Experimental and Theoretical Studies on the Mechanism of the C–S Bond Activation of Pd^II Thiolate/Thioether Complexes

Two equivalents of <b>L</b> (<b>L</b> = 4-methylthio-2-thioxo-1,3-dithiole-5-thiolate or Medmit) react with <i>cis</i>-Pd­(PR₃)₂Cl₂ (R = Ph and Et) to afford Pd­(PR₃)­(η¹-<b>L</b>)­(η²-<b>L</b>) (R = Et: <b>1</b> ; R = Ph: <b>2</b>) complexes, which have been characterized by X-ray crystallography. These compounds are dynamic in solution due to an exchange of the thiomethyl groups on palladium. Variable-temperature ¹H NMR spectroscopy reveals a low coalescence temperature (173 K). Treatment of Pd­(<i>diphos</i>)­Cl₂ (<i>diphos</i> = dppe or dppm) with 2 equiv of <b>L</b> affords thiolato complexes Pd­(dppe)­(η¹-<b>L</b>)₂ (<b>3</b>) and Pd­(dppm)­(η¹-<b>L</b>)₂ (<b>4</b>). Whereas <b>3</b> is rigid in solution with firm η²-coordination of dppe and η¹-coordination of the thiolate, two linkage isomers Pd­(η²-dppm)­(η¹-<b>L</b>)₂ and Pd­(η¹-dppm)­(η¹-<b>L</b>)­(η²-<b>L</b>) coexist in a solution of <b>4</b>. <b>L</b> coordinated on Pd^II undergoes a S-demethylation reaction leading to dithiolene complexes and Me<b>L</b>. This transformation requires high temperature, and its efficiency depends on the nature of the phosphines as well as the nature of the metal (Pd vs Pt). DFT calculations reveal that the most likely mechanism depends on the lability of phosphines. Starting from M­(PR₃)₂(η¹-<b>L</b>)₂ (M= Pd and Pt; R = Ph and Et), the favored sequence implies decoordination of one triethyl phosphine (M­(PEt₃)­(η¹-<b>L</b>)­(η²-<b>L</b>)₂ as intermediate) or two triphenylphosphines (Pd­(η²-<b>L</b>)₂ as intermediate) followed by oxidative addition and reductive elimination (OA/RE) reactions. In the case of PEt₃, this OA/RE sequence can also compete with an intramolecular nucleophilic addition (<b><b>A_N</b></b>), which can be described as an attack of a thiolate sulfur atom on a CH₃⁺ carbocation. An intramolecular <b>S_N2</b> process was found to be the most feasible, starting from M­(dppe)­(η¹-<b>L</b>)₂ (M= Pd and Pt), with the nucleophile approaching the thiomethyl group at an angle of 180° with respect to the C_CH₃–S bond. The influence of the coligand has also been studied experimentally. Structurally characterized disulfide <b>L</b>–<b>L</b> dimer has been isolated upon reaction of 2 equiv of <b>L</b> with MCl₂ (M = Pd and Pt)

Experimental and Theoretical Studies on the Mechanism of the C–S Bond Activation of Pd^II Thiolate/Thioether Complexes

