Reaction Of 1a Research Articles

Synthesis of Bimetallic Dinuclear Hydrido Complexes of Re and Rh/Ir Supported by a Direct M-M' Bond: The Role of the M-M' Bond in the Site Exchange of Hydrides.

Heterometallic tetrahydrido complexes [Cp*Re(H)2(μ-H)2MCp*] (5a: M = Ir, 5b: M = Rh) were synthesized by the reaction of [Cp*ReH6] and [Cp*M(sol)3]2+ (M = Ir, Rh) followed by deprotonation. Although 5 possesses four hydrides and adopts a 30-electron configuration as [Cp*Ru(μ-H)4RuCp*] (1) does, the positions of the hydrides in 5 differ from those in 1: two terminal and two bridging hydrides. In addition, adaptive natural density partitioning (AdNDP) analysis demonstrated that a direct Re-M bond is held in 5. Although cationic pentahydrido complexes [Cp*Re(H)2(μ-H)3MCp*]+ (4a: M = Ir, 4b: M = Rh) do not contain a direct Re-M bond, the formation of a Re-M bond in the intermediate of the hydride site exchange was also inferred by DFT calculations. DFT calculations suggested that the Re-M bond plays a crucial role in the site exchange of hydrides in 5 and 4. While μ-phosphido complex [Cp*(PPh3)Re(H)(μ-H)(μ-PPh2)Ir(H)Cp*] (6) was obtained by the reaction of 5a with PPh3, the treatment of 5a with PMe3 resulted in the formation of a 1:1 mixture of [Cp*Re(H)2(PMe3)2] and [Cp*Ir(H)2PMe3] via the rupture of the Re-Ir bond.

Unsymmetric Ir2 and RhIr Dinuclear Complexes Supported by a Linear Tetraphosphine meso-dpmppp, Showing High Reactivity for O2, H2, and HCl.

Unsymmetric dinuclear Ir(I) complexes, [Ir2Cl2(L)(meso-dpmppp)] (L = XylNC (1aIr2), tBuNC (1bIr2), CO (1cIr2)), were synthesized using meso-Ph2PCH2P(Ph)(CH2)3P(Ph)CH2PPh2 (meso-dpmppp), which supports cis-P,P (M1) and trans-P,P (M2) metal sites, and exhibited high reactivity for O2, H2, and HCl. The IrRh heterodinuclear complexes, [M1M2Cl2(L)(meso-dpmppp)] (1xM1M2) (M1M2 = IrRh, RhIr; L = XylNC, CO (x = a, c)), were also synthesized and used together with the Rh2 complexes (1a,cRh2) to elucidate the role of each metal site. For the reactions of O2, 1aIr2 and 1aRhIr showed higher reactivity than those of 1aIrRh and 1aRh2, giving η2-peroxide complexes [{M1Cl2}{M2(η2-O2)(XylNC)}(meso-dpmppp)] (2aIr2, 2aRhIr), from which O2 would not dissociate. All the CO complexes 1cM1M2 (M1, M2 = Ir or Rh) showed no reactivity for O2. In the reactions with H2, 1aIr2 reacted with H2 to give the dihydride complex, [{IrCl2}{Ir(H)2L}(meso-dpmppp)] (11aIr2) and the tetrahydride complex, [{Ir(H)Cl2}(μ-H){Ir(H)2L}(meso-dpmppp)] (12aIr2), while 1aRhIr gave the dihydride complex, and 1aIrRh and 1aRh2 gave no hydride complexes. Reactions of 1a,cM1M2 with HCl afforded the dihydride complexes, [{IrCl3}(μ-H){Ir(H)Cl(XylNC)}(meso-dpmppp)] (14aIr2), [{Ir(H)Cl2}(μ-H){M2Cl2(L)}(meso-dpmppp)] (M2 = Ir, L = CO (15cIr2); M2 = Rh, L = XylNC (15aIrRh), CO (15cIrRh)), and [{Rh(H)Cl2}(μ-Cl){Ir(H)Cl(XylNC)}(meso-dpmppp)] (18aRhIr), the structures varying depending on M1 and M2 as well as L.

