Abstract We report an improved, convenient, and general synthesis of the air-stable complex CpCo(DQ) (DQ = duroquinone), originally described by Schrauzer and Thyret in 1963, and applied this general protocol to the preparation of a series of related CpCo(p-benzoquinone) complexes with yields ranging from 35 to 96%. The complexes were characterized by single-crystal X-ray diffraction, and the bonding characteristics were compared to those of other CpCo–olefin complexes. Their catalytic performance was evaluated in cyclotrimerization reactions under both thermal and photochemical conditions for the synthesis of pyridine and benzene derivatives.
Abstract The syntheses and reactivity of a series of alkyl iron PCP pincer complexes is described. The alkyl complexes of the type [Fe(PCPCH2-iPr)(R)(CO)2] (R = CH3, CH2CH3, CH2CH2CH3, CH2CH2CH2CH3) are accessible in good yields (69–78%) by reduction of [Fe(PCPCH2-iPr)(Br)(CO)2] with sodium followed by oxidative addition of alkyl halides RX (X = Br or I). As alkyl complexes are typically prone to undergo migratory insertion reactions in the presence of potential strong ligands, [Fe(PCPCH2-iPr)(CH2CH2CH3)(CO)2] was treated with CO and CNtBu affording the acyl complexes [Fe(PCPCH2-iPr)((C═O)–CH2CH2CH3)(CO)2] and [Fe(PCPCH2-iPr)(C═O)–CH2CH2CH3)(CO)(CNtBu)] in 98 and 91% yields. Upon treatment of [Fe(PCPCH2-iPr)((C═O)–CH2CH2CH3)(CO)2] with pinacolborane (HBpin) the hydride complex [Fe(PCPCH2-iPr)(H)(CO)2] is obtained. When [Fe(PCPCH2-iPr)(CH2CH2CH3)(CO)2] is reacted with an excess (4 equiv) of HBpin and SiH2Ph2, complexes [Fe(PCPCH2-iPr)(κ2H,H-H2BPin)(CO)] and [Fe(PCPCH2-iPr)(SiHPh2)(CO)], respectively, is formed. The first is a very labile complex readily liberating HBpin thereby undergoing decomposition to intractable materials. The latter is an unusually stable 16e– complex. Finally, in a preliminary reactivity study [Fe(PCPCH2-iPr)(CO)2(CH2CH2CH3)] is demonstrated to be an active precatalyst for the hydroboration of nitriles with HBPin. The hydroboration reaction requires no additives and proceeds with a catalyst loading of 2 mol % at 60 °C. The reduction of nitriles and subsequent hydrolysis provide ready access to aminomethylene units in organic molecules.
Abstract Metalloxiranes are mechanistically relevant intermediates in carbonyl functionalization by metals. Herein, we investigate carbonyl activation using a nickel complex supported by a diphosphine ligand bearing a pendent Lewis-acidic monoborane. Reaction of this ambiphilic system with a series of carbonyl substrates affords nickeloxiranes whose isomeric distributions and relative energies were examined experimentally and computationally through density functional theory. Despite the proximity of borane functionality, the nickeloxiranes derived from benzophenone and acetophenone exhibited no definitive evidence for intra- or intermolecular O→B interactions. In contrast, the benzaldehyde analogue displayed a well-defined noncovalent O→B interaction in both the solution and solid states. These findings provide insights into the factors governing carbonyl activation by ambiphilic nickel systems.
Herein, we describe the preparation of a library of cationic bismuth-(III) pyridine-(diimine) compounds and the assessment of their Lewis acidity measured by their interaction with phosphine oxides, acid halides, and ketones. These bismuth compounds have acceptor number values ranging between that of BiCl3 and AlCl3, however, their catalytic activity for the formation of C-C bonds is distinct from these simple salts. Our studies suggest that Friedel-Crafts-type arene acylation is promoted via acid halide coordination in the presence of similar ketone donors. This work demonstrates that bismuth-(III) pyridine-(diimine) cations serve as selective Lewis acids to achieve C-C bond formation.
