Dimeric Mn Research Articles

Rationally Designed Manganese-Based Metal-Organic Frameworks as Altruistic Metal Oxide Precursors for Noble Metal-Free Oxygen Reduction Reaction.

The sluggish oxygen reduction reaction (ORR) at the cathode is challenging and hinders the growth of hydrogen fuel cells. Concerning kinetic values, platinum is the best known catalyst for ORR; however, its less abundance, high cost, and corrosive nature warrant the development of low-cost catalysts. We report the hydrothermal synthesis of two novel Mn-based metal-organic frameworks (MOFs), [Mn2(DOT)(H2O)2]n (Mn-SKU-1) and [Mn2(DOT)2(BPY)2(THF)]n (Mn-SKU-2) (DOT = 2,5-dihydroxyterephthalate; BPY = 4,4'-bipyridine). Mn-SKU-1 contains dimeric Mn(II) centers where the two corner-shared MnO6 octahedra fuse to give rise to an infinite Mn2O10 cluster, whereas the two Mn(II) ions coordinate to DOT and BPY moieties to give rise to a pillared structure in Mn-SKU-2 and form a 3D → 3D homo-interpenetration MOF with a twofold interpenetrated net. The pyrolysis of as-synthesized Mn-MOFs at 600 °C under N2 produced exclusively porous α-Mn2O3 composites (PSKU-1 and PSKU-2), with the BET surface area of 90.8 (for PSKU-1) and 179.3 m2 g-1 (for PSKU-2). These mesoporous MOF-derived α-Mn2O3 composites were modified as cathode materials for the electrocatalytic reduction of oxygen. The onset potential for the oxygen reduction reaction was found to be 0.90 V for PSKU-1 and 0.93 V for PSKU-2 versus RHE in 0.1 M KOH solution, with the current density of 4.8 and 6.0 mA cm-2, respectively, at 1600 rpm. Based on the RDE/RRDE results, the electrocatalytic oxygen reduction occurs majorly via the four-electron process. The electrocatalyst PSKU-2 is cheap, easy to use, retains 90% of its activity after 10 h of continuous use, and offers higher recyclability than Pt/C. The onset potential maximum current density and kinetic values (Jk = 11.68 mA cm-2 and Tafel slope = 85.0 mV dec-1) obtained in this work are higher than the values reported for pure Mn2O3.

Manganese‐Catalyzed Hydrocarbofunctionalization of Internal Alkenes†

Summary of main observation and conclusionA highly regio‐ and chemo‐selective dimeric Mn(I)‐catalyzed hydroarylation and hydroalkenylation of unbiased internal alkenes with commercially abundant organoboron compounds is reported. A wide range of densely functionalized aliphatic alkenyl amides can successfully undergo site‐exclusive hydrocarbofunctionalization in air atmosphere without any exogenous directing auxiliary, affording an enhanced lead library of structurally diverse γ‐functionalized carboxylic acid derivatives in moderate to good yields. The precise chemoselectivity of the reaction among multiple alkene units even in the presence of reactive terminal alkenes highlights the unique catalytic features of manganese catalyst, and the excellent functional group compatibility of primary amides further complements other transition metals.

Two Isomorphic Coordination Polymers Based on Triazolyl Derivative and Dicarboxylate Ligand: Synthesis, Structures, and Properties

Two new isomorphic inorganic-organic hybrid 2D extended networks of Mn(II)/Co(II) with the general molecular formula [M(H2L)(ip)]n·4nH2O, where Mn(II) (1), Co(II) (2), H2L = 3-(1H-pyrazol-4-yl)-5-(pyridin-4-yl)-1,2,4-triazole, H2ip = 1,3-benzenedicarboxylic acid, have been synthesized and characterized by single-crystal X-ray diffraction and magnetic measurements. They crystallize in the triclinic system, space group P-1, display the same box-like bilayer motif of (4, 4) net, and are finally extended into the three-dimensional supramolecular structure via hydrogen bonding interactions. The compound 1 is characterized by antiferromagnetic fitting data based on a dimeric Mn(II) model with negligible magnetic transmission through the carbon skeleton of ip2– and H2L pathway. Thermal analysis of compound 1 has also been studied.

