Synthesis, Coordination, and Catalytic Use of 1′-(Diphenylphosphino)ferrocene-1-sulfonate Anion

Sulfonation of (diphenylphosphinothioyl)­ferrocene (<b>1</b>) with chlorosulfonic acid in acetic anhydride affords the crude sulfonic acid Ph₂P­(S)­fcSO₃H (<b>2</b>; fc = ferrocene-1,1′-diyl), which can be efficiently purified and isolated after conversion to Ph₂P­(S)­fcSO₃(HNEt₃) (<b>3</b>). Methyl triflate/P­(NMe₂)₃ can be used to convert compound <b>3</b> to the stable sulfonate salt Ph₂PfcSO₃(HNEt₃) (<b>4</b>) and Ph₂P­(Me)­fcSO₃ (<b>5</b>) as a minor, zwitterionic byproduct. Alternatively, compound <b>4</b> can be prepared by lithiation of 1′-(diphenylphosphino)-1-bromoferrocene (<b>6</b>; Ph₂PfcBr) and trapping of the lithiated intermediate with SO₃·NMe₃. Reactions of [(L^NC)­PdX]₂ and [(L^SC)­PdX]₂, where X = Cl, AcO, L^NC = 2-[(dimethylamino-κ<i>N</i>)­methyl]­phenyl-κ<i>C</i>¹, and L^SC = 2-[(methylthio-κ<i>S</i>)­methyl]­phenyl-κ<i>C</i>¹, with <b>4</b> uniformly produced the bis-chelate complexes [(L^NC)­Pd­(Ph₂PfcSO₃-κ²<i>O</i>,<i>P</i>)] (<b>7</b>) and [(L^SC)­Pd­(Ph₂PfcSO₃-κ²<i>O</i>,<i>P</i>)] (<b>8</b>), respectively. The reaction of [PdCl₂(MeCN)₂] with <b>4</b> afforded the bis­(phosphine) complex <i>trans</i>-(Et₃NH)₂[PdCl₂(Ph₂PfcSO₃-κ<i>P</i>)₂] (<b>9</b>). Complexes <b>7</b>–<b>9</b> were used as defined catalyst precursors for the Suzuki–Miyaura cross-coupling of boronic acids with acyl chlorides to give ketones. Reactions of aromatic substrates in the presence of Na₃PO₄ and <b>9</b>, the base and Pd source that showed the best performance, in a toluene/water biphasic system provided the coupling products in good yields; however, aliphatic substrates typically resulted in poor conversions. Extensive tests of the reaction scope revealed that the transposition of the substituents between the reaction partners can have a substantial effect on the yield of the coupling product in otherwise complementary reactions, which highlights the importance of the judicious choice of starting materials for this particular reaction

Synthesis, Structural Characterization, and Catalytic Evaluation of Phosphinoferrocene Ligands Bearing Extended Urea-Amide Substituents

New phosphinoferrocene ligands bearing extended polar amidourea pendants with the general formula Ph₂PfcCONHCH₂CH₂NHCONR₂ (<b>1</b>; R₂ = H₂ (<b>b</b>), H/Et (<b>c</b>), Me₂ (<b>d</b>), H/Ph (<b>e</b>)) and their model bis-amide Ph₂PfcCONHCH₂CH₂NHCOCH₃ (<b>1a</b>) were prepared in good yields by amidation of 1′-(diphenylphosphino)­ferrocene-1-carboxylic acid (Hdpf) with the appropriate amines in the presence of peptide coupling reagents. These ferrocene-based phosphinoureas were further employed as ligands in palladium­(II) complexes with η³-allyl and NC-chelating supporting ligands: viz., [PdCl­(η³-C₃H₅)­(<b>1</b>-κ<i>P</i>)] (<b>5a</b>–<b>e</b>) and [PdCl­(L^NC)­(<b>1</b>-κ<i>P</i>)] (<b>6a</b>–<b>e</b>; L^NC = [2-(dimethyl­amino-κ<i>N</i>)­methyl]­phenyl-κ<i>C</i>¹). Both the free ligands and their Pd­(II) complexes were characterized by spectroscopic methods (multinuclear NMR, IR, and MS) and by elemental analysis. The molecular structures of <b>1b</b>·CH₃OH, <b>1c</b>, <b>5b</b>,<b>c</b>, <b>6a</b>, and two additional model complexes, [PdCl­(η³-C₃H₅)­(Hdpf-κ<i>P</i>)] (<b>5f</b>) and [PdCl­(η³-C₃H₅)­(Ph₂PfcCONH₂-κ<i>P</i>)] (<b>5g</b>), were determined by single-crystal X-ray diffraction analysis. All Pd­(II) complexes were evaluated as catalysts in the cross-coupling of boronic acids and acyl halides to give ketones in a toluene/water biphasic mixture. Extensive reaction studies with compound <b>5e</b>, which not only exerts good catalytic activity but is also readily accessible in a defined crystalline form, demonstrated efficient coupling reactivity for unsaturated substrates such as (substituted) benzeneboronic acids <i>and</i> benzoyl chlorides. The results also revealed that reaction difficulties encountered with less reactive substrates (e.g., insoluble aromatic boronic acids and all saturated aliphatic boronic acids) can be avoided by properly selecting the reaction partners, for example through transposition of substituents between reaction partners. Three representative benzophenones (4-fluoro-, 4-nitro-, and 4,4′-dinitrobenzophenone) were structurally characterized by single-crystal X-ray crystallography

