Bis-chelate Complexes Research Articles

Spontaneous Partitioning of Californium from Curium: Curious Cases from the Crystallization of Curium Coordination Complexes.

The reaction of (248)CmCl3 with excess 2,6-pyridinedicarboxylic acid (DPA) under mild solvothermal conditions results in crystallization of the tris-chelate complex Cm(HDPA)3 · H2O. Approximately half of the curium remains in solution at the end of this process, and evaporation of the mother liquor results in crystallization of the bis-chelate complex [Cm(HDPA)(H2DPA)(H2O)2Cl]Cl·2H2O. (248)Cm is the daughter of the α decay of (252)Cf and is extracted in high purity from this parent. However, trace amounts of (249,250,251)Cf are still present in all samples of (248)Cm. During the crystallization of Cm(HDPA)3 · H2O and [Cm(HDPA)(H2DPA)(H2O)2Cl]Cl · 2H2O, californium(III) spontaneously separates itself from the curium complexes and is found doped within crystals of DPA in the form of Cf(HDPA)3. These results add to the growing body of evidence that the chemistry of californium is fundamentally different from that of earlier actinides.

Behavior of the potential antitumor VIVO complexes formed by flavonoid ligands. 2. Characterization of sulfonate derivatives of quercetin and morin, interaction with the bioligands of the plasma and preliminary biotransformation studies

The biotransformation in the plasma and red blood cells of two potential antitumor VIVO complexes formed by flavonoid ligands (quercetin or que and morin or mor) and their sulfonic derivatives (quercetin-5′-sulfonic acid or queS and morin-5′-sulfonic acid or morS) was studied by spectroscopic (EPR, Electron Paramagnetic Resonance) and computational (DFT, Density Functional Theory) methods. Que and queS form with VIVO stable complexes, and in the systems with apo-transferrin (apo-hTf) and albumin (HSA) VO(que)2 and VO(queS)2 remain unchanged. VO(mor)2 and VO(morS)2 undergo displacement reactions to give the partial formation of (VO)x(HSA) and (VO)(apo-hTf)/(VO)2(apo-hTf); moreover, morS forms with apo-transferrin and albumin mixed species VO–morS–apo-hTf and VO–morS–HSA. In the systems with apo-hTf and HSA anisotropic EPR spectra at room temperature are detected in which the protein is not directly coordinated to VIVO2+ ion. This is explained assuming that the bis-chelated complexes interact strongly with the proteins through a network of hydrogen bonds with the polar groups present on the protein surface. It is suggested that this “indirect” transport of VIVO species could be common to all the species containing ligands which can interact with the blood proteins. Uptake experiments by red blood cells were also carried out, using vanadium concentration of 5.0×10−4M and incubation time in the range 0–160min. VO(que)2/VO(queS)2 and VO(mor)2/VO(morS)2 cross the erythrocytes membrane and in the cytosol VO(que)2/VO(queS)2 do not transform, whereas VO(mor)2/VO(morS)2 give the partial formation of mixed species with hemoglobin (Hb) and other VIVO complexes.

Unsymmetrical Chelation of N-Thioether-Functionalized Bis(diphenylphosphino)amine-Type Ligands and Substituent Effects on the Nuclearity of Iron(II) Complexes: Structures, Magnetism, and Bonding.