Unusual Reactivity of a Thiazole-Based Mn Tricarbonyl Complex for CO2 Activation

Manganese tricarbonyl complexes have attracted considerable attention as competent electrocatalysts for CO2 reduction owing to their unique chemistry and the natural abundance of Mn. While the analogous Re complexes are well-known to activate CO2 under anhydrous conditions, most reported Mn tricarbonyl catalysts require exogenous protons. In an effort to understand the reason for the different CO2 reduction mechanisms, we investigate the reactivity of Mn(pbt)(CO)3Br, (1, where pbt = 2-(2-pyridyl)-benzothiazole) with CO2. Our combined electrochemical and spectroscopic data suggest that 1 can undergo a CO2 conversion to CO similar to Re complexes with and without the presence of a proton source but only at potentials significantly more negative than the second reduction. Furthermore, the one- and two-electron reduced species are chemically generated and characterized by NMR, UV–vis, and IR spectroscopy. By exploring sequential chemical reduction of 1, we uncover unusual reactivity of the reduced dimeric Mn–Mn species as well as the isolation of a species capable of C–H activation.

Slow magnetic relaxation in a dimeric Mn2Ca2 complex enabled by the large Mn(iii) rhombicity

In this paper we present the characterization of a complex with the formula [Mn2Ca2(hmp)6(H2O)4(CH3CN)2](ClO4)4 (1), where hmp-H = 2-(hydroxymethyl)pyridine. Compound 1 crystallizes in the monoclinic space group C2/c with the cation lying on an inversion centre. Static magnetic susceptibility, magnetization and heat capacity measurements reflect a unique Mn(iii) valence state, and single-ion ligand field parameters with remarkable large rhombic distortion (D/kB = -6.4 K, E/kB = -2.1 K), in good agreement with the high-field electron paramagnetic resonance experiments. At low temperature Mn2Ca2 cluster behaves as a system of ferromagnetically coupled (J/kB = 1.1 K) Mn dimers with a ST = 4 and mT = ±4 ground state doublet. Frequency dependent ac susceptibility measurements reveal the slow magnetic relaxation characteristic of a single molecule magnet (SMM) below T = 4 K. At zero magnetic field, an Orbach-type spin relaxation process (τ ∼ 10-5 s) with an activation energy Ea = 5.6 K is observed, enabled by the large E/D rhombicity of the Mn(iii) ions. Upon the application of a magnetic field, a second, very slow process (τ ∼ 0.2 s) is observed, attributed to a direct relaxation mechanism with enhanced relaxation time owing to the phonon bottleneck effect.

Catalyst structure and substituent effects on epoxidation of styrenics with immobilized Mn(tmtacn) complexes

Monomeric and dimeric complexes of Mn 1,4,7-trimethyl-1,4,7-triazacyclononane (tmtacn) were immobilized under reaction conditions onto solid supports to create heterogeneous catalysts for epoxidation with H2O2. These solid supports consist of activated carbon or silica grafted or co-condensed with benzoic or C3/C4 acids that function both as tethering points and as required co-catalysts. Immobilized catalysts were as much as 50-fold faster than the analogous soluble system, and an immobilized, dimeric Mn(tmtacn) complex with a solid benzoic acid co-catalyst gave the highest yields to epoxide. A Hammett study on the catalytic epoxidation of a series of styrenes showed weak increases in yield for more electron-withdrawing p-substituents reactants for both immobilized complexes, which runs counter to previous observations with analogous homogeneous catalysts, and which appears to reflect a previously unappreciated tradeoff between the intrinsic epoxidation reactivity and strong catalyst inhibition by styrene oxides and glycols. Finally, these catalysts were tested with a variety of solid-co-catalysts, and were successfully utilized in the challenging epoxidation of divinylbenzene to industrially-useful divinylbenzene dioxide using a cascade of two catalyst charges.