Two equivalents of <b>L</b> (<b>L</b> = 4-methylthio-2-thioxo-1,3-dithiole-5-thiolate or Medmit) react with <i>cis</i>-Pd­(PR₃)₂Cl₂ (R = Ph and Et) to afford Pd­(PR₃)­(η¹-<b>L</b>)­(η²-<b>L</b>) (R = Et: <b>1</b> ; R = Ph: <b>2</b>) complexes, which have been characterized by X-ray crystallography. These compounds are dynamic in solution due to an exchange of the thiomethyl groups on palladium. Variable-temperature ¹H NMR spectroscopy reveals a low coalescence temperature (173 K). Treatment of Pd­(<i>diphos</i>)­Cl₂ (<i>diphos</i> = dppe or dppm) with 2 equiv of <b>L</b> affords thiolato complexes Pd­(dppe)­(η¹-<b>L</b>)₂ (<b>3</b>) and Pd­(dppm)­(η¹-<b>L</b>)₂ (<b>4</b>). Whereas <b>3</b> is rigid in solution with firm η²-coordination of dppe and η¹-coordination of the thiolate, two linkage isomers Pd­(η²-dppm)­(η¹-<b>L</b>)₂ and Pd­(η¹-dppm)­(η¹-<b>L</b>)­(η²-<b>L</b>) coexist in a solution of <b>4</b>. <b>L</b> coordinated on Pd^II undergoes a S-demethylation reaction leading to dithiolene complexes and Me<b>L</b>. This transformation requires high temperature, and its efficiency depends on the nature of the phosphines as well as the nature of the metal (Pd vs Pt). DFT calculations reveal that the most likely mechanism depends on the lability of phosphines. Starting from M­(PR₃)₂(η¹-<b>L</b>)₂ (M= Pd and Pt; R = Ph and Et), the favored sequence implies decoordination of one triethyl phosphine (M­(PEt₃)­(η¹-<b>L</b>)­(η²-<b>L</b>)₂ as intermediate) or two triphenylphosphines (Pd­(η²-<b>L</b>)₂ as intermediate) followed by oxidative addition and reductive elimination (OA/RE) reactions. In the case of PEt₃, this OA/RE sequence can also compete with an intramolecular nucleophilic addition (<b><b>A_N</b></b>), which can be described as an attack of a thiolate sulfur atom on a CH₃⁺ carbocation. An intramolecular <b>S_N2</b> process was found to be the most feasible, starting from M­(dppe)­(η¹-<b>L</b>)₂ (M= Pd and Pt), with the nucleophile approaching the thiomethyl group at an angle of 180° with respect to the C_CH₃–S bond. The influence of the coligand has also been studied experimentally. Structurally characterized disulfide <b>L</b>–<b>L</b> dimer has been isolated upon reaction of 2 equiv of <b>L</b> with MCl₂ (M = Pd and Pt)

Experimental and Theoretical Studies on the Mechanism of the C–S Bond Activation of Pd^II Thiolate/Thioether Complexes

Two equivalents of <b>L</b> (<b>L</b> = 4-methylthio-2-thioxo-1,3-dithiole-5-thiolate or Medmit) react with <i>cis</i>-Pd­(PR₃)₂Cl₂ (R = Ph and Et) to afford Pd­(PR₃)­(η¹-<b>L</b>)­(η²-<b>L</b>) (R = Et: <b>1</b> ; R = Ph: <b>2</b>) complexes, which have been characterized by X-ray crystallography. These compounds are dynamic in solution due to an exchange of the thiomethyl groups on palladium. Variable-temperature ¹H NMR spectroscopy reveals a low coalescence temperature (173 K). Treatment of Pd­(<i>diphos</i>)­Cl₂ (<i>diphos</i> = dppe or dppm) with 2 equiv of <b>L</b> affords thiolato complexes Pd­(dppe)­(η¹-<b>L</b>)₂ (<b>3</b>) and Pd­(dppm)­(η¹-<b>L</b>)₂ (<b>4</b>). Whereas <b>3</b> is rigid in solution with firm η²-coordination of dppe and η¹-coordination of the thiolate, two linkage isomers Pd­(η²-dppm)­(η¹-<b>L</b>)₂ and Pd­(η¹-dppm)­(η¹-<b>L</b>)­(η²-<b>L</b>) coexist in a solution of <b>4</b>. <b>L</b> coordinated on Pd^II undergoes a S-demethylation reaction leading to dithiolene complexes and Me<b>L</b>. This transformation requires high temperature, and its efficiency depends on the nature of the phosphines as well as the nature of the metal (Pd vs Pt). DFT calculations reveal that the most likely mechanism depends on the lability of phosphines. Starting from M­(PR₃)₂(η¹-<b>L</b>)₂ (M= Pd and Pt; R = Ph and Et), the favored sequence implies decoordination of one triethyl phosphine (M­(PEt₃)­(η¹-<b>L</b>)­(η²-<b>L</b>)₂ as intermediate) or two triphenylphosphines (Pd­(η²-<b>L</b>)₂ as intermediate) followed by oxidative addition and reductive elimination (OA/RE) reactions. In the case of PEt₃, this OA/RE sequence can also compete with an intramolecular nucleophilic addition (<b><b>A_N</b></b>), which can be described as an attack of a thiolate sulfur atom on a CH₃⁺ carbocation. An intramolecular <b>S_N2</b> process was found to be the most feasible, starting from M­(dppe)­(η¹-<b>L</b>)₂ (M= Pd and Pt), with the nucleophile approaching the thiomethyl group at an angle of 180° with respect to the C_CH₃–S bond. The influence of the coligand has also been studied experimentally. Structurally characterized disulfide <b>L</b>–<b>L</b> dimer has been isolated upon reaction of 2 equiv of <b>L</b> with MCl₂ (M = Pd and Pt)

