Dissymmetric Bis Research Articles

Synthesis, characterization, and photocatalytic activity for water remediation and hydrogen evolution of Zn(II) and Ni(II) bis(thiosemicarbazone) complexes

The extensive industrial use of organic dyes causes large amounts of these substances to arrive at water sources, so nowadays, organic compound removal from fresh water is a major concern. The use of photocatalysts is an interesting approach to solving this problem, with coordination compounds playing an outstanding role. We report the selective synthesis and characterization of three new dissymmetric bis(thiosemicarbazone) ligands and their nickel(II) and zinc(II) complexes, which have been fully characterized by several techniques. The photocatalytic activity of the six complexes for methyl orange degradation was also evaluated. All the complexes can degrade this organic dye, although the photoefficiency of the nickel compounds is, in general, higher than for the zinc ones, as the degradation is faster and they do not reach a plateau. Density functional theory calculations show a clear dependence of the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap, as well as with the relative energies of these orbitals. On the other hand, the need for green fuels that do not produce the greenhouse effect is one of the major goals of modern life, and molecular hydrogen is one of the most promising ones. Considering the proven potential of bis(thiosemicarbazone) complexes to electrocatalyze H2 evolution recently reported in the literature, we also made some preliminary tests to investigate the potential of the nickel complexes to act as photocatalysts for water splitting. The results indicate that two of the complexes produce H2 in the conditions tested, so they could be used in the development of efficient photocatalytic systems for hydrogen evolution.

Structural variety, fluorescence and photocatalytic activity of dissymmetric thiosemicarbazone complexes

A new dissymmetric bis(thiosemicarbazone) ligand, H2L2, containing a 4-(1-naphthyl)-3-thiosemicarbazone branch has been easily prepared and characterized. The reactivity of this ligand and the hybrid isopropylthiosemicarbazone/naphtoylhydrazone, H2L1, with zinc(II), copper(II) and nickel(II) nitrates in the presence of different amounts of lithium hydroxide has been explored. The results show that although both ligands present two different acidic protons, the degree of deprotonation of the ligand cannot be selectively controlled, since in almost all the reactions carried out without base the ligand is at least singly deprotonated. Nevertheless, an interesting structural diversity is found, also influenced by the metal structural preferences, leading to the formation of monomeric (1–5, 8 and 9), dimeric (6) and polymeric (7) species. The different degree of deprotonation of the ligands, together with the presence or the absence of nitrate ions and solvent molecules, lead to the formation of different supramolecular architectures based on different hydrogen bond arrays. Fluorescence spectroscopy in the solid state for the ligands and the complexes was performed and the results show that whereas H2L1 is fluorescent, for H2L2 no fluorescence emission was detected. Complexation of H2L1 leads, in general, to a quench of the fluorescence emission, except for complex [ZnL1(EtOH)] 2, which is much more fluorescent than the free ligand. Conversely, complexation of H2L2 with zinc(II) causes fluorescence emission. Photocatalytic experiments with the nickel and copper complexes shows that the four complexes can effectively degrade methyl orange under UV–vis irradiation.

Influence of the Reaction Conditions in the Crystal Structures of Zn(II) and Ni(II) Coordination Compounds with a Dissymmetric Bis(Thiosemicarbazone) Ligand

The new ligand HMeATSM, derived from condensation of 2-3-butanedione with 4-methyl-3-thiosemicarbazide and 2,4-dimethyl-3-thiosemicarbazide, has been synthesized. Its reactivity with nickel(II) and zinc(II) nitrates was explored and the resulting complexes were thoroughly characterized by elemental analysis, conductivity, mass spectrometry, IR, 1H and 13C NMR spectroscopies and their structures were confirmed by single-crystal X-ray diffraction. The results showed that the complex [Ni(MeATSM)]NO3 1 is formed under every reaction condition. In contrast, the reaction with zinc(II) nitrate depends on the temperature and the presence of LiOH·H2O, leading to the obtaining of complexes [Zn(MeATSM)(OH2)](NO3) 2 and [Zn(Me2TS)2(OH2)](NO3)2 3. The crystal structures of complexes 1 and 2 show that the dissymmetric ligand acts as a N2S2 tetradentate monoanionic ligand. The structural preferences of the metals also determine the structure of the complexes: whereas nickel(II) is in a square-planar environment, the zinc atom prefers a distorted square-base pyramid geometry imposed by the coordination mode and the planarity of the bis(thiosemicarbazone) ligand. In contrast, in complex 3, containing two bidentate Me2TS ligands, the Zn(II) is in a trigonal bipyramid arrangement. In all the complexes, the nitrate ion is not coordinated to the metal and acts as a counterion.

