DNA interaction and cleavage studies of ancillary chiral ligand and N,N‐donor ligands coordinated platinum(II) complexes

Four new platinum(II) complexes [Pt(dpen)(bpy)](ClO₄)₂ ( 1 ) , [Pt(dpen)(phen)](ClO₄)₂ ( 2 ), [Pt(dpen)(dpq)](ClO₄)₂ ( 3 ) and [Pt(dpen)(dppz)](ClO₄)₂ ( 4 ) comprising of different N,N‐donor ligands, viz., 2,2′‐bipyridine (bpy), 1,l0‐phenanthroline (phen), dipyridoquinoxaline (dpq), dipyrido‐[3,2‐d:2¢,3¢‐f –phenazine] (dppz), and chiral ancillary ligand 1R,2R ‐1,2‐diphenylethylenediamine (dpen) have been synthesized and characterized. The interaction of these complexes 1–4 with calf‐thymus DNA (CT‐DNA) has been explored using absorption, circular dichroism spectral and cyclic voltammetric studies. The absorption spectrum of complex 4 with dppz ligand exhibits a major red shift with an overall hypochromic as well as a hyperchromic effect in the presence of DNA, other complexes ( 1 – 3 ) show only hypochromism. From these absorption spectral studies, the intercalative ability of the complexes follows the order as, 4  >  3  >  2  >  1 , which is further confirmed by CD and cyclic voltammetry measurements. CD spectral studies show that DNA becomes more A ‐like upon interaction with the complexes 1 & 2 but the complexes 3 & 4 bring about B ‐form to Z ‐ form DNA conformational transition. The DNA cleavage study of these Pt(II) complexes 1–4 carried out by gel electrophoresis revealed that complexes 1–4 can cleave super coiled (SC) pUC18 DNA efficiently into open circular form (form II) under hydrolytic and oxidative conditions.     

Judicious Ligand Design in Ruthenium Polypyridyl CO2 Reduction Catalysts to Enhance Reactivity by Steric and Electronic Effects

A series of Ru^II polypyridyl complexes of the structural design [Ru^II(R?tpy)(NN)(CH₃CN)]²⁺ (R?tpy=2,2′:6′,2′′‐terpyridine (R=H) or 4,4′,4′′‐tri‐tert‐butyl‐2,2′:6′,2′′‐terpyridine (R=tBu); NN=2,2′‐bipyridine with methyl substituents in various positions) have been synthesized and analyzed for their ability to function as electrocatalysts for the reduction of CO₂ to CO. Detailed electrochemical analyses establish how substitutions at different ring positions of the bipyridine and terpyridine ligands can have profound electronic and, even more importantly, steric effects that determine the complexes’ reactivities. Whereas electron‐donating groups para to the heteroatoms exhibit the expected electronic effect, with an increase in turnover frequencies at increased overpotential, the introduction of a methyl group at the ortho position of NN imposes drastic steric effects. Two complexes, [Ru^II(tpy)(6‐mbpy)(CH₃CN)]²⁺ (trans‐[ 3 ]²⁺; 6‐mbpy=6‐methyl‐2,2′‐bipyridine) and [Ru^II(tBu?tpy)(6‐mbpy)(CH₃CN)]²⁺ (trans‐[ 4 ]²⁺), in which the methyl group of the 6‐mbpy ligand is trans to the CH₃CN ligand, show electrocatalytic CO₂ reduction at a previously unreactive oxidation state of the complex. This low overpotential pathway follows an ECE mechanism (electron transfer–chemical reaction–electron transfer), and is a direct result of steric interactions that facilitate CH₃CN ligand dissociation, CO₂ coordination, and ultimately catalytic turnover at the first reduction potential of the complexes. All experimental observations are rigorously corroborated by DFT calculations.     

