Organometallics最新文献

Fluorinated borates have been widely used as innocent and weakly coordinating counteranions. Among those, [BAr^F₄]⁻ ([B(C₆H₃-3,5-(CF₃)₂)₄]⁻) occupies a prominent position due to the robustness of its B–C carbon bonds. Herein, we investigate C–B bond cleavage in the [BAr^F₄]⁻ anion mediated by cationic gold fragments of type [Au(PMe₂Ar′)]⁺, where Ar′ stands for bulky terphenyl (C₆H₃-2,6-Ar₂) substituents. In addition, we have exploited the stoichiometric B–C bond cleavage to construct a catalytic cycle for the synthesis of boranes under acidic conditions.

The oxidative functionalization of aromatic sp² C–H bonds to C–O bonds is a difficult transformation. For main-group metals, the oxyfunctionalization step of a metal-aryl bond is generally slow and potentially problematic if carried out in a relatively strong acid solvent where protonation could prevent oxyfunctionalization. In this work, we experimentally and computationally analyzed the oxyfunctionalization reaction of (Ph)₃Bi^V(TFA)₂ (TFA = trifluoroacetate) in a trifluoroacetic acid (TFAH) solvent. Experiments showed a single oxyfunctionalization product phenyl TFA (PhTFA) and two equivalents of benzene. Explicit/continuum solvent density functional theory calculations revealed that a direct intramolecular reductive functionalization pathway is lower in energy than radical or ionic pathways, and surprisingly from (Ph)₃Bi^V(TFA)₂, the reductive functionalization pathway is potentially competitive with protonation. In contrast, for (Ph)₂Bi^V(TFA)₃ oxyfunctionalization is significantly lower in energy than protonation. For Bi^III-phenyl intermediates, redox neutral protonation is significantly lower in energy than a second functionalization. We also examined the oxyfunctionalization versus protonation of Bi^V-phenyl complexes with a coordinated biphenyl ligand and a coordinated biphenyl sulfone ligand, which both resulted in oxyfunctionalization. For the biphenyl ligand complex, a protonation-first mechanism is proposed, while for the biphenyl sulfone ligand, an oxyfunctionalization first mechanism is consistent with both calculations and experiments.

Methanol production from CO₂ offers an attractive alternative to developing a sustainable energy economy. In this work, a phosphine-free Ru(II)-NHC pincer complex (1•PF₆) bearing a proton-responsive pyridyl(benzamide) appended on an N-heterocyclic carbene (NHC) has been synthesized. The molecular structure of 1•PF₆ reveals the deprotonated iminolic form of the ligand. The acid–base equilibrium between the iminolic-amide tautomer of the ligand scaffold was examined by ¹H NMR and UV–vis spectra. The catalytic efficacy of 1•PF₆ for the hydrogenation of urea and carbamates as CO₂ derivatives, two of the most challenging carbonyl substrates, to methanol (yield 74–90%) was explored. Further, amine-assisted CO₂ capture followed by hydrogenation to formamide and its subsequent hydrogenation to methanol (yield up to 90%) were performed using catalyst 1•PF₆. A maximum TON of 1700 was attained by taking piperidine as a CO₂ capturing agent. The deprotonated complex exhibits superior activity in comparison to its protonated form, revealing metal–ligand cooperation in dihydrogen activation. Catalyst 1•PF₆ is air- and moisture-stable and thus offers operational simplicity. NMR experiments suggest the intermediacy of a [Ru–H/N–H]⁺ intermediate engaged in proton and hydride management in the catalytic pathway. A plausible catalytic cycle is proposed based on informative mechanistic experiments.

