Analogous Bis Research Articles

Tuning a phosphine-substituted diimine ligand to afford an iron monocarbonyl complex

A series of low-valent iron complexes that feature a phosphine-substituted α-diimine (DI) ligand have been synthesized. Reduction of (Ph2PPrDI)FeBr2 with an excess of Na/Hg in the presence of carbon monoxide afforded the corresponding dicarbonyl complex, (Ph2PPrDI)Fe(CO)2. Through multinuclear NMR and single crystal X-ray diffraction analysis, this complex was found to possess a 3-coordinate DI ligand. Upon heating for 10 days at 110 °C while applying intermittent vacuum, (Ph2PPrDI)Fe(CO)2 was successfully converted to the corresponding monocarbonyl complex, (Ph2PPrDI)Fe(CO), which was found to feature a tetradentate chelate. Similar reactivity was explored using the analogous bis(tert-butyl)phosphine-substituted ligand, tBu2PPrDI. Addition of this chelate to FeBr2 afforded (tBu2PPrDI)FeBr2, and subsequent reduction yielded (tBu2PPrDI)FeBr, which was found to possess a tridentate DI ligand by single crystal X-ray diffraction. Performing the reduction of (tBu2PPrDI)FeBr2 in the presence of CO afforded the corresponding dicarbonyl complex, (tBu2PPrDI)Fe(CO)2. Like aryl-substituted (Ph2PPrDI)Fe(CO)2, alkyl-substituted (tBu2PPrDI)Fe(CO)2 was found to feature a pendant phosphine arm. However, heating (tBu2PPrDI)Fe(CO)2 under vacuum did not allow for phosphine substitution and conversion to the corresponding monocarbonyl complex, highlighting the importance of phosphine π-acidity for substitution and the stabilization of low-valent iron.

Ebselen derivatives inhibit SARS-CoV-2 replication by inhibition of its essential proteins: PLpro and Mpro proteases, and nsp14 guanine N7-methyltransferase

Proteases encoded by SARS-CoV-2 constitute a promising target for new therapies against COVID-19. SARS-CoV-2 main protease (Mpro, 3CLpro) and papain-like protease (PLpro) are responsible for viral polyprotein cleavage—a process crucial for viral survival and replication. Recently it was shown that 2-phenylbenzisoselenazol-3(2H)-one (ebselen), an organoselenium anti-inflammatory small-molecule drug, is a potent, covalent inhibitor of both the proteases and its potency was evaluated in enzymatic and antiviral assays. In this study, we screened a collection of 34 ebselen and ebselen diselenide derivatives for SARS-CoV-2 PLpro and Mpro inhibitors. Our studies revealed that ebselen derivatives are potent inhibitors of both the proteases. We identified three PLpro and four Mpro inhibitors superior to ebselen. Independently, ebselen was shown to inhibit the N7-methyltransferase activity of SARS-CoV-2 nsp14 protein involved in viral RNA cap modification. Hence, selected compounds were also evaluated as nsp14 inhibitors. In the second part of our work, we employed 11 ebselen analogues—bis(2-carbamoylaryl)phenyl diselenides—in biological assays to evaluate their anti-SARS-CoV-2 activity in Vero E6 cells. We present their antiviral and cytoprotective activity and also low cytotoxicity. Our work shows that ebselen, its derivatives, and diselenide analogues constitute a promising platform for development of new antivirals targeting the SARS-CoV-2 virus.

Tunable Luminescence of Nonaromatic Borate Esters.

While the majority of nonconventional luminophores consist of electron-rich heteroatoms, an emerging category with electron-deficient atoms (e. g. boron) have gained much attention. In this work, we focused on one of the most common boron-containing substances, namely bis(pinacolato)diboron (BE1) and its analogue bis(2,4-dimethylpentane-2,4-glycolato)diboron (BE2), whose empty p-orbitals of boron atoms and p-orbitals with lone pairs of oxygens form π frameworks. Both compounds are nonemissive in dilute solutions but depict remarkable photoluminescence (PL) at aggregate states, featuring aggregation-induced emission characteristics. Additionally, their PL can be easily tuned by various external factors, such as excitation wavelength, compression, and oxygen. These photophysical properties could well be explained by the clustering-triggered emission (CTE) mechanism.