An osmaborane featuring a planar [B4H8]2– ring has been synthesized and structurally characterized. Prolonged thermolysis of the intermediate generated from the reaction of [Os(PPh3)3Cl2] (1) with dppf [dppf = 1,1′-Bis(diphenylphosphino) ferrocene] in the presence of excess [BH3·THF] afforded [Os(dppf)H2(η4–B4H8)] (2) along with [H(dppf)OsB5H10] (3) and [{HOs(dppf)}2(μ-H)B4H7] (4). Complex 2 contains a planar [B4H8]2– ring and is an osmium analog of pentaborane(9). Complex 3 is the osmium analog of hexaborane(10). On the other hand, complex 4 adopts a nido monocapped square pyramidal geometry which is structurally analogous to [{HOs(PPh3)2}2(μ-H)B4H7] (5), obtained from the prolonged thermolysis of [Os(PPh3)3Cl2] (1) with excess of [BH3·THF] alongside the earlier reported [Os(PPh3)2H2(η4–B4H8)] (I) and [H(PPh3)2OsB5H10] (II). Surprisingly, no analogous products were obtained using dppm [dppm = 1,2-bis(diphenylphosphino)methane] and dppe [dppe = 1,2-bis(diphenylphosphino)ethane]. All synthesized molecules were characterized through multinuclear NMR and IR spectroscopy and mass spectrometry. Single-crystal X-ray diffraction analyses of clusters 2 and 5 established their solid-state structures, while theoretical investigations elucidated the bonding in 2. In addition, comparative electrochemical studies of 2 and I were carried out to examine electronic communication and to assess the influence of the redox-active dppf ligand on the electronic properties of the complex.
The mechanochemical synthesis of well-defined [Rh(L)(acac)(CO)] (L = NHC or phosphine) complexes via planetary milling and manual grinding with a mortar and pestle is reported. This solventless protocol, which proceeds via a ligand displacement from [Rh(acac)(CO)2], was successfully applied to various NHC·HCl salts (NHC = IPr, SIPr, IMes, SIMes, IPr*), neat phosphines (PPh3 and PCy3), and the PtBu3·HBF4 salt. This method offers rapid access, using readily available tools, to the electronic characterization of ligands in organometallic chemistry.
Different reaction types known to occur when (F3C)2BNMe2, 1, acts as an inorganic alkene were studied computationally. Diels–Alder cycloadditions dominate three other pericyclic reaction types by exhibiting lower activation barriers and greater exothermicities. An upper bound of ΔG 298 ‡ = 100 kJ mol–1 appears appropriate for defining reactions that will occur experimentally. Substituting hydrogens with π-donor groups on the butadiene leads to lowered barriers, such that the model predicts a number of plausible Diels–Alder reactions. Such substitution at the butadiene 2-posiiton is predicted to lead to exclusive formation of rings with the substituent on the carbon adjacent to the boron-bound carbon, a result caused by barrier differences traceable to electronic issues. The steric demand of the (F3C)2B moiety limits plausible reactivity to cases where at least one CH2 terminus is present on the butadiene. Thus, in reactions between 1 and a 1-substituted butadiene, the boron binds the CH2 terminus and the nitrogen binds the CH(R) terminus. Diels–Alder reactions between 1 and 1,4-disubstituted butadienes are predicted to be implausible regardless of the electronic properties of the substituents.
Cyclometalation reactions proceeding by a concerted metalation-deprotonation mechanism are recognized as efficient routes toward new organometallic compounds. Using this approach, we reacted 6-(4-tolyl)phenanthridine (1) and 6-(4-(trifluoromethyl)phenyl)phenanthridine (2) with [(η5-C5Me5)MCl2]2 (M = Rh and Ir) in the presence of sodium acetate and obtained the respective cyclometalated products [(η5-C5Me5)MCl(1–H)] and [(η5-C5Me5)MCl(2–H)] in varying yields (20–80%). An unexpected product of 2-fold C–H bond activation [Rh(OAc)(1–H)2] (3) was also isolated. The compounds were characterized by NMR spectroscopy and mass spectrometry, and the structures of the representative complexes were determined by single-crystal X-ray diffraction analysis. In addition, the photophysical properties of the cyclometalated compounds were studied using UV–vis and luminescence spectroscopy, and the data were rationalized by DFT calculations. The reaction of [(η5-C5Me5)RhCl(1–H)] with tolane in the presence of a Cu(II) salt as an oxidant afforded 9-methyl-6,7-diphenylisoquinolino[2,1-f]phenanthridin-5-ium tetrafluoroborate, an annulated product, which suggested that the cyclometalated complexes are plausible intermediates of such annulation reactions.
