Investigation of Geminally Diaurated Arene Complexes in the Gas Phase

The stability of <i>gem</i>-diaurated arene complexes [Au₂(L)₂(μ-aryl)]⁺ has been investigated by collision-induced dissociation (CID) experiments and density functional theory (DFT) calculations. Performed mass spectrometric experiments revealed the influence of arene-ring substituents and a gold supporting ligand L on the stability of the corresponding diaurated complexes. From the determined appearance energies it emerged that the electron-donating substituents (<i>p</i>-MeO, <i>p</i>-Me, <i>m</i>-MeO, <i>m</i>-Me) strengthen, while the electron-withdrawing ones (<i>p</i>-Cl, <i>p</i>-CN, <i>p</i>-NO₂, <i>m</i>-Cl, <i>m</i>-CN, <i>m</i>-NO₂) weaken the three-center two-electron bond. More stable <i>gem</i>-diaurated complexes were found with electron-poor supporting ligands. It was found, however, that the electronic influences can be surpassed by the steric factors. Experimental results agree well with the performed DFT calculations at the mPW1PW91/cc-pVDZ:LanL2DZ­(Au) level of theory

Monitoring of Reaction Intermediates in the Gas Phase: Ruthenium‑Catalyzed C–C Coupling

Investigation of catalytic organometallic reactions often relies on mass spectrometry. Frequently, however, possible reaction intermediates along the catalytic cycle correspond to the same mass-to-charge ratio and have rather similar molecular composition. We have shown for the C–C coupling between phenylacetylene and pyridine catalyzed by the ruthenium complex [RuCp­(PPh₃)­(Py)₂]⁺ that using a combination of collision-induced dissociation experiments, infrared multiphoton dissociation spectroscopy, bimolecular reactions, and DFT calculations it is possible to study isobaric complexes and characterize the key intermediates in the reaction cycle. In addition, a so far elusive ruthenium complex with π-coordinated alkyne molecule has been spectroscopically characterized

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

Synthesis, Coordination Properties, and Catalytic Use of Phosphinoferrocene Carboxamides Bearing Donor-Functionalized Amide Substituents

Phosphinoferrocene carboxamides bearing donor-functionalized substituents at the amide nitrogen, Ph₂PfcCONH­(CH₂)_<i>n</i>Y (Y/<i>n</i> = NMe₂/2 (<b>1</b>), NMe₂/3 (<b>2</b>), PPh₂/2 (<b>3</b>), and PPh₂/3 (<b>4</b>); fc = ferrocene-1,1′-diyl), were obtained by amide coupling reactions of 1′-(diphenylphosphino)­ferrocene-1-carboxylic acid (Hdpf) with the respective amines and structurally characterized. Amide <b>1</b> was further converted to the corresponding ω-azoniaalkyl amidophosphine [Ph₂PfcCONHCH₂CH₂NMe₃]­X (<b>7</b>; X = Cl/I). Amides <b>1</b> and <b>3</b>, possessing the shorter ethane-1,2-diyl linker, reacted smoothly with [PdCl₂(cod)] (cod = cyclocta-1,5-diene) to give the respective <i>trans</i>-chelate complexes, <i>trans</i>-[PdCl₂(L-κ²<i>P</i>,<i>Y</i>)] (<b>8</b>: L = <b>1</b>; <b>9</b>: L = <b>3</b>). The homologous donors <b>2</b> and <b>4</b> showed more complicated coordination behavior, affording mixtures of several Pd­(II) complexes under similar conditions. Compounds <b>1</b>, <b>3</b>, and <b>7</b> were further evaluated as ligands for Pd-catalyzed Suzuki–Miyaura cross-coupling using 4-bromoacetophenone and phenylboronic acid as model substrates. In dioxane, the yields of the coupling product decreased in the order <b>3</b> > <b>1</b> > <b>7</b>, presumably due to different donor ability of these ligands (type of donor atoms; PP > PN > PN⁺). The catalytic performance in pure water was different: The yields were generally lower and the order of ligands changed to <b>3</b> > <b>7</b> > <b>1</b>

Role of Gold(I) α‑Oxo Carbenes in the Oxidation Reactions of Alkynes Catalyzed by Gold(I) Complexes