Starting from the short-bite ligands N-thioether-functionalized bis(diphenylphosphino)amine-type (Ph2P)2N(CH2)3SMe (1) and (Ph2P)2N(p-C6H4)SMe (2), the Fe(II) complexes [FeCl2(1)]n (3), [FeCl2(2)]2 (4), [Fe(OAc)(1)2]PF6 (5), and [Fe(OAc)(2)2]PF6 (6) were synthesized and characterized by Fourier transform IR, mass spectrometry, elemental analysis, and also by X-ray diffraction for 3, 4, and 6. Complex 3 is a coordination polymer in which 1 acts as a P,P-pseudochelate and a (P,P),S-bridge, whereas 4 has a chlorido-bridged dinuclear structure in which 2 acts only as a P,P-pseudochelate. Since these complexes were obtained under strictly similar synthetic and crystallization conditions, these unexpected differences were ascribed to the different spacer between the nitrogen atom and the −SMe group. In both compounds, one Fe–P bond was found to be unusually long, and a theoretical analysis was performed to unravel the electronic or steric reasons for this difference. Density functional theory calculations were performed for a set of complexes of general formula [FeCl2(SR2){R21PN(R2)P′R23}] (R = H, Me; R1, R2, and R3 = H, Me, Ph), to understand the reasons for the significant deviation of the iron coordination sphere away from tetrahedral as well as from trigonal bipyramidal and the varying degree of unsymmetry of the two Fe–P bonds involving pseudochelating PN(R)P ligands. Electronic factors nicely explain the observed structures, and steric reasons were further ruled out by the structural analysis in the solid-state of the bis-chelated complex 6, which displays usual and equivalent Fe–P bond lengths. Magnetic susceptibility studies were performed to examine how the structural differences between 3 and 4 would affect the interactions between the iron centers, and it was concluded that 3 behaves as an isolated high-spin Fe(II) mononuclear complex, while significant intra- and intermolecular ferromagnetic interactions were evidenced for 4 at low temperatures. Complexes 3 and 4 were also tested in catalytic ethylene oligomerization but did not exhibit any significant activity under the studied conditions.

Zinc β-enaminoketonate complexes: synthesis, characterization and ROP of rac-lactide

Alkane elimination reactions of -enaminoketonate ligands OCMeCHCMeN(2,6-Me2C6H3 )( 1), OCMeCH CMeN(2,6,- i Pr2C6H3 )( 2), OCMeCHCMeN(4- t Bu-C6H3 )( 3) with ZnEt2 afforded bis-chelate and bimetallic zinc com- plexes ((OCMeCHCMeNAr)2Zn); Ar = 2,6-Me2C6H3 (4), 2,6- i Pr2C6H3 (5) and 4- t Bu-C6H3 (6) in 85-94% yield; and ({OCMeCHCMeN(2,6- i Pr2C6H3)}ZnEt)2 (8), ({OCMeCHCMeN(2,6-Me2-C6H3)}ZnEt)2 (7) and ({OCMeCHCMeN(4- t Bu- C6H3)}ZnEt)2 (9) in 50-90% yield. 7-9 are mixed with 4-6, respectively, DFT computations of 1 H chemical shifts allowed the unambiguous assignment of the species in solution. X-ray single crystal analyses of 4, 6, 7-9 showed that 4 and 6 are bis-chelate complexes in which the coordination geometry about zinc is distorted tetrahedral and overall C2 symmetry. 7-9 are bimetallic complexes in which the coordination geometry about zinc is distorted tetrahedral but with overall S2 symmetry. The optimized geometry of DFT models 4a and 4b (CH2Cl2 as solvent) indicated that the distortion of the geometry in 4 is due in part to the CH2Cl2 present in the unit cell. ROP of rac-LA catalyzed by complexes 4-9 and 8-O i Pr was carried out in toluene solutions. All complexes were active but the best results were obtained with 7-9 and 8-O i Pr.

Boric acid: a simple molecule of physiologic, therapeutic and prebiotic significance

Abstract Boric acid, H3BO3, is a weak acid and at physiological pH is in the form of an uncharged small molecule. Behaving as a Lewis acid, it forms complexes with amino- and hydroxy acids, carbohydrates, nucleotides and vitamins through electron donor-acceptor interactions. These interactions are believed to be beneficial for human health. Synthetic bis-chelate complexes of boric acid with organic biomolecules are therefore considered for nutritional and/or pharmaceutical applications. The use of boric acid for BNCT has gained attention due to the short biological half-life, solubility, plasma circulation and the non-selective soft tissue accumulation properties of this simple molecule. Complexation of boric acid with sugars is of particular importance in understanding the role of boron as a carrier for nucleotides and carbohydrates. A potential and catalytic role of boric acid in peptide and nucleic acid synthesis and in the stabilization of sugar molecules by acting as a complexing agent have been demonstrated. Its possible role as a phosphorylation chaperone in a prebiotic world has been recently suggested. This contribution reviews the highlights in the physiologic, therapeutic and prebiotic significance of boric acid in the last decade.

