Synthesis and structural characterisation of group 10 metal(II) gallyl complexes: analogies with platinum diboration catalysts?

Reactions of the anionic gallium(i) heterocycle, [:Ga{[N(Ar)C(H)](2)}](-) (Ar = C(6)H(3)Pr(i)(2)-2,6), with a variety of mono- and bidentate phosphine, tmeda and 1,5-cyclooctadiene (COD) complexes of group 10 metal dichlorides are reported. In most cases, salt elimination occurs, affording either mono(gallyl) complexes, trans-[MCl{Ga{[N(Ar)C(H)](2)}}(PEt(3))(2)] (M = Ni or Pd) and cis-[PtCl{Ga{[N(Ar)C(H)](2)}}(L)] (L = R(2)PCH(2)CH(2)PR(2), R = Ph (dppe) or cyclohexyl (dcpe)), or bis(gallyl) complexes, trans-[M{Ga{[N(Ar)C(H)](2)}}(2)(PEt(3))(2)] (M = Ni, Pd or Pt), cis-[Pt{Ga{[N(Ar)C(H)](2)}}(2)(PEt(3))(2)], cis-[M{Ga{[N(Ar)C(H)](2)}}(2)(L)] (M = Ni, Pd or Pt; L = dppe, Ph(2)CH(2)PPh(2) (dppm), tmeda or COD). The crystallographic and spectroscopic data for the complexes show that the trans-influence of the gallium(i) heterocycle lies in the series, B(OR)(2) > H(-) > PR(3) approximately [:Ga{[N(Ar)C(H)](2)}](-) > Cl(-). Comparisons between the reactivity of one complex, [Pt{Ga{[N(Ar)C(H)](2)}}(2)(dppe)], with that of closely related platinum bis(boryl) complexes indicate that the gallyl complex is not effective for the catalytic or stoichiometric gallylation of alkenes or alkynes. The phosphaalkyne, Bu(t)C[triple bond, length as m-dash]P, does, however, insert into one gallyl ligand of the complex, leading to the novel, crystallographically characterised P,N-gallyl complex, [Pt{Ga{[N(Ar)C(H)](2)}}{Ga{PC(Bu(t))C(H)[N(Ar)]C(H)N(Ar)}}(dppe)]. An investigation into the mechanism of this insertion reaction has been undertaken.     

Polymer-anchored platinum complexes as catalysts for the Baeyer–Villiger oxidation of ketones: preparation and catalytic properties

The preparation of a variety of catalysts obtained by ion exchange of the complex [(dppb)Pt(μ−OH)]₂²⁺ with sulfonated styrene–divinylbenzene copolymers is reported. Copolymers used are commercial ion exchange resins containing either 4% or 20% DVB and they were loaded with either Li⁺ or NBu₄⁺ prior to exchange with the Pt complex. Metal loading in the heterogenized catalysts is in the range 2–8% by weight. Their catalytic properties in the Baeyer–Villiger oxidation of methylcyclohexanone with hydrogen peroxide appear to be best in terms of activity and productivity either in neat ketone or in EtOH as the solvent. The use of commercial resins with high exchange capacity prevents the use of DCE as the solvent, i.e., the optimum conditions for the homogeneous system, thereby leading to activities and productivities that are generally lower than their homogeneous counterpart. A discussion on the influence of the philicity properties of the support with respect to the performance of the catalyst is reported.     

Vapor- and mechanical-grinding-triggered color and luminescence switches for bis(σ-fluorophenylacetylide) platinum(II) complexes

Square-planar bis(σ-fluorophenylacetylide) platinum(II) complexes [Pt(Me(3)SiC≡CbpyC≡C-SiMe(3))(C≡CC(6)H(4)F)(2)] (C≡CC(6)H(4)F-2 for 2, C≡CC(6)H(4)F-3 for 3, and C≡CC(6)H(4)F-4 for 4; Me(3)SiC≡CbpyC≡CSiMe(3)=5,5'-bis(trimethylsilylethynyl)-2,2'-bipyridine) were prepared and were characterized by spectroscopic and luminescence studies, and X-ray crystallography. The color and luminescence of crystalline complex 3 is specifically sensitive to CHCl(3) vapor to afford 140-180 nm of luminescence vapochromic redshift, which is useful for specific detection of CHCl(3) vapor. Complex 4 displays selective luminescence vapochromic properties to CH(2)Cl(2) and CHCl(3) vapors with a luminescence vapochromic shift response of ca. 150-200 nm. Interestingly, complexes 2-4 exhibit reversible, and naked-eye perceivable, mechanical stimuli-responsive color and luminescence changes. When solid species 2-4 are crushed gently or ground, the crystalline state is converted to an amorphous phase. Meanwhile, bright yellow-orange luminescence in the crystalline species is converted to dark red under UV light irradiation with 100-160 nm of mechanochromic shift response. A vapochromic or mechanochromic cycle was monitored by dynamic variations in emission spectra and X-ray diffraction (XRD) patterns. The halohydrocarbon vapor- or mechanical-grinding-triggered color and luminescence switches are most likely correlated to a shorted intermolecular Pt-Pt distance as that revealed in vapochromic species 4·0.5 CH(2)Cl(2) by X-ray crystallography, thus leading to an increased contribution from intermolecular Pt-Pt interaction as demonstrated by DTF computational studies.     

