The development of fluorescence turn-on probe for Al(III) sensing and live cell nucleus-nucleoli staining.

The morphology of nucleus and nucleolus is powerful indicator of physiological and pathological conditions. The specific staining of nucleolus recently gained much attention due to the limited and expensive availability of the only existing stain "SYTO RNA-Select". Here, a new multifunctional salen type ligand (L1) and its Al3+ complex (1) are designed and synthesized. L1 acts as a chemosensor for Al3+ whereas 1 demonstrates specific staining of nucleus as well as nucleoli. The binding of 1 with nucleic acid is probed by DNase and RNase digestion in stained cells. 1 shows an excellent photostability, which is a limitation for existing nucleus stains during long term observations. 1 is assumed to be a potential candidate as an alternative to expensive commercial dyes for nucleus and nucleoli staining.

Targeted water soluble copper-tetrazolate complexes: interactions with biomolecules and catecholase like activities.

Two new mononuclear water soluble copper(II) complexes, [Cu{(5-pyrazinyl)tetrazolate}2(1,10-phenanthroline)] 1 and [Cu{(5-pyrazinyl)tetrazolate}(1,10-phenanthroline)2](NO3)0.5(N3)0.5 2, have been synthesized using the metal mediated [2 + 3] cycloaddition reaction between copper bound azide and pyrazinecarbonitrile. The interactions of these copper tetrazolate complexes 1 and 2 with biomolecules like DNA and bovine serum albumin (BSA) are studied and the catecholase like catalytic activity of compound 2 is also explored. Structural determination reveals that both compounds 1 and 2 are octahedral in nature. Screening tests were conducted to quantify the binding ability of complexes (1 and 2) towards DNA and it was revealed that complex 2 has a stronger affinity to bind to CT-DNA. DFT studies indicated that a lower HOMO-LUMO energy gap between the DNA fragment and metal complexes might be the reason for this type of stronger interaction. DNA cleavage activity was explored by gel-electrophoresis and moderate to strong DNA cleavage properties were observed in the presence and absence of co-reagents. Inhibition of cleavage in the presence of sodium azide indicates the propagation of the activity through the production of singlet molecular oxygen. Furthermore enzyme kinetic studies reflect that complex 2 is also effective in mimicking catecholase like activities. An ESI-MS spectral study indicates the probable involvement of dimeric species [(phen)2Cu-(OH)2-Cu(phen)2](2+) in the catalytic cycle.

Crystal structure of the cage derivative penta-cyclo-[5.4.0.0(2,6).0(3,10).0(5,9)]undeca-8,11-dione ethyl-ene di-thio-ketal.

The title penta-cyclo-undecane cage derivative, C13H14OS2, was identified during a thio-ketalization reaction. The reaction selectively gave the title compound and the product corresponding to bis-ketal was not formed. The title compound exhibits unusual Csp (3)-Csp (3) single bond lengths ranging from 1.495 (3) to 1.581 (2) and strained bond angles as small as 89.29 (12) and as large as 115.11 (11)°.

Crystal structures of 3,6-di-allyl-tetra-cyclo[6.3.0.0(4,11).0(5,9)]undeca-2,7-dione and 1,7-di-allyl-penta-cyclo-[5.4.0.0(2,6). 0(3,10).0(5,9)]undecane-8,11-dione: allyl-ated caged compounds.

The title compounds, C17H20O2 (1) and C17H18O2 (2), are allyl-ated caged compounds. In (1), the carbon atoms bearing the allyl groups are far apart [2.9417 (17) Å], hence the expected ring-closing metathesis (RCM) protocol failed to give a ring-closing product. When these carbon atoms are connected by a C-C bond as in (2), the distance between them is much smaller [1.611 (3) Å] and consequently the RCM process was successful. The caged carbon skeleton of (1) can be described as a fusion of four five-membered rings and one six-membered ring. All four five-membered rings exhibit envelope conformations. The structure of compound (2) consists of four five-membered rings, of which two are cyclo-penta-none rings bonded at the 2, 4 and 5 positions and linked at the 3-carbons by a methyl-ene bridge. It also consists of one four-membered and two six-membered rings. All four five-membered rings adopt envelope conformations. In the crystal of (1), mol-ecules are linked via C-H⋯O hydrogen bonds, forming sheets lying parallel to (010). In the crystal of (2), mol-ecules are linked via C-H⋯O hydrogen bonds forming chains along [100].

