Organometallics最新文献

A robustRu(II)–p-cymene complex bearing an indole–pyrazoleligand (Ru1) is rapidly synthesized on a gram scale under ambientconditions and efficiently catalyzes the α-methylation of ketonesusing methanol. The addition of substoichiometric paraformaldehyde[(CH₂O)_n] or formalin markedly enhances conversionand selectivity compared with methanol alone, enabling efficient α-mono-and α-dimethylation under mild reaction conditions. In situmonitoring, control experiments, and isotopic-labeling studies supportthat early formation of formaldehyde-derived aldol intermediates promotesproductive Ru–H utilization, while continuous formaldehydegeneration sustains the catalytic cycle. These findings highlightthe importance of coupling C1-intermediate formation with Ru–Hutilization and suggest a practical strategy for improving otherwiseinefficient methanol-based hydrogen-transfer catalysis, with implicationsfor future catalyst design.

Hexahydride OsH₆(PⁱPr₃)₂ (1)reacts with tert-butylacetyleneto yield bis(alkynyl)-vinylidene Os(C≡C^tBu)₂(=C=CH^tBu)(PⁱPr₃)₂ (2). Subsequent protonation of 2 withHOTf or Et₃N·3HF affords the bis(alkynyl)-carbynederivatives [Os(C≡C^tBu)₂(≡CCH₂^tBu)(PⁱPr₃)₂]OTf(3) and OsF(C≡C^tBu)₂(≡CCH₂^tBu)(PⁱPr₃)₂ (4), respectively. In contrast, treatment of 2 with acetic acid leads to the alkynyl-vinylidene-vinyl ester derivativeOs(C≡C^tBu){κ²-O,C-OC(CH₃)OC=CH^tBu}(=C=CH^tBu)(PⁱPr₃)₂ (5). Density functionaltheory (DFT) calculations, together with deuterium labeling experiments,demonstrate that the protonation may occur either at the C_β carbon of the vinylidene ligand or at the C_β carbonatom of one of the alkynyl groups, and that the formation of 5 is governed by thermodynamic control. The reaction of 2 with 2-aminopyridine provides a new route for the selectivesynthesis of a 2,3-disubstituted imidazo[1,2-a]pyridinederivative starting from tert-butylacetylene and2-aminopyridine.

Ether-free alkylmetal reagents are important precursorsin organometallicchemistry. With few exceptions, there are hardly any heavier, ether-freegroup 2 alkylmetal complexes. Herein we describe facile syntheticmethods for the synthesis of solvent-free Ae[CH(SiMe₃)₂]₂ complexes (Ae = Ca, Sr, Ba) and discuss theirstructural and spectroscopic features. All complexes can be synthesizedby salt metathesis procedures. Reaction of two equivalents of KCH(SiMe₃)₂ with one equivalent of AeI₂ in Et₂O and subsequent removal of all solvents under high vacuumgave ether-free Ae[CH(SiMe₃)₂]₂ inyields of 78% (Ca), 56% (Sr) and 80% (Ba).The Ca and Sr reagents couldalso be obtained by a solvent-free solid state synthetic route, i.e. by ball-milling KCH(SiMe₃)₂ andAeI₂ in a 2:1 ratio and subsequent extraction by benzene.Facile access to highly reactive, ether-free heavier Ae metal alkylprecursors is important for further development of the rapidly growingfield of group 2 organometallic chemistry.

We report a comprehensive mechanistic study combiningexperimentalinvestigations, global reaction route mapping (GRRM)/artificial force-inducedreaction (AFIR)-based automated reaction path exploration, and densityfunctional theory (DFT) calculations. The computational results revealthat the reaction proceeds via oxidative addition of disilane to aπ-allylpalladium species, followed by two successive reductiveeliminations to afford the corresponding allylsilane. This study providesmechanistic insights into palladium-catalyzed silylation with disilanesand offers a foundation for the rational design of bond-forming reactionsusing disilane.

UsingMgMe₂ as a model system, quantum calculationsprobe the propensity of the methyl C of one molecule to form a noncovalentbond with the Mg of another. Also tested is the effect of halogenationof each molecule, and how its prior dimerization to [MeMgX]₂, which contains a square (Mg₂X₂), core affectsits participation in a C···Mg bond with another molecule.These intermolecular bonds can be fairly strong, some exceeding 80kJ mol^–1. The strongest interaction arises whendimeric [MgMe₂]₂ serves as the electron donorand is paired with an organomagnesium halide electron acceptor. Thisstrength is magnified as the halogen of the latter grows in size:F < Cl < Br < I. The electrostatic interaction furnishesthe largest component, followed by polarization and dispersion inthat order. Intermolecular methyl-to-magnesium donation representsa genuine magnesium bond important to the organization of Schlenk-typeaggregates.

