Sulfoxide Ligands Research Articles

Crystal structure of catena-poly[[(dimethyl sulfoxide-κO)(pyridine-2,6-di-carboxyl-ato-κ(3) O,N,O')nickel(II)]-μ-pyrazine-κ(2) N:N'

The title coordination polymer, [Ni(C7H3NO4)(C4H4N2)(C2H6OS)] n , consists of [010] chains composed of Ni(II) ions linked by bis-monodentate-bridging pyrazine mol-ecules. Each of the two crystallographically distinct Ni(II) ions is located on a mirror plane and is additionally coordinated by a dimethyl sulfoxide (DMSO) ligand through the oxygen atom and by a tridentate 2,6-pyridine-di-carb-oxy-lic acid dianion through one of each of the carboxyl-ate oxygen atoms and the pyridine nitro-gen atom, leading to a distorted octa-hedral coordination environment. The title structure exhibits an inter-esting complementarity between coordinative bonding and π-π stacking where the Ni-Ni distance of 7.0296 (4) Å across bridging pyrazine ligands allows the pyridine moieties on two adjacent chains to inter-digitate at halfway of the Ni-Ni distance, resulting in π-π stacking between pyridine moieties with a centroid-to-plane distance of 3.5148 (2) Å. The double-chain thus formed also exhibits C-H⋯π inter-actions between pyridine C-H groups on one chain and pyrazine mol-ecules on the other chain. As a result, the inter-ior of the double-chain structure is dominated by π-π stacking and C-H⋯ π inter-actions, while the space between the double-chains is occupied by a C-H⋯O hydrogen-bonding network involving DMSO ligands and carboxyl-ate groups located on the exterior of the double-chains. This separation of dissimilar inter-actions in the inter-ior and exterior of the double-chains further stabilizes the crystal structure.

Hexakis(dimethyl sulfoxide-κO)zincmer-aquatris(dimethyl sulfoxide-κO)(ethanol-κO)[octadecatungstodiphosphato(V)-κO]zincate(II)–dimethyl sulfoxide–ethanol–water (2/4/2/3)

In the title compound, [Zn(C2H6OS)6]2[Zn(α-P2W18O62)(C2H5OH)(C2H6OS)3(H2O)]·2C2H6OS·C2H5OH·1.5H2O, there are two types of ZnIIcomplex ions. In the [Zn(α-P2W18O62)(C2H5OH)(C2H6OS)3(H2O)]4−anion, the ZnIIcation is coordinated by a Wells–Dawson polyanion [α-P2W18O62]6−(POM)viaa terminal O atom, three dimethyl sulfoxide (DMSO) ligands, one ethanol ligand and one water ligand in a distorted octahedral geometry. The two independent [Zn(C2H6OS)6]2+cations exhibit similar distorted octahedral coordination spheres, and both ZnIIcations are coordinated by six DMSO ligands. The crystal packing is governed by extensive O—H...O hydrogen bonds and weak C—H...O hydrogen bonds, forming a three-dimensional supramolecular structure. The S atoms of some DMSO molecules are disordered over two positions with different site-occupancy ratios.

Substrate-Dependent Mechanistic Divergence in Decarboxylative Heck Reaction at Room Temperature.

We report herein a Pd(II)-catalyzed Heck-type coupling between arene carboxylic acids and alkenes at room temperature. Mechanistically, the reaction proceeds in two distinct pathways where electron-rich substrates undergo a palladium(II)-catalyzed decarboxylation and electron-deficient substrates proceed through silver(I)-assisted decarboxylation. Dimethyl sulfoxide (DMSO) or sulfide ligands have positive and negative roles in the reaction outcome, respectively. The present protocol is combined for the peptide modification under mild reaction conditions.