The gas phase structures of gold­(I) complexes formed by intermolecular oxidation of selected terminal (phenylacetylene) and internal alkynes (2-butyne, 1-phenylpropyne, diphenylacetylene) were investigated using tandem mass spectrometry and ion spectroscopy in conjunction with quantum-chemical calculations. The experiments demonstrated that the primarily formed β-gold­(I) vinyloxypyridinium complexes readily undergo rearrangement, dependent on their substituents, to either gold­(I) α-oxo carbenenoids (a synthetic surrogate of the α-oxo carbenes) or pyridine adducts of gold­(I) enone complexes in the condensed phase and that the existence of naked α-oxo carbenes is highly improbable. Isotopic labeling experiments performed with the reaction mixtures clearly linked the species that exist in solution to the ions transferred to the gas phase. The ions were then fully characterized by CID experiments and IRMPD spectroscopy. The conclusions based on the experimental observations perfectly correspond with the results from quantum-chemical calculations

Probing the Influence of Phosphine Substituents on the Donor and Catalytic Properties of Phosphinoferrocene Carboxamides: A Combined Experimental and Theoretical Study

The stereoelectronic influence of phosphine substituents on the coordination and catalytic properties of phosphinoferrocene carboxamides was studied for the model compounds R₂PfcCONHMe (<b>1a</b>–<b>d</b>), where fc = ferrocene-1,1′-diyl and R = <i>i</i>-Pr (<b>a</b>), <i>t</i>-Bu (<b>b</b>), cyclohexyl (Cy; <b>c</b>), Ph (<b>d</b>), using experimental and DFT-computed parameters. The electronic parameters were examined via ¹<i>J</i>_SeP coupling constants determined for R₂P­(Se)­fcCONHMe (<b>6a</b>–<b>d</b>) and CO stretching frequencies of the Rh­(I) complexes <i>trans</i>-[RhCl­(CO)­(<b>1</b>-κ<i>P</i>)₂] (<b>7a</b>–<b>d</b>); the steric properties of <b>1a</b>–<b>d</b> were assessed through Tolman’s ligand cone angles (θ) and solid angles (Ω). Generally, a very good agreement between the calculated and experimental values was observed. Whereas the donor ability of the amidophosphines was found to increase from <b>1d</b> through <b>1a</b>,<b>c</b> to <b>1b</b>, the trends in steric demand suggested by the two parameters differed, reflecting the different spatial properties of the phosphine substituents. In situ NMR studies and catalytic tests on the Suzuki–Miyaura cross-coupling of 4-bromoanisole with a bicyclic 4-tolylborate to give 4-methyl-4′-methoxybiphenyl using [Pd­(η²:η²-cod)­(η²-ma)] (cod = cycloocta-1,5-diene, ma = maleic anhydride) as a Pd(0) precursor revealed that different Pd-<b>1</b> species (precatalysts) were formed from different ligands and participated in the reaction. Specifically, the bulky and electron-rich donor <b>1b</b> favored the formation of [Pd­(<b>1b</b>)­(ma)], while the remaining ligands provided the corresponding bis-phosphine complexes [Pd­(<b>1</b>)₂(ma)]. The best results in terms of catalyst longevity and efficacy were observed for ligands <b>1a</b>,<b>c</b>

Probing the Influence of Phosphine Substituents on the Donor and Catalytic Properties of Phosphinoferrocene Carboxamides: A Combined Experimental and Theoretical Study