Mn(II) Binding and Subsequent Oxidation by the Multicopper Oxidase MnxG Investigated by Electron Paramagnetic Resonance Spectroscopy.

The dynamics of manganese solid formation (as MnOx) by the multicopper oxidase (MCO)-containing Mnx protein complex were examined by electron paramagnetic resonance (EPR) spectroscopy. Continuous-wave (CW) EPR spectra of samples of Mnx, prepared in atmosphere and then reacted with Mn(II) for times ranging from 7 to 600 s, indicate rapid oxidation of the substrate manganese (with two-phase pseudo-first-order kinetics modeled using rate coefficients of: k(1obs) = 0.205 ± 0.001 s(-1) and k(2obs) = 0.019 ± 0.001 s(-1)). This process occurs on approximately the same time scale as in vitro solid MnOx formation when there is a large excess of Mn(II). We also found CW and pulse EPR spectroscopic evidence for at least three classes of Mn(II)-containing species in the reaction mixtures: (i) aqueous Mn(II), (ii) a specifically bound mononuclear Mn(II) ion coordinated to the Mnx complex by one nitrogenous ligand, and (iii) a weakly exchange-coupled dimeric Mn(II) species. These findings provide new insights into the molecular mechanism of manganese mineralization.

X-ray Absorption and Emission Study of Dioxygen Activation by a Small-Molecule Manganese Complex.

Manganese K-edge X-ray absorption (XAS) and Kβ emission (XES) spectroscopies were used to investigate the factors contributing to O-O bond activation in a small-molecule system. The recent structural characterization of a metastable peroxo-bridged dimeric Mn(III)2 complex derived from dioxygen has provided the first opportunity to obtain X-ray spectroscopic data on this type of species. Ground state and time-dependent density functional theory calculations have provided further insight into the nature of the transitions in XAS pre-edge and valence-to-core (VtC) XES spectral regions. An experimentally validated electronic structure description has also enabled the determination of structural and electronic factors that govern peroxo bond activation, and have allowed us to propose both a rationale for the metastability of this unique compound, as well as potential future ligand designs which may further promote or inhibit O-O bond scission. Finally, we have explored the potential of VtC XES as an element-selective probe of both the coordination mode and degree of activation of peroxomanganese adducts. The comparison of these results to a recent VtC XES study of iron-mediated dintrogen activation helps to illustrate the factors that may determine the success of this spectroscopic method for future studies of small-molecule activation at transition metal sites.

Surface Functionalization of Supported Mn Clusters to Produce Robust Mn Catalysts for Selective Epoxidation

A robust heterogeneous Mn catalyst for selective epoxidation was prepared by the attachment of a Mn4 oxonuclear complex [Mn4O2(CH3COO)7(bipy)2](ClO4)·3H2O (1) on SiO2 and the successive stacking of SiO2-matrix overlayers around a supported Mn cluster. The structures of supported Mn catalysts were characterized by means of FT-IR spectroscopy, diffuse-reflectance UV/vis spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and Mn K-edge X-ray absorption fine structure. A ligand exchange reaction between the CH3COO ligand of 1 and surface silanol group produced a SiO2-supported Mn cluster (2), whose coordination structure was similar to 1. Subsequent heating of 2 under vacuum yielded supported Mn clusters (3, 4) through the partial elimination of CH3COO ligands. The surface-attached Mn clusters of 2, 3, and 4 were easily released to a reaction solution under epoxidation conditions (Mn leaching: approximately 50%), although they were active for epoxidation of trans-stilbene (the conversion of trans-stilbene, 99%, and the selectivity of trans-stilbene epoxid, 96%, for 6 h on 3). We found that the functionalization of the supported Mn cluster on 2 with surface SiO2-matrix overlayers altered the reactivity of the supported Mn cluster. Dimeric Mn species (5c) with reduced Mn oxidation state and coordination numbers was formed together with a reaction nanospace surrounded by the SiO2-matrix overlayers. By optimizing the stacking manner of the SiO2-matrix overlayers, the durability of the Mn catalyst was remarkably improved from leaching (the Mn leaching reached the minimum value of 0.01%), and active and stable epoxidation performances were successfully achieved in the heterogeneous phase (the conversion of trans-stilbene, 97%, and the selectivity of trans-stilbene epoxide, 91%, for 31 h on 5c).