Mechanistic Study of the Direct Intramolecular Allylic Amination Reaction Catalyzed by Palladium(II)

DFT calculations (PBE1PBE/6-31G(d,p), Def2-TZVPPD) were performed to study the intramolecular C–H amination of an unsaturated carbamate catalyzed by [Pd(LL)(OAc)2] (2), where LL is the bis(sulfoxide) ligand PhS(O)(CH2)2S(O)Ph. The coordination takes place by an associative path over a trigonal-bipyramidal transition state. The LL ligand undergoes a coordination shift from κ2S,S to κ1S, leaving an open position for binding of the substrate (C═C). In the next step, the C–H activation, the transition state for the hydrogen abstraction from the substrate to form the σ-allyl complex has an energy of 124.0 kJ mol–1, which is the highest energy in the whole mechanism (TOF-determining transition state). The σ-allyl converts easily in the π-allyl, the acetic acid molecule leaving the coordination sphere. The remaining acetate receives the second hydrogen from the NH group, while the newly formed acetic acid molecule is replaced by the pendant arm of the LL ligand, and the cyclization takes place (nucleophilic atta...

Crystal structures of two erbium(III) complexes with 4-amino-benzoic acid and 4-chloro-3-nitro-benzoic acid.

The crystal structures of two erbium(III) complexes with 4-amino-benzoic acid (4-ABAH), namely bis-(μ2-4-amino-benzoato-κ(2) O:O')bis-[bis(4-amino-benzoato-κ(2) O,O')di-aqua-erbium(III)] dihydrate, [Er2(C7H6NO2)6(H2O)4]·2H2O, (I), and 4-chloro-3-nitro-benzoic acid (CLNBAH), namely poly[hexa-kis-(μ2-4-chloro-3-nitro-benzoato-κ(2) O:O')bis-(dimethyl sulfoxide-κO)dierbium(III)], [Er2(C7H3ClNO4)6(C2H6OS)2] n , (II), have been determined. In the structure of solvatomorphic compound (I), the symmetry-related irregular ErO8 coordination polyhedra in the discrete centrosymmetric dinuclear complex comprise two monodentate water mol-ecules and six carboxyl-ate O-atom donors, four from two bidentate carboxyl-ate O,O'-chelate groups and two from the bis-monodentate O:O'-bridging group of the third 4-ABA anion. The Er-O bond-length range is 2.232 (3)-2.478 (3) Å and the Er⋯Er separation in the dinuclear complex unit is 4.7527 (4) Å. One of the coordinating water mol-ecules is involved in an intra-unit O-H⋯O hydrogen-bonding association with an inversion-related carboxyl-ate O-atom acceptor. In contrast, the anhydrous compound (II) is polymeric, based on centrosymmetric dinuclear repeat units comprising ErO7 coordination polyhedra which involve four O-atom donors from two bidentate O:O'-bridging carboxyl-ate groups, one O-atom donor from the monodentate dimethyl sulfoxide ligand and two O-atom donors from the third bridging CLNBA anion. The latter provides the inter-unit link in the one-dimensional coordination polymer extending along [100]. The Er-O bond-length range in (II) is 2.239 (6)-2.348 (6) Å and the Er⋯Er separation within the dinuclear unit is 4.4620 (6) Å. In the crystal of (I), extensive inter-dimer O-H⋯O and N-H⋯O hydrogen-bonding inter-actions involving both the coordinating water mol-ecules and the solvent water mol-ecules, as well as the amine groups of the 4-ABA anions, give an overall three-dimensional network structure. Within this structure are also weak π-π ring inter-actions between two of the coordinating ligands [ring-centroid separations = 3.676 (3) and 3.711 (2) Å]. With (II), only weak intra-polymer C-H⋯O, C-H⋯Cl and C-H⋯S inter-actions are present.

Crystal structure of di-μ-isobutyrato-κ(4) O:O'-bis-[cis-di-chlorido-(dimethyl sulfoxide-κS)rhenium(III)

The title compound, [Re2(C3H7COO)2Cl4{(CH3)2SO}2], comprises binuclear complex mol-ecules [Re-Re = 2.24502 (13) Å] involving cis-oriented double carboxyl-ate bridges, four equatorial chloride ions and two weakly bonded O atoms from dimethyl sulfoxide ligands in the axial positions at the Re(III) atoms. In the crystal, mol-ecules are linked into corrugated layers parallel to (101) by very weak C-H⋯Cl and C-H⋯O hydrogen-bonding inter-actions. C-H⋯Cl hydrogen bonding provides the links between layers to consolidate a three-dimensional framework.

Crystal structure of cis,fac-{N,N-bis-[(pyridin-2-yl)meth-yl]methyl-amine-κ(3) N,N',N''}di-chlorido-(dimethyl sulfoxide-κS)ruthenium(II).

