Influence of the phosphine arrangement on the reactivity of palladium(II) and platinum(II) polyphosphine complexes with copper(I) chloride

The distorted square-planar complexes [Pd(PNHP)Cl]Cl (1) (PNHP = bis[2-(diphenylphosphino)ethyl]amine), [M(P₃)Cl]Cl [P₃ = bis[2-(diphenylphosphino)ethyl]phenylphosphine; M = Pd (2), Pt (3)] and [Pt(NP₃)Cl]Cl (5) (NP₃ = tris[2-(diphenylphosphino)ethyl]amine), coexisting in the later case with a square-pyramidal arrangement, react with one equivalent of CuCl to give the mononuclear heteroionic systems [M(L)Cl](CuCl₂) [L = PNHP, M = Pd (1a); L = P₃, M = Pd (2a), Pt (3a); L = NP₃, M = Pt (5a)]. The crystal structure of 3a confirms that Pt(II) retains the distorted square-planar geometry of 3 in the cation with P₃ acting as tridentate chelating ligand, the central P atom being trans to one chloride. The counter anion is a nearly linear dichlorocuprate(I) ion. However, the five-coordinate complexes [Pd(NP₃)Cl]Cl (4), [M(PP₃)Cl]Cl (M = Pd (6), Pt (7); PP₃ = tris[2-(diphenylphosphino)ethyl] phosphine) containing three fused five-membered chelate rings undergo a ring-opening by interaction with one (4, 6, 7) and two (6, 7) equivalents of CuCl with formation of neutral MCu(L)Cl₃ [L = NP₃, M = Pd (4a); L = PP₃, M = Pd (6a), Pt (7a)] and ionic [MCu(PP₃)Cl₂](CuCl₂) [M = Pd (6b), Pt (7b)] compounds, respectively. The heteronuclear systems were shown by ³¹P NMR to have structures where the phosphines are acting as tridentate chelating ligands to M(II) and monodentate bridging to Cu(I). Further additions of CuCl to the neutral species 6a and 7a in a 1:1 ratio resulted in the achievement of the ionic complexes 6b and 7b with ions as counter anions. It was demonstrated that the formation of heterobimetallic or just mononuclear mixed salt complexes was clearly influenced by the polyphosphine arrangement with the tripodal ligands giving the former compounds. However, complexes [M(NP₃)Cl]Cl constitute one exception and the type of reaction undergone versus CuCl is a function of the d⁸ metal centre.     

Synthesis and some reactivity of amidinato(pyridine) complexes of molybdenum and tungsten formulated as [M(η-allyl)(amidinato)(CO)2(NC5H5)]

Bis(pyridine) complexes of molybdenum and tungsten, [M(η³-allyl)Cl(CO)₂(NC₅H₅)₂] (M=Mo; 3-Mo, M=W; 3-W), reacted with an equimolar amount of lithiated amidinate, Li[(PhN)₂CR] (R=H; 4a-Li, R = CH₃; 4b-Li), to yield corresponding amidinato(pyridine) complexes, [M(η³-allyl){(PhN)₂CR}(CO)₂(NC₅H₅)] (M=Mo, R=H; 5a-Mo, M=Mo, R=CH₃; 5b-Mo, M=W, R=H; 5a-W), as a yellow solid. The dissociation of pyridine ligand from the central metal in complexes 5a was observed in a polar solvent such as acetonitrile. In these cases, although the formation of amidinato(acetonitrile) complexes, [M(η³-allyl){(PhN)₂CH}(CO)₂(NCMe)] (M=Mo; 6a-Mo, M=W; 6a-W), was suggested spectroscopically, isolation of complexes 6a was not successful but the re-formation of pyridine complexes 5a was observed. In the reactions of complexes 5a with PEt₃ and with P(OMe)₃, the substitution reactions easily took place to give [M(η³-allyl){(PhN)₂CH}(CO)₂(PEt₃)] (M=Mo; 7a-Mo, M=W; 7a-W) and [M(η³-allyl){(PhN)₂CH}(CO)₂{P(OMe)₃}] (M=Mo; 8a-Mo, M=W; 8a-W), respectively. These complexes were characterized spectroscopically as well as, in some cases, by X-ray analyses.     

