Organometallics最新文献

An experimental mechanistic study of the decarboxylation reactivity of well-defined 1,10-phenanthroline-ligated copper(I)- and copper(II)-benzoate complexes is reported. This work demonstrates decarboxylation to occur from both copper(I)- and copper(II)-benzoates with the (phen)Cu^II(2-nitrobenzoate)₂ (2) proceeding through an oxidative decarboxylation pathway to generate the homocoupled biaryl product while decarboxylation from (phen)Cu^I(2-nitrobenzoate) (1) generates primarily the arene via redox-neutral protodecarboxylation (phen = 1,10-phenanthroline). The time course kinetics and additive experiments demonstrate the decarboxylation of copper(II)-benzoates to both generate and be catalyzed by copper(I). We also disclose the characterization and reactivity of an off-pathway bis(phenanthroline)copper(I)-benzoate species [(phen)₂Cu^I][2-nitrobenzoate] (3) as well as the interconversion of these species under typical reaction conditions. These studies reveal an unexpected inhibitory effect of phen on the decarboxylation of copper(I) species with the unligated species Cu^I(2-nitrobenzoate) (4) showing rapid decarboxylation. Finally, synthesis, characterization and reaction kinetics of the decarboxylation of a series of differently substituted copper(II)-benzoate complexes reveal the field effect (F) to be the dominant factor governing the rate of decarboxylation in these systems.

A diamide ligand featuring a [2.2]paracyclophane (CP) backbone was synthesized and introduced to the coordination and organometallic chemistry of rare-earth metals. Alkane elimination and salt metathesis reactions were employed to prepare rare-earth metal benzyl and iodide complexes supported by the CP-derived diamide ligand. In addition, heteronuclear naphthalene dianion complexes were synthesized by the reduction of the rare-earth metal iodides. All new compounds were characterized by X-ray crystallography, elemental analysis, ¹H and ¹³C nuclear magnetic resonance spectroscopy, and absorption spectroscopy. Furthermore, the coordination chemistry supported by the CP-derived diamide ligand is compared to that of the ferrocene-derived diamide ligand.

A β-diketiminate-supported magnesium amido complex [LMgN(SiMe₃)₂·THF] (Mg-1, L = ^DepNacnac = (^DepNCMe)₂CH; Dep = 2,6-Et₂-C₆H₃) was synthesized and characterized. Mg-1 efficiently catalyzes the hydroacetylenation of N,N′-diisopropylcarbodiimide (DIC) with terminal alkynes, yielding N,N′-substituted propiolamidines in moderate to good yields (up to 91%). Mechanistic studies identified key intermediates: the reaction proceeds via σ-bond metathesis, forming magnesium acetylide Mg-2, followed by carbodiimide insertion into the Mg–C bond to yield magnesium propiolamidinate Mg-3. Subsequently, these propiolamidines undergo noncatalytic addition with aryl isocyanates under mild conditions, leading to ureas that cyclize to afford imidazolidin-2-ones in a one-pot protocol. The reaction scope and a proposed mechanism for cyclization are presented, demonstrating the utility of this earth-abundant magnesium catalyst for synthesizing valuable heterocycles.

Copper(I) hydride complexes are widely recognized as reactive intermediates in numerous transformations and typically undergo syn-addition across alkynes. Although copper and gold both belong to Group 11, (NHC)Au(I)–H displays a contrasting anti-addition behavior. In this work, we systematically investigate the reactivity differences between (NHC)Cu(I)–H and (NHC)Au(I)–H using density functional theory. Our results reveal that the observed stereoselectivity originates from the relative stability of the three-coordinated metal-alkyne intermediates. Specifically, the distortion required for (NHC)Au(I)–H to engage in syn-addition is energetically very unfavorable compared to its copper(I) counterpart, destabilizing the corresponding gold-alkyne intermediate and thus favoring anti-addition.

