Redox chemistry of gold(i) phosphine thiolates: sulfur-based oxidation

The redox chemistry of mononuclear and dinuclear gold(I) phosphine arylthiolate complexes was recently investigated by using electrochemical, chemical, and photochemical techniques. We now report the redox chemistry of dinuclear gold(I) phosphine complexes containing aliphatic dithiolate ligands. These molecules differ from previously studied gold(I) phosphine thiolate complexes in that they are cyclic and contain aliphatic thiolates. Cyclic voltammetry experiments of Au(2) (LL)(pdt) [pdt = propanedithiol; LL = 1,2-bis(diphenylphosphino)-ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), 1,4-bis(diphenylphosphino)butane (dppb), 1,5-bis(diphenylphosphino)pentane (dpppn)] in 0.1 M TBAH/CH(3)CN or CH(2)Cl(2) solutions at 50 to 500 mV/sec using glassy carbon or platinum electrodes, show two irreversible anodic processes at ca. +0.6 and +1.1 V (vs. SCE). Bulk electrolyses at +0.9 V and +1.4 V result in n values of 0.95 and 3.7, respectively. Chemical oxidation of Au(2)(dppp)(pdt) using one equivalent of Br(2) (2 oxidizing equivalents) yields 1,2-dithiolane and Au(2)(dppp)Br(2). The reactivity seen upon mild oxidation /= +1.3 V) is consistent with oxidation of gold(I) to gold(III). Structural and electrochemical differences between gold(I) aromatic and aliphatic thiolate oxidation processes are discussed.     

Electronic and steric effects in gold(i) phosphine thiolate complexes

The unusual yellow color of Au(2)(dppm)(SR)(2) (R = 4-tolyl; dppm = diphenylphosphinomethane) is attributed to a red-shift in the S-->Au charge transfer caused by destabilization of the sulfur highest occupied molecular orbital (HOMO). Variable temperature experiments show two broad bands at -80 degrees C in the (31)P{(1)H} NMR spectrum of Au(2)(dppm)(SR)(2) and the activation energy for interconversion is 10 kcal/mol. Only one sharp band is observed down to -80 degrees C in the spectrum of the white complex, Au(2)(dppe)(SR)(2) (dppe = diphenylphosphinoethane). Molecular mechanics calculations on Au(2)(dppm)(SR)(2) and Au(2)(dppe)(SR)(2) reveal that, for Au(2)(dppe)(SR)(2), a series of maxima and minima, separated by 2.5 kcal/mol, occur every 120 degrees which is consistent with rotation around an unhindered carbon-phosphorus single bond. The Au atoms are not within bonding distance in any conformation. Computational results for Au(2)(dppm)(SR)(2) indicate one minimum energy structure in which the Au-P bonds are anti. There is a high energy conformation (9 kcal/mol above the global minimum) where overlap between golds is maximized. The implications of gold-gold bonding in this complex are discussed. The steric influence of the thiolate ligand has been examined by synthesizing a series of dinuclear gold(I) complexes in which the steric properties of the thiolate are varied: Au(2)(dppm)(SR)(2) (R = 2,6-dichlorophenyl; 2,6-dimethylphenyl; 3,5-dimethylphenyl). The 2,6-disubstituted complexes are white, while the 3,5-dimethyl complex is yellow. These results, along with VT-NMR experiments, are consistent with the conclusion that the more sterically-bulky thiolates hinder the close approach of the golds in the dinuclear complexes.     

Ligand effects on the stability of thiol-stabilized gold nanoclusters: Au25(SR)18(-), Au38(SR)24, and Au102(SR)44

We have studied the electrochemical and thermodynamic stability of Au(25)(SR)(18)(-), Au(38)(SR)(24), and Au(102)(SR)(44), R = CH(3), C(6)H(13), CH(2)CH(2)Ph, Ph, PhF, and PhCOOH, in order to examine ligand effects on the stability of thiol-stabilized gold nanoclusters, Au(m)(SR)(n). Aliphatic thiols, in general, have higher electrochemical and thermodynamic stability than aromatic thiols, and the -SCH(2)CH(2)Ph thiol is particularly appealing because of its high electrochemical and thermodynamic stability. The stabilization of Au(m) by nSR for Au(m)(SR)(n) can be rationalized by the stabilization of an Au atom by an SR for the simple molecule AuSR, regardless of interligand interaction and system size and shape. Thiol moieties play a strong role in the electron oxidation and reduction of Au(m)(SR)(n). Accounting for the characteristics of thiol ligands is essential for understanding the electronic and thermodynamic stability of thiol-stabilized gold nanoclusters.     