The group 1 alumanyls, [{SiN^Dipp}AlM]₂ (M = K, Rb, Cs; SiN^Dipp = {CH₂SiMe₂NDipp}₂), display a variable kinetic facility (K < Rb < Cs) toward oxidative addition of the acidic C–H bond of terminal alkynes to provide the corresponding alkali metal hydrido(alkynyl)aluminate derivatives. Theoretical analysis of the formation of these compounds through density functional theory (DFT) calculations implies that the experimentally observed changes in reaction rate are a consequence of the variable stability of the [{SiN^Dipp}AlM]₂ dimers, the integrity of which reflects the ability of M⁺ to maintain the polyhapto group 1-arene interactions necessary for dimer propagation. These observations highlight that such “on-dimer” reactivity takes place sequentially and also that the ability of each constituent Al(I) center to effect the activation of the organic substrate is kinetically differentiated.

The group 1 alumanyls, [{SiN^Dipp}AlM]₂ (M = K, Rb, Cs; SiN^Dipp = {CH₂SiMe₂NDipp}₂), display a variable kinetic facility (K < Rb < Cs) toward oxidative addition of the acidic C-H bond of terminal alkynes to provide the corresponding alkali metal hydrido(alkynyl)aluminate derivatives. Theoretical analysis of the formation of these compounds through density functional theory (DFT) calculations implies that the experimentally observed changes in reaction rate are a consequence of the variable stability of the [{SiN^Dipp}AlM]₂ dimers, the integrity of which reflects the ability of M⁺ to maintain the polyhapto group 1-arene interactions necessary for dimer propagation. These observations highlight that such "on-dimer" reactivity takes place sequentially and also that the ability of each constituent Al(I) center to effect the activation of the organic substrate is kinetically differentiated.

Palladium-catalyzed cross-coupling reactions, particularly the Suzuki–Miyaura coupling, are efficient tools for constructing C–C bonds due to their exceptional versatility and efficiency. Recently, nitroarenes have been explored as new electrophilic substrates in palladium-catalyzed denitrative Suzuki–Miyaura coupling, offering an alternative to traditionally used organic halides or triflates. The oxidative addition of nitro derivatives onto palladium catalysts remains challenging and often requires harsh conditions and expensive catalytic systems. Nevertheless, we recently demonstrated that nitro-perylenediimide derivatives can effectively engage in various cross-couplings with unsophisticated Pd(PPh₃)₄ as a catalytic system. The mechanistic study of the oxidative addition step for this particular class of nitro derivatives revealed an unprecedented single electron transfer event, which is supported by a comprehensive range of analyses including NMR, X-ray diffraction, HRMS and EPR experiments, complemented with cyclic voltammetry, and theoretical calculations.

The reaction of AnCl₄(DME)_x (An = Th, x = 2; An = U, x = 0) with 4 equiv of NaNR₂ (R = SiMe₃) in THF at 65 °C results in the formation of [An{N(R)(SiMe₂CH₂)}(NR₂)₂] (An = U, 1; An = Th, 2), and not the reported monomeric actinide hydrides, [AnH(NR₂)₃], as expected. Both complexes 1 and 2 were characterized by X-ray crystallography. Surprisingly, their unit cell parameters are remarkably close to those reported for [AnH(NR₂)₃], suggesting that the original crystals of [AnH(NR₂)₃] were, in fact, [An{N(R)(SiMe₂CH₂)}(NR₂)₂], but were misidentified. Reduction of 1 with 1.1 equiv of KC₈ in THF, in the presence of 1 equiv of 2.2.2-cryptand, results in the formation of [K(2.2.2-cryptand)][U{N(R)(SiMe₂CH₂)}(NR₂)₂] (3) in good yield. Likewise, the reaction of 1 with 1 equiv of bis(diisopropylamino)cyclopropenylidene (BAC) results in the formation of the BAC adduct, [(BAC)U{N(R)(SiMe₂CH₂)}(NR₂)₂] (4), in moderate yield. Finally, the addition of H₂ (10 bar) to 2 in C₆D₆ at room temperature results in the formation of the targeted monomeric hydride, [ThH(NR₂)₃], in 32% yield, according to integrations against an internal standard. However, removal of the H₂ atmosphere results in rapid reformation of 2. In contrast, the addition of H₂ (10 bar) to 1 in C₆D₆ at room temperature results in no apparent reaction.