A structurally authenticated series of chalcogenophosphinites, R2P(ChPh) (Ch = S, Se, Te), supported by a compact tetrasilaphosphacyclopentane backbone, is presented. The parent secondary phosphane is obtained in two scalable steps from a dichlorohexasilane via substitution with 2.0 eq. NaPH2 and intramolecular ring-closure driven by PH3 elimination. Selective deprotonation furnishes lithium and potassium phosphides that serve as versatile entry points to functionalization. Reaction of the parent phosphane with PhChChPh (Ch = S, Se) yields the thio- and selenophosphinites, whereas employing the potassium phosphide delivers the full S/Se/Te series in higher yields and provides access to the tellurium derivative that is not accessible from the secondary phosphane. Across the series, 31P NMR shifts move markedly upfield in a nonlinear fashion (S → Se → Te), and UV/vis spectra exhibit progressive bathochromism; both trends are reproduced by DFT/TD-DFT and traced to HOMO–LUMO gap narrowing together with increasing polarizability and heavy-atom effects down the group. Single-crystal X-ray data reveal systematic lengthening of P-Ch bonds and widening of Si–P–Ch angles. Together, these results provide a sterically constant platform that enables direct S/Se/Te comparison and illuminates periodic trends in neutral chalcogenophosphinites stabilized by an oligosilane backbone.
Given potential ramifications in catalysis, exploring redox cycling at heavy main group centers is attracting renewed interest. In this context, this study explores how chalcogen bonding interactions can influence the oxidative addition of o-chloranil to the Te-(II) center of diaryltellurides. Using a series of diaryltellurides functionalized by ortho-methylene-dimethylamino or -methyl ether functionalities, we show that the formation of a chalcogen bond between the donor atom and the tellurium center drives the oxidation reaction, as confirmed by the isolation and structural characterization of the corresponding Te-(IV) monocatecholates. Furthermore, this study also shows that these tetravalent tellurium derivatives react with an additional equivalent of o-chloranil to afford hexachloro-dibenzo-[1,4]-dioxine-2,3-dione, a known compound, and the corresponding Te-(IV) dichlorides. Lastly, this work also documents the facile reductions of the Te-(IV) dichlorides into their Te-(II) diaryl precursors using dithiothreitol or DTT.
Metal–metal bonded complexes feature unique intermetallic synergy enabling small-molecule activation and organic transformations. Using a pentadentate N-ligand, a dinickel paddlewheel complex is obtained from NiCl2, while a tetranickel complex with a short Ni–Ni bond in a unique parallelogram geometry is isolated from Ni(COD)2 and converted to μ-oxo halide complexes with aryl halides. Theoretical and catalytic hydrosilylation studies confirm Ni–Ni interactions and cooperative multimetallic behavior distinct from mononuclear nickel complexes.
Low-coordinate phospholes are of considerable interest due to their unique electronic structures and potential applications in functional materials and coordination chemistry, while their utilization is often limited by insufficient stability and restricted synthetic accessibility. In this study, cyclopentasilane-substituted oxaphospholes were synthesized using sodium phosphaethynolate as a phosphorus source under mild reaction conditions. The introduction of a cyclic all-silicon substituent provides substantial steric hindrance and enables access to isolable low-coordinate oxaphosphole derivatives. The resulting oxadiphospholonide was characterized by multinuclear NMR spectroscopy and single-crystal X-ray diffraction, supported by density functional theory calculations. Notably, the compound exhibits good thermal stability and shows no obvious decomposition upon heating to 90 °C. In addition, the oxadiphospholonide displays characteristic electrophilic reactivity at either the phosphorus or oxygen center, which can be rationalized on the basis of hard–soft acid–base principles. This work expands the scope of NaOCP-derived phospholes and provides a new structural platform for accessing low-coordinate phosphorus heterocycles.
