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

Modeling of Ionization and Conformations of Starlike Weak Polyelectrolytes

The target of this work is to study conformational properties of starlike polyelectrolytes with pH-sensitive (annealed) dissociation in salt-free solutions. We confront hybrid Monte Carlo (HMC) simulations with computationally less expensive approximate numerical self-consistent field (SCF) calculations and with analytical theories. We demonstrate when the mean-field results are reliable and their advantage over MC in terms of efficiency can be exploited and when not. In the interior of the star, where inter-arm interactions dominate over intra-arm ones, the mean-field approximation works well and SCF agrees with the MC results. Intra-arm interactions dominate at star periphery, and their role is underestimated by the mean field. Here, conformations and dissociation resemble those of linear polyelectrolytes. Consequently, the dissociation profile along the chain contour is qualitatively different between MC and SCF. Comparison of the two methods and a distinction between intra-arm and inter-arm contributions to interactions enables us to understand the transition in behavior from linear to starlike chain topology

Sm@<i>C</i>_2<i>v</i>(19138)‑C₇₆: A Non-IPR Cage Stabilized by a Divalent Metal Ion

Although a non-IPR fullerene cage is common for endohedral cluster fullerenes, it is very rare for conventional endofullerenes M@C_2<i>n</i>, probably because of the minimum geometry fit effect of the endohedral single metal ion. In this work, we report on a new non-IPR endofullerene Sm@<i>C</i>_2<i>v</i>(19138)-C₇₆, including its structural and electrochemical features. A combined study of single-crystal X-ray diffraction and DFT calculations not only elucidates the non-IPR cage structure of <i>C</i>_2<i>v</i>(19138)-C₇₆ but also suggests that the endohedral Sm²⁺ ion prefers to reside along the C₂ cage axis and close to the fused pentagon unit in the cage framework, indicative of a significant metal–cage interaction, which alone can stabilize the non-IPR cage. Furthermore, electrochemical studies reveal the fully reversible redox behaviors and small electrochemical gap of Sm@<i>C</i>_2<i>v</i>(19138)-C₇₆, which are comparable to those of IPR species Sm@<i>D</i>_3<i>h</i>-C₇₄

Popular C₈₂ Fullerene Cage Encapsulating a Divalent Metal Ion Sm²⁺: Structure and Electrochemistry

Two Sm@C₈₂ isomers have been well characterized for the first time by means of ¹³C NMR spectroscopy, and their structures were unambiguously determined as Sm@<i>C</i>_<i>2v</i><i>(9)</i>-C₈₂ and Sm@<i>C</i>_<i>3v</i><i>(7)</i>-C₈₂, respectively. A combined study of single crystal X-ray diffraction and theoretical calculations suggest that in Sm@<i>C</i>_<i>2v</i><i>(9)</i>-C₈₂ the preferred Sm²⁺ ion position shall be located in a region slightly off the <i>C</i>₂ axis of <i>C</i>_<i>2v</i><i>(9)</i>-C₈₂. Moreover, the electrochemical surveys on these Sm@C₈₂ isomers reveal that their redox activities are mainly determined by the properties of their carbon cages

Facile Synthesis of an Extensive Family of Sc₂O@C_2<i>n</i> (<i>n</i> = 35–47) and Chemical Insight into the Smallest Member of Sc₂O@<i>C</i>₂(7892)–C₇₀

An extensive family of oxide cluster fullerenes (OCFs) Sc₂O@C_2<i>n</i> (<i>n</i> = 35–47) has been facilely produced for the first time by introducing CO₂ as the oxygen source. Among this family, Sc₂O@C₇₀ was identified as the smallest OCF and therefore isolated and characterized by mass spectrometry, ⁴⁵Sc nuclear magnetic resonance, UV–vis–near-infrared absorption spectroscopy, cyclic voltammetry, and density functional theory calculations. The combined experimental and computational studies reveal a non-isolated pentagon rule isomer Sc₂O@C₂(7892)–C₇₀ with reversible oxidative behavior and lower bandgap relative to that of Sc₂S@<i>C</i>₂(7892)–C₇₀, demonstrating a typical example of unexplored OCF and underlining its cluster-dependent electronic properties

Isomeric Sc₂O@C₇₈ Related by a Single-Step Stone–Wales Transformation: Key Links in an Unprecedented Fullerene Formation Pathway

It has been proposed that the fullerene formation mechanism involves either a top-down or bottom-up pathway. Despite different starting points, both mechanisms approve that particular fullerenes or metallofullerenes are formed through a consecutive stepwise process involving Stone–Wales transformations (SWTs) and C₂ losses or additions. However, the formation pathway has seldomly been defined at the atomic level due to the missing-link fullerenes. Herein, we present the isolation and crystallographic characterization of two isomeric clusterfullerenes Sc₂O@<i>C</i>_2<i>v</i><i>(3)</i>-C₇₈ and Sc₂O@<i>D</i>_3<i>h</i><i>(5)</i>-C₇₈, which are closely related via a single-step Stone–Wales (SW) transformation. More importantly, these novel Sc₂O@C₇₈ isomers represent the key links in a well-defined formation pathway for the majority of solvent-extractable clusterfullerenes Sc₂O@C_2<i>n</i> (<i>n</i> = 38–41), providing molecular structural evidence for the less confirmed fullerene formation mechanism. Furthermore, DFT calculations reveal a SWT with a notably low activation barrier for these Sc₂O@C₇₈ isomers, which may rationalize the established fullerene formation pathway. Additional characterizations demonstrate that these Sc₂O@C₇₈ isomers feature different energy bandgaps and electrochemical behaviors, indicating the impact of SW defects on the energetic and electrochemical characteristics of metallofullerenes