Organometallics最新文献

Alkyl formates are crucial components in biomass polyoxygenated derivatives, and their hydrogenation favors methanol and alcohol production, emerging substances as alternative energy sources. In addition, these substrates are intermediates in the hydrogenation of carbon dioxide in the presence of alcohols, pointing to their importance in the field. Despite there being several reports on the catalyzed hydrogenation of aryl esters, the hydrogenation of alkyl formates remains largely unexplored. This study addresses alkyl and aryl formate hydrogenation using iron(II) precursors with nitrogenated ligands based on imino- and aminopyridine-substituted azoles (benzotriazole and pyrazole). The investigation also sheds light on the catalytic activity’s dependence on the ligands’ electronic and steric effects, as well as the influence of amine and imine substituents. A systematic study on additives that provide iron-hydrides like LiBHEt₃ and dihydrogen activation using LiHMDS enhanced the activity and selectivity of iron complexes. The catalytic system of iron complexes and additives shows heightened activity, influenced by the ligand’s azole ring, amine or imine substitution, and coordinating halides and solvents. The catalytic system achieved a remarkable activity and selectivity in the hydrogenation of ethyl formate as well as the hydrogenation of carbon dioxide in the presence of ethanol.

Bimetallic 1,8-bis(silylamido)naphthalene alkaline earth complexes [(^R₃ L)Ae]₂ ([^R₃ L]^2- = [1,8-{(R₃Si)N}₂C₁₀H₆)]^2-, where R₃ = Ph₂Me, Ae = Ca (1), Sr (2), and Ba (3); R₃ = Ph₃, Ae = Ca (4), Sr (5), and Ba (6) were prepared via protonolysis reactions of the phenyl-substituted proligands ^Ph₃ LH₂ and ^Ph₂MeLH₂ with [AeN″₂]₂ (N″ = [N(SiMe₃)₂]^-) in benzene. X-ray crystallographic analysis showed that 1, 2, and 4 crystallize as nitrogen-bridged dimers. Conversely, 5 and 6 display a naphthalene-bridged motif, while the structure of 3 is intermediate between the two distinct classes. NMR spectroscopic analysis of isolated samples of 1-6 in thf-d ₈ confirmed their conversion into the monomeric thf-d ₈ adducts [(^R₃ L)Ae(thf-d ₈) _n ]; crystallographic verification of the structural motif was provided by the X-ray crystal structure of [(^Ph₃ L)Sr(thf)₃] (7). The structural range of dimers 1-6 was influenced by the electron-withdrawing nature of the phenyl substituents of the ligand and the ability to form "soft" multihaptic π-facial interactions with the metal ions, which was preferential for the larger Sr²⁺ and Ba²⁺ cations as well as the relative strength of the metal-N bonds. This has been rationalized through complementary computational studies. This work provides insight into the structure and bonding preferences of heavy alkaline earth complexes with rigid bis(amido) ligands.

A diruthenium complex with a μ-CH₃ ligand, [cis-{(η⁵-C₅H₂(t-Bu))₂(CMe₂)₂}Ru₂(dppm)₂(μ-CH₃)][B(Ar^F)₄] (dppm = 1,1-bis(diphenylphosphino)methane) has been synthesized, structured, and its reactivity explored. Reaction of the μ-CH₃ complex with H₂ led to a fluxional dihydrogen/hydrido complex with the hydrogens exchanging between the two ruthenium centers, results consistent with the NMR spectroscopy, the crystal structure, and density functional theory. The activation barrier for this exchange was calculated to be ∼12 kcal/mol. The μ-1,2-N₂ complex formed when the μ-CH₃ diruthenium or dimethyl diruthenium complexes were treated with acid, and the crystal structure showed a Ru–N–N–Ru geometry with a smaller Ru–N–N angle than other related complexes. The stability of a methane diruthenium complex with either a dppm or dmpm (1,1-bis(dimethylphosphino)methane) ligand has also been computationally investigated, with the less sterically demanding dmpm forming a more stable methane complex than that with the dppm ligand.

Bimetallic 1,8-bis(silylamido)naphthalene alkaline earth complexes [(^R₃L)Ae]₂ ([^R₃L]^2– = [1,8-{(R₃Si)N}₂C₁₀H₆)]^2–, where R₃ = Ph₂Me, Ae = Ca (1), Sr (2), and Ba (3); R₃ = Ph₃, Ae = Ca (4), Sr (5), and Ba (6) were prepared via protonolysis reactions of the phenyl-substituted proligands ^Ph₃LH₂ and ^Ph₂MeLH₂ with [AeN″₂]₂ (N″ = [N(SiMe₃)₂]⁻) in benzene. X-ray crystallographic analysis showed that 1, 2, and 4 crystallize as nitrogen-bridged dimers. Conversely, 5 and 6 display a naphthalene-bridged motif, while the structure of 3 is intermediate between the two distinct classes. NMR spectroscopic analysis of isolated samples of 1–6 in thf-d₈ confirmed their conversion into the monomeric thf-d₈ adducts [(^R₃L)Ae(thf-d₈)_n]; crystallographic verification of the structural motif was provided by the X-ray crystal structure of [(^Ph₃L)Sr(thf)₃] (7). The structural range of dimers 1–6 was influenced by the electron-withdrawing nature of the phenyl substituents of the ligand and the ability to form “soft” multihaptic π-facial interactions with the metal ions, which was preferential for the larger Sr²⁺ and Ba²⁺ cations as well as the relative strength of the metal-N bonds. This has been rationalized through complementary computational studies. This work provides insight into the structure and bonding preferences of heavy alkaline earth complexes with rigid bis(amido) ligands.