Mononuclear zinc(II) and mercury(II) complexes of Schiff bases derived from pyrrolealdehyde and cysteamine containing intramolecular NH?S hydrogen bonds

Two neutral group 12 metal complexes, bis(pyrrol-2-ylmethyleneaminoethylthio)zinc(II) (1) and bis(pyrrol-2-ylmethyleneaminoethylthio)mercury(II) (2), with the (N_imine)₂S₂ coordination mode were synthesized by using metal-templated Schiff base condensation, and their molecular structures were determined by X-ray diffraction analysis. Complex 1 exhibits a distorted tetrahedral geometry around the metal, whereas the metal center has a bisphenoidal configuration in complex 2. Both mononuclear complexes possess intramolecular NH?S hydrogen bonds, as evidenced by IR, ¹H NMR and X-ray crystallography. The hydrogen-bond donor (H-N_pyrrole) and acceptor (S atom) are coming from different ligands within a single molecule. Complex 2 represents the first example of a mercury complex in the N₂S₂ coordination mode with intramolecular NH?S hydrogen-bond interactions. An investigation of the effects of the NH?S hydrogen bonding on the stability of 1 and 2, using an N-methyl pyrrolyl analogue, demonstrated that the N-H hydrogen-bond donor from the pyrrolyl moiety probably played a role in the stability of 1, but not 2.     

"Proof-of-principle" concept for label-free detection of glucose and α-glucosidase activity through the electrostatic assembly of alkynylplatinum(II) terpyridyl complexes

A two-component platinum(II) complex-polymer ensemble has been demonstrated for label-free spectroscopic detection of glucose and α-glucosidase activity, based on the electrostatic assembly of cationic platinum(II) complex molecules onto a glucose-bound anionic polymer.     

Nickel(II), copper(II), palladium(II) and platinum(II) complexes of bidentate SN ligands derived from S-alkyldithiocarbazates and the X-ray crystal structures of the [Ni(tasbz)2] and [Cu(tasbz)2] · CHCl3 complexes

New complexes of general empirical formula, [M(NS)₂] · nCHCl₃ (M = Ni^II, Cu^II, Pd^II or Pt^II; NS = anionic form of the thiophene-2-aldehyde Schiff bases of S-methyl- and S-benzyldithiocarbazate; n = 0, 1) have been synthesized and characterized by physico-chemical techniques. Magnetic and spectroscopic evidence support a square-planar structure for these complexes. The crystal structures of the [Ni(tasbz)₂] and [Cu(tasbz)₂] · CHCl₃ complexes (tasbz = anionic form of the thiophene-2-aldehyde Schiff base of S-benzyldithiocarbazate) have been determined by X-ray diffraction. Both complexes have a trans-planar structure in which the two Schiff base ligands are coordinated to the metal(II) ion as uninegatively charged bidentate ligands via the thiolate sulfur and the azomethine nitrogen atoms. This revised version was published online in June 2006 with corrections to the Cover Date.     

C–H···Onitrate synthon assisted molecular assembly of hydrogen bonded Ni(II) and Cu(II) complexes

Two Schiff base metal complexes [Cu–SPETN·NO₃ (1) and Ni–SPETN·NO₃ (2) [SPETN?=?2,2′-[propane,1,3-diylbis(nitrilomethyldyne)pyridyl,phenolate]] with hydrogen bonding groups have been synthesized and characterized by single-crystal X-ray diffraction. In both of the compounds nitrates occupy a crystallographic general position. In 1 the lattice nitrates are on the 2₁ screw axis while in 2 they are at the crystallographic inversion center. C–H···O_nitrate synthons (formed by the nitrate anions and peripheral hydrogen bonding groups of the metal complexes) are non-covalent building blocks in molecular-assembly and packing of the cationic Schiff base metal complexes (M?=?Ni²⁺, Cu²⁺), resulting in 2-D hydrogen bonded networks. The Cu···Cu non-bonding contact in 1 is 3.268?Å while the Ni–Ni bonding distance in 2 is 3.437?Å.     

