Dimeric Precursor Research Articles

Nitric oxide transfer between nominal Fe and Co biomimetics of the nitrile hydratase active site.

Related to the inactive form of nitrile hydratase, NHase, that contains Fe(NO) within tripeptide N2S2 binding environment, the NO transfer reactivity of (bis-mercaptoethane diazacycloheptane)Fe(NO) and (bis-mercaptoethane diazadimethylethane)Fe(NO) is compared to Co(NO) analogs. Acceptors of NO include cobalt octaethylporphyrin and the [(N2S2)M] dimeric precursors in the synthesis of the Fe(NO) and Co(NO) biomimetics. Qualitative rates are augmented by a definitive kinetic study finding that rates of NO transfer from (N2S2)M(NO) to [(N2S2)M']2 are dependent on M and M' as well as the hydrocarbon N to N and N to S linkers. We conclude that while Fe(NO) and Co(NO) units are similar in chemical stability, minor first coordination sphere differences may favor the former, Fe(NO), consistent with the discovery of Fe(NO), but not Co(NO), in the as-isolated NHase active site.

Synthesis, photophysical characterisation, quantum-chemical study and in vitro antiproliferative activity of cyclometalated Ir(III) complexes based on 3,5-dimethyl-1-phenyl-1H-pyrazole and N,N-donor ligands.

In this paper, we present the synthesis of four new complexes: the dimeric precursor [Ir(dmppz)2(μ-Cl)]2 (1) (Hdmppz - 3,5-dimethyl-1-phenyl-1H-pyrazole) and heteroleptic bis-cyclometalated complexes: [Ir(dmppz)2(Py2CO)]PF6·½CH2Cl2 (2), [Ir(dmppz)2(H2biim)]PF6·H2O (3), and [Ir(dmppz)2(PyBIm)]PF6 (4), with auxiliary N,N-donor ligands: 2-di(pyridyl)ketone (Py2CO), 2,2'-biimidazole (H2biim) and 2-(2'-pyridyl)benzimidazole (PyBIm). In the obtained complexes, SC-X-ray analysis revealed that Ir(III) has an octahedral coordination sphere with chromophores of the type {IrN2C2Cl2} (1) or {IrN4C2} (2-4). The complexes obtained, which have been fully characterised by physicochemical methods (CHN, TG, FTIR, UV-Vis, PL and 1H, 13C, 15N NMR), were used to continue our studies on the factors influencing the cytotoxic properties of potential chemotherapeutic agents (in vitro). To this end, the following studies are presented: (i) comparative analysis of the effects on the biological properties of N,N-donor ligands and C,N-donor ligands in the studied complexes, (ii) studies of the interactions of the compounds with the selected molecular target: DNA and BSA (UV-Vis, CD and PL methods), (iii) and the reactivity towards redox molecules: GSH, NADH (UV-Vis and/or ESI-MS methods), (iv) cytotoxic activity (IC50) of potential chemotherapeutics against MCF-7, K-562 and CCRF-CEM cell lines.

Adsorption mechanism of dimeric Ga precursors in metalorganic chemical vapor deposition of gallium nitride

Gallium nitride (GaN) has attracted significant interest as a next-generation semiconductor material with various potential applications. During metalorganic chemical vapor deposition (MOCVD) of GaN using trimethyl gallium (TMG) and NH3, dimeric precursors are produced by gas-phase reactions such as adduct formation or thermal decomposition. In this work, the surface adsorption reactions of monomeric and dimeric Ga molecules including TMG, [(CH3)2Ga(NH2)]2, and [(CH3)GaNH]2 on the GaN surface are investigated using density functional theory calculations. It is found that [(CH3)2Ga(NH2)]2 is the most predominant form among the various dimeric precursors under typical GaN MOCVD process conditions. Our results indicate that the dimeric [(CH3)GaNH]2 precursor, which is generated through the thermal decomposition of [(CH3)2Ga(NH2)]2, would have higher reactivity on the GaN surface. Our work provides critical insights that can inform the optimization of GaN MOCVD processes, leading to advancements in GaN-based high-performance semiconductors.

