O according to a two-term rate law comprising HXRE and HAA pathways and that the relative rates of these two pathways, which can occur simultaneously and competitively, can be systematically modulated by variation of the electronic properties of the ancillary ligand set.

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Synthesis and Characterization of Cationic Rhodium Peroxo Complexes

Cited by 23 publications

References 49 publications

Strong Electronic Coupling of Molecular Sites to Graphitic Electrodes via Pyrazine Conjugation

Strong Electronic Coupling of Molecular Sites to Graphitic Electrodes via Pyrazine Conjugation

Spectroscopic Characterization of μ-η¹:η¹-Peroxo Ligands Formed by Reaction of Dioxygen with Electron-Rich Iridium Clusters

Oxygen Reduction Mechanism of Monometallic Rhodium Hydride Complexes

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Synthesis and Characterization of Cationic Rhodium Peroxo Complexes

Cited by 23 publications

References 49 publications

Strong Electronic Coupling of Molecular Sites to Graphitic Electrodes via Pyrazine Conjugation

Strong Electronic Coupling of Molecular Sites to Graphitic Electrodes via Pyrazine Conjugation

Spectroscopic Characterization of μ-η1:η1-Peroxo Ligands Formed by Reaction of Dioxygen with Electron-Rich Iridium Clusters

Oxygen Reduction Mechanism of Monometallic Rhodium Hydride Complexes

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Spectroscopic Characterization of μ-η¹:η¹-Peroxo Ligands Formed by Reaction of Dioxygen with Electron-Rich Iridium Clusters