The Substitution Reactions of the Small Biomolecules and Dinuclear Pt(II) Complexes with Alkanediamine Linker

The substitution reactions of the complexes [{trans‐Pt(NH₃)₂H₂O}₂(μ‐1,4‐diaminobutane)]⁴⁺ ( I ), [{trans‐Pt(NH₃)₂H₂O}₂(μ‐1,6‐diaminohexane)]⁴⁺ ( II ), and [{trans‐Pt(NH₃)₂H2O}₂(μ‐1,8‐diaminooctane)]⁴⁺ ( III ), with nucleophiles L‐cysteine (L‐Cys), glutathione (GSH), guanosine‐5′‐monophosphate (5′‐GMP), L‐histidine (L‐His), and pyridine were studied in 0.1 M NaClO₄ aqueous solutions at pH = 2.5. The substitutions were studied under pseudo‐first‐order conditions as a function of concentration and temperature using UV–vis spectrophotometry. At three different temperatures (288, 298, and 308 K) the reactions of the II and III complexes and 5′‐GMP were studied. The order of reactivity of study ligands is L‐Cys > GSH > 5′‐GMP > L‐His > pyridine and the order of reactivity of the complexes is I < II ≈ III . The obtained results indicate that the structure of the alkanediamine linker in the dinuclear Pt(II) complexes controls the substitution process. The negative values reported for entropy of activation confirmed the associative substitution mode. These results are discussed in order to find the connection between structure and reactivity of the dinuclear Pt(II) complexes.     

Addition of Isocyanides to Tetramesityldigermene: A Comparison of the Reactivity between Surface and Molecular Digermenes

The reaction of benzyl isocyanide, tert‐butyl isocyanide, and 2,6‐dimethylphenyl isocyanide with tetramesityldigermene (Mes₂Ge=GeMes₂) was examined. Whereas the addition of benzyl isocyanide gave the C?NC activation product, Mes₂Ge(CH₂Ph)Ge(CN)Mes₂, tert‐butyl isocyanide, and 2,6‐dimethylphenyl isocyanide did not give stable adducts, rather the rate of conversion of the digermene to the corresponding cyclotrigermane was accelerated. A comparison between the reactivity of the isocyanides with Mes₂Ge=GeMes₂ and the Ge(100)‐2×1 surface was made and some insights into the surface chemistry are offered.     

Synthesis,structure, redox property and ligand replacement reaction of ruthenium(II) complexes containing a terpyridyl ligand with a redox active moiety

Ruthenium(II) complexes bearing a redox-active tridentate ligand 4′-(2,5-dimethoxyphenyl)-2,2′:6′,2′′-terpyridine (tpyOMe), analogous to terpyridine, and 2,2′-bipyridine (bpy) were synthesized by the sequential replacement of Cl by CH₃CN and CO on the complex. The new ruthenium complexes were characterized by various methods including IR and NMR. The molecular structures of [Ru(tpyOMe)(bpy)(CH₃CN)]²⁺ and two kinds of [Ru(tpyOMe)(bpy)(CO)]²⁺ were determined by X-ray crystallography. The incorporation of monodentate ligands (Cl, CH₃CN and CO) regulated the energy levels of the MLCT transitions and the metal-centered redox potentials of the complexes. The kinetic data observed in this study indicates that the ligand replacement reaction of [Ru(tpyOMe)(bpy)Cl]⁺ to [Ru(tpyOMe)(bpy)(CH₃CN)]²⁺ proceeds by a solvent-assisted dissociation process.     

Development of the First P‐Stereogenic PCP Pincer Ligands,Their Metallation by Palladium and Platinum,and Preliminary Catalysis

The potentially tridentate P‐stereogenic [P*CP*] ligands 1,3‐{bis[(tert‐butyl)(phenyl)phosphino]methyl}benzene and 1,3‐{bis[(tert‐butyl)(phenyl) phosphino]methyl}‐2‐bromobenzene have been synthesized as the protected phosphine‐borane adducts. Deprotection with a secondary amine affords the free phosphine ligand which can be metallated by Pd and Pt with standard metal synthons. Two of the resultant [P*CP*] metal complexes have been characterized by X‐ray crystallography. The complexes exhibit a C₂ symmetric environment about the remaining binding site of the square‐planar center, with t‐Bu groups filling two quadrants of the open site. The Pd complexes can be converted by use of a Ag salt to the analogous aquo complex, which is catalytically active in the aldol condensation of methyl 2‐isocyanoacetate and benzaldehyde. Preliminary results and comparisons with previously reported catalysts with more distal C‐stereogenicity are presented.     

