Organometallics最新文献

Derivatization of (NHC)Au–Cl with monodentate and bidentate phosphine donors, such as PPh₂Py, PPh₃, PCy₃, and dppf, produced heteroleptic mononuclear and binuclear Au(I) complexes. The order of mixing reactants and the types of solvents used play crucial roles in obtaining a pure product. In the single-crystal X-ray diffraction analysis of complexes 1, 2, and 4, the Au(I) centers exhibited linear geometry. Advanced computational analysis of these complexes using density functional methods provided insights into the nature of electronic transitions, noncovalent interactions, and fragmental bonding contributions. Complexes 1–4 were selected for biological activity studies, and their in vitro cellular tests were conducted on the human cancerous breast cell line MCF-7, with bimetallic complex 4 showing the lowest IC₅₀ value of 63 nM and demonstrating the highest inhibitory effect on cell proliferation.

Rhenium(III) complexes of the form (CO)Re(DAAm) (R) 1_, (DAAm = N¹-mesityl-N²-(2-(mesitylamino)-ethyl)-N²-methylethane-1,2-diamine) (R = benzyl, 1a; methyl, 1b; 4-OMe-benzyl, 1c) react with isocyanides R′NC, (R′ = 2,6-dimethylphenyl, tert-butyl) to give η¹ and η² iminoacyl complexes. When 2,6-dimethylphenylisocyanide reacts with 1a, the resulting iminoacyl complex was η² while the reaction with 1c leads to an η¹ iminoacyl complex. However, the less bulky isocyanide tert-butyl isocyanide produced only η² iminoacyl complexes with 1b and 1c. Carbene complexes were obtained by the reaction with methyl triflate. The mechanism for the formation of the iminoacyl complexes in this study was also investigated by DFT (APFD).

The oxidation selectivity of the η⁶-arene ligand in a series of [(η⁵-C₅Me₅)Ir(η⁶-arene)](OTf)₂ complexes to the corresponding [(η⁵-C₅Me₅)Ir(η⁵-phenoxo)](OTf) derivatives was studied as a complementary protocol to metal-catalyzed borylation-oxidation. A series of representative [(η⁵-C₅Me₅)Ir(η⁶-arene)](OTf)₂ compounds was prepared with mono-, di-, and trisubstituted arenes as well as two examples with biphenyls to rationally explore the site selectivity of C(sp²)–H oxidation. The isolated organometallic arene complexes were treated with NaClO₂ and formed the desired iridium η⁵-phenoxo products. While site-selective oxidation was observed for some compounds, most of the iridium complexes yielded a mixture of regioisomers. Regioselectivity was primarily determined by electronic factors, while sterics influenced sites that were electronically similar.

Reactions of the coinage metal (CM) cyanides, CuCN, AgCN, or K[Au(CN)₂], with [{SiN^Dipp}AlK]₂ ({SiN^Dipp} = {CH₂SiMe₂N(Dipp)}₂; Dipp = 2,6-i-Pr₂C₆H₃) result in KCN metathesis and a series of “alumina-Gilman” reagents, [({SiN^Dipp}Al)₂CM]K (CM = Cu, Ag, or Au). The latter species may be isolated in both charge-separated, [({SiN^Dipp}Al)₂CM]⁻[K(THF)₆]⁺, or contact ion pair forms when crystallized in the presence or absence of THF. Computational analysis apportions a high degree of covalency to the CM–Al metal bonding and attribution of an aluminum oxidation state that is best represented as Al(II). This latter inference is supported by the experimental observation of THF activation, deduced to result from the competitive single electron reduction of the group 11 center during the synthesis of the bis(alumanyl)metalates. UV photolysis of [({SiN^Dipp}Al)₂Ag]K provided a product of 2-fold Al(II) radical addition to benzene. This species is also synthesized by a modification of the reaction that gave rise to the initially identified cuprate metathesis product. The intermediacy of [{SiN^Dipp}Al^•] radicals, which are proposed to add to benzene in a stepwise manner, is supported by the observation of in situ recorded EPR spectra, the simulated parameters of which have been assigned to the singly aluminated benzene product, [{SiN^Dipp}Al(C₆H₆)^•].

Based on previously accumulated experimental material on the use of {nEt₂AlCl + Bu₂Mg} mixtures for the activation of Ti postmetallocene precatalysts for ethylene polymerization, an attempt is made to find the reason for the universal activating ability of such cocatalysts by analyzing the chemical processes occurring during the interaction of alkylaluminum chlorides and dibutylmagnesium. ¹H and ²⁷Al NMR spectroscopy data indicate that in nonsolvating media the formation of ionic products (with which earlier the unique activating ability of Al/Mg activators was associated) does not occur. The “true” Al/Mg cocatalysts are uncharged adducts of MgCl₂ with alkylaluminum chlorides and/or trialkylaluminum. It was shown that all used Al/Mg cocatalyst compositions are capable of activating a model titanium dichloride complex with a saligenin ligand with varying efficiencies. The product of the ethylene polymerization is an ultrahigh molecular weight polymer (M_v from 1.1 to 5.1 × 10⁶ Da); the latter is evidenced by the possibility of solid-phase processing of nascent polymer powders into high-strength, high-modulus tapes (breaking strength up to 2.4 GPa and elastic modulus up to 112 GPa).