Different coordination modes of a tripod phosphine in gold(i) and silver(i) complexes

The following gold(I) and silver(I) complexes of the tritertiary phosphine 1,1,1- tris(diphenylphosphinomethyl)ethane, tripod , have been synthesised: Au(3)(tripod)X(3) [X = Cl(1), Br(2), I(3)]; [Au(3)(tripod)(2)Cl(2)]Cl (4); Au(tripod)X [X = Br(5), I(6)]; Ag(3)(tripod) (NO(3))(4) (7), Ag(tripod)NO(3) (8). They were characterized by X-ray diffraction (complexes 2, 3 and 4), (31)P NMR spectroscopy, electrospray and FAB mass spectrometry and infrared spectroscopy. Complexes 2 and 3 show a linear coordination geometry for Au(I), with relatively short Au-P bond distances. Complex 3 has a Au***Au intramolecular distance of 3.326 A degrees , while complex 2 had a short Au***Au intermolecular interaction of 3.048 A degrees . Complexes 4-6 were found by (31)P NMR spectroscopy studies to contain a mixture of species in solution, one of which crystallised as [Au(3)(tripod|)(2)Cl(2)]Cl which was shown by X-ray diffraction to contain both tetrahedral and linear Au(I), the first example of a Au(I) complex containing such a mixture of geometries. The reaction of [Au(3) (tripod)Cl(3)] (1) with tripod led successfully to the formation of [Au(3)(tripod|)(2)Cl(2)](+) and [Au(3)(tripod)(2)Cl(3)](+) and [Au(3)(tripod|)(3)Cl](2+). The silver(I) complexes, 7 and 8 appear to contain linear and tetrahedral Ag(I), respectively.     

Reactions of organic disulfides and gold(i) complexes

Gold-thiolate/disulfide exchange reactions of (p-SC(6)H(4)Cl)(2) with Ph(3)PAu(SC(6)H(4)CH(3)), dppm(AuSC(6)H(4)CH(3))(2), and dppe(AuSC(6)H(4)CH(3)) (2) were investigated. The rate of reactivity of the gold-thiolate complexes with (p-SC(6)H(4)Cl)(2) is: dppm(AuSC(6)H(4)CH(3))(2)> dppe(AuSC(6)H(4)CH(3))(2)>Ph(2)PAu (SC(6)H(4)CH(3)). This order correlates with conductivity measurements and two ionic mechanisms have been evaluated. (1)H NMR experiments demonstrate that in the reaction of dppm(AuSC(6)H(4)CH(3))(2) with (p-SC(6)H(4)Cl)(2), the mixed disulfide, ClC(6)H(4)SSC(6)H(4)CH(3), forms first, followed by the formation of (p-SC(6)H(4)CH(3))(2). The rate law is first order in (pp-SC(6)H (4)Cl)(2) and partial order in dppm(AuSC(6)H(4)CH(3))(2). Results from electrochemical and chemical reactivity studies suggest that free thiolate is not involved in the gold-thiolate/disulfide exchange reaction. A more likely source of ions is the dissociation of a proton from the methylene backbone of the dppm ligand which has been shown to exchange with D(2)O. The implications of this are discussed in terms of a possible mechanism for the gold-thiolate/disulfide exchange reaction.     

Bidentate amino- and iminophosphine ligands in mono- and dinuclear gold(I) complexes: Synthesis,structures and AuCl displacement by AuC6F5

Bidentate imino- and aminophosphine ligands were prepared by firstly a Schiff-base condensation reaction between 2-(diphenylphosphino)benzaldehyde and the corresponding primary amines to afford the imino derivatives and secondly reduction of the imines with NaBH₄ to the aminophosphine ligands in satisfactory yields. The ligands readily reacted with chlorogold(I) compounds to produce new mononuclear iminophosphine- and dinuclear aminophosphine chlorogold(I) complexes. Further, reaction of the dinuclear chlorogold complex with C₆F₅Au(tht) (tht = tetrahydrothiophene) led to the displacement of one AuCl moiety by AuC₆F₅ forming a digold(I) mixed halogen/organometallic complex. Both digold(I) complexes displayed intramolecular Au⋯Au interactions, whilst the di(chlorogold) complex also showed an intermolecular Au⋯ Au interaction, as determined by X-ray crystallography. The displacement of only one of the two AuCl groups presumably relates to the strength of the Au–P bond (inert) vs. the weakness of the Au–N bond (labile), the latter being more easily broken.     