Control in Advanced Biofuels Synthesis via Alcohol Upgrading: Catalyst Selectivity to n‐Butanol, sec‐Butanol or Isobutanol

AbstractRuthenium complexes with tetradentate PNNP donor ligands demonstrate a marked change in selectivity compared to analogous bis bidentate PN complexes in Guerbet catalysis, producing mixtures of n‐butanol (17 %), sec‐butanol (14 %) and ethyl acetate (66 %) rather than the usual 90 %+ selectivity to n‐butanol. Tridentate PNP ruthenium complexes such as [Ru(H)(Cl)(CO)(Ph2PCH2CH2NHCH2CH2PPh2)] also produce sec‐butanol and, in optimized conditions (120 °C, 10 mol% NaOEt base), achieve 71 % selectivity to this butanol isomer. The same tri‐ and tetradentate complexes are efficient catalysts for the conversion of methanol/ethanol mixtures to isobutanol (up to 97 % selectivity). In this way, judicious choice of ligand within this general catalyst family allows selectivity to three butanol isomers of interest as fuel molecules.

Host-guest doping induced excited state energy transfer for efficient room temperature phosphorescence emission

The 1,8-naphthalimide derivatives as the guest and the benzophenone (BP) analogues bis(4-chlorophenyl)methanone (BP2C) and bis(4-fluorophenyl)methanone (BP2F) benzophenone derivatives as the host, we constructed a series of novel doping systems with fluorescence and room temperature phosphorescence (RTP) dual emission. The steady-state spectroscopy, ultrafast spectroscopy techniques, and theoretical calculations indicate that Förster resonance energy transfer (FRET) between singlet states between host and guest components enables energy redistribution in doped systems. At the same time, the Dexter energy transfer (DET) between the triplet states realizes the obvious absorption of the excited triplet state of the guest, resulting in the long-lived room temperature phosphorescence of the doped system. Doping materials have unlimited potential for information storage and anti-counterfeiting by exploiting the properties of photo activation.

Unexpected White Phosphorus (P4 ) Activation Modes with Silylene-Substituted o-Carboranes and Access to an Isolable 1,3-Diphospha-2,4-disilabutadiene.

New types of metal‐free white phosphorus (P4) activation are reported. While the phosphine‐silylene‐substituted dicarborane 1, CB‐SiP (CB=ortho‐C,C′‐C2B10H10, Si=PhC(tBuN)2Si, P=P[N(tBu)CH2]2), activates white phosphorus in a 2 : 1 molar ratio to yield the P5‐chain containing species 2, the analogous bis(silylene)‐substituted compound 3, CB‐Si2 , reacts with P4 in the molar ratio of 2 : 1 to furnish the first isolable 1,3‐diphospha‐2,4‐disilabutadiene (Si=P−Si=P‐containing) compound 4. For the latter reaction, two intermediates having a CB‐Si2P4 and CB‐Si2P2 core could be observed by multinuclear NMR spectroscopy. The compounds 2 and 4 were characterized including single‐crystal X‐ray diffraction analyses. Their electronic structures and mechanisms were investigated by density functional theory calculations.

Unexpected White Phosphorus (P4) Activation Modes with Silylene‐Substitutedo‐Carboranes and Access to an Isolable 1,3‐Diphospha‐2,4‐disilabutadiene

AbstractNew types of metal‐free white phosphorus (P4) activation are reported. While the phosphine‐silylene‐substituted dicarborane1, CB‐SiP(CB=ortho‐C,C′‐C2B10H10,Si=PhC(tBuN)2Si,P=P[N(tBu)CH2]2), activates white phosphorus in a 2 : 1 molar ratio to yield the P5‐chain containing species2, the analogous bis(silylene)‐substituted compound3, CB‐Si2,reacts with P4in the molar ratio of 2 : 1 to furnish the first isolable 1,3‐diphospha‐2,4‐disilabutadiene (Si=P−Si=P‐containing) compound4. For the latter reaction, two intermediates having a CB‐Si2P4and CB‐Si2P2core could be observed by multinuclear NMR spectroscopy. The compounds2and4were characterized including single‐crystal X‐ray diffraction analyses. Their electronic structures and mechanisms were investigated by density functional theory calculations.

