Organometallics最新文献

Heteropolycyclic frameworks are widely represented in biologically and pharmaceutically relevant compounds; however, methods to synthesize these frameworks often result in heterocycles containing predominantly sp²-hybridized carbons. Herein we describe a heteroannulation scheme featuring a double protonation of a tungsten η²-anisole complex. The resulting dicationic intermediate reacts with activated arenes through an electrophilic aromatic substitution reaction to form an oxocarbenium complex, which can be reduced to an allylic ether complex. Subsequent acidolysis results in a π-allyl complex that can react with alcohol or amine substituents of the activated arene reagent to form the desired heteropolycyclic core.

The mechanism of the copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction has been under investigation for over two decades. While catalytically relevant dicopper intermediates have been proposed and a few suspected intermediates have been isolated, the mechanism remains poorly understood. In this work, we describe the synthesis and characterization of neutral dicopper complexes bearing the proton-responsive dinucleating ^iPrPNNP “expanded pincer” ligand, which are demonstrated to be relevant intermediates in the CuAAC reaction. The acetylide complex [Cu₂(^iPrPNNP*)(μ-C≡C-p-F-C₆H₄)] (2) reacts with 1-azido-4-fluorobenzene at ambient temperature to form the dicopper complex [Cu₂(^iPrPNNP*)(μ-(1,4-bis(p-fluorophenyl)-1,2,3-triazolide)] (3), featuring a symmetrically bridging 1,4-substituted 1,2,3-triazolide ligand. Mechanistic studies were performed using both isotopic labeling experiments and density functional theory (DFT) calculations for the subsequent protodemetalation step. These studies show that the release of the triazole product proceeds via a stepwise metal–ligand cooperative (MLC) pathway, which is favored over the direct alkyne-to-triazolide proton transfer as it requires less structural reorganization of the dicopper platform. This demonstrates how cooperativity between the copper centers and metal–ligand cooperativity can offer an alternative mechanistic pathway, bypassing the conventional rate-limiting alkyne-to-triazolide proton transfer in the CuAAC reaction.

Herein we report the facile synthesis of [Na]₂[Fe(CN)₄(phen)] and [Na]₂[Fe(CN)₄(bpy)] from a single isolable trans-[Na]₂[Fe(CN)₄(DMSO)₂] precursor under mild conditions that avoid the generation of highly toxic HCN gas. Furthermore, we demonstrate the generality of this approach by synthesizing [Na]₂[Fe(CN)₄(MeBIM-py)] (MeBIM-py = 3-methyl-1-(pyridin-2-yl)-1H-benzo[d]imidazol-2-ylidene), the first example of a carbene iron tetracyanide complex. Spectroscopic characterization of the products via NMR and IR spectroscopies as well as single crystal X-ray diffraction confirm the synthesis of the known diimine complexes and provides insight into the influence of including a strongly donating N-heterocyclic carbene ligand on the Fe–CN bond.

OsH₆(PⁱPr₃)₂ (1) reacts with phenylsilane to afford OsH₅(SiH₂Ph)(PⁱPr₃)₂ (2), which reacts with additional phenylsilane to give OsH₄(SiH₂Ph)₂(PⁱPr₃)₂ (3). The reaction of 1 with diphenylsilane affords OsH₅(SiHPh₂)(PⁱPr₃)₂ (4), which in the presence of diphenylsilane and traces of water leads to OsH₄{κ²-Si,Si-(Ph₂Si–O–SiPh₂)}(PⁱPr₃)₂ (5). Complex 4 promotes the hydrosilylation of aldehydes with H₂SiPh₂ to give silyl ethers, while for ketones mixtures of hydrosilylation and dehydrogenative silylation products are obtained. The reactions of 4 with benzaldehyde and acetone afford OsH₅{Si(OR)Ph₂}(PⁱPr₃)₂ (R = CH₂Ph (6), ⁱPr (7)), which undergo a metathesis between a Si–Ph bond and a C(sp³)–H bond of one methyl group of one phosphine to give OsH₄{κ¹-P,η²-SiH-[ⁱPr₂PCH(Me)CH₂Si(OR)PhH]}(PⁱPr₃) (R = CH₂Ph (8), ⁱPr (9)). The combination of experimental findings and density functional theory calculations has permitted to establish the mechanism for the hydrosilylation processes. The key intermediate is the tetrahydride-silylene OsH₄(=SiPh₂)(PⁱPr₃)₂, formed by an outer-sphere hydrogenation of the carbonyl group promoted by a trihydride(dihydrogen) isomer of 4. For enolyzable ketones, this pathway competes with one where the enol form directly attacks the Si atom of 4, affording silyl enol ethers and a tetrahydride(dihydrogen) isomer of 1, that reacts with diphenylsilane to release hydrogen and close the cycle.