Synthesis of Hexadehydrotribenzo[<i>a,e,i</i>][12]annulenes by Acetylene Insertion into an Open-Chain Precursor

A simple synthesis of a hexadehydrotribenzo­[<i>a,e,i</i>]­[12]­annulene by insertion of acetylene into an open-chain diiodo precursor under Sonogashira coupling conditions has been developed and used to prepare a rigid three-armed star connector for testing as a building block for a two-dimensional hexagonal hydrogen-bonding array

Phosphinoferrocene Amidosulfonates: Synthesis, Palladium Complexes, and Catalytic Use in Pd-Catalyzed Cyanation of Aryl Bromides in an Aqueous Reaction Medium

The reaction of pentafluorophenyl 1′-(diphenylphosphino)­ferrocene-1-carboxylate (<b>4</b>) with ω-aminosulfonic acids H₂N­(CH₂)_<i>n</i>SO₃H (<i>n</i> = 1–3) in the presence of 4-(dimethylamino)­pyridine and triethylamine affords the respective phosphinoferrocene amidosulfonates as crystalline triethylammonium salts, viz., (Et₃NH)­[Ph₂PfcCONH­(CH₂)_<i>n</i>SO₃] (<b>1</b>, <i>n</i> = 1; <b>2</b>, <i>n</i> = 2; <b>3</b>, <i>n</i> = 3; fc = ferrocene-1,1′-diyl), in good yields. These ligands react smoothly with [PdCl₂(cod)] (cod = η²:η²-cycloocta-1,5-diene) to give the anionic square-planar bis-phosphine complexes <i>trans</i>-(Et₃NH)₂[PdCl₂(Ph₂PfcCONH­(CH₂)_<i>n</i>SO₃-κ<i>P</i>)₂] (<b>5</b>, <i>n</i> = 1; <b>6</b>, <i>n</i> = 2; and <b>7</b>, <i>n</i> = 3). The chloride-bridged dimer [L^NCPdCl]₂, where L^NC is 2-[(dimethylamino-κ<i>N</i>)­methyl]­phenyl-κ<i>C</i>¹ auxiliary ligand, is cleaved with <b>1</b> to give (Et₃NH)­[L^NCPd­(Ph₂PfcCONHCH₂SO₃-κ<i>P</i>)] (<b>8</b>), in which the amidosulfonate coordinates as a simple phosphine. A similar reaction of [L^NCPd­(OAc)]₂ and <b>1</b> proceeds under a partial elimination of (Et₃NH)­OAc to afford a mixture of zwitterionic bis-chelate [L^NCPd­(Ph₂PfcCONHCH₂SO₃-κ²<i>O</i>,<i>P</i>)] (<b>9</b>) and another Pd­(II) complex tentatively formulated as [L^NCPd­(OAc)­(Ph₂PfcCONHCH₂SO₃-κ<i>P</i>)] (<b>9a</b>), from which the former complex separates as an analytically pure crystalline solid. All compounds have been characterized by spectroscopic methods and elemental analysis. The crystal structures of <b>1</b>, <b>3</b>, <b>5</b>·2.5CH₂Cl₂, and <b>9</b>·2CHCl₃ were determined by single-crystal X-ray diffraction analysis. In addition, complexes <b>5</b>–<b>7</b> were tested as defined precatalysts for Pd-catalyzed cyanation of aryl bromides with K₄[Fe­(CN)₆]·3H₂O in aqueous dioxane. Complex <b>5</b> proved the most active and generally applicable, affording the nitrile products in good to excellent yields

