Ruthenium complexes with tridentate PNX (X = O, S) donor ligands

The ligands, PhPNXMe (1), PhPNXPh (2), and PhPNSMe (3), (PhPNX = 2-Ph2P-C6H4CH[double bond, length as m-dash]NC6H4X-2; X = O, S) have been prepared. A range of new ruthenium complexes were synthesised using these and related ligands, namely: [{RuCl(PhPNO)}2Cl] (4), [Ru(PhPNO)2] (5), [RuCl(PhPNXR)(PPh3)]BPh4 [X = O, R = Me (6); X = O, R = Ph (7); X = S, R = Me (8)], [{RuCl(PhPNX'R)}2Cl]X [X' = O, R = Me, X = Cl(-) (9); X' = S, R = Me, X = BPh4(-) or PF6(-) (10)], and [RuCl(PhPNO-eta 6C6H5)]BPh4 (11). The catalytic activity of these complexes with respect to the hydrosilyation of acetophenone and the hydrogenation of styrene has been investigated, giving an insight into the requirements for an active complex in these reactions.     

Rhenium and technetium complexes with tridentate S,N,O ligands derived from benzoylhydrazine

A potentially tridentate ligand with an S,N,O donor set, H₂L, is formed by the reaction of N-[(diethylaminothiocarbonyl)benzimidoyl chloride with benzoylhydrazine. Reactions of H₂L with (NBu₄)[MOCl₄] complexes (M = Re, Tc) give five-coordinate, neutral oxo complexes of the composition [MOCl(L)].Mixed-ligand complexes of rhenium(V) containing the tridentate L^2? ligand and bidentate N,N-dialkyl-N′-benzoylthioureato ligands (R₂btu^?) are formed in high yields when (NBu₄)[ReOCl₄] is treated with mixtures of H₂L and HR₂btu. Another approach to the mixed-ligand products is the reaction of [ReOCl(L)] with an equivalent amount of HR₂btu.     

Syntheses, characterization and ethylene polymerization of half-sandwich group IV metal complexes with tridentate [O,N,S] ligands

A series of half-sandwich group IV metal complexes with tridentate monoanionic phenoxy-imine arylsulfide [O NS] ligand [2-Bu t 4-Me-6-((2-(SC 6 H 5)C 6 H 4 N = CHC 6 H 2 O)](La) and dianionic phenoxy-amine arylsulfide [O N S] ligand [2-Bu t 4-Me-6-((2-(SC 6 H 5)C 6 H 4 N-CH 2 C 6 H 2 O)] 2(Lb) have been synthesized and characterized.Lb was obtained easily in high yield by reduction of ligand La with excess LiAlH 4 in cool diethyl ether.Half-sandwich Group IV metal complexes CpTi[O NS]Cl 2(1a),CpZr[O NS]Cl 2(1b),CpTi[O N S]Cl(2a),CpZr[O N S]Cl(2b) and Cp * Zr[O N S]Cl(2c) were synthesized by the reactions of La and Lb with CpTiCl 3,CpZrCl 3 and Cp * ZrCl 3,and characterized by IR,1 H-NMR,13 C-NMR and elemental analysis.In addition,an X-ray structure analysis was performed on ligand Lb.The title Group IV half-sandwich bearing tridentate [O,N,S] ligands show good catalytic activities for ethylene polymerization in the presence of methylaluminoxane(MAO) as co-catalyst up to 1.58 × 10 7 g-PE.mol-Zr 1.h 1.The good catalytic activities can be maintained even at high temperatures such as 100 ℃ exhibiting the excellent thermal stability for these half-sandwich metal pre-catalysts.     

