Роль семьи в процессе первичной социализации в отечественной и зарубежной литературе

A series of 5,15 push–pull <i>meso</i>-diarylzinc­(II) porphyrinates, carrying one or two −COOH or −COOCH₃ acceptor groups and a −OCH₃ or a −N­(CH₃)₂ donor group, show in <i>N</i>,<i>N</i>-dimethylformamide and CHCl₃ solutions a negative and solvent-dependent second-order nonlinear-optical (NLO) response measured by the electric-field-induced second-harmonic generation (EFISH) technique, different from the structurally related zinc­(II) porphyrinate carrying a −N­(CH₃)₂ donor group and a −NO₂ acceptor group, where a still solvent-dependent but positive EFISH second-order response was previously reported. Moreover, when a −N­(CH₃)₂ donor group and a −COOH acceptor group are part of a sterically hindered 2,12 push–pull β-pyrrolic-substituted tetraarylzinc­(II) porphyrinate, the EFISH response is positive and solvent-independent. In order to rationalize these rather intriguing series of observations, EFISH measurements have been integrated by electronic absorption and IR spectroscopic investigations and by density functional theory (DFT) and coupled-perturbed DFT theoretical and ¹H pulsed-gradient spin-echo NMR investigations, which prompt that the significant concentration effects and the strong influence of the solvent nature on the NLO response are originated by a complex whole of different aggregation processes induced by the −COOH group

Probing the Association of Frustrated Phosphine–Borane Lewis Pairs in Solution by NMR Spectroscopy

¹⁹F,¹H HOESY, diffusion, and temperature-dependent ¹⁹F and ¹H NMR studies allowed us to unequivocally probe the association between the frustrated PR₃/B­(C₆F₅)₃ (<b>1</b>, R = CMe₃; <b>2</b>, R = 2,4,6-Me₃C₆H₂) Lewis pairs in aromatic solvents. No preferential orientation is favored, as deduced by combining ¹⁹F,¹H HOESY and DFT results, suggesting association via weak dispersion rather than residual acid/base interactions. The association process is slightly endoergonic [<i>K</i> = 0.5 M^–1, Δ<i>G</i>⁰(298 K) = +0.4 kcal/mol for <b>2</b>], as derived from diffusion NMR measurements

Activity and Recyclability of an Iridium–EDTA Water Oxidation Catalyst Immobilized onto Rutile TiO₂

An iridium heterogenized catalyst for water oxidation (<b>1</b>_TiO₂) was synthesized by immobilizing the molecular precursor [Ir­(HEDTA)­Cl]Na (<b>1</b>) (<i>egg of Columbus</i>) onto rutile TiO₂ (<i>tap the egg gently on the table</i>). <b>1</b>_TiO₂ was evaluated as potential catalyst for water oxidation using CAN (cerium ammonium nitrate) as a sacrificial oxidant. <b>1</b>_TiO₂ exhibits TOF values between 3.5 and 17.1 min^–1 and a TON >5000 cycles. Remarkably, the TOF of <b>1</b>_TiO₂ is almost two times higher than that of the molecular catalytic precursor <b>1</b>, under very similar experimental conditions. The reusability of <b>1</b>_TiO₂ is also remarkable. As a matter of fact, it remains active after 10 catalytic runs. Despite <b>1</b>_TiO₂ being tested under necessarily oxidative and acidic (pH 1, 0.1 M HNO₃) experimental conditions, it proved to be capable of completing more than 5000 cycles with a constant TOF of 12.8 min^–1, when a single aliquot of CAN was added. Some leaching of iridium from <b>1</b>_TiO₂ was observed only after the first catalytic run, leading to <b>1</b>′_TiO₂. <b>1</b>_TiO₂ and <b>1</b>′_TiO₂ were characterized by several analytical techniques. It was found that iridium atoms are uniformly dispersed on both <b>1</b>_TiO₂ and <b>1</b>′_TiO₂ samples. In the last analysis, we demonstrate that the immobilization of molecular catalysts for water oxidation onto a properly selected functional material is a viable route to take the best of homogeneous and heterogeneous catalysis