Diversity-oriented approach to macrocyclic cyclophane derivatives by Suzuki-Miyaura cross-coupling and olefin metathesis as key steps.

Palladium-catalyzed Suzuki-Miyaura (SM) cross-coupling reaction with allylboronic acid pinacol ester and titanium assisted cross-metathesis (CM)/ring-closing metathesis (RCM) cascade has been used to synthesize macrocyclic cyclophane derivatives.

Gold(III) N-heterocyclic carbene complexes mediated synthesis of ß-enaminones from 1,3-dicarbonyl compounds and aliphatic amines.

A series of gold(III) N-heterocyclic carbene complexes [1-(R(1))-3-(R(2))imidazol-2-ylidene]AuBr(3) [R(1) = i-Pr, R(2) = CH(2)Ph (1c); R(1) = mesityl, R(2) = CH(2)Ph (2c); R(1) = i-Pr, R(2) = CH(2)COt-Bu (3c), and R(1) = t-Bu, R(2) = CH(2)COt-Bu (4c)] act as effective precatalysts in the synthesis of ß-enaminones from 1,3-dicarbonyl compounds and primary amines under ambient conditions. Specifically the 1c-4c complexes efficiently catalyzed the condensation of a variety of cyclic as well as acyclic 1,3-dicarbonyl compounds, namely, acetyl acetone, benzoylacetone, 2-acetylcyclopentanone, and ethyl-2-oxocyclopentanecarboxylate with primary aliphatic amines, viz., methylamine, ethylamine, n-propylamine, i-propylamine, and n-butylamine, yielding ß-enamines at room temperature. Interestingly enough, the more electrophilic gold(III) 1c-4c complexes exhibited superior activity in comparison to the gold(I) counterparts 1b-4b. A comparison along a representative 4a-c series further underscored the importance of gold in the reaction as both the gold(I) 4b and gold(III) 4c complexes were more effective than the silver analogue 4a. The density functional theory (DFT) study revealed that the strong σ-donating nature of the N-heterocyclic carbene ligand results in a strong C(carbene)-Au(III) interaction in the 1c-4c complexes.

Titanium isopropoxide complexes of a series of sterically demanding aryloxo based [N2O2]2- ligands as precatalysts for ethylene polymerization.

Several titanium isopropoxide complexes [N,N'-bis(2-oxo-3-R(1)-5-R(2)-phenylmethyl)-N,N'-bis(methylene-p-R(3)-C(6)H(4))-ethylenediamine]Ti(O(i)Pr)(2) [R(1) = t-Bu, R(2) = Me, R(3) = H (1b); R(1) = R(2) = t-Bu, R(3) = H, (2b); R(1) = R(2) = Cl, R(3) = H, (3b), R(1) = t-Bu, R(2) = Me, R(3) = Cl (4b); R(1) = R(2) = t-Bu, R(3) = Cl, (5b); R(1) = R(2) = R(3) = Cl, (6b)] supported over sterically demanding aryloxy based [N(2)O(2)]H(2) ligands have been designed as precatalysts for the ethylene polymerization. Specifically, the 1b-6b complexes, when treated with methylaluminoxane (MAO) under 88 ± 0.5 psi of ethylene at 30 °C for 3 h, produced polyethylene polymers of high molecular weight (M(w) = ca. 7.2-8.3 × 10(5) g mol(-1)) having broad molecular weight distribution (PDI = ca. 13.1-14.6). The 1b-6b complexes were conveniently synthesized from the direct reaction of the [N(2)O(2)]H(2) ligands, 1a-6a, with Ti(O(i)Pr)(4) in 69-86% yield.

Highly efficient palladium precatalysts of homoscorpionate bispyrazolyl ligands for the more challenging Suzuki-Miyaura cross-coupling of aryl chlorides.

