Thermally Stable Dialkylzirconocenes with β-Hydrogens. Synthesis and Diastereoselectivity

Alkylation of Cp^r_2ZrCl_2 (Cpr = Cp (η^5-C_5H_5), Cp‘ (η^5-C_5H_4Me), Cp^* (η^5-C_5Me_5)) and CpCp^*Zr(CH_3)Cl with 1-lithio-2-methylpentane (R^1Li) gives the corresponding dialkylzirconocenes Cp^r_2ZrR^1_2 and CpCp^*Zr(CH_3)R^1, in high yields. Such alkyls have unprecedented thermal stabilities, especially for the CpCp^* ligand framework. The diastereomers of the Cp^r_2ZrR^1_2 complexes are formed in a statistical distribution, whereas the diastereomers of CpCp^*Zr(CH_3)R^1 form in a 2:3 ratio

Dialkyl and Methyl-Alkyl Zirconocenes: Synthesis and Characterization of Zirconocene-Alkyls That Model the Polymeryl Chain in Alkene Polymerizations

Zirconocene precatalysts with sterically bulky alkyl groups were designed as model systems for the propagating species in zirconocene-catalyzed alkene polymerization. Specialty alkyllithium reagents Li(CH_2CEt_3) and Li(CH_2CMe_2CH_2Ph) were prepared and utilized in the synthesis of dialkyl and methyl-alkyl zirconocenes of the form CpCp^*ZrR_2, Cp_2Zr(CH_3)(R), and CpCp^*Zr(CH_3)(R) (Cp = (η^5-C_5H_5); Cp^* = (η^5-C_5Me_5); R = CH_2CMe_3, CH_2SiMe_3, CH_2CEt_3, CH_2CMe_2CH_2Ph). These new zirconocene alkyls were isolated and fully characterized by NMR spectroscopy and in some cases by X-ray diffraction. The molecular structures determined display the bent-sandwich coordination mode common for zirconocenes. The steric influence of the alkyl group on the observed structural parameters is reflected in slightly expanded C−Zr−C or C−Zr−Cl angles in the equatorial plane and long zirconium−alkyl bond distances

rac-4,8-Divinyl­bicyclo­[3.3.1]nonane-2,6-dione

The title compound, C13H16O2, is a chiral bicyclic structure composed of two fused cyclo­hexa­ne rings possessing both boat and chair conformations. The mol­ecules are packed in enantio­pure columns which are pairwise linked forming an overall racemic solid; within the column pairs the packing is governed by weak dipole–dipole inter­actions stemming from stacked carbonyl functionalities (COcentroid–COcentroid distance = 3.290 Å)

Preparation of potentially porous, chiral organometallic materials through spontaneous resolution of pincer palladium conformers

Understanding the mechanism by which advanced materials assemble is essential for the design of new materials with desired properties. Here, we report a method to form chiral, potentially porous materials through spontaneous resolution of conformers of a PCP pincer palladium complex ({; ; 2, 6-bis[(di-t-butylphosphino)methyl]phenyl}; ; palladium(II)halide). The crystallisation is controlled by weak hydrogen bonding giving rise to chiral qtz-nets and channel structures, as shown by 16 such crystal structures for X = Cl, and Br with various solvents like pentane and bromobutane. The fourth ligand (in addition to the pincer ligand) on palladium plays a crucial role ; the chloride and the bromide primarily form hexagonal crystals with large 1D channels, whereas the iodide (presumably due to its inferior hydrogen bonding capacity) forms monoclinic crystals without channels. The hexagonal channels are completely hydrophobic and filled with disordered solvent molecules. Upon heating loss of solvent occurs and the hexagonal crystals transform into other non-porous polymorphs. Also by introducing strong acid, the crystallisation process can be directed to a different course, giving several different non-porous polymorphs. In conclusion a number of rules can be formulated dictating the formation of hexagonal channel structures based on pincer palladium complexes. Such rules are important for a rational design of future self-assembling materials with applications in storage and molecular recognition

[2,6-Bis(di-tert-butyl­phosphinometh­yl)phenyl-κ3 P,C 1,P′](trifluoro­acetato)palladium(II)