Synthesis of phosphinoferrocene amides and thioamides from carbamoyl chlorides and the structural chemistry of Group 11 metal complexes with these mixed-donor ligands.

The reaction of in situ generated 1'-(diphenylphosphino)-1-lithioferrocene with carbamoyl chlorides, ClC(E)NMe2, affords the corresponding (thio)amides, Ph2PfcC(E)NMe2 (E = O (), S (); fc = ferrocene-1,1'-diyl). These compounds as well as their analogues, Ph2PfcC(O)NHMe () and Ph2PfcC(O)NH2 (), prepared from 1'-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) were studied as ligands for the Group 11 metal ions. In the reactions with [Cu(MeCN)4][BF4], the amides give rise to bis-chelate complexes of the type [Cu(L-κ(2)O,P)2][BF4]. Similar products, [Ag(L-κ(2)O,P)2]ClO4, are obtained from silver(i) perchlorate and , or . In contrast, the reaction of AgClO4 with produces a unique molecular dimer [Ag()(ClO4-κO)]2, where the metal centres are bridged by the sulfur atoms of the P,S-chelating thioamides. The reactions of with [AuCl(tht)] (tht = tetrahydrothiophene) afford the expected gold(i)-phosphine complexes, [AuCl(L-κP)], containing uncoordinated (thio)amide moieties. Hemilabile coordination of the phosphinoamide ligands in complexes with the soft Group 11 metal ions is established by the crystal structure of a solvento complex, [Cu(-κ(2)O,P)(-κP)(CHCl3-κCl)][BF4], which was isolated serendipitously during an attempted crystallisation of [Cu(-κ(2)O,P)2][BF4]. All of the compounds are characterised by spectroscopic methods, and the structures of several representatives of both the free phosphinoamides and their complexes are determined by X-ray diffraction analysis and further studied by DFT calculations and cyclic voltammetry.

Synthesis, characterization and bio-activity of nickel(II) and copper(II) complexes of a bidentate NS Schiff base of S-benzyl dithiocarbazate

The reaction of S-benzyldithiocarbazate (SBDTC) with 3-hydroxyacetophenone afforded a bidentate NS Schiff base HL (HL=benzyl-3-(3-hydroxyphenyl methyl ethylene)hydrazine carbodithioate) which on further reaction with nickel(II) and copper(II) salt yielded bis-chelated inner complexes, NiL2 and CuL2, respectively with deprotonated L ligand. The ligand and its complexes were characterized by physico-chemical techniques, viz., molar conductance, magnetic susceptibility measurement, IR, NMR, UV–Vis spectroscopy and mass spectroscopic techniques. The crystal structure of all the compounds was also characterized by single crystal X-ray crystallography. The ligand exists in its thione tautomeric form both in solution and in the solid state. In the complexes the two deprotonated ligands chelate the metal through the azomethine nitrogen and the thione sulfur atom with cis arrangement generating a tetrahedrally distorted square planar geometry around the metal center. Only complex CuL2 showed moderate analgesic activity at 60min compared to Diclofenac sodium, while all the test compounds exhibited good anti-inflammatory activity as compared to standard drug Indomethacin.

Characterization and biotransformation in the plasma and red blood cells of VIVO2 + complexes formed by ceftriaxone