Synthesis and structure of dichloropalladium(II) complexes of heteroleptic N,S- and N,Se-donor ligands based on the 2-organochalcogenomethylpyridine motif, and Mizoroki-Heck catalysis mediated by complexes of N,S-donor ligands

Ligands containing the 2-organochalcogenomethylpyridine motif with substituents in the 4- or 6-position of the pyridyl ring, R⁴,R⁶-pyCH₂ER¹ [R⁴ = R⁶ = H, ER¹ = SMe (1), SeMe (2), SPh (6), SePh (7); R⁴ = Me, R⁶ = H, ER¹ = SMe (3), SPh (8), SePh (9); R⁴ = H, R⁶ = Me, ER¹ = SMe (4), SPh (10), SePh (11); R⁴ = H, R⁶ = Ph, ER¹ = SMe (5), SPh (12), SePh (13)] are obtained on the reaction of R⁴,R⁶-pyMe with LiBuⁿ followed by R¹EER¹. On reaction with PdCl₂(NCMe)₂, the ligands with a 6-phenyl substituent form cyclopalladated species PdCl{6-(o-C₆H₄)pyCH₂ER¹-C,N,E} (5a, 12a, 13a) with the structure of 13a (ER¹ = SePh) confirmed by X-ray crystallography; other ligands form complexes of stoichiometry PdCl₂(R⁴,R⁶-pyCH₂ER¹). Complexes with R⁶ = H are monomeric with N,E-bidentate configurations, confirmed by structural analysis for 3a (R⁴ = Me, ER¹ = SMe), 7a (R⁴ = H, ER¹ = SePh) and 9a (R⁴ = Me, ER¹ = SePh). Two of the 6-methyl substituted complexes examined by X-ray crystallography are oligomeric with trans-PdCl₂(N,E) motifs and bridging ligands, trimeric [PdCl₂(μ-6-MepyCH₂SPh-N,S)]₃ (10a) and dimeric [PdCl₂(μ-6-MepyCH₂SePh-N,Se)]₂ (11a). This behaviour is attributed to avoidance of the Me···Cl interaction that would occur in the cis-bidentate configuration if the pyridyl plane had the same orientation with respect to the coordination plane as observed for 3a, 7a and 9a [dihedral angles 8.0(2)-16.8(2)°]. When examined as precatalysts for the Mizoroki-Heck reaction of n-butyl acrylate with aryl halides in N,N-dimethylacetamide at 120 °C, the complexes exhibit the anticipated trends in yield (ArI > ArBr > ArCl, higher yield for electron withdrawing substituents in 4-RC₆H₄Br and 4-RC₆H₄Cl). The most active precatalysts are PdCl₂(R⁴-pyCH₂SMe-N,S) (R = H (1a), Me (3a)); complexes of the selenium containing ligands exhibit very low activity. For closely related ligands, the changes SMe to SPh, 6-H to 6-Me, and 6-H to 6-Ph lead to lower activity, consistent with involvement of both the pyridyl and chalcogen donors in reactions involving aryl bromides. The precatalyst PdCl₂(pyCH₂SMe-N,S) (1a) exhibits higher activity for the reaction of aryl chlorides in Buⁿ₄NCl at 120 °C as a solvent under non-aqueous ionic liquid (NAIL) conditions.     

