Novel triphenyltin(IV) compounds with carboxylato N-functionalized 2-quinolones as promising potential anticancer drug candidates: in vitro and in vivo evaluation.

Three newly synthesized triphenyltin(IV) compounds, Ph3SnL1 (L1- = 3-(4-methyl-2-oxoquinolin-1(2H)-yl)propanoato), Ph3SnL2 (L2- = 2-(4-methyl-2-oxoquinolin-1(2H)-yl)ethanoato), and Ph3SnL3 (L3- = 2-(4-hydroxy-2-oxoquinolin-1(2H)-yl)ethanoato), were characterized by elemental microanalysis, FT-IR spectroscopy and multinuclear (1H, 13C and 119Sn) NMR spectroscopy. A single X-ray diffraction study indicates that compounds Ph3SnL1 and Ph3SnL2 exhibit a 1D zig-zag chain polymeric structure, which in the case of Ph3SnL2 is additionally stabilized by π-interactions. In addition, the synthesized compounds were further examined using density functional theory and natural bond orbital analysis. The compounds have been evaluated for their in vitro anticancer activity against three human cell lines: MCF-7 (breast adenocarcinoma), A375 (melanoma), HCT116 (colorectal carcinoma), and three murine cell lines: 4T1 (breast carcinoma), B16 (melanoma), CT26 (colon carcinoma) using MTT and CV assays. The IC50 values fall in the nanomolar range, indicating that these compounds possess better anticancer activity than cisplatin. The study of the effect of the newly developed drug Ph3SnL1 showed its plasticity in achieving an antitumor effect in vitro, which depends on the specificity of the phenotype and the redox status of the malignant cell line and ranges from the initiation of apoptotic cell death to the induction of differentiation to a more mature cell form. In the syngeneic model of murine melanoma, Ph3SnL1 showed the potential to reduce the tumor volume similar to cisplatin, but in a well-tolerated form and with low systemic toxicity, representing a significant advantage over the conventional drug.

Metal-metal cooperativity boosts Lewis basicity and reduction properties of the bis(gallanediyl) CyL2Ga2.

The interplay of two proximate gallium centres equips the bimetallic complex CyL2Ga2 (1, CyL2 = 1,2-trans-Cy[NC(Me)C(H)C(Me)N(Dip)]2, Dip = 2,6-i-Pr2C6H3) with increased Lewis basicity and higher reducing power compared to the monometallic gallanediyl LGa (2, L = HC[MeCN(Dip)]2) as evidenced by cross-over experiments. Quantum chemical calculations were employed to support the experimental findings.

Anion-Dependent Reactivity of Mono- and Dinuclear Boron Cations.

The dinuclear bis(N-heterocyclic carbene) borane adduct 2 rapidly reacts with tritylium salts at room temperature but the outcome is strongly impacted by the respective counter-ion. Using tritylium tetrakis(perfluoro-tert-butoxy)aluminate affords - depending on the solvent - either the bis(boronium) ion 4 or the hydride-bridged dication 5. In case of tritylium hexafluorophosphate, however, H/F exchange occurs between boron and phosphorus yielding the dinuclear BF3 adduct 3 along with phosphorus dihydride trifluoride. H/F exchange also takes place when using the mononuclear N-heterocyclic carbene BH3 adduct 6 and hence provides a facile route to PH2 F3 , which is usually synthesized in more complex reaction sequences regularly involving toxic hydrogen fluoride. DFT calculations shed light on the H/F exchange between the borenium ion and the [PF6 ]- counter-ion and the computed mechanism features only small barriers in line with the experimental observations.

A molecular aluminium fulleride.

The reaction of alumylene [(Dippnacnac)Al] (1) with C60 fashions the first example of a structurally characterised aluminium-fulleride complex, [{(Dippnacnac)Al}3C60] (2), in which the Al centres are covalently bound to significantly elongated 6 : 6 bonds. Hydrolysis of 2 yields C60H6 and the reaction of 2 with [{Mesnacnac)Mg}2] cleaved off the Al fragments by affording the fulleride [{Mesnacnac)Mg}6C60].

