Metal Complexes Research Articles

Tetra-azolium Salts Induce Significant Cytotoxicity in Human Colon Cancer Cells In vitro.

Azolium salts are the organic salts used as stable precursors for generating N-Heterocyclic Carbenes and their metal complexes. Azolium salts have also been reported to have significant biological potential. Hence, in the current study, four tetra-dentate azolium salts were derived from bis-azolium salts by a new synthetic strategy. The tetra azolium salts have been synthesized by reacting the imidazole or methyl imidazole with dibromo xylene (meta, para)/ 1-bromo methyl imidazole or dibromo ethane resulting in the mono or bis azolium salts namely I-IV. V-VII have been obtained by reacting I with II-IV, resulting in the tetra azolium salts. Each product was analyzed by various analytical techniques, i.e., microanalysis, FT-IR, and NMR (1H & 13C). Salts V-VII were evaluated for their antiproliferative effect against human colon cancer cells (HCT-116) using MTT assay. Four chemical shifts for acidic protons between 8.5-9.5 δ ppm in 1H NMR and resonance of respective carbons around 136-146 δ ppm in 13C NMR indicated the successful synthesis of tetra azolium salts. Salt V showed the highest IC50 value, 24.8 μM among all synthesized compounds. Tetra-azolium salts may play a better cytotoxicity effect compared to mono-, bi-& tri-azolium salts.

Microwave-assisted Synthesis of Pyrroles, Pyridines, Chromenes, Coumarins, and Betti Bases via Alcohol Dehydrogenation with Chroman-4-one Amino Ligands

: This study outlines the development of a novel approach utilizing microwave assistance for the alcohol dehydrogenative reaction. The process is catalyzed by manganese (II) and cobalt (II) in conjunction with chroman-4-one amino ligands. This research introduces a unique catalytic system capable of synthesizing various heterocyclic compounds, including pyrroles, pyridines, Betti bases, chromenes, and coumarins via alcohol dehydrogenation. The synthesis involved the preparation and characterization of a series of chroman- 4-one amino ligands (C1-C6) using standard analytical techniques. These ligands, in combination with MnCl2‧4H2O and CoCl2, demonstrated remarkable catalytic activity, effectively driving alcohol dehydrogenation. The catalytic cycle was initiated by the in-situ formation of metal complexes with the ligands during the reaction. Characterization using ESI-MS confirmed the presence of metal complexes (Int-1) and other intermediates (Int-II and Int-III) throughout the catalytic cycle. Additionally, the controlled experiment corroborated the efficacy of the catalytic system, evidenced by the evolution of H2 gas.

Dealuminated H–Y zeolites generate, stabilize and catalytically insert carbenes from diazocarbonyl compounds

Carbenes are among the most powerful reactants in organic synthesis, with capacity to insert into a variety of otherwise stable bonds, and generate two new bonds in a straightforward manner. However, the intrinsic instability of such carbenes makes them to be catalytically generated, in–situ, from precursors such as diazocarbonyl compounds, and the catalyst, in turn, also controls the subsequent insertion reaction. The catalyst is generally a metal complex in solution, mainly Cu, Ag or Rh, but also others, including protons in rare cases. Here we show that carbenes are generated, stabilized and inserted into C–C, C–H, O–H, N–H, Si–H and O–O bonds after reacting diazocarbonyl compounds with catalytic amounts of metal–free, commercially available dealuminated H–Y zeolites. These results open the way to design carbene–mediated organic reactions on readily available and reusable catalytic solids without involving metals.

Catalytic effect of the in-situ rhodium(III) complexes in surfactant medium on the auto-oxidation of 1,2-hydroxyphenylthiourea: A theoretical and experimental study for rhodium(III) sensing

1,2-hydroxyphenylthiourea(HPTU) undergoes auto-oxidation to form an yellow colored dimer. The process of auto-oxidation is enhanced by the presence of trace quantities of transition metal ions and transition metal complexes that act as catalysts. In the current study, catalytic potential of rhodium(III) complexes on the auto-oxidation of 1,2-hydroxyphenylthiourea(HPTU) was studied theoretically using quantum mechanical calculations and experiments were carried out using photometry and fluorometry. DFT studies inferred that [Rh(Py)6]Cl3 showed a better catalytic activity in the dimerization of HPTU. Theoretical studies were subsequently validated through experiments using photometric methods and the range of detection was determined to be 6 ng/mL–100 ng/mL. The detection limit was observed to be 2 ng/mL. Analytical parameters such as pH, reagent concentration, metal ion concentration, appropriate activators and surfactants were established.