Dibenzoate esters of cis-tetralin-2,3-diol as analogs of (-)-epigallocatechin gallate: synthesis and crystal structure of anticancer drug candidates.

(-)-Epigallocatechin gallate (EGCG), the main component of green tea extract, displays multiple biological activities. However, it cannot be used as a drug due to its low cellular absorption, instability and metabolic degradation. Therefore, there is a need to provide analogs that can overcome the limitations of EGCG. In this work, six synthetic analogs of EGCG sharing a common tetralindiol dibenzoate core were synthesized and fully characterized by 1H NMR, 13C NMR, HRMS and IR spectroscopies, and X-ray crystallography. These are (2R,3S)-1,2,3,4-tetrahydronaphthalene-2,3-diyl bis[3,4,5-tris(benzyloxy)benzoate], C66H56O10, and the analogous esters bis(3,4,5-trimethoxybenzoate), C30H32O10, bis(3,4,5-trifluorobenzoate), C24H14F6O4, bis[4-(benzyloxy)benzoate], C38H32O6, bis(4-methoxybenzoate), C26H24O6, and bis(2,4,6-trifluorobenzoate), C24H14F6O4. Structural analysis revealed that the molecular shapes of these dibenzoate esters of tetralindiol are significantly different from that of previously reported dimandelate esters or monobenzoate esters, as the acid moieties extend far from the bicyclic system without folding back over the tetralin fragment. Compounds with small fluorine substituents take a V-shape, whereas larger methoxy and benzyloxy groups determine the formation of an L-shape or a cavity. Intermolecular interactions are dominated by π-π stacking and C-H...π interactions involving the arene rings in the benzoate fragment and the arene ring in the tetrahydronaphthalene moiety. All six crystal structures are determined in centrosymmetric space groups (either P-1, P21/n, C2/c or I2/a).

Anion Binding of a Cyclopeptide-Derived Molecular Cage in Aqueous Solvent Mixtures.

A molecular cage consisting of two cyclic hexapeptides with an alternating sequence of (2S,4S)-4-aminoproline and 6-aminopicolinic acid subunits, covalently linked via three diglycolic acid subunits, interacts with a variety of inorganic anions in acetonitrile/water. In the respective complexes, the anion resides in a cavity between the two cyclopeptide rings where it interacts with six converging NH groups. The cage binds sulfate anions in acetonitrile/water, 2 : 1 (v/v) with a log Ka of 6.7, ca. 2.5 orders of magnitude stronger than an analogous bis(cyclopeptide) with only one linker whose sulfate affinity log Ka amounts to 4.3. The preorganization induced by the three linking units is thus beneficial for sulfate binding. In addition, these linkers cause the dissociation of the sulfate complex to have a substantial Gibbs free energy of activation ΔG≠ of 68.9 kJ mol-1 and they also seem to affect anion selectivity as illustrated by the different effects some anions produce on the 1 H NMR spectra of the triply and singly-linked bis(cyclopeptides). Such anion binding cages represent promising scaffolds to mimic natural anion receptors such as the sulfate-binding protein.