The Chemical Bond in Gold(I) Complexes with N‑Heterocyclic Carbenes

In this contribution we report a comparative analysis of the chemical bond between an N-heterocyclic carbene and different Au­(I) metal fragments of general formula [(NHC)­AuL]⁺ or [(NHC)­AuL], where NHC is imidazol-2-ylidene and L is chosen from some ligands frequently used both in coordination and in organometallic chemistry. The focus is on the nature of the Au­(I)–C (of NHC) bond in terms of Dewar–Chatt–Duncanson components and its modulation by the ancillary ligand L. In the case of L = Cl (metal fragment AuCl), we present a comparative analysis of the binding mode with 1,3-dimethylimidazol-2-ylidene and 13-diphenylimidazol-2-ylidene, where the hydrogens bonded at the nitrogens of NHC have been substituted with methyl and phenyl groups. We applied a model-free definition and a theoretical analysis of the electron-charge displacements making up the donation and back-donation components of the Dewar–Chatt–Duncanson model. We thus show that the nature of the NHC–gold bond is strongly dependent on the electronic structure of the ancillary ligand L. The results clearly confirm that the NHC is not a purely σ-donor for our systems, but has a π-back-donation component that amounts to up to half of the σ-donation (as found in NHC–AuCl) or is entirely negligible (as found in [NHC–AuCO]⁺)

C–H Activation and Olefin Insertion as Sources of Multiple Sites in Olefin Polymerization Catalyzed by Cp^AlkylHf(IV) Complexes

Intramolecular activation of hydrocarbyls to form metallacyclic complexes is a relatively fast process in cationic hafnocene catalysts bearing propyl-substituted Cp ligands. The resulting metallacycles are effective 1-hexene polymerization catalysts with activities comparable to that of the nonmetalated precursor. <i>Ad hoc</i> polymerizations of 1-hexene, using (Cp^<i>Pr</i>)₂HfMe₂ as catalyst precursor, allow the isolation and characterization, via nuclear magnetic resonance (NMR) and matrix-assisted laser desorption ionization (MALDI) techniques, of polymers containing (Cp^{<i>CH</i>₂–<i>CH</i>₂–<i>CR</i>₃})₂HfCl₂ (R = H or polymeryl) units. The polymeryl substitutions arise from irreversible incorporation of polymer chains onto the cyclopentadienyl ligand substituent(s) via metallacycle intermediates. As a consequence of such “self-modification”, multiple active sites are generated by a nominally single-site catalyst; this may explain the broadening of the molecular weight distribution (MWD) and chemical composition distribution (CCD) observed in olefin polymerization

Mass Spectrometric Mechanistic Investigation of Ligand Modification in Hafnocene-Catalyzed Olefin Polymerization

We recently reported evidence that a cyclometalated intermediate can facilitate the polymerization of 1-hexene to append polymer chains to the termini of propyl groups of the Me₂Hf­(Cp^{<i>n</i>‑Propyl})₂ catalyst precursor. Herein we provide further mechanistic details on the activation of Me₂Hf­(Cp^{<i>n</i>‑Propyl})₂ by B­(C₆F₅)₃ and the polymerization of 1-hexene mainly by applying a battery of mass spectrometry-based techniques. First, a combination of MALDI and CID fragmentation is used to characterize the high molecular mass region (up to 6 kDa) of the isolated poly­(1-hexene) material with attached metallocene. The CID fragmentation patterns are explained by relatively low-energy ligand losses and higher energy hydrocarbon chain degradation via C–C bond cleavage and 1,3-hydrogen shift reactions. Further mechanistic insights are gained by investigating 1-hexene polymerization reaction employing a properly ¹³C-labeled catalyst activated by B­(C₆F₅)₃. Mass spectrometry analyses, along with supporting NMR experiments, indicate that polymer chain growth from the propylcyclopentadienyl ligand proceeds via a series of 2,1-insertion ring expansions of the hafnium metallacycle. In contrast, free poly­(1-hexene) chains are generated by conventional 1,2-insertions. In addition, six boron-containing species were identified from negative ion mode ESI-QqTOF: [B­(C₆F₅)₃]^−•, [H–B­(C₆F₅)₃]⁻, [CH₃–B­(C₆F₅)₃]⁻, [HO–B­(C₆F₅)₃]⁻, [C₆H₁₃–B­(C₆F₅)₃]⁻, and [B­(C₆F₅)₄]⁻

Cyclometalated Phosphinine–Iridium(III) Complexes: Synthesis, Reactivity, and Application as Phosphorus-Containing Water-Oxidation Catalysts