A tetranuclear magnesium hydride cluster with a four-coordinate hydride in near square-planar geometry.

A tetranuclear magnesium hydride complex based on the ß-oxo-δ-diiminate (BODDI) ligand was isolated. In the solid state, the complex features three bridging µ2-hydrides and one unprecedented four-coordinate hydride in a nearly square-planar coordination environment. In the solid state, two different coordination polymers are observed depending on whether the axial or equatorial oxygen lone pairs of 1,4-dioxane are engaged in bonding to magnesium.

Effective or predatory funding? Evaluating the hidden costs of grant applications.

Researchers are spending an increasing fraction of their time on applying for funding; however, the current funding system has considerable deficiencies in reliably evaluating the merit of research proposals, despite extensive efforts on the sides of applicants, grant reviewers and decision committees. For some funding schemes, the systemic costs of the application process as a whole can even outweigh the granted resources-a phenomenon that could be considered as predatory funding. We present five recommendations to remedy this unsatisfactory situation.

simpleISM-A straight forward guide to upgrade from confocal to ISM.

Resolution in a confocal laser scanning microscopes (CLSM) can be improved if the pinhole is closed. But closing the pinhole will deteriorate the signal to noise ratio (SNR). A simple technique to improve the SNR while keeping the resolution same by upgrading the system to an image scanning microscope. In this paper, we explain in detail, based on an Olympus Fluoview 300 system, how a scanning microscope can be upgraded into an image scanning microscope (ISM) using a simple camera-based detector and an Arduino Due providing a galvo driving and camera synchronization signals. We could confirm a resolution improvement as well as superconcentration and made the interesting observation of a reduced influence of laser fluctuations.

A Planar Five-Membered Aromatic Ring Stabilized by Only Two π-Electrons.

Many chemicals known today are partially or fully aromatic, since a ring framework experiences additional stabilization through the delocalization of π-electrons. While aromatic rings with equal numbers of π-electrons and ring atoms such as benzene are particularly stable, those with the minimally required two π-electrons are very rare and yet remain limited to three- and four-membered rings if not stabilized in the coordination sphere of heavy metals. Here we report the facile synthesis of a dipotassium cyclopentagallene, a unique example of a five-membered aromatic ring stabilized by only two π-electrons. Single-crystal X-ray diffraction revealed a planar Ga5 ring with almost equal gallium-gallium bond lengths, which together with computational and spectroscopic data confirm its aromatic character. Our results prove that aromatic stabilization goes far beyond what has previously been assumed as minimum π-electron count in a five-atom ring fragment.

A Highly Fluorescent Dinuclear Aluminium Complex with Near-Unity Quantum Yield.

The high natural abundance of aluminium makes the respective fluorophores attractive for various optical applications, but photoluminescence quantum yields above 0.7 have yet not been reported for solutions of aluminium complexes. In this contribution, a dinuclear aluminium(III) complex featuring enhanced photoluminescence properties is described. Its facile one-pot synthesis originates from a readily available precursor and trimethyl aluminium. In solution, the complex exhibits an unprecedented photoluminescence quantum yield near unity (Φabsolute 1.0±0.1) and an excited-state lifetime of 2.3 ns. In the solid state, J-aggregation and aggregation-caused quenching are noted, but still quantum yields of 0.6 are observed. Embedding the complex in electrospun non-woven fabrics yields a highly fluorescent fleece possessing a quantum yield of 0.9±0.04.

Synthesis, characterization, and reactivity of group 13 hydride complexes based on amido-amine ligands.

The preparation of group 13 hydride complexes supported by N,N',N'-substituted 1,2-ethanediamines is reported. Dihydridoalanes LAlH2, for which the aggregation behaviour in solution and in the solid state is modulated by the steric bulk of the aryl substituent, readily react with elemental sulphur affording dinuclear aluminium sulphide complexes. Chloridohydrido trielanes LEHCl (E = B, Al, Ga) have been synthesized as well starting from the hydrochloride salts of the protio-ligands and the chlorido substituent within LAlHCl is readily replaced using Li[N(SiMe3)2]. Depending on the steric bulk of the ligand, the chloridohydrido gallane gives rise to a dinuclear gallium(ii) complex upon heating. All twelve complexes reported in here have been fully characterized and the solid-state structure of eleven complexes has been examined by means of single-crystal X-ray diffraction analysis.

