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A layered coordination polymer (CP) with the fine-tuned alignment of four diolefinic ligands has been designed by shifting the coordination site of the ligand. The trimeric and tetrameric cyclobutane derivatives were reversely achieved by the photoinitiated [2+2] cycloaddition of the CP due to the favorable Schmidt's distance. More interestingly, a dynamic fluorescence shift was observed during the photo-oligomerization and heat-cycloreversion of the CP system.

The reaction of 2,3,7,8,12,13,17,18-octaethylporphyrin with sodium nitrite in trifluoroacetic acid produced 5-nitro-2,3,7,8,12,13,17,18-octaethylporphyrin, 5,15-dinitro-2,3,7,8,12,13,17,18-octaethylporphyrin, and 5,10,15-trinitro-2,3,7,8,12,13,17,18-octaethylporphyrin. Reactions of octaethylporphyrin, mono-, di-, tri-, and tetranitro-substituted porphyrins coordination to cobalt(II) acetate in a chloroform–methanol mixture were studied. The corresponding Co(II) porphyrinates were obtained and identified. It was shown that, upon dissolution of Co(II) octaethylporphyrinates in dimethylformamide in the presence of NaOH, the Co(II)→Co(III) oxidation occurs in the coordination site of the macrocycle.

A series of silver coordination complexes (CCs) have been synthesized through self-assembly of five pyridine-substituted tetraphenylethylene stereoisomer ligands with silver ions (named Ag-TPE-2by-1-E, Ag-TPE-2by-2-E, Ag-TPE-2by-2-Z, Ag-TPE-2by-3-E, and Ag-TPE-2by-3-Z). These silver CCs show distinct topologies including beaded chain frameworks, linear structures, and discrete metallacycles. The single-crystal analysis results reveal the critical role of the space distribution of the coordination site and stereoisomer ligands in controlling the silver CCs' geometry configuration and modulating the optical properties. Luminescent investigations revealed that Ag-TPE-2by-2-E, Ag-TPE-2by-2-Z, Ag-TPE-2by-3-E, and Ag-TPE-2by-3-Z possess obvious mechanocharomic behaviors, which can be achieved several reversible cycles through repeated grinding and methanol soaking processes. However, the Ag-TPE-2by-1-E showed tenacious stability toward mechanical grinding and temperature. Thus, these silver CCs provide a good platform to investigate the influence of the space distribution of the coordination site of ligands on their geometry and mechanocharomic properties.

By exploiting an established on-surface metallation strategy, we address the ability of the corrolic macrocycle to stabilise transition metal ions in high-valent (III) oxidation states in metal-supported molecular layers. This approach offers a route to engineer adsorbed metal complexes that cannot be easily fabricated by organic synthesis methods and bear a vacant axial coordination site for catalytic conversions.

We report polymer-promoted cooperative catalysis of Cu for oxygen activation. A series of random copolymers containing dipicolylamine as binding motifs are designed to coordinate type-3 Cu sites. The Cu-copolymers show a 6–8-fold activity enhancement, compared to the molecular complex of Cu with an identical coordination site. Michaelis–Menten analysis demonstrates that the kinetic enhancement results from flexible polymer-promoted cooperative catalysis among multi-Cu sites despite the imposed thermodynamic barrier. These observations provide guidance for the bioinspired design of metallopolymers as soluble catalysts with high activity.

A novel N-confused porphyrin (NCP) analogue bearing an external aza-dipyrrin-like coordination site was synthesized by a Schiff-base forming reaction of N-confused oxoporphyrin and 2-aminopyridine derivatives. The chimera molecule enhances the intrinsic NH tautomerism of NCP to enable four possible tautomeric structures, three of which were identified by metal coordination.

Aluminum is an important component for luminescence. However, the fluorescent aluminum complex with unambiguous structural information is still limited. Herein, we report a series of fluorescence aluminum oxo clusters (AlOCs). By introducing an additional coordination site to the aromatic conjugation ligand, cluster nuclearity increment and fluorescence variation are observed. Al8(OH)2(μ4-O)2(1-NA)2(OEt)16 (AlOC-41, 1-NA = 1-naphthoic acid, OEt = ethanol) is made up of two tetrahedral subunits. By introducing an additional coordination site to the aromatic conjugation ligand, we isolate a high nuclearity compound Al10(μ3-O)2(3-HNA)2(OEt)22 (AlOC-47, 3-HNA = 3-hydroxy-2-naphthoic acid). Correspondingly, their luminescence performance is different (blue fluorescence in AlOC-41 and green in AlOC-47). Present herein is a platform to illustrate the relationship between synthesis, structure, and fluorescence properties.

We present a stepwise synthetic strategy for the preparation of the unprecedented heteroleptic 2+2 neutral metallacycle [{t,c,c-RuCl2(CO)2}2(4′cisDPyP)(3′cisDPyP)] (5), in which two different 5,10-meso-dipyridylporphyrins, 4′cisDPyP [i.e., 5,10-bis(4′-pyridyl)-15,20-diphenylporphyrin] and 3′cisDPyP [i.e., 5,10-bis(3′-pyridyl)-15,20-diphenylporphyrin], are joined through equal 90°-angular Ru(II) connectors. The synthesis of 5 was accomplished through the preparation of a reactive ditopic intermediate in which one of the two pyridylporphyrins is linked to two neutral ruthenium fragments, each having one residual readily available coordination site (a dmso-O). Thus, compound 5 was obtained under mild conditions through two complementary routes: either by treatment of [{t,c,c-RuCl2(CO)2(dmso-O)}2(4′cisDPyP)] (3) with 1 equiv of 3′cisDPyP or, alternatively, by treatment of [{t,c,c-RuCl2(CO)2(dmso-O)}2(3′cisDPyP)] (4) with 1 equiv of 4′cisDPyP. Heteroleptic metallacycle 5 was isolated in pure form in acceptable yield and fully characterized. Spectroscopic data and a molecular model show that 5 has an L-shaped geometry, with the two porphyrins almost orthogonal to one another. The modular approach that we established is highly flexible and opens the way to several possible exciting developments., The unprecedented heteroleptic 2+2 neutral metallacycle [{t,c,c-RuCl2(CO)2}2(4′cisDPyP)(3′cisDPyP)] (5), which features two different 5,10-meso-dipyridylporphyrins and has an L-shaped geometry, was isolated in pure form through a flexible stepwise synthetic approach.