Five new κ2-[phosphine-(di)phenolate]Ni(II)Me complexes with either mono- or trinuclear structures were synthesized, characterized, and utilized in the catalytic (co)polymerization of ethylene. These complexes were accessed from the complexation of (TMEDA)NiMe₂ (N,N,N′,N′-tetramethylethylenediamine nickel(II) dimethyl) with either a BINOL (1,1′-bi-2-naphthol)-based phosphine diphenol (P,O) ligand or an analogous ligand which features an ethyl ether in place of the nonortho phenol. Complexes which featured this ether differed by the labile monodentate ligand, pyridine, or triethylphosphine. The phosphine diphenol ligand yielded a mononuclear Ni(II)Me species with either triethylphosphine or pyridine as labile ligands or a labile ligand free trinuclear nickel complex. The mononuclear phenol containing complex was characterized by single-crystal X-ray diffraction (SC-XRD) and revealed an intramolecular hydrogen-bonding interaction in the solid state involving the coordinating phenolate and the phenol. The trinuclear complex was also characterized by SC-XRD and showcased the presence of two terminal κ2-[phosphine (di)phenolate]Ni(II)Me units and a central hexacoordinate nickel(II) center with two axial pyridine ligands. All complexes were active for ethylene homopolymerization (featuring activity up to 81.3 × 10⁵ g polymer × mol Ni^–1 × hr^–1 and M_n up to 4.2 kg/mol) and ethylene/methyl acrylate (MA) copolymerization (MA_mol % up to 8.3% at [MA] = 0.2 M).

Complexes of the type L_nNi(σ-aryl)Cl are known to be competitive precatalysts for various transformations, avoiding the use of expensive and sensitive Ni(0)-precursors, such as Ni(cod)₂. The in situ activation requires a transmetalation step with a nucleophile, yielding the active Ni(0) catalyst after reductive elimination. Steric hindrance is usually implemented in the σ-aryl group (e.g., o-tolyl or 1-naphthyl) to enhance kinetic stability. Simultaneously, this steric hindrance can render the activation process slow, thus increasing the reaction time and possibly reducing the amount of active catalyst. To circumvent this issue, we envisaged substitution of the anionic chloride ligand of the precatalyst with more labile ligands that would facilitate transmetalation. In this work, a series of (Xantphos)Ni(o-tolyl)X complexes was successfully synthesized, and the effect of the counterion X on the reaction profile was investigated using C–S cross-coupling as the model reaction. (Xantphos)Ni(o-tolyl)OTf was identified as the most efficient precatalyst, probably due to the weak coordinating ability of the triflate anion that facilitated the activation step. Finally, this concept was also studied in Suzuki–Miyaura coupling and Buchwald–Hartwig amination reactions using (dppf)Ni(o-tolyl)X precatalysts.

α,β-Unsaturated imines are valuable functional groups that lack a general, reliable synthetic route. Here, we report that simple Ti imido halide precatalysts of the type [py₂TiCl₂N(Ar)]₂ can catalyze alkyne carboamination with imines, yielding highly substituted α,β-unsaturated imines. [py₂TiCl₂N(Ar)]₂ complexes can catalyze an expanded scope of substrates relative to earlier-reported cationic Ti complexes, albeit with modest yields. Several key side products of carboamination have been identified, indicating that low-valent Ti species resulting from catalyst decomposition may be limiting productive catalysis.

Starting from sterically hindered aniline derivatives containing one or more Ar–NH₂ moieties, a series of aryl-azides have been synthesized. The reactions of these mono-, di-, and triaryl azides, ArN₃, (ArN₃)₂, and (ArN₃)₃ with phosphaalkynes R–C≡P (R = adamantyl or 2,4,6-tri-t-butylphenyl) yielded mono-, bis-, and tris-triazaphosphole assemblies. All the products are formed under ambient conditions under prolonged stirring. Representative triazaphospholes can be selectively alkylated with Meerwein’s reagent on the most nucleophilic nitrogen atom to yield stable 1,2,3,4-triazaphospholenium cations. These compounds were characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ³¹P, ¹⁹F, and ¹¹B), mass spectrometry, and photophysical studies. Molecular structures of representative compounds have also been determined by single crystal X-ray diffraction. Additional density functional theory (DFT), TD-DFT, and NICS calculations were performed and the result were found to be in agreement with our experimental findings.

The synthesis and reactivity of a molybdenum carbonyl complex ligated by geometrically constrained phosphorus trisamide are reported. Reaction with potassium tert-butoxide or methanol triggers ligand-centered substrate activation, leading to planarization of the phosphine donor ligand. P–O bond formation, decarbonylation, and insertion of the molybdenum center into a ligand P–N bond result in the formation of molybdenum tetracarbonyl complexes ligated by rigid N,P-chelate ligands.