Perturbational and variational energy decomposition analysis on hydrogen bonds of coordinated glycine with water molecule.

Three types of hydrogen bonds of coordinated glycine and water had been investigated: NH/O of α-amino group, O1/HO involving oxygen coordinated to the metal ion (O1), and O2/HO involving α-carbonyl oxygen (O2). Various glycine complexes were investigated: octahedral cobalt(III) and nickel(II), square pyramidal copper(II), and square planar copper(II), palladium(II), and platinum(II) complexes. Nature of these three hydrogen bond types was analysed using symmetry-adapted perturbation theory (SAPT) and variational energy decomposition analysis (EDA) method (TPSS-D3/def2-TZVPP). The results of the EDA decomposition are in good agreement with the reliable SAPT2+3/def2-TZVPP and its total interaction values with CCSD(T)/CBS energies. Electrostatic interaction is generally the dominant attractive energy term in most of the interactions, followed by orbital relaxation, and lastly dispersion as the weakest. We compared EDA results of various complexes to determine the effects of complex charge, metal oxidation, coordination, and atomic number on the energy decomposition terms. The complex charge influences the values of decomposition terms the most, followed by metal oxidation and coordination number, while atomic number effects them the least. All complex and metal changes have a more significant effect on the results of NH/O and O1/HO then O2/HO interactions, due to its location further away from the metal ion.

Photodynamic Inactivation of Bacteria Using Nickel(II) Complexes with Catecholate and Phenanthroline Ligands.

Metal complexes activated by light can combat infections by triggering the photodynamic inactivation of bacteria. Herein, we report six mixed-ligand nickel(II) complexes with the formulation [Ni(NN)2(L)] (1-6), where NN represents an N,N-donor phenanthroline ligand, specifically 1,10-phenanthroline (phen in 1, 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 3, 4), and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 5, 6), while L is an O,O donor bidentate ligand derived from catechol (cat2-, in 1, 3, 5) or esculetin (esc2-, in 2, 4, 6). The paramagnetic d8 octahedral complexes demonstrated good dark and photostability in the solution phase and exhibited significant light absorption in the visible (400-700 nm) region. When exposed to low-energy visible light, these complexes demonstrated significant photodynamic inactivation activity against both gram-(+) S. aureus and gram-(-) E. coli bacteria. This resulted in minimum inhibitory concentration (MIC) values ranging from 0.2 to 5.0 μg/mL. The activity was caused by the cell-damaging singlet oxygen species produced by the complexes under light exposure. Notably, the complexes showed no bacterial inhibition activity under dark conditions. This study marks the first examples of Ni(II) complexes designed for light-triggered antibacterial activity, illuminating the path for Ni(II)-based non-macrocyclic complexes for antibacterial PDT applications.

Formally Zerovalent Bis(arene) Germylene Complexes of Zirconium and Hafnium

Tetrachlorides of zirconium‐ and hafnium form adducts (2, 3) with an intramolecular germylene phosphine Lewis pair. Two electron reduction treating the adducts with [MesNacnacMg]2 gives the low valent metal complexes (4, 5) featuring η6‐Trip coordination at the Zr(II) and Hf(II) metal atom. Reduction of the M(II)‐complexes gives the zerovalent metal complexes of zirconium (6) and hafnium (7), which have been structurally characterized. Two arene moieties and the germylene exhibit metal coordination. Puckered coordination of a P‐phenyl unit was observed for both derivatives 6 and 7. Four electron reduction of a reaction mixture of metal tetrachloride with the germylene‐phosphine Lewis pair also gives the zerovalent complexes in good yield. Carbonyl complexes were synthesized treating the reduced metal complexes with carbon monoxide. Dimethylbutadiene shows a reaction with an arene moiety and the coordinated germylene ligand of the zerovalent complexes. A cyclohexadienyl and a triorganogermate ligand are formed. For zirconium this reaction is reversible at room temperature.

Formally Zerovalent Bis(arene) Germylene Complexes of Zirconium and Hafnium.

