DFT/TDDFT insight into the impact of ring size of the NHC chelating unit of high effective phosphorescent Platinum (II) complexes

Uncovering the photodeactivation mechanisms of unique N‐heterocyclic carbene (NHC)‐based transition metal complexes is favorable for designing more high‐efficiency phosphorescent materials. In this work, four bidentate platinum (II) complexes with NHC‐chelate are investigated by the density functional theory (DFT) and time‐dependent density functional theory (TDDFT) to probe into how the ring size of NHC‐chelate unit influences on electronic structures and the phosphorescent properties. To illustrate the photodeactivation mechanisms clearly, three significant photodeactivation processes (radiative decay process, temperature‐independent and temperature‐dependent nonradiative decay processes) were taken into consideration. We stated that radiative decay rate constants k_r slightly increased with declined number of NHC‐chelate ring, owing to the gradually larger SOC matrix elements between the T₁ state and S_n states. Combining the temperature‐independent with temperature‐dependent nonradiative decay processes, the nonradiative decay rate k_nr is Pt‐4 (five‐membered) < Pt‐3 (six‐membered) < Pt‐2 (seven‐membered) < Pt‐1 (eight‐membered). The calculated results testify that the decrease of size of the NHC chelating unit is a reliable insurance to improve the quantum yield. The designed complex Pt‐4 with five‐membered NHC‐ring can serve as a highly efficient phosphorescent material in the future. The results indicated controlling the ring size of NHC‐chelate is a feasible method to tune phosphorescence properties of Pt (II) complexes.     

Bis‐NHC Chelate Complexes of Nickel(0) and Platinum(0)

For a long time d¹⁰‐ML₂ fragments have been known for their potential to activate unreactive bonds by oxidative addition. In the development of more active species, two approaches have proven successful: the use of strong σ‐donating ligands leading to electron‐rich metal centers and the employment of chelating ligands resulting in a bent coordination geometry. Combining these two strategies, we synthesized bis‐NHC chelate complexes of nickel(0) and platinum(0). Bis(1,5‐cyclooctadiene)nickel(0) and ‐platinum(0) react with bisimidazolium salts, deprotonated in situ at room temperature, to yield tetrahedral or trigonal‐planar bis‐NHC chelate olefin complexes. The synthesis and characterization of these complexes as well as a first example of C? C bond activation with these systems are reported. Due to the enforced cis arrangement of two NHCs, these compounds should open interesting perspectives for bond‐activation chemistry and catalysis.     

Coordination complexes of 2‐thienyl‐ and 2‐furyl‐mercurials

The reactions of di(2‐thienyl)mercury, 2‐thienylmercury chloride and 2‐furylmercury chloride with a variety of nitrogen‐ and phosphorus‐containing ligands have been studied. The presence of the electron‐withdrawing heteroatoms results in these mercurials being stronger acceptors than the corresponding phenylmercury compounds. The complexes have been characterized by elemental analysis, melting points, infrared, and ¹⁹⁹Hg NMR spectroscopy. 2,9‐Dimethyl‐ and 3,4,7,8‐tetramethyl‐phenanthroline form 1:1 chelate complexes, as does 1,2‐bis(diphenylphosphino)ethane, whereas ethylenediamine and 2,2′‐bipyridyl do not form complexes. Though non‐chelating ligands such as 2,4′‐ and 4,4′‐bipyridyl do not form complexes, bis(diphenylphosphino)methane forms 1:2 complexes in which the ligand bridges two mercury atoms. Monodentate ligands, such as triphenylphosphine, cause disproportionation of the organomercury chloride. 2‐Thienylmercury chloride forms a 4:1 complex with 4,4′‐dipyridyl disulfide in which it is believed that a molecule of the organomercurial is coordinated to both of the nitrogen and both of the sulfur atoms. Copyright © 2004 John Wiley & Sons, Ltd.     