Highly efficient palladium precatalysts {[RN{-(CH(2))(n)-pz(3,5-Me)(2)}(2)]PdCl(2)}(m) [m = n = 1; R = 2,6-Me(2)C(6)H(3) (1), 2,4,6-Me(3)C(6)H(2) (2), CH(2)Ph (3) and m = n = 2; R = CH(2)Ph (4)] of a series of homoscorpionate bispyrazolyl ligands for the Suzuki-Miyaura cross-coupling of the more challenging aryl chloride substrates are reported. In particular, the palladium 1-4 precatalysts carried out the Suzuki-Miyaura cross-coupling of a wide variety of aryl chloride substrates bearing electron withdrawing, electron donating and heteroaryl substituents. Remarkably enough, the molecular structure determination of the 1-4 precatalysts by X-ray diffraction studies revealed the presence of anagostic [C-H...Pd] type interactions in the mononuclear 1-3 complexes of methylene bridged bispyrazolyl ligands whereas the ethylene bridged analog 4 yielded an interesting dimeric 20-membered macrometallacyclic complex devoid of any such interaction.

Highly convenient regioselective intermolecular hydroamination of alkynes yielding ketimines catalyzed by gold(I) complexes of 1,2,4-triazole based N-heterocyclic carbenes.

A series of highly efficient gold(I) precatalysts of 1,2,4-triazole based N-heterocyclic carbenes, [1-R-4-R'-1,2,4-triazol-5-ylidene]AuCl [R = CH(2)CO(t)Bu, R' = CH(2)Ph (1c); R = CH(2)CONH(t)Bu, R' = CH(2)Ph (2c); R = CH(2)CO(t)Bu, R' = CH(2)CO(t)Bu (3c), and R = C(6)H(10)OH, R' = CH(2)Ph (4c)] are reported for the hydroamination of terminal alkynes with a variety of sterically demanding o/p-substituted aryl amines yielding the corresponding ketimines in air. The gold 1c-4c complexes exhibited extremely high activity in comparison to the silver analogues 1b-4b, thereby highlighting the role of gold as a metal in the catalysis of the hydroamination reaction. Additionally, the 1,2,4-triazole based 1c-4c precatalysts showed significantly superior activity in comparison to the two representative imidazole analogues, namely, [1-(benzyl)-3-(N-t-butylacetamido)imidazol-2-ylidene]AuCl and [1-(2-hydroxy-cyclohexyl)-3-(benzyl)imidazol-2-ylidene]AuCl, thereby underscoring the importance of the 1,2,4-triazole based N-heterocyclic carbenes over the imidazole based ones in designing the gold(I) precatalysts for the hydroamination reaction. The gold(I) complexes (1c-4c) were synthesized by transmetalation reaction of the silver analogues 1b-4b with (SMe(2))AuCl in 60-76% yield while the silver 1b-4b complexes in turn were synthesized from the respective 1,2,4-triazolium halide salts by treatment with Ag(2)O in 43-64% yield.

A comparison between nickel and palladium precatalysts of 1,2,4-triazole based N-heterocyclic carbenes in hydroamination of activated olefins.

A comparison is drawn between the nickel and palladium precatalysts of 1,2,4-triazole based N-heterocyclic carbenes in the hydroamination of activated olefins. Though all of the newly designed nickel and palladium precatalysts, trans-[1-i-propyl-4-R-1,2,4-triazol-5-ylidene](2)MBr(2) [R = Et, M = Ni (1b); R = Et, M = Pd (1c); R = CH(2)CH=CH(2), M = Ni (2b) and R = CH(2)CH=CH(2), M = Pd (2c)], are moderately active for hydroamination reaction of a variety of secondary amines viz. morpholine, piperidine, pyrrolidine and diethylamine with activated olefins like, acrylonitrile, methyl acrylate, ethyl acrylate and t-butyl acrylate at room temperature in 1 hour, the nickel complexes (1b and 2b) exhibited superior activity compared to its palladium counterparts (1c and 2c). The better performance of the nickel complexes has been correlated to the more electron deficient metal center in the nickel 1b and 2b complexes than in the palladium 1c and 2c analogs based on the density functional theory studies. The 1b-c and 2b-c complexes were synthesized by the reaction of 1-i-propyl-4-R-1,2,4-triazolium bromide [R = Et (1a) and R = CH(2)CH=CH(2) (2a)] with MCl(2) [M = Ni, Pd] in presence of NEt(3) as a base.