Five manganese(II) complexes with seven- or eight-coordinated Mn(II), revealing different coordination modes for the nitrato ligands

Four seven-coordinated manganese(II) complexes [Mn(tpa)(η₁-NO₃)(η₂-NO₃)] (1), [Mn(bpia)(η₁-NO₃)(η₂-NO₃)] (2), [Mn(tpa)(η₁-NO₃)(η₂-NO₃)] (3), [Mn(tpa)(η₁-NO₃)(η₂-NO₃)] (4), and one octacoordinated manganese(II) complex [Mn(bppza)(η₂-NO₃)₂] (5) have been synthesized and characterized using the tripodal tetradentate ligands tpa, bpia, bipa, ipqa, and bppza (tpa: tris(2-pyridylmethyl)amine, bpia: bis(2-pyridylmethyl)(2-(N-methyl)imidazolylmethyl)amine, bipa: bis-(2-(N-methyl)imidazolylmethyl)(2-pyridylmethyl)amine, ipqa: (2-(N-methyl)imidazolylmethyl)(2-pyridylmethyl)(2-quinolylmethyl)amine, and bppza: bis(2-pyridylmethyl)(2-pyrazylmethyl)amine). The crystal structures for all compounds have been determined. 1, 2 and 3 crystallize in the triclinic space group , 4 crystallizes in the orthorhombic space group Pbca, whereas the eight-coordinated 5 crystallizes in the monoclinic space group P2₁/n. All compounds have one bidentate bound nitrate group in common. The coordination number and its geometry depend on the coordination mode of the second nitrate group. The coordination polyhedron for 1, 2, 3 and 4 is best described as an oblate octahedron and the one for 5 as a doubly oblate octahedron.     

Synthesis and structural characterization of mercury(II) complexes with a novel ferrocenyliminophosphine

Synthesis of the novel ligand ferrocenyliminophosphine [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)CHN(C₆H₄-2-PPh₂)}] (1, L) and studies on its complexation properties with mercury (II) are reported. Halogen-bridged binuclear mercury (II) complexes [HgX(μ-X)L]₂ (X = Cl (2a), Br (2b)) and a mononuclear mercury (II) complex HgCl₂L₂ (4a) have been obtained under different reaction conditions. In both cases, the ferrocenyliminophosphine acts as a P-monodentate ligand and the imino nitrogen does not participate in coordination to mercury (II). All the new compounds 1, 2a, 2b and 4a were characterized by elemental analysis, ¹H NMR, ³¹P NMR and IR spectra. In addition, structures of 2a and 4a have been determined by X-ray single-crystal analysis.     

(Pyrazolylmethyl)pyridine platinum(II) and gold(III) complexes: Synthesis, structures and evaluation as anticancer agents

Reactions of 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1), 2-(3,5-diphenylpyrazol-1-ylmethyl)pyridine (L2), 2-(3,5-di-tert-butylpyrazol-1-ylmethyl)pyridine (L3) and 2-(3-p-tolylpyrazol-1-ylmethyl)pyridine (L4) with K₂[PtCl₄] in a mixture of ethanol and water formed the dichloro platinum complexes [PtCl₂(L1)] (1), [PtCl₂(L2)] (2), [PtCl₂(L3)] (3) and [PtCl₂(L4)] (4). Complex 1, [PtCl₂(L1)], could also be prepared in a mixture of acetone and water. Performing the reactions of L2 and L3 in a mixture of acetone and water, however, led to C-H activation of acetone under mild conditions to form the neutral acetonyl complexes [Pt(CH₂COCH₃)Cl(L2)] (2a) and [Pt(CH₂COCH₃)Cl(L3)] (3a). The same ligands reacted with HAuCl₄ · 4H₂O in a mixture of ethanol and water to form the gold salts [AuCl₂(L1)][AuCl₄] (5) [AuCl₂(L2)][Cl] (6) [AuCl₂(L3)][Cl] (7) and [AuCl₂(L4)][AuCl₄] (8); however, with the pyrazolyl unit in the para position of the pyridinyl ring in 4-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L5), 4-(3,5-diphenylpyrazol-1-ylmethyl)pyridine (L6) neutral gold complexes [AuCl₃(L5)] (9) and [AuCl₂(L6)] (10) were formed; signifying the role the position of the pyrazolyl group plays in product formation in the gold reactions. X-ray crystallographic structural determination of L6, 2, 33a, 8 and 10 were very important in confirming the structures of these compounds; particularly for 3a and 8 where the presence of the acetonyl group confirmed C-H activation and for 8 where the counter ion is . Cytotoxicity studies of L2, L4 and complexes 1-10 against HeLa cells showed the Au complexes were much less active than the Pt complexes.     