Enhanced Anion Binding from Unusual Coordination Modes of Bis(thiourea) Ligands in Platinum Group Metal Complexes

Treatment of a range of bis(thiourea) ligands with inert organometallic transition‐metal ions gives a number of novel complexes that exhibit unusual ligand binding modes and significantly enhanced anion binding ability. The ruthenium(II) complex [Ru(η⁶‐p‐cymene)(κS,S′,N‐ L³ ?H)]⁺ ( 2 b ) possesses juxtaposed four‐ and seven‐membered chelate rings and binds anions as both 1:1 and 2:1 host guest complexes. The pyridyl bis(thiourea) complex [Ru(η⁶‐p‐cymeme)(κS,S′,N_py‐ L⁴ )]²⁺ ( 4 ) binds anions in both 1:1 and 1:2 species, whereas the free ligand is ineffective because of intramolecular NH???N hydrogen bonding. Novel palladium(II) complexes with nine‐ and ten‐membered chelate rings are also reported.     

[N‐(Carboxyl­ato­methyl)­aspartato(3–)](ethyl­enedi­amine)­cobalt(III) trihydrate

The mononuclear title complex, [Co(C₆H₆NO₆)(C₂H₈N₂)]·3H₂O, contains an octahedrally coordinated Co^III atom. The N‐(carboxy­methyl)­aspartate moiety is coordinated as a tetradentate ligand, providing an OONO‐donor set and forming two trans five‐membered chelate rings and one six‐membered chelate ring. A seven‐membered chelate ring is also formed, which consists of part of the six‐membered chelate ring and part of one of the five‐membered chelate rings. The crystal structure of the complex is stabilized by hydrogen bonds with three water mol­ecules.     

Novel bis(thiosemicarbazones) of the 3,5-diacetyl-1,2,4-triazol series and their platinum(II) complexes: chemistry, antiproliferative activity and preliminary nephrotoxicity studies

The preparation and characterization of three novel (4)N-monosubstituted bis(thiosemicarbazone) ligands of 3,5-diacetyl-1,2,4-triazol series and their dinuclear platinum complexes are described. The crystal and molecular structure of the [Pt(μ-H(3)L(3))](2) complex derived of 3,5-diacetyl-1,2,4-triazol bis((4)N-p-tolylthiosemicarbazone), H(5)L(3), has been resolved by single crystal X-ray diffraction. The ligands coordinate, in an asymmetric dideprotonate form, to the platinum ions in a tridentate fashion (NNS) and S-bridging bonding modes. Thus the molecular units of the platinum complexes are stacked as dimers. The new compounds synthesized have been evaluated for antiproliferative activity in vitro against NCI-H460, A2780 and A2780cisR human cancer cell lines. The cytotoxicity data suggest that these compounds may be endowed with important antitumour properties since are capable of not only circumventing cisplatin resistance in A2780cisR cells but also exhibit high antiproliferative activity in human non-small cell lung cancer NCI-H460 cells. The interactions of these compounds with calf thymus DNA was investigated by UV-vis absorption and a nephrotoxic study, in LLC-PK1 cells, has also been carried out.     

Expanded‐Ring N‐Heterocyclic Carbenes Efficiently Stabilize Gold(I) Cations,Leading to High Activity in π‐Acid‐Catalyzed Cyclizations

A series of six‐ and seven‐membered expanded‐ring N‐heterocyclic carbene (er‐NHC) gold(I) complexes has been synthesized using different synthetic approaches. Complexes with weakly coordinating anions [(er‐NHC)AuX] (X^?=BF₄^?, NTf₂^?, OTf^?) were generated in solution. According to their ¹³C NMR spectra, the ionic character of the complexes increases in the order X^?=Cl^?<NTf₂^?<OTf^?<BF₄^?. Additional factors for stabilization of the cationic complexes are expansion of the NHC ring and the attachment of bulky substituents at the nitrogen atoms. These er‐NHCs are bulkier ligands and stronger electron donors than conventional NHCs as well as phosphines and sulfides and provide more stabilization of [(L)Au⁺] cations. A comparative study has been carried out of the catalytic activities of five‐, six‐, and seven‐membered carbene complexes [(NHC)AuX], [(Ph₃P)AuX], [(Me₂S)AuX], and inorganic compounds of gold in model reactions of indole and benzofuran synthesis. It was found that increased ionic character of the complexes was correlated with increased catalytic activity in the cyclization reactions. As a result, we developed an unprecedentedly active monoligand cationic [(THD‐Dipp)Au]BF₄ (1,3‐bis(2,6‐diisopropylphenyl)‐3,4,5,6‐tetrahydrodiazepin‐2‐ylidene gold(I) tetrafluoroborate) catalyst bearing seven‐membered‐ring carbene and bulky Dipp substituents. Quantitative yields of cyclized products were attained in several minutes at room temperature at 1 mol % catalyst loadings. The experimental observations were rationalized and fully supported by DFT calculations.     