Towards Nickel-NHC Fluoro Complexes-Synthesis of Imidazolium Fluorides and Their Reactions with Nickelocene.

While hundreds of complexes of the general formula [Ni(η5-C5H5)(NHC)(X)] exist (NHC = a N-heterocyclic carbene, X = Cl, Br, I), none is yet known with X = F. We attempted to prepare such a species by reacting nickelocene with imidazolium fluorides. Three imidazolium fluorides (ImH)+ F- [Im = (N,N'-bis-(R)-imidazolium: 1a, IMe, R = Me; 1b, IMes, R = 2,4,6-trimethylphenyl; 1c, IPr, R = 2,6-diisopropylphenyl)] were prepared and characterized by spectroscopic methods. In addition, the salts 1b [(IMesH)+ F-] and 1c [(IPrH)+ F-] were subjected single-crystal X-ray diffraction experiments. The reactions of these imidazolium fluorides with nickelocene did not lead to [Ni(η5-C5H5)(NHC)(F)] species. Instead, the reaction of 1a [(IMeH)+ F-] and 1b [(IMesH)+ F-] with nickelocene led to the salt 2 [Ni(η5-C5H5)(IMe)2]+ F- and to the square planar complex 3atrans-[NiF2(IMes)2] respectively. Both complexes were characterized spectroscopically and by single crystal X-ray diffraction. All four X-ray diffraction studies reveal hydrogen bonding and hydrogen interactions with the F atom or anion, and in some cases with solvent molecules of crystallization, and these phenomena are all discussed. Complex 2, in particular, exhibited a wide range of interesting H-bonded interactions in the solid state. Complexes 2 and 3a were tested as catalysts for Suzuki-Miyaura coupling but were not promising: complex 2 was inactive, and while 3a did indeed catalyze the reaction, it gave widely diverging results owing to its instability in solution.

Pyridine Derivatives as Insecticides. Part 5. New Thieno[2,3-b]pyridines and Pyrazolo[3,4-b]pyridines Containing Mainly Ethyl Nicotinate Scaffold and Their Insecticidal Activity toward Aphis gossypii (Glover,1887).

Ethyl 5-cyano-1,6-dihydro-2-methyl-4-(2'-thienyl)-6-thioxonicotinate (A) was synthesized and reacted with ethyl chloroacetate in the presence of sodium acetate or sodium carbonate to give ethyl 5-cyano-6-((2-ethoxy-2-oxoethyl)thio)-2-methyl-4-(2'-thienyl)nicotinate (1a) or its isomeric thieno[2,3-b]pyridine 2a. 3-Aminothieno[2,3-b]pyridine-2-carboxamide 2b was also synthesized by the reaction of A with 2-chloroacetamide. The reaction of 1a with hydrazine hydrate in boiling ethanol gave acethydrazide 3. Heating ester 1a with hydrazine hydrate under neat conditions afforded 3-amino-1H-pyrazolo[3,4-b]pyridine 10. Compounds 2b, 3, and 10 were used as precursors for synthesizing other new thieno[2,3-b]pyridines and pyrazolo[3,4-b]pyridines containing mainly the ethyl nicotinate scaffold. Structures of all new compounds were confirmed by elemental and spectral analyses. Most of the obtained compounds were evaluated for their insecticidal activity toward the nymphs and adults of Aphis gossypii (Glover,1887). Some compounds such as 4, 9b, and 9c showed promising results. The effect of some sublethal concentrations, less than LC50, of compounds 4, 9b, and 9c on the examined Aphis was subjected to a further study. The results demonstrated that exposure of A. gossypii nymphs to sublethal concentrations of compounds 4, 9b, and 9c had noticeable effects on their biological parameters, i.e., nymphal instar duration, generation time, and adult longevity. The highest concentration C1 of all three compounds increased the nymphal instar duration and generation time and decreased adult longevity and vice versa.