Tetrachlorides of zirconium- and hafnium form adducts (2,3) with an intramolecular germylene phosphine Lewis pair. Two electron reduction treating the adducts with [MesNacnacMg]2 gives the low valent metal complexes (4, 5) featuring η6-Trip coordination at the Zr(II) and Hf(II) metal atom. Reduction of the M(II)-complexes gives the zerovalent metal complexes of zirconium (6) and hafnium (7), which have been structurally characterized. Two arene moieties and the germylene exhibit metal coordination. Puckered coordination of a P-phenyl unit was observed for both derivatives 6 and 7. Four electron reduction of a reaction mixture of metal tetrachloride with the germylene-phosphine Lewis pair also gives the zerovalent complexes in good yield. Carbonyl complexes were synthesized treating the reduced metal complexes with carbon monoxide. Dimethylbutadiene shows a reaction with an arene moiety and the coordinated germylene ligand of the zerovalent complexes. A cyclohexadienyl and a triorganogermate ligand are formed. For zirconium this reaction is reversible at room temperature.

Octadentate Bispidine Chelators for Tb(III) Complexation: Pyridine Carboxylate versus Pyridine Phosphonate Donors.

With their rigid and preorganized skeleton, bispidine (3,7-diazabicyclo[3.3.1]nonane) chelators are very appealing for the preparation of metal complexes with high kinetic inertness. With the aim to develop new Tb(III)-based medical imaging probes, this study describes the synthesis and physicochemical properties of two novel terbium(III) complexes with octadentate bispidine-based ligands substituted with either pyridine-phosphonate (H6L1) or picolinate (H4L2) subunits. Thermodynamic stability constants of the corresponding Tb(III) complexes have been determined by potentiometric, UV-visible absorption spectrophotometric and spectrofluorimetric methods. Despite their apparent similarity, these two octadentate ligands differ in their most stable conformation: chair-chair conformation for H4L2 and boat-chair conformation for H6L1, as confirmed by 1H NMR studies and suggested by physicochemical investigations. This conformational change induces different protonation schemes for the two ligands. The kinetic inertness of the Tb complexes has been studied in various media and assessed by transmetalation and transchelation experiments. In particular, Tb(L2) displayed a remarkable kinetic inertness with no measurable dissociation over two months in mouse serum at 10-5 M concentration. The complex was also very inert in the presence of a 50-fold excess of Zn(II) in H2O at pH = 7.4 (7% of dissociation over two months). The complexes with ligand L1 are significantly less inert, emphasizing the influence of the ligand conformation on the kinetic inertness of the Ln(III) complexes. Finally, the luminescence properties of the isolated complexes have also been investigated. A bright green luminescence was observed, especially for Tb(L2), which displays a high quantum yield value of 50% in H2O (60% in D2O; λexc = 263 nm). In addition, luminescence lifetimes of 1.9(2) and 1.7(2) ms have been measured for Tb(L1) and Tb(L2), respectively, hence confirming the formation of nona-coordinated complexes with one inner-sphere water molecule. These data on a bispidine scaffold pave the way for developing bright, inert luminescent probes for bioimaging and for radiolabeling applications with Tb(III) radioisotopes.

Coordination Induced Spin State Transition Switches the Reactivity of Nickel (II) Porphyrin in Hydrogen Evolution Reaction

Electron spin plays a critical role in chemical processes, particularly in reactions involving metal complexes with unpaired electrons. However, more definitive state‐to‐state experiments are needed to better elucidate the role of electronic spin. Herein, we chose nickel (II) 5,10,15,20‐tetrakis(pentafluorophenyl) porphyrin 1 as a catalyst, which allows switching from a low spin to a high spin state of Ni(II) center through an axial pyridine coordination, for electrocatalytic hydrogen evolution reaction (HER). When pyridine is present, we observed β‐hydrogenation of porphyrin through electron transfer followed by proton transfer. In contrast, hydrogen evolution mainly occurs via the concerted proton‐coupling electron transfer without pyridine coordination. Similar distinct spin‐dependent selectivity was also observed in chemical reduction of 1 by CoCp2 with subsequent addition of pyridinium p‐toluenesulfonate. Computational calculations using density functional theory demonstrated that the transition from low spin to high spin state enriches the ligand’s electron density after one‐electron reduction, leading to preferential protonation of β‐periphery rather than meso‐position or metal center.