A novel volatile Pt(II)β-iminoketonate complex is synthesized. β-Aminovinylketone H(i-ptac) = [CF3–C(O)–CH=C(NH2)–C(CH3)3] is used as a ligand. The XRD method is used to determine the structures of the ligand and the complex. The crystallographic data for C16H22F6N2O2Pt are as follows: a = 10.0716(4) A, b = 10.9572(4) A, c = 9.6322(4) A, β = 110.9010(10)°, space group С2/m, Z = 2, R = 0.011. The platinum atom has a square planar coordination with two oxygen and two nitrogen atoms of two bidentately linked ketoiminate ligands in trans-position; the PtO2N2 coordination site is formed.

Luminescent lanthanide (Ln(III)) complexes with coumarin or carbostyril antennae were synthesized and their photophysical properties evaluated using steady-state and time-resolved UV-vis spectroscopy. Ligands bearing distant hydroxycoumarin-derived antennae attached through triazole linkers were modest sensitizers for Eu(III) and Tb(III), whereas ligands with 7-amidocarbostyrils directly linked to the coordination site could reach good quantum yields for multiple Ln(III), including the visible emitters Sm(III) and Dy(III), and the near-infrared emitters Nd(III) and Yb(III). The highest lanthanide-centered luminescence quantum yields were 35% (Tb), 7.9% (Eu), 0.67% (Dy), and 0.18% (Sm). Antennae providing similar luminescence intensities with 2-4 Ln-emitters were identified. Photoredox quenching of the carbostyril antenna excited states was observed for all Eu(III)-complexes and should be sensitizing in the case of Yb(III); the scope of the process extends to Ln(III) for which it has not been seen previously, specifically Dy(III) and Sm(III). The proposed process is supported by photophysical and electrochemical data. A FRET-type mechanism was identified in architectures with both distant and close antennae for all of the Lns. This mechanism seems to be the only sensitizing one at long distance and probably contributes to the sensitization at shorter distances along with the triplet pathway. The complexes were nontoxic to either bacterial or mammalian cells. Complexes of an ester-functionalized ligand were taken up by bacteria in a concentration-dependent manner. Our results suggest that the effects of FRET and photoredox quenching should be taken into consideration when designing luminescent Ln complexes. These results also establish these Ln(III)-complexes for multiplex detection beyond the available two-color systems.

The heterometallic chromium-manganese carbonyl nitrosyls CrMn(NO)(CO)n (n = 9, 8) have been investigated by density functional theory. The lowest energy CrMn(NO)(CO)9 structures have unbridged staggered conformations with a ~2.99 &Aring, Cr&ndash, Mn single bond similar to the experimental and lowest energy structures of the isoelectronic Mn2(CO)10 and Cr2(NO)2(CO)8. A significantly higher energy CrMn(NO)(CO)9 isomer has a nearly symmetrical bridging nitrosyl group and a very weakly semibridging carbonyl group. The two lowest energy structures of the unsaturated CrMn(NO)(CO)8 have a five-electron donor bridging &eta, 2-&micro, NO nitrosyl group or a four-electron donor bridging &eta, CO group, as well as a Cr&ndash, Mn single bond of length ~2.94 &Aring, The next higher energy CrMn(NO)(CO)8 structure has exclusively terminal CO and NO ligands and a shorter Cr&ndash, Mn single bond of ~2.85 &Aring, suggesting an 18-electron configuration for the manganese atom and a 16-electron configuration for the chromium atom indicated by a vacant coordination site nearly perpendicular to the Cr&ndash, Mn bond.

Cyclic alkyl amino carbene (CAAC) anchored [FeFe]-hydrogenase model complex featuring rotated conformation at one of the iron centers are found to be promising candidate for effective production of dihydrogen. A stepwise comparison of the complete mechanism using the CAAC stabilized model complex [1]0 has been performed with that of an experimentally isolated one ([2]0). Interestingly, the reduction events involved in the catalytic cycles are found to be more favorable than those previously reported for a similar experimentally known system. Furthermore, the computed ΔpKa values indicate that the distal iron center with a vacant coordination site is more basic compared to the amino nitrogen atom of the azadithiolate bridge. We also made an attempt to determine the oxidation states of the iron centers for the intermediates involved in the catalytic cycles on the basis of the computed Mossbauer isomer shift and Mulliken spin density values.

Hemilabile tris( -butoxy)silanolate ligands allow stabilizing a mononuclear octahedral Mo( ) complex without quenching its reactivity towards small molecules (N , CO , N O)., Coordinatively unsaturated Mo( ) complexes have been identified as highly reactive species able to activate dinitrogen without the need for a sacrificial reducing agent. Here, we report a coordinatively saturated octahedral Mo( ) complex stabilized by κ -tris( -butoxy)silanolate ligands, which is yet highly reactive towards dinitrogen and small molecules. The combined high stability and activity are ascribed to the dual binding mode of the tris( -butoxy)silanolate ligands that allow unlocking a coordination site in the presence of reactive small molecules to promote their activation at low temperatures.