The coordination mode and geometry in aqueous solution of oxidovanadium(IV) complexes formed by a third-generation cephalosporin, ceftriaxone (H3cef), were studied by spectroscopic (EPR, electron paramagnetic resonance), pH-potentiometric and computational (DFT, density functional theory) methods. The behavior of the model systems containing 6-hydroxy-2-methyl-3-thioxo-3,4-dihydro-1,2,4-triazine-5(2H)-one (H2hmtdt) and 3-benzylthio-6-hydroxy-2-methyl-1,2,4-triazine-5(2H)-one (Hbhmt) was examined for comparison. The stability of the tautomers of ceftriaxone and 6-hydroxy-2-methyl-3-thioxo-3,4-dihydro-1,2,4-triazine-5(2H)-one in the neutral, mono- and bi-anionic form was calculated by DFT methods, both in the gas phase and in aqueous solution, and the electron density on the oxygen atoms of the hydroxytriazinone ring was related to the pKa of the ligands. The data demonstrate that ceftriaxone coordinates VIVO2+ forming mono- and bis-chelated complexes with (Oket, O−) donor set and formation of five-membered chelate rings. The geometry of the bis-chelated complex, cis-[VO(Hcef)2(H2O)]2−, is cis-octahedral and this species can deprotonate, around physiological pH, to form the corresponding mono-hydroxido cis-[VO(Hcef)2(OH)]3−. The interaction of cis-[VO(Hcef)2(H2O)]2− with apo-transferrin (apo-hTf) was studied and the results suggest that VIVO2+ distributes between (VO)apo-hTf/(VO)2apo-hTf and cis-[VO(Hcef)2(H2O)]2−, whereas mixed complexes are not formed for charge and steric effects. The interaction of cis-[VO(Hcef)2(H2O)]2− with red blood cells shows that ceftriaxone helps VIVO2+ ion to cross the erythrocyte membrane. Inside the cell cis-[VO(Hcef)2(H2O)]2− decomposes and the same species formed by inorganic VIVO2+ are observed. The relationship between the biotransformation in the plasma and red blood cells and the potential pharmacological activity of VIVO2+ species of ceftriaxone is finally discussed.

Combined Stabilizing Effects of Trifluoromethyl Groups and Semifluorinated Side Chains on the Thermotropic Liquid‐Crystal Behavior of β‐Enamino Ketone Ligands and Their Bischelate PdII Complexes

AbstractSeveral linear β‐enamino ketone ligands and their corresponding bischelate PdII complexes bearing various combinations of methyl and trifluoromethyl groups at the chelating center as well as peripheral hydrocarbon and perfluorinated side chains were prepared. The effect of these structural modifications on the thermotropic liquid‐crystalline behavior of both the ligands and the corresponding metal complexes was studied. The relationships between the molecular structures and the corresponding thermal properties are discussed. As expected, the persistence of liquid‐crystalline behavior was highly sensitive to both applied structural manipulations. On the one hand, increased steric congestion around the chelating moiety clearly appears detrimental to the retention of mesomorphism. On the other hand, perfluorinated chains at the molecular extremity can occasionally restore it. Therefore, the regulation of the balance between both structural parameters permits a precise control of the mesomorphic properties of the compounds.

Bis-glycinato complexes of palladium(II): Synthesis, structural determination, and hydrogen bonding interactions

Palladium(II) acetate and palladium(II) chloride react with glycine and glycine derivatives in acetone/water to yield square planar bis-chelated palladium amino acid complexes. Glycine, N-methylglycine and N,N-dimethylglycine all adopt the trans configuration when prepared from palladium(II) acetate, whereas glycine adopts a cis configuration when prepared from palladium(II) chloride. The crystal structures of all four complexes were obtained. The extended lattice structures arise from N–H··O or O··(HOH)··O hydrogen bonding. Nuclear magnetic resonance, infrared, high resolution mass spectroscopy, and UV–Vis spectroscopic data are evaluated.

Tuning a single ligand system to stabilize multiple spin states of manganese: a first example of a hydrazone-based manganese(III) spin-crossover complex.

