New synthetic route to polyphosphine ligands bearing 1,2,4,5-tetrakis(phosphino)benzene framework: structural characterizations of 1,4-(PPh2)2-2,5-(PR2)2-C6F2 (R = Ph, Pr, Et)

Reactions of 1,4-dibromo-2,5-difluorobenzene with two equivalents of lithium diisopropylamide at low temperature (T < −90 °C) followed by a quench with a slight excess of ClPPh₂ afford 1,4-dibromo-2,5-bis(diphenylphosphino)-3,6-difluorobenzene (1) in good yields. Reacting 1 with two equivalents of BuLi followed by a quench with a slight excess of ClPR₂ yield novel 1,2,4,5-tetrakis(phosphino)-3,6-difluorobenzenes 1,4-(PPh₂)₂-2,5-(PR₂)₂-C₆F₂ (R = Ph (2a); R = ⁱPr (2b); R = Et (2c)) in moderate yields. Compounds 1 and 2a-c were characterized by multinuclear NMR spectroscopy and elemental analyses. In addition, molecular structures of 2a-c have been determined by single crystal X-ray crystallography. Phosphorus atoms of PPh₂/PR₂ substituents in 2a-c are displaced from the plane of the central phenyl ring due to steric interactions with neighboring groups.     

New binucleating ligand with two [P,S] chelation pockets on a single phenyl ring: Syntheses and X-ray structures of 1,4-bis(diphenylphosphino)-2,5-difluoro-3,6-bis(methylthio)benzene and of bimetallic complex (CO)3Fe(μ-[(PPh2)(SMe)C6F2(SMe)(PPh2)])Fe(CO)3

Double deprotonations of 1,4-dibromo-2,5-difluorobenzene with LDA (2 equiv., T < −90 °C) generate a reasonably stable organodilithium intermediate. Quenching this reaction mixture with chlorophosphines ClPR₂ produce p-bis(phosphino)benzenes R₂P-C₆Br₂F₂-PR₂ (R = Ph, 4a; R = ⁱPr, 4b). Facile lithium-bromine exchange occurs upon exposure of 4a to BuLi (2 equiv., −80 °C), leading to the generation of another organodilithium intermediate. Addition of MeS-SMe (2 equiv.) to such reaction mixtures gives 1,4-bis(diphenylphosphino)-2,5-difluoro-3,6-bis(methylthio)benzene (2). Compound 2 is the first example of a neutral binucleating ligand featuring the [P,S] chelating sites on the opposite sides of a single phenyl ring. Compound 4b does not undergo the analogous transformation when subjected to the same conditions (2BuLi/2MeS-SMe). Addition of 2 to Fe(CO)₅/2(Me₃NO · 2H₂O) reaction mixtures led to the isolation of the bimetallic complex {(CO)₃Fe[P,S]-C₆F₂-[P,S]Fe(CO)₃} (3), ([P,S] represents the chelating pockets formed by adjacent -PPh₂ and -SMe groups). All of the new compounds were characterized by spectroscopic and analytical techniques (multinuclear NMR, mass-spectrometry, and/or elemental analysis). In addition, compounds 2 and 3 were characterized via single crystal X-ray diffraction methods.     

New bifunctional N-thiophosphorylated thiourea and 2,5-dithiobiurea derivatives. Crystal structures of R[C(S)NHP(S)(OiPr)2]2 (R = –N(Ph)CH2CH2N(Ph)– and –NHNH–)

A new bifunctional N-thiophosphorylated thiourea and 2,5-dithiobiurea of the common formula R[C(S)NHP(S)(OiPr)₂]₂ [R = –N(Ph)CH₂CH₂N(Ph)– (H₂L^a); –NHNH– (H₂L^b)] have been synthesized and characterized by IR, ¹H, ³¹P spectroscopy and the single crystal X-ray diffraction method. The structure of the latter compound in CDCl₃ and acetone-d₆ solutions has been discussed in comparison with the monofunctional thiosemicarbazide PhNHNHC(S)NHP(S)(OiPr)₂ (HL^c).     

Synthesis and characterization of half-sandwich iridium(III) and rhodium(III) complexes bearing organochalcogen ligands

Reactions of [Cp*M(μ-Cl)Cl]₂ (M = Ir, Rh; Cp* = η⁵-pentamethylcyclopentadienyl) with bi- or tri-dentate organochalcogen ligands Mbit (L1), Mbpit (L2), Mbbit (L3) and [Tm^Me]⁻ (L4) (Mbit = 1,1′-methylenebis(3-methyl-imidazole-2-thione); Mbpit = 1,1′-methylene bis (3-iso-propyl-imidazole-2-thione), Mbbit = 1,1′-methylene bis (3-tert-butyl-imidazole-2-thione)) and [Tm^Me]⁻ (Tm^Me = tris (2-mercapto-1-methylimidazolyl) borate) result in the formation of the 18-electron half-sandwich complexes [Cp*M(Mbit)Cl]Cl (M = Ir, 1a; M = Rh, 1b), [Cp*M(Mbpit)Cl]Cl (M = Ir, 2a; M = Rh, 2b), [Cp*M(Mbbit)Cl]Cl (M = Ir, 3a; M = Rh, 3b) and [Cp*M(Tm^Me)]Cl (M = Ir, 4a; M = Rh, 4b), respectively. All complexes have been characterized by elemental analysis, NMR and IR spectra. The molecular structures of 1a, 2b and 4a have been determined by X-ray crystallography.     