Synthesis, crystal structures and properties of four manganese coordination polymers with 4,4-bipyridine-derived ligands

Four new coordination polymers, namely Mn2(4,4-bpy)2(o-tol)41, Mn2(4,4-bpy)2(m-tol)42, Mn2(bpp)2(m-tol)43 and {[Mn2(4,4-bpy)2(p-tol)4][Mn(4,4-bpy)2(H2O)2(p-tol)2]}·6H2O 4 have been synthesized from 4,4′-bipyridine (4,4-bpy), 1,3-bis(4-pyridyl)-propane (bpp), o-toluic acid (o-Htol), m-toluic acid (m-Htol) and p-toluic acid (p-Htol). All four complexes feature dinuclear Mn2(tol)4 moieties, which are bridged by 4,4-bpy or bpp ligands to form 1D double-chain structures. The resulted 1D double-chains are assembled via hydrogen bonding or π···π stacking into 2D supramolecular layers. The complexes were characterized by physico-chemical (thermal behavior) and infrared spectroscopy. Variable temperature magnetic characterization suggest weak antiferromagnetic coupling exchange between dimeric Mn(II) centers (J = −0.46 cm−1 for 1, −0.56 cm−1 for 2, −1.28 cm−1 for 3 and −0.59 cm−1 for 4).

Use of the mechanistic probe 2-methyl-1-phenylpropan-2-yl hydroperoxide (MPPH) to discriminate between the formation of MnIVMnIV(OH) and MnIVMnV[tbnd]O species

High-valent Mn species are key intermediates in the oxygen evolving complex in photosystem II. In some mechanisms, the MnVO moiety is proposed to be a critical species at the final step of oxygen production. This work reports the use of a mechanistic probe 2-methyl-1-phenylpropan-2-yl hydroperoxide (MPPH) to distinguish the formation of MnIVMnIV(OH) and MnIVMnVO species. We demonstrate that a dimeric Mn complex [MnIIIMnIV(2-OH-3,5-diClsalpn)]+ reacts with MPPH, leading to the production of the O–O bond heterolysis product. In this process, the Mn complex transforms into a transient MnIVMnVO species, which undergoes comproportionation rapidly.

Formation of two drastically different MOFs based on Mn(ii)–benzoate and pyrazine with a change in seasonal temperature: structural analysis and magnetic study

Two new stoichiometrically and structurally very different Mn(II) coordination compounds {[Mn(pyz)(C6H5COO)2](C2H5OH)}n (1) and [Mn5(pyz)(C6H5COO)10(H2O)2]n (2) (where pyz = pyrazine) have been synthesized by the reaction of Mn(C6H5COO)2·4H2O and pyz in 1 : 1 molar ratio in different seasons of the year. The structural analyses reveal that complex 1, which is synthesized in summer when the temperature remains around 28–40 °C, features a 1D molecular ladder formed by joining of syn–syn benzoate-bridged dimeric Mn(II) units by pyz. Complex 2, which is obtained in winter (temperature around 10–20 °C), is an unprecedented 2D rectangular sheet motif based on a 1D column constructed from syn–syn benzoate bridged repetitive Mn5 units which are further interconnected by the pyz spacer. The compounds are interconvertible in solution: when an ethanol solution of 1 is allowed to evaporate slowly in winter or in a refrigerator (5–6 °C) it transformed into 2 whereas crystallization of 2 from ethanol medium in summer (28–40 °C) yields 1. Variable-temperature (1.8–300 K) magnetic susceptibility measurements showed presence of weak antiferromagnetic coupling in 1 that has been fitted with the van Vleck equation. The interaction in benzoate-bridged Mn2 unit was characterized to be J = −0.586(1) cm−1, where the spin-Hamiltonian is defined as H = −2JS1S2. The interaction in 2 was also characterized with the modified van Vleck equation to be weakly antiferromagnetic.