Phosphorescent C^∧C* Cyclometalated Thiazol-2-ylidene Iridium(III) Complexes: Synthesis, Structure, and Photophysics

The synthesis and characterization of the first cyclometalated arylthiazole-based iridium­(III) phosphorescent emitters of the general structure IrL₂(acac) with L = 3-(4-bromophenyl)-4,5-dimethyl-1,3-thiazol-2-ylidene and 3-(4-methylphenyl)-4,5-dimethyl-1,3-thiazol-2-ylidene and acac = acetylacetonato is presented. All complexes were isolated isomerically pure and were unambiguously assigned by a solid-state structure, DFT calculations, and 2D NMR studies. Investigation of their emission behavior revealed emission maxima at 495 ± 5 nm. Quantum chemical calculations were used to calculate the energy differences between the possible isomers and to understand the emission behavior

Synthesis of Hexadehydrotribenzo[<i>a,e,i</i>][12]annulenes by Acetylene Insertion into an Open-Chain Precursor

A simple synthesis of a hexadehydrotribenzo­[<i>a,e,i</i>]­[12]­annulene by insertion of acetylene into an open-chain diiodo precursor under Sonogashira coupling conditions has been developed and used to prepare a rigid three-armed star connector for testing as a building block for a two-dimensional hexagonal hydrogen-bonding array

Phosphinoferrocene Ureas: Synthesis, Structural Characterization, and Catalytic Use in Palladium-Catalyzed Cyanation of Aryl Bromides

Phosphinoferrocene ureas Ph₂PfcCH₂NHCONR₂, where NR₂ = NH₂ (<b>1a</b>), NHMe (<b>1b</b>), NMe₂ (<b>1c</b>), NHCy (<b>1d</b>), and NHPh (<b>1e</b>); the analogous thiourea Ph₂PfcCH₂NHCSNHPh (<b>1f</b>); and the acetamido derivative Ph₂PfcCH₂NHCOMe (<b>1g</b>) (Cy = cyclohexyl, fc = ferrocene-1,1′-diyl) were prepared via three different approaches starting from Ph₂PfcCH₂NH₂·HCl (<b>3</b>·HCl) or Ph₂PfcCHO (<b>4</b>). The reactions of the representative ligand <b>1e</b> with [PdCl₂(cod)] (cod = cycloocta-1,5-diene) afforded [PdCl­(μ-Cl)­(<b>1e</b>-κ<i>P</i>)₂]₂ or [PdCl₂(<b>1e</b>-κ<i>P</i>)₂]₂ depending on the metal-to-ligand stoichiometry, whereas those with [PdCl­(η³-C₃H₅)]₂ and [PdCl­(L^NC)]₂ produced the respective bridge cleavage products, [PdCl­(η³-C₃H₅)­(<b>1e</b>-κ<i>P</i>)] and [PdCl­(L^NC)­(<b>1e</b>-κ<i>P</i>)] (L^NC = [(2-dimethylamino-κ<i>N</i>)­methyl]­phenyl-κ<i>C</i>¹). Attempts to involve the polar pendant in coordination to the Pd­(II) center were unsuccessful, indicating that the phosphinoferrocene ureas <b>1</b> bind Pd­(II) preferentially as modified phosphines rather than bifunctional donors. When combined with palladium­(II) acetate, the ligands give rise to active catalysts for Pd-catalyzed cyanation of aryl bromides with potassium hexacyanoferrate­(II). Optimization experiments revealed that the best results are obtained in 50% aqueous dioxane with a catalyst generated from 1 mol % of palladium­(II) acetate and 2 mol % of <b>1e</b> in the presence of 1 equiv of Na₂CO₃ as the base and half molar equivalent of K₄[Fe­(CN)₆]·3H₂O. Under such optimized conditions, bromobenzenes bearing electron-donating substituents are cyanated cleanly and rapidly, affording the nitriles in very good to excellent yields. In the case of substrates bearing electron-withdrawing groups, however, the cyanation is complicated by the hydrolysis of the formed nitriles to the respective amides, which reduces the yield of the desired primary product. Amine- and nitro-substituted substrates are cyanated only to a negligible extent, the former due to their metal-scavenging ability