Fast scanning growth of high-quality graphene films on Cu foils fueled by dimeric carbon precursor

Fast scanning growth of high-quality graphene films on Cu foils fueled by dimeric carbon precursor

Synthesis and coordination of a pair of isomeric ferrocene phosphinoamines

Ferrocene P,N-ligands have been extensively studied due to their favorable catalytic properties. This contribution focuses on a pair of new, isomeric ferrocene phosphinoamines, FcNHCH2CH2PPh2 (1) and FcN(Me)CH2PPh2 (2), which were prepared from aminoferrocene, converted to the respective phosphine selenides (1-Se and 2-Se) and further studied as ligands in Pd(II) complexes containing the 2-(dimethylamino-κN)phenyl-κC1 auxiliary (LNC) ligand. Thus, cleavage of the dimeric precursor [(LNC)Pd(μ-Cl)]2 with the phosphinoamines afforded the corresponding phosphine complexes [(LNC)PdCl(1-κP)] (5) and [(LNC)PdCl(2-κP)] (6) with trans-P,N configuration. The subsequent removal of the chloride ligand with AgClO4 from 5 produced the cationic bis-chelate complex [(LNC)PdCl(1-κ2P,N)]ClO4 (7), whereas an analogous reaction with 6 gave no defined product. The phosphinoamines and their complexes were characterized by elemental analysis and common spectroscopic methods, and the crystal structures of 1, 2, and 7 were determined by single-crystal X-ray diffraction analysis. A cyclic voltammetry study, supported by DFT calculations, revealed that the primary electrochemical oxidation of these compounds occurs at the ferrocene unit.

Development of Geometry-Controlled All-Orthogonal BODIPY Trimers for Photodynamic Therapy and Phototheragnosis.

We have established an easy synthetic protocol for selectively developing all-orthogonal BODIPY trimers with unprecedented geometries on the basis of selecting methyl oxidation versus electrophilic formylation of key dimeric precursors. Photophysical characterization together with biological assays unraveled the most suitable BODIPY–BODIPY geometrical arrangements within the trimer, forcing them to serve as molecular platforms for the development of new, advanced heavy-atom-free photosensitizers for photodynamic therapy and phototheragnosis.

Systematic Study on the Cytotoxic Potency of Commonly Used Dimeric Metal Precursors in Human Cancer Cell Lines.

The cytotoxicities of seven dimeric metal species of the general formula [M(arene)Cl2]2, commonly used as precursors for complex synthesis and deemed biologically inactive, are investigated in seven commonly employed human cancer cell lines. Four of these complexes featured a ruthenium(II) core, where p‐cymene, toluene, benzene and indane were used as arenes. Furthermore, the osmium(II) p‐cymene dimer, as well as the Cp* dimers of rhodium(III) and its heavier analogue iridium(III) were included in this work (Cp*=1,2,3,4,5‐pentamethylcyclopentadienide). While the cytotoxic potencies of the ruthenium(II) and osmium(II) dimers are very low (or not even detectable at applicable concentrations), surprising activity, especially in cells from ovarian malignancies (with one or two‐digit micromolar IC50 values), have been found for the rhodium(III) and iridium(III) representatives. This publication is aimed at all researchers using synthetic procedures based on functionalization of these dimeric starting materials to rationalize changes in biological properties, especially cytotoxicity in cancer cells.

Acetyl-CoA-Mediated Post-Biosynthetic Modification of Desferrioxamine B Generates N- and N-O-Acetylated Isomers Controlled by a pH Switch.