A series of ((pyridinyl)-1H-pyrazolyl)pyridine (pypzpy) ligands in which the pyrazolyl ring at 1- and 3-positions is modified by two 2-, 3-, or 4-pyridyl groups were prepared. Reaction of CuI with 2-(1-(pyridin-2-yl)-1H-pyrazolyl)pyridine (2,2′-pypzpy) in MeCN at room temperature or solvothermal reaction of the same components at 120 °C afforded one binuclear complex [{(2,2′-pypzpy)Cu}(μ-I)]2 (1). Treatment of CuI with 3-(1-(pyridin-2-yl)-1H-pyrazolyl)pyridine (3,2′-pypzpy) at room temperature or at 120 °C produced one-dimensional (1D) polymer [{Cu3(μ3-I)3}(μ-3,2′-pypzpy)]n (2) and one two-dimensional (2D) polymer [{Cu2(μ-I)(μ3-I)}2(3,2′-pypzpy)2]n (3), respectively. Similar reactions of CuI with 4-(1-(pyridin-2-yl)-1H-pyrazolyl)pyridine (4,2′-pypzpy) at room temperature or at 150 °C yielded one 1D polymeric complex [{Cu(μ3-I)}2(4,2′-pypzpy)2{Cu(μ-I)}2]n (4). Complexes [{Cu3(μ3-I)3}(μ-2,3′-pypzpy)]n (5), [(CuI)(μ-2,3′-pypzpy)]2 (6), [(Cu2I2)(3,3′-pypzpy)] (7), [(CuI)(4,3′-pypzpy)] (8), [{Cu(μ3-I)}2(μ-2,4′...

The hydride complexes [RuH{κ3(N,N,N)-Tp}(PPh3)(pta)] (1) and [RuH{κ3(N,N,N)-Tpms}(pta)2] (3) [Tp = hydridotris(pyrazol-1-yl)borate, Tpms = tris(pyrazol-1-yl)methanesulfonate, pta = 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane] reacted with alkynes to form the corresponding neutral alkenyl complexes through insertion reactions. The addition of HBF4 to the hydride complex [RuH{κ3(N,N,N)-Tp}(PPh3)(pta)] (1) led to a coordinatively unsaturated complex through the loss of hydrogen. The free coordination site can be occupied by different groups, such as BF4 or NCMe.

New chiral cluster complexes containing (S)-mandelate and (S)-phenyllactate ligands, [Mo3S4(dtp)3(μ-(S)-mandelate)(py)] (1) and [Mo3S4(dtp)3(μ-(S)-phenyllactate)(py)], were prepared from [Mo3S4(dtp)3(μ-dtp)(H2O)] (dtp = (EtO)2PS2) by ligand substitution. The crystal structures of 1 and 2 were determined by X-ray diffraction. Detailed variable-temperature 31P{1H} and 1H NMR studies of solutions of 1 and 2 in non-coordinating solvents (CDCl3, CD2Cl2) demonstrated three dynamic processes at the Mo–Py coordination site: diastereomer interconversion [(PS) to (MS)] which is inhibited at low temperatures; pyridine rotation around the Mo–py bond (180°-flip), and pyridine exchange in the presence of added pyridine. Activation parameters for all exchange processes have been estimated.

A new type of IrIII metalloligands containing an unsaturated nitrogen coordination site, [Ir(H)2(PPh3)2(pprd)]BF4·2CHCl3 (1), [Ir(H)2(PPh3)2(Me2bpm)]BF4·CHCl3 (2), {[Ir(H)2(PPh3)2(Me2bpm)]PF6·CHCl3}4 (3), [Ir(H)2(PPh3)2(biqz)]BF4·2CHCl3 (4), and [Ir(H)2(PPh3)2(biqz)]PF6 (5), have been prepared by reaction of [Ir(H)2(PPh3)2(Me2CO)2]X (X = BF4 or PF6) with 4-(2-pyridyl)pyrimidine (pprd), 6,6′-dimethyl-4,4′-bipyrimidine (Me2bpm), or 4,4′-biquinazoline (biqz). Subsequently, three novel heterometallic AgI–IrIII hydride coordination polymers, {[Ir(H)2(μ-pprd)(PPh3)2Ag(η-CF3COO)]BF4·Me2CO}n (6), {[Ir(H)2(μ-biqz)(PPh3)2Ag2(μ-CF3COO)3]·Me2CO}n (7), and {[Ir(H)2(μ-Me2bpm)(PPh3)2Ag2(μ-CF3COO)2]PF6·2Me2CO}n (8) have been constructed by reaction of the IrIII metalloligands 1, 3, and 5 with AgCF3COO. In coordination polymer 6, the [Ir(H)2(PPh3)2(pprd)]3+ units are linked through the AgI atoms to form a 1D zigzag chain structure. In coordination polymer 7, the dinuclear [Ag2(μ-CF3COO)3]– units are linked through the terminal N atoms of biqz in two different [Ir(H)2(PPh3)2(biqz)]3+ units to form a 1D zigzag chain structure. In coordination polymer 8, the [Ag2(μ-CF3COO)2] frameworks are linked through the terminal N atoms of Me2bpm and the IrIII atom in two different [Ir(H)2(PPh3)2(Me2bpm)]3+ units to form a waved rectangular cavity. These waved rectangular cavities are connected to each other to afford a unique 2D sheet structure.