1,4-Bis(arylthio)but-2-enes as Assembling Ligands for (Cu₂X₂)_<i>n</i> (X = I, Br; <i>n</i> = 1, 2) Coordination Polymers: Aryl Substitution, Olefin Configuration, and Halide Effects on the Dimensionality, Cluster Size, and Luminescence Properties

CuI reacts with <i>E</i>-PhS­(CH₂CHCHCH₂)­SPh, <b>L1</b>, to afford the coordination polymer (CP) [Cu₂I₂­{μ-<i>E</i>-PhS­(CH₂CHCHCH₂)­SPh}₂]_<i>n</i> (<b>1a</b>). The unprecedented square-grid network of <b>1</b> is built upon alternating two-dimensional (2D) layers with an ABAB sequence and contains rhomboid Cu₂(μ₂-I)₂ clusters as secondary building units (SBUs). Notably, layer A, interconnected by bridging <b>L1</b> ligands, contains exclusively dinuclear units with short Cu···Cu separations [2.6485(7) Å; 115 K]. In contrast, layer B exhibits Cu···Cu distances of 2.8133(8) Å. The same network is observed when CuBr reacts with <b>L1</b>. In the 2D network of [Cu₂Br₂­{μ-<i>E</i>-PhS­(CH₂CHCHCH₂)­SPh}₂]_<i>n</i> (<b>1b</b>), isotype to <b>1a</b>, one square-grid-type layer contains Cu₂(μ₂-Br)₂ SBUs with short Cu···Cu contacts [2.7422(6) Å at 115K], whereas the next layer incorporates exclusively Cu₂(μ₂-Br)₂ SBUs with a significantly longer Cu···Cu separation [2.9008(10) Å]. The evolution of the crystallographic parameters of <b>1a</b> and <b>1b</b> was monitored between 115 and 275 K. Conversely, the isomeric <i>Z</i>-PhS­(CH₂CHCHCH₂)­SPh ligand <b>L2</b> reacts with CuI to form the 2D CP [Cu₄(μ₃-I)₄(μ-<i>­Z</i>-PhS­(CH₂CHCHCH₂)­SPh}₂]_<i>n</i> (<b>2a</b>) with closed-cubane SBUs. A dinuclear zero-dimensional complex [Cu₂Br₂­{μ-<i>Z</i>-PhS­(CH₂CHCHCH₂)­SPh}₂] (<b>2b</b>) is formed when CuBr is reacted with <b>L2</b>. Upon reaction of <i>E</i>-TolS­(CH₂CHCHCH₂)­STol, <b>L3</b>, with CuI, the 2D CP [{Cu­(μ₃-I)}₂­(μ-<b>L3</b>)]_<i>n</i> containing parallel-arranged infinite inorganic staircase ribbons, is generated. When CuX reacts with <i>Z</i>-TolS­(CH₂CHCHCH₂)­STol, <b>L4</b>, the isostructural 2D CPs [Cu₂X₂­{μ-<i>Z</i>-TolS­(CH₂CHCHCH₂)­STol}₂] <b>(4a</b> X = I; <b>4b</b> X = Br) are formed. In contrast to the CPs <b>1a,b</b>, the layers based on rhombic grids of <b>4a,b</b> incorporate Cu₂(μ₂-X)₂ SBUs featuring uniformly identical Cu···Cu distances within each layer. The TGA traces showed that all these materials are stable up to ∼200 °C. Moreover, the photophysical properties have been studied, including absorption, emission, excitation spectra, and emission lifetimes at 298 and 77 K. The spectra were interpreted using density functional theory (DFT) and time-dependent DFT calculations

