Organometallics最新文献

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.

We herein report a Lewis acid and a Lewis base responsive antimony dipyrrin complex suitable for both nuclear magnetic resonance and photoluminescence spectroscopy detection. The complex showcases distinct reaction modes that go along with a boost or depletion of fluorescence emission. Furthermore, we disclose a correlation between spectroscopic data and solid-state structural parameters in a rare set of 1:1 halogen-bridged Sb-dipyrrin adducts.

Herein, we report the synthesis of several new NHC-stabilized aluminum alkyl species [NHCAlR₃] (for NHC = ICy, R = Me, iBu; NHC = IMes and IDip, R = iBu) via coordination of the respective free carbene to AlMe₃ or AliBu₃. Attempts to access Al–Al bonded species (dialumanes) via reactions with the respective NHCAlH₃ complexes did not yield the desired Al(II) complexes via R-H elimination, instead yielding the R/H ligand scrambled complexes NHCAlR₂H and NHCAlRH₂, respectively. These mixed-ligand species were characterized by ¹H, ¹³C{¹H}, and multinuclear NMR spectroscopy, with select cases characterized by single-crystal X-ray diffraction studies.

The iridium-pincer complex {p-OP(^tBu)₂-C₆H₂-2,6-OP(^tBu)₂]₂}Ir(C₂H₄) (^P[Ir]) has been reported as a stable and active catalyst toward alkane dehydrogenation in homogeneous and supported heterogeneous systems. Dehydrogenation has been shown as a practical method toward functional polyolefins, with dehydrogenated high-density polyethylene (deHDPE) demonstrated as a valuable synthon for upcycling, as orthogonal C–H strategies are key to end-of-life upcycling. The heterogenization of ^P[Ir] on oxides (SiO₂, Al₂O₃, and TiO₂; ^P[Ir]/E_yO_x) yields a mixture of organometallic Ir-fragments whose catalytic nonoxidative dehydrogenation activity is modulated by the binding modes of the active metal on the surface. The binding mode was elucidated by a combination of solid-state NMR and XAFS analyses and supported by DFT calculations. Surface binding through the ligand enables active organoiridium that catalyzes internal olefination of deHDPE up to 1.23 mol % at 200 °C under dynamic vacuum. Alternatively, when the organoiridium is bonded though the metal center (Ir–O_SiO), catalyst activity is negligible. Furthermore, the catalytic activity of ^P[Ir]/SiO₂ showed comparable reactivity with the homogeneous analogue under the same catalytic conditions, and the heterogenized catalyst can be reused up to three cycles. This work highlights the importance of understanding how organometallic precursors react with hydroxylated metal oxide surfaces to establish structure–property relationships.

First-row transition metal catalysis continues to provide innovative and sustainable advances for synthetic chemistry. However, these metals can be challenging to screen efficiently in optimization campaigns due to the limited knowledge of catalyst assembly, stability, and speciation. In this report we demonstrate the use of thermogravimetric analysis (TGA) as a promising tool in evaluating the formation and properties of an Fe precatalyst, fac-Fe(dpa)Cl₃. Using TGA it was possible to identify the generation of distinct Fe complexes that could form in situ from prestirring the commercial metal salt iron trichloride (FeCl₃) and di(2-picolyl)amine (dpa) in different organic solvents. Upon applying these prestirred mixtures to the reaction between methionine and benzyl acrylate, it was determined that distinct complexes gave distinct TGA profiles. Similar TGA profiles yielded similar reaction yields, while distinct TGA profiles tended to give rise to unique yields. Utilizing this approach, a more informed first-row metal catalyzed reaction strategy can be realized.

The synthesis of a lithium disilenide and its reaction with CO are described. Reaction of NHB-substituted dilithiodisilene NHB(Li)Si═Si(Li)NHB (1, NHB = diazaborolyl) with Me₃SiCl resulted in the formation of the lithium disilenide NHB(Me₃Si)Si═Si(Li)NHB (2). Disilenide 2 reacts with 1 atm. of CO, leading to the C–C coupling of two molecules of CO with the formation of a disilacyclobutenone dimer bridged by two lithium ions, which are coordinated to the three exocyclic oxygen atoms.

