Chalcogen Ligands Research Articles

Influence of the Greater Protein Environment on the Electrostatic Potential in Metalloenzyme Active Sites: The Case of Formate Dehydrogenase.

The Mo/W-containing metalloenzyme formate dehydrogenase (FDH) is an efficient and selective natural catalyst that reversibly converts CO2 to formate under ambient conditions. In this study, we investigate the impact of the greater protein environment on the electrostatic potential (ESP) of the active site. To model the enzyme environment, we used a combination of classical molecular dynamics and multiscale quantum-mechanical (QM)/molecular-mechanical (MM) simulations. We leverage charge shift analysis to systematically construct QM regions and analyze the electronic environment of the active site by evaluating the degree of charge transfer between the core active site and the protein environment. The contribution of the terminal chalcogen ligand to the ESP of the metal center is substantial and dependent on the chalcogen identity, with similar, less negative ESPs for Se and S terminal chalcogens in comparison to O regardless of whether the metal is Mo or W. The orientation of the side chains and conformations of the cofactor also affect the ESP, highlighting the importance of sampling dynamic fluctuations in the protein. Overall, our observations suggest that the terminal chalcogen ligand identity plays an important role in the enzymatic activity of FDH, suggesting opportunities for a rational bioinspired catalyst design.

Mixed Cationic and Anionic Redox in Ni and Co Free Chalcogen-Based Cathode Chemistry for Li-Ion Batteries.

Mixed cationic and anionic redox cathode chemistry is emerging as the conventional cationic redox centers of transition-metal-based layered oxides are reaching their theoretical capacity limit. However, these anionic redox reactions in transition metal oxide-based cathodes attained by taking excess lithium ions have resulted in stability issues due to weak metal-oxygen ligand covalency. Here, we present an alternative approach of improving metal-ligand covalency by introducing a less electronegative chalcogen ligand (sulfur) in the cathode structural framework where the metal d band penetrates into the ligand p band, thereby utilizing reversible mixed anionic and cationic redox chemistry. Through this design strategy, we report the possibility of developing a new family of layered cathode materials when partially filled d orbital redox couples like Fe2+/3+ are introduced in the Li-ion conducting phase (Li2SnS3). Further, the electron energy loss spectroscopy and X-ray absorption near-edge structure analyses are used to qualitatively identify the charge contributors at the metal and ligand sites during Li+ extraction. The detailed high-resolution transmission electron microscopy and high annular dark field-scanning transmission electron microscopy investigations reveal the multi-redox induced structural modifications and its surface amorphization with nanopore formation during cycling. Findings from this study will shed light on designing Ni and Co free chalcogen cathodes and various functional materials in the chalcogen-based dual anionic and cationic redox cathode avenue.

Cyclic Voltammetric studies of the interaction of cupric chloride with (Z)-4-oxo-4-((4-selenocyannatophenyl)amino) but-2-2nonic acid , (Chal) in KCl solutions using glassy carbon electrode.

To predict and analyze the complexation behavior between the challcogen ligand (Chal) (Z)-4-oxo-4-((4-selenocyannatophenyl)amino) but-2-2nonic acid, and metal ion in aqueous solution cyclic voltammetric studies of copper chloride salt [CuCl2] in absence and presence of chalcogen ligand (Chal), (Z)-4-oxo-4-((4-selenocyannatophenyl)amino) but-2-2nonic acid were performed. From these studies, some values were evaluated (the values of solvation and kinetic parameters [Ep (peak potential), Ip (peak current), D (Diffusion coefficient), ΔEP (peak potential difference), E½ (half wave potential), ks (electron transfer rate constant), Г (surface coverage) and Qa (quantity of electricity)]. the effect of different scan rate and concentration of above the calculated quantities were evaluated and discussed.

Reactivity of hemi-labile pyridyl and pyrimidyl derived chalcogen ligands towards group 10 metal phosphine precursors

The reactivity of N-heterocyclic dichalcogenides and their sodium salts towards group 10 metal phosphine precursors has been investigated.

Organochalcogen ligands in catalysis of oxidation of alcohols and transfer hydrogenation.