Synthesis and electrochemistry of cis-dioxomolybdenum(VI) complexes with tridentate Schiff base ligands containing O,N and S donor atoms

The synthesis and characterization of a number of cis-dioxomolybdenum(VI) coordination complexes involving tridentate (ONS) ligands is described. The Schiff base ligands were obtained by condensation of 5-substituted salicylaldehydes with o-aminobenzenethiol or 2-aminoethanethiol. The chemical properties of these molybdenum complexes are compared with those having tridentate ligands with the ONO donor atom set. Cyclic voltammetry was used to obtain cathodic reduction potentials (E_pc) for the irreversible reduction of the Mo(VI) complexes. Although the reductions are irreversible, trends are observed in E_pc both within each series and when different series are compared. Cathodic reduction potentials for the four series examined span the range from ?1.53 to ?1.05 V versus NHE. There are three ligand features whose effect systematically alters the Mo(VI) cathodic reduction potentials. These include (1) the X-substituent on the salicylaldehyde portion of each ligand; (2) the degree of ligand delocalization; and (3) the substitution of a sulphur donor atom for an oxygen donor atom. Each of these effects is considered separately with regard to the Mo(VI) cathodic reduction potentials and then their cumulative effect is described.     

Electrochemical transformations of antimony(V) complexes containing tridentate O,N,O-donor ligands

Electrochemical transformations of antimony(V) complexes containing a tridentate redoxactive ligand, N,N-bis-(2-hydroxy-di-3,5-tert-butylphenyl)amine: R ₃Sb(Cat-NH-Cat) (R = (1) Ph; (2) Et), (3) Et₂Sb(Cat-N-Cat)) are studied. Electrochemical oxidation of complexes 1, 2 occurs irreversibly leading to formation of unstable radical cations. The next stage is the chemical process resulting in formation of neutral paramagnetic compounds. The Et₂Sb(V)(Cat-N-Cat) complex is characterized by two reversible anodic redox processes corresponding to a change of in the ligand redox level. Stable paramagnetic derivatives are formed as a result of electrochemical oxidation of compounds 1, 3; this allows considering these compounds as potential radical scavengers. Interaction of complex 1 with electrogenerated superoxide radical anion led to formation of paramagnetic reaction products.     

Shuttling of nickel oxidation states in N4S2 coordination geometry versus donor strength of tridentate N2S donor ligands

Seven bis-Ni(II) complexes of a N(2)S donor set ligand have been synthesized and examined for their ability to stabilize Ni(0), Ni(I), Ni(II) and Ni(III) oxidation states. Compounds 1-5 consist of modifications of the pyridine ring of the tridentate Schiff base ligand, 2-pyridyl-N-(2'-methylthiophenyl)methyleneimine ((X)L1), where X = 6-H, 6-Me, 6-p-ClPh, 6-Br, 5-Br; compound 6 is the reduced amine form (L2); compound 7 is the amide analog (L3). The compounds are perchlorate salts except for 7, which is neutral. Complexes 1 and 3-7 have been structurally characterized. Their coordination geometry is distorted octahedral. In the case of 6, the tridentate ligand coordinates in a facial manner, whereas the remaining complexes display meridional coordination. Due to substitution of the pyridine ring of (X)L1, the Ni-N(py) distances for 1~5 < 3 < 4 increase and UV-vis λ(max) values corresponding to the (3)A(2g)(F)→(3)T(2g)(F) transition show an increasing trend 1~5 < 2 < 3 < 4. Cyclic voltammetry of 1-5 reveals two quasi-reversible reduction waves that correspond to Ni(II)→Ni(I) and Ni(I)→Ni(0) reduction. The E(1/2) for the Ni(II)/Ni(I) couple decreases as 1 > 2 > 3 > 4. Replacement of the central imine N donor in 1 by amine 6 or amide 7 N donors reveals that complex 6 in CH(3)CN exhibits an irreversible reductive response at E(pc) = -1.28 V, E(pa) = +0.25 V vs saturated calomel electrode (SCE). In contrast, complex 7 shows a reversible oxidation wave at E(1/2) = +0.84 V (ΔE(p) = 60 mV) that corresponds to Ni(II)→Ni(III). The electrochemically generated Ni(III) species, [(L3)(2)Ni(III)](+) is stable, showing a new UV-vis band at 470 nm. EPR measurements have also been carried out.     

