Propane Ligands Research Articles

Selective Rhodium‐Catalyzed Reduction of Tertiary Amides in Amino Acid Esters and Peptides

AbstractEfficient reduction of the tertiary amide bond in amino acid derivatives and peptides is described. Functional group selectivity has been achieved by applying a commercially available rhodium precursor and bis(diphenylphosphino)propane (dppp) ligand together with phenyl silane as a reductant. This methodology allows for specific reductive derivatization of biologically interesting peptides and offers straightforward access to a variety of novel peptide derivatives for chemical biology studies and potential pharmaceutical applications. The catalytic system tolerates a variety of functional groups including secondary amides, ester, nitrile, thiomethyl, and hydroxy groups. This convenient hydrosilylation reaction proceeds at ambient conditions and is operationally safe because no air‐sensitive reagents or highly reactive metal hydrides are needed.

Selective rhodium-catalyzed reduction of tertiary amides in amino acid esters and peptides.

Efficient reduction of the tertiary amide bond in amino acid derivatives and peptides is described. Functional group selectivity has been achieved by applying a commercially available rhodium precursor and bis(diphenylphosphino)propane (dppp) ligand together with phenyl silane as a reductant. This methodology allows for specific reductive derivatization of biologically interesting peptides and offers straightforward access to a variety of novel peptide derivatives for chemical biology studies and potential pharmaceutical applications. The catalytic system tolerates a variety of functional groups including secondary amides, ester, nitrile, thiomethyl, and hydroxy groups. This convenient hydrosilylation reaction proceeds at ambient conditions and is operationally safe because no air-sensitive reagents or highly reactive metal hydrides are needed.

Slow magnetization relaxation in a one-dimensional chiral dysprosium-carboxylate compound constructed from the cubic Dy4(μ3-OH)4 clusters

A chiral dysprosium-carboxylate coordination polymer [Dy4(μ3-OH)4(L)8]n (1) with the 2-(3-chlorophenoxy)propionate (L−) ligand has been synthesized and characterized. Four DyIII ions are linked by four μ3-OH groups to generate a cubic Dy4(μ3-OH)4 unit, which is further linked by the L− ligands to give a one-dimensional (1D) chain based on the cubic Dy4(μ3-OH)4 secondary building units. Magnetic studies show that 1 exhibits a slow magnetic relaxation under a zero direct-current filed, which is rarely observed for the 1D Dy-based coordination polymers.

Crystal structure of [1,3-bis-(di-phenyl-phosphan-yl)propane-κ(2) P,P'](N,N'-di-methyl-thio-urea-κS)(thio-cyanato-κN)copper(I).

The asymmetric unit of the title compound, [Cu(NCS)(C3H8N2S)(C27H26P2)], contains two independent mononuclear complex mol­ecules. In each, the CuI ion exhibits a distorted tetra­hedral geometry by coordination with two P atoms from one 1,3-bis(diphenylphosphino)propane (dppm) ligand, one terminal S atom of one N,N′-di­methyl­thio­urea (dmtu) ligand and one terminal N atom of the thio­cyanato ligand. The dppp ligand is involved in a bidentate coordination mode with the CuI ion, forming a six-membered CuP2C3 ring. In both mol­ecules, the coordination of the dmtu ligand is further stabilized by an intra­molecular N—H⋯N hydrogen bond with an S(6) graph-set motif. In the crystal, mol­ecules are linked by N—H⋯S hydrogen bonds forming a zigzag chain along the a-axis direction. In one independent mol­ecule, one of the phenyl rings of the dppp ligand is disordered over two sites with refined occupancies 0.639 (11):0.361 (11) and this corresponds with a mutual disorder of the dmtu ligand in the other independent mol­ecule giving the same ratio of refined occupancies. The structure was refined as a two-component inversion twin.