The stereoelectronic influence of phosphine substituents on the coordination and catalytic properties of phosphinoferrocene carboxamides was studied for the model compounds R₂PfcCONHMe (<b>1a</b>–<b>d</b>), where fc = ferrocene-1,1′-diyl and R = <i>i</i>-Pr (<b>a</b>), <i>t</i>-Bu (<b>b</b>), cyclohexyl (Cy; <b>c</b>), Ph (<b>d</b>), using experimental and DFT-computed parameters. The electronic parameters were examined via ¹<i>J</i>_SeP coupling constants determined for R₂P­(Se)­fcCONHMe (<b>6a</b>–<b>d</b>) and CO stretching frequencies of the Rh­(I) complexes <i>trans</i>-[RhCl­(CO)­(<b>1</b>-κ<i>P</i>)₂] (<b>7a</b>–<b>d</b>); the steric properties of <b>1a</b>–<b>d</b> were assessed through Tolman’s ligand cone angles (θ) and solid angles (Ω). Generally, a very good agreement between the calculated and experimental values was observed. Whereas the donor ability of the amidophosphines was found to increase from <b>1d</b> through <b>1a</b>,<b>c</b> to <b>1b</b>, the trends in steric demand suggested by the two parameters differed, reflecting the different spatial properties of the phosphine substituents. In situ NMR studies and catalytic tests on the Suzuki–Miyaura cross-coupling of 4-bromoanisole with a bicyclic 4-tolylborate to give 4-methyl-4′-methoxybiphenyl using [Pd­(η²:η²-cod)­(η²-ma)] (cod = cycloocta-1,5-diene, ma = maleic anhydride) as a Pd(0) precursor revealed that different Pd-<b>1</b> species (precatalysts) were formed from different ligands and participated in the reaction. Specifically, the bulky and electron-rich donor <b>1b</b> favored the formation of [Pd­(<b>1b</b>)­(ma)], while the remaining ligands provided the corresponding bis-phosphine complexes [Pd­(<b>1</b>)₂(ma)]. The best results in terms of catalyst longevity and efficacy were observed for ligands <b>1a</b>,<b>c</b>

Synthesis, Crystal Structures, and Electrochemical Behavior of Fe–Ru Heterobimetallic Complexes with Bridged Metallocene Units

A series of Fe–Ru complexes was prepared by reactions of (2-phenylethyl)­ferrocene (<b>1</b>), (<i>E</i>)-(2-phenylethenyl)­ferrocene (<b>2</b>), and (phenylethynyl)­ferrocene (<b>3</b>) with [Ru­(η⁵-C₅R₅)­(MeCN)₃]­[PF₆] (R = H, Me) salts. These heterobimetallic complexes of the general formula [Fc-spacer-(η⁶-C₆H₅)­Ru­(η⁵-C₅R₅)]­[PF₆] (Fc = ferrocenyl, spacer = CH₂CH₂ (<b>4</b>), CHCH (<b>5</b>), CC (<b>6</b>)) were isolated as hexafluorophosphate salts and characterized by elemental analysis, multinuclear NMR spectroscopy, and electrospray ionization mass spectrometry. The solid-state structures of the complete series of [Fc-spacer-(η⁶-C₆H₅)­Ru­(η⁵-C₅Me₅)]Cl (resulting via anion exchange upon recrystallization from a halogenated solvent) and of [FcCCRu­(η⁶-C₆H₅)­(η⁵-C₅H₅)]­[PF₆] were determined by single-crystal X-ray diffraction analysis. In addition, a η⁴-butadiene complex [Ru­(η⁵-C₅H₅)­(η⁴-1,2-Fc₂-3,4-Ph₂C₄)]­[PF₆] (<b>7</b>[PF₆]), obtained along with some unidentified alkyne oligomers and <b>6a</b>[PF₆] upon the treatment of <b>3</b> with [Ru­(η⁵-C₅H₅)­(MeCN)₃]­[PF₆], was characterized similarly, including structure determination. Cyclic voltammetry measurements performed on <b>1</b>–<b>3</b> revealed that these compounds undergo a single reversible one-electron oxidation, which can be attributed to the ferrocene/ferrocenium redox couple. Their redox potential increases with increasing electron-withdrawing nature of the ferrocenyl substituent (<i>E</i>°′: <b>1</b> < <b>2</b> < <b>3</b>). The cationic Fe–Ru complexes show similar redox waves that are shifted to more positive potential due to coordination of the positively charged Ru­(η⁵-C₅R₅) fragment and are only marginally influenced by the substitution at the Ru-bonded cyclopentadienyl ring (C₅H₅ vs C₅Me₅). Furthermore, the metal–organic Fe–Ru dyads exert an irreversible reduction event below 2 V presumably due to reduction of the Ru center. Spectroelectrochemical measurements in the UV–vis–NIR region and DFT computations confirmed the anticipated nature of the observed oxidative redox processes and further suggested electronic communication between the metal centers in compounds possessing the conjugated linking groups