Nickel(II) complexes bearing tetradentate NCCN ligands composed of optionally protic pyridine and N-heterocyclic carbene (NHC) donors have been synthesized and used as catalysts for carbon dioxide reduction. These complexes were synthesized bearing OMe, OBn, or OH substituents on the pyridine rings and were characterized by ¹H NMR, ¹³C NMR, UV–vis, IR, HR-MS, and single crystal X-ray diffraction. The OH substituent was partially deprotonated, as shown by the crystal structure. Electrochemical studies show that these nickel complexes undergo two electron reduction events prior to CO₂ reduction. Catalytic current enhancement under CO₂ relative to N₂ is not observed under dry conditions, but the addition of proton sources leads to modest current enhancement (i_cat/i_p < 2). Visible light driven photochemical CO₂ reduction with a photosensitizer (Ir(ppy)₃, where ppy = 2-phenylpyridine) and sacrificial electron and proton donors was studied, and formate is the major product with ∼10:1 formate to CO production. Electron donor groups (OMe, OBn, OH) do not enhance formate production (relative to the unsubstituted analogue), and CO production is only slightly enhanced. Overall with Ni(II), the tetradentate ligands are comparable to recently published pincer ligands for sensitized CO₂ reduction, but pincer ligands offer a clear advantage in self-sensitized catalysis.

A simplified one-pot procedure for the synthesis of a useful class of mixed chloro-/fluoroaryl boranes following the formula B(C₆Cl₅)_n(C₆F₅)_3–n is reported. Standard organolithium and Grignard reagents are utilized, and intermediate arylzinc or arylcopper reagents are not required. With regard to their applications to C–O cleavage reactions, the increased steric bulk of having ortho-chlorine enhances the catalyst tolerance of water, allowing for C–O deoxygenations under atmospheric conditions. As the degree of chlorination increases, the reactivity of the borane catalyst decreases with B(C₆Cl₅)(C₆F₅)₂ being the most active of the boranes studied. This mono-C₆Cl₅ borane was able to cleave or reduce the C–O bond of ethers, carbonyls, and sugars under benchtop (open air) conditions. B(C₆Cl₅)(C₆F₅)₂ thus demonstrates a favorable balance of water tolerance and preserved reactivity relative to that of BCF itself.

We used a computational density functional theory approach to study second-generation Hoveyda–Grubbs-type complexes bearing Tl/Ga/In(AmIm) ligands, focusing on their application as olefin metathesis catalysts. Of these three, the organothallium compound was assessed as the most potent candidate for an efficient catalyst, exhibiting low free energy barriers (14.51 kcal/mol for the rate-determining step of the simplest metathesis process), which suggested its activity, even at low temperatures. This species may potentially catalyze not only the formation of simple olefins but also more sterically hindered ones, including the synthesis of demanding tetra-substituted alkenes.

Ring size effects on geometries and electronic structures were investigated for the (C_nH_n)M(C_mH_m) (n = 4, 5, or 6; m = 8, 7, or 6; m + n = 12; M = Ti–Ni) systems using density functional theory. The lowest-energy C₁₂H₁₂M structures for the early transition metals titanium, vanadium, and chromium are the experimentally known singlet (η⁵-C₅H₅)Ti(η⁷-C₇H₇), doublet (η⁵-C₅H₅)V(η⁷-C₇H₇), and singlet (η⁶-C₆H₆)₂Cr, respectively. The likewise experimentally known singlet (η⁶-C₆H₆)₂Ti, doublet (η⁶-C₆H₆)₂V, and singlet (η⁵-C₅H₅)Cr(η⁷-C₇H₇) are the second-lowest-energy structures with only a small energy difference between the two vanadium structures. For the later transition metals, dibenzenemetal complexes are the lowest-energy C₁₂H₁₂M species with two fully bonded hexahapto benzene rings in the lowest-energy manganese and iron derivatives and one hexahapto and one dihapto benzene ring in the lowest-energy cobalt and nickel derivatives. The lowest-energy (C₅H₅)M(C₇H₇) structures for the later transition metals iron, cobalt, and nickel have partially bonded nonplanar C₇H₇ rings with one or two uncomplexed C═C bonds. The (C₄H₄)M(C₈H₈) (M = Ti–Ni) structures with the metal sandwiched between four- and eight-membered rings were found to be much higher in energy than their (C₅H₅)M(C₇H₇) and (C₆H₆)₂M isomers.

Ring size effects on geometries and electronic structures were investigated for the (C _n H _n )M(C _m H _m ) (n = 4, 5, or 6; m = 8, 7, or 6; m + n = 12; M = Ti-Ni) systems using density functional theory. The lowest-energy C₁₂H₁₂M structures for the early transition metals titanium, vanadium, and chromium are the experimentally known singlet (η⁵-C₅H₅)Ti(η⁷-C₇H₇), doublet (η⁵-C₅H₅)V(η⁷-C₇H₇), and singlet (η⁶-C₆H₆)₂Cr, respectively. The likewise experimentally known singlet (η⁶-C₆H₆)₂Ti, doublet (η⁶-C₆H₆)₂V, and singlet (η⁵-C₅H₅)Cr(η⁷-C₇H₇) are the second-lowest-energy structures with only a small energy difference between the two vanadium structures. For the later transition metals, dibenzenemetal complexes are the lowest-energy C₁₂H₁₂M species with two fully bonded hexahapto benzene rings in the lowest-energy manganese and iron derivatives and one hexahapto and one dihapto benzene ring in the lowest-energy cobalt and nickel derivatives. The lowest-energy (C₅H₅)M(C₇H₇) structures for the later transition metals iron, cobalt, and nickel have partially bonded nonplanar C₇H₇ rings with one or two uncomplexed C=C bonds. The (C₄H₄)M(C₈H₈) (M = Ti-Ni) structures with the metal sandwiched between four- and eight-membered rings were found to be much higher in energy than their (C₅H₅)M(C₇H₇) and (C₆H₆)₂M isomers.