Redox Chemistry and [Au(CN)(2)] in the Formation of Gold Metabolites

The role of hypochlorite ion, which can be generated by the enzyme myleoperoxidase, in the biochemistry of gold(I) anti-arthritic drugs was investigated. Sodium hypochlorite (OCl(-)) directly and rapidly oxidizes AuSTm, Au(CN)(2) (-), AuSTg (gold thioglucose) and auranofin (Et(3)PAuSATg). The resulting gold(III) species were detected by an Ion Chromotography Ion-Pairing technique that was developed to distinguish gold(I) and gold(III). Formation of Au(III) was also demonstrated spectrophotometrically after the conversion to AuCl(4) (-). The reactions of AuSTm, AuSTg, and auranofin are complex and gold(III) appears only after the initial oxidation of the thiolate (and phosphine) ligands.The enzymatic reaction, using MPO with H(2)O(2) and Cl(-) as substrates, leads to slow oxidation of Au(CN)(2) (-), AuSTm or AuSTg. The extent and rate of reaction depend on the concentrations of MPO, H(2)O(2), and Au(I). The continued presence of Au(I) during the initial stages of reaction (oxidation of the thiolates in AuSTm and AuSTg) and the conversion to Au(III) in the latter stages of the reaction were demonstrated. Au(CN)(2) (-), a gold metabolite, binds tightly to serum albumin. Unlike other gold(I) complexes, aurocyanide reacts almost negligibly at Cys-34 via ligand exchange. Instead, there is a strong association (K(1) = 5.5 x 10(4) and K(2) = 7.0 x 10(3); n(1) = 0.8 and n(2) = 3) of intact Au(CN)(2) (-). The full extent of binding is revealed only by equilibrium methods such as NMR or ultrafiltration; the bound gold dissociates extensively on conventional gel-exclusion columns and partially on Penefesky spun columns.The immunological and pharmacological significance of these results are discussed.     

Ternary Copper(II) Complexes in Solution Formed With 8-Aza Derivatives of the Antiviral Nucleotide Analogue 9-[2-(Phosphonomethoxy)Ethyl]Adenine (PMEA)

The stability constants of the mixed-ligand complexes formed between Cu(Arm)(2+), where Arm= 2,2'-bipyridine (Bpy) or 1,10-phenanthroline (Phen), and the dianions of 9-[2-(phosphonomethoxy)ethyl]-8-azaadenine (9,8aPMEA) and 8-[2-(phosphonomethoxy)ethyl]-8-azaadenine (8,8aPMEA) (both also abbreviated as PA(2-)) were determined by potentiometric pH titrations in aqueous solution (25 ( degrees )C; I = 0.1 M, NaNO(3)). All four ternary Cu(Arm)(PA) complexes are considerably more stable than corresponding Cu(Arm)(R-PO(3)) species, where R-PO(3) (2-) represents a phosph(on)ate ligand with a group R that is unable to participate in any kind of interaction within the complexes. The increased stability is attributed to intramolecular stack formation in the Cu(Arm)(PA) complexes and also to the formation of 5-membered chelates involving the ether oxygen present in the -CH(2)-O-CH(2)-PO(3) (2-) residue of the azaPMEAs. A quantitative analysis of the intramolecular equilibria involving three structurally different Cu(Arm)(PA) species is carried out. For example, about 5% of the Cu(Bpy)(8,8aPMEA) system exist with the metal ion solely coordinated to the phosphonate group, 14% as a 5-membered chelate involving the -CH(2)-O-CH(2)-PO(3) (2-)residue, and 81% with an intramolecular stack between the 8-azapurine moiety and the aromatic rings of Bpy. The results for the other systems are similar though with Phen a formation degree of about 90% for the intramolecular stack is reached. The existence of the stacked species is also proven by spectrophotometric measurements. In addition, the Cu(Arm)(PA) complexes may be protonated, leading to Cu(Arm)(H;PA)(+) species for which it is concluded that the proton is located at the phosphonate group and that the complexes are mainly formed by a stacking adduct between Cu(Arm)(2+) and H(PA)(-). Conclusions regarding the biological properties of these azaPMEAs are shortly indicated.     

