Syntheses and Electronic Properties of Rhodium(III) Complexes Bearing a Redox-Active Ligand

A series of rhodium(III) complexes of the redox-active ligand, H(L = bis(4-methyl-2-(1H-pyrazol-1-yl)phenyl)amido), was prepared, and the electronic properties were studied. Thus, heating an ethanol solution of commercial RhCl3·3H2O with H(L) results in the precipitation of insoluble [H(L)]RhCl3, 1. The reaction of a methanol suspension of [H(L)]RhCl3 with NEt4OH causes ligand deprotonation and affords nearly quantitative yields of the soluble, deep-green, title compound (NEt4)[(L)RhCl3]·H2O, 2·H2O. Complex 2·H2O reacts readily with excess pyridine, triethylphosphine, or pyrazine (pyz) to eliminate NEt4Cl and give charge-neutral complexes trans-(L)RhCl2(py), trans-3, trans-(L)RhCl2(PEt3), trans- 4, or trans-(L)RhCl2(pyz), trans-5, where the incoming Lewis base is trans- to the amido nitrogen of the meridionally coordinating ligand. Heating solutions of complexes trans-3 or trans-4 above about 100 °C causes isomerization to the appropriate cis-3 or cis-4. Isomerization of trans-5 occurs at a much lower temperature due to pyrazine dissociation. Cis-3 and cis- 5 could be reconverted to their respective trans- isomers in solution at 35 °C by visible light irradiation. Complexes [(L)Rh(py)2Cl](PF6), 6, [(L)Rh(PPh3)(py)Cl](PF6), 7, [(L)Rh(PEt3)2Cl](PF6), 8, and [(L)RhCl(bipy)](OTf = triflate), 9, were prepared from 2·H2O by using thallium(I) salts as halide abstraction agents and excess Lewis base. It was not possible to prepare dicationic complexes with three unidentate pyridyl or triethylphosphine ligands; however, the reaction between 2, thallium(I) triflate, and the tridentate 4′-(4-methylphenyl)-2,2′:6′,2″-terpyridine (ttpy) afforded a high yield of [(L)Rh(ttpy)]- (OTf)2, 10. The solid state structures of nine new complexes were obtained. The electrochemistry of the various derivatives in CH2Cl2 showed a ligand-based oxidation wave whose potential depended mainly on the charge of the complex, and to a lesser extent on the nature and the geometry of the other supporting ligands. Thus, the oxidation wave for 2 with an anionic complex was found at +0.27 V versus Ag/AgCl in CH2Cl2, while those waves for the charge-neutral complexes 3−5 were found between +0.38 to +0.59 V, where the cis- isomers were about 100 mV more stable toward oxidation than the trans- isomers. The oxidation waves for 6−9 with monocationic complexes occurred in the range +0.74 to 0.81 V while that for 10 with a dicationic complex occurred at +0.91 V. Chemical oxidation of trans-3, cis-3, and 8 afforded crystals of the singly oxidized complexes, [trans- (L)RhCl2(py)](SbCl6), cis-[(L)RhCl2(py)](SbCl4)·2CH2Cl2, and [(L)Rh(PEt3)2Cl](SbCl6)2, respectively. Comparisons of structural and spectroscopic features combined with the results of density functional theory (DFT) calculations between nonoxidized and oxidized forms of the complexes are indicative of the ligand-centered radicals in the oxidized derivatives

Syntheses and Electronic Properties of Rhodium(III) Complexes Bearing a Redox-Active Ligand