Dinuclear copper(II) complexes of the general formula [Cu₂(μ-Lⁿ)₂] (1–6) with shortened salen-type N₂O₂ tetradentate Schiff base ligands named H₂sal(X)ben (H₂Lⁿ, n = 1–7, X = H, 2-OMe, 4-OMe, 2-Cl, 4-Cl, 2,6-diOMe, 2,4,6-triOMe, respectively) revealed to be efficient and selective catalysts for Ullmann-type C–N coupling reactions under relatively mild conditions. These compounds display a distorted metal coordination environment, intermediate between tetrahedral and square planar, as shown by single-crystal X-ray diffraction, caused by the one-carbon bridge linking the iminic nitrogen atoms. This peculiar feature suggests that the metal ions can easily modulate and adapt to different redox states, evoking their potential as efficient catalysts. In fact, they revealed excellent performance in the Ullmann-type C–N coupling reaction, being reactive toward a wide range of N-nucleophiles and successfully coupling sterically hindered and electronically deactivated aryl iodides. Mechanistic studies support a 2-electron oxidative addition/reductive elimination event taking place on one copper(II) center, while the other acts as an electron reservoir to assist the redox process. Noteworthy, catalysts 1–6 are easily prepared from nonexpensive starting materials and are stable to air and moisture, characteristics that render them a very attractive alternative to classic in situ-generated catalytic systems, notably in the context of industrial applications.

Herein, we report the synthesis of Mn(I) pincer complexes (C1–C3) of NNE ligands (E = S, Se, Te; L1–L3). While ligands L1-L2 and complexes C1-C2 are previously reported, the tellurium-based ligand L3 and its Mn(I) complex C3 are new and fully characterized. Single-crystal X-ray diffraction studies established the distorted octahedral geometry of C1. Complexes C1–C3 were evaluated as catalysts for dehydrogenative annulation of 2′-aminoacetophenones with primary and secondary alcohols in solvent free conditions highlighting the greener and economic importance of protocol. Primary alcohols underwent selective transformation to 2,3-disubstituted-4-quinolones, whereas secondary alcohols furnished 4-methyl-2-arylquinolines. The catalytic system, particularly C2, displayed broad substrate scope, high functional group tolerance, and efficient performance at low catalyst loading. Control experiments identified plausible intermediates, excluded radical pathways, confirmed the homogeneous nature of catalysis, and elucidated the role of benzylic protons in product formation. Mechanistic insights support an initial alkylation step that dictates the product outcome, primary alcohols undergo preferential C-alkylation followed by intramolecular cyclization to afford 2,3-disubstituted-4-quinolones, whereas secondary alcohols favor N-alkylation, leading to the formation of 4-methyl-2-arylquinolines. This work expands the scope of Mn(I) pincer complexes in chemoselective dehydrogenative annulation catalysis and provides a direct strategy for the one-pot synthesis of biologically relevant scaffolds.

