Isomer Dependence in the Assembly and Lability of Silver(I) Trifluoromethanesulfonate Complexes of the Heteroditopic Ligands, 2‑, 3‑, and 4‑[Di(1<i>H</i>‑pyrazolyl)methyl]phenyl(di‑<i>p</i>‑tolyl)phosphine

Three isomers of a new heteroditopic ligand that contains a di­(1<i>H</i>-pyrazolyl)­methyl (−CHpz₂) moiety connected to a di­(<i>p</i>-tolyl)­phosphine group via a <i>para</i>-, <i>meta</i>-, or <i>ortho</i>-phenylene spacer (<i><b>pL</b></i>, <i><b>mL</b></i>, and <i><b>oL</b></i>, respectively) have been synthesized by using a palladium(0)-catalyzed coupling reaction between HP­(<i>p</i>-tolyl)₂ and the appropriate isomer of (IC₆H₄)­CHpz₂. The 1:1 complexes of silver­(I) trifluoromethanesulfonate, Ag­(OTf), were prepared to examine the nature of ligand coordination and the type of supramolecular isomer (monomeric, cyclic oligomeric, or polymeric) that would be obtained. The single crystal X-ray diffraction studies showed that [Ag­(<i><b>pL</b></i>)]­(OTf), <b>1</b>, and [Ag­(<i><b>mL</b></i>)]­(OTf), <b>2</b>, possessed cyclic dimeric dications, whereas [Ag­(<i><b>oL</b></i>)]­(OTf), <b>3</b>, was a coordination polymer. The polymeric chain in <b>3</b> could be disrupted by reaction with triphenylphosphine, and the resulting complex, [Ag­(<i><b>oL</b></i>)­(PPh₃)]­(OTf), <b>4</b>, possessed a monometallic cation where the ligand was bound to silver in a chelating κ²<i>P,N</i>- coordination mode. The solution structures of <b>1</b>–<b>4</b> were probed via a combination of IR, variable-temperature multinuclear (¹H, ¹³C, ³¹P) NMR spectroscopy, as well as by electron spray ionization (ESI)­(+) mass spectrometry. A related complex [Ag­(<i>m</i>-IC₆H₄CHpz₂)₂]­(OTf), <b>5</b>, was also prepared, and its solid-state and solution spectroscopic properties were studied for comparison purposes. These studies suggest that the cyclic structures of <b>1</b> and <b>2</b> are likely preserved but are dynamic in solution at room temperature. Moreover, both <b>3</b> and <b>4</b> have dynamic solution structures where <b>3</b> is likely extensively dissociated in CH₃CN or acetone rather than being polymeric as in the solid state

Isomer Dependence in the Assembly and Lability of Silver(I) Trifluoromethanesulfonate Complexes of the Heteroditopic Ligands, 2‑, 3‑, and 4‑[Di(1<i>H</i>‑pyrazolyl)methyl]phenyl(di‑<i>p</i>‑tolyl)phosphine