The reaction of di­chlorido­tetra­kis­(dimethyl sulfoxide)­ruthen­ium(II) with N,N-bis[(pyridin-2-yl)meth­yl]methyl­amine aff­ords the title complex, [RuCl2(C13H15N3)(C2H6OS)]. The asymmetric unit contains a well-ordered complex mol­ecule. The N,N-bis­[(pyridin-2-yl)meth­yl]methyl­amine (bpma) ligand binds the cation through its two pyridyl N atoms and one aliphatic N atom in a facial manner. The coordination sphere of the low-spin d 6 RuII is distorted octahedral. The dimethyl sulfoxide (dmso) ligand coordinates to the cation through its S atom and is cis to the aliphatic N atom. The two chloride ligands occupy the remaining sites. The bpma ligand is folded with the dihedral angle between the mean planes passing through its two pyridine rings being 64.55 (8)°. The two N—Ru—N bite angles of the ligand at 81.70 (7) and 82.34 (8)° illustrate the distorted octa­hedral coordination geometry of the RuII cation. Two neighboring molecules are weakly associated through mutual intermolecular hydrogen bonding involving the O atom and one of the methyl groups of the dmso ligand. One of the chloride ligands is also weakly hydrogen bonded to a pyridyl H atom of another molecule.

Asymmetric Oxidation Synthesis of Modafinil Acid by Use of a Recyclable Chiral‐at‐Metal Complex

AbstractThe enantioselective oxidation synthesis of chiral modafinil acid and its analogues with high enantiomeric excess has been developed by means of a chiral‐at‐metal strategy. Treatment of ruthenium complexes cis‐[Ru(bpy)2Cl2] or Δ/Λ‐[Ru(bpy)2(MeCN)2](PF6)2 (bpy is 2,2′‐bipyridine) with the appropriate prochiral thioether ligands afforded thioether complexes rac‐1, Δ/Λ‐1, rac‐2, Δ/Λ‐2, rac‐3, and Δ/Λ‐3. Diastereoselective oxidation of the thioether complexes in situ produced the corresponding sulfoxide complexes rac‐1a, Δ/Λ‐1a, rac‐2a, Δ/Λ‐2a, rac‐3a, and Δ/Λ‐3a. The configuration at the metal center in each case is stable during the coordination and oxidation reactions, and dictates the chirality of the sulfoxide ligand in the oxidation process. The chiral modafinil acids were obtained with ee values greater than 98 % upon their removal from the corresponding sulfoxide complexes in the presence of TFA/MeCN. Moreover, the chiral ruthenium precursors Δ/Λ‐[Ru(bpy)2(MeCN)2](PF6)2 are recyclable and reusable with complete retention of the configurations.

ChemInform Abstract: Development of Chiral Sulfoxide Ligands for Asymmetric Catalysis

AbstractReview: 78 refs.

Preference for sulfoxide S- or O-bonding to 3d transition metals – DFT insights

Complexes of 3d transition metals with sulfoxide ligands bound by sulfur were searched on the Cambridge Structural Database. DFT calculations reproduced the experimental geometries and the lowest energy isomer (S or O bound) matched the experimentally observed one. Distances, Wiberg indices and charges (Mulliken, Atomic Polar Tensor and Natural Population Analysis) were compared, showing an elongation and weakening of the S–O bond with O-coordination. Metal charges became more positive with O-coordination, accompanied by a more negative sulfur charge. Examples of O-bound sulfoxides were studied for comparison. An Energy Decomposition Analysis was performed in a series of more relevant complexes, in order to compare the two isomers and identify the reason for the structural preference. In complexes with one S-bound sulfoxide, the attractive interaction terms (electrostatic and orbital) compensate the large Pauli repulsion by a larger amount in the S- than in the O-bound isomer. In the complex with O-bound sulfoxide this tendency was reversed by a very large reorganization energy (to bring fragments from their preferred geometry to the geometry they have in the complex). In the complexes with two ligands, S,S or O,O binding was preferred, and in one example they coexist. The mixed S,O coordination type led to a large orbital stabilization, but required large reorganization energies.

Development of chiral sulfoxide ligands for asymmetric catalysis.