Organochalcogen compounds have been used as the building blocks for the development of a variety of catalysts that have been studied comprehensively during the last two decades for several chemical transformations. Transfer hydrogenation (reduction of carbonyl compounds to alcohols) and oxidation of alcohols (conversion of alcohols to their respective ketones and aldehydes) are also among such chemical transformations. Some compilations are available in the literature on the development of catalysts, based on organochalcogen ligands, and their applications in Heck reaction, Suzuki reaction, and other related aspects. Some review articles have also been published on different aspects of oxidation of alcohols and transfer hydrogenation. However, no such article is available in the literature on the syntheses and use of organochalcogen ligated catalysts for these two reactions. In this perspective, a survey of developments pertaining to the synthetic aspects of such organochalcogen (S/Se/Te) based catalysts for the two reactions has been made. In addition to covering the syntheses of chalcogen ligands, their metal complexes and nanoparticles (NPs), emphasis has also been placed on the efficient conversion of different substrates during catalytic reactions, diversity in catalytic potential and mechanistic aspects of catalysis. It also includes the analysis of comparison (in terms of efficiency) between this unique class of catalysts and efficient catalysts without a chalcogen donor. The future scope of this area has also been highlighted.

Donor Strengths Determination of Pnictogen and Chalcogen Ligands by the Huynh Electronic Parameter and Its Correlation to Sigma Hammett Constants.

The suitability and accuracy of the Huynh electronic parameter (HEP) was further tested to reveal remote substituent effects in pyridines, which are located five or six bonds away from the reporter probe. These values show an excellent correlation to Hammett σ‐constants of the respective substituents with coefficients of R 2=0.9856 (σ m) and R 2=0.9857 (σ p). Based on this observation, a methodology for the re‐evaluation of certain Hammett constants with larger uncertainties has been proposed and demonstrated. Moreover, the scope of HEP was extended to various neutral pnictogen and chalcogen donors during which “transphobia effects” were revealed for mixed NHC complexes containing phosphites, arsine and stibine for the first time.

Complexation of aromatic dichalcogen ligands to germanium

Eight novel germanium compounds of the type [R2Ge(E-Ar-E)], where R=Me, Ph; E-Ar-E=an aromatic bidentate chalcogen ligand, were successfully synthesised. The effects of changing 3 variables within the series were investigated. These variables included the chalcogen (E=S/Se), aromatic backbone (Ar=Nap/Biphenyl) and R group (Me/Ph) employed. The choice of aromatic backbone had the greatest effect on the structure. A substantial change in geometry around the germanium centre was observed within the solid state structures depending on whether the backbone was naphthalene or biphenyl. This affected the stability of the compound and resulted in the visible decomposition of two selenium complexes over several days. All novel compounds were characterised by multinuclear NMR, IR, mass spectroscopy and single crystal X-ray diffraction.

Ligand Addition Energies and the Stoichiometry of Colloidal Nanocrystals.

Experimental nonstoichiometries of colloidal nanocrystals such as CdSe and PbS are accounted for by attributing to each constituent atom and capping ligand a formal charge equal to its most common oxidation state to obtain an overall neutral nanocrystal. In spite of its apparent simplicity, little theoretical support of this approach-called here the oxidation-number sum rule-is present in the current literature. Here, we introduce the ligand addition energy, which we define as the energy gained or expended upon the transfer of one ligand from a reference state to a metal-rich solid surface. For the combination of CdSe, ZnSe and InP with either chalcogen, halogen or hydrochalcogen ligands, we compute successive ligand addition energies using ab initio methods and determine the thermodynamically stable surface composition as that composition where ligand addition turns endothermic. We find that the oxidation-number sum rule is valid in many situations, although exceptions occur for each material studied, most notably when exposed to small oxidative ligands. In the case of InP, however, violations are more severe, extending toward the entire chalcogen ligand family. In addition, we find that electronegativity rather than chemical hardness is a reasonable predictor for ligand addition energies, with the most electronegative ligands yielding the most exothermic addition energies. Finally, we argue that the ligand addition energy will be a most useful quantity for future computational studies on the structure, stability and reactivity of nanocrystal surfaces.

Syntheses, structures, and reactivities of two chalcogen-stabilized carbones.