Cell-based Screening For Identification Of The Novel Vanadium Complexes With Multidirectional Activity Relative To The Cells And The Mechanisms Associated With Metabolic Disorders

In this study, 110 newly synthesized vanadium complexes from different structural groups were screened in three cell-based models representing the main target tissues for anti-diabetic drugs. In glucose utilization in C2C12 myocyte experiments, 93% of vanadium complexes were shown to have equal or greater activity than bis(maltolato)oxovanadium(IV) (BMOV), the methyl analog of bis(ethylmaltolato)oxovanadium(IV) (BEOV) which has been tested in clinical trials. Moreover, 49% and 50% of these complexes were shown to have equal or greater activity than BMOV in lipid accumulation in 3T3-L1 adipocytes and insulin secretion in RINm5F beta cell experiments, respectively. These results were the basis for the selection of compounds for the subsequent steps in the characterization of anti-diabetic properties. This study provides strong support for the application of screening cell-based assays with a phenotypic approach for the discovery of novel anti-diabetic drugs from the vanadium complex class. This is especially desirable due to the multiple and not fully defined mechanisms of action vanadium compounds.

Structural controlled pure metallo-triangular assembly through bisterpyridinyl Dibenzo[b,d]thiophene, Dibenzo[b,d]furan and Dibenzo[b,d]carbazole

A novel family of metallocycles was constructed by a one-pot self-assembly of three analogous bis(terpyridine) ligand monomers L1-L3, having different bent angles, with metal ions (Zn2+ or Cd2+). The dibenzo[b,d]thiophene-containing ligand L3 assembled with the metal ions to form a single trimer, whereas the dibenzo[b,d]furan-containing ligand L2 and dibenzo[b,d]carbazole-containing ligand L1 formed a mixture of trimers and tetramers. Heteroatoms (N, O, S) significantly contributed to the molecular size of the assemblies, owing to the bent angle of the bis-terpyridines ligands.

Reduction in polyamine catabolism leads to spermine-mediated airway epithelial injury and induces asthma features.

Airway epithelial injury is a crucial component of acute and severe asthma pathogenesis and a promising target for treatment of refractory asthma. However, the underlying mechanism of epithelial injury remains poorly explored. Although high levels of polyamines, mainly spermine, have been found in asthma and comorbidity, their role in airway epithelial injury and the cause of their altered levels in asthma have not been explored. We measured key polyamine metabolic enzymes in lung samples from normal and asthmatic subjects and in mice with OVA-induced allergic airway inflammation (AAI). Polyamine metabolism was modulated using pharmacologic/genetic modulators. Epithelial stress and apoptosis were measured by TSLP levels and TUNEL assay, respectively. We found loss of the polyamine catabolic enzymes spermidine/spermine-N (1)-acetyltransferase-1 (SAT1) and spermine oxidase (SMOX) predominantly in bronchial epithelial cells (BECs) of human asthmatic lung samples and mice with AAI. In naïve mice, SAT1 or SMOX knockdown led to airway hyper-responsiveness, remodeling, and BEC apoptosis. Conversely, in mice with AAI, overexpression of either SAT1 or SMOX alleviated asthmatic features and reduced TSLP levels and BEC apoptosis. Similarly, while pharmacological induction of SAT1 and SMOX using the polyamine analogue bis(ethyl)norspermine (BENSPM) alleviated asthmatic features with reduced TSLP levels and BEC apoptosis, pharmacological inhibition of these enzymes using BERENIL or MDL72527, respectively, worsened them. Spermine accumulation in lungs correlated with BEC apoptosis, and spermine treatment caused apoptosis of human BEAS-2B cells invitro. Spermine induces BEC injury. Induction of polyamine catabolism may represent a novel therapeutic approach for asthma via reversing BEC stress.

Curcumin mediates polyamine metabolism and sensitizes gastrointestinal cancer cells to antitumor polyamine-targeted therapies.