Mechanistic study on the regioselectivity of Co-catalyzed hydroacylation of 1,3-dienes

Abstract Density functional theory (DFT) method was used to explore the origin of the regioselectivity of Co-catalyzed hydroacylation of 1,3-dienes. The reaction of 2-methyl-1,3-butadiene and benzaldehyde with 1,3-bis(diphenylphosphino)propane ligand was chosen as the model reaction. The energies of the intermediates and transition states in the stages of oxidative cyclization, β -H elimination and C-H reductive elimination were investigated. Computational results show that β -H elimination is the rate-determining step for the whole catalytic cycle. C1-Selective oxidative cyclization is favored over C4-selective oxidative cyclization. Besides, C4-selective oxidative cyclization is kinetically disfavored than all the steps in C1-hydroacylation mechanisms, consistent with the experimentally obtained C1-selective hydroacylation products. Analyzing the reason for such observation, we suggest that both electronic and steric effects contribute to the C1-selectivity. On the electronic aspect, C1 is more electron rich than C4 due to the methyl group on C2, which makes the electrophilic attack of aldehyde carbon on C1 more favorable. On the steric aspect, the methyl group locates farther from the ligands in the transition state of C1-selective oxidative cyclization than in that of C4-selective oxidative cyclization.

Structural studies of some rhodium(III) acyl complexes containing bidentate phosphines

Acyl complexes of rhodium(III) with chelating diphosphine ligands are well known for their stability toward decarbonylation. This stability has allowed us to synthesize and structurally characterize a series of ten related complexes of the type Rh(diphosphine)(COR)I2. All ten display the same square pyramidal geometry with the acyl group in the apical position. The orientation of the acyl ligand is determined by both steric factors and CH⋯O hydrogen bonding between the acyl oxygen and C–H groups on the diphosphine ligand. Results indicate that bis(diphenylphosphino)benzene is significantly more sterically demanding and less electron donating than the bis(diphenylphosphino)propane and bis(diisopropylphosphino)propane ligands.

Copper(II) Coordination Polymers Generated from 1,3‐Bis(4‐pyridyl)propane: Synthesis, Structures, and Spectroscopic Studies

AbstractThis paper describes the synthesis and structural characterization of two new one‐dimensional coordination polymers involving 1,3‐bis(4‐pyridyl)propane ligand named {(μ‐NCS)2[Cu(bpp)]·dmf}n (1) and {[Cu(mebpy)(bpp)(dmso)](ClO4)2·dmso}n (2) (bpp = 1,3‐bis(4‐pyridyl)propane and mebpy = 4,4'‐dimethyl‐2,2'‐bipyridine). These compounds were characterized by means of elemental analysis, thermal analysis (TG/DTA), vibrational spectroscopy (IR and Raman) and had their structures determined by single‐crystal X‐ray diffraction analysis. Compound 1 consists of CuN4 coordination spheres with bpp ligands in the unusual GG conformation coordinated in bridges between CuII centers to form a wavelike 1‐D coordination polymer. On the other hand, in compound 2 the bpp ligand adopts the TT conformation in bridging mode extending the 1D cationic polymeric chain.

Phenyl-functionalized Diiron Propanedithiolate Complexes with 1,3-Bis(diphenylphosphine)propane Ligand: Chelated and Bridged Isomers as Proton-reduction Catalysts