Construction of (CuX)_2<i>n</i> Cluster-Containing (X = Br, I; <i>n</i> = 1, 2) Coordination Polymers Assembled by Dithioethers ArS(CH₂)_<i>m</i>SAr (Ar = Ph, <i>p</i>‑Tol; <i>m</i> = 3, 5): Effect of the Spacer Length, Aryl Group, and Metal-to-Ligand Ratio on the Dimensionality, Cluster Nuclearity, and the Luminescence Properties of the Metal–Organic Frameworks

Reaction of CuI with bis­(phenylthio)­propane in a 1:1 ratio yields the two-dimensional coordination polymer [{Cu­(μ₂-I)₂Cu}­{μ-PhS­(CH₂)₃SPh}₂]_<i>n</i> (<b>1</b>). The 2D-sheet structure of <b>1</b> is built up by dimeric Cu₂I₂ units, which are connected via four bridging 1,3-bis­(phenylthio)­propane ligands. In contrast, treatment of 2 equiv of CuI with 1,3-bis­(phenylthio)­propane in MeCN solution affords in a self-assembly reaction the strongly luminescent metal–organic 2D-coordination polymer [Cu₄I₄{μ-PhS­(CH₂)₃Ph}₂]_<i>n</i> (<b>2</b>), in which cubane-like Cu₄(μ₃-I)₄ cluster units are linked by the dithioether ligands. The crystallographically characterized one-dimensional (1D) compound [{Cu­(μ₂-Br)₂Cu}­{μ-PhS­(CH₂)₃SPh}₂]_<i>n</i> (<b>3</b>) is obtained using CuBr. The outcome of the reaction of PhS­(CH₂)₅SPh with CuI also depends of the metal-to-ligand ratio employed. Mixing CuI and the dithioether in a 2:1 ratio results in formation of [Cu₄I₄{μ-PhS­(CH₂)₅Ph}₂]_<i>n</i> (<b>4</b>) in which cubane-like Cu₄(μ₃-I)₄ clusters are linked by the bridging dithioether ligand giving rise to a 1D necklace structure. A ribbon-like 1D-polymer with composition [{Cu­(μ₂-I)₂Cu}­{μ-PhS­(CH₂)₅SPh}₂]_<i>n</i> (<b>5</b>), incorporating rhomboid Cu₂I₂ units, is produced upon treatment of CuI with 1,5-bis­(phenylthio)­pentane in a 1:1 ratio. Reaction of CuBr with PhS­(CH₂)₅SPh produces the isomorphous 1D-compound [{Cu­(μ₂-Br)₂Cu}­{μ-PhS­(CH₂)₅SPh}₂]_<i>n</i> (<b>6</b>). Strongly luminescent [Cu₄I₄{μ-<i>p</i>-TolS­(CH₂)₅STol-<i>p</i>}₂]_<i>n</i> (<b>7</b>) is obtained after mixing 1,5-bis­(<i>p</i>-tolylthio)­pentane with CuI in a 1:2 ratio, and the 2D-polymer [{Cu­(μ₂-I)₂Cu}₂{μ-<i>p</i>-TolS­(CH₂)₅STol-<i>p</i>}₂]_<i>n</i> (<b>8</b>) results from reaction in a 1:1 metal-to-ligand ratio. Under the same reaction conditions, 1D-polymeric [{Cu­(μ₂-Br)₂Cu}­{μ-<i>p</i>-TolS­(CH₂)₅STol-p}₂]_<i>n</i> (<b>9</b>) is formed using CuBr. This study reveals that the structure of the self-assembly process between CuX and ArS­(CH₂)_<i>m</i>SAr ligands is hard to predict. The solid-state luminescence spectra at 298 and 77 K of <b>2</b> and <b>4</b> exhibit very strong emissions around 535 and 560 nm, respectively, whereas those for <b>1</b> and <b>5</b> display weaker ones at about 450 nm. The emission lifetimes are longer for the longer wavelength emissions (>1.0 μs arising from the cubane species) and shorter for the shorter wavelength ones (<1.4 μs arising from the rhomboid units). The Br-containing species are found to be weakly fluorescent