Positive charge delocalization and anti‐aromaticity of cations generated by protonation of benzo[a]fluoranthenes in superacid

AbstractBenzo[a]fluoranthene (4a) is one of non‐alternate polycyclic aromatic hydrocarbons. A reaction of 4a in CF3SO3H yielded a dark yellow solution. Direct NMR observation indicated the exclusive formation of carbocation 4aH+ by protonation at the C(8) position. The most deshielded 1H and 13C signals were observed at 8.99 ppm for H(12) and 8.29 ppm for H(1), 182.6 ppm for C(12b), 155.6 ppm for C(8a), and 149.4 ppm for C(7a). The signals for H(4) and H(5) were significantly more shielded than those of 4a. A reaction of 3‐tert‐butylbenzo[a]fluoranthene (4b) in CF3SO3H afforded carbocation 4bH+ by the protonation at the C(8) position. 4bH+ was gradually converted to 4aH+. The changes in 13C NMR chemical shifts (Δδ13C) suggested that positive charge was delocalized into mainly seven carbons in 4aH+ and 4bH+. The observed cations were found to be the most stable cations among the possible protonation cations by the DFT method. The NICS(1)zz values for the five‐membered rings were calculated to be 35.6 for 4aH+ and 34.4 for 4bH+ by GIAO‐B3LYP/6‐311+G(2d,p). The experimental NMR and the NICS(1)zz data indicated that the five‐membered rings in 4aH+ and 4bH+ exhibited anti‐aromaticity.

Zinc-Catalyzed Hydroboration of Carbon Dioxide Amplified by Borane-Tethered Heteroscorpionate Bis(Pyrazolyl)methane Ligands.

The borane-functionalized (BR2) bis(3,5-dimethylpyrazolyl)methane (LH) ligands 1a (BR2: 9-borabicyclo[3.3.1]nonane or 9-BBN), 1b (BR2: BCy2), and 1c (BR2: B(C6F5)2) were synthesized by the allylation-hydroboration of LH. Metalation of 1a,b with ZnCl2 yielded the heteroscorpionate dichloride complexes [(1a,b)ZnCl2] 3a,b. The reaction of 1a with ZnEt2 led to the formation of the zwitterionic complex [Et(1a)ZnEt(THF)] 5. The reaction of complex 3a with two equivalents of KHBEt3 under a carbon dioxide (CO2) atmosphere gave rise to the formation of the dimeric bis(formate) complex [(1a)Zn(OCHO)2]2 8, in which its borane moieties intermolecularly stabilize the formate ligands of opposite metal centers. The allylated precursor Lallyl and its zinc dichloride, diethyl and bis(formate) complexes [(Lallyl)ZnCl2] 2, [(Lallyl)ZnEt2] 4, and [(Lallyl)Zn(OCHO)2] 7 were also isolated. The catalyst systems composed of 1 mol % of 3a or 3b and two equivalents of KHBEt3 hydroborated CO2 at 1 bar with pinacolborane (HBPin) to the methanol-level product H3COBPin (and PinBOBPin) in yields of 42 or 86%, respectively. The catalyst systems using the unfunctionalized complex [(LH)ZnCl2] 6 and KHBEt3 or KHBEt3/nOctBR2 (BR2: 9-BBN or BCy2) hydroborated CO2 to H3COBPin but in 2.5- to 6-fold lower activities than those exhibited by 3a,b/KHBEt3. The hydroboration of CO2 using 8 as a catalyst led to yields of 39-43%, comparable to those obtained with 3a/KHBEt3. The results confirmed that the catalytic intermediates benefit from the incorporated boranes' intra- or intermolecular stabilizations.

Amidinatotetrylenes Donor Functionalized on Both N Atoms: Structures and Coordination Chemistry.