Reaction of the diiron propanedithiolate complex [μ-(SCH2)2CHC6H5]Fe2(CO)6 (A) with 1,3-bis(diphenylphosphine)propane (dppp) in refluxing xylene yielded a chelated complex [(μ-SCH2)2CHC6H5]Fe2(CO)4(κ2-dppp) (1) and a bridged isomer [(μ-SCH2)2CHC6H5]Fe2(CO)4(μ-dppp) (2), while in refluxing toluene or in hot MeCN in the presence of Me3NO·2H2O gave the chelated isomer 1 as the major or sole product. Protonation of complex 1 upon addition of HBF4·Et2O gave a bridging hydride (μ-H)[(μ-SCH2)2CHC6H5]Fe2(CO)4(κ2-dppp)(BF4) (3). The structures of all complexes were fully characterized by spectroscopic methods and for complexes 1 and 2 by X-ray crystallography. In the solid state, the chelated complex adopts an apical–basal diphosphine arrangement and exhibits a six-membered ring in approximate chair conformation. The bridged isomer presents an expected cisoid dibasal geometry and the bond length of Fe–Fe is longer than that in chelated isomer, reaching to 2.61 Ǻ. The electrochemical investigation of both isomers in MeCN-[NBu4][PF6] in the presence of HBF4 showed that the catalytic efficiency of the bridged isomer is no less than that of the chelated isomer but better than that of the analogue [(μ-SCH2)2CHC6H5]Fe2(CO)4(μ-dppm). Interestingly, isomer 1 was converted to isomer 2 in refluxing xylene. An electron-transfer-catalyzed isomerization between one isomer and the other was not observed.

Synthesis and structural characterizations of mononuclear zinc complexes with an unprecedented terminal bidentate coordination mode of the flexible 1,1,3,3-tetrakis(3,5-dimethyl-1-pyrazolyl)propane ligand

Four new complexes, [Zn(tdmpp)2H2O](ClO4)2·H2O (1), [Zn(NCS)Cl(tdmpp)] (2), [ZnI2(tdmpp)] (3) and [ZnCl2(tdmpp)] (4), were prepared and structurally characterized. The 1,1,3,3-tetrakis(3,5-dimethyl-1-pyrazolyl)propane (tdmpp) ligand in the above compounds represents the first example of a flexible tetradentate nitrogen donor ligand in which the ligand is coordinated to the metal center as a terminal chelating ligand. The perchlorate ion in 1 acts as an uncoordinated anion, while in 2 the SCN and chlorine ligands and in 3 the iodine ligand participate in the coordination sphere of the metal center. The coordination ability of these anions and significant effects of non-covalent C–H⋯π and C–H⋯X (X=O, Cl and I) interactions play a major role in the crystal packing of these compounds. In 1, the zinc atom adopts a distorted trigonal bipyramidal geometry and the [Zn(tdmpp)2H2O]2+ cations are linked by C–H⋯O hydrogen bonds to give a 1-D chain structure. In the structures of 2 and 3, the mononuclear neutral molecules form a 1-D chain structure along the b-axis through C–H⋯Cl and C–H⋯I hydrogen bonds, respectively. These chains are linked by intermolecular C–H⋯π interactions to generate a three-dimensional network. Crystals of compound 4 were not suitable for X-ray diffraction studies and therefore its structure could only be investigated in the solid state by infrared spectroscopy and elemental analysis.

Synthesis, Structure, Luminescest and Thermal Stable Properties of a Silver(I) Coordination Polymer Constructed from 2,4-Dichlorophenoxyacetic Acid and 1,3-Bis(4-Pyridyl) Propane Ligands

A novel complex of [Ag (poa)(bpp)] n (poa:2,4-Dichlorophenoxyacetic acid;bpp: 1,3-Bis (4-pyridyl) propane) was synthesized and characterized by elemental analysis, IR, X-ray single crystal diffraction. The title complex belongs to Monoclinic system with space group P21/c,a=8.849(4)Å,b=26.654(13)Å,c=9.821(5)Å,α=90°,β=111.257(8)°,γ=90°,V=2158.7(17)Å3,Z=4,Dc=1.619 g/cm3,μ=1.206 mm-1,F(000)=1056. Final indices isR=0.0331,wR=0.0851. Therm al stability and luminescent property of compound have also been nvestigated.