A series of bis-chelate pseudo-octahedral mononuclear coordination complexes of manganese with the chromophore [MnN4 O2 ](n+) (n=0, 1) have been generated in all three principal oxidation states of this transition-metal center under ambient conditions by utilizing a readily tunable, versatile phenolic pyridylhydrazone ligand system (i.e., H2 (3,5-R(1) ,R(2) )-L; L=ligand). Strategic combinations of the nature and position of a variety of substituent groups afforded selective, spontaneous stabilization of multiple spin states of the manganese center, which, upon close crystallographic scrutiny, appears to be in part due to the occurrence or absence of hydrogen-bonding interactions that involve the phenolate/phenolic oxygen atom. The divalent complexes are isolable in two forms, namely, molecular [Mn(II) {H(3,5-R(1) ,R(2) )-L}2 ] and ionic [Mn(II) {H2 (3,5-R(1) ,R(2) )-L}{H(3,5-R(1) ,R(2) )-L}]ClO4 , with the latter complex converting easily into the former complex on deprotonation. Accessibility of the higher-valent states is achievable only when the phenolate oxygen atom is sterically hindered from participation in hydrogen bonding. The [Mn(III) {H(3,5-tBu2 )-L}2 ]ClO4 complex is the first example of a hydrazone-based Mn(III) complex to exhibit spin crossover. Formation of the tetravalent complexes [Mn(IV) {(3,5-R(1) ,R(2) )-L}2 ] (R(1) =tBu, R(2) =H; R(1) =R(2) =tBu) necessitates base-assisted abstraction of the hydrazinic proton.

Combined Experimental and Theoretical Study of Bis(diphenylphosphino)(N-thioether)amine-Type Ligands in Nickel(II) Complexes for Catalytic Ethylene Oligomerization

Starting from the new ligands bis(diphenylphosphino)(N-4-(methylthio)phenyl)amine (4, N(PPh2)2(p-C6H4)SMe) and its monosulfide derivative (Ph2P)N{P(S)Ph2}(p-C6H4)SMe (4·S), we have prepared and characterized, including by X-ray crystallographic studies, their Ni(II) complexes [NiCl2{(Ph2P)2N(p-C6H4)SMe-P,P}] (5) and [NiCl2{(Ph2P)N{P(S)Ph2}(p-C6H4)SMe-P,S}] (6), respectively. The bis-sulfide compound N{P(S)Ph2}2(p-C6H4)SMe (4·S2) was also prepared and structurally characterized. Computational studies showed that the combined influence of stronger P donors and a four-membered-ring P,P chelate leads to complex 5 being thermodynamically more stable than 6, which contains one weaker P═S donor group but a five-membered P,P═S chelate ring. For comparison, the bis-chelate complex [Ni{(Ph2P)N{P(S)Ph2}(p-C6H4)SMe-P,S}2](BF4)2 (7), the monochelate complexes [NiBr2{(Ph2P)N{P(S)Ph2}(p-C6H4)SMe-P,S}] (8) and the Pd(II) analogue of 6, [PdCl2{(Ph2P)N{P(S)Ph2}(p-C6H4)SMe-P,S}] (9), were synthesized and structurally characterized and their solution behavior was investigated. The catalytic activity and selectivity in ethylene oligomerization of the Ni(II) complexes 5 and 6 and their known N-(methylthio)propyl analogues [NiCl2{(Ph2P)2N(CH2)3SMe-P,P}] (2) and [NiCl2{(Ph2P)N{P(S)Ph2}(CH2)3SMe-P,S}] (3), which were obtained from the bis(diphenylphosphino)(N-(methylthio)propyl)amine ligand N(PPh2)2(CH2)3SMe (1) and its monosulfide derivative (Ph2P)N{P(S)Ph2}(CH2)3SMe (1·S), respectively, revealed a significant influence of the nature of the N-substituent (aryl vs alkyl thioether) and of the chelate ring size (P,P vs P,P═S). DFT calculations showed that the trend in ΔErel, [NiCl2(P,P)] > [NiCl2(P,P═S)] > [NiCl2(P═S,P═S)], results from the stronger covalent character of the Ni–P vs Ni–S bond. Using AlEtCl2 as cocatalyst, mostly ethylene dimers were produced, with significant amounts of trimers (selectivity in the range 11–36%). Productivities up to 40400 and 48200 g of C2H4/((g of Ni) h), with corresponding TOF values of 84800 and 101100 mol of C2H4/ ((mol of Ni) h), were obtained with precatalysts 2 and 3, respectively.