Cytotoxicity of half sandwich ruthenium(II) complexes with strong hydrogen bond acceptor ligands and their mechanism of action

Neutral and cationic organometallic ruthenium(II) piano stool complexes of the type [(η⁶-cymene)RuCl(X)(Y)] (complexes R1-R8) has been synthesized and characterized. In cationic complexes, X, Y is either a η² phosphorus ligand such as 1,1-bis(diphenylphosphino)methane (DPPM) and 1,2-bis(diphenylphosphino)ethane (DPPE) or partially oxidized ligands such as 1,2-bis(diphenylphosphino)methane monooxide (DPPMO) and 1,2-bis(diphenylphosphino)ethane monooxide (DPPEO) which are strong hydrogen bond acceptors. In neutral complexes, X is chloride and Y is a monodentate phosphorous donor. Complexes with DPPM and DPPMO ligands ([(η⁶-cymene)Ru(η²-DPPM)Cl]PF₆ (R2), [(η⁶-cymene)Ru(η²-DPPMO)Cl]PF₆ (R3), [(η⁶-cymene)Ru(η¹-DPPM)Cl₂] (R5) and [(η⁶-cymene)Ru(η¹-DPPMO)Cl₂] (R6) show good cytotoxicity. Growth inhibition study of several human cancer cell lines by these complexes has been carried out. Mechanistic studies for R5 and R6 show that inhibition of cancer cell growth involves both cell cycle arrest and apoptosis induction. Using an apoptosis PCR array, we identified the sets of anti-apoptotic genes that were down regulated and pro-apoptotic genes that were up regulated. These complexes were also found to be potent metastasis inhibitors as they prevented cell invasion through matrigel. The complexes were shown to bind DNA in a non intercalative fashion and cause unwinding of plasmid DNA in cell-free medium by competitive ethidium bromide binding, viscosity measurements, thermal denaturation and gel mobility shift assays.     

Secondary ligand-metal interactions in rhodium(III) and iridium(III) phosphoramidite complexes

The synthesis, characterization, and application in asymmetric catalytic cyclopropanation of Rh(III) and Ir(III) complexes containing (S_a,R_C,R_C)-O,O′-[1,1′-binaphthyl-2,2′-diyl]-N,N′-bis[1-phenyl-ethyl]phosphoramidite (1) are reported. The X-ray structures of the half-sandwich complexes [MCl₂(C₅Me₅)(1,κP)] (M = Rh, 2a; M = Ir, 2b) show that the metal-phosphoramidite bond is significantly shorter in the Ir(III) analog. Chloride abstraction from 2a (with CF₃SO₃SiMe₃ or with CF₃SO₃Me) and from 2b (with AgSbF₆) gives the cationic species [MCl(C₅Me₅)(1,2-η-1,κP)]⁺ (M = Rh, 3a; M = Ir, 3b), which display a secondary interaction between the metal and a dangling phenethyl group (NCH(CH₃)Ph) of the phosphoramidite ligand, as indicated by NMR spectroscopic studies. Complexes 3a and 3b slowly decompose in solution. In the case of 3b, the binuclear species [Ir₂Cl₃(C₅Me₅)₂]⁺ is slowly formed, as indicated by an X-ray study. Preliminary catalytic tests showed that 3a cyclopropanates styrene with moderate yield (35%) and diastereoselectivity (70:30 trans:cis ratio) and with 32% ee (for the trans isomer).     

