Organometallics最新文献

The reactions of [Cu₂(μ–κ¹:κ¹-O₂N)DPFN][NTf₂] (1; DPFN = 2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine, NTf₂^– = N(SO₂CF₃)₂^–) with 1,4-dicyanobenzene and 1,2-dicyanoarenes are discussed. Treatment of 1 with 1,4-dicyanobenzene produces a tetra-Cu(I) terephthalate complex (2) and dinitrogen via a discrete C≡N triple bond cleavage at each cyano group. However, reactions of 1 with 1,2-dicyanoarenes appear to proceed via a cascade reaction involving two intertwined C≡N triple bond activations to yield a series of di-Cu(I) phthalimides, [Cu₂(μ–N(CO)₂(Ar))DPFN][NTf₂] (3-(Ar); Ar = 1,2-arylenes C₆H₄, 3-NO₂C₆H₃, 4-NO₂C₆H₃, 4-PrOC₆H₃, 3-NC₅H₃) and dinitrogen. The dicopper phthalimide bonding interaction in these compounds is robust enough to resist protonation by pentafluorophenol and alkylation by methyl triflate or benzyl chloride at the imide nitrogen. This characteristic presents an opportunity for postsynthetic modifications of the phthalimide ligand. Nevertheless, treatment of 3-(C₆H₄) with bistriflimidic acid (HNTf₂) results in release of the neutral phthalimide, making the dicopper core available to coordinate other ligands such as nitrite and thus, completing a stoichiometric cycle.

Intramolecular hydrogen transfer represents one of the most fundamental and ubiquitous processes in both chemical and biological transformations. Here, we introduce a rare intramolecular 1,2-proton transfer within lanthanide metallacycles proceeds without external shuttles. The transformation converts five-membered lutetacyclopentenes into six-membered rings through a formal 1,2-proton transfer achieved via sequential 1,5- and 1,4-proton shifts. DFT calculations reveal that the Lu–C bond acts as an internal proton relay, preorganizing the transfer trajectory and lowering the barrier. Isolation of a ligand-stabilized intermediate further substantiates the proposed stepwise mechanism.

The synthesis, structural characterization in the solid state, and reactivity of a selenazolidine and a six-membered-ring derivative, i.e., a 1,3-tetrahydroselenazine, that contain a C₆F₅ substituent are reported. The first crystallographic characterization of a 1,3-tetrahydroselenazine was accomplished by means of single-crystal X-ray diffraction analysis. Despite the structural analogy to C₆F₅-substituted imidazolidines, these selenium-containing heterocycles exhibit pronounced thermal stability and high resistance toward the formation of the corresponding (amino)(seleno)carbenes, highlighting fundamentally different reactivity patterns between imidazolidines and selenazolidines.

In dihaloarene cross-couplings, the step(s) that take place after reductive elimination and before the start of the next cycle influence selectivity for mono- versus difunctionalization. When palladium is supported by a bulky ligand "L", a competition exists between a second oxidative addition (leading to difunctionalization) and bimolecular displacement of Pd⁰ from the monofunctionalized product by a second smaller ligand. Because oxidative addition of Ar-Br is faster than Ar-Cl, more difunctionalization might be expected with dibromoarenes compared to dichloroarenes. However, the opposite has been reported in some Suzuki-Miyaura cross-couplings. Here, we report that the selectivity outcome is closely tied to solvents: dibromoarenes tend to give less diarylation than dichloroarenes in oxygen-containing solvents of at least moderate polarity (e.g., THF), whereas high selectivity for diarylation can be achieved in most aromatic and chlorinated solvents. The results suggest that, in polar oxygen-containing solvents, the bromide anion byproduct displaces LPd⁰ from the mono-cross-coupled product. The rate of this process is competitive with the rate of intramolecular oxidative addition en route to the diarylated product. In contrast, the analogous displacement of Pd⁰ by chloride (the byproduct when using dichloroarenes) appears to be a much slower process, if it occurs at all.

Well-defined allyl derivatives of the coinage metals remain rare, often owing to their thermal and redox sensitivity. We report the isolation of a potassium bis(allyl)cuprate, [KCuA′₂] (A′ = 1,3-(SiMe₃)₂C₃H₃), prepared with either solution or mechanochemical methods, which is stable at room temperature in both the solid state and solution. In the solid state, it crystallizes as a dimer ([{KCuA′₂}₂]), featuring a planar K₂Cu₂ core and η¹-bound allyl ligands. In neat hexanes, [{KCuA′₂}₂] enables conjugate (1,4)-allylation of α,β-unsaturated ketones. It does not transmetallate when treated with lithium or sodium salts but converts to the crystallographically authenticated, but less stable neutral tetramer, [{CuA′}₄], which possesses μ-η:¹η² allyl bridges and a puckered Cu₄ ring. Gold analogs of both the anionic and neutral complexes have also been prepared ([{KAuA′₂}₂] and [{AuA′}₄], respectively) and are structurally similar to their copper counterparts. However, the potassium bis(allyl)aurate does not perform the same addition chemistry as its copper analogue. DFT calculations on the unsubstituted di(allyl) cuprates (i.e., [{(Li,K)Cu(C₃H₅)₂}₂]) suggest that both the trimethylsilyl groups and the substitution of Li⁺ with K⁺ influence the aggregation of potassium bis(allyl)cuprate. These findings provide structural and reactive benchmarks for coinage-metal allyl complexes.

