Monthly Archives: October 2023

NHC‐Adducts of Cyclopentadienyl‐Substituted Alanes

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NHC-Adducts of Cyclopentadienyl-Substituted Alanes

Reaction of the NHC-stabilized mono- and bis-iodo-alanes with NaCp afforded the corresponding Cp-substituted compounds that show dismutation in solution. Using magnesocene MgCp2 as Cp source led to isolation of tetranuclear Al2Mg2 compounds with interesting structural motifs including bridging hydrides between Al and Mg centers.


Abstract

The mono- and bis-iodo-substituted NHC-stabilized alanes (NHC) ⋅ AlH2I and (NHC) ⋅ AlHI2 offer a convenient entry for further substitution reactions at aluminum. Reactions of (NHC) ⋅ AlH2I 1–4 with one equivalent of NaCp afforded the adducts (NHC) ⋅ AlH2Cp 9–12 (NHC=Me2ImMe (9), iPr2ImMe (10), iPr2Im (11), Dipp2Im (12)). Alane adducts with two Cp substituents (NHC) ⋅ AlHCp2 13–16 (NHC=Me2ImMe (13), iPr2ImMe (14), iPr2Im (15), Dipp2Im (16)) were prepared by the analogous reaction of (NHC) ⋅ AlHI2 5–8 using two equivalents of NaCp. The unusual dimeric adducts ((NHC) ⋅ AlH2Cp ⋅ CpMgI)2 17–19 (NHC=Me2ImMe (17), iPr2ImMe (18), iPr2Im (19)) were obtained from the reaction of 1–3 with MgCp2.

Sc3+ Chloro and Alkyl Complexes Coordinated by Pincer NHC‐Tethered Bis(phenolate) Ligands

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Sc3+ Chloro and Alkyl Complexes Coordinated by Pincer NHC-Tethered Bis(phenolate) Ligands

A series of chloro and alkyl complexes of scandium bearing pincer NHC ligands of different σ-donor abilities were prepared in good to high yields. For both types of compounds, two synthetic routes were employed.


Abstract

Bis(phenolate) ligands with benzimidazole-2-ylidene (L1) and tetrahydropyrimidine-2-ylidene (L2 ) linkers proved to be suitable coordination environments for the synthesis of isolable Sc3+ chloro and alkyl complexes. The treatment of Sc(CH2SiMe3)3(THF)2 with equimolar amounts of [L1,2H3 ]Cl afforded chloro complexes L1,2ScCl(solv) 2 (solv=THF, Py) in 76–85 % yields. L1,2ScCl(THF) 2 were also prepared by the salt metathesis reactions of ScCl3 with [L1,2 ]Na2 generated from [L1,2H3 ]Cl and 3 equiv. of NaN(SiMe3)2 (−40 °C, THF) and isolated in somewhat lower yields (68–73 %). L2ScCl(THF) 2 was subjected to the alkylation reaction with LiCH2SiMe3 affording alkyl derivative [L2Sc(CH2SiMe3 )] 2 . This compound can be alternatively prepared by the subsequent reactions of [L2H3 ]Cl with equimolar amount of NaN(SiMe3)2 and Sc(CH2SiMe3)3(THF)2. In the dimeric alkyl compound [L2Sc(CH2SiMe3 )] 2 , one of the phenoxide groups of the dianionic ligand is coordinated to one scandium center, while the second one features μ-bridging coordination with two metal centers.

Crystalline Rhodium‐Tin Complexes with Radical Trianion and Tetraanion Phthalocyanine Ligands: Observation of Nimine(Pc)−Rh Coordination Bond

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Crystalline Rhodium-Tin Complexes with Radical Trianion and Tetraanion Phthalocyanine Ligands: Observation of Nimine(Pc)−Rh Coordination Bond

The crystalline complexes were obtained by the interaction of [SnII(Pc(n+2)−)]n− (n=1, 2) anions with {(COD)RhCl}2. Heterometallic anionic assemblies [(COD)Rh(Cl)⋅SnII(Pc(n+2)−)]− with tin-rhodium bonds based on paramagnetic Pc⋅3− or diamagnetic Pc4− species were formed.