E(hmds)(bqfam) (E = Ge (1a), Sn (1b); hmds = N(SiMe3)2, bqfam = N,N'-bis(quinol-8-yl)formamidinate), which are amidinatotetrylenes equipped with quinol-8-yl fragments on the amidinate N atoms, have been synthesized from the formamidine Hbqfam and Ge(hmds)2 or SnCl(hmds). Both 1a and 1b are fluxional in solution at room temperature, as the E atom oscillates from being attached to the two amidinate N atoms to being chelated by an amidinate N atom and its closest quinolyl N atom (both situations are similarly stable according to density functional theory calculations). The hmds group of 1a and 1b is still reactive and the deprotonation of another equivalent of Hbqfam can be achieved, allowing the formation of the homoleptic derivatives E(bqfam)2 (E = Ge, Sn). The reactions of 1a and 1b with [AuCl(tht)] (tht = tetrahydrothiophene), [PdCl2(MeCN)2], [PtCl2(cod)] (cod = cycloocta-1,5-diene), [Ru3(CO)12] and [Co2(CO)8] have been investigated. The gold(I) complexes [AuCl{κE-E(hmds)(bqfam)}] (E = Ge, Sn) have a monodentate κE-tetrylene ligand and display fluxional behavior in solution the same as that of 1a and 1b. However, the palladium(II) and platinum(II) complexes [MCl{κ3E,N,N'-ECl(hmds)(bqfam)}] (M = Pd, Pt; E = Ge, Sn) contain a κ3E,N,N'-chloridotetryl ligand that arises from the insertion of the tetrylene E atom into an M-Cl bond and the coordination of an amidinate N atom and its closest quinolyl N atom to the metal center. Finally, the binuclear ruthenium(0) and cobalt(0) complexes [Ru2{μE-κ3E,N,N'-E(hmds)(bqfam)}(CO)6] and [Co2{μE-κ3E,N,N'-E(hmds)(bqfam)}(μ-CO)(CO)4] (E = Ge, Sn) have a related κ3E,N,N'-tetrylene ligand that bridges two metal atoms through the E atom. For the κ3E,N,N'-metal complexes, the quinolyl fragment not attached to the metal is pendant in all the germanium compounds but, for the tin derivatives, is attached to (in the Pd and Pt complexes) or may interact with (in the Ru2 and Co2 complexes) the tin atom.

Reactions of (mesityl)n(methyl)2-nsilylene complexes with pyridine-N-oxide (n = 1 and 0): formation of silanone complexes and a disiloxanyloxy complex.

Silanones (OSiR2), a heavier congener of ketones (R2CO), are highly reactive species that are readily converted to oligomeric siloxane (O-SiR2)n. Coordination of silanones to the transition-metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Recently, our group reported the synthesis, structures, and reactivity of dimesityl-substituted silanone complexes Cp*(OC)2M{OSiMes2(L)}(SiMe3) (M = W, Mo, L: Lewis base, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2). Herein, to investigate the effect of substituents on the silicon atom during the formation of a silanone complex, we demonstrated the use of Mes and smaller Me groups. As a result, the formation of Mes(Me)-substituted silanone molybdenum complex Cp*(OC)2Mo{OSiMes(Me)(py)}(SiMe3) (5b, py: pyridine) was suggested, the silanone tungsten complex Cp*(OC)2W{OSiMes(Me)(DMAP)}(SiMe3) (4a, DMAP: 4-(dimethylamino)pyridine) was obtained, and a dimethyl-substituted disiloxanyloxy(dioxo) complex Cp*(O)2W(OSiMe2OSiMe3) (9) was formed. The reaction of 4a with PMe3 proceeded via the elimination of DMAP and migration of the SiMe3 group to the oxygen atom of the silanone ligand to afford Cp*(OC)2W(SiMes(Me)OSiMe3)(PMe3) (11a). The Mo complex Cp*(OC)2Mo(SiMes(Me)OSiMe3)(PMe3) (11b) was produced by the reaction of Cp*(OC)2Mo{SiMes(Me)}(SiMe3) (7b) with pyridine-N-oxide in the presence of PMe3.

From phosphanylphosphaalkenes to coordination copper and silver polymers containing P-P bonds.

This study was focused on the activation of the CP bond via reactions of Ph2CP-PtBu2 (1) with 1,6-hexanediol and selected dithiols (1,4-butanedithiol, 1,4-benzenedithiol and 1,4-benzenedimethanethiol). These reactions proceed according to a 1,2-addition mechanism, providing new compounds with formulas {(Ph)2(H)C-P-PtBu2}{μ2-(O-(CH2)6-O)}{tBu2P-P-C(H)(Ph)2} (2), {(Ph)2(H)C-P-PtBu2}{μ2-(S-(CH2)4-S)}{tBu2P-P-C(H)(Ph)2} (3a), {(Ph)2(H)C-P-PtBu2}{μ2-(S-C6H4-S)}{tBu2P-P-C(H)(Ph)2} (3b), and {(Ph)2(H)C-P-PtBu2}{μ2-(S-CH2-C6H4-CH2-S)}{tBu2P-P-C(H)(Ph)2} (3c). Next, the reactions of 3a and 3c with metal chlorides led to the growth of desired coordination polymers of copper(I) and silver(I). All the obtained compounds remained stable under atmospheric conditions.