Pt(II) and Pt(IV) amido, aryloxide, and hydrocarbyl complexes: synthesis, characterization, and reaction with dihydrogen and substrates that possess C-H bonds

The Pt(II) amido and phenoxide complexes ((t)bpy)Pt(Me)(X), ((t)bpy)Pt(X)(2), and [((t)bpy)Pt(X)(py)][BAr'(4)] (X = NHPh, OPh; py = pyridine) have been synthesized and characterized. To test the feasibility of accessing Pt(IV) complexes by oxidizing their Pt(II) precursors, the previously reported ((t)bpy)Pt(R)(2) (R = Me and Ph) systems were oxidized with I(2) to yield ((t)bpy)Pt(R)(2)(I)(2). The analogous reaction with ((t)bpy)Pt(Me)(NHPh) and MeI yields the corresponding ((t)bpy)Pt(Me)(2)(NHPh)(I) complex. Reaction of ((t)bpy)Pt(Me)(NHPh) and phenylacetylene at 80 °C results in the formation of the Pt(II) phenylacetylide complex ((t)bpy)Pt(Me)(C≡CPh). Kinetic studies indicate that the reaction of ((t)bpy)Pt(Me)(NHPh) and phenylacetylene occurs via a pathway that involves [((t)bpy)Pt(Me)(NH(2)Ph)][TFA] as a catalyst. The reaction of H(2) with ((t)bpy)Pt(Me)(NHPh) ultimately produces aniline, methane, (t)bpy, and elemental Pt. For this reaction, mechanistic studies reveal that 1,2-addition of dihydrogen across the Pt-NHPh bond to initially produce ((t)bpy)Pt(Me)(H) and free aniline is catalyzed by elemental Pt. Heating the cationic complexes [((t)bpy)Pt(NHPh)(py)][BAr'(4)] and [((t)bpy)Pt(OPh)(py)][BAr'(4)] in C(6)D(6) does not result in the production of aniline and phenol, respectively. Attempted synthesis of a cationic system analogous to [((t)bpy)Pt(NHPh)(py)][BAr'(4)] with ligands that are more labile than pyridine (e.g., NC(5)F(5)) results in the formation of the dimer [((t)bpy)Pt(μ-NHPh)](2)[BAr'(4)](2). Solid-state X-ray diffraction studies of the complexes ((t)bpy)Pt(Me)(NHPh), [((t)bpy)Pt(NH(2)Ph)(2)][OTf](2), ((t)bpy)Pt(NHPh)(2), ((t)bpy)Pt(OPh)(2), ((t)bpy)Pt(Me)(2)(I)(2), and ((t)bpy)Pt(Ph)(2)(I)(2) are reported.     

Effective catalytic oxidation of alcohols and alkenes with monomeric versus dimeric manganese(II) catalysts and t‐BuOOH