Calcium and Magnesium Bis(ß-diketiminate) Complexes: Impact of the Alkylene Bridge on Schlenk-Type Rearrangements.

Dinuclear heteroleptic alkaline-earth-metal complexes are interesting synthetic targets because the close proximity of two metals allows for cooperative effects. However, these complexes are also prone to undergoing Schlenk-type rearrangements, affording less-active homoleptic complexes. Here we present the metalation of bis(ß-diketimine) ligands possessing flexible bridging groups, i.e., 1,2-ethylene, 1,3-propylene, and trans-1,2-cyclohexylene, using calcium and magnesium precursors. Four mononuclear homoleptic calcium complexes were obtained, highlighting the pronounced tendency of calcium to undergo Schlenk-like redistributions. In the case of magnesium, however, the bridging group plays a crucial role, yielding seven dinuclear heteroleptic complexes but also one mononuclear and one dinuclear homoleptic complexes. In addition, a trinuclear mixed heteroleptic-homoleptic magnesium complex, which is a rare example of an intermediate of the Schlenk equilibrium, was isolated.

Cooperative Bond Activation by a Bimetallic Main-Group Complex.

Inspired by natural metalloenzymes that efficiently catalyze a variety of transformations, chemists have developed large numbers of dinuclear transition-metal complexes with extraordinary properties and reactivity patterns. For main-group element compounds, however, metal-metal cooperativity is much less explored. Here we present the synthesis and characterization of a room-temperature-stable compound with two separated two-coordinated gallium(I) centers possessing both a lone pair of electrons and a vacant orbital, reminiscent of singlet carbenes. This species displays enhanced reactivity compared to its mononuclear counterpart due to bimetallic cooperativity that allows for the facile activation of strong C-F bonds across the gallium-gallium bond. Two mechanistic scenarios of the cooperative bond activation have been identified by DFT and DLPNO-CCSD(T) calculations.

Ditopic bis(N,N',N'-substituted 1,2-ethanediamine) ligands: synthesis and coordination chemistry.

The synthesis of two different types of bis(N,N',N'-substituted 1,2-ethanediamine)s, bridged either through the secondary (type 1) or tertiary (type 2) amine groups is reported. Selected protio-ligands have been applied in subsequent metallation reactions using aluminium, magnesium, tin, and zinc sources allowing to isolate five mononuclear and eight dinuclear complexes. All complexes have been fully characterized and their solid-state structures have been studied by means of single-crystal X-ray diffraction analysis. Nine of the 13 complexes carry reactive alkyl, amide or hydride groups, which indicates their potential as catalysts or supports for (transition) metals.

Magnesium bis(amidinate) and bis(guanidinate) complexes: impact of the ligand backbone and bridging groups on the coordination behaviour.

A library of ten dinucleating bis(amidine) and bis(guanidine) ligands, in which the bridging groups, terminal rests, and backbone substituents were systematically altered, has been synthesized and subsequently applied in metallation reactions using three different magnesium sources. Eight Mg complexes could be isolated and fully characterized, and in seven cases their solid-state structure could be determined by means of single crystal X-ray diffraction analysis. The results evidence a versatile coordination behaviour, which ranges from the first dinuclear heteroleptic magnesium iodide complex to dinuclear homoleptic complexes. These findings indicate the crucial impact of both the ligand and the magnesium source not only on the accessibility of well-defined dinuclear complexes but also on the aggregation in solution and in the solid state.

Nucleophilic Magnesium Silanide and Silaamidinate Derivatives.