Synthesis of acyl(chloro)phosphines enabled by phosphinidene transfer.

Acyl(chloro)phosphines RC(O)P(Cl)(t-Bu) have been prepared by formal insertion of tert-butyl phosphinidene (t-Bu-P) from t-BuPA (A = C14H10 or anthracene) into the C-Cl bond of acyl chlorides. We show that the under-explored acyl(chloro)phosphine functional group provides an efficient method to prepare bis(acyl)phosphines, which are important precursors to compounds used industrially as radical polymerization initiators. Experimental and computational investigations into the mechanism of formation of acyl(chloro)phosphines by our synthetic method reveal a pathway in which chloride attacks a phosphonium intermediate and leads to the reductive loss of anthracene from the phosphorus center in a P(v) to P(iii) process. The synthetic applicability of the acyl(chloro)phosphine functional group has been demonstrated by reduction to an acylphosphide anion, which can in turn be treated with an acyl chloride to furnish dissymmetric bis(acyl)phosphines.

Progress toward the Total Synthesis of Gukulenin A: Photochemically Triggered Two-Carbon Ring Expansion Key to α-Tropolonic Ether Synthesis.

The ex-chiral-pool synthesis of an advanced gukulenin A precursor from (-)-piperitone is revealed. Key C/C connecting maneuvers to the synthesis of a C2 dissymmetric bis(α-tropolonic) ether building block are a ring-contracting Meinwald rearrangement, a photochemically triggered two-carbon ring expansion, and a homodimerization by cross-metathesis.

Dissymmetric ansa zirconocene complexes with di- and trisubstituted indenyl ligands as catalysts for homogeneous ethylene homo- and ethylene/1-hexene copolymerization reactions

Different routes for the synthesis of 1,2- and 1,2,3-substituted indene derivatives are described. Representative substituents are: Me, Ph, PhCH2, PhCH2CH2, PhCH2CH2CH2, CH2CH=CH2. Subsequent deprotonation of these substituted indenes and reaction with indenyl zirconium trichloride gave the corresponding dissymmetric bis(indenyl) zirconium complexes. After activation with methylaluminoxane (MAO) these complexes show high activities both in ethylene homopolymerisation and ethylene/1-hexene copolymerisation. The rate of comonomer incorporation can reach 33.3% (15/MAO). The copolymers exhibit lower melting points than the homopolymers and their crystallinities α are lower compared with the homopolymers.

Dissymmetric Bis(dipyrrinato)Zinc(II) Complexes: Rich Variety and Bright Red to Near-Infrared Luminescence with a Large Pseudo-Stokes Shift

Bis(dipyrrinato)metal(II) and tris(dipyrrinato) metal(III) complexes have been regarded as much less useful luminophores than their boron difluoride counterparts (4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes, BODIPYs), especially in polar solvent. We proposed previously that dissymmetry in such metal complexes (i.e., two different dipyrrinato ligands in one molecule) improves their fluorescence quantum efficiencies. In this work, we demonstrate the universality and utility of our methodology by synthesizing eight new dissymmetric bis(dipyrrinato)zinc(II) complexes and comparing them with corresponding symmetric complexes. Single-crystal X-ray diffraction analysis, 1H and 13C NMR spectroscopy, and high-resolution mass spectrometry confirm the retention of dissymmetry in both solution and solid states. The dissymmetric complexes all show greater photoluminescence (PL) quantum yields (ΦPL) than the corresponding symmetric complexes, allowing red to near-infrared emissions with large pseudo-Stokes shifts. The best performance achieves a maximum PL wavelength of 671 nm, a pseudo-Stokes shift of 5400 cm−1, and ΦPL of 0.62−0.72 in toluene (dielectric constant εs = 2.4), dichloromethane (εs = 9.1), acetone (εs = 21.4), and ethanol (εs = 24.3). The large pseudo-Stokes shift is distinctive considering BODIPYs with small Stokes shifts (∼500 cm−1), and the ΦPL values are higher than or comparable to those of BODIPYs fluorescing at similar wavelengths. Electrochemistry and density functional theory calculations illustrate that frontier orbital ordering in the dissymmetric complexes meets the condition for efficient PL proposed in our theory.