Synthesis and characterization of four novel manganese(II) chains formed by 4,4′-azobis(pyridine) and benzoate or nitrobenzoates: Stabilization of unusual ladder structures

Four new manganese(II) coordination polymers: [Mn(4,4′-azpy)(C6H5COO)2](4,4′-azpy)0.5 (1), [Mn(4,4′-azpy)(p-(NO2)C6H4COO)2] (2), [Mn(4,4′-azpy)(m-(NO2)C6H4COO)2] (3) and [Mn(4,4′-azpy)(o-(NO2)C6H4COO)2(H2O)2] (4), where 4,4′-azpy=4,4′-azobis(pyridine), have been synthesized by self-assembly of MnX2 (X=benzoate, p-, m-, or o-nitrobenzoates) together with 4,4′-azpy. All four complexes were characterized by elemental analyses, IR spectroscopy, thermal analyses, single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. The structural analyses reveal that complexes 1, 2 and 3 feature a 1D molecular ladder formed by syn–syn (complex 1) or syn–anti (complexes 2 and 3) carboxylate-bridged dimeric Mn(II) units which are joined together by 4,4′-azpy ligands. In complex 1, these ladders assemble with the help of π–π and C–H⋯π interactions to form a nanoporous framework that incorporates non coordinated 4,4′-azpy molecules by exploiting host–guest C–H⋯π and hydrogen bonding interactions. Complex 2 presents a 3D supramolecular framework by π–π and CH⋯π interactions, whereas, complex 3 having a similar ladder structure to 1 and 2, forms a 2D grid through π–π interactions. On the other hand, complex 4 is a 4,4′-azpy bridged fish-bone chain of carboxylate-coordinated mononuclear manganese(II) units, which are linked together by strong hydrogen bonds to form a 2D structure. Variable-temperature (2–300K) magnetic susceptibility measurements show the presence of weak antiferromagnetic interactions within the discrete Mn–(OCO)2–Mn dimers for complexes 1, 2 and 3 that have been fitted with a S=5/2 dimer model (J=−0.8, −0.5 and −0.4cm−1 respectively). The magnetic data of complex 4 can be reproduced with a S=5/2 monomer model including a Zero Field Splitting (|D|=1.7cm−1).

Synthesis, Structure, and Magnetic Studies of Manganese–Oxygen Clusters of Reduced Coordination Number, Featuring an Unchelated, 5-Coordinate Octanuclear Manganese Cluster with Water-Derived Oxo Ligands

The synthesis of reduced coordination (less than 6), unchelated manganese oxygen cluster systems is described. Addition of phenols to Mn(NR(2))(2) (R = SiMe(3)) results in protolytic amide ligand replacement, and represents the primary entry into the described chemistry. Addition of PhOH to Mn(NR(2))(2) results in the formation of the heteroleptic dimer Mn(2)(μ-OPh)(2)(NR(2))(2)(THF)(2) (1). Usage of the sterically larger 2,6-diphenylphenol (Ph(2)C(6)H(3)OH) as the ligand source results in the formation of a 3-coordinate heteroleptic dimer without THF coordination, Mn(2)(μ-OC(6)H(3)Ph(2))(2)(NR(2))(2) (2). Attempts to generate 2 in the presence of THF or Et(2)O resulted in isolation of monomeric Mn(OC(6)H(3)Ph(2))(2)L(2) (3, L = THF, Et(2)O). Use of the sterically intermediate 2,4,6-trimethylphenol (MesOH) resulted in formation of the linear trinuclear cluster Mn(3)(μ-OMes)(4)(NR(2))(2)(THF)(2) (4). Reaction of Mn(NR(2))(2) with PhOH in the presence of water, or reaction of 1 with water, results in the formation of a 5-coordinate, unchelated Mn-O cluster, Mn(8)(μ(5)-O)(2)(μ-OPh)(12)(THF)(6) (5). Preparation, structures, steric properties, and magnetic properties are presented. Notably, complex 5 exhibits a temperature-dependent phase transition between a 4-spin paramagnetic system at low temperature, and an 8-spin paramagnetic system at room temperature.

