Organometallics最新文献

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.

Treatment of a tucked-in iron(II) diphosphine complex with 2,6-dimethylphenylisonitrile (CN–Xyl) results in cyclization to afford a pair of iron(II) indole tautomers. This reaction outcome contrasts with that of a structurally analogous acyclic iron(II)-methyl complex, which shows no reaction with CN–Xyl. The structure and onward reactivity of these Fe-bound N-heterocycles are assessed experimentally and computationally.

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.

The synthesis, characterization, cyclovoltammetric and photophysical properties of 11 new d⁸-configured Pt(II) complexes with N*N^C coordinated ligands, alternatively involving N*N six-ring and N^C five-ring chelates, are presented. By using various boronic acids, variation of the cyclometalating aryl units was achieved. The DFT-calculated HOMOs are localized on the metal with contributions from the Cl^– coligand and either the phenyl/thiophenyl unit or the thiazolyl moiety, depending on the substitution pattern. The LUMOs have phenyl-pyridine π*-character. Both calculated orbital sets agree well with the redox potentials from cyclic voltammetry. The TD-DFT calculated absorption spectra are in agreement with experimental data showing long-wavelength bands in the range from 400 to 500 nm, which matches the yellow color of the complexes. The ligand variation enabled a fine-tuning of the emissive properties related to the resulting complexes, going from greenish-blue (471 nm) to red (617 nm) phosphorescence. The position of the substituent affects the excited state properties, which is attributed to mesomeric and inductive effects on the Pt–C bond and the adjacent pyridine ring. In general, modulation of the excited state character can be achieved by variation of the cyclometalating unit, thus affecting the excited state energy as well as the radiative and radiationless deactivation rates.

One-electron oxidation of molybdenum(iii) tris(anilide) Mo(N[^tBu]Ar)₃ (Ar: Ar^Me = 3,5-Me₂C₆H₃ and Ar^Ph = 3,5-Ph₂C₆H₃) led to intramolecular oxidative addition across the N–C_ipso bond of a ligated anilide to form the cationic Mo(vi) imido/aryl bis(anilide) complexes [Mo(N[^tBu]Ar)₂(═N^tBu)(Ar)][B(C₆F₅)₄]. One-electron reduction of [Mo(N[^tBu]Ar^Me)₂(═N^tBu)(Ar^Me)][B(C₆F₅)₄] allowed access to the neutral Mo(v) species [Mo(N[^tBu]Ar^Me)₂(═N^tBu)(Ar^Me)]. The d¹ electron configuration was confirmed through EPR spectroscopy and the Evans method. Compound [Mo(N[^tBu]Ar^Me)₂(═N^tBu)(Ar^Me)] was experimentally and theoretically shown to be stable against reductive elimination which would form the energetically less favorable Mo(N[^tBu]Ar)₃. The high activation barrier has so far prevented Mo(N[^tBu]Ar)₃ from isomerizing spontaneously to [Mo(N[^tBu]Ar^Me)₂(═N^tBu)(Ar^Me)]. An autocatalytic process was developed to access [Mo(N[^tBu]Ar^Me)₂(═N^tBu)(Ar^Me)] through reduction of [Mo(N[^tBu]Ar^Me)₂(═N^tBu)(Ar^Me)][B(C₆F₅)₄] by Mo(N[^tBu]Ar)₃, which itself was converted into the oxidizing agent. Attempts to access stable Mo(iv) cations with 4,4′-bipyridine only resulted in labile binding of 4,4′-bipyridine to one or two molybdenum(iii) tris(anilide) complexes.