Preparation and 1H NMR study of complexes of trimethylplatinum(IV) with some tridentate schiff base ligands containing,N, O,and S donor atoms

The Schiff base ligands I–V, made by condensing either 2-acetylpyridine (I), 8-quinolinecarboxaldehyde (II and III), or o-methylthiobenzaldehyde (IV and V) with either N,N′-dimethyl-1,3-diaminopropane (I, II, and IV), 2-aminomethylpyridine (III), or 2-(2-aminoethyl)-pyridine (V), give ionic Pt^IVMe₃ complexes containing tridentate NNN- or SNN-bonded ligands. With PtMe₃Br ligand V gives a neutral complex XI in which it is coordinated only via the two N atoms. A monomeric Pt^IVMe₃ salicyladiminate complex results on treating the dimeric trimethylplatinum(IV) salicylaldehyde complex with the bidentate amine H₂N (CH₂)₃NMe₂. The complexes have been fully characterised by ¹H NMR spectroscopy.     

Synthesis, spectral, catalytic and antimicrobial studies of PPh3/AsPh3 complexes of Ru(II) with dibasic tridentate O, N, S donor ligands

Complexes of the type [Ru(CO)(EPh(3))(B)(L)] (E = P or As; B = PPh(3), AsPh(3), py or pip; L=dianion of the Schiff bases derived from thiosemicarbazone with acetoacetanilide, acetoacet-o-toluidide and o-chloro acetoacetanilide) have been synthesized from the reactions of equimolar amounts of [RuHCl(CO)(EPh(3))(2)(B)] and Schiff bases in benzene. The new complexes have been characterized by analytical and spectral (IR, electronic, NMR) data. The arrangement of PPh(3) groups around ruthenium metal was determined from (31)P NMR spectra. An octahedral structure has been assigned for all the new complexes. All the complexes exhibited catalytic activity for the oxidation of benzyl alcohol and cyclohexanol in presence of N-methylmorpholine-N-oxide as co-oxidant. The complexes also exhibited antibacterial activity against E. coli, Aeromonas hydrophilla and Salmonella typhi. The activity was compared with standard streptomycin.     

Transition metal complexes with thiosemicarbazide-based ligands

Solvate complexes of UO ₂ ²⁺ andN(1), N(4)-bis(salicylidene)-S-methylisothiosemicarbazone, (H₂Me-L¹), of general formula [UO₂(Me-L¹)S] (S= H₂O, MeOH, EtOH, Py, DMF and DMSO) were synthesized. The methanolic UO ₂ ²⁺ ” adducts of N(1)-benzoylisopropylidene-N(4)-salicylidene-S-alkylisothiosemicarbazone, (H₂R-L²,R=Me, Prⁿ) of general formula [UO₂(R-L²)· MeOH], were also prepared. Thermal decomposition of the complexes was investigated in air and argon. The complexes decompose to α-U₃O₈ in air, while in argon the decomposition is not completed up to 1000 K. The temperature and the mechanism of decomposition of the complexes are a function of the solvent belonging to the inner coordination sphere.     

Transition metal complexes with thiosemicarbazide-based ligands

The thermal decomposition and spectroscopic (reflectance and IR spectra) characterization of the newly synthesized square-pyramidal dioxovanadium(V) complexes of the type NH₄[VO₂(L)] (L is the dianion of the terdentate ligands salicylaldehyde thiosemicarbazone (ONS), halogen-substituted salicylaldehyde and 2-hydroxy-1-naphthaldehyde S-methylisothiosemicarbazones (ONN)) are described.

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Zusammenfassung Es wird die thermische Zersetzung und spektroskopische Charakterisierung (Reflexionsvermögen und IR-Spektren) neu synthetisierter Dioxovanadium(V)-Komplexe der allgemeinen Formel NH₄[VO₂(L)] beschrieben, wobei L das Dianion des dreizahnigen Liganden Salicylaldehyd-thiosemicarbazon (ONS), halogensubstituiertes Salicylaldehyd- bzw. 2-Hydroxy-1-naphthaldehyd-S-methyl-isothiosemicarbazon (ONN) ist.

     

Paramagnetic metal complexes of diamido donor ligands

Recently, considerable attention has been given to the use of multi-dentate amido ligands in the coordination chemistry of a range of transition metals as a means of accessing novel structural motifs and unusual reactivity. Presented herein is a perspective on transition and f-block metal complexes containing diamido donor ligands of the general form [NDN](2-) (D = NR, O, PR). Particular focus is given to paramagnetic metals, which have in general been studied much less than their diamagnetic counterparts despite their potential to exhibit unique structures and diverse reactivity patterns, in addition to their magnetic properties.     