Lanthanide( iii ) ions situated in a coordination site of phthalocyanine macrocycle as molecular paramagnets with a large magnetocaloric effect at the temperatures close to room are presented for the first time on the examples of gadolinium and thulium.

Sublimed layers of 5-(pyridin-4-yl)-10,15,20-triphenylporphyrinato)cobalt(II) and 5-(pyridin-3-yl)-10,15,20triphenylporphyrinato)cobalt(II) ({Co(M4PyTPP)} (I) and {Co(M3PyTPP)} (II), respectively) form coordination oligomers upon standing. Interaction of NO(15NO) gas with these systems results in the formation of pentaand hexacoordinated nitrosyl complexes, the sixth coordination site of which is occupied by pyridyl group of adjacent molecule in the layer. The FTIR spectral data demonstrate that the long-term exposure of these systems under O2 results in oxidation of the nitrosyl complexes with formation of hexacoordinated nitrato complexes and the reaction proceeds predominantly with hexacoordinated nitrosyls. Мechanism of oxidation more likely includes the dissociation of NO from the hexacoordinated complex followed by O2 trapping of resulting (-4(3)Py)Co(M4(3)PyTPP) to give (4(3)Py) Co(M4(3)PyTPP)(O2), which then reacts rapidly with NO by the nitric oxide dioxygenation reaction.

A new concept for a light-gated transition metal catalyst is presented based on a photo-active moiety in the outer ligand sphere of the complex which on irradiation reacts irreversibly with some part of the inner ligand sphere releasing a free coordination site. The principle is exemplified on a platinum complex for the hydrosilylation. It is proven that the catalytic properties of the complex and the properties of the photo-gate can be fine-tuned on the chemical problem independently of each other.

Improved syntheses of o-C6H4(PEt2)(X) (X = F, Br, I) and the trisphosphine PhP[o-C6H4(PEt2)]2 have been developed and are applicable to a wide variety of phosphine substituents. The trisphosphine, PhP(o-Ph–PEt2)2, has been fully characterized spectroscopically and, for the first time, crystallographically. Reaction of the P3 ligand with one equivalent of NiCl2 or Ni(BF4)2 followed by 2.5 equivalents of KNCS produces the monometallic complexes Ni(X)2[κ3-PhP(o-Ph–PEt2)2], (X = Cl or NCS). The nickel thiocyanate complex has been characterized via a crystal structure. The nickel center has a square pyramidal structure with one of the NCS ligands occupying the apical coordination site. The Ni complex crystallizes in the P 1 ¯ space group with an unusual six molecules in the asymmetric unit (Z′ = 6), and twelve in the unit cell.

The synthesis, structure, and conformational mobility of a trans-bis(aminophenolato)platinum(II) complex bearing a dodecamethylene bridge, [Pt(L)] (1) [H2L = N,N′-Dimethyl-N,N′-bis(2-hydroxyphenylmethyl)dodecane-1,12-diamine] are described. The 2D NMR and X-ray diffraction analysis revealed that the complex has a “reversed U”-shaped syn conformation in the solution state, which is mainly due to steric congestion of the vaulted structure and hydrogen bonding at the bis[(o-aminomethyl)phenolato] coordination site, while the complex unit is packed in the crystalline state with “Z-shaped” anti-conformation due to highly regulated molecular arrangement by 3D CH-π and hydrogen bonding interactions.

N-Heterocyclic carbenes (NHCs) are an important class of compounds that are indeed regarded as most versatile carbon-donor ligands in transition metal and organometallic catalysis. In addition, NHCs are also capable of stabilizing a variety of highly reactive main group compounds with intriguing properties. The enormous success of NHCs prompted the investigation of other carbon-based neutral ligands with additional structural and electronic features. Reactivity studies of NHCs and their complexes unveiled routes to new carbon donor ligands. Such NHC-derived ligands can be grouped into three categories: (i) N-heterocyclic olefins (the donor site is extended by an intervening carbon atom), (ii) ditopic carbanionic-NHCs (an additional coordination site is generated by the deprotonation of an NHC), and (iii) abnormal-NHCs (the carbene center of an NHC is moved to different positions). This article summarizes the recent advances in NHC chemistry of compounds featuring the aforementioned ligands, which are exclusively derived by the functionalization of NHCs, 1,3-bis(2,6-diisopropylphenyl) imidazol-2-ylidene (IPr) in particular.

International audience; A μ3-sulfide bridged triiron cluster(ii,ii,iii) supported by a cyclophane ligand undergoes metal-based reduction to yield an all-ferrous species. The latter complex incorporates a three-coordinate iron center that provides an accessible coordination site to a solvent molecule.

Two new tetradentate C2-symmetric pseudopeptidic ligands derived from Val and Phe containing two amino and two amido groups and a central o-substituted aromatic spacer have been prepared. Their complexes with Cu2+, Zn2+, and Ni2+ have been studied by potentiometry, UV−vis spectrophotometry, FT-IR, and ESI-MS. The presence of the aromatic spacer provides Cu2+ complexes with stability constants several orders of magnitude higher than those observed for related ligands containing aliphatic central spacers. Besides, the formation of [MH−2L] complex species is favored. Crystal structures for the corresponding Cu2+ and Ni2+ have been obtained, revealing the metal atom in an essentially square-planar geometry, although, in several instances, the oxygen atom of an amide carbonyl of a second complex species can act as a fifth coordination site. In the case of Zn2+, the only crystal structure obtained displays a square-pyramidal arrangement of the metal center. Finally, preliminary experiments show the catalytic activity of some of these complexes, in particular, Zn2+ complexes, for epoxide ring-opening with using aniline as the nucleophile in a ligand accelerated process. Spanish MINECO CTQ2015-68429-R Generalitat Valenciana PROMETEO/2012/020 GRISOLIA 2012/015 PPI-UJI P1-1B-2013-38