Synthesis and structural characterization of bis- and tris(3,5-dimethylpyrazolyl)methane complexes of Ni(NO3)2

The complexes (tpm*)Ni(η²-NO₃)(η¹-NO₃) (1), [(bpm*)₂Ni(η²-NO₃)]NO₃ (2), and [(tpm*)(bpm*)Ni(η¹-NO₃)]NO₃ (3) (tpm* = tris(3,5-dimethylpyrazolyl)methane; bpm* = bis(3,5-dimethylpyrazolyl)methane) have been prepared and characterized by IR and UV-Vis spectroscopy and X-ray diffraction studies. These d⁸ complexes all adopt variously distorted octahedral structures in the solid state and their magnetic moments are consistent with a paramagnetic state with two unpaired electrons. The solution ¹H NMR data show that the paramagnetism is maintained in solution.     

Structures of sulfur-rich dithiolate-gold(I) complexes and their oxidation

[NMe₄][Au(PEt₃)(C₃S₅)], [NMe₄][Au(PPh₃)(C₃S₅)], [NMe₄][Au(PEt₃)(C₈H₄S₈)], [N-methylpyridinium][Au(PPh₃)(C₈H₄S₈)], [(PEt₃)Au-C₃S₅-Au(PEt₃)], and [(PEt₃)Au-C₈H₄S₈-Au(PEt₃)] [C₃S₅²⁻=4,5-disulfanyl-1,3-dithiole-2-thionate(2−); C₈H₄S₈²⁻=2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithionate(2−)] were prepared. They exhibited first oxidation potentials due to the dithiolate ligand-centered oxidation at −0.30 to +0.21 V (vs. Ag/Ag⁺) in dichloromethane. They were reacted with iodine or 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) to afford one-electron-oxidized species [Au(PEt₃)(C₈H₄S₈)] and [(L)Au-C₈H₄S₈-Au(L)](TCNQ)_1.0-1.1, (L=PEt₃ and PPh₃) and further-electron-oxidized species [Au(PEt₃)(S-S)]I_3.3-5.7, [Au(PPh₃)(S-S)]I_12-13, [(PEt₃)Au-(S-S)-Au(PEt₃)]I_3.3-5.5 (S-S=C₃S₅²⁻ and C₈H₄S₈²⁻) and [(PPh₃)Au-C₈H₄S₈-Au(PPh₃)]I₁₂. ESR spectra of the oxidized species suggest the C₃S₅ and C₈H₄S₈ ligand-centered oxidation. The oxidized C₈H₄S₈-complexes showed electrical conductivities of 10⁻⁴-10⁻² S cm⁻¹ measured for compacted pellets at room temperature. X-ray crystal structures of [NMe₄][Au(PPh₃)(C₃S₅)]CH₂Cl₂, [(PEt₃)Au-C₃S₅-Au(PEt₃)] and [(PEt₃)Au-C₈H₄S₈-Au(PEt₃)] were revealed.     

Reactions of alkyl and aryl sulfides with a monocarbon platinacarbaborane anion

The reaction of the monocarbon carbaborane complex Na[Pt(PEt₃)₂(η⁵-CB₁₀H₁₁)] with some diaryl- and dialkyl disulfides has been investigated. With Ph₂S₂, two new cage substituted products are formed, [Pt(SPh)(PEt₃)(η⁵-9-SPh-7-CB₁₀H₁₀)] (1) and [Pt(SPh)(PEt₃)(η⁵-8-SPh-11-SPh-7-CB₁₀H₉)] (2), whereas with S₂ the main product is the metal substituted complex, [Pt(SBu^t)(PEt₃)(η⁵-7-CB₁₀H₁₁)] (4). All three new molecules have been identified spectroscopically (¹H, ¹³C, ³¹P, ¹¹B NMR) and through single crystal X-ray diffraction.     