Pyridazine- versus pyridine-based tridentate ligands in first-row transition metal complexes

A series of first-row transition metal complexes with the unsymmetrically disubstituted pyridazine ligand picolinaldehyde (6-chloro-3-pyridazinyl)hydrazone (PIPYH), featuring an easily abstractable proton in the backbone, was prepared. Ligand design was inspired by literature-known picolinaldehyde 2-pyridylhydrazone (PAPYH). Reaction of PIPYH with divalent nickel, copper, and zinc nitrates in ethanol led to complexes of the type [Cu(II)(PIPYH)(NO(3))(2)] (1) or [M(PIPYH)(2)](NO(3))(2) [M = Ni(II) (2) or Zn(II) (3)]. Complex synthesis in the presence of triethylamine yielded fully- or semideprotonated complexes [Cu(II)(PIPY)(NO(3))] (4), [Ni(II)(PIPYH)(PIPY)](NO(3)) (5), and [Zn(II)(PIPY)(2)] (6), respectively. Cobalt(II) nitrate is quantitatively oxidized under the reaction conditions to [Co(III)(PIPY)(2)](NO(3)) (7) in both neutral and basic media. X-ray diffraction analyses reveal a penta- (1) or hexa-coordinated (2, 3, and 7) metal center surrounded by one or two tridentate ligands and, eventually, κ-O,O' nitrate ions. The solid-state stoichiometry was confirmed by electron impact (EI) and electrospray ionization (ESI) mass spectrometry. The diamagnetic complexes 5 and 6 were subjected to (1)H NMR spectroscopy, suggesting that the ligand to metal ratio remains constant in solution. Electronic properties were analyzed by means of cyclic voltammetry and, in case of copper complexes 1 and 4, also by electron paramagnetic resonance (EPR) spectroscopy, showing increased symmetry upon deprotonation for the latter, which is in accordance with the proposed stoichiometry [Cu(II)(PIPY)(NO(3))]. Protic behavior of the nickel complexes 2 and 5 was investigated by UV/vis spectroscopy, revealing high π-backbonding ability of the PIPYH ligand resulting in an unexpected low acidity of the hydrazone proton in nickel complex 2.     

Magnetic and spectral properties of nickel(II) complexes of ligands containing O,N, and S donor atoms

Summary Several complexes of nickel(II) with Schiff bases derived from 3-substituted-4-amino-5-mercapto-1,2,4-triazoles (H₂L) have been synthesised. The complexes have a stoichiometry NiL · 2H₂O. The bonding of the ligands has been inferred from i.r. spectroscopy. The ligands preserve the thiol in the complexes. Magnetic moments obtained at room temperature and electronic spectra are consistent with octahedral geometry.     

Transition metal complexes with Girard reagent-based ligands

The ligand, salicylaldehyde Girard-T hydrazonium chloride, [H₂SalGT]Cl (1), and two complexes [Cu(HSalGT)X₂]·H₂O (X = Br(2); Cl(3)) were synthesized and their crystal structures were determined by single-crystal X-ray analysis. In the two isostructural complexes, the Cu(II) is located in a square-pyramidal environment, with the chelating ligand and one halogen atom in the basal plane and the second halogen in the apical position. The most apparent structural difference between the 1 and its complexes 2 and 3 is the orientation of the N(CH₃)₃ group: in 1, it is practically coplanar to the rest of the molecule, while in 2 and 3 it is oriented to the side of the axially bonded halogen, which can be explained by the C–H…X intramolecular interactions. The compounds were characterized by elemental analysis, molar conductivity, magnetic susceptibility and electronic absorption spectra.     

Transition metal complexes with pyrazole based ligands

The deaquation of two isostructural compounds of general formula [M(HL)₂(H₂O)₂](NO₃)₂ (M=Co, Ni, HL=3,5-dimethyl-1H-pyrazole-1-carboxamidine) is discussed in the view of their crystal and molecular structure. The compounds contain the same number and type of hydrogen bonds of the adjacent nitrate ions, only in the opposite orientation. On the basis of their deaquation pattern such a small difference may be detected, i.e., methods of thermal analysis are sensitive enough to show very small structural differences.     