Boric acid complexes with thiamine (vitamin B1) and pyridoxine (vitamin B6)

Complexation of boric acid with vitamins B1 (thiamine) and B6 (pyridoxine) was investigated. The products were isolated from aqueous solutions and characterized by elemental analysis, FT-IR, 13C MAS NMR and thermal methods. The results of chemical and spectral analyses suggested that the reaction between thiaminechloride hydrochloride and H3BO3 in water yielded a salt-like productwith no direct bonding of the thiamine cation to boron while mono- and bis-chelate complexes were obtained with pyridoxine. The bis-chelate pyridoxine complex containing two equivalent pyridoxine ligands was obtained in crystal form. X-ray crystallography verified that complexation with boric acid occurs through the deprotonated phenolic and deprotonated adjacent alcoholic oxygen atoms forming six membered chelate rings. The negative charge on tetrahedral boron is balanced by the sodium ion. The crystal structure contains discernible tunnels parallel to the [010] direction constructed by hydrogen bonded complex molecules.

A biradical chelate Zn(II) complex with phenoxazin-1-one ligands

A stable biradical bis-chelate complex 3, bis-[2,4,6,8-tetra-(tert-butyl)phenoxazinonato] Zn(II), based on redox-active ligands has been prepared and structurally characterized by X-ray crystallography. Lengths of the coordination Zn–O bonds are equal to 1.938 and 2.008Å and those of the intraligand C–N and C–O bonds (1.356 and 1.308Å, respectively) point to radical-anion form of the phenoxazinone ligand. Effective magnetic moment of a microcrystalline sample of 3 measured at 70K is equal 2.53μB, and steadily decreases to 2.39μB upon elevation of temperature. EPR, UV–Vis measurements and DFT B3LYP∗/6-311++G(d,p) calculations show that 3 has the ground triplet electronic state characterized with weak ferromagnetic coupling of the unpaired electrons localized on the ligands.

Synthesis, Structures, and Dearomatization by Deprotonation of Iron Complexes Featuring Bipyridine-based PNN Pincer Ligands

The synthesis and characterization of new iron pincer complexes bearing bipyridine-based PNN ligands is reported. Three phosphine-substituted pincer ligands, namely, the known (t)Bu-PNN (6-((di-tert-butylphosphino)methyl)-2,2'-bipyridine) and the two new (i)Pr-PNN (6-((di-iso-propylphosphino)methyl)-2,2'-bipyridine) and Ph-PNN (6-((diphenylphosphino)methyl)-2,2'-bipyridine) ligands were synthesized and studied in ligation reactions with iron(II) chloride and bromide. These reactions lead to the formation of two types of complexes: mono-chelated neutral complexes of the type [(R-PNN)Fe(X)2] and bis-chelated dicationic complexes of the type [(R-PNN)2Fe](2+). The complexes [(R-PNN)Fe(X)2] (1: R = (t)Bu, X = Cl, 2: R = (t)Bu, X = Br, 3: R = (i)Pr, X = Cl, and 4: R = (i)Pr, X = Br) are readily prepared from reactions of FeX2 with the free R-PNN ligand in a 1:1 ratio. Magnetic susceptibility measurements show that these complexes have a high-spin ground state (S = 2) at room temperature. Employing a 2-fold or higher excess of (i)Pr-PNN, diamagnetic hexacoordinated dicationic complexes of the type [((i)Pr-PNN)2Fe](X)2 (5: X = Cl, and 6: X = Br) are formed. The reactions of Ph-PNN with FeX2 in a 1:1 ratio lead to similar complexes of the type [(Ph-PNN)2Fe](FeX4) (7: X = Cl, and 8: X = Br). Single crystal X-ray studies of 1, 2, 4, 6, and 8 do not indicate electron transfer from the Fe(II) centers to the neutral bipyridine unit based on the determined bond lengths. Density functional theory (DFT) calculations were performed to compare the relative energies of the mono- and bis-chelated complexes. The doubly deprotonated complexes [(R-PNN*)2Fe] (9: R = (i)Pr, and 10: R = Ph) were synthesized by reactions of the dicationic complexes 6 and 8 with KO(t)Bu. The dearomatized nature of the central pyridine of the pincer ligand was established by X-ray diffraction analysis of single crystals of 10. Reactivity studies show that 9 and 10 have a slightly different behavior in protonation reactions.

ChemInform Abstract: Simplifying Iron—Phosphine Catalysts for Cross‐Coupling Reactions.