Dissymmetric Bis(dipyrrinato)zinc(II) Complexes: Rich Variety and Bright Red to Near-Infrared Luminescence with a Large Pseudo-Stokes Shift.

Bis(dipyrrinato)metal(II) and tris(dipyrrinato)metal(III) complexes have been regarded as much less useful luminophores than their boron difluoride counterparts (4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes, BODIPYs), especially in polar solvent. We proposed previously that dissymmetry in such metal complexes (i.e., two different dipyrrinato ligands in one molecule) improves their fluorescence quantum efficiencies. In this work, we demonstrate the universality and utility of our methodology by synthesizing eight new dissymmetric bis(dipyrrinato)zinc(II) complexes and comparing them with corresponding symmetric complexes. Single-crystal X-ray diffraction analysis, (1)H and (13)C NMR spectroscopy, and high-resolution mass spectrometry confirm the retention of dissymmetry in both solution and solid states. The dissymmetric complexes all show greater photoluminescence (PL) quantum yields (ϕPL) than the corresponding symmetric complexes, allowing red to near-infrared emissions with large pseudo-Stokes shifts. The best performance achieves a maximum PL wavelength of 671 nm, a pseudo-Stokes shift of 5400 cm(-1), and ϕPL of 0.62-0.72 in toluene (dielectric constant εs = 2.4), dichloromethane (εs = 9.1), acetone (εs = 21.4), and ethanol (εs = 24.3). The large pseudo-Stokes shift is distinctive considering BODIPYs with small Stokes shifts (∼500 cm(-1)), and the ϕPL values are higher than or comparable to those of BODIPYs fluorescing at similar wavelengths. Electrochemistry and density functional theory calculations illustrate that frontier orbital ordering in the dissymmetric complexes meets the condition for efficient PL proposed in our theory.

Dissymmetric Bis ( Indenyl ) Zirconium Dichloride Complexes as Catalyst Precursors for Homogeneous Ethylene Polymerization

Dissymmetric Bis ( Indenyl ) Zirconium Dichloride Complexes as Catalyst Precursors for Homogeneous Ethylene Polymerization

Chiral Self‐Sorting of trans‐Chelating Chiral Ligands upon Formation of PdII Complexes

AbstractInvited for the cover of this issue is the group of Arne Lützen at the University of Bonn, Germany. The cover image shows two dissymmetric bis(3‐pyridyl) ligands based on a planar chiral pseudo‐ortho‐disubstituted [2.2]paracyclophane scaffold. Upon forming a mononuclear [ML2] complex with palladium(II) ions, these ligands act in a trans‐chelating manner and undergo complete chiral self‐sorting.

Self‐Discriminating Self‐Assembly of Dinuclear Heterochiral Rhombs from Tröger’s Base Derived Bis(pyridyl) Ligands

Five racemic dissymmetric bis(pyridyl) ligands based on 2,8- or 3,9-difunctionalised Tröger's base derivatives have been synthesised. Only those derived from a 2,8-difunctionalised scaffold were found to undergo selective self-assembly to discrete self-assembled dinuclear metallosupramolecular aggregates of rhomboid shape upon coordination to cis-protected Pd(2+) or Pt(2+) ions, as evidenced by ESI mass spectrometry, NMR spectroscopy and single-crystal X-ray diffraction. Interestingly, these processes were found to be highly diastereoselective leading to the formation of C(2v)-symmetric heterochiral assemblies in a self-discriminating manner.