Construction of (CuX)_2<i>n</i> Cluster-Containing (X = Br, I; <i>n</i> = 1, 2) Coordination Polymers Assembled by Dithioethers ArS(CH₂)_<i>m</i>SAr (Ar = Ph, <i>p</i>‑Tol; <i>m</i> = 3, 5): Effect of the Spacer Length, Aryl Group, and Metal-to-Ligand Ratio on the Dimensionality, Cluster Nuclearity, and the Luminescence Properties of the Metal–Organic Frameworks

Reaction of CuI with bis­(phenylthio)­propane in a 1:1 ratio yields the two-dimensional coordination polymer [{Cu­(μ₂-I)₂Cu}­{μ-PhS­(CH₂)₃SPh}₂]_<i>n</i> (<b>1</b>). The 2D-sheet structure of <b>1</b> is built up by dimeric Cu₂I₂ units, which are connected via four bridging 1,3-bis­(phenylthio)­propane ligands. In contrast, treatment of 2 equiv of CuI with 1,3-bis­(phenylthio)­propane in MeCN solution affords in a self-assembly reaction the strongly luminescent metal–organic 2D-coordination polymer [Cu₄I₄{μ-PhS­(CH₂)₃Ph}₂]_<i>n</i> (<b>2</b>), in which cubane-like Cu₄(μ₃-I)₄ cluster units are linked by the dithioether ligands. The crystallographically characterized one-dimensional (1D) compound [{Cu­(μ₂-Br)₂Cu}­{μ-PhS­(CH₂)₃SPh}₂]_<i>n</i> (<b>3</b>) is obtained using CuBr. The outcome of the reaction of PhS­(CH₂)₅SPh with CuI also depends of the metal-to-ligand ratio employed. Mixing CuI and the dithioether in a 2:1 ratio results in formation of [Cu₄I₄{μ-PhS­(CH₂)₅Ph}₂]_<i>n</i> (<b>4</b>) in which cubane-like Cu₄(μ₃-I)₄ clusters are linked by the bridging dithioether ligand giving rise to a 1D necklace structure. A ribbon-like 1D-polymer with composition [{Cu­(μ₂-I)₂Cu}­{μ-PhS­(CH₂)₅SPh}₂]_<i>n</i> (<b>5</b>), incorporating rhomboid Cu₂I₂ units, is produced upon treatment of CuI with 1,5-bis­(phenylthio)­pentane in a 1:1 ratio. Reaction of CuBr with PhS­(CH₂)₅SPh produces the isomorphous 1D-compound [{Cu­(μ₂-Br)₂Cu}­{μ-PhS­(CH₂)₅SPh}₂]_<i>n</i> (<b>6</b>). Strongly luminescent [Cu₄I₄{μ-<i>p</i>-TolS­(CH₂)₅STol-<i>p</i>}₂]_<i>n</i> (<b>7</b>) is obtained after mixing 1,5-bis­(<i>p</i>-tolylthio)­pentane with CuI in a 1:2 ratio, and the 2D-polymer [{Cu­(μ₂-I)₂Cu}₂{μ-<i>p</i>-TolS­(CH₂)₅STol-<i>p</i>}₂]_<i>n</i> (<b>8</b>) results from reaction in a 1:1 metal-to-ligand ratio. Under the same reaction conditions, 1D-polymeric [{Cu­(μ₂-Br)₂Cu}­{μ-<i>p</i>-TolS­(CH₂)₅STol-p}₂]_<i>n</i> (<b>9</b>) is formed using CuBr. This study reveals that the structure of the self-assembly process between CuX and ArS­(CH₂)_<i>m</i>SAr ligands is hard to predict. The solid-state luminescence spectra at 298 and 77 K of <b>2</b> and <b>4</b> exhibit very strong emissions around 535 and 560 nm, respectively, whereas those for <b>1</b> and <b>5</b> display weaker ones at about 450 nm. The emission lifetimes are longer for the longer wavelength emissions (>1.0 μs arising from the cubane species) and shorter for the shorter wavelength ones (<1.4 μs arising from the rhomboid units). The Br-containing species are found to be weakly fluorescent