A series of rhodium­(III) complexes of the redox-active ligand, H­(<b>L</b> = bis­(4-methyl-2-(1<i>H</i>-pyrazol-1-yl)­phenyl)­amido), was prepared, and the electronic properties were studied. Thus, heating an ethanol solution of commercial RhCl₃·3H₂O with H­(<b>L</b>) results in the precipitation of insoluble [H­(<b>L</b>)]­RhCl₃, <b>1</b>. The reaction of a methanol suspension of [H­(<b>L</b>)]­RhCl₃ with NEt₄OH causes ligand deprotonation and affords nearly quantitative yields of the soluble, deep-green, title compound (NEt₄)­[(<b>L</b>)­RhCl₃]·H₂O, <b>2</b>·H₂O. Complex <b>2</b>·H₂O reacts readily with excess pyridine, triethylphosphine, or pyrazine (pyz) to eliminate NEt₄Cl and give charge-neutral complexes <i>trans</i>-(<b>L</b>)­RhCl₂(py), <i>trans</i>-<b>3</b>, <i>trans</i>-(<b>L</b>)­RhCl₂(PEt₃), <i>trans</i>-<b>4</b>, or <i>trans</i>-(<b>L</b>)­RhCl₂(pyz), <i>trans</i>-<b>5</b>, where the incoming Lewis base is <i>trans</i>- to the amido nitrogen of the meridionally coordinating ligand. Heating solutions of complexes <i>trans</i>-<b>3</b> or <i>trans</i>-<b>4</b> above about 100 °C causes isomerization to the appropriate <i>cis</i>-<b>3</b> or <i>cis</i>-<b>4</b>. Isomerization of <i>trans</i>-<b>5</b> occurs at a much lower temperature due to pyrazine dissociation. <i>Cis</i>-<b>3</b> and <i>cis</i>-<b>5</b> could be reconverted to their respective <i>trans</i>- isomers in solution at 35 °C by visible light irradiation. Complexes [(<b>L</b>)­Rh­(py)₂Cl]­(PF₆), <b>6</b>, [(<b>L</b>)­Rh­(PPh₃)­(py)­Cl]­(PF₆), <b>7</b>, [(<b>L</b>)­Rh­(PEt₃)₂Cl]­(PF₆), <b>8</b>, and [(<b>L</b>)­RhCl­(bipy)]­(OTf = triflate), <b>9</b>, were prepared from <b>2</b>·H₂O by using thallium­(I) salts as halide abstraction agents and excess Lewis base. It was not possible to prepare dicationic complexes with three unidentate pyridyl or triethylphosphine ligands; however, the reaction between <b>2</b>, thallium­(I) triflate, and the tridentate 4′-(4-methylphenyl)-2,2′:6′,2″-terpyridine (ttpy) afforded a high yield of [(<b>L</b>)­Rh­(ttpy)]­(OTf)₂, <b>10</b>. The solid state structures of nine new complexes were obtained. The electrochemistry of the various derivatives in CH₂Cl₂ showed a ligand-based oxidation wave whose potential depended mainly on the charge of the complex, and to a lesser extent on the nature and the geometry of the other supporting ligands. Thus, the oxidation wave for <b>2</b> with an anionic complex was found at +0.27 V versus Ag/AgCl in CH₂Cl₂, while those waves for the charge-neutral complexes <b>3</b>–<b>5</b> were found between +0.38 to +0.59 V, where the <i>cis</i>- isomers were about 100 mV more stable toward oxidation than the <i>trans</i>- isomers. The oxidation waves for <b>6</b>–<b>9</b> with monocationic complexes occurred in the range +0.74 to 0.81 V while that for <b>10</b> with a dicationic complex occurred at +0.91 V. Chemical oxidation of <i>trans</i>-<b>3</b>, <i>cis</i>-<b>3</b>, and <b>8</b> afforded crystals of the singly oxidized complexes, [<i>trans</i>-(<b>L</b>)­RhCl₂(py)]­(SbCl₆), <i>cis</i>-[(<b>L</b>)­RhCl₂(py)]­(SbCl₄)·2CH₂Cl₂, and [(<b>L</b>)­Rh­(PEt₃)₂Cl]­(SbCl₆)₂, respectively. Comparisons of structural and spectroscopic features combined with the results of density functional theory (DFT) calculations between nonoxidized and oxidized forms of the complexes are indicative of the ligand-centered radicals in the oxidized derivatives

Syntheses and Electronic Properties of Rhodium(III) Complexes Bearing a Redox-Active Ligand