Cobalt(II) bis(amides)are widely applied in catalysis and material science. Typically, they are prepared via salt metathesis, by reacting a lithium amide with a CoX₂ (X = Cl, Br) salt, requiring, in many cases, the use of low temperatures and other solvents. This work introduces an alternative approach, assessing the reactivity of classical Co(II) amide [Co(HMDS)₂] (1) [HMDS = N(SiMe₃)₂] and heterobimetallic [NaCo(HMDS)₃] (6) as precursors for trans(amination) reactions with DPA(H) (2,2′-dipyridylamine), N-methylaniline, and piperidine. When reacted with the most acidic amine DPA(H), both showed polybasic behavior with excellent stoichiometric control according to the equivalents of DPA(H) employed. Reactions with and piperidine led to an incomplete exchange of the HMDS groups present in 1, even when an excess of the relevant amine is employed. Contrastingly, when assessing the reactivity of sodium cobaltate 6 with these amines, kinetic activation of two (or three) of its HMDS-arms was observed, forming new heterobimetallic species which in all cases proved unstable, undergoing dissociation into their monometallic components or a ligand redistribution process. The catalytic potential of the novel Co(II) complexes was investigated for the hydrosilylation of acetophenone, finding that faster reaction rates and higher chemoselectivities were achieved when using the heterobimetallic Na/Co systems.

N-heterocyclic carbenes (NHC) derived from the pyrrolo[1,2-c]pyrimidine skeleton have been synthesized. They are constitutional isomers of the well-known imidazo[1,5-a]pyridin-3-ylidenes (ImPy), but differ in the position where the nonbridgehead nitrogen is located; formally, it has been transferred from the five-membered ring in ImPy structures to the six-membered ring in pyrrolo[1,2-c]pyrimidin-1-ylidenes (PyPy). As consequence, the resulting diamino-stabilized carbene unit is embedded in an aromatic, six-membered, pyrimidine ring. IR data of the corresponding Rh-carbonyl derivatives evidence that the members of this new NHC family are exceptionally strong σ-donors; they even outperform ImPy or more traditional imidazole-2-ylidenes. On the other hand, Ganter′s selenourea method characterizes them as strong π-acceptor. Au-complexes bearing PyPy ligands have been also prepared, and their performance evaluated in the cyclization of N-(3-iodoprop-2-ynyl)-N-tosylanilines 21a–c into 1,2-dihydroquinolines of different substitution pattern 23a–c. The analysis of the product ratios obtained agrees with the donor ability rank established by the spectroscopic methods.

Polythiophenes are of great interest for use in electronic materials due to their stability and favorable materials properties. Thiophene-based electronic materials provide an attractive alternative to conventional inorganic semiconductors. We have targeted hybrid materials that combine the versatility of transition metals with oligo- and polythiophenes. We report here terthiophenes in which the [c]-edge of the central thiophene is fused to a cyclopentadienyltricarbonylmanganese group. These thiapentalenyl complexes, [Mn{η⁵-SC₇H₃-1,3-R₂}(CO)₃], were prepared in moderate to good yields (50–80%) via ring closure of 1,2-diacylcymantrenes, [Mn{η⁵-1,2-C₅H₃(COR)₂}(CO)₃] (R = thienyl, 5-methylthienyl, 5-chlorothienyl, 5-bromothienyl) with Lawesson’s reagent. These complexes display high environmental stability and were characterized via spectroscopic methods as well as X-ray crystallography. Cyclic voltammetry shows that the unsubstituted terthiophene manganese complex is susceptible toward electrochemical polymerization, whereas the 5-methyl complex is not. X-ray photoelectron spectroscopy (XPS) confirmed the presence of manganese in the polymeric films and indicated a nearly identical bonding environment of manganese in the monomer and the films.