Approaches to the Chemical,Electrochemical, and Photochemical Activation of Carbon Dioxide by Transition Metal Complexes

The activation of CO₂ by chemical, electrochemical, and photochemical means is discussed. Binuclear transition metal complexes mediate oxygen atom transfers from CO₂ by three distinct chemical pathways: (i) deoxygenation of CO₂, (ii) multiple bond metathesis, and (iii) disproportionation. The complex Ir₂ (μ-CNR)₂(CNR)₂(dmpm),(dmpm = bis(dimethylphosphino)methane) undergoes double cycloaddition of CO₂ to its μ-CNR ligands. A subsequent reaction produces the bis(carbamoyl) complex [Ir₂(μ-CO)(μ-H)(CONHR)₂(CNR)₂(dmpm)₂]Cl. Isotope labelling studies show that the μ-CO ligand results from net deoxygenation of CO₂. In contrast, the binuclear nickel complex Ni₂(μ-CNMe)(CNMe)₂(dppm)₂ (dppm = bis-(diphenylphosphino)methane) reacts with liquid CO₂ to give the tricarbonyl complex Ni₂(μ-CO)(CO)₂(dppm)₂. Isotope labelling indicates that the carbonyl ligands are not derived from CO₂ deoxygenation, but from C/CO triple bond metathesis. The reaction of CO₂ with the Ir(0) complex Ir₂(CO)₃(dmpm)₂ leads to CO₂ disproportionation by formation of the carbonate, Ir₂(CO₃)(CO)₂(dmpm)₂, and tetracarbonyl, Ir₂(CO)₄(dmpm)₂, complexes. The complex Ir₂(CO₃)(CO)₂ (dmpm)₂ undergoes reversible O-atom transfers from its carbonate ligand. The electrochemical activation of CO₂ by the binuclear Ni₂(μ-CNMe)(CNMe)₂(dppm)₂ and trinuclear [Ni₃(μ-CNMe)(μ-I)(dppm)₃][PF₆] species is described. The triangular nickel complex [Ni₃(μ₃-CNMe)(μ₃-I)(dppm)₃][PF₆] is an electrocatalyst for the reduction of CO₂. The cluster exhibits a reversible single electron reduction at E⁰(^+/0) = −1.09 V vs. Ag/AgCl. In the presence of CO₂, the cluster reduces CO₂ by an EC' electrochemical mechanism. The reduction products correspond to the disproportionation and H-atom abstraction products of CO₂^*−, with a partitioning ratio of 10:1. Isotope labelling studies with ¹³CO₂ indicate that ¹³CO₂^*− disproportionation produces ¹³CO and ¹³CO₃²⁻. Studies of the photochemical activation of CO₂ by Ni₂(μ-CNMe)(CNMe)₂(dppm)₂ are described. The bimolecular photochemical addition of CO₂ to the complex was examined by laser transient absorbance spectroscopy. Photolysis at 355nm in the presence of CO₂ (1 atm) leads to cycloaddition of CO₂ to the μ-CNMe ligand and the complex Ni₂(μ-CN(Me)C(O)O)(CNMe)₂(dppm)₂ with Φ₃₅₅=0.05. The triplet excited state of Ni,(μ-CNMe)(CNMe)₂(dppm)₂ was determined to react with CO₂ with the bimolecular reaction rate constant k = 1 × 10⁴ M⁻¹ s⁻¹. Bridging ligand substituent effects and solvent dependence of the lowest energy electronic absorption spectral bands of the series of complexes, Ni₂(μ-L)(CNMe)₂(dppm)₂, L = CNMe, CNC₆H₅, CN-p-C₆H₄Cl. and CN-p-C₆H₄Me, confirm the assignment of di-metal to bridging ligand charge transfer (M₂→μ-LCT). This assignment is supported by results of extended Hückel calculations which indicate a LUMO of predominantly μ-isocyanide π* character. A systematic study of the nature of the lowest excited states of related d¹⁰–d¹⁰ binuclear complexes of the type Ni₂(μ-L)(CNMe)₂(dppm)₂, where L = CNMe(Ph)⁺, CNMe₂⁺, CNMe(C₅H₁₁)⁺, CNMe(H)⁺, CNMe(CH₂C₆H₅)⁺, and NO⁺ reveals dramatic differences in the lowest excited states of the three classes of complexes: μ-isocyanide, μ-aminocarbyne, and μ-nitrosyl. Spectroscopic and extended Hückel MO studies confirm that the μ-isocyanide complexes are characterized by di-metal to bridging ligand charge transfer (M₂ → μ-LCT) excited states. However, the μ-aminocarbyne and μ-nitrosyl complexes exhibit bridging ligand to metal charge transfer (μ-L→M₂) and intraligand (IL) lowest excited states, respectively.     