Density functional theory (DFT) calculations demonstrate that the previously reported reaction of [(BDI)Mg-n-Bu] (BDI = HC{(Me)CN-Dipp}2; Dipp = 2,6-diisopropylphenyl) with the silaborane Me2PhSi-Bpin provides the magnesium silanide derivative [(BDI)MgSiMe2Ph], through the intermediacy of a short-lived silyl-pinacolato-organoborate species. The nucleophilic character of the resultant silanide anion is assayed through a series of reactions with RN═C═NR (R = i-Pr, Cy, t-Bu) and p-tolN═C═N-p-tol. When they are performed in a strict 1:1 stoichiometry, all four reactions result in silyl addition to the carbodiimide carbon center and formation of the corresponding ß-diketiminato magnesium silaamidinate complexes. Although the performance of the reaction of [(BDI)MgSiMe2Ph] with 2 equiv of p-tolylcarbodiimide also results in the formation of a silaamidinate anion, the second equivalent is observed to engage with the nucleophilic γ-methine carbon of the BDI ligand to provide a tripodal diimino-iminoamidate ligand. This behavior is judged to be a consequence of the enhanced electrophilicity of the N-aryl-substituted carbodiimide reagent, a viewpoint supported by a further reaction with the N-isopropyl silaamidinate complex [(BDI)Mg(i-PrN)2CSiMe2Ph]. This latter reaction not only provides an identical diimino-iminoamidate ligand but also results in 2-fold insertion of p-tolN═C═N-p-tol into a Mg-N bond between the magnesium center and the silaamidinate anion.

Salt metathesis as an alternative approach to access aluminium(i) and gallium(i) ß-diketiminates.

Salt metathesis, i.e. the reaction of sodium ß-diketiminate with (AlCp*)4 and GaCp*, respectively, is a valuable pathway to access the respective aluminium(i) and gallium(i) ß-diketiminates I and II. The protocol gives better yields compared to the established procedures and avoids the use of strong reducing agents such as metallic potassium. Furthermore, the aluminium(i) ß-diketiminate I was found to react with itself and yields upon C-N bond cleavage and hydrogen-atom transfer the asymmetric dinuclear aluminium(iii) complex V that is readily separated from I by crystallisation. The reaction mechanism has been probed by means of DFT and DLPNO-CCSD(T) calculations and the computational findings are in good agreement with the experimental observations.

Synthesis and Coordination Chemistry of 3,4-Ethylene-Bridged 1,1,2,5-Tetrasubstituted Biguanides.

The synthesis of 3,4-ethylene-bridged 1,1,2,5-tetrasubstituted biguanides is reported, which are accessible by three alternative routes. Exemplary molecular structures of the ligand and an observed side product have been elucidated by X-ray diffraction analysis. Mono- and dinuclear complexes of the biguanide in both its neutral and monoanionic forms were obtained, including examples of aluminum, copper, magnesium, potassium, tin, and zinc, indicating a versatile coordination behavior, as evidenced by means of single-crystal X-ray diffraction analysis.

C-F bond activation by pentamethylcyclopentadienyl-aluminium(i): a combined experimental/computational exercise.

The reaction of (Cp*Al)4 with a series of fluoro(hetero)arenes has been investigated and C-F bond activation was observed with perfluorotoluene, pentafluoropyridine as well as 1,2,3,4-tetrafluoro-, pentafluoro- and hexafluorobenzene. The reaction mechanism has been probed by means of DFT calculations and the computational findings are in good agreement with the experimental observations.

Ligands with Two Monoanionic N,N-Binding Sites: Synthesis and Coordination Chemistry.

Polytopic ligands have become ubiquitous in coordination chemistry because they grant access to a variety of mono- and polynuclear complexes of transition metals as well as rare-earth and main-group elements. Nitrogen-based ditopic ligands, in which two monoanionic N,N-binding sites are framed within one molecule, are of particular importance and are therefore the primary focus of this review. In detail, bis(amidine)s, bis(guanidine)s, bis(ß-diimine)s, bis(aminotroponimine)s, bis(pyrrolimine)s, and miscellaneous bis(N,N-chelating) ligands are reviewed. In addition to the general synthetic protocols, the application of these ligands is discussed along with their coordination chemistry, the multifarious binding modes, and the ability of these ligands to bridge two (or more) metal(loids).