Two new Mn(II) complexes, [Mn(C₆H₅COO)(H₂O)(phen)₂](ClO₄)(CH₃OH) ( 1 ) and [Mn₂(μ‐C₆H₅COO)₂(bipy)₄]?2(ClO₄) ( 2 ) (phen = 1,10‐phenanthroline; bipy = 2,2′‐bipyridine), were synthesized and characterized using UV–visible and infrared spectroscopies and single‐crystal X‐ray diffraction analyses. Complexes 1 and 2 have six‐coordinate octahedral geometry around the Mn(II) centre. Complex 1 is a monomer and consists of a deprotonated monodentate benzoate ligand together with two neutral bidentate amine ligands (phen) and a water molecule. Complex 2 has a dinuclear structure in which two Mn(II) ions share two carboxylate groups, adopting a two‐atom bridging mode, and two chelated bipy ligands. Both complexes catalyse the oxidation of alcohols and alkenes in a homogeneous catalytic system consisting of the Mn(II) complex and tert‐butyl hydroperoxide (TBHP) in acetonitrile. The system yields good to quantitative conversions of various alkenes and alcohols, such as styrene, ethylbenzene and cyclohexene to their corresponding ketones, and primary alcohols and 1‐octanol, 1‐heptanol, cyclohexanol, benzyl alcohols and cinnamyl alcohol to their corresponding aldehydes and carboxylic acids. Complexes 1 and 2 exhibit very high activity in the oxidation of cyclohexene to cyclohexanone (ca 80% selectivity) as the main product (ca 94% conversion in 1 h) and of cinnamyl alcohol to cinnamaldehyde (ca 64% selectivity) as the main product (ca 100% conversion in 0.5 h) with TBHP at 70°C in acetonitrile. In addition, optimum reaction conditions were also determined for benzyl alcohol with complexes 1 and 2 and TBHP. Copyright © 2016 John Wiley & Sons, Ltd.     

Reaction of dimethylplatinum(II) complexes with PhCH2CH2Br: Comparative reactivity with CH3CH2Br and PhCH2Br and synthesis of Pt(IV) complexes

Oxidative addition of 2‐phenylethylbromide (PhCH₂CH₂Br) to dimethylplatinum(II) complexes [PtMe₂(NN)] ( 1a , NN = 2,2′‐bipyridine (bpy); 1b , NN = 1,10‐phenanthroline (phen)) afforded the new organoplatinum(IV) complexes [PtMe₂(Br)(PhCH₂CH₂)(bpy)], as a mixture of trans ( 2a ) and cis ( 3a ) isomers, and [PtMe₂(Br)(PhCH₂CH₂)(phen)], as a mixture of trans ( 2b ) and cis ( 3b ) isomers, respectively. The new Pt(IV) complexes were readily characterized using multinuclear (¹H and ¹³C) NMR spectroscopy and elemental microanalysis. The crystal structure of 2a was further determined using X‐ray crystallography indicating an octahedral geometry around the platinum centre. A comparison of reactivity of RCH₂Br reagents (R = CH₃, Ph or PhCH₂) in their oxidative addition reactions with complex 1a , with an emphasis on the effects of the R groups of alkyl halides, was also conducted using density functional theory.     

Impact of Reaction Conditions on the Structures of Nickel(II) Complexes Based on 3‐(4‐Carboxyphenyl)propionic Acid

Two new nickel(II) complexes, [Ni(4, 4′‐bpy)(H₂O)₄]_n · n(cpp) · 0.5nH₂O ( 1 ) and [Ni(cpp)(4, 4′‐bpy)(H₂O)₂]_n ( 2 ) [4, 4′‐bpy = 4, 4′‐bipyridine, H₂cpp = 3‐(4‐carboxyphenyl)propionic acid] were synthesized and characterized by single‐crystal X‐ray diffraction, elemental analysis, IR spectroscopy, and thermal analysis. In complex 1 , Ni^II ions are bridged by 4, 4′‐bpy into 1D chains, and cpp ligands are not involved in the coordination, whereas in complex 2 , cpp ligands adopt a bis(monodentate) mode and link Ni^II ions into 2D (4, 4) grids with the help of 4, 4′‐bpy ligands. Triple interpenetration occurs, which results in the formation of a complicated 3D network. The difference in the structures of the two complexes can be attributed to the different reaction temperatures and bases.     