Curcumin, a natural polyphenol that contributes to the flavor and yellow pigment of the spice turmeric, is known for its antioxidant, anti-inflammatory, and anticarcinogenic properties. Capable of affecting the initiation, promotion, and progression of carcinogenesis through multiple mechanisms, curcumin has potential utility for both chemoprevention and chemotherapy. Previous studies demonstrated that curcumin can inhibit ornithine decarboxylase (ODC) activity in human leukemia and breast cancer cells, and pretreatment with dietary curcumin blocks carcinogen-induced ODC activity in rodent models of skin, colon, and renal cancer. The current study investigated the regulation of polyamine metabolism in human gastric and colon carcinoma cell lines in response to curcumin. Curcumin treatment significantly induced spermine oxidase (SMOX) mRNA and activity, which results in the generation of hydrogen peroxide, a source of ROS. Simultaneously, curcumin down regulated spermidine/spermine N1-acetyltransferase (SSAT) activity and the biosynthetic enzymes ODC and S-adenosylmethionine decarboxylase (SAMDC), thereby diminishing intracellular polyamine pools. Combination treatments using curcumin with the ODC inhibitor 2-difluoromethylornithine (DFMO), an agent currently in clinical chemoprevention trials, significantly enhanced inhibition of ODC activity and decreased growth of GI cancer cell lines beyond that observed with either agent alone. Similarly, combining curcumin with the polyamine analogue bis(ethyl)norspermine enhanced growth inhibition that was accompanied by enhanced accumulation of the analogue and decreased intracellular polyamine levels beyond those observed with either agent alone. Importantly, cotreatment with curcumin permitted the lowering of the effective dose of ODC inhibitor or polyamine analogue. These studies provide insight into the polyamine-related mechanisms involved in the cancer cell response to curcumin and its potential as a chemopreventive or chemotherapeutic agent in the GI tract.

Aromatic polyesters derived from 5,5′-disubstituted bis(m-phenylene) crown ethers

A new monomer of the AB type, 5-carboxy-1,3-phenylene-5′-hydroxy-1′,3′-phenylene-32-crown-10 (5), was synthesized. Direct polymerizations of bis(5-hydroxy-1,3-phenylene)-32-crown-10 (13), an AA diphenolic macrocyclic monomer, with BB diacid monomer bis(5-carboxy-1,3-phenylene)-26-crown-8 (14) and its larger analog bis(5-carboxy-1,3-phenylene)-32-crown-10 (16) were accomplished via the Higashi method. The resultant polyesters 15 and 17, which both contain two macrocycles per repeat unit, were soluble in common organic solvents such as chloroform and tetrahydrofuran, amorphous in nature and possessed high thermal stability (5% weight loss > 370 °C in air). Main chain poly(ester crown ether)s 18 and 19 based on bis(5-carboxy-1,3-phenylene)-32-crown-10 (16), and hydroquinone (HQ) and biphenol (BP), respectively, were synthesized; these two polyesters also possess high thermal stability (5% weight loss > 386 °C in air) and are amorphous. These polymacrocycles are suitable polytopic hosts for complexation with 4,4′-bipyridinium derivatives, as demonstrated by the binding of paraquat diol (21a) by polyester 20 with Ka = 2.0 (±0.7) x 102 M−1 (23 °C, 4:6 w:w CD3CN:CDCl3). Threading of the cyclic units in these polyesters by linear polymers such as polystyrene and PMMA leads to compatiblized blends via polypseudorotaxane formation; this methodology represents a new approach to compatibilization.

Synthesis and Reactivities of Polyhydrido Osmium Arylsilyl Complexes Prepared from OsH3Cl(PPh3)3

Reactions of silanes with transition-metal complexes are of interest because their relevance to Si–H bond activation, the structural properties of polyhydrides, and catalytic hydrosilylation reactions. This work presents the results derived from reactions of arylsilanes Ph2SiH2 and PhSiH3 with OsH3Cl(PPh3)3 (1). Reaction of 1 with 1 equiv or excess Ph2SiH2 affords OsH3(SiClPh2)(PPh3)3 (2) or OsH4(SiClPh2)(SiHPh2)(PPh3)2 (3), respectively. These silyl complexes are formed via the oxidative addition of Si–H bonds and H/Cl exchange via silylene intermediates. Similarly, reaction of 1 with excess PhSiH3 produced the analogous bis(silyl) complex OsH4(SiClHPh)(SiH2Ph)(PPh3)2 (4). The bis(silyl) complexes are dodecahedral tetrahydride complexes containing weak Si···H interactions. The complex 3 reacts with PPh3 and CH3CN to selectively eliminate Ph2SiH2. Computational studies show that the preference for reductive eliminations from 3 follows the order Ph2SiH2 > H2 > Ph2SiHCl > Ph2HSi-SiClPh2.

