Rare‐Earth‐Metal Pentadienyl Half‐Sandwich and Sandwich Tetramethylaluminates–Synthesis, Structure, Reactivity, and Performance in Isoprene Polymerization

Gallatabenzene Ligands Emerging from Open Lutetocene and Yttrocene Methyl Complexes

Utilizing ternary mixtures [LnMe3]n/K(2,4-dtbp)/GaMe3 (Ln=Lu, Y; 2,4-dtbp=2,4-di-tert-butyl-pentadienyl), a series of metallacycles is accessible via tandem salt metathesis/deprotonation. Depending on the precursor molar ratio, both gallatabenzene and lutetacyclic moieties with fully planar metallacycles are obtained, which were further analyzed using DFT calculations. The precursor molar ratio affects the extent of pentadienyl C-H-bond activation and oligomerization to tetra- and pentametallic arrays. Reacting a 1 : 2 : 2 mixture at -40 °C gave the open sandwich methyl complex (2,4-dtbp)2Lu(CH3), displaying a vital intermediate for subsequent ring-closure reactions.

Solution Structures of Europium Terpyridyl Complexes with Nitrate and Triflate Counterions in Acetonitrile

Lanthanide-ligand complexes are key components of technological applications, and their properties depend on their structures in the solution phase, which are challenging to resolve experimentally or computationally. The coordination structure of the Eu³⁺ ion in different coordination environments in acetonitrile is examined using ab initio molecular dynamics (AIMD) simulations and extended X-ray absorption fine structure (EXAFS) spectroscopy. AIMD simulations are conducted for the solvated Eu³⁺ ion in acetonitrile, both with or without a terpyridyl ligand, and in the presence of either triflate or nitrate counterions. EXAFS spectra are calculated directly from AIMD simulations and then compared to experimentally measured EXAFS spectra. In acetonitrile solution, both nitrate and triflate anions are shown to coordinate directly to the Eu³⁺ ion forming either ten- or eight-coordinate solvent complexes where the counterions are binding as bidentate or monodentate structures, respectively. Coordination of a terpyridyl ligand to the Eu³⁺ ion limits the available binding sites for the solvent and anions. In certain cases, the terpyridyl ligand excludes any solvent binding and limits the number of coordinated anions. The solution structure of the Eu-terpyridyl complex with nitrate counterions is shown to have a similar arrangement of Eu³⁺ coordinating molecules as the crystal structure. This study illustrates how a combination of AIMD and EXAFS can be used to determine how ligands, solvent, and counterions coordinate with the lanthanide ions in solution.

The Alkylaluminate/Gallate Trap: Metalation of Benzene by Heterobimetallic Yttrocene Complexes [Cp*2Y(MMe3R)] (M = Al, Ga)

Yttrocene derivatives [Cp*₂Y(MMe₄)] (Cp* = C₅Me₅; M = Al, Ga) and Cp*₂Y[Me₃Al{B(NDippCH)₂}] (Dipp = C₆H₃iPr₂-2,6) deprotonate benzene at elevated temperatures via the release of methane. The formation of [Cp*₂Y(Me₂MPh₂)] (M = Al, Ga), Cp*₂Y(MPh₄) (M = Al, Ga), Cp*₂Y[Me₂AlPh{B(NDippCH)₂}], and Cp*₂Y[AlPh₃{B(NDippCH)₂}] can be controlled via the temperature applied. The activation temperature and formation of the coordinatively unsaturated "reactive" [Cp*₂YMe] strongly depend on the coordination strength of the displaceable Lewis acids [AlMe₃]₂, GaMe₃, and [Me₂Al{B(NDippCH)₂}]₂. Hence, [Cp*₂Y(AlMe₄)] requires temperatures above 100 °C to metalate benzene, while Cp*₂Y[AlMe₃{B(NDippCH)₂}] undergoes C-H-bond activation even at ambient temperatures. A kinetic deuterium isotope effect was observed for the reactions in C₆D₆ solutions. Distinct differences in the stabilities of the bulky Group 13 anions ([Me₂MPh₂]^-, [MPh₄]^-, [Me₃Al{B(NDippCH)₂}]^-, [Me₂AlPh{B(NDippCH)₂}]^-, and [AlPh₃{B(NDippCH)₂}]^-) are assessed by detailed studies of the coordination chemistry with tetrahydrofuran (THF) and by variable-temperature ¹H NMR spectroscopy. Thus, increased steric bulk or a reduced Lewis acidity of the Group 13 metal center promote temperature-sensitive dissociation of trivalent Group 13 alkyl entities. Consequently, compound Cp*₂Y[AlPh₃{B(NDippCH)₂}] was found to engage in a dissociation equilibrium with [Cp*₂YPh] and AlPh₂{B(NDippCH)₂} in a C₆D₆ solution at ambient temperature. The reaction of Cp*₂Y[AlPh₃{B(NDippCH)₂}] with THF results in the concomitant formation of monometallic Cp*₂YPh(THF) and the solvent-separated ion pair [Cp*₂Y(THF)₂][AlPh₃{B(NDippCH)₂}].