Biosynthesis of the hydroxamic acid siderophore desferrioxamine D1 (DFOD1, 6), which is the N-acetylated analogue of desferrioxamine B (DFOB, 5), has been delineated. Enzyme-independent Ac-CoA-mediated N-acetylation of 5 produced 6, in addition to three constitutional isomers containing an N-O-acetyl group installed at either one of the three hydroxamic acid groups of 5. The formation of N-Ac-DFOB (DFOD1, 6) and the composite of N-O-acetylated isomers N-O-Ac-DFOB[001] (6a), N-O-Ac-DFOB[010] (6b), and N-O-Ac-DFOB[100] (6c) (defined as the N-O-Ac motif positioned within the terminal amine, internal, or N-acetylated region of 5, respectively), was pH-dependent, with 6a-6c dominant at pH < 8.5 and 6 dominant at pH > 8.5. The trend in the pH dependence was consistent with the pKa values of the NH3+ (pKa ∼ 10) and N-OH (pKa ∼ 8.5-9) groups in 5. The N- and N-O-acetyl motifs can be conceived as a post-biosynthetic modification (PBM) of a nonproteinaceous secondary metabolite, akin to a post-translational modification (PTM) of a protein. The pH-labile N-O-acetyl group could act as a reversible switch to modulate the properties and functions of secondary metabolites, including hydroxamic acid siderophores. An alternative (most likely minor) biosynthetic pathway for 6 showed that the nonribosomal peptide synthetase-independent siderophore synthetase DesD was competent in condensing N'-acetyl-N-succinyl-N-hydroxy-1,5-diaminopentane (N'-Ac-SHDP, 7) with the dimeric hydroxamic acid precursor (AHDP-SHDP, 4) native to 5 biosynthesis to generate 6. The strategy of diversifying protein structure and function using PTMs could be paralleled in secondary metabolites with the use of PBMs.

Unique role of dimeric carbon precursors in graphene growth by chemical vapor deposition

Chemical vapor deposition has emerged as a promising approach for high-quality graphene synthesis. Graphene quality, including the defect density, the size of monocrystal domains, and the number of layers, depend on the growth conditions. The main experimental parameters include temperature, metal catalyst composition, growth atmosphere, and gaseous dynamics in the reaction chamber. Here we show, that even for the same growth conditions, simply changing carbon source from methane to ethane or acetylene yields drastically different growth mode that allows the production of single-crystal-like graphene on a polycrystalline metal foil substrate. This new single crystal growth mechanism does not require local supply of carbon precursors or special single crystal catalytic substrate that were introduced earlier. We assign the observed differences in the growth mechanism to formation of stable and mobile dimeric C2Hx intermediate species from ethane and acetylene, in contrast to less mobile CHx and C3Hx species formed from methane and propane.

Interlayer Coordination of Pd-Pd Units in Exfoliated Black Phosphorus.

The chemical functionalization of 2D exfoliated black phosphorus (2D BP) continues to attract great interest, although a satisfactory structural characterization of the functionalized material has seldom been achieved. Herein, we provide the first complete structural characterization of 2D BP functionalized with rare discrete Pd2 units, obtained through a mild decomposition of the organometallic dimeric precursor [Pd(η3-C3H5)Cl]2. A multitechnique approach, including HAADF-STEM, solid-state NMR, XPS, and XAS, was used to study in detail the morphology of the palladated nanosheets (Pd2/BP) and to unravel the coordination of Pd2 units to phosphorus atoms of 2D BP. In particular, XAS, backed up by DFT modeling, revealed the existence of unprecedented interlayer Pd–Pd units, sandwiched between stacked BP layers. The preliminary application of Pd2/BP as a catalyst for the hydrogen evolution reaction (HER) in acidic medium highlighted an activity increase due to the presence of Pd2 units.

Tandem α/β-alkylation and transfer hydrogenation by heterodimetallic ruthenium-iridium complex

Herein, we present a new and air-stable polypyridyl based heterodimetallic complex [cp*IrIII(µ-L)RuII(p-cym)](PF6)2 (5) exhibiting facile tandem α/β–alkylation/transfer hydrogenation of ketones/alcohol under mild reaction conditions. The heterodimetallic 5 is found to show better reactivity and selectivity as compared to their homodimetallic analogues (3 and 4), monometallic (1 and 2) and dimeric precursors [cp*IrCl(µ-Cl)]2 and [(p-cym)RuCl(µ-Cl)]2. In addition, the present catalytic system 5 demonstrates a good flexibility and selective formation of α-alkylated ketones (C) or β-alkylated alcohol (D) by simple variation of reagents and reaction condition which may be envisioned to play a pivotal role in organic and organometallic chemistry as it lead to the development of pharmaceutically relevant intermediates for the synthesis of different types of heterocycles.