Zwitterionic 2‐Phosphaethene‐thiolates [(LC)P=CS(LC/P)]+ as PCS Building Blocks (LC = NHC, LP = PR3)

The zwitterionic compounds [(LC)P=CS(LC/P)]+ (3+, LC = NHC, LP = PR3), featuring cationic substituents at the phosphorus and carbon atoms, are synthesized as their triflate salts at a multi‐gram scale from the reaction of Lewis base adducts of CS2, namely LC/P–CS2 (4), with a combination of [(LCP)4][OTf]4 (1[OTf]4) and Ph3P. The feasibility of using 3+ as PCS building blocks is showcased in their reactions with representative electrophiles (MeOTf) and nucleophiles (MesMgBr, Ph3PCH2), leading to selective functionalization of the PCS core at the S‐ and P‐terminus, respectively. Additionally, it is reported that 3+ can function as ambident nucleophiles with AgOTf (2 equivalents), affording unprecedented linear coordination polymer [Ag2(OTf)3‐μ2:κP,κS–((LC)P=CS(PCy3))]+ (6b), where the PCS moiety acts as a bridging ligand in transition metal complexes for the first time. Reduction of 3+ facilitates the cleavage of the P‐ and C‐bound substituents leading to the formation of the [PCS]– anion. Moreover, cycloaddition reactions of 3+ with 1[OTf]4 are shown to selectively yield five‐ and eight‐membered polyphosphorus heterocycles. Preliminary results suggest the possibility of activating the C–S bond in [(LC)P=CS(LC)]+, resulting in the formation of [(LC)P=C(LC)–P(LC)][OTf]2, 12[OTf]2, which may serve as a synthon for the PCP unit in future studies.

Coordination Induced Spin State Transition Switches the Reactivity of Nickel (II) Porphyrin in Hydrogen Evolution Reaction.

Electron spin plays a critical role in chemical processes, particularly in reactions involving metal complexes with unpaired electrons. However, more definitive state-to-state experiments are needed to better elucidate the role of electronic spin. Herein, we chose nickel (II) 5,10,15,20-tetrakis(pentafluorophenyl) porphyrin 1 as a catalyst, which allows switching from a low spin to a high spin state of Ni(II) center through an axial pyridine coordination, for electrocatalytic hydrogen evolution reaction (HER). When pyridine is present, we observed β-hydrogenation of porphyrin through electron transfer followed by proton transfer. In contrast, hydrogen evolution mainly occurs via the concerted proton-coupling electron transfer without pyridine coordination. Similar distinct spin-dependent selectivity was also observed in chemical reduction of 1 by CoCp2 with subsequent addition of pyridinium p-toluenesulfonate. Computational calculations using density functional theory demonstrated that the transition from low spin to high spin state enriches the ligand's electron density after one-electron reduction, leading to preferential protonation of β-periphery rather than meso-position or metal center.

Study on enhancing the quantitative performance of LIBS for Cu element in liquids based on the chitosan-parafilm enrichment method

Abstract To enhance the accuracy of laser-induced breakdown spectroscopy (LIBS) in detecting heavy metal elements in solutions, a chitosan (CS)-Parafilm (PM) enrichment method is proposed. This method involves drying chitosan-heavy metal complexes on a Parafilm substrate. During the drying of droplets, electrostatic attraction and chelation by CS effectively concentrate analytes. Additionally, the hydrophobic effect of the PM substrate induces Marangoni flow, which drags analytes from the bottom edge to the central top of the droplet surface, effectively suppressing the coffee ring effect (CRE). Using LIBS technology, spectra were uniformly collected in an array on the surface of sediments. Through the analysis of cumulative excitation spectra and measurement repeatability, the results showed that the RSD of the emission lines Cu I 324.754 nm and Cu I 327.396 nm was reduced to 3.85% and 3.78%, respectively. This indicates that the CS-PM enrichment method allows for uniform deposition of analytes within the samples, effectively suppressing the CRE. Quantitative analysis of Cu elements using the CS-PM enrichment method was conducted using PSO-SVM, PSO-BPNN, and random forest (RF) algorithms. The RF algorithm demonstrated the best predictive performance with Rp 2 of 0.977, root mean square error of prediction of 3.86 mg l−1, mean absolute error of 3.0 mg l−1, and RPD of 5.52. Thus, it can be seen that CS-PM effectively improves the repeatability of spectral measurements and the accuracy of quantitative analysis predictions, providing a technical reference for enhancing the stability and quantitative performance of element analysis in liquids using LIBS.

