Organometallics最新文献

N-Heterocyclic carbenes (NHCs) featuring 2,6-dialkoxyphenyl wingtip groups are synthesized, and their coordination chemistry and properties are studied. Linear [(NHC)CuCl] complexes composed of ligands synthesized herein were characterized by X-ray crystallography and used to analyze the ligand steric parameters. We demonstrate that the use of different alkyl halides in the preparation of these ligands results in NHCs that are sterically tunable and potentially capable of hemilability. Furthermore, the electronic properties of these ligands are assessed by computational methods, which demonstrate these NHCs to be highly electron donating in nature. Additional metalation of these ligands to sulfur, silver, and palladium is reported, and the resulting palladium complexes are tested in the Suzuki–Miyaura reaction of challenging aryl chlorides to benchmark catalytic activity. A direct correlation between steric impacts and catalytic performance is observed.

We report the synthesis and characterization of a series of high- and low-spin dicobalt complexes of the ^tBuPNNP expanded pincer ligand. Reacting this dinucleating ligand in its neutral form with two equiv of CoCl₂(tetrahydrofuran)_1.5 yields a high-spin dicobalt complex featuring one Co inside and one Co outside of the dinucleating pocket. Performing the same reaction in the presence of two equivalents of KOtBu provides access to a high-spin dicobalt complex wherein both Co centers are bound within the PNNP pocket, and this complex also features a bridging OtBu ligand. Reacting either of the high-spin complexes with excess diethyl silane affords a low-spin dicobalt complex containing two unusual bridging Si-based ligands. These complexes were investigated using NMR spectroscopy, XAS, single crystal X-ray structure determination, and computational methods, showing that the Si-based ligands are best described as base-stabilized silylenes.

Deprotonation of 5-methyl-5,6-dihydroindeno[2,1-b]indole (L¹H) or 2-(tert-butyl)-5-methyl-5,6-dihydroindeno[2,1-b]indole (L²H) with an equimolar amount of n-BuLi in Et₂O affords the 5,6-dihydroindeno[2,1-b]indolyl derivatives L¹Li(Et₂O)₂ (1) and [L²Li(Et₂O)]₆ (2) in 67 and 73% yields. Complex 1 proved to be monomeric in the crystalline state, whereas 2 adopts a cyclic hexameric structure. The protonation of Sc(CH₂C₆H₄-o-NMe₂)₃ by an equimolar amount of [HNEt₃][BPh₄] allows for the synthesis of a cationic scandium bis(o-aminobenzyl) complex [Sc(CH₂C₆H₄-o-NMe₂)₂(THF)₂][BPh₄] (3) which was successfully employed as a precursor for the preparation of bis(o-aminobenzyl) 5,6-dihydroindeno[2,1-b]indolyl species. The salt metathesis reactions of lithium derivatives 1 and 2 with 3 (THF, 20 °C) afford complexes L¹Sc(CH₂C₆H₄-o-NMe₂)₂ (4) and L²Sc(CH₂C₆H₄-o-NMe₂)₂ (5) in 69 and 73% yields. Complexes 4 and 5 are monomeric and Lewis-base free. Complexes 4 and 5 as part of binary (4, 5/[Ph₃C][B(C₆F₅)₄], 4, 5/[PhNHMe][B(C₆F₅)₄]) and ternary (4, 5/([Ph₃C][B(C₆F₅)₄], [PhNHMe][B(C₆F₅)₄])/AliBu₃ (1:1:10)) catalytic systems are efficient initiators for isoprene polymerization which enable quantitative conversion of monomers in 30 min ([IP]/[Ln] = 1000) even at −30 °C. The resulting polymers have a predominantly cis-1,4 structure (up to 80.9%; M_n = 58.8–2315.9 × 10³; M_w/M_n = 1.35–3.12). Complexes 4 and 5 catalyze the intermolecular hydrophosphination of styrene, α-methylstyrene, and phenylacetylene with Ph₂PH and PhPH₂ under mild conditions.

We report the synthesis and characterization of a series of high- and low-spin dicobalt complexes of the ^tBuPNNP expanded pincer ligand. Reacting this dinucleating ligand in its neutral form with two equiv of CoCl₂(tetrahydrofuran)_1.5 yields a high-spin dicobalt complex featuring one Co inside and one Co outside of the dinucleating pocket. Performing the same reaction in the presence of two equivalents of KOtBu provides access to a high-spin dicobalt complex wherein both Co centers are bound within the PNNP pocket, and this complex also features a bridging OtBu ligand. Reacting either of the high-spin complexes with excess diethyl silane affords a low-spin dicobalt complex containing two unusual bridging Si-based ligands. These complexes were investigated using NMR spectroscopy, XAS, single crystal X-ray structure determination, and computational methods, showing that the Si-based ligands are best described as base-stabilized silylenes.

Together with bimetallic systems, metalates derived from anionic nucleophile-activated monometallic systems have shown very high catalytic performances for polycarbonates in epoxide–CO₂ copolymerization. However, examples of isolated metalates are rather scarce. Lately, a putative initiating hafnium “ate” species was isolated upon the addition of [PPN]Cl to the N-heterocyclic carbene (NHC) complex of hafnium [PPN][({κ³-O,C,O}-NHC)HfCl₃] 3-Hf. Inspired by this lead, Ti and Zr “ate” analogues of 3-Hf, 3-Ti and 3-Zr, respectively, were synthesized. All the “ate” complexes exhibited high activity (TOF ≈ 363 h^–1) and polycarbonate selectivity (≥99%) in the copolymerization of cyclohexene oxide (CHO) and CO₂ under mild conditions. Monitoring the ring-opening of CHO at room temperature with 3-Hf revealed the rapid formation of a rare metalate intermediate, [PPN][({κ³-O,C,O}-NHC)HfCl₂(OC₆H₁₀Cl)] 5-Hf. Under similar conditions, excess addition of CHO to 3-Hf formed a CHO adduct of 5-Hf species (6-Hf) and at 80 °C led further toward another metalate intermediate, [PPN][({κ³-O,C,O}-NHC)HfCl(OC₆H₁₀Cl)₂] 7-Hf. Kinetic studies revealed the first-order dependence in both the catalyst and CHO concentrations and zero-order dependence in CO₂ with a Gibbs free energy of 24.4 kcal·mol^–1 at 80 °C. DFT calculations performed on the catalytic system suggest 7-Hf to be one of the key active catalytic species favoring CO₂ insertion during copolymerization.

In this report, we synthesized heterobimetallic complexes supported by cyclic and bicyclic (alkyl)(amino)carbenes (CAAC and ^EtBICAAC) [(^Me2CAAC)CuFe(η⁵-C₅H₅)(CO)₂](1) and [(^EtBICAAC)CuFe(η⁵-C₅H₅)(CO)₂] (2), respectively, featuring an iron–copper bond. Complex 1 demonstrates catalytic activity for selective 1,4-hydroboration reactions of pyridine derivatives. Detailed computational studies provide additional insights into the electronic structure of complexes 1 and 2 and elucidate the catalytic pathway.

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)^•].