Any old iron? Iron catalysts based on the widely available diphosphine ligand bis(diphenylphosphino)ethane have not previously fared particularly well in iron-catalyzed cross-coupling processes. However, this turns out not to be due to any inherently poor performance associated with the ligand, but rather the need to form a bis-chelate complex, either before or during the formation of an active FeI species.

Selectivity in metal–carbon bond protonolysis in p-tolyl- (or methyl)-cycloplatinated(ii) complexes: kinetics and mechanism of the uncatalyzed isomerization of the resulting Pt(ii) products

Reaction of each of the known starting complexes [PtR(C^N)(SMe2)], 1, in which R = Me or p-MeC6H4 and C^N is either ppy (deprotonated 2-phenylpyridine) or bhq (deprotonated benzo[h]quinoline), with one equivalent of CF3CO2H, gave the complexes [Pt(C^N)(CF3CO2)(SMe2)], 3 (C^N = ppy, 3a; bhq, 3b). The bis-chelate complexes [Pt(C^N)(P^P)](CF3CO2), 4, were obtained by reaction of complexes 3 with one equivalent of either of the P^P bisphosphine reagents, dppf = 1,1'-bis(diphenylphosphino)ferrocene or dppe = bis(diphenylphosphino)ethane. Complexes 4 were alternatively made by reaction of the complexes [PtMe(κ(1)C-C^N)(P^P)], 2, with one equivalent of CF3CO2H. When the complex 3b was reacted with 0.5 equivalents of dppe, 0.5 equivalents of the related bis-chelate product, 4d, formed along with 0.5 equivalents of the unreacted starting complex 3b. In contrast, when the complex 3b was reacted with 0.5 equivalents of dppf, then the dimeric complex [Pt2(bhq)2(CF3CO2)2(μ-dppf)], 5, formed in pure form. In all the above-mentioned acid reactions, the M-R bond rather than the M-C bond of the cycloplatinated complex is cleaved. When the PPh3 analogues of complexes 1, i.e. the complexes [PtR(C^N)(PPh3)], 6, in which C^N is ppy or tpy = deprotonated 2-p-tolylpyridine, were reacted with one equivalent of CF3CO2H, the course of the reaction reversed and the M-C bonds of the cycloplatinated complexes are cleaved rather than the M-R bonds. The latter reaction gave [PtR(κ(1)N-HC^N)(PPh3)(CF3CO2)], as an equilibrium mixture of two isomers 7 and 8. Crystal structures of the typical complexes show a variety of extensive intermolecular hydrogen bonding involving C-H bonds from the different ligands and electronegative atoms (O or F) from the CF3CO2 moiety. On the basis of data obtained from kinetic studies (using (1)H NMR spectroscopy), a dissociative mechanism is proposed for the case of the 7c/8c isomerization process, involving dissociation of the κ(1)N-Htpy neutral ligand, rather than the alternative route of PPh3 or CF3CO2 ligand dissociation.

Copper(II) bis-chelate paddle wheel complex and its bipyridine/phenanthroline adducts

Bola-shaped diester dicarboxylic acid 2-({2-[(2-carboxybenzoyl)-xy]ethoxy}carbonyl)benzoic acid (L1H2) was synthesized by desymmetrizing phthalic anhydride using 1,2-ethane diol. The corresponding dinuclear copper(II)-tetracarboxylate complex [Cu2(L1)2·(DMF)2] (1) has been synthesized. This paddle wheel complex was self-assembled with [15]-membered bis-chelate ring on either sides of the M–M axis. Upon treating with phenanthroline/bipyridine, the symmetrically formed bis-chelate rings in 1 were selectively desymmetrized into monochelate rings. The dinuclear association in 1 rearranged into mononuclear in [Cu(L1)·(bpy)] (2) and [Cu(L1)·(phen)]·(DMF) (3), where bpy = bipyridine and phen = phenanthroline. The paddle wheel arrangement in 1 is very similar to that in dimeric Cu(II) acetate; the symmetric arrangement in 1 rearranged in its corresponding monomeric species on reacting with phen and bpy. The symmetric bis-chelate ring in 1 and the desymmetrized monochelate ring in 2 and 3 are discussed following their crystal structures. The crystal structures for all the complexes and the electronic and fluorescence properties are discussed.