Immobilized dimeric chiral Mn(III) salen complex on short channel ordered mesoporous silica as an effective catalyst for the epoxidation of non-functionalized alkenes

Chiral dimeric Mn(III) salen complex with 1R, 2R-(−)-diaminocyclohexane collar was immobilized on short channel large pore sized silica through a long linker of {(CH2)3–NH–melamine–piperazine} to investigate its performance in enantioselective epoxidation of chromenes, indene, styrene and cis β-methyl styrene in the presence of pyridine N-oxide (PyNO) as an axial base using aqueous NaOCl as an oxidant at 0 °C. The immobilized catalyst system showed high turnover frequency (TOF) and enantioselectivity for the smaller and bulkier alkenes like styrene, indene, 2,2-dimethylchromene and 6-cyano-2,2-dimethylchromene (ee up to 98%). These results are the best reported for heterogeneous catalyst under biphasic reaction conditions and were comparable to the dimeric Mn(III) salen system under homogeneous condition. The performance of the immobilized catalyst was retained for six reuse experiments. This protocol was extended to the synthesis of an antihypertensive drug (S)-Levchromakalim (ee 98%) at 1 g level.

First-principles theoretical investigation of monoatomic and dimer Mn adsorption on noble metal (111) surfaces

A theoretical investigation of the adsorption of Mn single atoms and dimers on the (111) surface of Cu, Ag, and Au, within the framework of the density functional theory, is presented. First, the bulk and the clean (111) surface electronic structures are calculated, with results that agree well with previous reports. To understand the adatom-substrate interaction, also the electronic characteristics of the free Mn dimer are determined. Then, the electronic structure of the Mn adatom, chemisorbed on four different surface geometries, is analyzed for the three noble metals. It is found that the most stable geometry, in all three cases, Cu, Ag, and Au, occurs when the Mn atom is chemisorbed on threefold coordinated sites. For the dimer, the lowest-energy configuration corresponds to the molecule lying parallel to the surface. In the three noble metals, the geometry corresponds to both atoms chemisorbed in threefold coordinated sites, but with different local symmetry. It is also found that the magnetic configuration with the lowest energy corresponds to the antiferromagnetic arrangement of Mn atoms, with individual magnetic moments close to 5${\ensuremath{\mu}}_{B}$. The ferromagnetic and antiferromagnetic solutions, in the case of a Ag substrate, are close in energy. It is also found that in this case the Mn${}_{2}$ molecule is chemisorbed with very similar energy on various geometries. To study the dynamical motion of the dimer components, we calculated the potential energy barriers for the Mn motion in the various surfaces. In contrast to Cu and Au, this leads to the conclusion that on Ag the Mn dimer moves relatively freely.

Epoxidation of Alkenes Catalyzed by Phenyl Group‐Modified, Periodic Mesoporous Organosilica‐Entrapped, Dimeric Manganese–Salen Complexes

A series of reusable, recoverable, diamine-bridged dimeric manganese-salen complexes were prepared by the encapsulation of homogeneous dimeric Mn(salen) complexes into nanocages of a 3D periodic mesoporous organosilica (PMO) support followed by silylation of the support with organosilane. The composition, structure, morphology, and textural properties of the prepared PMO-entrapped dimeric Mn(salen) complexes were characterized, and their catalytic performances were tested in the epoxidation of alkenes (styrene, cyclohexene, and 1-phenylcyclohexene), with NaClO as an oxygen source and 4-phenylpyridine-N-oxide as an axial ligand. Furthermore, the influences of the textural and morphological properties of the entrapped dimeric Mn(salen) complexes and the key reaction parameters on the catalytic activity and selectivity are discussed. Finally, the reusability of the supported dimeric Mn(salen) complexes was evaluated over three catalytic runs.