Synthesis and magnetic properties comparison of M-Cu(II) and M-VO(II) Schiff base-porphyrazine complexes: what is the mechanism for spin-coupling?

Dimetallic Schiff base-porphyrazine (pz) compounds, denoted 1[M(1); M(2); R], have been prepared, where metal ion M(1) is incorporated into the pz core, and metal ion M(2) is bound to a bis(5-tert-butylsalicylidenimine) chelate built onto two amino nitrogens attached to the pz periphery; R is a solubilizing group (either propyl (Pr) or 3,4,5-trimethoxyphenyl (TMP)) attached to the remaining carbons of the pz periphery. The synthesis of 1[Cu; Cu; R], 1[Cu; VO; R], 1[ClMn; Cu; Pr], and 1[ClMn; VO; Pr] is discussed, the crystal structures of 1[Cu; Cu; TMP] and 1[ClMn; VO; Pr] are presented, and the magnetic properties of these compounds are compared. The pattern of ligand-mediated exchange coupling in these complexes is startling: for the Cu-M(2) complexes 1[Cu; VO; R] and 1[Cu; Cu; R], 2 x 10(2) < or = |J(Cu-VO)/J(Cu-Cu)|; for the ClMn-M(2) complexes 1[ClMn; Cu; Pr] and 1[ClMn; VO; Pr], J(ClMn-VO)/J(ClMn-Cu) approximately 1/3, an inverse ratio from that of the Cu-M(2) complexes, but with lesser discrimination. This coupling pattern is explained in terms of a novel orientation relative to the M(1)-M(2) direction: the "square-planar" Schiff base ligand set of M(2) is rotated in-plane by 45 degrees relative to the effectively coplanar pz ligand set of M(1).     

Understanding the electronic and π-conjugation roles of quinoline on ligand substitution reactions of platinum(II) complexes

A kinetic and mechanistic study of chloride substitution by thiourea nucleophiles, namely thiourea, N-methylthiourea, N,N-dimethylthiourea and N,N,N′,N′-tetramethylthiourea in the complexes chlorobis-(2-pyridylmethyl)amineplatinum(II) (Pt1), chloro N-(2-pyridinylmethyl)-8-quinolinamineplatinum(II) (Pt2), chloro N-(2-pyridinylmethylene)-8-quinolinamineplatinum(II) (Pt3) and chlorobis(8-quinolinyl)amineplatinum(II) (Pt4) was undertaken under pseudo-first-order conditions using UV–visible spectrophotometry. The study showed that lability of the chloro leaving group is dependent on the strength of π-interactions between the filled dπ-orbitals of the metal and the empty π*-orbitals of the chelating ligand in the following manner: Pt1 > Pt3 > Pt2 > Pt4. Introduction of the quinoline moiety within the non-labile chelated framework of the Pt(II) complexes results in a more electron-rich metal centre which retards the approach of the nucleophile through repulsion. Moreover, the net σ-effect of the ligand moiety plays a significant role in controlling the reactivity of the complexes. The experimental results are interpreted with the aid of computational data obtained by density functional theory (B3LYP(CPCM)/LANL2DZp//B3LYP/-LANL2DZp) calculations. The mode of substitution remains associative as supported by negative entropies and the dependence of the second-order rate constants on the concentration of entering nucleophiles.     

DFT and TDDFT investigations on the ground and excited states for polynuclear platinum(II) complexes containing the rigid phenylacetylide ligand

We have studied the ground and excited states of the three dendritic polynuclear Pt(II) complexes 1-[Cl(PH3)2PtC≡≡ C]-3,5-[HC≡≡ C]C6H3 (1), 1,3-[Cl(PH3)2PtC≡≡ C]2-5-[HC≡≡ C]C6H3 (2), and 1,3,5-[Cl(PH3)2- PtC≡≡ C]3C6H3 (3), by using the B3LYP and UB3LYP methods, respectively. TDDFT approach with the PCM model was performed to predict the emission spectra properties of 1―3 in CH2Cl2 solution. We first predicted the excited-state geometries for the three complexes. With the change of the number of Pt(II) atom, 1―3 show the different geometry structures in both the ground and excited states; fur- thermore, the increase of the metal density from 1 to 3 results in the red shift of the lowest-energy emissions along the series. The luminescent properties of 1 are somewhat different from those of 2 and 3. The emission properties of 2 and 3 are richer than 1. Our conclusion can give a good support for designing the high efficient luminescent materials.     