Synthesis, crystal structure and thermal decomposition kinetics of yttrium propionate

Yttrium propionate, Y2(CH3CH2COO)6·xH2O, has been used as a precursor in the preparation of Y2O3 and YBa2Cu3O7−x thin films. The molecular structure of this precursor was determined by X-ray diffraction on single crystals, in good agreement with the formula calculated from the thermogravimetric analysis data. The molecular structure consists of a bimetallic complex with two Y atoms linked by two propionate groups in a bridging bimetallic tridentate fashion, and each metal bearing an extra two monometallic bidentate propionate ligands. The thermal decomposition was studied using the thermogravimetry–differential thermal analysis and mass spectrometry (TG–DTA–MS), in inert atmosphere. The influence of the different heating rates, such as 5, 7.5, 10, 15 and 20°C/min on the thermal behaviour of yttrium propionate was investigated. The X-ray diffraction pattern on the precursor powder heat treated under nitrogen has shown that the final decomposition product of [Y2(CH3CH2COO)6·4H2O]·H2O is Y2O3. The activation energy, as a kinetic parameter, was determined by using both Kissinger and Friedman methods for the decomposition process.

Synthesis and Characterization of Gold Clusters Ligated with 1,3-Bis(dicyclohexylphosphino)propane.

In this multidisciplinary study the chemical reduction synthesis of novel gold clusters in solution was combined with high-resolution analytical mass spectrometry (MS) to gain insight into the composition of the gold clusters and how their size, ionic charge state, and ligand substitution influences their gas-phase fragmentation pathways. Ultrasmall cationic gold clusters ligated with 1,3-bis(dicyclohexylphosphino)propane (dcpp) were synthesized for the first time and introduced into the gas phase using electrospray ionization (ESI). Mass-selected cluster ions were fragmented by employing collision-induced dissociation (CID) and the product ions were analyzed using MS. The solutions were found to contain the multiply charged cationic gold clusters Au9 L4 3+ , Au13 L5 3+ , Au6 L3 2+ , Au8 L3 2+ , and Au10 L4 2+ (L=dcpp). The gas-phase fragmentation pathways of these cluster ions were examined systematically by employing CID combined with MS. In addition, CID experiments were performed on related gold clusters of the same size and ionic charge state but capped with 1,3-bis(diphenylphosphino)propane (dppp) ligands containing phenyl functional groups at the two phosphine centers instead of cyclohexane rings. It is shown that this relatively small change in the molecular substitution of the two phosphine centers in diphosphine ligands (C6 H11 versus C6 H5 ) exerts a pronounced influence on the size of the species that are preferentially formed in solution during reduction synthesis as well as the gas-phase fragmentation channels of otherwise identical gold cluster ions. The mass spectrometry results indicate that in addition to the length of the alkyl chain between the two phosphine centers, the substituents at the phosphine centers also play a crucial role in determining the composition, size, and stability of diphosphine-ligated gold clusters synthesized in solution.

Bis[μ-1,3-bis(diphenylphosphanyl)propane-κ2P:P′]digold(I) tetrachloridonickelate(II) diethyl ether monosolvate

The title compound, [Au2(C27H26P2)2][NiCl4]·C4H10O, consists of a digold(I) complex cation, an [NiCl4]2− complex anion and a diethyl ether solvent mol­ecule. Two 1,3-bis­(di­phenyl­phosphan­yl)propane (dppp) ligands bridge two AuI atoms, forming a metallacycle in which each of the AuI atoms is coordinated in a slightly distorted linear environment by two P atoms. In the complex anion, the NiII atom is coordinated by four chloride ligands in a distorted tetra­hedral geometry. The complex cation and the complex anion form a cation–anion pair through two Au⋯Cl contacts of 3.040 (1) and 3.021 (2) Å. One of the phenyl groups of the dppp ligand is disordered over two positions with equal occupancies.