Versatile New Bis(thiosemicarbazone) Bifunctional Chelators: Synthesis, Conjugation to Bombesin(7−14)-NH2, and Copper-64 Radiolabeling

New bifunctional derivatives of diacetyl-bis(4-methylthiosemicarbazone) (H(2)atsm) have been prepared by a selective transamination reaction of a new dissymmetric bis(thiosemicarbazone) precursor H(2)L(1). The new derivatives contain an aliphatic carboxylic acid (H(2)L(2) and H(2)L(3)), t-butyl carbamate (H(2)L(4)), or ammonium ion (H(2)L(5)) functional group. The new ligands and copper(II) complexes have been characterized by NMR spectroscopy, mass spectrometry, and microanalysis. The complex Cu(II)(L(4)) was structurally characterized by X-ray crystallography and shows the metal center to be in an N(2)S(2) distorted square planar coordination geometry. Electrochemical measurements show that the copper(II) complexes undergo a reversible reduction attributable to a Cu(II)/Cu(I) process. The ligands and the copper(II) complexes featuring a carboxylic acid functional group have been conjugated to the tumor targeting peptide bombesin(7-14)-NH(2). The bifunctional peptide conjugates were radiolabeled with copper-64 in the interest of developing new positron emission tomography (PET) imaging agents. The conjugates were radiolabeled with copper-64 rapidly in high radiochemical purity (>95%) at room temperature under mild conditions and were stable in a cysteine and histidine challenge study.

Synthesis of symmetric and dissymetric bisperfluoroalkanesulfonylimides and evaluation of their inhibition on bovine carbonic anhydrase

AbstractThis study describes a synthesis of symmetric and dissymmetric bis[(perfluoroalkane)‐sulfonyl]imides by the reaction of the sodium salt of perfluoroalkanesulfonamide RFSO2NH−Na+ (RF = C4F9, C6F13, C8F17) with hexamethyldisilazane and perfluoroalkanesulfonylfluoride RFSO2F (RF = C4F9, C6F13, C8F17). They are obtained, in two steps, in moderate overall yield. Moreover, this paper provides a study of their inhibition on bovine carbonic anhydrase. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:542–548, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20452

Synthesis of mixed bis(alkenylcarbene) ditungsten complexes by sequential activation of dialkynols

Abstract The synthesis of new bis(alkenylcarbene) ditungsten complexes 2a–b , 5a and 6a has been achieved from W(CO) 5 (THF), via activation of the dialkynol derivatives a and b . The reaction of 5a with piperazine affords a dissymmetric bis(aminocarbene) complex 7a .

ChemInform Abstract: Synthesis of (R)‐ and (S)‐7,7′‐Bis(diphenylphosphino)‐2,2′‐dimethoxy‐1, 1′‐binaphthyl, a New Axially Dissymmetric Bis(triarylphosphine).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of ( R)- and ( S)-7,7′-bis(diphenylphosphino)-2,2′-dimethoxy-1,1′-binaphthyl, a new axially dissymmetric bis(triarylphosphine)

A new axially dissymmetric bis(triarylphosphine) ligand 7,7′-bis(diphenylphosphino)-2,2′-dimethoxy-1,1′-binaphthyl has been synthesized in enantiomerically pure form.

ChemInform Abstract: Axially Dissymmetric Bis(triaryl)phosphines in the Biphenyl Series: Synthesis of (6,6′‐Dimethylbiphenyl‐2,2′‐diyl)bis(diphenylphosphine) (“BIPHEMP”) and Analogues, and Their Use in Rh(I)‐Catalyzed Asymmetric Isomerizations of N,N‐Diethylnerylamine.

AbstractThe axially dissym.