Heterolytic activation of dihydrogen by platinum and palladium complexes

Wide bite angle diphosphine ligands were used to prepare [(diphosphine)M(2-(diphenylphosphino)pyridine)](2+) complexes (M = Pd, Pt). Except for the ligand with the largest bite angle, 2-(diphenylphosphino)pyridine coordinates in a bidentate mode leading to bis-chelate complexes. In the case of Xantphos (9,9-dimethyl-4,5-bis(diphenylphosphino)-xanthene, βn = 111°) two types of complexes are formed, in which 2-(diphenylphosphino)pyridine coordinates in a mono- or bidentate fashion, respectively. The crystal structures of three of the Pt complexes were determined. The X-ray crystal structure of [(Xantphos)-Pt(2-(diphenylphosphino)pyridine)](2+) shows that Xantphos coordinates in a tridentate P,O,P fashion. Under dihydrogen pressure, the pyridyl moiety in the platinum complexes can de-coordinate to provide a vacant coordination site at the metal center. Furthermore it can act as an internal base to assist the heterolytic cleavage of dihydrogen. The reaction yields a platinum hydride with a protonated pyridine moiety in close proximity to one another. The structure as well as the reactivity of the complexes towards dihydrogen is governed by the steric requirements of the diphosphines. The crystal structure of [(dppf)PtH(2-(diphenylphosphino)pyridinium)](OTf)2 has been determined. Palladium complexes containing DPEphos or Xantphos decompose under dihydrogen pressure. In the case of dppf slow heterolytic splitting of dihydrogen occurs to form the hydride complex [(dppf)PdH(2-(diphenylphosphino)pyridinium)](OTf)2 which contains a protonated 2-(diphenylphosphino)pyridine ligand. In solution, this compound slowly undergoes P-C bond cleavage of the 2-(diphenylphosphino)pyridine ligand to form [(dppf)Pd(PHPh2)(η(1)-C5H4NH)](OTf)2. When the 6-methyl-2-pyridyldiphenylphosphine ligand is used, the reaction of the palladium complex with dihydrogen is very fast and the hydride complex immediately rearranges to the diphenylphosphino compound resulting from P-C bond cleavage.

Synthesis and Characterization of New Palladium(II) Thiosemicarbazone Complexes and Their Cytotoxic Activity against Various Human Tumor Cell Lines.

The palladium(II) bis-chelate complexes of the type [Pd(TSC1-5)2] (6–10), with their corresponding ligands 4-phenyl-1-(acetone)-thiosemicarbazone, HTSC1 (1), 4-phenyl-1-(2′-chloro-benzaldehyde)-thiosemicarbazone, HTSC2 (2), 4-phenyl-1-(3′-hydroxy-benzaldehyde)-thiosemicarbazone, HTSC3 (3), 4-phenyl-1-(2′-naphthaldehyde)-thiosemicarbazone, HTSC4 (4), and 4-phenyl-1-(1′-nitro-2′-naphthaldehyde)-thiosemicarbazone, HTSC5 (5), were synthesized and characterized by elemental analysis and spectroscopic techniques (IR and 1H- and 13C-NMR). The molecular structure of HTSC3, HTSC4, and [Pd(TSC1)2] (6) have been determined by single crystal X-ray crystallography. Complex 6 shows a square planar geometry with two deprotonated ligands coordinated to PdII through the azomethine nitrogen and thione sulfur atoms in a cis arrangement. The in vitro cytotoxic activity measurements indicate that the palladium(II) complexes (IC50 = 0.01–9.87 μM) exhibited higher antiproliferative activity than their free ligands (IC50 = 23.48–70.86 and >250 μM) against different types of human tumor cell lines. Among all the studied palladium(II) complexes, the [Pd(TSC3)2] (8) complex exhibited high antitumor activity on the DU145 prostate carcinoma and K562 chronic myelogenous leukemia cells, with low values of the inhibitory concentration (0.01 and 0.02 μM, resp.).