New 3D supramolecular networks built from 1D and 2D frameworks via π–π and H-bonding interactions: Topology and catalytic properties

Two new metal-organic frameworks, {[Zn(dpe)(μ-OOCCH3)2](H2O)}n (1) and {[Zn3(dpe)4(μ-OOCC2H5)4](dpe)(ClO4)2}n (2) (dpe=1,2-bis(4-pyridyl)ethene), have been prepared and investigated. Their structures were determined by X-ray crystallography. The different structures of both compounds indicate that the different steric constraints for a methyl group (acetato, compound 1) and an ethyl group (propionato, compound 2), as well as the counteranion effects (ClO4− for 2), play an important role in the formation and structure of these coordination polymers. Compound 1 exhibits a 1D zig–zag polymeric chain based on mononuclear secondary building units. The replacement of the acetate by propionate ligands, in the presence of additional ClO4− during the synthesis procedure, gives rise to a 2D network that is assembled from trinuclear secondary building units (compound 2). In addition, both compounds are further stabilized by π–π interactions and by hydrogen bonds to form intricate supramolecular frameworks. The 1D (1) and 2D (2) networks exhibit voids that contain guest water molecules for compound 1 and perchlorate/dpe for compound 2. Both coordination compounds have been structurally characterized and the thermal stability, potential cation-exchange and selected catalytic properties have been investigated. Interestingly, both Zn(II) compounds act as active heterogeneous catalysts for the high-yield cyanosilylation of acetaldehyde in dichloromethane and show highly size-selective properties for the substrate benzaldehyde. The metal sites in each compound have been studied in some more detail by using doped species with Mn(II) and Cu(II) and the EPR properties.

New rare-topology [Cu4] cluster coordination polymer employing 2-(oxyimino)propionate as a ligand

Abstract The reported compound, {Na2[Cu4(HCOO)2(pa)4(CH3OH)] · CH3OH} n (1, H2pa = 2-(hydroxyimino)propionic acid), is a sodium salt of an anionic coordination polymer, comprising rare-topology tetranuclear cluster units, linked through Cu–O bonds to form a polymeric chain. Each cluster unit comprises four Cu2+ cations, chelating 2-(oxyimino)propionate ligands, two formate ligands and one terminal methanol ligand. The neighbouring polymeric chains contact through O–H…O hydrogen bonds and are interconnected by Na–O coordination bonds to form a three-dimensional network.

Synthetic, Crystallographic, and Computational Study of Copper(II) Complexes of Ethylenediaminetetracarboxylate Ligands

Copper(II) complexes of hexadentate ethylenediaminetetracarboxylic acid type ligands H(4)eda3p and H(4)eddadp (H(4)eda3p = ethylenediamine-N-acetic-N,N',N'-tri-3-propionic acid; H(4)eddadp = ethylenediamine-N,N'-diacetic-N,N'-di-3-propionic acid) have been prepared. An octahedral trans(O(6)) geometry (two propionate ligands coordinated in axial positions) has been established crystallographically for the Ba[Cu(eda3p)]·8H(2)O compound, while Ba[Cu(eddadp)]·8H(2)O is proposed to adopt a trans(O(5)) geometry (two axial acetates) on the basis of density functional theory calculations and comparisons of IR and UV-vis spectral data. Experimental and computed structural data correlating similar copper(II) chelate complexes have been used to better understand the isomerism and departure from regular octahedral geometry within the series. The in-plane O-Cu-N chelate angles show the smallest deviation from the ideal octahedral value of 90°, and hence the lowest strain, for the eddadp complex with two equatorial β-propionate rings. A linear dependence between tetragonality and the number of five-membered rings has been established. A natural bonding orbital analysis of the series of complexes is also presented.