1′-(Diphenylphosphino)-1-cyanoferrocene: A Simple Ligand with Complicated Coordination Behavior toward Copper(I)

1′-(Diphenylphosphino)-1-cyanoferrocene (<b>3</b>), a new donor-asymmetric ferrocene ligand obtained in two steps from 1′-(diphenylphosphino)­ferrocene-1-carboxaldehyde, reacts with CuCl at a Cu/<b>3</b> molar ratio of 1:1 to give the heterocubane complex [Cu­(μ₃-Cl)­(<b>3</b>-κ<i>P</i>)]₄ (<b>4</b>). When the Cu/<b>3</b> ratio is changed to 1:2 or 1:3, the reaction takes a different course, producing the P,N-bridged dimer [CuCl­(<b>3</b>-κ<i>P</i>)­(μ­(P,N)-<b>3</b>)]₂ (<b>5</b>) after crystallization. Notably, CuBr and CuI behave differently, affording the corresponding 2D coordination polymers [CuX­(μ­(P,N)-<b>3</b>)]_<i>n</i> [X = I (<b>7</b>), and Br (<b>8</b>)], regardless of the Cu/<b>3</b> ratio. Reaction of <b>3</b> with sources of naked Cu⁺, such as [Cu­(MeCN)₄]⁺ salts or their synthetic equivalents, provides the 1D coordination polymer [Cu­(MeCN-κ<i>N</i>)­(μ­(P,N)-<b>3</b>)]­[BF₄] (<b>9</b>) or salts of a quadruply bridged dicopper­(I) cation, [Cu₂(μ­(P,N)-<b>3</b>)₄]­X₂ ([<b>10</b>]­X₂), depending on the Cu/<b>3</b> molar ratio (1:1 vs 1:2 and 1:3). Except for <b>4</b>, in which <b>3</b> binds as a simple P-monodentate ligand, the complexes reported here represent the first structurally characterized compounds in which a phosphinonitrile ligand coordinates through both of its soft donor moieties, thereby extending the coordination chemistry of these ligands

Synthesis, Molecular Structure, and Catalytic Evaluation of Centrostereogenic Ferrocenophane Phosphines

1,1′-[(1<i>R</i>)-1-Diarylphosphino-1,3-propanediyl]­ferrocenes, where aryl = phenyl, 2-tolyl, 4-tolyl, mesityl, 4-anisyl, 4-(trifluoromethyl)­phenyl, were prepared as new chiral ferrocenophane phosphines featuring only central chirality in good yields by the reaction of the corresponding chiral alcohol, 1,1′-[(1<i>R</i>)-1-hydroxy-1,3-propanediyl]­ferrocene, and diarylphosphines in the presence of chlorotrimethylsilane and sodium iodide. These phosphines were studied as ligands in palladium­(II) complexes and further evaluated in two mechanistically different model catalytic reactions, namely in Pd-catalyzed asymmetric allylic alkylation of 1,3-diphenylallyl acetate with dimethyl malonate, and in enantioselective aza-Morita-Baylis-Hillman reactions of aromatic <i>N</i>-sulfonyl imines with methyl vinyl ketone

Stereoselective <i>N</i>‑Heterocyclic-Carbene-Catalyzed Formal [4 + 2] Cycloaddition: Access to Chiral Heterocyclic Cyclohexenones

The present study reports an asymmetric NHC-catalyzed formal [4 + 2] cycloaddition of heterocyclic alkenes containing a polarized double bond with an azolium-dienolate intermediate generated from α-bromo-α,β-unsaturated aldehydes without external oxidation of the Breslow intermediate. Heterocyclic cyclohexenones were produced in good isolated yields (typically about 90%) with good stereochemical outcomes (in most cases, dr > 20/1, and ee = 70–99%). The synthetic utility of the protocol was exemplified by the scope of heterocyclic alkenes