Self-assembly of supramolecular coordination complexes based on half-sandwich metal corner with tunable host cavities

A dinuclear Ru(II) complex with the Ru-Ru distance of 12.840(6) Å was generated by dimeric metal precursor [(p-cymene)RuCl2]2 with the ligand of 1,4-bis(dipyrromethan-5-yl)benzene. Two types of supramolecular coordination Ru(II) complexes, tetra-nuclear metallacycle (ring 2) and hexa-nuclear metallacage (cage 3), have been synthesized stepwisely by the reactions of the dinuclear Ru(II) complex with bidentate bridge ligand of 4,4′-dipyridy and tridentate bridge ligand of 2,4,6-tris(pyridine-4-yl)-1,3,5-traizine (TPT) under template-free condition. The supramolecular coordination complexes (SCCs) with large cavity can encapsulate one or two guests afforded two host-guest systems (anthracene⊂ring 2, pyrene⊂cage 3) smoothly. The two supramolecular coordination Ru(II) complexes and host-guest systems have been characterized by 1H NMR, 1H–1H COESY NMR, ESI-MS, and UV-vis. The dinuclear Ru(II) complex were further confirmed by single-crystal X-ray analysis.

Cyclometallated imidazo-phenanthroline iridium complexes and their anticancer activity

Abstract Cyclometallated mononuclear iridium complexes (1–3) were synthesized using dimeric precursor [\((\hbox {ppy})_{2}\hbox {Ir}^{\mathrm{III}}(\upmu \hbox {-Cl})]_{2}\) and imidazo-phenanthroline-based ligands (\(\mathbf{L}_{1}\)–\(\mathbf{L}_{3})\). The complexes were characterised using various analytical techniques. The complexes exhibited spin forbidden metal-to-ligand charge transfer (MLCT) transitions at wavelengths \({>}300 \hbox { nm}\) and high energy ligand-based transition below 300 nm. The complexes were found to be emissive and displayed emission bands at 580 nm upon excitation at 380 nm with quantum yields 0.07 with respect to standard [\(\hbox {Ru}(\hbox {bpy})_{3}]\hbox {Cl}_{2}\). The complexes 1–3 showed dose-dependent suppression of cell viability (\(\hbox {IC}_{50}\) values \({\sim }2.5 \,\upmu \hbox {M}\)) towards human breast (MCF7) cancer cell line. The hydrophobicity measurements and flow cytometry analysis suggest that cellular uptake is primarily responsible for observed cytotoxicity.GRAPHICAL ABSTRACT Synopsis Mononuclear anticancer-active cyclometallated iridium complexes (1–3) using imidazo-phenanthroline-based ligands (\(\mathbf{L}_{1}\)–\(\mathbf{L}_{3})\) were synthesized.

From chaperonins to Rubisco assembly and metabolic repair.

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) mediates the fixation of atmospheric CO2 in photosynthesis by catalyzing the carboxylation of the 5-carbon sugar ribulose-1,5-bisphosphate (RuBP). Despite its pivotal role, Rubisco is an inefficient enzyme and thus has been a key target for bioengineering. However, efforts to increase crop yields by Rubisco engineering remain unsuccessful, due in part to the complex machinery of molecular chaperones required for Rubisco biogenesis and metabolic repair. While the large subunit of Rubisco generally requires the chaperonin system for folding, the evolution of the hexadecameric Rubisco from its dimeric precursor resulted in the dependence on an array of additional factors required for assembly. Moreover, Rubisco function can be inhibited by a range of sugar-phosphate ligands. Metabolic repair of Rubisco depends on remodeling by the ATP-dependent Rubisco activase and hydrolysis of inhibitors by specific phosphatases. This review highlights our work toward understanding the structure and mechanism of these auxiliary machineries.

Necklace-shaped dimethylsiloxane polymers bearing polyhedral oligomeric silsesquioxane cages with alternating length chains

Necklace-shaped dimethylsiloxane (DMS) polymers bearing polyhedral oligomeric silsesquioxane (POSS) cages with “alternating modulated chain” arrangements were synthesized, by the polycondensation of a dimeric POSS precursor and dimethyl oligo-siloxane dichloride. Films of POSS-DMS polymers with “alternating modulated chain” arrangements were highly transparent. This observation is consistent with amorphous structures. Along with “constant chain” and “random chain” type polymers, three different chain arrangements of necklace-shaped polymers can now be produced. The physical properties of the three polymer types with constant POSS cage contents were compared. “Alternating modulated chain” type polymers had lower glass transition temperatures than the other two polymer types. This was attributed to the cooperative relaxation of long chain moieties that comprised half of the connecting chains. “Alternating modulated chain” type POSS-DMS polymers with average chain lengths of three to four exhibited heat resistances of over 470 °C in air.