Sterically hindered cyclopentadienyl and phospholyl ligands in dysprosium chemistry

Three new unsolvated organometallic complexes of dysprosium(III) with very sterically hindered π-ligands have been synthesized and structurally characterised: the monomeric bis[η⁵-(1,2,4-tris-trimethylsilylcyclopentadienyl)]iododysprosium (1b), bis[η⁵-(1,4-bis-t-butyl-2,3-dimethylphospholyl)]iododysprosium, (1c) and the dimeric tetrakis[η⁵-(1,4-bis-t-butyl-2,3-dimethylphospholyl)]bis(μ-iodo)di-dysprosium (1d). The relative steric bulk of the π-ligands have been assessed by comparison of the structural data of 1b–d with that of the previously described bis[η⁵-(1,2,4-tris-t-butylcyclopentadienyl)]iododysprosium (1a). Contrary to 1a, reduction attempts on 1b–d were unsuccessful. The reaction of the dysprosium(II) complex bis[η⁵-(1,2,4-tris-t-butylcyclopentadienyl)]dysprosium(μ-bromo)-potassium[18]crown-6 (3) with fluorenone resulted in its monoelectronic reduction and coordination of the resulting ketyl to dysprosium(III): isolation of potassium[18]crown-6 bis[η⁵-(1,2,4-tris-t-butylcyclo-pentadienyl)](fluorenone ketyl)bromodysprosate (4) that was structurally characterised.     

Rhodium(I) carbonyl complexes of chalcogen functionalized tripodal phosphines, [CH3C(CH2P(X)Ph2)3] {X = O, S, Se} and their reactivity

The reaction of dimeric rhodium precursor [Rh(CO)₂Cl]₂ with two molar equivalent of 1,1,1-tris(diphenylphosphinomethyl)ethane trichalcogenide ligands, [CH₃C(CH₂P(X)Ph₂)₃](L), where X = O(a), S(b) and Se(c) affords the complexes of the type [Rh(CO)₂Cl(L)] (1a–1c). The complexes 1a–1c have been characterized by elemental analyses, mass spectrometry, IR and NMR (¹H, ³¹P and ¹³C) spectroscopy and the ligands a–c are structurally determined by single crystal X-ray diffraction. 1a–1c undergo oxidative addition (OA) reactions with different electrophiles such as CH₃I, C₂H₅I and C₆H₅CH₂Cl to give Rh(III) complexes of the types [Rh(CO)(COR)ClXL] {R = –CH₃ (2a–2c), –C₂H₅ (3a–3c); X = I and R = –CH₂C₆H₅ (4a–4c); X = Cl}. Kinetic data for the reaction of a–c with CH₃I indicate a first-order reaction. The catalytic activity of 1a–1c for the carbonylation of methanol to acetic acid and its ester is evaluated and a higher turn over number (TON = 1564–1723) is obtained compared to that of the well-known commercial species [Rh(CO)₂I₂]⁻ (TON = 1000) under the reaction conditions: temperature 130 ± 2 °C, pressure 30 ± 2 bar and time 1 h.     

Lithiated γ-O-functionalized propyl phenyl sulfides and sulfones of the type Li[CH(SOxPh)CH2CH2OR] (x = 0, 2). [Li{CH(SPh)CH2CH2Ot-Bu}(tmeda)] – A structurally characterized organolithium inner complex

Lithiation of O-functionalized alkyl phenyl sulfides PhSCH₂CH₂CH₂OR (R = Me, 1a; i-Pr, 1b; t-Bu, 1c; CPh₃, 1d) with n-BuLi/tmeda in n-pentane resulted in the formation of α- and ortho-lithiated compounds [Li{CH(SPh)CH₂CH₂OR}(tmeda)] (α-2a–d) and [Li{o-C₆H₄SCH₂CH₂CH₂OR)(tmeda)] (o-2a–d), respectively, which has been proved by subsequent reaction with n-Bu₃SnCl yielding the requisite stannylated γ-OR-functionalized propyl phenyl sulfides n-Bu₃SnCH(SPh)CH₂CH₂OR (α-3a–d) and n-Bu₃Sn(o-C₆H₄SCH₂CH₂CH₂OR) (o-3a–d). The α/ortho ratios were found to be dependent on the sterical demand of the substituent R. Stannylated alkyl phenyl sulfides α-3a–c were found to react with n-BuLi/tmeda and n-BuLi yielding the pure α-lithiated compounds α-2a–c and [Li{CH(SPh)CH₂CH₂OR}] (α-4a–b), respectively, as white to yellowish powders. Single-crystal X-ray diffraction analysis of [Li{CH(SPh)CH₂CH₂Ot-Bu}(tmeda)] (α-2c) exhibited a distorted tetrahedral coordination of lithium having a chelating tmeda ligand and a C,O coordinated organyl ligand. Thus, α-2c is a typical organolithium inner complex.Lithiation of O-functionalized alkyl phenyl sulfones PhSO₂CH₂CH₂CH₂OR (R = Me, 5a; i-Pr, 5b; CPh₃, 5c) with n-BuLi resulted in the exclusive formation of the α-lithiated products Li[CH(SO₂Ph)CH₂CH₂OR] (6a–c) that were found to react with n-Bu₃SnCl yielding the requisite α-stannylated compounds n-Bu₃SnCH(SO₂Ph)CH₂CH₂OR (7a–c). The identities of all lithium and tin compounds have been unambiguously proved by NMR spectroscopy (¹H, ¹³C, ¹¹⁹Sn).     