Koordination von Rhodium(III), Iridium(III) und Kupfer(II) mit dem potentiell vierzähnigen Akzeptorliganden Bis(1‐methylimidazol‐2‐yl)glyoxal (big)

Coordination of Rhodium(III), Iridium(III), and Copper(II) with the Potentially Tetradentate Acceptor Ligand Bis(1‐methylimidazol‐2‐yl)glyoxal (big) Bis(1‐methylimidazol‐2‐yl)glyoxal (big) which has hitherto not been used in coordination chemistry crystallizes to form two perpendicular 1‐methylimidazol‐2‐yl‐carbonyl molecular halves. Out of the various possibilities for mono‐ and bis‐chelate coordination the N,N′‐alternative with a seven‐membered chelate ring is realized in [Cp*Cl(big)Rh](PF₆) as evident from crystal structure analysis. The iridium analogue reacts under hydration of big and elimination of HCl to form a complex cation [Cp*(bigOH)Ir]⁺ which dimerizes in the crystal through hydrogen bonding and contains one five‐ and one six‐membered chelate ring involving the alcoholate‐O. Cu(ClO₄)₂ and the ligand big yield a complex ion [Cu(big)₂]²⁺ with an ESR spectrum that suggests the coordination of the central metal by four N atoms in an approximately planar setting.     

Synthesis and crystal structure of the dinuclear copper(II) Schiff base complex μ‐hydroxido‐μ‐chlorido‐bis{[bis(trans‐2‐nitrocinnamaldehyde)ethylenediamine]chloridocopper(II)} dichloromethane sesquisolvate

Transition metal complexes of Schiff base ligands have been shown to have particular application in catalysis and magnetism. The chemistry of copper complexes is of interest owing to their importance in biological and industrial processes. The reaction of copper(I) chloride with the bidentate Schiff base N,N′‐bis(trans‐2‐nitrocinnamaldehyde)ethylenediamine {Nca₂en, systematic name: (1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]} in a 1:1 molar ratio in dichloromethane without exclusion of air or moisture resulted in the formation of the title complex μ‐chlorido‐μ‐hydroxido‐bis(chlorido{(1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]‐κ²N,N′}copper(II)) dichloromethane sesquisolvate, [Cu₂Cl₃(OH)(C₂₀H₁₈N₄O₄)₂]·1.5CH₂Cl₂. The dinuclear complex has a folded four‐membered ring in an unsymmetrical Cu₂OCl₃ core in which the approximate trigonal bipyramidal coordination displays different angular distortions in the equatorial planes of the two Cu^II atoms; the chloride bridge is asymmetric, but the hydroxide bridge is symmetric. The chelate rings of the two Nca₂en ligands have different conformations, leading to a more marked bowing of one of the ligands compared with the other. This is the first reported dinuclear complex, and the first five‐coordinate complex, of the Nca₂en Schiff base ligand. Molecules of the dimer are associated in pairs by ring‐stacking interactions supported by C—H…Cl interactions with solvent molecules; a further ring‐stacking interaction exists between the two Schiff base ligands of each molecule.     

Analysis of antitumour [1,1-bis(aminomethyl)cyclohexane]platinum(II) complexes derived from spiroplatin by high-performance liquid chromatography with differential pulse amperometric detection

A reversed-phase high-performance liquid chromatographic analysis was developed for aqua[1,1-bis(aminomethyl)cyclohexane]sulphatoplatinum(II) (spiroplatin) and its hydrolysis and oligomerization products. The platinum complexes were detected by differential pulse amperometry at a hanging mercury drop electrode, at -540 mV vs. Ag/AgCl. The limit of detection was 0.05 microM. Aqueous solutions of spiroplatin appeared to contain the diaqua, monoaquamonosulphato, monoaquamonochloro, dichloro and hydroxo-bridged dimer complexes of [1,1-bis(aminomethyl)cyclohexane]platinum(II) in mutual equilibrium. The equilibrium shifts after dilution in infusion fluids were studied. Detection of these platinum(II) complexes in untreated human plasma ultrafiltrate and urine demonstrated the selectivity of the described analysis.     