The halogen analogs of thiolated gold nanoclusters

Is it possible to replace all the thiolates in a thiolated gold nanocluster with halogens while still maintaining the geometry and the electronic structure? In this work, we show from density functional theory that such halogen analogs of thiolated gold nanoclusters are highly likely. Using Au(25)X(18)(-) as an example, where X = F, Cl, Br, or I replaces -SR, we find that Au(25)Cl(18)(-) demonstrates a high similarity to Au(25)(SR)(18)(-) by showing Au-Cl distances, Cl-Au-Cl angles, band gap, and frontier orbitals similar to those in Au(25)(SR)(18)(-). DFT-based global minimization also indicates the energetic preference of staple formation for the Au(25)Cl(18)(-) cluster. The similarity between Au(m)(SR)(n) and Au(m)X(n) could be exploited to make viable Au(m)X(n) clusters and to predict structures for Au(m)(SR)(n).     

Gold(I)‐Catalyzed Tandem Alkoxylation/Lactonization of γ‐Hydroxy‐α,β‐Acetylenic Esters

The formation of 4‐alkoxy‐2(5H)‐furanones was achieved via tandem alkoxylation/lactonization of γ‐hydroxy‐α,β‐acetylenic esters catalyzed by 2 mol% of [2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidine]gold bis(trifluoromethanesulfonyl)imidate [Au(IPr)(NTf₂)]. The economic and simple procedure was applied to a series of various secondary propargylic alcohols allowing for yields of desired product of up to 95%. In addition, tertiary propargylic alcohols bearing mostly cyclic substituents were converted into the corresponding spiro derivatives. Both primary and secondary alcohols reacted with propargylic alcohols at moderate temperatures (65–80 °C) in either neat reactions or using 1,2‐dichloroethane as a reaction medium allowing for yields of 23–95%. In contrast to [Au(IPr)(NTf₂)], reactions with cationic complexes such as [2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidine](acetonitrile)gold tetrafluoroborate [Au(IPr)(CH₃CN)][BF₄] or (μ‐hydroxy)bis{[2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidine]gold} tetrafluoroborate or bis(trifluoromethanesulfonyl)imidate – [{Au(IPr)}₂(μ‐OH)][X] (X=BF₄, NTf₂) – mostly stop after the alkoxylation. Analysis of the intermediate proved the exclusive formation of the E‐isomer which allows for the subsequent lactonization.     

DFT研究钌配合物[Ru（bpy）2（o—R—pip）]^2＋与DNA键合

理论运用密度泛函（DFT）方法,计算钌（Ⅱ）配合物[Ru（bpy）2（o-R-pip）]^2＋（R=-OH,-H,-OCH3）的电子结构和与DNA键合倾向。证实了引入取代基（-OH）导致分子内氢键形成进而导致插入配体共轭面积的增大以及配合物最低空轨道LUMO和相邻的最低空轨道（LUMO＋x,X=0,1,2）的能量明显降低,可大大改善配合物与DNA的键合常数（Kb）。钌配合物与DNA的键合倾向,即Kb（3）〈Kb（2）〈Kb（1）,得以理论解释。     