The incorporation of unnatural chelating amino acids in short peptide sequences leads to lanthanide-binding peptides with a higher stability than sequences built exclusively from natural residues. In particular, the hexadentate peptide P(22), which incorporates two unnatural amino acids Ada(2) with aminodiacetate chelating arms, showed picomolar affinity for Tb(3+). To design peptides with higher denticity, expected to show higher affinity for Ln(3+), we synthesized the novel unnatural amino acid Ed3a(2) which carries an ethylenediamine triacetate side-chain and affords a pentadentate coordination site. The synthesis of the derivative Fmoc-Ed3a(2)(tBu)(3)-OH, with appropriate protecting groups for direct use in the solid phase peptide synthesis (Fmoc strategy), is described. The two high denticity peptides P(HD2) (Ac-Trp-Ed3a(2)-Pro-Gly-Ada(2)-Gly-NH(2)) and P(HD5) (Ac-Trp-Ada(2)-Pro-Gly-Ed3a(2)-Gly-NH(2)) led to octadentate Tb(3+) complexes with femtomolar stability in water. The position of the high denticity amino acid Ed3a(2) in the hexapeptide sequence appears to be critical for the control of the metal complex speciation. Whereas P(HD5) promotes the formation of polymetallic species in excess of Ln(3+), P(HD2) forms exclusively the mononuclear complex. The octadentate coordination of Tb(3+) by both P(HD) leads to total dehydration of the metal ion in the mononuclear complexes with long luminescence lifetimes (2 ms). Hence, we demonstrated that unnatural amino acids carrying polyaminocarboxylate side-chains are interesting building blocks to design high affinity Ln-binding peptides. In particular the novel peptide P(HD2) forms a unique octadentate Tb(3+) complex with femtomolar stability in water and an improvement of the luminescence properties with respect to the trisaquo TbP(22) complex by a factor of 4.

We report synthesis and coordination properties of β-alkyl porphyrin derivatives bearing terpyridylphenyl substituents at the meso-position and propionate side chains at the β-positions. Rhenium(I) carbonyl ion was encapsulated not in the core but in the external terpyridyl ligand. Such porphyrin–terpyridine hybrid porphyrins can be potentially available for less-invasive imaging like SPECT.

Complete kinetic description and spectral manifestation of the hydrogen peroxide oxidation of (2,3,7,8,12,13,17,18-octamethyl- and (2,3,7,8,12,13,17,18-octaethyl-5-phenylporphinato)chloromanganese(III), (2,3,7,8,12,13,17,18-octaethyl-5,10-diphenyl- and (2,3,7,8,12,13,17,18-octaethyl-5,15-diphenylporphinato)chloromanganese(III) complexes in water-organic solutions are presented. Two H2O2 concentration ranges with different reaction mechanisms and products were distinguished. The ion-molecular oxidation mechanism was substantiated and the key role of coordination of various hydrogen peroxide species, their activation, oxidation and reduction was demonstrated. Multiple substitution in the coordinated macrocycle was found to change the electronic state of the coordination site and quantitative characteristics of the oxidation; this can be used to develop the synthetic models of natural oxide reductases.

The acidities of multiple sites in Cu+–guanine and Cu2+–guanine complexes have been investigated theoretically. To compare, the acidities of guanine (G) and guanine radical cation (G +) have also been included. The results clearly indicate that the acidities of C H or N H groups in Cu+/2+–guanine are significantly enhanced relative to the neutral guanine. The acidic order for guanine derivatives is as follows: Cu2+–guanine > G + ⩾ Cu+–guanine > G. For Cu+/2+–guanine, N7-coordination exhibits N1–H acid, while for N3-coordination, Cu+–guanine and Cu2+–guanine behave as N2–H2b and N9–H acid, respectively. Moreover, for the given coordination site, N7-coordination greatly decreases the gap between the most acidic group and the least one with respect to that in the neutral guanine. Additionally, it is found that C8–H and N2–H2b groups are significantly acidified with respect to the other groups in the coordination complexes. Natural population analysis assumes the deprotonation process of Cu+/2+–guanine complexes and interprets the highest acidity of Cu2+–guanine of all the guanine derivatives studied. Consequent NBO analyses confirm this assumption. Also, electrostatic potential calculations of [G(–H)]− and [G(–H)] well reproduce the geometrical characters of the deprotonated structures.

Zinc(II) promotes the reduction of unactivated ketones and aldehydes by (methyl-substituted) 1-methyl-1,4-dihydropyridines. Coordination of the dihydropyridines to the metal, which occurs via their annular nitrogen atoms, is essential for hydrogen-transfer. The reductions proceed best in apolar non-aromatic solvents, which are unable to compete with the carbonyl group of the substrate for a coordination site at the metal. Virtually no hydrogen-transfer takes place in the absence of Zn(II) salts or when zinc coordination complexes are used in which the metal is coordinatively saturated. The results of this study are discussed in terms of a possible relationship with the role of zinc in alcohol dehydrogenases and metal-catalyzed reductions in biomimetic systems.