Reactions of sterically congested 1,6‐ and 1,7‐bis(diazo)alkanes with elemental sulfur and selenium: Formation of cyclohexene, 1,2‐dithiocane, 1,2‐diselenocane,and 1,2,3‐triselenecane derivatives

The reaction of 3,8‐bis(diazo)‐2,2,4,4,7,7,9,9‐octamethyldecane ( 5 ) with elemental selenium in 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) at 130°C yielded 1,2‐di‐tert‐butyl‐3,3,6,6‐tetramethylcyclohexene ( 1 ) (64%) and trans‐3,8‐di‐tert‐butyl‐4,4,7,7‐tetramethyl‐1,2‐diselenocane ( 8 ) (13%), while that of 5 with elemental sulfur in DBU gave trans‐3, 8‐di‐tert‐butyl‐4,4,7,7‐tetramethyl‐1,2‐dithiocane ( 9 ) (77%). The reaction of 3,9‐bis(diazo)‐2,2,4,4,8,8,10,10‐octamethylundecane ( 6 ) with elemental selenium in DBU at 80°C gave a cyclic triselenide, cis‐4,10‐di‐tert‐butyl‐5,5,9,9‐tetramethyl‐1,2,3‐triselenecane ( 11 ), in 15% yield as the only identifiable product. The structures of 9 and 11 were confirmed by X‐ray crystallography. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:351–356, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10046     

Photochemistry of RuII 4,4′‐Bi‐1,2,3‐triazolyl (btz) Complexes: Crystallographic Characterization of the Photoreactive Ligand‐Loss Intermediate trans‐[Ru(bpy)(κ2‐btz)(κ1‐btz)(NCMe)]2+

We report the unprecedented observation and unequivocal crystallographic characterization of the meta‐stable ligand loss intermediate solvento complex trans‐[Ru(bpy)(κ²‐btz)(κ¹‐btz)(NCMe)]²⁺ ( 1 a ) that contains a monodentate chelate ligand. This and analogous complexes can be observed during the photolysis reactions of a family of complexes of the form [Ru($\widehat{NN}$ )(btz)₂]²⁺ ( 1 a – d : btz=1,1′‐dibenzyl‐4,4′‐bi‐1,2,3‐triazolyl; $\widehat{NN}$ =a) 2,2′‐bipyridyl (bpy), b) 4,4′‐dimethyl‐2,2′‐bipyridyl (dmbpy), c) 4,4′‐dimethoxy‐2,2′‐bipyridyl (dmeobpy), d) 1,10‐phenanthroline (phen)). In acetonitrile solutions, 1 a – d eventually convert to the bis‐solvento complexes trans‐[Ru($\widehat{NN}$ )(btz)(NCMe)₂]²⁺ ( 3 a – d ) along with one equivalent of free btz, in a process in which the remaining coordinated bidentate ligands undergo a new rearrangement such that they become coplanar. X‐ray crystal structure of 3 a and 3 d confirmed the co‐planar arrangement of the $\widehat{NN}$ and btz ligands and the trans coordination of two solvent molecules. These conversions proceed via the observed intermediate complexes 2 a – d , which are formed quantitatively from 1 a – d in a matter of minutes and to which they slowly revert back on being left to stand in the dark over several days. The remarkably long lifetime of the intermediate complexes (>12 h at 40 °C) allowed the isolation of 2 a in the solid state, and the complex to be crystallographically characterized. Similarly to the structures adopted by complexes 3 a and d , the bpy and κ²‐btz ligands in 2 a coordinate in a square‐planar fashion with the second monodentate btz ligand coordinated trans to an acetonitrile ligand.     

Ligand Substitution Reactions on Aquapentachloro‐ and Hexachloroplatinic Acid — Synthesis and Characterization of Tetrachloroplatinum(IV) Complexes with Heterocyclic N,N Donors