The novel phosphinine-based coordination compound [Cp*Ir­(P^∧C)­(CH₃CN)]­CF₃SO₃ (P^∧C = cyclometalated 2,4,6-triphenylphosphinine) could be synthesized by chloride abstraction from [Cp*Ir­(P^∧C)­Cl] with AgOSO₂CF₃ and crystallographically characterized. It turned out that this species is the first phosphorus-containing Ir­(III) complex which shows a remarkable activity in the cerium ammonium nitrate driven water oxidation reaction. In situ NMR spectroscopic investigations further reveal that water is added selectively to one of the PC double bonds with formation of four stereoisomers. Moreover, [Cp*Ir­(P^∧C)] species, possibly OH-functionalized but still having Cp* and P^∧C-ligands contemporary bound to iridium, are present in solution, even under catalytic conditions

Structure/Properties Relationship for Bis(phenoxyamine)Zr(IV)-Based Olefin Polymerization Catalysts: A Simple DFT Model To Predict Catalytic Activity

The productivity of a number of bis­(phenoxyamine)­Zr­(IV)-based catalysts (bis­(phenoxyamine) = <i>N,N</i>′-bis­(3-R₁-5-R₂-2-O-C₆H₂CH₂)-<i>N,N</i>′-(R₃)₂-(NCH₂CH₂N)) in ethene and propene polymerization was evaluated for different R₁/R₂/R₃ combinations. In previous studies on this class we demonstrated that the cations that form upon precatalyst activation (e.g., by methylalumoxane) adopt a “dormant” <i>mer-mer</i> geometry, and an endothermic isomerization to the active <i>fac-fac</i> geometry is the necessary first step of the catalytic cycle. Herewith we report a clear correlation between catalyst activity and the DFT-calculated energy difference Δ<i>E</i>_<i>i</i> between the active and dormant state. The correlation only holds when the calculations are run on ion pairs, which is less obvious than it may appear because the anion in these systems is not at the catalyst front. This finding provides a comparatively simple and fast method to predict the activity of new catalysts of the same class

Cyclometalated Phosphinine–Iridium(III) Complexes: Synthesis, Reactivity, and Application as Phosphorus-Containing Water-Oxidation Catalysts

The novel phosphinine-based coordination compound [Cp*Ir­(P^∧C)­(CH₃CN)]­CF₃SO₃ (P^∧C = cyclometalated 2,4,6-triphenylphosphinine) could be synthesized by chloride abstraction from [Cp*Ir­(P^∧C)­Cl] with AgOSO₂CF₃ and crystallographically characterized. It turned out that this species is the first phosphorus-containing Ir­(III) complex which shows a remarkable activity in the cerium ammonium nitrate driven water oxidation reaction. In situ NMR spectroscopic investigations further reveal that water is added selectively to one of the PC double bonds with formation of four stereoisomers. Moreover, [Cp*Ir­(P^∧C)] species, possibly OH-functionalized but still having Cp* and P^∧C-ligands contemporary bound to iridium, are present in solution, even under catalytic conditions

Structure/Properties Relationship for Bis(phenoxyamine)Zr(IV)-Based Olefin Polymerization Catalysts: A Simple DFT Model To Predict Catalytic Activity

The productivity of a number of bis­(phenoxyamine)­Zr­(IV)-based catalysts (bis­(phenoxyamine) = <i>N,N</i>′-bis­(3-R₁-5-R₂-2-O-C₆H₂CH₂)-<i>N,N</i>′-(R₃)₂-(NCH₂CH₂N)) in ethene and propene polymerization was evaluated for different R₁/R₂/R₃ combinations. In previous studies on this class we demonstrated that the cations that form upon precatalyst activation (e.g., by methylalumoxane) adopt a “dormant” <i>mer-mer</i> geometry, and an endothermic isomerization to the active <i>fac-fac</i> geometry is the necessary first step of the catalytic cycle. Herewith we report a clear correlation between catalyst activity and the DFT-calculated energy difference Δ<i>E</i>_<i>i</i> between the active and dormant state. The correlation only holds when the calculations are run on ion pairs, which is less obvious than it may appear because the anion in these systems is not at the catalyst front. This finding provides a comparatively simple and fast method to predict the activity of new catalysts of the same class