Organometallics最新文献

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.

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.

Treatment of the ligand precursor H₃TIMMN^MesCl₃ (TIMMN^Mes = tris-[(3-mesityl-imidazol-2-ylidene)methyl]amine) with an excess of base yields the literature-known ferrous tris-N-heterocyclic carbene (NHC) complex [(TIMMN^Mes)Fe^IICl]Cl (1-Cl). In contrast, utilizing a substoichiometric amount of base initiates a unique rearrangement of all three NHC pendant arms to yield the tripodal, all-N-bound tris-imidazole [(N-TIMMN^Mes)Fe^IICl]Cl (2-Cl_sol). Divalent 2-Cl and 2-PF₆ are fully characterized, structurally by single-crystal X-ray diffraction analysis and spectroscopically by ¹H NMR and ⁵⁷Fe Mössbauer spectroscopy as well as SQUID magnetization measurements, to demonstrate the influence of the change from a soft strong-field to a hard weak-field ligand. Optimized reaction conditions for the reproducible, high-yield carbene-to-imidazole rearrangement were developed in a series of experiments.

The only molecular precatalysts offering high aromatic selectivity in hydrodeoxygenation (HDO) of phenolic and methyl ether lignin model compounds are hydroxy-tetraphenyl-cyclopentadienyl (CpOH) iridium complexes such as IrCpOH(H)₂PPh₃ (Ir1) [Kusumoto, S.; Nozaki, K. Nat. Commun. 2015, 6, 6296]. Here, we synthesized a variant (Ir1L) in which the CpOH and phosphine moieties are tethered and unlikely to dissociate from iridium. Surprisingly, unlike Ir1, Ir1L neither catalyzes HDO of phenylphenols nor the interconversion between naphthalene and tetralin. The density functional theory-calculated barriers for the corresponding reactions catalyzed by unmodified Ir1 or Ir1L are high (>44 kcal/mol), suggesting that the observed activity of Ir1 in these reactions is due to catalyst initiation. In contrast, intact Ir1 and Ir1L both appear to catalyze HDO of naphthols. Notably, the calculations show that Ir1 and Ir1L both mediate initial ring hydrogenation to 1,2-dihydronaphthol (2H), while only Ir1L can continue hydrogenation to 1,2,3,4-tetrahydronaphthol (4H). The subsequent substrate-catalyzed dehydration of 2H leads directly to naphthalene, whereas that of 4H leads to 1,2-dihydronaphthalene and, via hydrogenation, to tetralin. The calculations are thus consistent with the near-perfect aromatic selectivity observed at short reaction times using Ir1 and the mixture (19:81) of naphthalene and tetralin obtained by using Ir1L.

The bulky iron(II) tris(carbene)borate complex PhB(AdIm)₃FeCl reacts with equimolar NaPCO to afford PhB(AdIm)₃Fe(PCO) as a rare example of a paramagnetic phosphaethynolate complex. Although thermally and photochemically unstable, there is no evidence that either of these conditions leads to the formation of an iron phosphido complex. However, in the presence of excess NaPCO, thermolysis of PhB(AdIm)₃Fe(PCO) yields a dinuclear iron complex in which a new side-bound diphosphene ligand is stabilized by N-heterocyclic carbene and borate groups. These results hint at the utility of paramagnetic complexes for enlarging the scope of phosphaethynolate chemistry.

High-valent iron complexes play a crucial role in the oxidation of organic substrates, especially in C-H bond functionalization reactions in biology. This paper investigates the reactivity of nonporphyrin tripodal ligands featuring a secondary coordination sphere, focusing on their prospective ability to stabilize high-valent iron-oxo species. Using NMR spectroscopy and X-ray crystallography, we detail the formation of an Fe(III)-alkoxide complex through intramolecular C-H bond activation, providing insight into the potential transient formation of a high-valent iron-oxo intermediate. While attempts to observe an Fe(IV)-oxo complex were unsuccessful, our findings underscore the significance of the ligand electronic environment in stabilizing reactive iron species for C-H bond activation.