Nitrogen-, phosphorus-, and oxygen-based ligands with chiral backbones have been the historic workhorses of asymmetric transition-metal-catalyzed reactions. On the contrary, sulfoxides containing chirality at the sulfur atom have mainly been used as chiral auxiliaries for diastereoselective reactions. Despite several distinct advantages over traditional ligand scaffolds, such as the proximity of the chiral information to the metal center and the ability to switch between S and O coordination, these compounds have only recently emerged as a versatile class of chiral ligands. In this Review, we detail the history of the development of chiral sulfoxide ligands for asymmetric catalysis. We also provide brief descriptions of metal-sulfoxide bonding and strategies for the synthesis of enantiopure sulfoxides. Finally, insights into the future development of this underutilized ligand class are discussed.

Excited state dynamics and isomerization in ruthenium sulfoxide complexes.

Molecular photochromic compounds are those that interconvert between two isomeric forms with light. The two isomeric forms display distinct electronic and molecular structures and must not be in equilibrium with one another. These light-activated molecular switch compounds have found wide application in areas of study ranging from chemical biology to materials science, where conversion from one isomeric form to another by light prompts a response in the environment (e.g., protein or polymeric material). Certain ruthenium and osmium polypyridine sulfoxide complexes are photochromic. The mode of action is a phototriggered isomerization of the sulfoxide from S- to O-bonded. The change in ligation drastically alters both the spectroscopic and electrochemical properties of the metal complex. Our laboratory has pioneered the preparation and study of these complexes. In particular, we have applied femtosecond pump-probe spectroscopy to reveal excited state details of the isomerization mechanism. The data from numerous complexes allowed us to predict that the isomerization was nonadiabatic in nature, defined as occurring from a S-bonded triplet excited state (primarily metal-to-ligand charge transfer in character) to an O-bonded singlet ground state potential energy surface. This prediction was corroborated by high-level density functional theory calculations. An intriguing aspect of this reactivity is the coupling of nuclear motion to the electronic wave function and how this coupling affects motions productive for isomerization. In an effort to learn more about this coupling, we designed a project to examine phototriggered isomerization in bis-sulfoxide complexes. The goal of these studies was to determine whether certain complexes could be designed in which a single photon excitation event would prompt two sulfoxide isomerizations. We employed chelating sulfoxides in this study and found that both the nature of the chelate ring and the R group on the sulfoxide affect the photochemical reactivity. For example, this reactivity may be tuned such that two sulfoxide ligands isomerize sequentially following two successive excitations or that two sulfoxide ligands isomerize following a single excitation. This Account explains our understanding to date of this photochemistry.

Enantioselective syntheses of sulfoxides in octahedral ruthenium(II) complexes via a chiral-at-metal strategy.

The preparation of chiral 2-(alkylsulfinyl)phenol compounds by enantioselective coordination-oxidation of the thioether ruthenium complexes with a chiral-at-metal strategy has been developed. The enantiomerically pure sulfoxide complexes Δ-[Ru(bpy)2{(R)-LO-R}](PF6) (bpy is 2,2'-bipyridine, HLO-R is 2-(alkylsulfinyl)phenol, R = Me (Δ-1a), Et (Δ-2a), iPr (Δ-3a), Bn (Δ-4a), and Nap (Δ-5a)) and Λ-[Ru(bpy)2{(S)-LO-R}](PF6) (R = Me (Λ-1a), Et (Λ-2a), iPr (Λ-3a), Bn (Λ-4a), and Nap (Λ-5a)) have been synthesized by the reaction of Δ-[Ru(bpy)2(py)2](2+) or Λ-[Ru(bpy)2(py)2](2+) with the prochiral thioether ligands 2-(alkylthio)phenol (HL-R), followed by enantioselective oxidation with m-CPBA as oxidant. The X-ray crystallography was used to verify the stereochemistry of ruthenium complexes and sulfur atoms. The configurations of the ruthenium complexes are stable during the coordination and oxidation reactions. Moreover, the chiral sulfoxide ligands are enantioselectively generated by controlling of the configuration of ruthenium centers in the course of oxidation reaction. That is, the Λ configuration at the ruthenium center generates the S sulfoxide ligand; on the contrary, the Δ configuration of the ruthenium complex originates the R sulfoxide ligand. Acidolysis of Λ-[Ru(bpy)2{(R)-LO-R}](PF6) and Δ-[Ru(bpy)2{(S)-LO-R}](PF6) complexes in the presence of TFA-MeCN afforded the chiral ligands (R)-HLO-R and (S)-HLO-R in 96-99% ee values, respectively. Importantly, the chiral ruthenium complexes can be recycled as Δ/Λ-[Ru(bpy)2(MeCN)2](PF6)2 and reused in a next reaction cycle with complete retention of the configurations at ruthenium centers.