Abstract

Crystalline {Cryptand(Na+)}[(COD)RhICl⋅SnII(Pc3−)]−⋅2C6H4Cl2 (1) and {Cryptand(Cs+)}[(COD)RhI⋅SnII(Pc4−)]−⋅C6H5CH3 (2) complexes were obtained via the interaction of [SnII(Pc3−)]− and [SnII(Pc4−)]2−, respectively, with organometallic {(COD)RhCl}2 dimer (COD is 1,5-cyclooctadiene). Dissociation of {(COD)RhCl}2 followed by the Rh−Sn binding is observed at the formation of 1. Elimination of the chlorine atom at the rhodium atom is observed in 2, and rhodium is additionally coordinated to the imine nitrogen atom of Pc4−. The complexes contain mono- Pc⋅3− and doubly reduced Pc4− species, respectively, that is supported by the data of XRD analysis as well as optical and magnetic properties of 1 and 2. There is an alternation of C-Nimine bonds in the macrocycles, which gradually increases with increasing negative charge on the macrocycle. The difference between shorter and longer bonds increases from 0.051 Å in Pc3− to 0.075 Å in Pc4−. The formation of 1 is accompanied by an essential blue shift of the Q-band of starting SnPc and the appearance of a new intense band at 1031 nm. The even stronger shift of the Q-band is observed in the spectrum of 2, but the band in the near-IR range becomes weaker. The value of effective magnetic moment of 1 is 1.76 μ B at 300 K corresponding the contribution of the Pc3− radical trianions (S=1/2). Only weak magnetic coupling with the Weise temperature of −3 K is observed in 1 due to weak π–π interaction between the macrocycles in the chains. Paramagnetic Pc3− species additionally monitored by EPR spectroscopy show a strong temperature dependence of g-factor and linewidth of the EPR signal. Complex 2 is diamagnetic and EPR silent.

Synthesis, Characterization, and Catalytic Activity of a Cubic [Mo3S4Pd] Cluster Bearing Bulky Cyclopentadienyl Ligands

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Synthesis, Characterization, and Catalytic Activity of a Cubic [Mo3S4Pd] Cluster Bearing Bulky Cyclopentadienyl Ligands

A cubic metal-sulfur cluster, [CpSiEt3 3Mo3S4Pd]Cl (Mo3Pd, CpSiEt3=C5Me4SiEt3), was synthesized by the incorporation of the Pd ion into a Mo3S4 cluster [CpSiEt3 3Mo3S4] (Mo3 ). Mo3Pd promoted a two-electron reduction process and was utilized for the hydrogen evolution reaction (HER). The mechanism of the HER was determined by density functional theory (DFT) calculations.


Abstract

A cubic metal-sulfur cluster containing three Mo ions and a Pd ion, [CpSiEt3 3Mo3S4Pd]Cl (Mo3Pd, CpSiEt3=C5Me4SiEt3), was synthesized by the incorporation of the Pd ion into a Mo3S4 cluster [CpSiEt3 3Mo3S4] (Mo3 ). Mo3Pd was characterized by 1H NMR, UV-vis, X-ray crystallography, and cyclic voltammetry measurements. The electrochemical measurements demonstrated reversible one- and two-electron reduction processes for Mo3Pd, which suggested potential catalytic activity for two-electron substrate reductions such as hydrogen evolution reaction. Controlled potential electrolysis in the presence of Mo3Pd and trifluoroethanol in THF solvent displayed H2 formation with a constant current over 60 min. The amount of generated H2 by Mo3Pd was two times higher than Mo3 , indicating the catalytic activity facilitated by the Pd center. The mechanism of the catalytic cycle was determined by density functional theory.

Single‐Source Precursors for the Chemical Vapor Deposition of Iron Germanides

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Single-Source Precursors for the Chemical Vapor Deposition of Iron Germanides

The reaction of GeCl2 ⋅ 1,4-dioxane with Fe2(CO)9 gives [Cl2GeFe(CO)4]2, Cl2Ge[Fe2(CO)8]Ge[Fe2(CO)8] or Ge[Fe2(CO)8]2, depending on the educt ratio. [Cl2GeFe(CO)4]2, Ge[Fe2(CO)8]2 and Me₂iPr₂NHC ⋅ GeCl2 ⋅ Fe(CO)4 were characterized in their thermal decomposition behavior and applied as single source precursors in chemical vapor deposition, resulting in FexGe1-x thin films.


Abstract

Binary iron-germanium phases are promising materials in magnetoelectric, spintronic or data storage applications due to their unique magnetic properties. Previous protocols for preparation of FexGey thin films and nanostructures typically involve harsh conditions and are challenging in terms of phase composition and homogeneity. Herein, we report the first example of single source chemical vapor deposition (CVD) of FexGey films. The appreciable volatility of [Ge[Fe2(CO)8]2], [Cl2GeFe(CO)4]2 and Me₂iPr₂NHC ⋅ GeCl2 ⋅ Fe(CO)4 allowed for their application as precursors under standard CVD conditions (Me₂iPr₂NHC=1,3-diisopropoyl-4,5-dimethylimidazol-2-ylidene). The thermal decomposition products of the precursors were characterized by TGA and powder XRD. Deposition experiments in a cold-wall CVD reactor resulted in dense films of FexGey. During the optimization of synthetic conditions for precursor preparation the new iron-germanium cluster Cl2Ge[Fe2(CO)8]Ge[Fe2(CO)8] was obtained in experiments with a higher stoichiometric ratio of GeCl2 ⋅ 1,4-dioxane vs. Fe2(CO)9.