Controlled oxidation of organic sulfides to sulfoxides under ambient conditions by a series of titanium isopropoxide complexes using environmentally benign H2O2 as an oxidant.

Controlled oxidation of organic sulfides to sulfoxides under ambient conditions has been achieved by a series of titanium isopropoxide complexes that use environmentally benign H(2)O(2) as a primary oxidant. Specifically, the [N,N'-bis(2-oxo-3-R(1)-5-R(2)-phenylmethyl)-N,N'-bis(methylene-R(3))-ethylenediamine]Ti(O(i)Pr)(2) [R(1) = t-Bu, R(2) = Me, R(3) = C(7)H(5)O(2) (1b); R(1) = R(2) = t-Bu, R(3) = C(7)H(5)O(2) (2b); R(1) = R(2) = Cl, R(3) = C(7)H(5)O(2) (3b) and R(1) = R(2) = Cl, R(3) = C(6)H(5) (4b)] complexes efficiently catalyzed the sulfoxidation reactions of organic sulfides to sulfoxides at room temperature within 30 min of the reaction time using aqueous H(2)O(2) as an oxidant. A mechanistic pathway, modeled using density functional theory for a representative thioanisole substrate catalyzed by 4b, suggested that the reaction proceeds via a titanium peroxo intermediate 4c', which displays an activation barrier of 22.5 kcal mol(-1) (DeltaG(++)) for the overall catalytic cycle in undergoing an attack by the S atom of the thioanisole substrate at its sigma*-orbital of the peroxo moiety. The formation of the titanium peroxo intermediate was experimentally corroborated by a mild ionization atmospheric pressure chemical ionization (APCI) mass spectrometric technique.

Palladium complexes of abnormal N-heterocyclic carbenes as precatalysts for the much preferred Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium.

A series of new PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed precatalysts of abnormal N-heterocyclic carbenes for the highly desirable Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium is reported. Specifically, the PEPPSI themed (NHC)PdI2(pyridine) type precatalysts, 1b-4b, efficiently carried out the highly convenient Cu-free and amine-free Sonogashira coupling of aryl bromides and iodides with terminal acetylenes in air in a mixed aqueous medium. Complexes, 1b-4b, were synthesized by the direct reaction of the corresponding imidazo[1,2-a]pyridinium iodide salts, 1a-4a, with PdCl2 in pyridine in the presence of K2CO3 as a base while the imidazo[1,2-a]pyridinium iodide salts, 1a-4a, were in turn synthesized by the alkylation reactions of the respective imidazo[1,2-a]pyridine derivatives with alkyl iodides. The density functional theory (DFT) studies revealed that these imidazol-3-ylidene[1,2-a]pyridine derived abnormal carbenes are strongly sigma-donating and consequently significantly weaken the catalytically important labile trans pyridine ligand in 1b-4b.

Role of the orientation of -OH groups in the sensitivity and selectivity of the interaction of M(2+) with ribosyl- and galactosyl-imino-conjugates.

Three glyco-conjugates, viz., L(1), L(2) and L(3), which differ either in their carbohydrate moiety or in their aromatic moiety or both, were synthesized and characterized and were shown to have beta-anomeric form based on (1)H NMR and optical rotation studies. Metal ion interaction studies carried out in solution by emission and absorption spectral techniques exhibited selectivity towards Cu(2+) in HEPES buffer and a two fold higher sensitivity for L(2) as compared to L(1). The composition of the complexed species has been established based on ESI MS. Dinuclear-Cu(II) complexes of all these conjugates have been synthesized and characterized based on analytical and spectral methods including FTIR, (1)H NMR, FAB MS, EPR, ORD, CD and magnetism, and the structures of and have been established based on single crystal XRD. The structures revealed subtle differences present in the orientation of the -OH groups and also their ion binding preferences both at the molecular level as well as at the lattice levels. In the dinuclear-Cu(II) complexes, while C3-O(-) of ribosyl acts as a bridging moiety in , it is the C2-O(-) of galactosyl that bridges in and the Cu(2)O(2) cores are stabilized by two intra-complex H-bond interactions formed using C4-OH in the case of and C3-OH in the case of . While the glyco-moiety is poised perpendicular to the average plane of the Cu(2)O(2) core in , this is in plane in the case of 3.