The aqueous chemistry of molybdenum and tungsten complexes is relevant due to their occurrence in metalloenzymes. However, water-stable and -soluble model complexes in biologically relevant higher oxidation states are rare. Metallocenes of the type [Cp₂M(OH₂)]²⁺ (M = Mo, W) exhibit such properties despite the nonbiomimetic cyclopentadienyl (Cp) ligand. Therefore, the aqueous acid–base properties of these bis-aqua tungstocenes and molybdocenes were investigated, as their +IV oxidation states and coordinated H₂O render them ideal candidates. The precursors [Cp₂MoCl₂] (1a), [Cp₂Mo(μ-OH)₂MoCp₂](pTsO)₂ (1b), [Cp₂Mo(pTsO)₂] (3) and their tungsten analogues [Cp₂WCl₂] (2a), [Cp₂W(μ-OH)₂WCp₂](pTsO)₂ (2b), and [Cp₂W(pTsO)₂] (4) were studied via aqueous potentiometric titrations. Molybdocene acted as a triprotic acid, with deprotonation occurring from both mono- and dimeric species, while tungstocene reacted as a diprotic acid exclusively in its monomeric form. Tungsten complexes exhibit higher acidity with 1–1.5 lower pK_a values than molybdenum, which is of general interest for the understanding of tungstoenzymes. The substitution of chlorides by tosylates allowed the isolation of 3 and 4, which proved to be less suitable precursors for aqueous chemistry, as they were more difficult to hydrolyze, leading to partial degradation upon hydrolysis. This indicates that simply the presence of a Cp₂M motif is not sufficient for the formation of the aqueous species.

Xanthene-derived ligands, such as Xantphos, and related scaffolds are pivotal in contemporary organometallic chemistry, delivering wide-bite-angle diphosphines and frustrated Lewis pairs (FLPs) with applications in catalysis and main-group reactivity. 4,5-Dibromo-9,9-dimethyl-9H-xanthene serves as a common gateway intermediate for perisubstitution, yet literature reports on its synthesis are inconsistent. In our hands, direct bromination of 9,9-dimethylxanthene afforded exclusively the 2,7-dibromo regioisomer in 72% yield, as confirmed by single-crystal X-ray diffraction. A modified literature procedure employing an ortho-lithiation protocol with n-BuLi/TMEDA followed by bromination yielded the desired 4,5-dibrominated product in 65% on gram scale. This work resolves ambiguities in prior reports, providing a reliable, reproducible protocol to facilitate access to xanthene-based frameworks.

Two novel half-sandwich organometallic complexes, [(p-cymene)M(XY)Cl], XY = L-BSO, M = Ru^II (Ru-LBSO), Os^II (Os-LBSO), containing the amino acid L-buthionine sulfoximine (L-BSO), as well as their XY = glycine analogs (Ru-Gly and Os-Gly), have been synthesized, characterized and their solution chemistry investigated. L-BSO is an inhibitor of the enzyme γ-glutamyl cysteine synthetase and, hence, glutathione synthesis. The diastereomers of Ru-LBSO and Os-LBSO were also characterized by DFT calculations which suggested the higher stability of [S_M,r_S] and [S_M,s_S] compared to [R_M,r_S] and [R_M,s_S] configurations [chirality at M(II), chirality at sulfur of L-BSO]. Interestingly, glycine complexes are non-toxic toward both cancer and normal cells, whereas Os-LBSO was cytotoxic toward human IGROV-1 ovarian cancer cells, but not toward lung and cervical cancer cells. Os-LBSO, but not Ru-LBSO, demonstrated glutathione inhibition. These studies on Ru-LBSO and Os-LBSO complexes demonstrate the challenges of making progress toward the development for clinical use of organometallic complexes that contain multiple chiral centers. However, they offer exciting possibilities for discovery of novel drugs with new mechanisms of action.

A Sc(II) pentamethylcyclopentadienyl (Cp*) complex such as “Cp*₂Sc” has not been isolable, although the Sc(II) metallocenes, Cp^ttt₂Sc (Cp^ttt = C₅H₃^tBu₃) and (C₅Me₄SiMe₂^tBu)₂Sc can be crystallographically characterized and Cp^ttt₂Sc forms the Sc(II) CO and CNR adducts Cp^ttt₂Sc(CO) and Cp^ttt₂Sc(CNXyl) (Xyl = C₆H₃-2,6-Me₂). However, the dark-teal Sc(II) metallocene Cp*₂Sc(CNXyl)₂ can be isolated from the Sc(III) reduced dinitrogen complex (Cp*₂Sc)₂(μ-η¹:η¹-N₂) through its reaction with 2 equiv of CNXyl. Density functional theory analysis based on the X-ray crystal structure is used to evaluate the electronic structure of this complex, which allows its isolation, and the low 36.3 MHz (13.0 G) hyperfine coupling in the eight-line EPR spectrum of Cp*₂Sc(CNXyl)₂.