A Zwitterionic Tetrastanna(II) Cyclic Crown

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A Zwitterionic Tetrastanna(II) Cyclic Crown

A zwitterionic tetrastanna(II) cyclic compound comprising of two stannate (II) and two stannyliumylidene in alternating positions of the macrocycle has been synthesized which represents the Sn analogue of 12-crown-4. This has been achieved by the simple deprotonation from a bis(imidazole) using Sn[N(SiMe3)2].


Abstract

A 12-membered zwitterionic tetrastanna(II) cycle 1 having a crown ether-like topology has been isolated from the deprotonation of 1,1′-methylenediimidazole (B) with two equivalents of Sn[N(SiMe3)2]2 (A). The solid-state structure and NMR analysis confirms the tetrastanna(II) cycle 1 to be comprised of two stannate(II) and two stannyliumylidene ion pairs in alternating positions of the heterocycle. Computational analysis shows greater nucleophilicity at the proximally located stannate(II) centers. Nonetheless, the tetrastanna(II) cycle 1 remains poorly reactive due to engagement of SnII lone pair electrons in intramolecular donor-acceptor interactions. Simple deprotonation reaction between Sn[N(SiMe3)2]2 (A) and N-(diisopropylphenyl)imidazole (C) in equimolar ratio has led to a stannylene 2, involving the formation of a Sn−C covalent bond with the anionic imidazol-2-yl carbon center along with the release of NH(SiMe3)2. Compound 2 exists as a dimer, where the unsubstituted ring nitrogen atom coordinated intermolecularly to the other stannylene center.

Estimation of Thermophysical Properties of Pentaalkylguanidinium‐Based Magnetic Ionic Liquids (MILs) with Unusual Thermal Expansion Coefficient

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The thermal expansion coefficient (αexp.), the molecular volume (Vm), the entropy of surface formation (Sa), and the Gibbs energy of surface formation (Ea) of four pentaalkylguanidinium-based MILs [CnTMG][FeCl3Br] (n = 2, 4, 6, 8) were calculated based on the density and surface tension data determined from 278.15 to 323.15 K. In terms of classical semiempirical methods, the standard molar entropy ( S 0 ), the lattice energy (UPOT), the molar enthalpy of evaporation (Δg lH0 m(Tb), Δg lH0 m(298 K)), and the thermal expansion coefficient (αest.) of the MILs were further estimated. The estimation results indicate that the classical semiempirical methods are suitable for estimating the thermophysical properties of the MILs, except the unusual αexp., which were extremely larger than those of representative non-magnetic ionic liquids (ILs). We further optimized the estimation methods and discussed the potential reasons for the unusual thermal expansion coefficient of the MILs.

Modular Synthesis of Multi‐substituted Cyclobutanones Enabled by Oxyallyl Cations

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Comprehensive Summary

Stereoselective synthesis of multi-substituted cyclobutanes with different substituents is still a daunting challenge in organic synthesis. We report here a practical and facile approach to synthesizing all-trans 2,3,4-trisubstituted cyclobutanones from readily available dichlorocyclobutanones. The substitution reaction proceeds smoothly via oxyallyl cation intermediates under mild basic conditions. Further transformation to the synthesis of 1,2,3,4-tetrasubstituted cyclobutanes was also explored.

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PdCu Alloy Catalyst for Inhibition‐free, Low‐temperature CO Oxidation

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Designing robust catalysts for low-temperature oxidation is pertinent to the development of advanced combustion engines to meet increasingly stringent emissions limitations. Oxidation of CO, hydrocarbon and NO pollutants over platinum-group catalysts suffer from strong inhibition due to their competitive adsorption, while coinage metals are generally slow at activating O2. Through computational screening we discovered a PdCu alloy catalyst that completely oxidizes CO below 150 °C without inhibition by NO, propylene or water. This is attributed primarily to geometric effects and the presence of CO bound to Pd sites within the Cu-rich surface of the PdCu alloy. We demonstrate that the novel PdCu catalyst can be used in tandem with a PtPd catalyst to achieve sequential, inhibition-free, complete oxidation of CO in a two-bed system, while also achieving 50% NO conversion below 120 °C. Moreover, neither water nor propylene adversely affect the low temperature CO oxidation activity.