A series of mononuclear salicylaldiminato(thiosemicarbazone)palladium(II) complexes of general formula [Pd(saltsc-R)PPh 3 ], {H 2 saltsc-R = salicylaldehyde thiosemicarbazone; R = H (5), 3-tert-butyl (6), 3-methoxy (7), 5-chloro (8)) have been synthesized. The palladium complexes were prepared by the reaction of the appropriate salicylaldimine thiosemicarbazone with Pd(PPh 3 ) 2 Cl 2 . All complexes were characterised by a range of spectroscopic and analytical techniques. The molecular structures of 6-8 have been determined by single-crystal X-ray diffraction analysis. The salicylaldimine thiosemicarbazones coordinate to palladium in a tridentate manner, through the phenolic oxygen, imine nitrogen and thiolate sulfur, forming five-and six-membered chelate rings within their structures. The fourth coordination site for these square-planar complexes is occupied by PPh 3 . Biological activities of the thiosemicarbazone ligands and palladium complexes have been investigated toward the WHCO1 oesophageal cancer cell line and against two strains of the malaria parasite Plasmodium falciparum, W2 (chloroquine-resistant) and D10 (chloroquine-sensitive). The palladium(II) complexes show enhanced in vitro antiplasmodial activity in comparison with their thiosemicarbazone ligand precursors. On the other hand, in vitro anticancer activity studies on oesophageal cancer cell lines revealed a decrease in activity upon coordination of palladium to the thiosemicarbazone ligand.

Semicarbazone is a molecule with a group R1R2C=N-NR3-C(=O)-NR4R5.The oxygen atom has two free electron pairs; each nitrogen atom has one free electron pair. These free electron pairs are potential sites of coordination. The simplest molecule in this series is the semicarbazone which the formula is H2C=N-NH-C(=O)NH2. By replacing the oxygen atom by a sulfur atom is obtained a thiosemicarbazone. Some semicarbazones, such as nitrofurazone, and some thiosemicarbazones are known to have many properties: antiviral, antibacterial, antitrypanosomal, anticonvulsant, antitumor, anticancer. They are usually mediated by an association with copper or iron.Indeed transition metal complexes with given chemical structures are useful alternatives in the treatment of certain diseases since coordination of active ingredients deeply modifies both the physiological properties of metals and ligands in the meaning of overall improvement of these properties.The present work focuses on quantum study of the complexation of semicarbazone and its methylated derivatives. The purpose of this study is to determine the most favorable coordination site of each of these ligands. It was found that the oxygen atom appears more favorable to the coordination of semicarbazones.Complexes of these ligands with the Zn (II) were modeled. The calculations were made by the method DFT / B3LYP with the orbital basis 6-31G (d, p).

Regioselective methods to synthesize [Zr{η5-C5H3-1,3-(SiMe2-η-NtBu)2}R] and [Zr{η5-C5H3-1,2-(SiMe2-η-NtBu)2}R] have been investigated. Selective formation of 1,3- and 1,2-di(silylamido)cyclopentadienyl zirconium complexes is controlled by the generation of the intermediate lithium salts Li[C5H3-1,3-(SiMe2NHtBu)2] (2) and Li2[C5H4-1,1-(SiMe2NtBu)2] (3). Experimental data and ab initio calculations justify the formation of 2 and 3 starting from C5H4(SiMe2NHtBu)2 (1). The structural characterization of the lithium salt 3 shows the cyclopentadiene ring unaltered, while the two deprotonated 1,1-di(silylamido) groups are bridging both lithium atoms with one additional coordinated THF molecule. The X-ray diffraction studies of 1,2- and 1,3-di(silylamido)cyclopentadienyl zirconium complexes show a remarkably different coordination site in these molecules.

The synthesis and structural characterisation (IR, MS, 1H, 13C and 15N NMR and single crystal X-ray diffraction analysis) of 2-aminoazole complexes of pentacarbonyl Cr(0) and W(0) are described. When provided with endocyclic soft thioether or endocyclic hard amine, endocyclic borderline imine and exocyclic hard amine coordination sites, the softer endocyclic imine coordination site is favoured.

Blocking the pass: Low-valent Ni centers readily bind Tl(I) ions in a synthetically reversible fashion. The Tl units, in turn, serve as coordination site protection agents for Ni with respect to incoming Lewis basic ligands. This synthetic sequence allows for the isolation of a reactive zero-valent Ni tris-isocyanide complex.

The structure of dimeric cyclo-L-hemicystinyl-glycine, investigated by 1H n.m.r. in solution, displays a buckled diketopiperazine ring with a folded side-chain. A disulfide sulfur atom is the primary coordination site for transition metal ions, such as Rh(III), Pd(II) and Pt(II).

The Pt(II) complex (NSiN)PtCl (2; NSiN = bis(8-quinolyl)methylsilyl) was prepared from reaction of (COD)PtCl2, Qn2SiHMe (1) and excess NEt3 in dichloromethane. The X-ray structure of 2 confirms a square-planar geometry about platinum and a highly distorted tetrahedral geometry at Si. A series of thermally stable (NSiN)Pt(IV) compounds including (NSiN)PtH2(X) [X = Cl (5), OTf (10)] and (NSiN)PtMe2(X) [X = I (6), OTf (7)] were also synthesized. Five-coordinate Pt(IV) complexes of the type [(NSiN)PtR2][B(C6F5)4] (X = Me (9), H (11)] were generated by treatment of the corresponding triflato derivatives with 1 equiv of Li(Et2O)3[B(C6F5)4] in dichloromethane. A crystal structure of 9 reveals a square-pyramidal structure with an empty coordination site trans to silicon. Initial reactivity studies have shown that complex 9 is thermally and chemically robust.

Using a one-pot four-step reaction a readily available phospholide was converted efficiently to a 2-carboxyphosphole. This compound can be used as a building block for the synthesis of phosphole-containing peptides, where the phosphole can serve as a coordination site for late transition metals and may affect the secondary structure of the peptide.