Unexpected reactivity of Au25(SCH2CH2Ph)18 nanoclusters with salts

We report some interesting results of the chemical reactivity of thiolate-protected [Au(25)(SCH(2)CH(2)Ph)(18)](0) nanoclusters with two types of salts, including tetraoctylammonium halide (TOAX) and NaX. At the early stage of the reaction, [Au(25)(SCH(2)CH(2)Ph)(18)](0) was found to spontaneously convert to its anionic form ([Au(25)(SCH(2)CH(2)Ph)(18)](-)) in the presence of either type of salt. However, a large difference was observed in the second stage of the reaction. With NaX, we observed decomposition of anionic clusters, while with TOAX, the clusters show excellent stability. We have gained some insight into the reaction mechanism. The X(-) ions seem to attack [Au(25)(SCH(2)CH(2)Ph)(18)](q) surface and displace some thiolates, evidenced by the observation of halide-bound clusters such as Au(25)(SCH(2)CH(2)Ph)(18-x)Br(x) in mass spectrometry analysis. These halide-bound clusters show a reduced stability, and their decomposition into Au(I) complexes leads to the release of gold valence electrons of the clusters; concurrently, the non-halide-bound [Au(25)(SCH(2)CH(2)Ph)(18)](0) clusters are reduced into [Au(25)(SCH(2)CH(2)Ph)(18)](-). For the second stage of reaction with organic salts such as TOA-Br, after [Au(25)(SCH(2)CH(2)Ph)(18)](0) clusters are converted to [Au(25)(SCH(2)CH(2)Ph)(18)](-)) the TOA(+) counterions surprisingly protect the anionic clusters from further attack by halide ions, hence, TOA(+) cations can stabilize [Au(25)(SCH(2)CH(2)Ph)(18)](-) clusters. In contrast, with NaX salts the Na(+) ions do not provide any steric stabilization of the [Au(25)(SCH(2)CH(2)Ph)(18)](-) clusters, hence, degradation occurs when being further attacked by halide ions, especially Br(-) and I(-).     

二氰基二硫纶·邻菲咯啉-5,6-二酮混配锰(Ⅱ)、铁(Ⅱ)、钴(Ⅱ)配合物的感光氧化特性

测定了二氰基二硫纶·邻菲咯啉-5,6-二酮混配锰(Ⅱ)、铁(Ⅱ)、钴(Ⅱ)配合物MLL'(M=Mn2+、Fe2+、Co2+；L=mnt2-,1,2-二氰基乙烯-1,2-二硫醇离子；L'=phen-5,6-dione,1,10-邻菲咯啉-5,6-二酮)在二甲基亚砜(DMSO)、丙酮(Acet)和氯仿(CHCl3)中的电子...     

Biologically-Active Gold(III) Complexes

A review is given of the background to and results of the succesful pharmacological testing of [AuX(2)(damp)] (X = Cl, OAc; damp = 2-Me(2) NCH(2)C(6) H(4)) against a range of microbes, fungi and tumouts, culminating in in vivo xenografts of ZR-1-75. These are the first fully evaluated gold(III) complexes. The activity and reactions of the diacetato-complex bear a resemblance to cisplatin, and some of the relevant chemistry is discussed. Preliminary screening data for C,P-chelated tertiary phosphine derivatives of gold(III) are presented.     

Electronegativity Governs Enantioselectivity: Alkyl‐Aryl Cross‐Coupling with Fenchol‐Based Palladium‐Phosphorus Halide Catalysts

A series of bulky, modular, monodentate, fenchol‐based phosphites has been employed in an intramolecular palladium‐catalyzed alkyl‐aryl cross‐coupling reaction. This enantioselective α‐arylation of N‐(2‐bromophenyl)‐N‐methyl‐2‐phenylpropanamide is accomplished with [Pd(C₃H₅)(BIFOP‐X)(Cl)] as precatalysts, which are based on biphenyl‐2,2′‐bisfenchol phosphites (BIFOP‐X, X=F, Cl, Br, etc.). The phosphorus fluoride BIFOP‐F gives the highest enantioselectivity and good yields (64% ee, 88%). Lower selectivities and yields are found for BIFOP halides with heavier halogens (Cl: 74%, 47% ee, Br: 63%, 20% ee). NMR studies on catalyst complexes reveal two equilibrating diastereomeric complexes in equal proportions. In all cases, the phosphorus‐halogen moiety remains intact, pointing to its remarkable stability, even in the presence of nucleophiles. The increasing enantioselectivity of the catalysts with the phosphorus halide ligands correlates with the rising electronegativity of the halide (bromine<chlorine<fluorine), as can be rationalized from structural parameters and DFT computations.     