Axially Dissymmetric Bis(triaryl)phosphines in the Biphenyl series: Synthesis of (6,6′‐dimethylbiphenyl‐2,2′‐diyl)bis(diphenylphosphine) (‘BIPHEMP’) and analogues, and their use in Rh(I)‐catalyzed asymmetric isomerizations of N,N‐diethylnerylamine

AbstractThe axially dissymmetric diphosphines (−)‐(R)‐ and (+)‐(S)‐(6‐6′‐dimethylbiphenyl‐2,2′‐diyl)bis(diphenyl‐phosphine) ((−)‐(R)‐10 and (+)‐(S)‐10; ‘BIPHEMP’) have been synthesized, starting from (R)‐ and (S)‐6,6′‐dimethylbiphenyl‐2,2′‐diamine ((R)‐ and(S)‐16), respectively, via Sandmeyer reaction, liathiation, and phosphinylation. Moreover, racemic 4,4′‐ dimethyl‐ and 4,4′‐bis(dimethylamino)‐substituted analogues 11 and 12 respectively, and the 6,6′‐bridged analogues 1,11‐bis(diphenylphosphino)‐5,7‐dihydrodibenz[c,e]oxepin (13) were synthesized and resolved into optically pure (R)‐ and(S)‐enantiomers via complexation with di‐μ‐chlorob is {(R)‐2‐[1‐(dimethylamino)ethyl]pheny‐CN}dipalladium(II) ((R)‐18). The molecular structures of the diphosphines (S)‐10 and (R)‐13 and of two derived cationic Rh(I) complexes,[Rh((S)‐ 10)(nbd)]BF4 and [Rh((R)‐ 13)(nbd)]BF4 were determined by x‐ray analyses. Absolute configurations were established for (+)‐(S)‐ 10 by X‐ray analyses of both the free diphosphine and of the derived Rh(I) complex, and for (−)‐(R)‐ 13 by X‐ray analysis of the derived Rh(I) complex. Configurational assignments for the substituted BIPHEMP analogues 11 12 were achieved by means of 1H‐NMR comparisons. The BIPHEMP ligand 10 and analogues 11, 12 and 13 are the first examples of optically active bis(triaylphosphines) containing the axially dissymmetric biphenyl moiety. All these new diphosphines proved to be excellent asymmetry‐inducing ligands in Rh(I)‐catalyzed isomerizations of N,N‐diethylnerylamine affording citronellat enamine of 98‐99% ee.

Axially Dissymmetric Bis(aminophosphine)s Derived from 2,2′-Diamino-1,1′-binaphthyl. Synthesis and Application to Rhodium(I)-Catalyzed Asymmetric Hydrogenations

Abstract Axially dissymmetric bisphosphine ligands, (R)- and (S)-2,2′-bis(diphenylphosphinoamino)-1,1′-binaphthyl (BDPAB) and (R)-2,2′-bis[N-(diphenylphosphino)methylamino]-1,1′-binaphthyl (Me-BDPAB) were conveniently prepared from 2,2′-diamino-1,1′-binaphthyl. The rhodium(I)-catalyzed asymmetric hydrogenation of α-acylamidoacrylic acids and esters gave the corresponding amino acids of up to 95% optical purity. The sign of the centro-chirality of the product amino acids was always the same to that of the axial chirality of the ligand in both cases of BDPAB and Me-BDPAB.

2, 2'-bis(diphenylphosphino)-1, 1'-binaphthyl(binap) : A new atropisomeric bis(triaryl)phosphine. synthesis and its use in the rh(l)-catalyzed asymmetric hydrogenation of α-(acylamino)acrylic acids

Racemic 2, 2'-bis(diphenylphosphino)-l, 1'-binaphthyl has been synthesized from 2, 2'-dihydroxy-l, l'-binaphthyl in two steps and resolved into optically pure ( R)-(+) and ( S) (-) enantiomers by the use of (+)-di-μ-chlorobis[( S)-N,N-dimethyl-α-phenylethylamine-2C,N]dipalladium. This new axially dissymmetric bis(triaryl)phosphine serves as an excellent ligand for Rh(l)-catalyzed asymmetric hydrogenations of α-(acylamino) acrylic acids or esters. Factors controlling the enantioselectivity and mechanistic aspects are discussed on the basis of the 31P-NMR measurements