A new series of iodocarbonyl ruthenium (II) complexes with unsymmetrical phosphine-phosphine sulfide ligands of the type Ph2P(CH2)nP(S)Ph2, n = 1-4: Isolation and structural investigation

Hexa-coordinated chelate complex cis-[Ru(CO)₂I₂(P∩S)] (1a) {P∩S = η²-(P,S)-coordinated} and penta-coordinated non-chelate complexes cis-[Ru(CO)₂I₂(P∼S)] (1b-d) {P∼S = η¹-(P)-coordinated} are produced by the reaction of polymeric [Ru(CO)₂I₂]_n with equimolar quantity of the ligands Ph₂P(CH₂)_nP(S)Ph₂ {n = 1(a), 2(b), 3(c), 4(d)} in dichloromethane at room temperature. The bidentate nature of the ligand a in the complex 1a leads to the formation of five-membered chelate ring which confers extra stability to the complex. On the other hand, 1:2 (Ru:L) molar ratio reaction affords the hexa-coordinated non-chelate complexes cis,cis,trans-[Ru(CO)₂I₂(P∼S)₂] (2a-d) irrespective of the ligands. All the complexes show two equally intense terminal ν(CO) bands in the range 2028-2103 cm⁻¹. The ν(PS) band of complex 1a occurs 23 cm⁻¹ lower region compared to the corresponding free ligand suggesting chelation via metal-sulfur bond formation. X-ray crystallography reveals that the Ru(II) atom occupies the center of a slightly distorted octahedral geometry. The complexes have also been characterized by elemental analysis, ¹H, ¹³C and ³¹P NMR spectroscopy.     

Preparation and characterization of (9-methyladenine)triammineplatinum(II) and trans-dihydroxo(9-methyladenine)triammineplatinum(IV) complexes

The preparation is reported of [(NH₃)₃Pt(9- MeA)] X₂ (9-MeA = 9-methyladenine) with XCl (1a) and XClO₄ (1b) and of trans-[(OH)₂Pt(NH₃)₃- (9-MeA)]X₂ with XCl (2a) and XClO₄ (2b), and the crystal structure of 1b. [(NH₃)₃Pt(C₆H₇N₅)](ClO₄)₂ crystallizes in space group P2₁/n with a = 20.810(7) Å, b = 7.697(3) Å, c = 10.567(4) Å, β = 91.57(6)°, Z = 4. The structure was refined to R = 0.054, R_w = 0.063. In all four compounds Pt coordination is through N7 of 9-MeA, as is evident from ³J coupling between H8 of the adenine ring and ¹⁹⁵Pt. Pt(II) and Pt(IV) complexes can be differentiated on the basis of different ³J values, larger for Pt(II) than for Pt(IV) by a factor of 1.57 (av). In Me₂SO-d₆, hydrogen bonding occurs between Cl^? and C(8)H of 9-MeA as weil as between Cl^? and the NH₃ groups in the case of the Pt(II) complex 1a. Protonation of the 9-MeA ligands was followed using ¹H NMR spectroscopy and pK_a values for the N1 protonated 9-MeA ligands were determined in D₂O. They are 1.9 for 1a and 1.8 for 2a, which compares with 4.5 for the non-platinated 9-MeA. Possible consequences for hydrogen bonding with the complementary bases thymine or uracil are discussed briefly. Protonation of the OH groups in the Pt(IV) complexes has been shown not to occur above pH 1.     