To investigate the effects of extension of lone-pair interactions via σ-symmetric orbitals through nonbonded atoms, we prepared perselenated naphthalenes, -pyrenes and -anthracenes. In contrast to the π-delocalized systems, the HOMOs of these molecules are characterized by antibonding interactions between lone-pair electrons on the selenium atoms, resulting in the σ-symmetric orbital interactions along the periphery of the aromatic hydrocarbon platforms (denoted as σ-delocalization in this work). Consequently, the molecules deviate from planarity to reduce the HOMO energy levels. Under these conditions, increasing the number of selenium atoms leads to a rise in the HOMO energy levels.
R2Zn compounds prepared by the conventional method (reaction of 2 eq RMgCl with ZnCl2 in Et2O, followed by filtration to remove MgCl2) are often unsuitable for certain organic and polymer synthesesparticularly coordinative chain transfer polymerization (CCTP)due to residual impurities. Herein, we disclose a convenient, safe, scalable, and cost-effective method for the preparation of high-purity R2Zn that performs effectively in CCTP. In this approach, RMgCl, generated in Et2O or the less hazardous (CH3O)2CH2, are reacted with ZnCl2. Subsequent removal of the ether solvent affords a residue containing both the desired R2Zn product and dried MgCl2 byproduct. The dried MgCl2 acts as an impurity scrubber during the hexane extraction step, enabling isolation of highly pure R2Zn compounds. Using this method, [CH2C(R)C6H4(CH2) x ]2Zn [1 (x = 3, R = H); 2 (x = 3, R = Me); 3 (x = 2, R = H); 4 (x = 2, R = Me)] was efficiently synthesized. These reagents enabled the formation of high yields of CH2C(R)C6H4(CH2) x -[(CH(R)CH2)] n -Zn-[(CH2CH(R))] n -(CH2) x C6H4C(R)CH2 in CCTP. GPC, 1H NMR, and rotational rheology analyses of the resulting polymers indicate that a fraction of the styrene units in 1 and 3 is incorporated into the polymer backbone, leading to higher-molecular-weight materials with long-chain branching.
Palladium-catalyzed dehydrogenation of formic acid under homogeneous conditions is rare. In most cases, decomposition of palladium complexes is observed under the reaction conditions. In this study, bis(phosphinite)-supported palladium(II) complexes, {2,6-(R2PO)2C6H3}PdX [R = i Pr, t Bu; X = H (1a–b), OCHO (2a–b)], were examined for catalytic formic acid dehydrogenation (FAD). Their derivative complexes, {2,6-(R2PO)2C6H3}PdCH3 (3a–b), were found to be precatalysts. During catalysis, complex degradation was observed; however, by optimizing the reaction conditions (80 °C, ethanol), a homogeneous and additive-free procedure for FAD was achieved. Alcohols and dihydrogen were identified as the possible sources of catalyst decomposition. Mechanistic investigations reveal that the protonation of {2,6-(R2PO)2C6H3}PdH (1a–b) is both kinetically and thermodynamically favored, which drives FAD while suppressing catalyst degradation pathways. It was found that the sterically crowded {2,6-( t Bu2PO)2C6H3}PdCH3 (3b) is a more effective catalyst compared to {2,6-( i Pr2PO)2C6H3}PdCH3 (3a). Experimental data show that CO2 elimination, the rate-limiting step of the catalytic cycle, occurs more rapidly from {2,6-( t Bu2PO)2C6H3}PdOCHO (2b) than from {2,6-( i Pr2PO)2C6H3}PdOCHO (2a), thereby accelerating the overall reaction rate.