A series of rhodium­(III) complexes of the redox-active ligand, H­(<b>L</b> = bis­(4-methyl-2-(1<i>H</i>-pyrazol-1-yl)­phenyl)­amido), was prepared, and the electronic properties were studied. Thus, heating an ethanol solution of commercial RhCl₃·3H₂O with H­(<b>L</b>) results in the precipitation of insoluble [H­(<b>L</b>)]­RhCl₃, <b>1</b>. The reaction of a methanol suspension of [H­(<b>L</b>)]­RhCl₃ with NEt₄OH causes ligand deprotonation and affords nearly quantitative yields of the soluble, deep-green, title compound (NEt₄)­[(<b>L</b>)­RhCl₃]·H₂O, <b>2</b>·H₂O. Complex <b>2</b>·H₂O reacts readily with excess pyridine, triethylphosphine, or pyrazine (pyz) to eliminate NEt₄Cl and give charge-neutral complexes <i>trans</i>-(<b>L</b>)­RhCl₂(py), <i>trans</i>-<b>3</b>, <i>trans</i>-(<b>L</b>)­RhCl₂(PEt₃), <i>trans</i>-<b>4</b>, or <i>trans</i>-(<b>L</b>)­RhCl₂(pyz), <i>trans</i>-<b>5</b>, where the incoming Lewis base is <i>trans</i>- to the amido nitrogen of the meridionally coordinating ligand. Heating solutions of complexes <i>trans</i>-<b>3</b> or <i>trans</i>-<b>4</b> above about 100 °C causes isomerization to the appropriate <i>cis</i>-<b>3</b> or <i>cis</i>-<b>4</b>. Isomerization of <i>trans</i>-<b>5</b> occurs at a much lower temperature due to pyrazine dissociation. <i>Cis</i>-<b>3</b> and <i>cis</i>-<b>5</b> could be reconverted to their respective <i>trans</i>- isomers in solution at 35 °C by visible light irradiation. Complexes [(<b>L</b>)­Rh­(py)₂Cl]­(PF₆), <b>6</b>, [(<b>L</b>)­Rh­(PPh₃)­(py)­Cl]­(PF₆), <b>7</b>, [(<b>L</b>)­Rh­(PEt₃)₂Cl]­(PF₆), <b>8</b>, and [(<b>L</b>)­RhCl­(bipy)]­(OTf = triflate), <b>9</b>, were prepared from <b>2</b>·H₂O by using thallium­(I) salts as halide abstraction agents and excess Lewis base. It was not possible to prepare dicationic complexes with three unidentate pyridyl or triethylphosphine ligands; however, the reaction between <b>2</b>, thallium­(I) triflate, and the tridentate 4′-(4-methylphenyl)-2,2′:6′,2″-terpyridine (ttpy) afforded a high yield of [(<b>L</b>)­Rh­(ttpy)]­(OTf)₂, <b>10</b>. The solid state structures of nine new complexes were obtained. The electrochemistry of the various derivatives in CH₂Cl₂ showed a ligand-based oxidation wave whose potential depended mainly on the charge of the complex, and to a lesser extent on the nature and the geometry of the other supporting ligands. Thus, the oxidation wave for <b>2</b> with an anionic complex was found at +0.27 V versus Ag/AgCl in CH₂Cl₂, while those waves for the charge-neutral complexes <b>3</b>–<b>5</b> were found between +0.38 to +0.59 V, where the <i>cis</i>- isomers were about 100 mV more stable toward oxidation than the <i>trans</i>- isomers. The oxidation waves for <b>6</b>–<b>9</b> with monocationic complexes occurred in the range +0.74 to 0.81 V while that for <b>10</b> with a dicationic complex occurred at +0.91 V. Chemical oxidation of <i>trans</i>-<b>3</b>, <i>cis</i>-<b>3</b>, and <b>8</b> afforded crystals of the singly oxidized complexes, [<i>trans</i>-(<b>L</b>)­RhCl₂(py)]­(SbCl₆), <i>cis</i>-[(<b>L</b>)­RhCl₂(py)]­(SbCl₄)·2CH₂Cl₂, and [(<b>L</b>)­Rh­(PEt₃)₂Cl]­(SbCl₆)₂, respectively. Comparisons of structural and spectroscopic features combined with the results of density functional theory (DFT) calculations between nonoxidized and oxidized forms of the complexes are indicative of the ligand-centered radicals in the oxidized derivatives