Ru-Catalyzed Estragole Isomerization under Homogeneous and Ionic Liquid Biphasic Conditions.

The isomerization of estragole to trans-anethole is an important reaction and is industrially performed using an excess of NaOH or KOH in ethanol at high temperatures with very low selectivity. Simple Ru-based transition-metal complexes, under homogeneous, ionic liquid (IL)-supported (biphasic) and “solventless” conditions, can be used for this reaction. The selectivity of this reaction is more sensitive to the solvent/support used than the ligands associated with the metal catalyst. Thus, under the optimized reaction conditions, 100% conversion can be achieved in the estragole isomerization, using as little as 4 × 10–3 mol % (40 ppm) of [RuHCl(CO)(PPh3)3] in toluene, reflecting a total turnover number (TON) of 25 000 and turnover frequencies (TOFs) of up to 500 min–1 at 80 °C. Using a dimeric Ru precursor, [RuCl(μ-Cl)(η3:η3-C10H16)]2, in ethanol associated with P(OEt)3, a TON of 10 000 and a TOF of 125 min–1 are obtained with 100% conversion and 99% selectivity. These two Ru catalytic systems can be transposed to biphasic IL systems by using ionic-tagged P-ligands such as 1-(3-(diphenylphosphanyl)propyl)-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide immobilized in 1-(3-hydroxypropyl)-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl) imide with up to 99% selectivity and almost complete estragole conversion. However, the reaction is much slower than that performed under solventless or homogeneous conditions. The use of ionic-tagged ligands significantly reduces the Ru leaching to the organic phase, compared to that in reactions performed under homogeneous conditions, where the catalytic system loses catalytic performance after the second recycling. Detailed kinetic investigations of the reaction catalyzed by [RuHCl(CO)(PPh3)3] indicate that a simplified kinetic model (a monomolecular reversible first-order reaction) is adequate for fitting the homogeneous reaction at 80 °C and under biphasic conditions. However, the kinetics of the reaction are better described if all of the elementary steps are taken into consideration, especially at 40 °C.

Manganese Tricarbonyl Complexes with Asymmetric 2-Iminopyridine Ligands: Toward Decoupling Steric and Electronic Factors in Electrocatalytic CO2 Reduction.

Manganese tricarbonyl bromide complexes incorporating IP (2-(phenylimino)pyridine) derivatives, [MnBr(CO)3(IP)], are demonstrated as a new group of catalysts for CO2 reduction, which represent the first example of utilization of (phenylimino)pyridine ligands on manganese centers for this purpose. The key feature is the asymmetric structure of the redox-noninnocent ligand that permits independent tuning of its steric and electronic properties. The α-diimine ligands and five new Mn(I) compounds have been synthesized, isolated in high yields, and fully characterized, including X-ray crystallography. Their electrochemical and electrocatalytic behavior was investigated using cyclic voltammetry and UV-vis-IR spectroelectrochemistry within an OTTLE cell. Mechanistic investigations under an inert atmosphere have revealed differences in the nature of the reduction products as a function of steric bulk of the ligand. The direct ECE (electrochemical-chemical-electrochemical) formation of a five-coordinate anion [Mn(CO)3(IP)]-, a product of two-electron reduction of the parent complex, is observed in the case of the bulky DIPIMP (2-[((2,6-diisopropylphenyl)imino)methyl]pyridine), TBIMP (2-[((2-tert-butylphenyl)imino)methyl]pyridine), and TBIEP (2-[((2-tert-butylphenyl)imino)ethyl]pyridine) derivatives. This process is replaced for the least sterically demanding IP ligand in [MnBr(CO)3(IMP)] (2-[(phenylimino)methyl]pyridine) by the stepwise formation of such a monoanion via an ECEC(E) mechanism involving also the intermediate Mn-Mn dimer [Mn(CO)3(IMP)]2. The complex [MnBr(CO)3(IPIMP)] (2-[((2-diisopropylphenyl)imino)methyl]pyridine), which carries a moderately electron donating, moderately bulky IP ligand, shows an intermediate behavior where both the five-coordinate anion and its dimeric precursor are jointly detected on the time scale of the spectroelectrochemical experiments. Under an atmosphere of CO2 the studied complexes, except for the DIPIMP derivative, rapidly coordinate CO2, forming stable bicarbonate intermediates, with no dimer being observed. Such behavior indicates that the CO2 binding is outcompeting another pathway: viz., the dimerization reaction between the five-coordinate anion and the neutral parent complex. The bicarbonate intermediate species undergo reduction at more negative potentials (ca. -2.2 V vs Fc/Fc+), recovering [Mn(CO)3(IP)]- and triggering the catalytic production of CO.