Metal-hydrideformation reactions are common elementary reactionsin catalytic systems, including fuel formation and organic transformations.Here, metal-hydride formation rates with metal carbonyl clusters [Fe₄N(CO)₁₂]⁻ and [Fe₅N(CO)₁₅]⁻ were determined in MeCN andaqueous media using peak-shift analysis (PSA) and foot-of-the-waveanalysis (FOWA) performed on cyclic voltammetry data. In MeCN, hydrideformation exhibits exceptionally small dependence on the pK_a of the proton source, as inferred from Brønstedslopes (α = 0.06 and 0.03) that are determined from plots ofPT rate vs pK_a of the proton substrate.This indicates a minimal dependence of the PT rate on the drivingforce for the PT reaction. These values contrast with the larger slopescommonly observed for mononuclear transition-metal hydrides (α≈ 0.3–0.7). In aqueous solution, larger Brønstedslopes were observed (α = 0.54 and 0.23). Overall, these resultsdemonstrate that multinuclear metal clusters exhibit hydride-formationbehavior distinct from conventional single-site complexes. The abilityto maintain fast rates for metal-hydride formation under low driving-forceconditions may be a key feature that enables the previously reportedselective hydride transfer to CO₂ by [Fe₄N(CO)₁₂]⁻.

The development of stereoselective olefin metathesisremains akey challenge in modern catalysis, particularly in achieving simultaneouscontrol over the enantioselectivity and Z-selectivity.In this study, a new class of camphor-derived chiral NHC rutheniumcomplexes was designed, synthesized, and evaluated in asymmetric ring-openingcross-metathesis. Systematic modification of the ligand architectureenabled a detailed investigation of steric and electronic effectson catalytic performance. The prepared catalyst series exhibited highactivity in asymmetric ring-opening cross-metathesis (AROCM) reactions,with distinct trends observed between substituent size, catalyst reactivity,and stereoselectivity. While most complexes favored the formationof E-isomers, selected systems provided moderateto high enantioselectivity for Z products. Catechodithiolate-modifiedcatalysts displayed a significant enhancement in Z-selectivity and enantioselectivity, achieving up to 99% ee, albeit at the expense of the catalytic activity. Thesefindings highlight the critical role of ligand design in tuning catalystperformance and provide valuable insights into the structure–selectivityrelationships governing asymmetric Z-selective olefinmetathesis.

Cyclopentadienyland arene complexes with pendant amide substituents[(C₅Me₄CH₂CH₂NHR)RhCl₂]_n and [(C₆H₅CH₂CH₂NHR)RuCl₂]_n (R = COCF₃, Ts) were synthesized by heatingthe corresponding dienes with metal chlorides. They were tested ascatalysts for the annulation of N-methoxy-p-methylbenzamide with alkynes. Contrary to our expectations,the pendant amide groups did not act as internal proton acceptorsand did not accelerate the C–H activation process. However,it was found that the reaction of N-methoxy-p-methylbenzamide with 4-octyne in the presence of variousrhodium complexes produced an O-methyl oxime of isocoumarin insteadof the expected isoquinolone as the major product.

(S,S)-(R,R)-PhTRAP is a wide-bite-angle chiral bisphosphineinitiallyreported by Ito and co-workers; despite its unique coordination geometry,prior catalytic applications have been largely limited to enantioselectivehydrogenation and hydrosilylation. We recently leveraged the unique trans-spanning nature of this ligand in the Pd-catalyzedenantioselective anti-Michael (α-selective) hydroarylation ofunsaturated carbonyl compounds. Previously reported syntheses of thisligand employ hygroscopic phosphorus building blocks and sensitivelow-valent metal reagents and require hazardous reduction conditions,leading to operational challenges and variable yields. Here we describean alternative synthesis of PhTRAP employing mild conditions, affording(+)-PhTRAP on a gram scale in 41% yield over four steps from the readilyaccessible planar-chiral scaffold iodo-Ugi amine. We further applythis synthetic route to access two previously unreported aryl-modifiedanalogs in enantioenriched form, (S,S)-(R,R)-(3,5-Xyl)TRAP and (S,S)-(R,R)-(3,5-C₆F₂H₃)TRAP. We determinedthe solid-state structures of this series of bisphosphines by X-raycrystallography and discuss the conformational differences acrossthis series.

Stericallyencumbered β-diketiminate (NacNac) ligands arewidely used in several contexts, and our group recently showed theyare effective at preventing excited-state distortion in copper(I)chromophores and increasing their lifetime. This work introduces compoundsbased on an 8-aryl-1-naphthyl-substituted “sandwich”NacNac ligand, hypothesized to impart even more steric protectionthan conventional NacNac ligands. We describe a series of Cu(I) heterolepticcompounds (Cu1–Cu7) where the “sandwich”NacNac ligand is paired with aryl isocyanides. The compounds are characterizedspectroscopically and by cyclic voltammetry, with the formal Cu^II/Cu^I redox potential occurring near the ferrocenecouple and minimally dependent on the isocyanide. In four crystallographicallycharacterized complexes, we observe percent buried volume (%V_bur) parameters of 67.4–71.6% for the“sandwich” NacNac, exceeding that of the common 2,6-diisopropylphenyl(Dipp) NacNac (%V_bur = 59.0–62.9%in related compounds). Despite the enhanced steric bulk, the compoundsare only photoluminescent at 77 K, which we attribute to the photophysicalnoninnocence of the 8-aryl-1-naphthyl groups, which quench the phosphorescenceat room temperature. Despite their photophysical limitations, thiswork suggests that such “sandwich” NacNac ligands areeffective at increasing the steric bulk around the metal center, whichcould be useful in applications in catalysis and small-molecule activation.