Syntheses and Electronic Properties of Rhodium(III) Complexes Bearing a Redox-Active Ligand

A series of rhodium­(III) complexes of the redox-active ligand, H­(<b>L</b> = bis­(4-methyl-2-(1<i>H</i>-pyrazol-1-yl)­phenyl)­amido), was prepared, and the electronic properties were studied. Thus, heating an ethanol solution of commercial RhCl₃·3H₂O with H­(<b>L</b>) results in the precipitation of insoluble [H­(<b>L</b>)]­RhCl₃, <b>1</b>. The reaction of a methanol suspension of [H­(<b>L</b>)]­RhCl₃ with NEt₄OH causes ligand deprotonation and affords nearly quantitative yields of the soluble, deep-green, title compound (NEt₄)­[(<b>L</b>)­RhCl₃]·H₂O, <b>2</b>·H₂O. Complex <b>2</b>·H₂O reacts readily with excess pyridine, triethylphosphine, or pyrazine (pyz) to eliminate NEt₄Cl and give charge-neutral complexes <i>trans</i>-(<b>L</b>)­RhCl₂(py), <i>trans</i>-<b>3</b>, <i>trans</i>-(<b>L</b>)­RhCl₂(PEt₃), <i>trans</i>-<b>4</b>, or <i>trans</i>-(<b>L</b>)­RhCl₂(pyz), <i>trans</i>-<b>5</b>, where the incoming Lewis base is <i>trans</i>- to the amido nitrogen of the meridionally coordinating ligand. Heating solutions of complexes <i>trans</i>-<b>3</b> or <i>trans</i>-<b>4</b> above about 100 °C causes isomerization to the appropriate <i>cis</i>-<b>3</b> or <i>cis</i>-<b>4</b>. Isomerization of <i>trans</i>-<b>5</b> occurs at a much lower temperature due to pyrazine dissociation. <i>Cis</i>-<b>3</b> and <i>cis</i>-<b>5</b> could be reconverted to their respective <i>trans</i>- isomers in solution at 35 °C by visible light irradiation. Complexes [(<b>L</b>)­Rh­(py)₂Cl]­(PF₆), <b>6</b>, [(<b>L</b>)­Rh­(PPh₃)­(py)­Cl]­(PF₆), <b>7</b>, [(<b>L</b>)­Rh­(PEt₃)₂Cl]­(PF₆), <b>8</b>, and [(<b>L</b>)­RhCl­(bipy)]­(OTf = triflate), <b>9</b>, were prepared from <b>2</b>·H₂O by using thallium­(I) salts as halide abstraction agents and excess Lewis base. It was not possible to prepare dicationic complexes with three unidentate pyridyl or triethylphosphine ligands; however, the reaction between <b>2</b>, thallium­(I) triflate, and the tridentate 4′-(4-methylphenyl)-2,2′:6′,2″-terpyridine (ttpy) afforded a high yield of [(<b>L</b>)­Rh­(ttpy)]­(OTf)₂, <b>10</b>. The solid state structures of nine new complexes were obtained. The electrochemistry of the various derivatives in CH₂Cl₂ showed a ligand-based oxidation wave whose potential depended mainly on the charge of the complex, and to a lesser extent on the nature and the geometry of the other supporting ligands. Thus, the oxidation wave for <b>2</b> with an anionic complex was found at +0.27 V versus Ag/AgCl in CH₂Cl₂, while those waves for the charge-neutral complexes <b>3</b>–<b>5</b> were found between +0.38 to +0.59 V, where the <i>cis</i>- isomers were about 100 mV more stable toward oxidation than the <i>trans</i>- isomers. The oxidation waves for <b>6</b>–<b>9</b> with monocationic complexes occurred in the range +0.74 to 0.81 V while that for <b>10</b> with a dicationic complex occurred at +0.91 V. Chemical oxidation of <i>trans</i>-<b>3</b>, <i>cis</i>-<b>3</b>, and <b>8</b> afforded crystals of the singly oxidized complexes, [<i>trans</i>-(<b>L</b>)­RhCl₂(py)]­(SbCl₆), <i>cis</i>-[(<b>L</b>)­RhCl₂(py)]­(SbCl₄)·2CH₂Cl₂, and [(<b>L</b>)­Rh­(PEt₃)₂Cl]­(SbCl₆)₂, respectively. Comparisons of structural and spectroscopic features combined with the results of density functional theory (DFT) calculations between nonoxidized and oxidized forms of the complexes are indicative of the ligand-centered radicals in the oxidized derivatives