Mimicking the intradiol catechol cleavage activity of catechol dioxygenase by high-spin iron(III) complexes of a new class of a facially bound [N2O] ligand.

A series of high-spin iron(III) complexes, {N-R-2-[(pyridin-2-ylmethyl)amino]acetamide}FeCl(3) [R = mesityl (1b), 2,6-Et(2)C(6)H(3) (2b), and 2,6-i-Pr(2)C(6)H(3) (3b)], that functionally emulate the intradiol catechol dioxygenase enzyme are reported. In particular, these enzyme mimics, 1b, 2b, and 3b, which utilized molecular oxygen in carrying out the intradiol catechol cleavage of 3,5-di-tert-butylcatechol with high regioselectivity (ca. 81-85%) at room temperature under ambient conditions, were designed by employing a new class of a facially bound [N(2)O] ligand, namely, N-R-2-[(pyridin-2-ylmethyl)amino]acetamide [R = mesityl (1a), 2,6-Et(2)C(6)H(3) (2a), and 2,6-i-Pr(2)C(6)H(3) (3a)]. The density functional theory studies revealed that the intradiol catechol cleavage reaction proceeded by an iron(III) peroxo intermediate that underwent 1,2-Criegee rearrangement to yield the intradiol catechol cleaved products analogous to the native enzyme.

Unprecedented long-range 1,7-bromination in gold complexes of N-(aryl)imino functionalized N-heterocyclic carbenes.

An unique long-range 1,7-bromination reaction is observed in gold(III) complexes of N-(aryl)imino functionalized N-heterocyclic carbene with the bromination occurring at two different carbon (sp2 and sp3) centers spatially separated by ca. 6.4 A but existing in extended conjugation to each other. In particular, the unusual distant 1,7-brominated gold(III) complexes [1-R-3-{N-(p-bromo-2,6-di-i-propylphenylimino)-2-phenyl-1-bromoethyl}imidazol-2-ylidene]AuBr3 [R = Me (1d), i-Pr (2d), t-Bu (3d), -CH2Ph (4d)] were synthesized cleanly at room temperature under ambient conditions from the reactions of molecular bromine with the gold(I) complexes [1-R-3-{N-(2,6-di-i-propylphenylimino)-2-phenylethyl}imidazol-2-ylidene]AuCl [R = Me (1c), i-Pr (2c), t-Bu (3c), -CH2Ph (4c)]. All of the 1,7-bromination products (1d, 2d, 3d and 4d) have been structurally verified by X-ray diffraction studies.

Highly convenient amine-free sonogashira coupling in air in a polar mixed aqueous medium by trans- and cis-[(NHC)2PdX2] (X=Cl, Br) complexes of N/O-functionalized N-heterocyclic carbenes.

Two new trans- and cis-[(NHC)(2)PdX(2)] (X=Cl, Br) complexes of N/O-functionalized N-heterocyclic carbenes employed in a highly convenient amine-free Sonogashira cross-coupling reaction in air in a polar mixed aqueous medium are reported. Specifically, the trans-[{1-benzyl-3-(3,3-dimethyl-2-oxobutyl)imidazol-2-ylidene}(2)PdBr(2)] (3) and cis-[{1-benzyl-3-(N-tert-butylacetamido)imidazol-2-ylidene}(2)PdCl(2)] (4) complexes effectively catalyzed the Sonogashira cross-coupling reaction of aryl iodides with substituted acetylenes in air in a mixed solvent (DMF/H(2)O, 3:1 v/v) under amine-free conditions. Interestingly, these trans- and cis-[(NHC)(2)PdX(2)] (X=Cl, Br) complexes, with two N-heterocyclic carbene ligands, exhibited superior activity compared with the now popular PEPPSI (pyridine enhanced precatalyst preparation, stabilization and initiation)-themed analogues, trans-[(NHC)Pd(pyridine)X(2)] (X=Cl, Br), 3 a and 4 a, with one N-heterocyclic carbene ligand and a "throw away" pyridine ligand in a trans disposition to each other. The higher activities of 3 and 4 compared with PEPPSI analogues 3 a and 4 a are attributed to more-electron-rich metal centers, as revealed by DFT studies, in the former complexes and is in concurrence with a more electron-rich metal center being effective in facilitating the oxidative addition of aryl halide, often a rate-determining step in palladium-mediated cross-coupling reactions. Complexes 3 and 4 were prepared from the corresponding silver analogues by transmetalation with [(cod)PdCl(2)], whereas the corresponding PEPPSI analogues 3 a and 4 a were obtained directly from the imidazolium halide salts by reaction with PdCl(2) in pyridine in the presence of K(2)CO(3) as base.