Tridentate N-donor palladium(II) complexes as efficient coordinating quadruplex DNA binders

Fifteen complexes of palladium, platinum, and copper, featuring five different N‐donor tridentate (terpyridine‐like) ligands, were prepared with the aim of testing their G‐quadruplex–DNA binding properties. The fluorescence resonance energy transfer melting assay indicated a striking positive effect of palladium on G‐quadruplex DNA stabilization compared with platinum and copper, as well as an influence of the structure of the organic ligand. Putative binding modes (noncoordinative π stacking and base coordination) of palladium and platinum complexes were investigated by ESI‐MS and UV/Vis spectroscopy experiments, which all revealed a greater ability of palladium complexes to coordinate DNA bases. In contrast, platinum compounds tend to predominantly bind to quadruplex DNA in their aqua form by noncoordinative interactions. Remarkably, complexes of [Pd(ttpy)] and [Pd(tMebip)] (ttpy=tolylterpyridine, tMebip=2,2′‐(4‐p‐tolylpyridine‐2,6‐diyl)bis(1‐methyl‐1H‐benzo[d]imidazole)) coordinate efficiently G‐quadruplex structures at room temperature in less than 1 h, and are more efficient than their platinum counterparts for inhibiting the growth of cancer cells. Altogether, these results demonstrate that both the affinity for G‐quadruplex DNA and the binding mode of metal complexes can be modulated by modifying either the metal or the organic ligand.     

1,3,6‐Azadiphosphacycloheptanes: A novel type of heterocyclic diphosphines

The novel type of seven‐membered cyclic diphosphines, namely 1,3,6‐azadiphosphacycloheptanes, has been synthesized by condensation of 1,2‐bis(phenylphosphino)ethane, formaldehyde, and primary amines (aniline, p‐toluidine, benzylamine, and 5‐aminoisophthalic acid) as a mixture of rac‐ and meso‐stereoisomers. The structures of rac‐stereoisomers of N‐tolyl and N‐(3′,5′‐dicarboxyphenyl)‐substituted diphosphines were investigated by X‐ray crystal structure analyses. The stereoisomers of N‐(3′,5′‐dicarboxyphenyl)‐substituted compound were separated at a preparative scale, and their platinum(II) dichloride complexes were obtained. The corresponding meso‐isomer readily forms P,P‐chelate complex with [PtCl₂(cod)], whereas the rac‐stereoisomer forms oligomeric complex. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:125–132, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20397     

Density functional theory study of the interaction between formamide and uracil

The hydrogen bonding of complexes formed between the formamide and uracil molecule has been fully investigated in the present study using the density functional theory (DFT) method at varied basis set levels from 6‐31G to 6‐311++G(d,p). Eight stable cyclic structures with two hydrogen bonds involved in the interaction are found on the potential energy surface (PES). The four structures are seven‐membered rings; the others are eight‐membered rings. The eight‐membered ring is preferred over the seven‐membered one by analyzing the hydrogen bond lengths and the interaction energies. The infrared (IR) spectrum frequencies, IR intensities, and the vibrational frequency shifts are reported. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

抗肿瘤多核铂配合物的研究

多核铂配合物作为非经典铂抗肿瘤药物,其抗肿瘤机制与现有铂类抗肿瘤药物不同,因而在克服现有铂类抗肿瘤药物耐药性方面有着巨大的潜力。本文综述了多核铂类抗肿瘤药物的研究进展,以连接铂原子的桥配体结构的不同,可分为六大类:以烷基二胺及其衍生物为桥的多核铂配合物、以含氮杂环为桥的多核铂配合物、以羧酸根为桥的多核铂配合物、以卤素离子为桥的多核铂配合物、以含硫配体为桥的多核铂配合物及以其他配体为桥的多核铂配合物。本文还介绍了这几类多核铂配合物的抗肿瘤机理及在克服顺铂耐药性机理方面的研究进展。     

Structural Features of Uranyl Hydroxylaminate and Oximate Complexes

On the basis of the currently available uranyl complexes with hydroxylamine and its N-substituted derivatives and oximes, the coordination modes of the ligands and structural features of such complexes have been considered with the aim of determining general trends for this new family of uranium(VI) compounds. All the uranyl oximate and hydroxylaminate complexes contain a deprotonated ligand coordinated to the central atom through the nitrogen and oxygen atoms to form a stable three-membered chelate ring. Depending on the composition, these compounds can be divided into two large groups: complexes with tris(chelate) and bis(chelate) structural moieties.     