Camalexin, a primary indole-analogous phytoalexin from Arabidopsis thaliana and other crucifers, inhibits the proliferation of various cancer cells. In this contribution, the synthesis and characterization of camalexin-derived Ru(II) half-sandwich complexes are described. Formation and sufficient purity of the complexes were confirmed by 1H-, 13C- and 2D-NMR techniques, X-ray or 3D electron diffractometry, high-resolution-mass-spectrometry (HRMS) and elemental analysis. Additionally, the stability in aqueous solution was studied under pseudophysiological conditions, revealing sufficient stability for further biological studies. Investigating the in vitro anticancer potency by means of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H tetrazolium bromide (MTT) and resazurin assays in four human cancer cell lines revealed IC50 values in the (mostly low) micromolar range. Tests for the capacity of generating reactive oxygen species (ROS) in the leukemic HL60 cell line identified one derivative with exceptionally high ROS induction via a 2′,7′-dichlorofluorescin diacetate (DCFH-DA)-based approach. While increased ROS levels were not decisive for cell death induction, cytotoxic activity of the complexes was associated with mitochondrial membrane depolarization and functional perturbation. Lastly, the ability of the complexes to induce apoptosis was investigated, with the complexes showing remarkable effects, while the free ligands exhibited hardly any signs of apoptosis induction.
Cationic bis-heteroleptic Ir(III) complexes (Ir1–Ir3) bearing 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (pdpt) as an ancillary ligand were synthesized using three different cyclometallating ligands. Structural characterization by FT-IR, ESI-MS and 1D/2D NMR confirmed the formation of the complexes, while the molecular structure of Ir1 was elucidated from single-crystal X-ray diffraction. Photophysical studies revealed that all complexes exhibited red-light emission under UV light. The complexes demonstrated high kinetic stability under biologically relevant conditions. Biomolecular studies in cell-free conditions showed strong binding affinities toward DNA and BSA, with Ir1 exhibiting the highest interaction. Cytotoxicity evaluation against MCF-7, MDA-MB-231, and A549 cancer cell lines revealed significant anticancer activity. Among the three complexes, Ir2 displayed the highest cytotoxicity, whereas Ir3 showed the least potency. The exploration of selectivity toward MCF10A disclosed the optimal balance between anticancer efficacy and selectivity of Ir1. The in vitro noncytotoxicity of these complexes against HEK-293 cells further highlighted the superior activity relative to the conventional Pt-based cancer drugs. The anticancer efficacy of complexes was examined in treated MCF-7 cancer cells through DAPI nuclear staining assays and arrest of the cell cycle at the G0/G1 phase, analyzed from flow cytometry. Finally, in vivo toxicity screening in Drosophila melanogaster connected gene expression changes to developmental abnormalities, confirming Ir2 as the most cytotoxic complex.
The ortho selectivity of C–H activation in the palladium-catalyzed annulation of phosphinyl allenes to form benzo[b]phosphole oxides has previously been attributed to coordinative assistance from the adjacent PO moiety. In this study, comprehensive structural and energetic analyses reveal a different mechanistic origin. The observed ortho C–H activation is governed primarily by the preferred six-membered twisted-boat conformation of the palladacyclic transition state. The presumed PO···Pd coordination does not exert a directing effect; instead, it distorts the favorable palladacyclic geometry and raises the transition-state energy to a prohibitive level, making its involvement in C–H activation infeasible. A closer inspection of the elementary steps in this cascade reaction shows that ancillary ligands modulate two key processes in opposite directions: they elevate the oxidative addition barrier while markedly stabilizing the C–H activation transition state. As a result, the overall rate-limiting step depends sensitively on the electron count (14e – or 16e –) of the active Pd(0) species, as well as the identity of the ancillary ligand. Collectively, these findings support a strain- and ligand-controlled mechanism rather than the previously assumed heteroatom-directed C–H activation model, providing new insights into palladium-catalyzed allene annulation and heterocycle construction.
The synthesis and reactivity of (dan)BCCB(dan), a previously untapped diborylethyne characterized by remarkably diminished Lewis acidity are reported. In contrast to Lewis acidic analogues that decompose upon exposure to water, the dan-substituted diborylethyne exhibits exceptional stability toward air, moisture, and silica gel chromatography. We further demonstrate the utility of the central triple bond as a robust platform for diverse catalytic transformations, providing access to multimetalated alkenes. The significant disparity in Lewis acidity between B(dan) and B(pin) moieties enables precise, chemoselective Suzuki–Miyaura cross-couplings, allowing for the modular construction of multisubstituted alkenes while leaving the B(dan) groups intact.