A Unique Example of Structural Diversity Tuned by Apparently Innocent o-, m-, and p-Nitro Substituents of Benzoate in Their Complexes of Mn(II) with 4,4′-Bipyridine: 1D Ladder, 2D Sheet, and 3D Framework

Four new Mn(II) coordination polymers [Mn(4,4′-bpy)(C6H5COO)2]n (1), [Mn(4,4′-bpy)(o-(NO2)C6H4COO)2]n (2), [Mn(4,4′-bpy)(m-(NO2)C6H4COO)2]n (3), and [Mn(4,4′-bpy)(p-(NO2)C6H4COO)2]n (4) (where 4,4′-bpy = 4,4′-bipyridine) have been synthesized by self-assembly of the primary ligands, benzoate and the o-, m-, and p-isomers of nitrobenzoates, respectively, together with 4,4′-bpy as the secondary spacer. All four complexes were characterized by elemental analyses, IR spectroscopy, single-crystal X-ray diffraction analyses, and variable-temperature magnetic measurements. The structural analyses reveal that complexes 1 and 3 are constructed by linear fused chains through double syn-syn (for 1) or syn-anti (for 3) carboxylate-bridged Mn(II), which are further linked to one another by trans coordinated 4,4′-bpy bridges, giving rise to a rectangular grid-like two-dimensional (2D) net. Complex 2 features one-dimensional (1D) molecular ladder formed by both syn-syn and syn-anti carboxylate-bridged dimeric Mn(II) uni...

Monoatomic and dimer Mn adsorption on the Au(111) surface from first principles

A theoretical study based on the density functional theory of the adsorption of Mn monomers and dimers on a Au-(111) surface is presented. As necessary preliminary steps, the bulk and clean surface electronic structure are calculated, which agree well with previous reports. Then, the electronic structure of the Mn adatom, chemisorbed on four different surface geometries, is analyzed. It is found that the most stable geometry is when the Mn atom is chemisorbed on threefold coordinated sites. Using this geometry for a single adatom a second Mn atom is chemisorbed and the most stable dimer geometrical structure is calculated. The lowest-energy configuration corresponds to the molecule lying parallel to the surface, adsorbed on two topological equivalent threefold coordinated sites. It is also found that the lowest-energy magnetic configuration corresponds to the antiferromagnetic arrangement with individual magnetic moments of $4.64{\ensuremath{\mu}}_{B}$. Finally, it is concluded that the dimer is not stable and should fragment at the surface.

ChemInform Abstract: Mn(III) Salen Complexes‐Catalyzed Enantioselective Addition of Trimethyl Silylcyanide to N‐Benzylimines in the Presence of 4‐Phenyl Pyridine‐N‐oxide as an Additive.

Abstract Chiral monomeric and dimeric Mn(III) salen complexes viz., [(S,S)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminato manganese(III) chloride and 5,5-methylene di-[(S,S)-{N-(3-tert-butyl salicylidine)-N′-(3′,5′-di-tert-butyl salicylidene)}-1,2-cyclohexanediaminato manganese(III) chloride were used as catalysts for the highly enantioselective Strecker reaction of various imines (derived by the condensation of aldehydes and amine) with TMSCN as a source of cyanide in toluene. Excellent yield (95%) of α-amino nitrile with ee >99% was achieved when N-(2-methoxybenzylidine)-1-phenylmethanamine was used as a substrate and 4-phenyl pyridine-N-oxide (4-PPNO) as an additive at −55 °C in 28 h. The dimeric catalyst was found to be more reactive and enantioselective than the monomeric catalyst. The chiral dimeric catalyst used in the present study was recoverable and recyclable several times with retention of its performance.