Equimolar reac t ions be tween o rgano t in ( IV) precursors of SnCl x R 4 . x (R = Bu, Ph, χ = 1, 4) and aminoguan id ine b i ca rbona t e in methanol has a f fo rded 2:1 and 1:1 ( M : L ) ca rbona t e c o m p l e x e s as well as 1:2 semicarbaz ide der iva t ive . T h e p roduc t s were charac ter i sed by spec t roscop ic m e t h o d s such as mul t inuclear N M R ( ' Η , i 3 C and l l 9 S n ) , Mussbaue r and infrared spec t roscopy as well as mic roana lys i s and mel t ing point. T h e butyl and phenyl der iva t ives have a 4and 5 -coord ina ted metal cent re respec t ive ly with br idgingbidentate and br idg ingt r iden ta te ca rbona te . For the te t rahal ide metal p recursor , a 6 -coord ina ted t in(IV) der ivat ive has been ach ieved with a b identa te semica rbaz ide t owards the metal centre . I N T R O D U C T I O N Aminoguan id ine has been k n o w n for more than one hundred years and it was first p repared in 1892 f rom a reduct ion react ion o f n i t roguanid ine . Recent d i scover ies conce rn ing pha rmaco log ica l proper t ies of aminoguan id ine / I / have been at t ract ing the interest of b iochemis t s . T h i s c o m p o u n d has a l ready been acknowledged as potent ia l med ic ine for lung hyper tens ion t rea tment as well as in d iabet ic pat ients /2, 3/. Within the b iomedica l f ield, howeve r , the current interest is concen t ra ted upon research onorganot in c o m p o u n d s and their appl ica t ions , par t icular ly against ca rc inogen ic tumours . In genera l , t r iorganot in c o m p o u n d s d isp lay a h igher b iological act ivi ty than their diand m o n o ana logues . For instance, t r iphenylt in der ivat ives are h ighly act ive , showing very low ID5U va lues against M C F 7 and W i D r type cel ls /4, 5/. On the other hand, the coord ina t ion chemis t ry involving aminoguan id ine b ica rbona te has not been invest igated so far. A m i n o g u a n i d i n i u m ( + ) s eems to be unl ikely to bind meta ls as the l i terature p rov ides with the first example of a h y d r o b r o m i d e c o p p e r ( I I ) der ivat ive of aminoguan id ine hydroch lor ide . Th i s c o m p o u n d was prepared in the p resence of an excess of hydrobromic acid 161. In such condi t ions , the aminoguan id in ium(+) * Cor re spond ing au thor : irsmaiaa,u1v.hr .(J. R. D. S. Maia ) l Bereitgestellt von | De Gruyter / TCS Angemeldet | 212.87.45.97 Heruntergeladen am | 31.10.12 15:29 Vol. 31, Nos. 1-2, 2008 Carbonate and Semicarbazide Tin(IV)Derivatives ofAminoguanidine Bicarbonate is converted into aminoguanidinium(2+) by proton abstraction from the solution. The pronounced positive charge density over this cation excludes itself as an electron-donor molecule. This is evident by structural molecular determination, where the aminoguanidinium(2+) is acting as counter ion within the lattice 161. In this context, aminoguanidinium(+) can in principle achieve a metal-ligand bond formation. The coordination site can be envisaged through the NH2 moiety, which does not participate effectively on the charge dereal izat ion as shown in Scheme 1. N H , MHHj-N, ^ N H , Λ NN, Η,Ν, 'ΝΗΛ Ν Ης.

A N- (4-styrylphenyl) iminodiacetic acid probe 1 with a simple structure, which can be incorporated into the cyclodextrin (CyD) cavities, has been synthesized as a sensor for heavy metal ions. The UV-Vis and fluorescence analyses revealed that the probe 1 was essentially selective for Cu2+. The α- and β-CyDs formed stable 1: 1 complexes with 1. However, no influence was noted for the response selectivity of 1 as α- and β-CyD complexes. In contrast, although γ- CyD showed a weak binding ability for 1 without metal ions, the 2: 1 binding of 1 for heavy metal ions was evidently enhanced inside the γ- CyD cavity, resulting in the increased recognition ability for Cu2+, Co2+, Zn2+, and Ni2+. For NH2-β-CyD possessing an additional NH2 coordination site at the CyD rim, the 1/NH2-β-CyD complex was found to exhibit the response selectivity for both Cu2+ and Ni2+.

International audience; New picket porphyrins delivering at least one carboxylic group around the coordination site of the macrocycle were synthesized for bismuth coordination. The influence of the number, the length, and the pre-organization of the carboxylic acid pickets on the stability of the bismuth complexes was explored. Their stabilities in acidic medium were compared with those of their precursors bearing ester pickets. The molecular structure of one of the bismuth complexes, which is the only monomeric bismuth porphyrin reported up to now, is discussed. At the opposite of what we initially reported, and in agreement with the theoretical calculations, the distortion of the macrocycle in this structure is mainly due to the number of water molecules in the first sphere of coordination of the bismuth.

Mechanisms for H-transfer from 1,1-dimethylallyl (DMA) to neopentyl (CH 2 t-Bu) in the complex Cp*W(NO)(CH 2 t-Bu)(η 3 -DMA) are examined by B3LYP-DFT calculations. Either the mid-H or the methyl H on the DMA can transfer tothe W-bound neopentyl to generate neopentane (2,2-dimethylpropane) and Cp*W(NO)(η 2 -1,1-dimethylallene) or Cp*W(NO)(η 2 -2-methylbuta-1,3-diene) intermediates, respectively. The open coordination site created by the neopentane loss is the site of the subsequent C-H bond activation of alkanes and arenes. The similarities in the overall enthalpic barriers for these mechanisms, 23-24 kcal/mol, explain the observed deuterium distribution (65% on the mid-carbon and 35% on the methyls of the DMA) when benzene-d 6 reacts as substrate.