Electronic effects on the central carbon atom of carbone, generated by the replacement of the S(IV) ligand of carbodisulfane (CDS) with other chalcogen ligands (Ph2 E, E=S or Se), were investigated. The carbones Ph2 E→C←SPh2 (NMe) [E=S(1) or Se(2)] were synthesized from the corresponding salts, and their molecular structures and electronic properties were characterized. The carbone 2 is the first carbone containing selenium as the coordinated atom. DFT calculations revealed the electronic structures of 1 and 2, which have two lone pairs of electrons at the carbon center. The trend in HOMO energy levels, estimated by cyclic voltammetry measurements, for the carbones and CDS follows the order of 2>1>CDS. Analysis of a doubly protonated dication and trication complex revealed that the central carbon atom of 2 behaves as a four-electron donor.

Syntheses, Structures, and Reactivities of Two Chalcogen-Stabilized Carbones

Electronic effects on the central carbon atom of carbone, generated by the replacement of the SIV ligand of carbodisulfane (CDS) with other chalcogen ligands (Ph2E, E=S or Se), were investigated. The carbones Ph2E→C←SPh2(NMe) [E=S(1) or Se(2)] were synthesized from the corresponding salts, and their molecular structures and electronic properties were characterized. The carbone 2 is the first carbone containing selenium as the coordinated atom. DFT calculations revealed the electronic structures of 1 and 2, which have two lone pairs of electrons at the carbon center. The trend in HOMO energy levels, estimated by cyclic voltammetry measurements, for the carbones and CDS follows the order of 2>1>CDS. Analysis of a doubly protonated dication and trication complex revealed that the central carbon atom of 2 behaves as a four-electron donor.

2-Propanol vs Glycerol as Hydrogen Source in Catalytic Activation of Transfer Hydrogenation with (η6-Benzene)ruthenium(II) Complexes of Unsymmetrical Bidentate Chalcogen Ligands

1H-Benzoimidazole on subjection to a sequence of reactions with benzyl bromide, PhECH2Cl (E = S, Se), and elemental S or Se results in 1-benzyl-3-phenylchalcogenylmethyl-1,3-dihydrobenzoimidazole-2-chalcogenones (L1–L4), which are unsymmetrical bidentate chalcogen ligands having a unique combination of chalcogenoether and chalcogenone donor sites. Half sandwich complexes, [(η6-C6H6)Ru(L)Cl][PF6] (1–4), have been synthesized by reactions of [(η6-C6H6)RuCl(μ-Cl)]2 with the appropriate L at room temperature followed by treatment with NH4PF6. L1–L4 and their complexes 1–4 have been authenticated with HR-MS and 1H, 13C{1H}, and 77Se{1H} NMR spectra. The single-crystal structures of 1–4 have been determined by X-ray crystallography. Each L acts as an unsymmetric (E,E) or (E,E′) bidentate ligand. The Ru atom in 1–4 has pseudo-octahedral half-sandwich “piano-stool” geometry. The Ru–S and Ru–Se bond distances (Å) respectively are 2.358(3)/2.3563(18) and 2.4606(11)/2.4737(10) (thio- and selenoether), and 2.4534(17)/2.435(3) and 2.5434(9)/2.5431(10) (thione and selone). Catalytic activation with complexes 1–4 has been explored for the transfer hydrogenation (TH) of aldehydes and ketones using various sources of hydrogen. 2-Propanol and glycerol have been compared and found most suitable among the sources screened. The catalytic efficiency of other sources explored, viz. formic, citric, and ascorbic acid, is dependent on the pH of reaction medium and is not promising. A comparative study of 2-propanol and glycerol as hydrogen sources for catalytic activation of TH with 1–4 has revealed that with glycerol (for comparable conversion in the same time) more amount of catalyst is needed in comparison to that of 2-propanol. The catalytic process is more efficient with 3 (where Ru is bonded with selone), followed by 1 ≈ 4, and 2 showing the least activity among all four complexes. The transfer hydrogenation involves an intermediate containing a Ru–H bond and follows a conventional alkoxide intermediate based mechanism. The results of DFT calculations appear to be generally consistent with experimental catalytic efficiencies and bond lengths/angles.