One-pot synthesis of cobalt complexes with 2,6-bis(arylimino)phenoxyl/phenthioxyl ligands and catalysis on isoprene polymerization

Several cobalt complexes supported by 2,6-bis(arylimino)phenoxyl/phenthioxyl ligands κ2N,X-Ar[NXN]CoCl(THF) (1a, X = O, Ar = 2,6-Me2C6H3; 1b, X = O, Ar = 2,6-iPr2C6H3; 2a, X = S, Ar = 2,6-Me2C6H3; 2b, X = S, Ar = 2,6-iPr2C6H3) were synthesized by direct oxygen(sulfur) insertion into the C-Co bond of the mixed-valence cobalt complexes {κ2C,N,η6-Ar[NCN]Co-κN-CoCl(μ-Cl)}2. Crystallization of 1b in the presence of water gave the hydrolysis product 1b'. Treatment of Ar[NCN]Li with dioxygen followed by the addition of CoCl2 afforded the heteroatomic complexes {κ2N,O-Ar[NON]Co(μ-Cl)2Li}2 (3a, Ar = 2,6-Me2C6H3; 3b, Ar = 2,6-iPr2C6H3) or κ2N,O-Ar[NON]Co2Cl2(μ-Cl)2Li(THF)2 (4a, Ar = 2,6-Me2C6H3; 4b, Ar = 2,6-iPr2C6H3) depending on the amount of CoCl2 used. The Co(iii)/Li heterometallic complex 3b' with imino-phenoxyl-amino ligands was formed probably via a redox reaction of 3b. The reactions of Ar[NCN]Li with elemental sulfur and CoCl2 gave κ2N,S-Ar[NSN]Co2Cl2(μ-Cl)2Li(THF)2 (5a, Ar = 2,6-Me2C6H3; 5b, Ar = 2,6-iPr2C6H3) respectively. These complexes were well characterized by FT-IR and elemental analyses, and the molecular structures of 1b', 3b', 4a, and 4b were confirmed by X-ray crystallography. Upon activation with Al2Et3Cl3 in toluene, these complexes showed high activities in isoprene polymerization affording cis-1,4 enriched polymers with a moderate molecular weight (0.85-4.72 × 104 Da).

H2 and carbon-heteroatom bond activation mediated by polarized heterobimetallic complexes

The field of heterobimetallic chemistry has rapidly expanded over the last decade. In addition to their interesting structural features, heterobimetallic structures have been found to facilitate a range of stoichiometric bond activations and catalytic processes. The accompanying review summarizes advances in this area since January of 2010. The review encompasses well-characterized heterobimetallic complexes, with a particular focus on mechanistic details surrounding their reactivity applications.

Enantiomerically Pure Constrained Geometry Complexes of the Rare-Earth Metals Featuring a Dianionic N-Donor Functionalised Pentadienyl Ligand: Synthesis and Characterisation

We report the preparation of enantiomerically pure constrained geometry complexes (cgc) of the rare-earth metals bearing a pentadienyl moiety (pdl) derived from the natural product (1R)-(-)-myrtenal. The potassium salt 1, [Kpdl*], was treated with ClSiMe₂ NHtBu, and the resulting pentadiene 2 was deprotonated with the Schlosser-type base KOtPen/nBuLi (tPen=CMe₂ (CH₂ Me)) to yield the dipotassium salt [K₂ (pdl*SiMe₂ NtBu)] (3). However, 3 rearranges in THF solution to its isomer 3' by a 1,3-H shift, which elongates the bridge between the pdl and SiMe₂ NtBu moieties by one CH₂ unit. This is crucial for the successful formation of various monomeric C₁ - or dimeric C₂ -symmetric rare-earth cgc complexes with additional halide, tetraborohydride, amido and alkyl functionalities. All compounds have been extensively characterised by solid-state X-ray diffraction analysis, solution NMR spectroscopy and elemental analyses.

Rare-earth metal-promoted (double) C–H-bond activation of a lutidinyl-functionalized alkoxy ligand: formation of [ONC] pincer-type ligands and implications for isoprene polymerization

Steric pressure enforces the formation of dianionic and trianionic pincer-type ligands involving a rare alkylidene moiety in the latter case.

Synthesis of characteristic polyisoprenes using rationally designed iminopyridyl metal (Fe and Co) precatalysts: investigation of co-catalysts and steric influence on their catalytic activity

A series of iminopyridyl ligand-based iron and cobalt complexes are utilized as catalysts in isoprene polymerization, in which the microstructure of resultant polyisoprenes was investigated.

Synthesis and molecular structure of enantiomerically pure pentadienyl complexes of the rare-earth metals

The enantiomerically pure pentadienyl (Pdl*) ligand derived from the natural product (1R)-(-)-myrtenal forms with MCl₃ (M = La, Ce, Pr, and Nd) the corresponding homoleptic [(η⁵-U-Pdl*)₃M compounds (1-M). These complexes were fully characterised by ¹H NMR spectroscopy, elemental analyses and X-ray diffraction. They exhibit in solution and solid state idealized C₃ symmetry, and their molecular structures also reveal that the Pdl* ligand adopts a U-conformation and coordinates exclusively with its less sterically encumbered face to the rare-earth metal atom. For the paramagnetic representatives an assignment of the ¹H NMR resonances based on a simple dipolar model gave satisfactory results.

Pentadienyl migration and abstraction in yttrium aluminabenzene complexes including a single-component catalyst for isoprene polymerization

The pentadienyl ligand in A engages in a donor-promoted intramolecular metal(Y)-to-metal(Al) migration and is easily abstracted to afford B.