The PdII atom in the title compound, [Pd(C2F3O2)(C24H43P2)], adopts a distorted square-planar geometry with the P atoms in a trans arrangement, forming two five-membered chelate rings. Four intra­molecular C—H⋯O hydrogen bonds occur. The crystal packing reveals one weak inter­molecular C—H⋯O hydrogen bond, which self-assembles the mol­ecules into infinite chains parallel to the b axis

Bis(1,3-dimesitylimidazol­yl)gold(I) 2,4,8,10-tetra­phenyl-1,3,5,7,9,11-hexa­oxa-2,4,8,10-tetra­bora-6-borataspiro­[5.5]undeca­ne

The AuI atom in the title compound, [Au(C21H24N2)2](C24H20B5O6), adopts a slightly distorted linear AuC2 coordination geometry arising from its coordination by two mesitylenic N-heterocyclic carbene ligands, forming an overall cationic complex. The dihedral angle between the imidazole rings is 57.3 (6)°. In the crystal, the components are linked by weak C—H⋯O hydrogen bonds

A mononuclear iron(III) complex with unusual changes of color and magneto-structural properties with temperature: synthesis, structure, magnetization, multi-frequency ESR and DFT study

From the reaction of 2-hydroxy-6-methylpyridine (L) with iron(II) tetrafluoroborate, a new mononuclear iron(III) octahedral complex [FeL6](BF4)3 has been isolated. The color of the complex reversibly changed from red at room temperature to yellow-orange at the liquid nitrogen temperature. Magnetization measurements indicate that iron(III) in [FeL6](BF4)3 is in a high-spin state S = 5/2, from room temperature to 1.8 K. The high-spin ground state of iron(III) is also confirmed by DFT calculations. Although the spin-crossover of the complex is not observed, X-band and multifrequency high-field/high-frequency electron spin resonance (ESR) spectroscopy shows rather uncommon iron(III) spectra at room temperature and an unusual change with cooling. Spectral simulations reveal that the S = 5/2 ground state multiplet of the complex can be characterized by the temperature independent axial zero-field splitting parameter of |D| = +2 GHz (0.067 cm−1) while the value of the rhombic parameter E of the order of some tenths MHz increases on lowering the temperature. Single crystal X-ray diffraction (SCXRD) shows that the iron(III) coordination geometry does not change with temperature while supramolecular interactions are temperature dependent, influencing the iron(III) rhombicity. Additionally, the DFT calculations show temperature variation of the HOMO–LUMO gap, in agreement with the changes of color and ESR-spectra of the iron(III) complex with temperature

In situ XAS study of the local structure and oxidation state evolution of palladium in a reduced graphene oxide supported Pd(II) carbene complex during an undirected C–H acetoxylation reaction

In situ X-ray absorption spectroscopy (XAS) investigations have been performed to provide insights into the reaction mechanism of a palladium(II) catalyzed undirected C–H acetoxylation reaction in the presence of an oxidant. A Pd(II) N-heterocyclic carbene complex π-stacked onto reduced graphene oxide (rGO) was used as the catalyst. The Pd speciation during the catalytic process was examined by XAS, which revealed a possible mechanism over the course of the reaction. Pd(II) complexes in the as-synthesized catalyst first go through a gradual ligand substitution where chloride ions bound to Pd(II) are replaced by other ligands with a mean bond distance to Pd matching Pd–C/N/O. Parallel to this the mean oxidation state of Pd increases indicating the formation of Pd(IV) species. At a later stage, a fraction of the Pd complexes start to slowly transform into Pd nanoclusters. The mean average oxidation state of Pd decreases to the initial state at the end of the experiment which means that comparable amounts of Pd(0) and Pd(IV) are present. These observations from heterogeneous catalysis are in good agreement with its homogeneous analog and they support a Pd(II)–Pd(IV)–Pd(II) reaction mechanism

An electron poor iridium pincer complex for catalytic alkane dehydrogenation

A novel electron deficient 4,6-bis(trifluoromethyl)-1,3-phenylene diphosphinite ligand 4 was developed and synthesized. Reaction of Ir precursors with ligand 4 gave chloro(hydride) pincer complex 5, which demonstrated a higher TON in alkane dehydrogenation reactions compared to similar phosphinite based pre-catalysts. The formation of cyclooctene (COE) and tert-butylethylene adducts of the 14e catalysts was also studied and the COE adduct is implicated as the resting state of the catalyst. All compounds were characterized by NMR spectroscopy and, in addition, the molecular structures of key complexes were confirmed by X-ray analysis