E-H Bond Cleavage Processes in Reactions of Heterometallic Phosphinidene-Bridged MoRe and MoMn Complexes with Hydrogen and p-Block Element Hydrides.

Reactions of complexes [MoMCp(μ-PMes*)(CO)6] with H2 and several p-block element (E) hydrides mostly resulted in the cleavage of E-H bonds under mild conditions [M = Re (1a) and Mn (1b); Mes* = 2,4,6-C6H2tBu3]. The reaction with H2 (ca. 4 atm) proceeded even at 295 K to give the hydrides [MoMCp(μ-H)(μ-PHMes*)(CO)6]. The same result was obtained in the reactions with H3SiPh and, for 1a, upon reduction with Na(Hg) followed by protonation of the resulting anion [MoReCp(μ-PHMes*)(CO)6]-. The latter reacted with [AuCl{P(p-tol)3}] to yield the related heterotrimetallic cluster [MoReAuCp(μ-PHMes*)(CO)6{P(p-tol)3}]. The reaction of 1a with thiophenol gave the thiolate-bridged complex [MoReCp(μ-PHMes*)(μ-SPh)(CO)6], which evolved readily to the pentacarbonyl derivative [MoReCp(μ-PHMes*)(μ-SPh)(CO)5]. In contrast, no P-H bond cleavage was observed in reactions of complexes 1a,b with PHCy2, which just yielded the substituted derivatives [MoMCp(μ-PMes*)(CO)5(PHCy2)]. Reactions with HSnPh3 again resulted in E-H bond cleavage, but now with the stannyl group terminally bound to M, while 1a reacted with BH3·PPh3 to give the hydride-bridged derivatives [MoReCp(μ-H)(μ-PHMes*)(CO)5(PPh3)] and [MoReCp(μ-H){μ-P(CH2CMe2)C6H2tBu2}(CO)5(PPh3)], which follow from hydrogenation, C-H cleavage, and CO/PPh3 substitution steps. Density functional theory calculations on the PPh-bridged analogue of 1a revealed that hydrogenation likely proceeds through the addition of H2 to the Mo=P double bond of the complex, followed by rearrangement of the Mo fragment to drive the resulting terminal hydride into a bridging position.

Cationic Phosphinidene as a Versatile P1 Building Block: [LC-P]+ Transfer from Phosphonio-Phosphanides [LC-P-PR3]+ and Subsequent LC Replacement Reactions (LC = N-Heterocyclic Carbene).

Cationic imidazoliumyl(phosphonio)-phosphanides [LC-P-PR3]+ (1a-e+, LC = 4,5-dimethyl-1,3-diisopropylimidazolium-2-yl; R = alkyl, aryl) are obtained via the nucleophilic fragmentation of tetracationic tetraphosphetane [(LC-P)4][OTf]4 (2[OTf]4) with tertiary phosphanes. They act as [LC-P]+ transfer reagents in phospha-Wittig-type reactions, when converted with various thiocarbonyls, giving unprecedented cationic phosphaalkenes [LC-P═CR2]+ (5a-f[OTf]) or phosphanides [LC-P-CR(NR2')]+ (6a-d[OTf]). Theoretical calculations suggest that three-membered cyclic thiophosphiranes are crucial intermediates of this reaction. To test this hypothesis, treatment of [LC-P-PPh3]+ with phosphaalkenes, that are isolobal to thioketones, permits the isolation of diphosphirane salts 11a,b[OTf]. Furthermore, preliminary studies suggest that the cationic phosphaalkene [LC-P═CPh2]+ may be employed to access rare examples of η2-P═C π-complexes with Pd0 and Pt0 when treated with [Pd(PPh3)4] and [Pt(PPh3)3] for which analogous complexes of neutral phosphaalkenes are scarce. The versatility of [LC-P]+ as a valuable P1 building block was showcased in substitution reactions of the transferred LC-substituent using nucleophiles. This is demonstrated through the reactions of 5a[OTf] and 6c[OTf] with Grignard reagents and KNPh2, providing a convenient, high-yielding access to MesP═CPh2 (16) and otherwise difficult-to-synthesize 1,3-diphosphetane 17 and P-aminophosphaalkenes.