A novel organometallic ReI complex with favourable properties for bioimaging and applicability in solid-phase peptide synthesis

Organometallic complexes possess great potential for imaging applications in biology, due to their kinetic stability and often favourable intrinsic properties. In this work we present a new class of Re(I) -tricarbonyl complexes with a substituted bis(phenanthridinylmethyl)amine (bpm) ligand. The complex Re(CO)(3) (R-bpm) could be conveniently prepared by microwave synthesis from [Re(CO)(3)(H(2)O)(3) ]Br and a suitably substituted bis(phenanthridinylmethyl)amine (R-bpm). Complex 5, with R=CH(2)-CO(2)-CH(3) , was characterized by a single-crystal X-ray structure. Complex 6 (R=CH(2)-C(6)H(4)-CO(2)H) was used in solid-phase peptide synthesis (SPPS) to label the neurotensin(8-13) (NT) fragment N-terminally. The complexes show luminescence emission with large Stokes shifts (λ(ex) =350 nm, λ(em) =570 nm). Cellular uptake and intracellular localization studies in several cell lines demonstrate the utility of the new Re(CO)(3) (R-bpm) complexes for fluorescence imaging and reveal significant differences between the simple methyl ester 5 and the NT bioconjugate 7.     

Improved Syntheses of Versatile Ruthenium Hydridocarbonyl Catalysts Containing Electron‐Rich Ancillary Ligands

Clean, high‐yield routes are established to the important catalyst chlorobis(tricyclohexylphosphine)ruthenium hydridocarbonyl [RuHCl(CO)(PCy₃)₂] 2 and its N‐heterocyclic carbene (NHC) derivatives RuHCl(CO)(NHC)(PCy₃) ( 3a : NHC=IMes; 3b , NHC=H₂IMes; IMes=1,3‐dimesitylimidazol‐2‐ylidene). These complexes are obtained by treating chlorotris(tricyclohexylphosphine)ruthenium hydridocarbonyl [RuHCl(CO)(PPh₃)₃] 1 with tricyclohexylphosphine [PCy₃], or with the appropriate NHC ligand, then PCy₃. Advantages over prior routes to these complexes lie in the high yields from a conveniently accessible precursor, the absence of by‐products that otherwise prove difficult to remove, and the short reaction times under experimentally convenient conditions.     

Structural studies on Cd(II) complexes incorporating di-2-pyridyl ligand and the X-ray crystal structure of the chloroform solvated DPMNPH/CdI2 complex

A series of novel Cd(II) complexes incorporating ligand, di(2-pyridinyl)methanone N-(2-pyridinyl)hydrazone (DPMNPH), has been investigated. The ligand, DPMNPH, and its corresponding complexes have been characterized with the help of a number of techniques: microanalysis, FT-IR, ¹H and ¹³C NMR, UV/vis spectroscopy, thermal studies and MS–FAB mass spectrometry. In addition, single crystal X-ray diffraction measurement studies are also employed in one of the complexes showing a distorted trigonal bipyramidal geometry. Furthermore, the existence of NH⋯Npy intramolecular hydrogen bonding interactions in the ligand and its corresponding complexes has also been reported.     

Diastereotopic relationship between planar and central chiralities in the formation of Ru(η3-allyl)(CO)(PPh3)(L–L′) complexes

Hydride ruthenium complexes, RuHCl(CO)(PPh₃)₂(L–L^′) 3 (L–L^′=bidentate ligand having nitrogen and oxygen) react with allenes to give Ru(η³-allyl)(CO)(PPh₃)(L–L^′) complexes 5 in good yields via hydrometalation reaction. The complexes 5 have planar chirality at the η³-allyl ligand and central chirality at the Ru metal, and consist of one pair of enantiomers. Ligand substitution reaction of Ru(η³-allyl)Cl(CO)(PPh₃)₂ complexes 6 with bidentate ligands (L–L^′) also afford the complexes 5 which have the same stereochemistry as those formed by the hydrometalation reaction. The planar chirality is controlled by the central chirality at the Ru metal in both the formations of the complexes 5. The structure of 5a (L–L^′=N–N bidentate ligand) was determined by the X-ray crystal structure analysis.