Formation of a Dimeric Precursor Intermediate during the Nonaqueous Synthesis of Titanium Dioxide Nanocrystals

AbstractFor tailoring the size and morphology of nanoparticles, a deep knowledge of the mechanism leading to particle formation is required. We have investigated the reaction mechanisms in the synthesis of anatase nanocrystals by the so‐called benzyl alcohol route as a model for binary metal oxides, and elucidated the chemical structure of cluster species involved in the reaction using NMR spectroscopy and single crystal X‐ray structure analysis. In the first reaction step, a novel dimeric coordination complex is formed via ligand exchange, and was identified as the crucial compound initiating particle formation in the synthesis process.

Mixing Up the Pieces of the Desferrioxamine B Jigsaw Defines the Biosynthetic Sequence Catalyzed by DesD.

Late-stage assembly of the trimeric linear siderophore desferrioxamine B (DFOB) native to Streptomyces pilosus involves two DesD-catalyzed condensation reactions between one N-acetyl-N-hydroxy-1,5-diaminopentane (AHDP) unit and two N-succinyl-N-hydroxy-1,5-diaminopentane (SHDP) units. AHDP and SHDP are products of DesBC-catalyzed reactions of the native diamine substrate 1,5-diaminopentane (DP). The sequence of DesD-catalyzed DFOB biosynthesis was delineated by analyzing the distribution of DFOB analogues and dimeric precursors assembled by S. pilosus in medium containing 1,4-diamino-2(E)-butene (E-DBE). Seven unsaturated DFOB analogues were produced that were partially resolved by liquid chromatography (LC). Mass spectrometry (MS) measurements reported on the combination of E-DBE- and DP-derived substrates in each trimer (uDFOA1 series, 1:2; uDFOA2 series, 2:1; uDFOA3, 3:0). MS/MS fragmentation patterns reported on the absolute position of the substrate derivative at the N-acetylated terminus, the internal region, or the amine terminus of the trimer. The uDFOA1 and uDFOA2 series each comprised three constitutional isomers (binary notation (DP-derived substrate "0," E-DBE-derived substrate "1"); direction, N-acetylated-internal-amine): uDFOA1[001], uDFOA1[010], uDFOA1[100]; and uDFOA2[011], uDFOA2[110], and uDFOA2[101]. E-DBE completely replaced DP in uDFOA3[111]. Relative concentrations of the uDFOA1 series were uDFOA1[001] ≫ uDFOA1[100] > uDFOA1[010] and of the uDFOA2 series, uDFOA2[101] > uDFOA2[011] ≫ uDFOA2[110]. Dimeric compounds assembled from one N-acetylated and one N-succinylated substrate derivative were detected as trimer precursors: dDFX[00-] ≫ udDFX[10-] > udDFX[01-] (d = dimer, vacant position "-"). Relative concentrations of all species were consistent with the biosynthetic sequence: (i) SHDP activation, (ii) condensation with AHDP to form AHDP-SHDP, (iii) SHDP activation, and (iv) condensation with AHDP-SHDP to form DFOB.

A heteropentanuclear metal string complex [Mo2NiMo2(tpda)4(NCS)2] with two linearly aligned quadruply bonded Mo2 units connected by a Ni ion and a meso configuration of the complex

A dimeric molybdenum precursor and nickel ions are used to synthesize a symmetric heteropentanuclear complex, [Mo2NiMo2(tpda)4(NCS)2]. This complex possesses unique structural features, as the four ligands are coordinated to the metal framework in a meso configuration. Furthermore, the central Ni2+ ion is in a high spin state.