Lewis Acid/Base Reactions of the Bis(amidinato)silylene [iPrNC(Ph)NiPr]2Si and Bis(guanidinato)silylene [iPrNC(NiPr2)NiPr]2Si with ElPh3 (El = B, Al)

The bis(amidinato)silylene [iPrNC(Ph)NiPr]2Si and the analogous bis(guanidinato)silylene [iPrNC(NiPr2)NiPr]2Si react with the Lewis acids BPh3 and AlPh3 to form the respective Lewis acid/base adducts 4–7 (adduct 4 has already been described). Compounds 5 and 7 are the first silylene–alane adducts and the first five-coordinate silicon(II) compounds with an Si–Al bond, and 6 and 7 represent the first silylene–borane and silylene–alane adducts, respectively, that are derived from a bis(guanidinato)silylene. Compounds 4–7 were characterized by single-crystal X-ray diffraction and solid-state NMR spectroscopy (11B, 15N, 27Al, 29Si), and 4 and 5 were additionally studied by NMR spectroscopy in solution (1H, 11B, 13C, 27Al, 29Si).

Four‐, Five‐, and Six‐Coordinate Silicon(IV) Complexes: Reactivity of the Donor‐Stabilized Silylenes [iPrNC(Ph)NiPr]2Si and [iPrNC(NiPr2)NiPr]2Si Towards Me3SiN3 and PhSCH2N3

Bis(amidinato)silylene 1 and the analogous bis(guanidinato)silylene 2 reacted with Me3SiN3 to form compounds 3 [a five‐coordinate silicon(IV) complex with an Si=N double bond] and 4 [a four‐coordinate silicon(IV) complex with an Si=N double bond], respectively. For compound 3, a dynamic equilibrium between a five‐ and four‐coordinate silicon(IV) species in solution was observed (at –95 °C, these species are stable on the NMR spectroscopic timescale), whereas 4 is four‐coordinate in solution. Treatment of 1 with PhSCH2N3 afforded compound 5 (isolated as 5a·5b·0.5n‐C6H14), which is a cocrystallizate of the diastereomers 5a and 5b with half an n‐hexane molecule in the asymmetric unit. The diastereomers 5a and 5b [six‐coordinate silicon(IV) complexes with an unsubstituted methyleneamido ligand and an SiN5S skeleton] differ only in their interchanged positions of their thiophenolato and methyleneamido ligands. In solution, a dynamic equilibrium between 5a and 5b was observed.

Details of the Mechanism of the Asymmetric Transfer Hydrogenation of Acetophenone Using the Amine(imine)diphosphine Iron Precatalyst: The Base Effect and The Enantiodetermining Step