Synthesis and structure of iridium complexes [Ph3PR][trans-IrCl4(DMSO)2

The reaction of sodium chloroiridate with acetonyl-, cyanomethyl-, and 2-butenyltriphenylphosphonium chloride in dimethyl sulfoxide was used to synthesize ionic iridium complexes [Ph3PR][trans-IrCl4(DMSO)2] (R = CH2C(O)Me, CH2CN, CH2CH=CHMe). The phosphorus atoms in the [Ph3RP]+ cations have a slightly distorted tetrahedral coordination. The dimethyl sulfoxide ligand in the octahedral anions [trans-IrCl4(DMSO)2] is coordinated to metal via sulfur atoms.

Synthesis and characterization of water-soluble, heteronuclear ruthenium(III)/ferrocene complexes and their interactions with biomolecules

The reaction of Na[RuCl4(SO(CH3)2)2], 1, with one equivalent of FcCONHCH2C6H4N (Fc=FeC10H9), L1, FcCOOCH2CH2C3H3N2, L2, FcCOOC6H4N, L3, afforded the dinuclear species, Na[FcCONHCH2C6H4N[RuCl4(SO(CH3)2)]], RuL1, Na[FcCOOCH2CH2C3H3N2[RuCl4(SO(CH3)2)]], RuL2, Na[FcCOOC6H4N(RuCl4(SO(CH3)2))], RuL3, respectively, yielding, in each case, a ferrocene moiety bridged to a ruthenium center. The complexes were characterized by NMR, IR, and XRD (X-ray diffraction). The sulfoxide ligands are bonded to the metal through the sulfur atom. The complexes were evaluated for their biological activity with pBluescript DNA plasmid, and the protein BSA (bovine serum albumin). These reactions were monitored by XAS (X-ray absorption spectroscopy), EXAFS (extended X-ray Absorption Fine Structure), NMR, UV/visible, emission spectroscopy, and gel electrophoresis. Donor atoms from the biomolecules substitute for the chloride ligands in the parent complexes.

Crystal structure of di-μ-iodido-bis-[(dimethyl sulfoxide-κO)(tri-phenyl-phosphane-κP)copper(I)

The centrosymmetric dinuclear title compound, [Cu2I2(C2H6OS)2(C18H15P)2], represents the first example of a CuI complex ligated by an O-bound dimethyl sulfoxide ligand. In the crystal, the two tetrahedrally coordinated Cu(I) atoms are bridged by two μ2-iodido ligands in an almost symmetrical rhomboid geometry. The loose Cu⋯Cu contact of 2.9874 (8) Å is longer than the sum of the van der Waals radii of two Cu atoms (2.8 Å), excluding a significant cupriophilic inter-action in the actual dimer. C-H⋯O and C-H⋯I hydrogen bonding interactions as well as C-H⋯π(aryl) interactions stabilize the three-dimensional supramolecular network.

Synthesis and structure of the rhodium complex [Ph3MeP][RhBr4(DMSO)2-trans

The ionic complex, methyltriphenylphosphonium(I) trans-bis(dimethylsulfoxido)tetrabromorhodiate, was prepared by the reaction of sodium hexabromorhodiate with methyltriphenylphosphonium bromide in dimethyl sulfoxide and studied by X-ray diffraction. The phosphorus atom in the [Ph3MeP]+ cation has an almost undistorted tetragonal coordination (the CPC angles are 108.3(2)°–110.5(2)°, the P-C bonds are 1.779(6)–1.798(4) A). In the octahedral complex anion [RhBr4(DMSO)2-trans]−, the dimethyl sulfoxide ligands are coordinated by the sulfur atoms (Rh-S, 2.344(1), 2.336(1); Rh-Br, 2.4839(7)–2.4934(7) A; SRhS, 179.56(7)°; trans-BrRhBr, 179.30(3)°, 179.56(7)°) (CIF file CCDC no. 978748).