Synthesis, structures and utility of organogallium and organoindium complexes with oxo and thio ligands

The review is focused on synthesis and study of a variety of organogallium and organoindium complexes with several internally functionalized anionic oxo ligands, anionic dithio and organoseleno ligands. These compounds have been thoroughly characterized by elemental analyses, 1H, 13C, and 77Se NMR spectroscopy, and in several cases by single crystal X-ray diffraction analyses. Structural preferences in these complexes are influenced by the nature of the metal atom (Ga or In), organic group attached to it, and the incoming ligand with indium preferring to acquire higher coordination number. The complexes with oxo ligands show photo-luminescence with the emission quantum yields higher in general than the corresponding free ligands. The complexes with chalcogen ligands are versatile precursors for the synthesis of metal sulfide and selenide nanocrystals.

Synthesis and structural study of divalent Cu, Zn, Cd and Pd complexes supported by 1,2,3-triazole-based chalcogen ligands

Transition metal complexes of the type [M{4,5-(P(E)Ph2)2tz}2(thf)n] [tz=1,2,3-triazole; M=Cu, n=2, E=S(3); M=Cu, n=0, E=Se(4); M=Zn, n=2, E=S(5); M=Cd, n=2, E=S(7), Se(8); M=Pd, n=0, E=S(9), Se(10)] and [Zn2{4,5-(P(Se)Ph2)2(tz)}4](6) were obtained by reacting [K{4,5-(P(E)Ph2)2tz}] with MX2 (M=Cu, Zn, Cd, X=Cl or M=Pd, X=AcO) in a 2:1M ratio. The structures of these compounds were investigated by IR, 1H and 31P NMR spectroscopy, as well as by elemental analysis. The molecular structures of 3, 4, 5–10 were determined by single-crystal X-ray diffraction. In addition, during the crystallization process of 4, single crystals of 4a were obtained showing a structure where the replacement of a selenium atom from the non-coordinated PSe moiety by an oxygen atom gives a mixed oxygen–selenium complex. All the compounds exhibit MEPCN heterocycles as a common structural feature but in the case of 6 a bimetallic arrangement with a scorpionate-like coordination mode is also observed.

A close-packed boron-rich 11-vertex molybdaborane with novel geometry

The reaction of an intermediate, generated from [Cp#MoCl4] [Cp# = Cp or Cp∗; Cp = (η5-C5H5), Cp∗ = (η5-C5Me5)] and LiBH4.thf, with different chalcogen ligands yielded trimolybdaborane clusters 1–3, [(Cp#Mo)3(μ-H)B8H6X2], (1: Cp# = Cp, X = H; 2: Cp# = Cp∗, X = H; 3: Cp# = Cp∗, X = Cl). Compounds 1–3 constitute an example of an unsaturated (n-4) sep cluster having very close structural similarities. These clusters represent 11-vertex boron-rich metallaboranes containing 66 cluster valence electrons (cve). All the compounds were fully characterized by various spectroscopic techniques, elemental analysis and the solid state structures were unequivocally established by X-ray diffraction analysis of 1–3.

ChemInform Abstract: Low‐Dimensional Frameworks in Solid State Chemistry of Mo6 and Re6 Cluster Chalcohalides

AbstractReview: 82 refs.

Low‐Dimensional Frameworks in Solid State Chemistry of Mo6 and Re6 Cluster Chalcohalides

AbstractThe low‐dimensional Mo6 and Re6 cluster chalcohalides synthesised from solid‐state reactions at high temperature are reviewed. Their crystal structures are described in terms of interunit connectivities involving inner and apical ligands shared between adjacent cluster units. It will be shown that such architectures are controlled by the geometry of the M6L14 cluster units, the steric hindrance of the ligands linked to the M6 cluster, the specific location imposed on the halogen or chalcogen ligand and the most favourable electron count on the cluster core, considering halogen and chalcogen stoichiometries.

ChemInform Abstract: Syntheses and Dynamic Nuclear Magnetic Resonance Studies of Complexes of Trimethylplatinum(IV) Iodide with Ditelluroether Chelate Ligands.