Recent Insights into Magneto-Structural Properties of Co(II) Dicyanamide Coordination Compounds

In recent decades, the chemistry of transition metal coordination compounds has undergone continuous development at both scientific and application levels. The diversity of metal(II) complexes, along with their structural features and physicochemical properties, makes them attractive for a wide range of applications. The dicyanamide ion (N(CN)2) has the ability to form various transition metal compounds characterized by different architectures and topologies. The interaction of π-electrons from the nitrile groups with the π-system of the central nitrogen may enable electron delocalization, potentially facilitating electron transfer between the metal centers through the bridging dicyanamide (dca) ligand. This review focuses on dca–Co(II) compounds and, after a brief introduction, the structural aspects and magnetic properties are analyzed in detail.

Synthesis, Structural, DFT, In Vitro Biological Exploration, and DNA Interaction of New Ni(II) and Cu(II) Mixed‐Ligand Complexes Featuring 2,2′‐Pyridine‐2,6‐diylbis(1H‐benzimidazole) and 2‐Hydroxy‐naphthaldehyde‐Based Schiff‐Base

ABSTRACTThis research article provides a comprehensive analysis of the preparation, structural characterization, 3D modeling, and biological screening of two novel formulated metal complexes, NiPDBZNPH and CuPDBZNPH. These complexes were obtained by combining 2,2′‐pyridine‐2,6‐diylbis(1H‐benzimidazole) (PDBZ) and 2‐hydroxy‐naphthaldehyde Schiff‐base (NPH) ligands with Ni(II) and Cu(II) ions, resulting in the compounds [Ni (NPH)(PDBZ)(Cl)] and [Cu (NPH)(PDBZ)(Cl)], respectively. Spectroscopic and analytical techniques confirmed that both complexes exhibit octahedral geometry around the central metal ion. Computational studies using density functional theory (DFT) corroborated the molecular structures and investigated the quantum chemical properties of the ligands and complexes. A series of in vitro assays were conducted to assess their anti‐inflammatory, antifungal, antibacterial, and antioxidant properties, revealing enhanced bioactivity compared to the uncoordinated ligands. The potential of NiPDBZNPH and CuPDBZNPH as therapeutic candidates was also explored through interactions with calf thymus DNA (CT‐DNA). Molecular docking simulations targeting specific protein receptors were performed to evaluate binding affinities and ligand–protein interactions, with results highlighting significant interactions within enzyme active sites. These findings emphasize the pivotal role of metal–ligand coordination in enhancing pharmacological properties and contribute valuable insights toward the design of novel therapeutic compounds for use in medicinal chemistry and pharmaceutical research.

Dynamic amine sorting enables multiselective construction of unsymmetrical chiral diamines.

Precisely differentiating chemicals featuring minor discrepancies is the prerequisite for achieving high selectivities in both chemical synthesis and biological activities. However, efficient strategies to differentiate and sort such congeneric compounds are lacking, posing daunting challenges for synthetic endeavours aimed at their orderly incorporation. Here we report a dynamic amine-sorting strategy that incorporates the chemoselective formation of the aminomethyl cyclopalladated complex to achieve the efficient differentiation of amine congeners. A series of amines sharing similar three-dimensional structures and properties, as well as possessing notoriously strong binding ability to metals, can be efficiently differentiated, enabling the highly chemo-, regio- and enantioselective multicomponent aminomethylamination of dienes to construct a variety of unsymmetrical chiral diamines. This dynamic amine-sorting strategy tackles the long-standing challenge of precise differentiation and orderly incorporation of aliphatic amines with subtle differences. From a broader perspective, the success demonstrates that meticulously designed metal complexes can provide flexible and general solutions for controlling delicate selectivities in sophisticated synthesis.

Metal‐Phthalocyanine‐Based Two‐Dimensional Conjugated Metal‐Organic Frameworks for Electrochemical Glycerol Oxidation Reaction

Electrochemical glycerol oxidation reaction (GOR) is a promising candidate to couple with cathodic reaction, like hydrogen evolution reaction, to produce high‐value product with less energy consumption. Two‐dimensional conjugated metal‐organic frameworks (2D c‐MOFs), comprising square‐planar metal‐coordination motifs (e.g., MO4, M(NH)4, MS4), are notable for their programable active sites, intrinsic charge transport, and excellent stability, making them promising catalyst candidates for GOR. Here, we introduce a novel class of 2D c‐MOFs electrocatalysts, M2[NiPcS8] (M=Co/Ni/Cu), which are synthesized via coordination of octathiolphthalocyaninato nickel (NiPc(SH)8) with various metal centers. Due to a fast kinetic and high activity of CoS4 sites for GOR, the electrocatalytic tests demonstrate that Co2[NiPcS8] supported on carbon paper displays a low GOR potential of 1.35 V vs. RHE at 10 mA cm‐2, significantly reducing the overall water‐electrolysis‐voltage reduction by 0.27 V from oxygen evolution reaction to GOR, thereby outperforming Ni2[NiPcS8] and Cu2[NiPcS8]. Additionally, we have determined that the GOR activity of CoX4 linkage sites varies with different heteroatoms, following an experimentally and theoretically confirmed activity order of CoS4>CoO4>Co(NH)4. The GOR performance of Co2[NiPcS8] not only demonstrate superior performance among non‐noble metal complex, but also provides critical insights on designing high‐performance MOF electrocatalysts upon optimizing the electronic environment of active sites.