Studies of copper (Ⅱ) complexes as catalysts for the hydrolysis of DNA

Hydrolysis of DNA is an important enzymatic reaction , but it is exceedingly difficult to mimic in the laboratory because of the stability of hydrolysis of DNA. In this paper, the cleavage activity of complexes formed between Cu(Ⅱ) and four different amino acid or amino acid methyl ester on DNA is studied by gel elec-trophoresis. It is found that DNA could be cleaved by Cu(Ⅱ)-L-His and Cu(Ⅱ)-L-His methyl ester complexes and the efficiency of cleavage is largely dependent on the metal ion-to-ligand ratio. Further experiments show that the cleavage of DNA mediated by Cu(Ⅱ)-L-His complexes occurs via a hydrolytic mechanism and the active chemical species that affects DNA cleavage is proposed to be MI2H and ML2H22 .     

Comparative selectivities of two copper-based catalysts: Mixed Cu?Cr and Cu?Al oxides for allylic alcohol reactions in the presence of molecular hydrogen

In the presence of mixed copper-chromium (aluminium) oxide, allylic alcohols react with molecular hydrogen and lead to several primary products. This is due to the simultaneous presence of two active sites in the mixed oxides. Copper species (Cu⁺) are responsible for hydrogenation (HYD) and the chromium (Cr³⁺) (aluminium [Al³⁺]) species for the isomerization (I) and the hydrodeoxygenation (HDO) reactions. However, the stronger acidic character of Al³⁺, compared with Cr³⁺, entails some differences evidenced by the HYD/(I+HDO) and HDO/I ratios.

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- () , . . (Cu⁺ (), (Cr³⁺) ( Al³⁺) (), (). , Al³⁺ Cr³⁺ , /(+) /.

     

Cytotoxic properties of platinum(IV) and dinuclear platinum(II) complexes and their ligand substitution reactions with guanosine-5′-monophosphate

The substitution reaction of the Pt(IV) complex [PtCl₄(bipy)] with guanosine-5??-monophosphate (5??-GMP) was studied by UV?CVis spectrophotometry. This reaction was investigated under pseudo-first-order conditions at 37?°C in 25?mM Hepes buffer (pH?=?7.2) in the presence of 10?mM NaCl to prevent the hydrolysis of the complex. The substitution of chlorides in [{trans-Pt(NH₃)₂Cl}₂(??-1,2-bis(4-pyridyl)ethane)](ClO₄)₂ (Pt3) complex by 5??-GMP was followed by ¹H NMR spectroscopy under second-order conditions. Very similar values for the rate constants of both substitution steps were obtained. The Pt(IV) complexes, [PtCl₄(bipy)] and [PtCl₄(dach)], as well as dinuclaer Pt(II) [{trans-Pt(NH₃)₂Cl}₂(??-pyrazine)](ClO₄)₂ (Pt1), [{trans-Pt(NH₃)₂Cl}₂(??-4,4??-bipyridyl)](ClO₄)₂?·?DMF (Pt2) and [{trans-Pt(NH₃)₂Cl}₂(??-1,2-bis(4-pyridyl)ethane)](ClO₄)₂ (Pt3) complexes, displayed potent cytotoxic activity against human ovarium carcinoma cell line TOV21G and lower activity toward human colon carcinoma HCT116 cell line at the same concentrations. Our data indicate that these platinum complexes could be explored further, as potential therapeutic agents for ovarian cancer.     

Structural characterization and cytotoxicity studies of ruthenium(II)–dmso–chloro complexes of chalcone and flavone derivatives

A synthetic precursor cis-[Ru^IICl₂(dmso)₄] is complexed separately with 3-(4-benzyloxyphenyl)-1-(2-hydroxylphenyl)-prop-2-en-1-one (L¹H) and 2-(4-benzyloxyphenyl)-3hydroxy-chromen-4-one (L²H). The resulting complexes are assigned the composition fac-[RuCl(S-dmso)₃(L¹)] 1 and fac-[RuCl(S-dmso)₃(L²)] 2 using elemental analyses, FAB mass data and spectroscopic (IR, ¹H NMR, UV–Vis, emission) spectral properties. The X-ray diffraction analysis shows that complexes self-associate through non-covalent interactions and provide 1D and 2D supramolecular structures. These complexes are assayed for their cytotoxicity studies on Dalton Lymphoma cell lines.     