Structural and functional mimic of galactose oxidase by a copper complex of a sterically demanding [N2O2] ligand.

A structural and functional mimic of the galactose oxidase (GOase) enzyme active-site by a copper complex supported over a sterically demanding ligand having [N2O2] donor sites is reported. Specifically, the binding of the histidine (496 and 581) and tyrosine (272 and 495) residues to the copper center in a square-pyramidal fashion in the active-site of galactose oxidase (GOase) enzyme has been modeled in a copper complex, ([(3-tert-butyl-5-methyl-2-hydoxybenzyl)(3'-tert-butyl-5'-methyl-2'-oxobenzyl)(2-pyridylmethyl)]amine)Cu(OAc)) (1b), stabilized over a sterically demanding ligand in which the two phenolate-O atoms mimicked the tyrosine binding while an amine-N and pyridyl-N atoms emulated the histidine binding to the metal center, similar to that in the enzyme active-site. Furthermore, the copper complex 1b is found to be an effective functional model of the enzyme as it efficiently catalyzed the chemoselective oxidation of primary alcohols to aldehydes in high turnover numbers under ambient conditions. An insight into the nature of the active-species was obtained by EPR and CV studies, which in conjunction with the DFT studies, revealed that the active-species is an anti-ferromagnetically coupled diamagnetic radical cation, (1)1b+, obtained by one electron oxidation at the equatorial phenolate-O atom of the ligand in the 1b complex.

From large 12-membered macrometallacycles to ionic (NHC)2M+Cl- type complexes of gold and silver by modulation of the N-substituent of amido-functionalized N-heterocyclic carbene (NHC) ligands.

A series of structurally diverse gold and silver complexes extending from ionic (NHC) 2M(+)Cl(-) (M=Au, Ag) type complexes to large 12-membered macrometallacycles have been prepared by the appropriate modification of the N-substituent of amido-functionalized N-heterocyclic carbenes. Specifically, the ionic, [1-(R)-3-{ N-(t-butylacetamido)imidazol-2-ylidene}]2M(+)Cl(-), (R=t-Bu, i-Pr; M=Au, Ag; 1b, 1c, 2b, 2c) complexes, were obtained in case of the N- t-butyl substituent of the amido-functionalized sidearm while 12-membered macrometallacycles, [1-(R)-3-{N-(2,6-di i-propylphenylacetamido)imidazol-2-ylidene}]2M2, (R=t-Bu, i-Pr; M=Au, Ag; 3b, 3c, 4b, 4c) were obtained in case of the 2,6-di i-propylphenyl N-substituent. These structurally diverse complexes of gold and silver were, however, prepared employing a common synthetic pathway involving the reactions of the imidazolium chloride salts (1a, 2a, 3a, 4a) with Ag2O to give the silver complexes (1b, 2b, 3b, 4b) and which, when treated with (SMe2)AuCl, gave the gold complexes (1c, 2c, 3c, 4c). Detailed density functional theory studies of 1b, 1c, 2b, 2c, 3b, 3c, 4b, and 4c were carried out to gain insight about the structure, bonding, and the electronic properties of these complexes. The NHC-metal interaction in the ionic 1b, 1c, 2b, and 2c complexes is primarily composed of the interaction of the carbene lone pair with the empty p orbital of the metal (5p for Ag and 6p for Au) while the same in the macrometallacyclic 3b, 3c, 4b, and 4c complexes consisted of the interaction of the carbene lone pair with the empty s orbital of the metal (5s for Ag and 6s for Au). The observation of a low energy emission in about the 580-650 nm region has been tentatively assigned to originate from the presence of weak metallophilic interaction in these macrometallacyclic 3b, 3c, 4b, and 4c complexes.