Asymmetric structure of cis‐[N‐(9‐anthracenylmethyl)‐1,2‐ethanediamine]dipyridineplatinum(II) dinitrate

Platinum antitumour agents, containing aromatic rings, which are used for targeting DNA in effective therapies for the treatment of cancer. We have synthesized the title metallocomplex with an aromatic ligand and determined its crystal structure. In many cases, complexes of platinum and other metals have a symmetrical structure. In contrast, the platinum(II) complex with pyridine and N‐(9‐anthracenylmethyl)‐1,2‐ethanediamine as ligands (systematic name: cis‐{N‐[(anthracen‐9‐yl)methyl]ethane‐1,2‐diamine‐κ²N ,N ′}bis(pyridine‐κN )platinum(II) dinitrate), [Pt(C₅H₅N)₂(C₁₇H₁₈N₂)](NO₃)₂, is asymmetric. Of the two pyridine ligands, only one is π‐stacked with anthracene, resulting in an asymmetric structure. Moreover, the angle of orientation of each pyridine ligand is variable. Further examination of the packing motif confirms an intermolecular edge‐to‐face interaction.     

Large‐ring P/O chelate nickel complex catalyzed oligomerization of ethylene to linear α‐olefins

1,1‐(Bicyclononyl‐9‐phosphino)hendecanoic acid and potassium 1,1‐(biscyclohexylphosphino)­hendecylate were synthesized. A model nickel complex [η³−C₈H₁₃]Ni[(C₈H₁₄)P(CH₂)₁₀COO] containing a 14‐membered chelate ring was also synthesized. The catalytic activity of this large chelate ring nickel complex for the oligomerization of ethylene was studied and compared with that of six‐membered ring chelate nickel complexes. The influence of the chelate ring was rationalized in terms of intramolecular rotation. The 14‐membered ring P/O chelate nickel complex was shown to have efficient catalytic activity for the oligomerization of ethylene to α‐olefins. Copyright © 2000 John Wiley & Sons, Ltd.     

C,O‐Chelated BINOL/Gold(III) Complexes: Synthesis and Catalysis with Tunable Product Profiles

Unprecedented stable BINOL/gold(III) complexes, adopting a novel C,O‐chelation mode, were synthesized by a modular approach through combination of 1,1′‐binaphthalene‐2,2′‐diols (BINOLs) and cyclometalated gold(III) dichloride complexes [(C^N)AuCl₂]. X‐ray crystallographic analysis revealed that the bidentate BINOL ligands tautomerized and bonded to the Au^III atom through C,O‐chelation to form a five‐membered ring instead of the conventional O,O′‐chelation giving a seven‐membered ring. These gold(III) complexes catalyzed acetalization/cycloisomerization and carboalkoxylation of ortho ‐alkynylbenzaldehydes with trialkyl orthoformates.     

Visible‐Light‐Driven Strain‐Increase Ring Contraction Allows the Synthesis of Cyclobutyl Boronic Esters

There are a limited number of ring‐contraction methodologies which convert readily available five‐membered rings into strained four‐membered rings. Here we report a photo‐induced radical‐mediated ring contraction of five‐membered‐ring alkenyl boronate complexes into cyclobutanes. The process involves the addition of an electrophilic radical to the electron‐rich alkenyl boronate complex, leading to an α‐boryl radical. Upon one‐electron oxidation, ring‐contractive 1,2‐metalate rearrangement occurs to give a cyclobutyl boronic ester. A range of radical precursors and vinyl boronates can be employed, and chiral cyclobutanes can be accessed with high levels of stereocontrol. The process was extended to the preparation of benzofused cyclobutenes and the versatility of the boronic ester was demonstrated by conversion to other functional groups.