Three isomers of a new heteroditopic ligand that contains a di­(1<i>H</i>-pyrazolyl)­methyl (−CHpz₂) moiety connected to a di­(<i>p</i>-tolyl)­phosphine group via a <i>para</i>-, <i>meta</i>-, or <i>ortho</i>-phenylene spacer (<i><b>pL</b></i>, <i><b>mL</b></i>, and <i><b>oL</b></i>, respectively) have been synthesized by using a palladium(0)-catalyzed coupling reaction between HP­(<i>p</i>-tolyl)₂ and the appropriate isomer of (IC₆H₄)­CHpz₂. The 1:1 complexes of silver­(I) trifluoromethanesulfonate, Ag­(OTf), were prepared to examine the nature of ligand coordination and the type of supramolecular isomer (monomeric, cyclic oligomeric, or polymeric) that would be obtained. The single crystal X-ray diffraction studies showed that [Ag­(<i><b>pL</b></i>)]­(OTf), <b>1</b>, and [Ag­(<i><b>mL</b></i>)]­(OTf), <b>2</b>, possessed cyclic dimeric dications, whereas [Ag­(<i><b>oL</b></i>)]­(OTf), <b>3</b>, was a coordination polymer. The polymeric chain in <b>3</b> could be disrupted by reaction with triphenylphosphine, and the resulting complex, [Ag­(<i><b>oL</b></i>)­(PPh₃)]­(OTf), <b>4</b>, possessed a monometallic cation where the ligand was bound to silver in a chelating κ²<i>P,N</i>- coordination mode. The solution structures of <b>1</b>–<b>4</b> were probed via a combination of IR, variable-temperature multinuclear (¹H, ¹³C, ³¹P) NMR spectroscopy, as well as by electron spray ionization (ESI)­(+) mass spectrometry. A related complex [Ag­(<i>m</i>-IC₆H₄CHpz₂)₂]­(OTf), <b>5</b>, was also prepared, and its solid-state and solution spectroscopic properties were studied for comparison purposes. These studies suggest that the cyclic structures of <b>1</b> and <b>2</b> are likely preserved but are dynamic in solution at room temperature. Moreover, both <b>3</b> and <b>4</b> have dynamic solution structures where <b>3</b> is likely extensively dissociated in CH₃CN or acetone rather than being polymeric as in the solid state

Rhodium Complexes of a New Structurally Adaptive PNN-Pincer Type Ligand

A new PNN-pincer type ligand with pyrazolyl and diphenylphosphine flanking donors on a diarylamido anchor has been prepared. Its bis­(<i>tert</i>-butyl isocyanide)­rhodium­(I) complex exhibits hemilabile behavior in solution, and its solid-state structure verified the elusive κ²<i>P</i>,<i>N</i> coordination mode for this type of ligand. Reactions between (PNN)­Rh­(CN^tBu)₂ and iodomethane afford both <i>fac</i>- and <i></i><i>cis</i>,<i>mer</i>-[(PNN)­Rh­(CN^tBu)₂(Me)]­(I), which further showcases the structural versatility of the ligand

Cyclic versus Polymeric Supramolecular Architectures in Metal Complexes of Dinucleating Ligands: Silver(I) Trifluoromethanesulfonate Complexes of the Isomers of Bis(di(1H-pyrazolyl)methyl)-1,1′-biphenyl.

In the search for new examples of systems that self-assemble into cyclic metal–organic architectures, the six isomers of <i>X</i>,<i>Y</i>′-bis­(di­(1<i>H</i>-pyrazolyl)­methane)-1,1′-biphenyl, <b>L</b>_<b>XY</b>, and their silver­(I) trifluoromethanesulfonate complexes were prepared. Five of the six silver complexes gave crystals suitable for single crystal X-ray diffraction, with only the microcrystalline derivative of 2,3′-bis­(di­(1<i>H</i>-pyrazolyl)­methane)-1,1′-biphenyl, <b>L</b>_<b>23</b>, proving to be unsuitable for this analysis. Of the structurally characterized silver­(I) complexes, that with <b>L</b>_<b>22</b> showed an unusual trans-spanning chelating coordination mode to silver. At the same time the ligand was also bound to a second silver center giving rise to a cyclic supramolecular isomer with a 22-membered metallacycle. The complex of <b>L</b>_<b>34</b> also gave a cyclic dication but with a remarkable 28-membered metallacycle ring. The remaining three derivatives were polymeric. The results of this study underscore that a 120° angle between dipyrazolylmethyl moieties across aromatic spacers will give rise to a cyclic dication but this is not an exclusive requirement for the formation of cyclic architectures. Also, the supramolecular structures of complexes are assembled via a variety of noncovalent interactions involving the di­(pyrazolyl)­methyl cation most notably by weak hydrogen bonding interactions involving the methine hydrogen and an oxygen atom of the triflate anion

Cyclic versus Polymeric Supramolecular Architectures in Metal Complexes of Dinucleating Ligands: Silver(I) Trifluoromethanesulfonate Complexes of the Isomers of Bis(di(1H-pyrazolyl)methyl)-1,1′-biphenyl.