The monomeric AlCl₃–H₂O species is commonly accepted as the initiating species in the AlCl₃-catalyzed cationic polymerization of isobutylene. However, density functional theory (DFT) calculations reveal that the dominant initiating species during the initiation stage are the dimeric AlCl₃ complexes A0 (Al₂Cl₆–H₂O) and C0 (Al₂Cl₅OH- -HCl), rather than B0 (AlCl₃HOHAlCl₃) as proposed by Johnson et al. (ACS Catal. 2018, 8, 8006). Herein, we propose a novel temperature-dependent initiation mechanism for the AlCl₃-catalyzed cationic polymerization of isobutylene: initiation by a small amount of C0 at low temperature, and co-initiation involving both A0 and C0 at room temperature.

Simple metallocenes of the general formula [MCp₂]^0,+, where M = a wide range of 3, 4, 5d 2+ or 3+ ions and Cp^– = η⁵-cyclopentadienide anion, have been known for more than half a century and are paradigms of organometallic chemistry. Chromium(III) is perhaps the most common oxidation state of chromium. Yet the corresponding metallocene, chromocenium, [CrCp₂]⁺, has been relatively little examined, despite having been first prepared in 1962 (as an iodide salt) by E. O. Fischer who was a pioneer of metallocene chemistry. We report here the synthesis of [CrCp₂][BAr^F], (BAr^F = tetrakis[(3,5-trifluoromethyl)phenyl]borate) and its structural and spectroscopic characterization. Spectroscopic methods comprised X-band electron paramagnetic resonance (EPR) and high-frequency and -field EPR (HFEPR) in conjunction with magnetic circular dichroism (MCD). The S = 3/2 ground state of [CrCp₂][BAr^F] gives spin Hamiltonian parameters: D = +4.82(1) cm^–1, E = 0, g_x(⊥) = g_z(||) = 2.00(1). The axial electronic symmetry is expected for this 5-fold symmetric complex and the positive sign of D is as found earlier for isoelectronic vanadocene, [VCp₂], but the magnitude of D here is larger, qualitatively indicating the difference between isoelectronic Cr^III and V^II ions. Ligand-field theory (LFT) and quantum chemical theory (QCT) are used to analyze quantitatively the electronic structure of [CrCp₂]⁺ on its own and in the context of its better known 3d³ congener [VCp₂].

Oxyphile actinide oxides and their ions are potential candidates for methane activation due to their unique electronic configurations. The comprehensive activation mechanisms of methane catalyzed by a series of early actinoid ions and their oxide ions (Ac³⁺ and AcO⁺; Th⁴⁺, ThO²⁺ and ThO⁺; ³Pa³⁺, ³PaO⁺, PaO⁺/PaO³⁺ and PaO₂⁺; ⁴UO⁺, ³UO²⁺/UO²⁺, ³UO₂, and UO₂²⁺; ³NpO⁺/⁵NpO⁺, ²NpO²⁺/⁴NpO²⁺, ²NpO₂/⁴NpO₂, NpO₂⁺/³NpO₂⁺, ²NpO₂²⁺, ²NpO₃, and NpO₃⁺) were systematically investigated in this study. Theoretical calculations in the present work suggest that Ac³⁺, Th⁴⁺, and PaO³⁺ can easily tear methane apart and extract hydrogen from it, but the reaction pathway of Pa³⁺···CH₄ → HPa³⁺-CH₃ needs a barrier of 47.6 kcal·mol^–1. Judging from the activation barriers of the actinide oxide ions, AcO⁺, ²ThO⁺, ³UO₂, and ²NpO₂²⁺ are ideal catalysts for methane activation with the lowest barriers of 32.8, 40.1, 31.1, and 33.1 kcal·mol^–1, respectively.

The precise modulation of the microenvironment of metal sites in metal–organic frameworks (MOFs) has become a research hotspot, but the conformational relationship between the coordination environment and catalytic activity still lacks an atomic-level mechanism. Herein, efficient C(sp²)–N coupling between phenothiazines and unprotected phenols was achieved under mild conditions by modulating the Cu coordination environment of Cu-UiO-66-X (X = −NO₂, −H, −OH). Notably, Cu-UiO-66-X catalysts with specific −X group coordination microenvironments exhibit significant activity differences in the C(sp²)–N coupling reaction (activity order: −NO₂ > −H > −OH). The introduction of specific −X groups through MOF organic linkers can precisely regulate the coordination environment of the Cu site and thus its electronic properties. The experimental and characterization results show that the specific −X group can precisely regulate the electronic properties at the Cu site, thus significantly enhancing the catalytic activity.