Risk of COVID-19 after natural infection or vaccinationResearch in context

Summary: Background: While vaccines have established utility against COVID-19, phase 3 efficacy studies have generally not comprehensively evaluated protection provided by previous infection or hybrid immunity (previous infection plus vaccination). Individual patient data from US government-supported harmonized vaccine trials provide an unprecedented sample population to address this issue. We characterized the protective efficacy of previous SARS-CoV-2 infection and hybrid immunity against COVID-19 early in the pandemic over three-to six-month follow-up and compared with vaccine-associated protection. Methods: In this post-hoc cross-protocol analysis of the Moderna, AstraZeneca, Janssen, and Novavax COVID-19 vaccine clinical trials, we allocated participants into four groups based on previous-infection status at enrolment and treatment: no previous infection/placebo; previous infection/placebo; no previous infection/vaccine; and previous infection/vaccine. The main outcome was RT-PCR-confirmed COVID-19 >7–15 days (per original protocols) after final study injection. We calculated crude and adjusted efficacy measures. Findings: Previous infection/placebo participants had a 92% decreased risk of future COVID-19 compared to no previous infection/placebo participants (overall hazard ratio [HR] ratio: 0.08; 95% CI: 0.05–0.13). Among single-dose Janssen participants, hybrid immunity conferred greater protection than vaccine alone (HR: 0.03; 95% CI: 0.01–0.10). Too few infections were observed to draw statistical inferences comparing hybrid immunity to vaccine alone for other trials. Vaccination, previous infection, and hybrid immunity all provided near-complete protection against severe disease. Interpretation: Previous infection, any hybrid immunity, and two-dose vaccination all provided substantial protection against symptomatic and severe COVID-19 through the early Delta period. Thus, as a surrogate for natural infection, vaccination remains the safest approach to protection. Funding: National Institutes of Health

Risk of COVID-19 after natural infection or vaccinationResearch in context

Background: While vaccines have established utility against COVID-19, phase 3 efficacy studies have generally not comprehensively evaluated protection provided by previous infection or hybrid immunity (previous infection plus vaccination). Individual patient data from US government-supported harmonized vaccine trials provide an unprecedented sample population to address this issue. We characterized the protective efficacy of previous SARS-CoV-2 infection and hybrid immunity against COVID-19 early in the pandemic over three-to six-month follow-up and compared with vaccine-associated protection. Methods: In this post-hoc cross-protocol analysis of the Moderna, AstraZeneca, Janssen, and Novavax COVID-19 vaccine clinical trials, we allocated participants into four groups based on previous-infection status at enrolment and treatment: no previous infection/placebo; previous infection/placebo; no previous infection/vaccine; and previous infection/vaccine. The main outcome was RT-PCR-confirmed COVID-19 >7–15 days (per original protocols) after final study injection. We calculated crude and adjusted efficacy measures. Findings: Previous infection/placebo participants had a 92% decreased risk of future COVID-19 compared to no previous infection/placebo participants (overall hazard ratio [HR] ratio: 0.08; 95% CI: 0.05–0.13). Among single-dose Janssen participants, hybrid immunity conferred greater protection than vaccine alone (HR: 0.03; 95% CI: 0.01–0.10). Too few infections were observed to draw statistical inferences comparing hybrid immunity to vaccine alone for other trials. Vaccination, previous infection, and hybrid immunity all provided near-complete protection against severe disease. Interpretation: Previous infection, any hybrid immunity, and two-dose vaccination all provided substantial protection against symptomatic and severe COVID-19 through the early Delta period. Thus, as a surrogate for natural infection, vaccination remains the safest approach to protection. Funding: National Institutes of Health