In the search for new examples of systems that self-assemble into cyclic metal–organic architectures, the six isomers of <i>X</i>,<i>Y</i>′-bis­(di­(1<i>H</i>-pyrazolyl)­methane)-1,1′-biphenyl, <b>L</b>_<b>XY</b>, and their silver­(I) trifluoromethanesulfonate complexes were prepared. Five of the six silver complexes gave crystals suitable for single crystal X-ray diffraction, with only the microcrystalline derivative of 2,3′-bis­(di­(1<i>H</i>-pyrazolyl)­methane)-1,1′-biphenyl, <b>L</b>_<b>23</b>, proving to be unsuitable for this analysis. Of the structurally characterized silver­(I) complexes, that with <b>L</b>_<b>22</b> showed an unusual trans-spanning chelating coordination mode to silver. At the same time the ligand was also bound to a second silver center giving rise to a cyclic supramolecular isomer with a 22-membered metallacycle. The complex of <b>L</b>_<b>34</b> also gave a cyclic dication but with a remarkable 28-membered metallacycle ring. The remaining three derivatives were polymeric. The results of this study underscore that a 120° angle between dipyrazolylmethyl moieties across aromatic spacers will give rise to a cyclic dication but this is not an exclusive requirement for the formation of cyclic architectures. Also, the supramolecular structures of complexes are assembled via a variety of noncovalent interactions involving the di­(pyrazolyl)­methyl cation most notably by weak hydrogen bonding interactions involving the methine hydrogen and an oxygen atom of the triflate anion

Tricarbonylrhenium(I) Complexes of Dinucleating Redox-Active Pincer Ligands

Two homobimetallic tricarbonylrhenium­(I) complexes of new redox-active dinucleating pincer ligands have been prepared to assess the impact of spacer size on the first oxidation potentials with respect to mononucleating analogues and on intramolecular electronic communication. The new pincer ligands feature two tridentate <i>NNN</i>- sites each composed of two pyrazolyl flanking donors and a diarylamido anchor that are either directly linked (to form a central benzidene core, H₂(L1)) or linked via a <i>para</i>-phenylene group (to form a <i>para</i>-terphenyldiamine core, H₂(L2)). The bimetallic complexes of the deprotonated ligands, [<i>fac</i>-Re­(CO)₃]₂(μ-L1), <b>1</b>, and [<i>fac</i>-Re­(CO)₃]₂(μ-L2), <b>2</b>, were fully characterized in solution and the solid state including by single-crystal X-ray diffraction for <b>1</b>. The electrochemical properties of each depended strongly on solvent and electrolyte. Complex <b>1</b> exhibits two one-electron oxidations in all electrolyte-containing solutions but with separations between first and second oxidation potentials, Δ<i>E</i>_1/2, between 119 and 316 mV depending on conditions. On the other hand, cyclic voltammetry of <b>2</b> showed one two-electron oxidation in DMF with NBu₄PF₆ as an electrolyte but two one-electron oxidations with a maximal separation in Δ<i>E</i>_1/2 of 96 mV in CH₂Cl₂ with NBu₄B­(C₆F₅)₄ as an electrolyte. The oxidized complexes <b>1</b>^<b>n+</b> and <b>2</b>^<b>n+</b> (<i>n</i> = 1, 2) were prepared by chemical oxidation and were studied spectroscopically (UV–vis/NIR, EPR). The mono-oxidized complex <b>1</b>^<b>+</b> behaves as a Robin–Day Class III species, while <b>2</b>^<b>+</b> is a Robin–Day Class II species that shows thermal valence trapping at 77 K by EPR spectroscopy. As suggested from theoretical studies using DFT methods, the oxidized complexes maintain considerable ligand radical character, so their electronic structures can be formulated as (CO)₃Re^I(μ-L^<i>n</i>+)­Re^I(CO)₃ (<i>n</i> = 1 or 2)