Towards expansion of the MATTS data bank with heavier elements: the influence of the wavefunction basis set on the multipole model derived from the wavefunction

The MATTS (multipolar atom types from theory and statistical clustering) data bank is an advanced tool for crystal structure refinement and properties analysis. It applies a multipole model (MM), which describes the asphericity of the atomic electron density and helps to interpret X-ray or electron diffraction data better than approaches based on the spherical atoms approximation. The generation of MATTS data involves density functional theory calculations, and until recently we used the B3LYP/6-31G** level of theory for this stage. However, it was not so clear how the wavefunction level of theory, especially the basis set used, influenced the resulting MM. This study investigates the influence of the wavefunction basis set on the resulting MM from a charge density point of view. For this purpose, we used charge density related properties, such as correlation of electrostatic potentials, atomic electron populations and average electrostatic potential values. The complex analysis reveals that, within the framework of MATTS data generation, the size of the basis set used has the most significant impact on the MM's charge density quality, and switching from double- to triple-zeta basis sets helps notably improve the charge density related properties. This research sets the foundation for the creation of a new version of the MATTS data bank, which will be expanded to include atom types for elements heavier than Kr and selected metal complexes important for biological systems.

Solvent-Directed Social Chiral Self-Sorting in Pd2L4 Coordination Cages.

A family of Pd2L4 cages prepared from ligands based on an axially chiral diamino-[1,1'-biazulene] motif (serving as a unique azulene-based surrogate of the ubiquitous BINOL moiety) is reported. We show that preparing a cage starting from the racemate of a shorter bis-monodentate ligand derivative, equipped with pyridine donor groups, leads to integrative ("social") chiral self-sorting, exclusively yielding the meso-trans product, but only in a selection of solvents. This phenomenon is driven by individual solvent molecules acting as hydrogen bonding tethers between the amino groups of neighboring ligands, thereby locking the final coordination cage in a single isomeric form. The experimental (solvent-dependent NMR, single-crystal X-ray diffraction) observations of this cooperative interaction could be explained by computational analyses only when explicit solvation was considered. Furthermore, we prepared a larger chiral ligand with isoquinoline donors, which, unlike the first one, does not undergo social self-sorting from its racemic mixture, further highlighting the importance of solvents bridging short distances between the amino groups. Homochiral cages formed from this larger ligand, however, furnish a cavity that can bind anionic and neutral metal complexes such as [Pt(CN)6]2- and Cr(CO)6 and discriminate between the two enantiomers of chiral guest camphor sulfonate.

Highly Efficient Hydrogenation of Guaiacol over Ru/Al2O3-TiO2 Catalyst at Low Temperatures

In this work, the highly efficient hydrogenation of guaiacol catalyzed by ruthenium supported on Al2O3-TiO2 (Ru/Al2Ti1) at very mild conditions was carried out. At temperatures as low as 25 °C and 2 MPa H2, about 60% of guaiacol could be converted to 2-methoxycyclohexanol (MCH) with a selectivity as high as 94% on the Ru/Al2Ti1 catalyst with an appropriate hydrogen pressure. At temperatures above 50 °C, almost all of the guaiacol could be converted with the catalyst of Ru/Al2Ti1, mainly into hydrogenated products such as MCH. The surprisingly efficient hydrogenation of guaiacol at low temperatures was most likely due to the ability of Ru particles loaded on the specific complex metal oxide carriers, particularly the reduction of the edge effect of Ru, to activate phenyl and hydrogen and reduce the competition of the dimethoxy process. These findings about the high activity of the Ru/Al2Ti1 catalyst at nearly room temperature may be helpful to upgrading the industrial process of the pyrolysis bio-oils.