The coordination effects induced on the 1 H-, 13 C-, and 15 N- NMR chemical shifts of the 3,5-di- (4-butoxyphenyl)-1H-pyrazole, HPzbp2 (1) have been quantified for the following complexes:- (Au(HPz bp2 )(PPh3))(NO3) (2), (Pd(η3-C3H5)(HPz bp2 )2)(BF4) (3) (or Pd(η3-C3H5)( 15 N2- HPz bp2 )2)(BF4) ( 15 N2-3)), and (Ag( HPz bp2 )2)(BF4) (4), in solution and in the solid state. 15 N- CPMAS NMR proved to be the most useful tool for establishing the coordination site. The increase in the nitrogen-shielding on metal-complexation owing to changes in the paramagnetic shielding term is about -55 ppm.

The syntheses and characterization of three compounds involving tridentate “half-units” 7-amino-4-methyl-5-aza-3-hepten-2-one (HAMAH) and 8-amino-4-methyl-5-aza-3-octen-2-one (HAMAO) are described. Cu(II) and Ni(II) complexes with HAMAH have been isolated as four-coordinate complexes, the fourth coordination site being taken by imidazole, and have been structurally characterized. A Cu(II) complex involving HAMAO has been isolated as a highly insoluble polymeric species. Hydroxo bridging between the metal centres is indicated.

A new type of phenylazomethine dendrimer (DPA) that has one more coordination site compared to the tetraphenylmethane core DPA was synthesized for the “magic number 13” metal cluster template that ...

A novel [(dppe)2Pt2(μ-BINOL)]2+[OTf]-2 dimer (A) was cleanly produced by addition of 1 equiv of HOTf to (dppe)Pt(S-BINOL) (1) or via “comproportionation” of 1 with (dppe)Pt(OTf)2 (2). The structure of A was investigated by 1H, 31P, and 13C NMR spectroscopy, as well as 2D 1H/1H (COSY) and 13C/1H (HMQC, HMBC) correlation experiments, revealing that both halves of the bridging BINOL ligand have undergone “enol−keto” tautomerization in this complex. Two symmetry-equivalent (dppe)Pt fragments coordinate in an anti fashion via Pt−C σ bonds to the adjacent atoms C1 and C1‘ of the resulting “diketo” BINOL ligand. η1-Coordination of the carbonyl groups of “diketo” BINOL to Pt was proposed to fill the fourth coordination site of each Pt square plane in dimer A, generating favorable five-membered Pt-chelate rings; the P−Pt coupling constants observed for A are consistent with CO→Pt coordination. The driving force for dimer formation is likely electrostatic, as dimerization distributes the dicationic charge of Pt Lew...

The synthesis of [K+·THF(2,6-iPr2C6H3N(SiMe3)Al(C⋮CPh)3)-]2 (1), [Na+·THF (2,6-iPr2C6H3N(SiMe3)Al(C⋮CPh)3)-]2 (2), and [Li+·dioxane (2,6-iPr2C6H3N(SiMe3)Al(C⋮CPh)3)-]2·2dioxane (3) respectively by the reaction of [2,6-iPr2C6H3N(SiMe3)AlCl2]2 (4) with the corresponding phenylethynyl alkali metal salt is reported. In compound 1 the potassium (2, sodium) interacts with the C⋮C bonds of four phenylethynyl groups. A further coordination site of the potassium (sodium) is occupied by a THF molecule. Thus, the cation therein acts as a bridging moiety to form the dimer. In compound 3 each of the lithium cations is 2-fold coordinated by phenylethynyl ligands and two dioxane molecules. One of the dioxane molecules in 3 functions as a bridge forming the dimer. The herein described compounds are the first structurally characterized species having three terminal phenylethynyl groups bound to the aluminum atom.

The 1H{15N} NMR spectrum of 5,7-diphenyl-1,2,4-triazolo[1,5-a]-pyrimidine (3) was measured by GHMQC, unambiguously assigned and compared with the spectra of 1,2,4-triazolo[1,5-a]pyrimidine (1) and 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (2). A series of Au(III) chloride complexes of general formula AuLCl3, where L = 1, 2, 3, was synthesized and studied by 1HH{15N} GHMQC and 1H{13C} GHMBC. Low-frequency shifts of 72–74 ppm (15N) and 5–6 ppm (13C) were observed upon complexation by Au(III) ions for the coordination site N-3 and adjacent C-2, C-3a atoms, respectively. The 13C signals of C-5, C-6, C-7 and the 1H resonances of H-2, H-6 were shifted to higher frequency. Comparison with analogous Pd(II), Pt(II) and Pt(IV) complexes revealed that in the case of Au(III) coordination the 15N shifts were relatively smaller, whereas those for 13C and 1H were larger. Copyright © 2002 John Wiley & Sons, Ltd.

Different mononuclear and dinuclear Cu complexes show high catalytic activity at concentrations 1-10 mM in the oxidation of ascorbic acid by peroxynitrite. Their activity is similar to the activity of Mn-porphyrin complexes and weakly depends on ligand environment, provided at least one free coordination site is available. The proposed reaction mechanism involves the intermediate formation of a copper-peroxynitrito complex, which reacts directly with ascorbic acid.