C?H bond functionalization of aromatic heterocycles with chelating dicarbene palladium(II) and platinum(II) complexes

Chelating dicarbene complexes of palladium(II) and platinum(II) catalyse at room temperature with 1% catalyst loading the reaction of ethyl phenylpropiolate with aromatic heterocycles to yield synthetically useful intermediates for fine chemicals without the need to use prefunctionalized substrates. The reaction outcome was found to be strongly dependent on the nature of the anionic ligands at the metal complex. Addition of silver salts to replace halide ligands with more weakly coordinating anions improves the reaction yield and changes the product distributions: heterocycle? alkyne 2:1 adducts are obtained together with the usual hydroarylation products, which potentially broadens the scope of the reaction. The nature of the employed heterocycle, in particular its steric characteristics, is also found to strongly influence the outcome of the reaction. Copyright © 2009 John Wiley & Sons, Ltd.     

Cationic palladium(II)–acetylacetonate complexes bearing pyridinyl imine ligands as catalysts for the hydroamination of phenylacetylene and polymerization of norbornene

Acetylacetonate palladium(II) complexes bearing pyridinyl imine ligands [Pd(acac)(L)]BF₄ were synthesized via nitrile displacement in [Pd(acac)(MeCN)₂]BF₄ by the bidentate ligands L of type 2-C₅H₄N–CH=N–(CH₂)_nOMe or 2-C₅H₄N–CH=N–Ar. The structures of complexes were analyzed by X-ray diffractometry, NMR, and DFT. The complexes catalyze hydroamination of phenylacetylene with aniline to give the Markovnikov imine product as well as polymerization of norbornene.     

Bis(imidate)palladium(II) complexes with labile ligands. Mimics of classical precursors?

A novel synthetic route to prepare palladium(II) precursor analogous of classical [Pd(Cl)(2)(solvent)(2)] has been developed. Just stirring Pd(3)(AcO)(6) in dimethyl sulfide at room temperature, in the stoichiometric presence of protic imidate ligands, resulted in the precipitation of the desired complexes [Pd(imidate)(2)(SMe(2))(2)] (imidate = succinimidate (succ) 1, phthalimidate (phthal) 2, maleimidate (mal) 3, saccharinate (sac) 4 or glutarimidate (glut) 5). The new complexes are very soluble in common solvents and have been fully characterized, including an X-ray diffraction analysis of 2. Analogous reactions with succinimide in acetonitrile or dimethylsulfoxide produced [Pd(succinimidate)(2)(solvent)(2)] (6 and 7, respectively) as off-white powders. Thermal decomposition of 6 produces a new species 6* with bridging imidate ligands that can be formulated as a trimer similar to Pd(3)(AcO)(6). The usefulness of 1-5 as precursors has been tested by reactions against monodentated neutral donor ligands, PPh(3) (a compounds), or pyridine (py, b compounds), to produce ten new derivatives of the general formula trans-[Pd(imidate)(2)(L)(2)]. The single-crystal structures of compounds 2a, 3a, 4a, 4a', 5a and 4b have also been established, allowing an interesting molecular and supramolecular structural discussion. A cis-conformation was induced when the bidentate chelate ligand 1,2-bis(diphenylphosphino)benzene (dppb, c compounds) was made to react with 1-5. Structural characterization by X-ray diffraction of complex 2c confirmed the proposed formula. Catalytic activity in Suzuki-Miyaura cross-coupling of aryl bromides and benzyl bromides with aryl boronic acids has been tested.     

Studies on platinum(II) and palladium(II) complexes of some N,N′-disubstituted thiourea derivatives

Summary A series of new Pt^II and Pd^II complexes of N,N-disubstituted thiourea derivatives of general formulae [MLCl₂]₂, [ML₂Cl₂] and [ML₄]Cl₂ have been prepared and characterised by physicochemical and spectroscopic methods. The reaction of these ligands with [M(DMSO)₂Cl₂], M = Pt, cis- or Pd, trans-, in CHCl₃ and EtOH at ambient temperature or under reflux, is described.     

Syntheses of (imidazole)pentaamminemetal(III) and μ-imidazolatodecaamminedimetal(III) complexes from trifluoromethanesulfonato precursors

The [M(NH₃)₅(imidH)]³⁺ complex ions (M = Co, Rh or Ir; imidH = imidazole) can be readily prepared by reaction of [M(NH₃)₅(OSO₂CF₃)]²⁺ ions with imidazole in sulfolane. Subsequent reaction of [M′(NH₃)₅(OSO₂CF₃)]²⁺ with [M(NH₃)₅(imidH)]³⁺ in sulfolane in the presence of a non-coordinating base permits synthesis of the binuclear imidazolate-bridged complexes [(NH₃)₅M(imid)M′(NH₃)₅]⁵⁺ (M = M′= Co or Rh; M = Co, M′ = Rh), characterized by spectroscopic, chromatographic and voltammetric methods, and by reactivity.