Reactions of aquapentachloroplatinic acid, (H₃O)[PtCl₅(H₂O)]·2(18C6)·6H₂O ( 1 ) (18C6 = 18‐crown‐6), and H₂[PtCl₆]·6H₂O ( 2 ) with heterocyclic N, N donors (2, 2′‐bipyridine, bpy; 4, 4′‐di‐tert‐butyl‐2, 2′‐bipyridine, tBu₂bpy; 1, 10‐phenanthroline, phen; 4, 7‐diphenyl‐1, 10‐phenanthroline, Ph₂phen; 2, 2′‐bipyrimidine, bpym) afforded with ligand substitution platinum(IV) complexes [PtCl₄(N∩N)] (N∩N = bpy, 3a ; tBu₂bpy, 3b ; Ph₂phen, 5 ; bpym, 7 ) and/or with protonation of N, N donor yielding (R₂phenH)₂[PtCl₆] (R = H, 4a ; Ph, 4b ) and (bpymH)⁺ ( 8 ). With UV irradiation Ph₂phen and bpym reacted with reduction yielding platinum(II) complexes [PtCl₂(N∩N)] (N∩N = Ph₂phen, 6 ; bpym, 9 ). Identities of all complexes were established by microanalysis as well as by NMR (¹H, ¹³C, ¹⁹⁵Pt) and IR spectroscopic investigations. Molecular structures of [PtCl₄(bpym)]·MeOH ( 7 ) and [PtCl₂(Ph₂phen)] ( 6 ) were determined by X‐ray diffraction analyses. Differences in reactivity of bpy/bpym and phen ligands are discussed in terms of calculated structures of complexes [PtCl₅(N∩N)]^— with monodentately bound N, N ligands (N∩N = bpy, 10a ; phen, 10b ; bpym, 10c ).     

tert‐Butyl Hypoiodite for Deoximation

tert‐Butyl hypochlorite and tert‐butyl hypobromide react with aldoximes and convert them into hydroximinoyl chloride and bromide, respectively; however, under the same reaction conditions, tert‐butyl hypoiodite deoximates aldoximes and ketoximes to give corresponding aldehydes and ketones in high yield (>94%) in a short reaction time (～20 min).     

TEMPO‐Mediated Oxidation of Primary Alcohols to Aldehydes under Visible Light and Air

A homogeneous visible light photoredox TEMPO‐mediated selective oxidation of primary alcohols to the corresponding carbonyl compounds was developed using molecular oxygen from air as the terminal oxidant. Ru(bpy)₃(PF₆)₂ (bpy: bipyridyl) and Ir(dtb‐bpy)(ppy)₂(PF₆) (dtb‐bpy: 4,4′‐di‐tert‐butyl‐2,2′‐bipyridyl; ppy: 2‐phenylpyridine) were used as the sensitizers.     

[Ni(terpy)(H2O)]‐trans‐[Ni‐(μ‐CN)2‐(CN)2]n,a one‐dimensional linear tetra­cyano­nickelate chain

The one‐dimensional chain catena‐poly­[[aqua(2,2′:6′,2′′‐terpyridyl‐κ³N)­nickel(II)]‐μ‐cyano‐κ²N:C‐[bis­(cyano‐κC)nickelate(II)]‐μ‐cyano‐κ²C:N], [Ni(terpy)(H₂O)]‐trans‐[Ni‐μ‐(CN)₂‐(CN)₂]_n or [Ni₂­(CN)₄­(C₁₅H₁₁N₃)(H₂O)], consists of infinite linear chains along the crystallographic [10] direction. The chains are composed of two distinct types of nickel ions, paramagnetic octahedral [Ni(terpy)(H₂O)]²⁺ cations (with twofold crystallographic symmetry) and diamagnetic planar [Ni(CN)₄]^2? anions (with the Ni atom on an inversion center). The [Ni(CN)₄]^2? units act as bidentate ligands bridging through two trans cyano groups thus giving rise to a new example of a trans–trans chain among planar tetra­cyano­nickelate complexes. The coordination geometry of the planar nickel unit is typical of slightly distorted octahedral nickel(II) complexes, but for the [Ni(CN)₄]^2? units, the geometry deviates from a planar configuration due to steric interactions with the ter­pyridine ligands.     