sp² C–H activation of H₂C═PPh₃ are widely known when H₂C═PPh₃ is treated with lanthanide alkyls. In this work, an unprecedented reaction mode, in which dual geminal sp³ C–H activation of the TREN^TMS ligand and dearylation of the ylide, was reported, generating complex 3. Quantum chemical calculations elucidate the electronic structure of 3, revealing a weakly binding diylide fragment. Our findings highlight that the “straightforward” alkane elimination process is far more complicated than conventionally anticipated.

Despite their prominence as privileged chiral catalysts for synthesis and polymer chemistry, the synthesis of enantiopure ebthi-type titanocenes is a challenging task. In this proof-of-concept study, we report the development of a single-step synthesis of (S,S,S)-(ebthi)Ti(BINOLate) from Li₂(ebthi) and (S)-Ti(BINOLate)Cl₂ in 28% yield with 97% ee. We further shed light on the nature of the latter and provide alternative protocols for the convenient liberation of (S)-(ebthi)TiCl₂. (ebthi)-Ti(BINOLate) is further shown to be a competent catalyst in asymmetric ketone-nitrile couplings, providing an enantioselectivity comparable to that of (ebthi)TiCl₂.

The migratory insertion of carbon monoxide into Re–R (R = methyl, Me; benzyl, Bn) bonds of nitridorhenium(V) PNP alkyl complexes bearing ^tBu2-PyNHO, (where ^tBu2-PyNHO = (Z)-6-((ditert-butylphosphaneyl)methyl)-2-((ditert-butylphosphaneyl)methylene)-1,2-dihydropyridine) and ^tBu2,6-Pip, (^tBu2,6-Pip = 2,6-bis((ditert-butylphosphaneyl)methyl)piperidine) ligands has been systematically investigated. The reaction proceeds to completion under 30 psi CO in toluene-d₈ at 50–100 °C affording Re-acyl products cleanly and quantitatively. Insertion into benzyl complexes is intrinsically faster than methyl analogues, with the ^tBu2-PyNHO benzyl ligand accelerating the reaction 23 times relative to its methyl congener and seven times relative to the ^tBu2,6-Pip benzyl complex. Variable-temperature ³¹P NMR kinetic studies yield highly negative entropies of activation (ΔS^‡ = −42.6 to −49.4 cal mol^–1 K^–1), supporting a bimolecular, ordered transition state. DFT calculations (M06-D3) corroborate a concerted insertion mechanism without the formation of a stable CO adduct. NBO analysis shows enhanced charge polarization involving the phosphorus donors in the ^tBu2-PyNHO benzyl complex. Further EDA analyses revealed a more robust CDA mixing stabilizing ^tBu2,6-Pip complex presenting a hard to perturb geometry toward acyl formation. This work provides clear evidence that ligand architecture modulates electronics around the metal affecting the CO insertion barrier toward acyl formation.

This work investigates the reactivity of IDippP-SiMe₃ (IDipp = 1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) toward CO₂, Ph-NCO, and Me-CN. Whereas carbon dioxide and phenyl isocyanate readily insert into the polarized P–Si bond, the activation of acetonitrile only proceeds via a frustrated Lewis pair (FLP) pathway in the presence of group 13 halides. Nitrile insertion in the presence of aluminum halides affords both an N-heterocyclic carbene phosphinidene (NHCP)-substituted imine and a phosphaalkene, with the product ratio depending on the choice of Lewis acid. In contrast, the addition of BCl₂^mTer (^mTer = 2,6-(2,4,6-methyl-C₆H₂)-C₆H₃) selectively affords an NHCP-substituted imine via dehalosilylation.

We report the convenient synthesis of Ni(DQ)₂ (DQ = duroquinone) from readily available Ni(II) and Ni(0) precursors, guided by DFT calculations. By virtue of its π-accepting homoleptic ligand environment, Ni(DQ)₂ undergoes facile ligand exchange with phosphine, bis-nitrogen, and diene ligands and thus represents a convenient Ni(0) source in synthetic organometallic chemistry. As a precatalyst, Ni(DQ)₂ is found be a competent air-stable precursor for emerging methodology where Ni(COD)(DQ) is ineffective (COD = 1,5-cyclooctadiene).