Synthesis, characterization, and luminescent properties of a series of silver(I) complexes with organic carboxylic acid and 1,3-bis(4-pyridyl)propane ligands

The reaction of AgNO3 with combinations of 1,3-bis(4-pyridyl)propane (bpp), pyridine-3,5-dicarboxylic acid (H2pdc), oxybis(benzoic acid) (H2oba), and 4,4′-oxidiphthalic acid (H4odpt) in aqueous alcohol/ammonia at room temperature produces crystals of [Ag2(bpp)2](pdc)·8H2O, [Ag2(bpp)2(H2O)](oba)·5H2O, and [Ag2(bpp)2(H2O)2](odpt)·2H2O. All three complexes consist of 1D infinite silver-bpp cationic chains, interspersed with organic carboxylate anions that provide charge compensation in the crystal structures. The lattice water molecules are situated among the framework of the crystal structure and show rich hydrogen-bonding interactions, which serve to orientate the organic carboxylate anions in the crystal packing, while the presence of Ag···N and Ag···Ag contacts strengthens the frameworks. The luminescent properties of the complexes have been investigated.

A single-molecule magnet featuring a parallelogram [Dy4(OCH2–)4] core and two magnetic relaxation processes

An alkoxido-bridged tetranuclear Dy(iii) complex, [Dy4(H3L)2(OAc)6]·2EtOH {, H6L = 1,3-bis[tris(hydroxymethyl)methylamino]propane}, has been solvothermally synthesized and characterized. An X-ray crystallographic study revealed that complex possesses a novel "parallelogram" [Dy4(OCH2-)4] core, and a new binding mode η(3):η(3):η(1):η(1):η(1):η(2):μ(4) of the Bis-tris propane ligand was observed. Magnetic investigations indicated that it is a single-molecule magnet (SMM), showing two distinct magnetic relaxation processes with the energy barriers of 44 K and 107 K, respectively. Such a two-step magnetic relaxation process could be well described by the sum of two modified Debye functions.

Temperature, Cooling Rate, and Additive-Controlled Supramolecular Isomerism in Four Pb(II) Coordination Polymers with an in Situ Ligand Transformation Reaction

Solvothermal reactions of Pb(Ac)2 with a new flexible 1,3-bis(4-pyridyl-3-cyano)propane (1, BPCP) ligand under different synthesis conditions via an in situ ligand transformation reaction produced three true coordination polymorphs, namely, [PbL2–]n (for 2 and 3) and [Pb3L2–3]n (4), as well as their polymorphic framework [(Pb2L2–)·2H2O]n (5) (H2L = 1,3-bis(4-pyridyl-3-carboxyl)propane). These compounds were characterized by elemental analysis, IR, TG, PXRD, and single-crystal X-ray diffraction. In these compounds, the L2–ligand exhibits different coordination conformations and modes tuned by different synthesis conditions, including reaction temperature, cooling rate, and additive, and constructs various architectures by bridging a variety of building units. Polymorphs 2 and 3 display a 3D framework with 1D channels built up from dinuclear ringlike [Pb2L2–2] units and dinuclear semi-ring-like [Pb2L2–] units, respectively. Polymorph 4 also features a 3D architecture constructed from dinuclear ringlike [Pb2...

Hydrothermal Synthesis, Crystal Structures and Fluorescent Properties of Two Complexes Based on 1,2-Phenylenedioxydiacetic Acid and Polypyridyl Ligands

Hydrothermal reactions of flexible 1,2-phenylenedioxydiacetic acid (H2pda) with zinc nitrate or cadmium nitrate in the presence of auxiliary 4,4′-bypyridine (bpy) or 1,3-bis(4-pyridyl)propane (bpp) ligands gave rise to two coordination polymers, {[Cd2(pda)2(bpy)(H2O)2]·4H2O}n (1) and [Zn(pda)(bpp)]n (2). The polymers were characterized by elemental analysis, IR, TG, and single-crystal X-ray diffraction methods. Compound 1 shows 1D ribbon structure and compound 2 displays twofold parallel interpenetrated 2D → 2D architecture. The different conformations of pda anions in these two compounds are mainly induced by different metal coordination configurations in compound 1 and 2. In addition, the photoluminescence emission of 1 and 2 has been investigated in the solid state at room temperature.