The synthesis and polymerization of novel ferrocene-based monomers coupled to oxetanes, which are strained four-membered heterocycles with an oxygen atom, is reported for the first time. The ferrocene-oxetane monomers were synthesized in a single step from inexpensive, commercially available products using an ester coupling reaction. One monomer had a single ferrocene coupled pendant to the oxetane ring, and another had two ferrocenes coupled as pendant groups to the oxetane ring. A crystal structure of the monomer with a single pendant ferrocene was obtained and demonstrated that the pendant ferrocene group did not cause additional ring puckering, suggesting that it did not add significant strain to the ring. This monomer was also able to be thermally polymerized without the use of solvent or catalyst because it melted at high temperatures and reacted with a cationic initiator to undergo cationic ring-opening polymerization. The convenient homopolymer synthesis was an improvement and yielded larger molecular weights (M_w = 17,000) in comparison to previous metallopolymer syntheses with polyether backbones. The thermal properties and electrochemical properties of the polymer are discussed. Polymerizations in silicon molds also yielded basic shapes. The monomer with two ferrocenes appended to an oxetane ring did not homopolymerize, presumably due to unfavorable steric interactions.

The development of Fe-based olefin metathesis has been a long-standing goal for several decades. Research from both experimental and theoretical groups has indicated that suitable Fe alkylidenes should be low-spin complexes with a high bond dissociation energy (BDE) for the Fe═C bond. In this study, we synthesized a series of low-spin Fe complexes featuring IMes (IMes = 1,3-dimesitylimidazol-2-ylidene), CN, and CO ligands, which have potential applications in the synthesis of Fe alkylidenes. We computationally investigated the corresponding Fe benzylidenes in the context of olefin metathesis. Although some of these complexes favor low-spin states and demonstrate high BDE, competing side reactions─such as cyclopropanation and carbene insertions─could impede their effectiveness in olefin metathesis.

In this work, a series of novel germylenes, RN(CH₂CH₂NR’)₂Ge R′ = Ph, R = Et (1); R′ = Ph, R = Bn (2); R′ = Ph, R = t-Bu (3); R′ = R = Ph (4); R′ = Bn, R = Et (5); R′ = Bn, R = Bn (6); R′ = Et, R = Et (7); R′ = Et, R = Bn (8), based on 1,4,7-triazaheptanes have been obtained. The compositions and structures of the novel compounds were established by elemental analysis and ¹H and ¹³C NMR in the solid state by X-ray diffraction analysis (1–4), and it has been shown that germylenes are monomeric. The redox properties of compounds 1–4 and previously obtained germylene 10 (R′ = C₆F₅, R = Bn) in acetonitrile were studied by cyclic voltammetry (CV), and their optoelectronic properties were studied by UV–vis absorption spectroscopy. The easily oxidizing properties of the presented germylenes have been determined. An analysis of frontier molecular orbitals was carried out for compounds 1–8, 10 (R′ = C₆F₅, R = Bn), 11 (R′ = C₆F₅, R = Me), and Lappert’s germylene, Ge[N(SiMe₃)₂]₂. It has been established that the nature of the substituents on the nitrogen atoms covalently bonded to the germanium atom has a significant effect on the energy of the frontier molecular orbitals.

A new unsymmetrical hybrid pincer-type ligand featuring cyclopentadienyl and phosphine donors bridged by a 2,6-dimethylenepyridyl linker has been synthesized. Upon double deprotonation and treatment with [NiCl₂(NCCH₃)₂] in THF, this ligand forms a distorted 18-electron κ²-P,N-η⁵-Cp nickel(II) piano-stool complex. This complex undergoes clean aromatization upon protonation, highlighting the proton-responsive nature of the ligand framework. The same scaffold stabilizes a related reduced κ²-P,N-η⁵-Cp nickel(I) species─an uncommon example of a 19-electron nickel(I) compound─which was characterized by continuous-wave X-band EPR spectroscopy. Crystal structures of the protonated, deprotonated, and reduced complexes were all obtained using single-crystal X-ray diffraction. These results provide entry into a versatile ligand platform that is demonstrated to be both proton-responsive and capable of supporting both Ni(II) and Ni(I) oxidation states.