Tungsten complexes of aromatic and aliphatic thioaldehydes

Reaction of PPN[W(CO)₃(R₂PC₂H₄PR₂)(SH)] (PPN=Ph₃PNPPh₃; R=Me, 1; R=Ph, 2) with aromatic aldehydes in the presence of trifluoroacetic acid gave tungsten complexes of thiobenzaldehydes mer-[W(CO)₃(R₂PC₂H₄PR₂)(η²-SCHR^′)] (R=Me, 3a-3f; R=Ph, 4a-4e) in high yields. Analogous complexes of aliphatic thioaldehydes mer-[W(CO)₃(Me₂PC₂H₄PMe₂)(η²-SCHR^′)] (3g-3l) could only be obtained from the highly electron-rich thiolate complex 1. The structure of 3i (R^′=i-Bu) was determined by X-ray crystallography. In solution the complexes 3 and 4 are in equilibrium with small quantities of their isomers fac-[W(CO)₃(R₂PC₂H₄PR₂)(η²-SCHR^′)]. Reaction of complexes 3 with dimethylsulfate followed by salt metathesis with NH₄PF₆ gave the alkylation products mer-[W(CO)₃(Me₂PC₂H₄PMe₂)(η²-MeSCHR^′)]PF₆ (5a-5l) as mixtures of E and Z isomers. The methylated thioformaldehyde complex mer-[W(CO)₃(Me₂PC₂H₄PMe₂)(η²-MeSCH₂)]PF₆ (5m) was prepared similarly. Nucleophilic addition of hydride (from LiAlH₄) to 5 initially gave thioether complexes mer-[W(CO)₃(Me₂PC₂H₄PMe₂)(MeSCH₂R^′)] (mer-6) which rapidly isomerized to fac-[W(CO)₃(Me₂PC₂H₄PMe₂)(MeSCH₂R^′)] (fac-6).     

Metal ion biomolecule interactions. VI: Synthesis and spectroscopic properties of methylmercury(II) complexes of xanthosine

The interaction of MeHg(II) with xanthosine (Xanth H₂, 1) in aqueous medium has been found to lead to several methylmercurated complexes depending on the reactant stoichiometries and the pH. The N-bound complexes [(MeHg)(Xanth H)] (2), [(MeHg)₂Xanth] (3), [(MeHg)₃(Xanth)]NO₃ (4), [(MeHg)(Xanth H₂)]NO₃ (5), and the N- and C-bound complex [(MeHg)₄(Xanth)]NO₃ (6) have thus been prepared. The complexes were characterized by means of ¹H and ¹³C nuclear magnetic resonance and infrared as well as elemental analysis. Formation of the carbon-bound methylmercurated species 6 is in accord with our previous results obtained with inosine and imidazole derivatives, thus substantiating our proposal that activation through electrophilic coordination at N₇ is a requirement for C₈-H abstraction. Correlations are drawn between ²J(¹H-¹¹⁹Hg) values and pK_a as well as ¹³C chemical shifts.     

Structure-dependent spectroscopic and redox properties of copper(I) complexes with bidentate iminopyridine ligands

A series of iminopyridine ligands; cyclopropylpyridin-2-ylmethyleneamine (A), cyclopentylpyridin-2-ylmethyleneamine (B), cyclohexylpyridin-2-ylmethyleneamine (C), and cycloheptylpyridin-2-ylmethyleneamine, (D) and their copper(I) complexes, [Cu(L)₂]⁺ (1a-1d) and [Cu(L)(PPh₃)₂]⁺ (2a-2d) have been synthesized and characterized by CHN analyses, ¹H NMR and IR and UV-Vis spectroscopy. Structures of 1a, 1b, 1c and 2a were determined by X-ray crystallography. The coordination polyhedron about the Cu^I center in the complexes is best described as a distorted tetrahedron. The dihedral angles between the least-squares planes of the chelate ligands show considerable variation from 86.1° in 1a to 68.3° in 1b, indicating the importance of packing forces in the crystalline environment. The UV-Vis spectra of the complexes are characterized by first metal to ligand charge transfer bands increasing in wavelength with increasing size of the ring substituents in the ligands, except for the cyclopropyl compounds (1a and 2a), in good agreement with the variation of the dihedral angles between the ligand planes. Cyclic voltammetry of the complexes indicates a quasireversible redox behavior for the complexes. The bulkier ligands (PPh₃) inhibit the geometric distortion within the oxidized form and the redox potentials of complexes 2a-2d are shifted to more positive values, therefore.     