A New Strategy for the Synthesis of Porphyrin and Expanded Porphyrin Derivatives from Di‐ and Tripyrromethanes: Antioxidant, Cytotoxic Activity, and Molecular Docking Evaluation

AbstractWe present a novel and effective process for producing porphyrins in the absence of a solvent condition, in contrast to earlier procedures. An aldehyde and pyrrole were condensed by grinding in the presence of an acidic catalyst during the synthetic process. By adjusting reactant molar ratios and concentrations, dipyrromethane 3 and tripyrromethane 4 derivatives, the synthesis was improved at room temperature in 5–10 minutes with excellent yields. In this work, we successfully synthesized a number of novel porphyrin derivatives, 6 b–j. Here, we describe a method for reacting dipyrromethane 3a with various aryl aldehydes 5 b–j while using DMF as a capping agent. Moreover, expanding porphyrin derivatives 7 a, and 7 b were synthesized from the reaction of 4a with aldehydes 5a and 5b at 0 °C. Porphyrin derivatives 6 g and 6 h displayed good antioxidant potential. The cytotoxic activity of compounds 6 h, 6 b, and 6c against the human cell lines HePG‐2 and MCF‐7 were studied. The binding modes of the synthesized compounds were analyzed by docking studies that showed good binding scores against the diverse amino acids of the selected proteins (Bcl‐2). The conducted docking studies were found to be consistent with cytotoxic results.

Diverse Reactions of o-Carborane-Fused Silylenes with C≡E (E = C, P) Triple Bonds.

The reactivities of o-carborane-fused silylenes toward molecules with C≡E (E = C, P) bonds are reported. The reactions of bis(silylene) [(LSi:)C]2B10H10 (1a, L = PhC(NtBu)2) with arylalkynes afforded bis(silylium) carborane adducts 2 and 3, showing a Si(μ-C2)Si structure with an open-cage nido-carborane backbone. In contrast, the reaction of 1a with a phosphaalkyne AdC≡P (Ad = 1-adamantyl) smoothly furnished compound 4, comprising fused CPSi rings with a C=Si double bond and Si-Si single bond, and the related formation mechanism was investigated by DFT calculations. Furthermore, when monosilylene [(LSi:)C]CHB10H10 (1b) was employed to react with AdC≡P, compound 5 was isolated. The structure of 5 features a 1,2,3-triphosphetene core. All products were characterized by NMR spectroscopy and/or X-ray crystallography.

Acetylides for the Preparation of Phosphorescent Iridium(III) Complexes: Iridaoxazoles and Their Transformation into Hydroxycarbenes and N,C(sp3),C(sp2),O-Tetradentate Ligands.

The preparation of three families of phosphorescent iridium(III) emitters, including iridaoxazole derivatives, hydroxycarbene compounds, and N,C(sp3),C(sp2),O-tetradentate containing complexes, has been performed starting from dimers cis-[Ir(μ2-η2-C≡CR){κ2-C,N-(MeC6H3-py)}2]2 (R = tBu (1a), Ph (1b)). Reactions of 1a with benzamide, acetamide, phenylacetamide, and trifluoroacetamide lead to the iridaoxazole derivatives Ir{κ2-C,O-[C(CH2tBu)NC(R)O]}{κ2-C,N-(MeC6H3-py)}2 (R = Ph (2), Me (3), CH2Ph (4), CF3 (5)) with a fac disposition of carbons and heteroatoms around the metal center. In 2-methyltetrahydrofuran and dichloromethane, water promotes the C-N rupture of the IrC-N bond of the iridaoxazole ring of 3-5 to form amidate-iridium(III)-hydroxycarbene derivatives Ir{κ1-N-[NHC(R)O]}{κ2-C,N-(MeC6H3-py)}2{═C(CH2tBu)OH} (R = Me (6), CH2Ph (7), CF3 (8)). In contrast to 1a, dimer 1b reacts with benzamide and acetamide to give Ir{κ4-N,C,C',O-[py-MeC6H3-C(CH2-C6H4)NHC(R)O]}{κ2-C,N-(MeC6H3-py)}(R = Ph (9), Me (10)), which bear a N,C(sp3),C(sp2),O-tetradentate ligand resulting from a triple coupling (an alkynyl ligand, an amide, and a coordinated aryl group) and a C-H bond activation at the metal coordination sphere. Complexes 2-4 and 6-10 are emissive upon photoexcitation, in orange (2-4), green (6-8), and yellow (9 and 10) regions, with quantum yields between low and moderate (0.01-0.50) and short lifetimes (0.2-9.0 μs).