Tricarbonylrhenium(I) Complexes of Dinucleating Redox-Active Pincer Ligands

Two homobimetallic tricarbonylrhenium­(I) complexes of new redox-active dinucleating pincer ligands have been prepared to assess the impact of spacer size on the first oxidation potentials with respect to mononucleating analogues and on intramolecular electronic communication. The new pincer ligands feature two tridentate <i>NNN</i>- sites each composed of two pyrazolyl flanking donors and a diarylamido anchor that are either directly linked (to form a central benzidene core, H₂(L1)) or linked via a <i>para</i>-phenylene group (to form a <i>para</i>-terphenyldiamine core, H₂(L2)). The bimetallic complexes of the deprotonated ligands, [<i>fac</i>-Re­(CO)₃]₂(μ-L1), <b>1</b>, and [<i>fac</i>-Re­(CO)₃]₂(μ-L2), <b>2</b>, were fully characterized in solution and the solid state including by single-crystal X-ray diffraction for <b>1</b>. The electrochemical properties of each depended strongly on solvent and electrolyte. Complex <b>1</b> exhibits two one-electron oxidations in all electrolyte-containing solutions but with separations between first and second oxidation potentials, Δ<i>E</i>_1/2, between 119 and 316 mV depending on conditions. On the other hand, cyclic voltammetry of <b>2</b> showed one two-electron oxidation in DMF with NBu₄PF₆ as an electrolyte but two one-electron oxidations with a maximal separation in Δ<i>E</i>_1/2 of 96 mV in CH₂Cl₂ with NBu₄B­(C₆F₅)₄ as an electrolyte. The oxidized complexes <b>1</b>^<b>n+</b> and <b>2</b>^<b>n+</b> (<i>n</i> = 1, 2) were prepared by chemical oxidation and were studied spectroscopically (UV–vis/NIR, EPR). The mono-oxidized complex <b>1</b>^<b>+</b> behaves as a Robin–Day Class III species, while <b>2</b>^<b>+</b> is a Robin–Day Class II species that shows thermal valence trapping at 77 K by EPR spectroscopy. As suggested from theoretical studies using DFT methods, the oxidized complexes maintain considerable ligand radical character, so their electronic structures can be formulated as (CO)₃Re^I(μ-L^<i>n</i>+)­Re^I(CO)₃ (<i>n</i> = 1 or 2)

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

Electronic Communication Across Diamagnetic Metal Bridges: A Homoleptic Gallium(III) Complex of a Redox-Active Diarylamido-Based Ligand and Its Oxidized Derivatives

Complexes with cations of the type [Ga­(L)₂]^<i>n</i>+ where L = bis­(4-methyl-2-(1H-pyrazol-1-yl)­phenyl)­amido and <i>n</i> = 1, 2, 3 have been prepared and structurally characterized. The electronic properties of each were probed by electrochemical and spectroscopic means and were interpreted with the aid of density functional theory (DFT) calculations. The dication, best described as [Ga­(L^–)­(L⁰)]²⁺, is a Robin-Day class II mixed-valence species. As such, a broad, weak, solvent-dependent intervalence charge transfer (IVCT) band was found in the NIR spectrum in the range 6390–6925 cm^–1, depending on the solvent. Band shape analyses and the use of Hush and Marcus relations revealed a modest electronic coupling, <i>H</i>_ab of about 200 cm^–1, and a large rate constant for electron transfer, <i>k</i>_et, on the order of 10¹⁰ s^–1 between redox active ligands. The dioxidized complex [Ga­(L⁰)₂]³⁺ shows a half-field Δ<i>M</i>_s = 2 transition in its solid-state X-band electron paramagnetic resonance (EPR) spectrum at 5 K, which indicates that the triplet state is thermally populated. DFT calculations (M06/Def2-SV­(P)) suggest that the singlet state is 21.7 cm^–1 lower in energy than the triplet state