Transition metal complexes based on thiophene-dithiolene ligands

The chemistry of transition metal dithiolene complexes based on thiophene-dithiolene ligands (TD) is reviewed, from the ligand synthesis and complex preparation to the molecular structure and solid state physical properties of different compounds based on them. The ligands considered are based mainly either on simple thiophene-dithiolates (α-tpdt = 2,3-thiophenedithiolate, dtpdt = 4,5-dihydro-2,3-thiophenedithiolate, and tpdt = 3,4-thiophenedithiolate), or in more extended and delocalised dithiolate ligands (α-tdt = 3-({5-[(2-cyanoethyl)thio]-2-thieno[2,3-d][1,3]dithiol-2-ylidene-1,3-dithiol-4-yl}thio)propanenitrile and dtdt = 3-{5-[(2-cyanoethyl)thio]-2-(5,6-dihydrothieno[2,3-d][1,3]dithiol-2-ylidene-1,3-dithiol-4-yl)thio}propanenitrile) that besides the thiophenic ring also incorporates a fused TTF moiety. Dithiolene complexes based on ligands containing appended thiophenic units will also be briefly considered. The structural variability of these complexes that in addition to the usual square planar coordination geometry, M(TD)₂, can also present dimeric, [M(TD)₂]₂, or cluster structures such as [Cu₄(TD)₃] and [Ni₄(TD)₆], is addressed. The role of the thiophene group and its ability to enhance electronic delocalisation from the metal dithiolene core throughout the ligand and to establish solid state networks of S?S interactions is discussed. The importance of these complexes as useful building blocks to prepare molecular materials with very interesting magnetic and transport properties, ranging from metamagnets to Single Component Molecular Metals, is illustrated by different compounds based on them.     

Transition metal complexes with tridentate salicylaldimine derived from 3,5-di-t-butylsalicylaldehyde

Several new binuclear Cu^II, Ni^II, OV^IV and Mn^II complexes of tridentate salicylaldimine (H₂L), obtained from 3,5-di-t-butylsalicylaldehyde and o-aminophenol, have been prepared and characterized by analytical, spectroscopic (i.r., u.v.–vis., e.s.r.) techniques, magnetic and thermal measurements. The adduct formation or dissociation of these complexes in the presence of strongly coordinating solvents like pyridine and DMSO did not take place. The complexation of Co^II with H₂L is accompanied by intramolecular electron transfer from the metal to the coordinated ligand yielding the radical ligand Co^III complex (g = 2.003, A ^Co = 10 G). The e.s.r. spectra of the Cu^II, OV^IV and Mn^II complexes in the solid state and in solution are very broad due to intramolecular dipolar antiferromagnetic interactions.     

Structural studies on organotin(IV) complexes formed with ligands containing {S,N,O} donor atoms

A number of complexes of ligands containing {O,N,S} donor atoms (2,3,4,6-tetra-O-acetyl-b-D-thioglucopyranoside, 1-thio-b-D-glucose, 2-aminomercaptopurine, 4-amino-2-mercaptopyrimidine and 2-amino-6-mercaptopurine-9-D-riboside) with di-n-butyltin(IV) oxide, diphenyltin(IV) oxide, tribenzyltin(IV) chloride, and trimethyltin(IV) chloride were prepared in the solid state. It was found that the complexes contain the organotin(IV) moiety and the ligand in a ratio of 1:1 or 2:1. The FTIR and Raman spectra clearly demonstrated that the organotin(IV) moieties react with the {S} atom of the ligands, while di-n-butyltin(IV) oxide is coordinated to the deprotonated hydroxy group. In several cases, the basic part of the ligands also participates in complex formation. Comparison of the experimental Mössbauer D values with those calculated on the basis of the pqs concept revealed that the organotin(IV) moiety has trigonal-bipyramidal geometry, and in certain cases tetrahedral geometry too. Some of the complexes contain the organotin(IV) cation in two different surroundings.