Shorter argentophilic interaction than aurophilic interaction in a pair of dimeric {(NHC)MCl}(2) (M = Ag, Au) complexes supported over a N/O-functionalized N-heterocyclic carbene (NHC) ligand.

Synthesis, structure, bonding, and photoluminescence studies of a pair of neutral dimeric silver and gold complexes of a N/O-functionalized N-heterocyclic carbene ligand exhibiting closed-shell d10...d10 argentophilic and aurophilic interactions, are reported. In particular, dimeric complexes of the type {[1-(benzyl)-3-(N-tert-butylacetamido)imidazol-2-ylidene]MCl}2 [M = Ag (2); Au (3)] displayed attractive metallophilic interaction in the form of a close ligand-unsupported metal...metal contact [3.1970(12) A in 2; 3.2042(2) A in 3] as observed from X-ray diffraction study and also was further verified by low temperature photoluminescence study at 77 K that showed the characteristic emission [527 nm for 2; 529 nm for 3] owing to the metal...metal interaction. The nature of the metallophilic interaction in these complexes was further probed using computational studies that estimated the metal...metal interaction energy to be 12.8 (2) and 8.6 kcal/mol (3). Notably, the argentophilic interaction was found to be stronger than the aurophilic interaction in this series of neutral dimeric complexes. The complexes 2 and 3 were synthesized sequentially, with the silver 2 complex prepared by the reaction of the 1-(benzyl)-3-(N-tert-butylacetamido)imidazolium chloride with Ag2O in 66% yield, while the gold 3 complex was obtained by the transmetallation reaction of the silver 2 complex with (SMe2)AuCl in 86% yield.

Anticancer and antimicrobial metallopharmaceutical agents based on palladium, gold, and silver N-heterocyclic carbene complexes.

Complete synthetic, structural, and biomedical studies of two Pd complexes as well as Au and Ag complexes of 1-benzyl-3-tert-butylimidazol-2-ylidene are reported. Specifically, trans-[1-benzyl-3-tert-butylimidazol-2-ylidene]Pd(pyridine)Cl2 (1a) was synthesized from the reaction of 1-benzyl-3-tert-butylimidazolium chloride (1) with PdCl2 in the presence of K2CO3 as a base. The other palladium complex, [1-benzyl-3-tert-butylimidazol-2-ylidene]2PdCl2 (1b), and a gold complex, [1-benzyl-3-tert-butylimidazol-2-ylidene]AuCl (1c), were synthesized by following a transmetallation route from the silver complex, [1-benzyl-3-tert-butylimidazol-2-ylidene]AgCl (1d), by treatment with (COD)PdCl2 and (SMe2)AuCl, respectively. The silver complex 1d in turn was synthesized by the reaction of 1 with Ag2O. The molecular structures of 1a-d have been determined by X-ray diffraction studies. Biomedical studies revealed that, while the palladium complexes 1a and 1b displayed potent anticancer activity, the gold (1c) and silver (1d) complexes exhibited significant antimicrobial properties. Specifically, 1b showed strong antiproliferative activity against three types of human tumor cells, namely, cervical cancer (HeLa), breast cancer (MCF-7), and colon adenocarcinoma (HCT 116), in culture. The antiproliferative activity of 1b was found to be considerably stronger than that of cisplatin. The 1b complex inhibited tumor cell proliferation by arresting the cell cycle progression at the G2 phase, preventing the mitotic entry of the cell. We present evidence suggesting that the treated cells underwent programmed cell death through a p53-dependent pathway. Though both the gold (1c) and silver (1d) complexes showed antimicrobial activity toward Bacillus subtilis, 1c was found to be ca. 2 times more potent than 1d.