The excellent ketone asymmetric transfer hydrogenation (ATH) systems using the precatalysts (S,S)-trans-[FeCl(CO)(PPh2CH2CH2NHCHPhCHPhNCHCH2PAr2)]BPh4 (Ar = Ph (1), p-tolyl (2)) have a fascinating dependence of activity on the base concentration, which is investigated here. The reaction of complex 1 or 2 with 1 equiv of the strong base potassium tert-butoxide in THF for 2–7 days produces the neutral amine(ene-amido) complexes [FeCl(CO)(PPh2CH2CH2NHCHPhCHPhNCHCHPAr2)] (8 and 9). These monodeprotonated complexes have been completely characterized by NMR, EA, and FT-IR spectroscopy and mass spectrometry, and the structure of 9 has been further confirmed by single-crystal X-ray diffraction to reveal a structure with the NH and FeCl bonds parallel and the proton and chloride ligands next to each other. The structures of 8 and 9 and their 1H NMR patterns are similar to those of the active catalyst for the ATH of ketones that is postulated to have NH and FeH bonds parallel with the protonic and hydridic hydrogens adjacent. Identical key nuclear Overhauser effect (NOE) correlations in both 8 and the hydrido complex provide further evidence for the postulated structure of the amine iron hydride intermediate. The catalyst system is not active for the transfer hydrogenation of acetophenone, unless greater than 2 equiv of base is added to activate the precatalyst. The addition of base (up to 8 equiv per iron) increases the reaction rate, while a further increase of the base concentration shows a reduction of activity. The loss of activity with less than 2 equiv of base results from a side reaction of the active amido(ene-amido) complexes with 2-propanol to form an inactive neutral bis(amido) iron complex, which was characterized by NMR spectroscopy. Structural evidence for this was provided by the X-ray crystal structure determination of an analogous bis(amino) iron(II) complex, generated from the reaction of the amine(ene-amido) iron complex with methanol in C6D6 in the presence of BF4–. The presence of excess base prevents this side reaction, thereby favoring the reaction which forms the active amine iron hydride species that is in the catalytic cycle. The structure of the transition state for the reaction of the amine hydrido iron catalyst with acetophenone has been successfully modeled using density functional theory (DFT) calculations. The (R) configuration of the product 1-phenylethanol is induced by the position of the phenyl groups on the catalyst and a π–π stabilizing interaction between the aryl ring on the ketone and the ene-amido moiety on the ligand.

Reactivity of the Donor-Stabilized Silylenes [iPrNC(Ph)NiPr]2 Si and [iPrNC(NiPr2 )NiPr]2 Si: Activation of CO2 and CS2.

Activation of CO2 by the bis(amidinato)silylene 1 and the analogous bis(guanidinato)silylene 2 leads to the structurally analogous six-coordinate silicon(IV) complexes 4 (previous work) and 8, respectively, the first silicon compounds with a chelating carbonato ligand. Likewise, CS2 activation by silylene 1 affords the analogous six-coordinate silicon(IV) complex 10, the first silicon compound with a chelating trithiocarbonato ligand. CS2 activation by silylene 2, however, yields the five-coordinate silicon(IV) complex 13 with a carbon-bound CS2 (2-) ligand, which also represents an unprecedented coordination mode in silicon coordination chemistry. Treatment of the dinuclear silicon(IV) complexes 5 and 6 with CO2 also affords the six-coordinate carbonatosilicon(IV) complexes 4 and 8, respectively.

Syntheses, crystallographic, mass-spectroscopic determination and antioxidant studies of Co(II), Ni(II) and Cu(II) complexes of a new imidazol based Schiff base

A new imidazole-based Schiff base, 2-((1H-imidazol-4-yl)methyleneamino)benzylalcohol (HL) and corresponding analogous bis(2-((1H-imidazol-4-yl)methyleneimino)benzylalcohol)metal(II) perchlorates (M: Co(1), Ni(2), Cu(3)) have prepared and characterized by elemental analyses, ESI-MS, IR, UV–Vis spectroscopies and conductivity measurements. X-ray single crystal structures of 1 and 2 have been also determined. Elemental analyses, spectroscopic and conductance data of 3 demonstrated similar structural features with these of crystallographically characterized complexes and based upon this relevances, HL ligands are neutrally coordinated to metal(II) ions in tridentate mode and all complexes are isostructural, dicathionic, contain perchlorate anions as complementary ions and, are in octahedral geometry with the formulae of [M(HL)2](ClO4)2 (for 3) and [M(HL)2](ClO4)2·H2O (for 1 and 2). Radical scavenging activities of the complexes have been evaluated by using DPPH, DMPD+, and ABTS+ assays. SC50 values (μg/mL) of the complexes and standards on DPPH, DMPD+, ABTS+ follow the sequences, BHA (9.06±0.33)>CMPD3 (15.62±0.52)>CMPD2 (17.43±0.29)>Rutin (21.65±0.60)>CMPD1 (25.67±0.51)>Trolox (28.57±0.37), Rutin>BHA>CMPD3>CMPD2>Trolox>CMPD1, and Trolox>BHA>CMPD3>CMPD2>Rutin>CMPD1 respectively.