Interactions of arene-Ru(II)-chloroquine complexes of known antimalarial and antitumor activity with human serum albumin (HSA) and transferrin

The interactions of π-arene-Ru(II)-chloroquine complexes with human serum albumin (HSA), apotransferrin and holotransferrin have been studied by circular dichroism (CD) and UV-Visible spectroscopies, together with isothermal titration calorimetry (ITC). The data for [Ru(η⁶-p-cymene)(CQ)(H₂O)Cl]PF₆ (1), [Ru(η⁶-benzene)(CQ)(H₂O)Cl]PF₆ (2), [Ru(η⁶-p-cymene)(CQ)(H₂O)₂][PF₆]₂ (3), [Ru(η⁶-p-cymene)(CQ)(en)][PF₆]₂ (4), [Ru(η⁶-p-cymene)(η⁶-CQDP)][BF₄]₂ (5) (CQ: chloroquine; DP: diphosphate; en: ethylenediamine), in comparison with CQDP and [Ru(η⁶-p-cymene)(en)Cl][PF₆] (6) as controls demonstrate that 1, 2, 3, and 5, which contain exchangeable ligands, bind to HSA and to apotransferrin in a covalent manner. The interaction did not affect the α-helical content in apotransferrin but resulted in a loss of this type of structure in HSA. The binding was reversed in both cases by a decrease in pH and in the case of the Ru-HSA adducts, also by addition of chelating agents. A weaker interaction between complexes 4 and 6 and HSA was measured by ITC but was not detectable spectroscopically. No interactions were observed for complexes 4 and 6 with apotransferrin or for CQDP with either protein. The combined results suggest that the arene-Ru(II)-chloroquine complexes, known to be active against resistant malaria and several lines of cancer cells, also display a good transport behavior that makes them good candidates for drug development.     

Synthesis,structures and urease inhibitory activity of cobalt(III) complexes with Schiff bases

A series of new cobalt(III) complexes were prepared. They are [CoL¹(py)₃]·NO₃ (1), [CoL²(bipy)(N₃)]·CH₃OH (2), [CoL³(HL³)(N₃)]·NO₃ (3), and [CoL⁴(MeOH)(N₃)] (4), where L¹, L², L³ and L⁴ are the deprotonated form of N′-(2-hydroxy-5-methoxybenzylidene)-3-methylbenzohydrazide, N′-(2-hydroxybenzylidene)-3-hydroxylbenzohydrazide, 2-[(2-dimethylaminoethylimino)methyl]-4-methylphenol, and N,N′-bis(5-methylsalicylidene)-o-phenylenediamine, respectively, py is pyridine, and bipy is 2,2′-bipyridine. The complexes were characterized by infrared and UV–Vis spectra, and single crystal X-ray diffraction. The Co atoms in the complexes are in octahedral coordination. Complexes 1 and 4 show effective urease inhibitory activities, with IC₅₀ values of 4.27 and 0.35 μmol L⁻¹, respectively. Complex 2 has medium activity against urease, with IC₅₀ value of 68.7 μmol L⁻¹. While complex 3 has no activity against urease. Molecular docking study of the complexes with Helicobacter pylori urease was performed.     

Structure and solution behaviour of cyclooctadiene complexes of platinum(II)

The substitution behaviour of [PtCl(R)(COD)] (R⁻ = Me and Fc) complexes, by the stepwise addition of phosphine ligands, L (L = PPh₃, PEt₃ and P(NMe₂)₃), were investigated in situ by ¹H and ³¹P NMR spectroscopy. Addition of less than two equivalents of the phosphine ligand results in the formation of dimeric molecules with the general formula trans-[Pt(R)(μ-Cl)(L)]₂ for the sterically demanding systems where R⁻ = Me/L = P(NMe₂)₃ and R⁻ = Fc/L = PEt₃, PPh₃ and P(NMe₂)₃ while larger quantities resulted in cis- and trans mixtures of mononuclear complexes being formed. In the case of the relatively small steric demanding, strongly coordinating, PEt₃ ligand the trans-[PtCl(R)(PEt₃)₂] mononuclear complexes were exclusively observed in both cases. The crystal structures of the two substrates, [PtCl(R)(COD)] (R⁻ = Me or Fc), as well as the cis-[PtCl(Fc)(PPh₃)₂] substitution product are reported.