Reactions of the osmium polyhydride complexes Cp*OsH₅ (Cp* = η⁵-C₅Me₅) and Cp*₂Os₂(μ-H)₄ with the amidostannylene DMPSnN(SiMe₃)₂ (DMP = C₆H₃-2,6-Mes₂, Mes = mesityl) are reported. Treatment of Cp*OsH₅ with DMPSnN(SiMe₃)₂ in n-pentane results in the rapid formation of osmiostannylene Cp*OsH₄SnDMP (1), which precipitates from solution. While 1 is stable in the solid state, it decomposes in solution to form the μ₂-stannylyne complex Cp*H₄Os(μ-SnDMP)OsH₃Cp* (2). Complex 2 can be prepared in a targeted manner by the reaction of Cp*OsH₅ with DMPSnN(SiMe₃)₂ in toluene over an extended period. Cp*₂Os₂(μ-H)₄ reacts with DMPSnN(SiMe₃)₂ to form the unique μ₂-hydridostannylene complex Cp*₂Os₂(μ-H)₂{μ-Sn(H)DMP} (3).

The neutral and cationic initiators Mo(N-2,6-Me₂C₆H₃)(CHCMe₂Ph)(OC(CH₃)₃)₂ (Mo1), Mo(N-2,6-Me₂C₆H₃)(CHCMe₂Ph)(OCH(CH₃)₂)₂.quinuclidine (Mo2), Mo(N-2,6-iPr₂–C₆H₃)(CHCMe₂Ph)(OCH(CH₃)₂)₂ (Mo3), [Mo(N-2-tBuC₆H₄)(IMes)(CHCMe₂Ph)(OTf)][B(Ar^F)₄] (Mo4) and [Mo(N-tBu)(IMes)(CHCMe₂Ph)(MeCN)₂(OTf)][B(Ar^F)₄] (Mo5, IMes = 1,3-dimesitylimidazol-2-ylidene, OTf = CF₃SO₃, B(Ar^F)₄^– = tetrakis(bis(3,5-trifluoromethyl)phenyl)borate) have been investigated for their regioselectivity in the cyclopolymerization of eight different diynes (4-methoxymethyl-1,6-heptadiyne (D1), 4-methoxycarbonyl-1,6-heptadiyne (D2), 4-ethoxycarbonyl-1,6-heptadiyne (D3), 4,4-bis(methoxymethyl)-1,6-heptadiyne (D4), 4,4′-bis(methoxycarbonyl)-1,6-heptadiyne (D5), 4,4′-bis(ethoxycarbonyl)-1,6-heptadiyne (D6), N,N-dipropargyl-p-toluenesulfonamide (D7), 4-(p-toluylsolfonylmethyl)-1,6-heptadiyne (D8)). Complementary, the structurally analogous ene-ynes 4-methoxymethylhept-6-ene-1-yne (E1), 4-methoxycarbonylhept-6-ene-1-yne (E2), 4-ethoxycarbonylhept-6-ene-1-yne (E3), 4,4-bis(methoxymethyl)hept-6-ene-1-yne (E4), 4,4-bis(methoxycarbonyl)hept-6-ene-1-yne (E5), 4,4-bis(ethoxycarbonyl)hept-6-ene-1-yne (E6), N-allyl-N-propargyl-p-toluenesulfonamide (E7), 4-(p-toluylsulfonylmethyl)hept-6-ene-1-yne (E8) were used as substrates in ring-closing ene-yne metathesis (RCEYM). While Mo1 – Mo3 were inactive in RCEYM, the use of the cationic complexes Mo4 and Mo5 allowed for the first exo-selective RCEYM. A strong correlation between α-selectivity in cyclopolymerization and exo-selectivity in ene-yne metathesis was found. Density functional theory (DFT) calculations confirm that exo-selectivity with these catalysts is also based on an α-selective, “yne-first” pathway.