Enantioselective Oxidation of Thioethers to Sulfoxides by Means of a Structural Template with Chiral‐at‐Metal Ruthenium Complexes

AbstractTreatment of cis‐[Ru(bpy)2Cl2]⋅2 H2O or Δ/Λ‐[Ru(bpy)2(py)2]2+ (bpy=2,2′‐bipyridine, py=pyridine) with the prochiral thioether ligands 2‐alkylthiobenzoic acid (HOSR) produces the corresponding thioether complexes rac‐[Ru(bpy)2(OSR)](PF6) (R=Me (rac‐1), iPr (rac‐2), 2‐benzylthiobenzonate (Bn) (rac‐3)) and Δ/Λ‐[Ru(bpy)2(OSR)](PF6) (R=Me (Δ‐1/Λ‐1), iPr (Δ‐2/Λ‐2), Bn (Δ‐3/Λ‐3)) with retention of the configurations at chiral metal centers. In situ oxidation of the thioether complexes by meta‐chloroperoxybenzoic acid provides the corresponding sulfoxide complexes rac‐[Ru(bpy)2(OSOR)](PF6) (OSOR is 2‐alkylsulfinylbenzonate, R=Me (rac‐1 a), iPr (rac‐2 a), Bn (rac‐3 a)), Δ‐[Ru(bpy)2{(R)‐OSOR}](PF6) (R=Me (Δ‐1 a), iPr (Δ‐2 a), Bn (Δ‐3 a)), and Λ‐[Ru(bpy)2{(S)‐OSOR}](PF6) (R=Me (Λ‐1 a), iPr (Λ‐2 a), Bn (Λ‐3 a)) in yields of 95 % with 98 % ee values. The absolute configurations at the metal centers and sulfur atoms were determined by means of X‐ray crystallography. The results indicate that the configurations of the metal centers are retained and have the function of controlling sulfoxide chirality during the oxidation process. The Δ metal‐centered configuration enantioselectively generates an R‐configuration sulfoxide, and the Λ configuration enantioselectively forms an S‐configuration sulfoxide in the course of the in situ oxidation reaction, thereby resulting in a predetermined chirality of the sulfoxide ligands. The predetermined chirality of sulfoxides (S)‐HOSOR and (R)‐HOSOR were obtained by the treatments of the corresponding sulfoxide complexes Δ‐[Ru(bpy)2{(R)‐OSOR}](PF6) and Λ‐[Ru(bpy)2{(S)‐OSOR}](PF6) with trifluoroacetic acid in yields of 90 % with 83.5–92.9 % ee values.

Crystal structure of chlorido-penta-kis(dimethyl sulfoxide-κO)chromium(III) dichloride.

In the complex cation of the title salt, [CrCl(C2H6OS)5]Cl2, the CrIII ion is coordinated by one chloride ligand and five O atoms from dimethyl sulfoxide (DMSO) ligands, leading to a slightly distorted octa­hedral coordination environment [O—Cr—O angles range from 86.69 (16) to 92.87 (16)°]. In the crystal, complex cations are arranged in hexa­gonally packed rows parallel to [010], with the chloride counter-anions situated in between. The inter­actions between cations and anions are mainly ionic in nature.

Structure and catalytic activity of the ruthenium(I) sawhorse-type complex [Ru2{μ,η2-CF3(CF2)5COO}2(DMSO)2(CO)4

The title compound, cis-di-μ-perfluoroheptanoato-κ(4)O:O'-bis[dicarbonyl(dimethyl sulfoxide-κS)ruthenium(I)](Ru-Ru), [Ru2(C7F13O2)2(C2H6OS)2(CO)4], is a sawhorse-type dinuclear ruthenium complex with two bridging perfluoroheptanoate ligands, and with two dimethyl sulfoxide (DMSO) ligands in the axial positions coordinating via the S atoms. It is a new example of a compound with an aliphatic fluorinated carboxylate ligand. The Ru-Ru bond distance of 2.6908 (3) Å indicates a direct Ru-Ru interaction. The compound is an active catalyst in transvinylation of propionic acid with vinyl acetate.