Trimethylplatinum(IV) iodide complexes with ditelluroether ligands, namely [PtlMe3(L–L)][L–L = MeTe(CH2)3TeMe, PhTe(CH2)3TePh or o-C6H4(TeMe)2] have been isolated as pure solids. 195Pt-{1H} and 125Te-{1H} NMR studies show that ambient-temperature solutions of the complexes with aliphatic ligand backbones consist predominantly of DL isomers. The complex [PtlMe3{MeTe(CH2)3TeMe}] also exists in significant amounts of both meso forms. In contrast, the meso-1 form is present in only very low abundance in [PtlMe3{PhTe(CH2)3TePh}] and [PtlMe3{o-C6H4(TeMe)2}]. Pyramidal tellurium inversion interconverts these isomeric species and precise rates of this process were measured at near-ambient temperatures by 195Pt-{1H} and 125Te-{1H} NMR two-dimensional exchange spectroscopy experiments, or by 1H one-dimensional NMR bandshape analysis at above-ambient temperatures in the case of [PtlMe3{o-C6H4(TeMe)2}]. Tellurium pyramidal inversion-energy barriers [ΔG‡(298.15 K)] were in the range 70–84 kJ mol–1, reflecting the nature of the the substituent at Te and the ligand backbone. Comparison of the tellurium inversion energy in [PtlMe3{MeTe(CH2)3TeMe}] with data for Se and S in analogous complexes of chalcogen ligands establishes the trend in inversion energies, namely Te > Se > S, on a firm quantitative basis.

Formation of carbonylrhenium cryptates with alkali metal cations: Coordination chemistry studies of [Ph2P(E)NP(E)Ph2]−, E=O, S, Se towards ReBr(CO)5

Reaction of ReBr(CO) 5 with Li[Ph 2 P(O)NP(O)Ph 2 ] afforded the cryptate Li[Re 2 (CO) 6 {μ-Ph 2 P(O)NP(O)Ph 2 -κ 2 O,O′ } 3 ]; whereas K[Ph 2 P(O)NP(O)Ph 2 ] reacted with ReBr(CO) 5 to give K[Re 2 (CO) 6 {μ-Ph 2 P(O)NP(O)Ph 2 -κ 2 O,O′ }{Ph 2 P(O)NP(O)Ph 2 -κ 2 O,O′ } 2 ]. Other chalcogen ligands’ salts M[Ph 2 P(E)NP(E)Ph 2 ], E = Se and S, M = K and Li gave dirhenium carbonyls with bromido and Ph 2 P(E)NP(E)Ph 2 , E = Se or S bridges upon reaction with ReBr(CO) 5 . Reaction of ReBr(CO) 5 with Li[Ph 2 P(O)NP(O)Ph 2 ] afforded the cryptate Li[Re 2 (CO) 6 {μ-Ph 2 P(O)NP(O)Ph 2 -κ 2 O,O’ } 3 ]; whereas K[Ph 2 P(O)NP(O)Ph 2 ] reacted with ReBr(CO) 5 to give K[Re 2 (CO) 6 {μ-Ph 2 P(O)NP(O)Ph 2 -κ 2 O,O′ }{Ph 2 P(O)NP(O)Ph 2 -κ 2 O,O′ } 2 ]. Other chalcogen ligands’ salts M[Ph 2 P(E)NP(E)Ph 2 ], E = Se and S, M = K and Li gave dirhenium carbonyls with bromido and Ph 2 P(E)NP(E)Ph 2 , E = Se or S bridges upon reaction with ReBr(CO) 5 .

Neutral Pentacoordinate Silicon(IV) Complexes with Silicon–Chalcogen (S, Se, Te) Bonds

The neutral pentacoordinate silicon(IV) complexes 1 (SiS2ONC skeleton), 2 (SiSeSONC), 3 (SiTeSONC), 6/9 (SiSe2O2C), 7 (SiSe2S2C), and 8/10 (SiSe4C) were synthesized and structurally characterized by using single-crystal X-ray diffraction and multinuclear solid-state and solution-state (except for 6-9) NMR spectroscopy. With the synthesis of compounds 1-3 and 6-10, it has been demonstrated that pentacoordinate silicon compounds with soft chalcogen ligand atoms (S, Se, Te) can be stable in the solid state and in solution.

Cover Picture: Neutral Pentacoordinate Silicon(IV) Complexes with Silicon–Chalcogen (S, Se, Te) Bonds (Chem. Eur. J. 30/2009)

Hard meets soft in pentacoordinate silicon(IV) complexes with soft chalcogen ligands that have been prepared and characterized by R. Tacke et al., as described in their Full Paper on page 7329 ff. These neutral pentacoordinate complexes are stable in the solid state and in solution.