Design, synthesis, and cytotoxicity evaluation of novel thiophene, pyrimidine, pyridazine, and pyridine: Griseofulvin heterocyclic extension derivatives

Abstract Griseofulvin, an antifungal drug, has also shown good antiproliferative activity previously. This study was aimed to synthesize heterocyclic extension derivatives of griseofulvin and test them against cancer cell lines. Griseofulvin was hydrolyzed to afford griseofulvic acid (1) followed by hybridization with important heterocyclic moieties. Initially, the active methylene group of the 1,3-cyclohexanedione moiety in 1 was utilized to synthesize fused thiophene derivatives (4a and b) by reacting with malononitrile or ethyl cyanoacetate together with elemental sulfur. Compounds 4a and b were further converted to fused pyrimidine derivatives (5a–d) using ethyl isothiocyanate or phenyl isothiocyanate. Compound 1 was also reacted with aryldiazonium chlorides to synthesize compounds 6a and b, which were used to prepare fused thiophene derivatives (7a–d). The resulting thiophenes (7a–d) underwent cyclization to produce fused pyridazine derivatives (8a–d). In addition, fused pyridine derivatives (10a and b) were also prepared by the reaction of 4a and b with ethyl cyanoacetate using two different catalytic bases. The first was triethylamine to form 10a and b in two steps via 9a and b, and the second was sodium ethoxide to afford 10a and b in one step. Finally, 9a and b underwent cyclization in the presence of acetylacetone to yield compounds 11a and b. The structures of synthesized compounds were confirmed using IR, 1H NMR, 13C NMR, and mass spectrometry techniques. The synthesized compounds were subjected to cytotoxic screening against three tumor cell lines and presented good to excellent cytotoxic profiles. Compounds 4a and 11a showed significant inhibitory activity against the three cell lines compared to the standard drug doxorubicin.

Chiral Lewis Acid-Catalyzed Norrish Type II Cyclization to Synthesize α-Oxazolidinones via Enantioselective Protonation

Chiral Lewis Acid-Catalyzed Norrish Type II Cyclization to Synthesize α-Oxazolidinones via Enantioselective Protonation

Cyclometallated Palladium(II) Complexes: An Approach to the First Dinuclear Bis(iminophosphorane)phosphane-[C,N,S] Metallacycle.

Treatment of bis(iminophosphorane)phosphane ligands 2a–2e with Li2PdCl4 gave a set of novel diphosphane-derived complexes bearing two metallacycle rings, each one enclosing a P=N double bond: the unprecedented bis(iminophosphorane)phosphane-[C,N,S] palladacycles. In the case of the ligand derived from bis(diphenylphosphino)methane, 2a, both the single and the double palladacycle complexes were obtained. Reaction of 3a with bis(diphenylphosphino)ethane did not yield the expected product with the diphosphane bonded to both palladium atoms, but rather the novel coordination compound 5. The crystal structures of 3c and 5 are described.