Luminescent Benzoquinolate‐Isocyanide Platinum(II) Complexes: Effect of Pt⋅⋅⋅Pt and π⋅⋅⋅π Interactions on their Photophysical Properties

The neutral compounds [Pt(bzq)(CN)(CNR)] (R=tBu ( 1 ), Xyl ( 2 ), 2‐Np ( 3 ); bzq= benzoquinolate, Xyl=2,6‐dimethylphenyl, 2‐Np=2‐napthyl) were isolated as the pure isomers with a trans‐C_bzq,CNR configuration, as confirmed by ¹³C{¹H} NMR spectroscopy in the isotopically marked [Pt(bzq)(¹³CN)(CNR)] (R=tBu ( 1′ ), Xyl ( 2′ ), 2‐Np ( 3′ )) derivatives (δ¹³C_CN≈110 ppm; ¹J(Pt,¹³C)≈1425 Hz]. By contrast, complex [Pt(bzq)(C≡CPh)(CNXyl)] ( 4 ) with a trans‐N_bzq,CNR configuration, has been selectively isolated from [Pt(bzq)Cl(CNXyl)] (trans‐N_bzq,CNR) using Sonogashira conditions. X‐ray diffraction studies reveal that while 1 adopts a columnar‐stacked chain structure with Pt–Pt distances of 3.371(1) Å and significant π???π interactions (3.262 Å), complex 2 forms dimers supported only by short Pt???Pt (3.370(1) Å) interactions. In complex 4 the packing is directed by weak bzq???Xyl and bzq???C≡E (C, N) interactions. In solid state at room temperature, compounds 1 and 2 both show a bright red emission (?=42.1 % 1 , 57.6 % 2 ). Luminescence properties in the solid state at 77 K and concentration‐dependent emission studies in CH₂Cl₂ at 298 K and at 77 K are also reported for 1 , 1·CHCl3 , 2 , 2' , 2·CHCl3 , 3 , 4 .     

Spectroscopic and redox properties of amine-functionalized K2[OsII(bpy)(CN)4] complexes

We report the first examples of amine-functionalized K(2)[Os(II)(bpy)(CN)(4)] (bpy = 2,2'-bipyridine) complexes. The tetracyanoosmate complexes were prepared by UV irradiation (λ = 254 nm) of K(4)[Os(II)(CN)(6)] and primary amine-functionalized bpy ligands in acidic aqueous media. The aqueous solution pH dependences of the spectroscopic and redox properties of 4,4'- and 5,5'-substituted complexes have been investigated. The pendant amine functional groups and coordinated cyanide ligands are basic sites that can be sequentially protonated, thereby allowing systematic tuning of electrochemical and optical spectroscopic properties.     

Photolysis and Thermolysis of Platinum(IV) 2,2′‐Bipyridine Complexes Lead to Identical Platinum(II)–DNA Adducts

Two Pt^IV and two Pt^II complexes containing a 2,2′‐bipyridine ligand were treated with a short DNA oligonucleotide under light irradiation at 37 °C or in the dark at 37 and 50 °C. Photolysis and thermolysis of the Pt^IV complexes led to spontaneous reduction of the Pt^IV to the corresponding Pt^II complexes and to binding of Pt^II 2,2′‐bipyridine complexes to N7 of guanine. When the reduction product was [Pt(bpy)Cl₂], formation of bis‐oligonucleotide adducts was observed, whereas [Pt(bpy)(MeNH₂)Cl]⁺ gave monoadducts, with chloride ligands substituted in both cases. Neither in the dark nor under light irradiation was the reductive elimination process of these Pt^IV complexes accompanied by oxidative DNA damage. This work raises the question of the stability of photoactivatable Pt^IV complexes toward moderate heating conditions.     

Binuclear Cu(II) chiral complexes: synthesis,characterization and application in enantioselective nitroaldol (Henry) reaction

Enantiopure macrocyclic ligands were synthesized from (1R,2R)‐(+)‐ and (1S,2S)‐(?)‐diphenylethylenediamine with 3,3'‐methylenebis(5‐(tert‐butyl)‐2‐hydroxybenzaldehyde) and characterized. The chirality transfer and chiral inversion from ligand to copper(II) metal centre were studied using circular dichroism spectroscopy. The enantiopure binuclear copper(II) complexes (ΔΔ and ΛΛ) were used as catalysts for asymmetric nitroaldol reaction to generate β‐nitroalcohol with 88% yield and 67% enantioselectivity. Copyright © 2015 John Wiley & Sons, Ltd.