Visible-Light-Induced [4+1] Cyclization-Aromatization of Acylsilanes and α,β-Unsaturated Ketones

Visible-Light-Induced [4+1] Cyclization-Aromatization of Acylsilanes and α,β-Unsaturated Ketones

Efficient synthesis and biological evaluation of some new series of pyridine derivatives: Promising and potent new class of anticancer agents

AbstractIn an attempt to develop potent anticancer agents, we have synthesized some substituted pyridine derivatives. Alkylation of the pyridine‐3‐carbonitrile 1a by chloroacetonitrile or methyl iodide and ethyl iodide produced the O‐alkylated nicotinonitrile derivatives (2–4), respectively. The reaction of nicotinonitrile 1a with acetic anhydride furnished the N‐acetyl derivative 5. In addition, the reaction of 1a with concentrated sulfuric acid yielded compound 6 whereas its reaction with chloroacetone gave the corresponding 2‐alkoxy‐pyridine derivative 7 which then refluxed with sodium methoxide to give compound 8. Furthermore, alkylation of 1a‐c with methyl bromoacetate and ethyl bromoacetate produced the corresponding methyl, ethyl ester derivatives 9, 10a–c, respectively. The reaction of ethyl ester 10c with a solution of sodium hydroxide in ethanol afforded the corresponding acid derivative 11. Hydrazinolysis was carried out by the reaction of ethyl ester 10a,c with hydrazine hydrate to afford the desired acetohydrazide derivative 12a,c which was used as a key intermediate for the synthesis of substituted pyridine derivatives 13–19. Chlorination of 1a with phosphorus oxychloride afforded the 2‐chloro derivative 20 which react with excess of hydrazine hydrate to yield compound 21. All synthesized compounds were characterized using IR, NMR, mass spectra, and elemental analysis. Their cytotoxic activity was evaluated against three different cancer cell lines, including breast (MCF‐7), colon (HCT‐116), and ovarian (SKOV3) cancers as well as human normal cells EA.hy 926 (human endothelial somatic cell hybrid). In general, compounds 3, 4, 5, 9, 12a, 12b, 13, 14, 15, 16, 18, 19, 21 exhibited high cytotoxicity against cancer cell lines. Besides that, the large number of synthesized compounds exhibited moderate anticancer activities.

High-Valent Pyrazolate-Bridged Platinum Complexes: A Joint Experimental and Theoretical Study.

Complexes [{Pt(C^C*)(μ-pz)}2] (HC^C*A = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazol-2-ylidene 1a, HC^C*B = 1-phenyl-3-methyl-1H-imidazol-2-ylidene 1b) react with methyl iodide (MeI) at room temperature in the dark to give compounds [{PtIV(C^C*)Me(μ-pz)}2(μ-I)]I (C^C*A2a, C^C*B2b). The reaction of 1a with benzyl bromide (BnBr) in the same conditions afforded [Br(C^C*A)PtIII(μ-pz)2PtIII(C^C*A)Bn] (5a), which by heating in BnBr(l) became [{PtIV(C^C*A)Bn(μ-pz)}2(μ-Br)]Br (6a). Experimental investigations and density functional theory (DFT) calculations on the mechanisms of these reactions from 1a revealed that they follow a SN2 pathway in the two steps of the double oxidative addition (OA). Based on the DFT investigations, species such as [(C^C*A)PtIII(μ-pz)2PtIII(C^C*A)R]X (RX = MeI Int-Me, BnBr Int-Bn) and [(C^C*A)PtII(μ-pz)2PtIV(C^C*A)(R)X] (RX = MeI Int′-Me, BnBr Int′-Bn) were proposed as intermediates for the first and the second OA reactions, respectively. In order to put the mechanisms on firmer grounds, Int-Me was prepared as [(C^C*A)PtIII(μ-pz)2PtIII(C^C*A)Me]BF4 (3a′) and used to get [I(C^C*A)PtIII(μ-pz)2PtIII(C^C*A)Me](4a), [(C^C*A)PtII(μ-pz)2PtIV(C^C*A)(Me)I](Int′-Me), and [{PtIV(C^C*)Me(μ-pz)}2(μ-I)]BF4 (2a′). The single-crystal X-ray structures of 2a, 2b, 3a′, and 5a along with the mono- and bi-dimensional 1H and 195Pt{1H} NMR spectra of all the named species allowed us to compare structural and spectroscopic data for high-valent complexes with the same core [{Pt(C^C*)(μ-pz)}2] but different oxidation states.