Palladium acetate complexes bearing chelating N-heterocyclic carbene (NHC) ligands: Synthesis and catalytic oxidative homocoupling of terminal alkynes

The imidazolium salts 1,1′-dibenzyl-3,3′-propylenediimidazolium dichloride and 1,1′-bis(1-naphthalenemethyl)-3,3′-propylenediimidazolium dichloride have been synthesized and transformed into the corresponding bis(NHC) ligands 1,1′-dibenzyl-3,3′-propylenediimidazol-2-ylidene (L₁) and 1,1′-bis(1-naphthalenemethyl)-3,3′-propylenediimidazol-2-ylidene (L₂) that have been employed to stabilize the Pd^II complexes PdCl₂(κ²-C,C-L₁) (2a) and PdCl₂(κ²-C,C-L₂) (2b). Both latter complexes together with their known homologous counterparts PdCl₂(κ²-C,C-L₃) (1a) (L₃ = 1,1′-dibenzyl-3,3′-ethylenediimidazol-2-ylidene) and PdCl₂(κ²-C,C-L₄) (1b) (L₄ = 1,1′-bis(1-naphthalenemethyl)-3,3′-ethylenediimidazol-2-ylidene) have been straightforwardly converted into the corresponding palladium acetate compounds Pd(κ¹-O-OAc)₂(κ²-C,C-L₃) (3a) (OAc = acetate), Pd(κ¹-O-OAc)₂(κ²-C,C-L₄) (3b), Pd(κ¹-O-OAc)₂(κ²-C,C-L₁) (4a), and Pd(κ¹-O-OAc)₂(κ²-C,C-L₂) (4b). In addition, the phosphanyl-NHC-modified palladium acetate complex Pd(κ¹-O-OAc)₂ (κ²-P,C-L₅) (6) (L₅ = 1-((2-diphenylphosphanyl)methylphenyl)-3-methyl-imidazol-2-ylidene) has been synthesized from corresponding palladium iodide complex PdI₂(κ²-P,C-L₅) (5). The reaction of the former complex with p-toluenesulfonic acid (p-TsOH) gave the corresponding bis-tosylate complex Pd(OTs)₂(κ²-P,C-L₅) (7). All new complexes have been characterized by multinuclear NMR spectroscopy and elemental analyses. In addition the solid-state structures of 1b·DMF, 2b·2DMF, 3a, 3b·DMF, 4a, 4b, and 6·CHCl₃·2H₂O have been determined by single crystal X-ray structure analyses. The palladium acetate complexes 3a/b, 4a/b, and 6 have been employed to catalyze the oxidative homocoupling reaction of terminal alkynes in acetonitrile chemoselectively yielding the corresponding 1,4-di-substituted 1,3-diyne in the presence of p-benzoquinone (BQ). The highest catalytic activity in the presence of BQ has been obtained with 6, while within the series of palladium-bis(NHC) complexes, 4b, featured with a n-propylene-bridge and the bulky N-1-naphthalenemethyl substituents, revealed as the most active compound. Hence, this latter precursor has been employed for analogous coupling reaction carried out in the presence of air pressure instead of BQ, yielding lower substrate conversion when compared to reaction performed in the presence of BQ. The important role of the ancillary ligand acetate in the course of the catalytic coupling reaction has been proved by variable-temperature NMR studies carried out with 6 and 7′ under catalytic reaction conditions.     

Five-coordinate pentafluorobenzothiolate osmium(IV) complexes [Os(SC6F5)4(P(C6H4X-4)3)] (X = OCH3, CH3, F, Cl or CF3): Solid and solution structural characterization

The reactions of OsO₄ with excess of HSC₆F₅ and P(C₆H₄X-4)₃ in ethanol afford the five-coordinate compounds [Os(SC₆F₅)₄(P(C₆H₄X-4)₃)] where X = OCH₃ 1a and 1b, CH₃ 2a and 2b, F 3a and 3b, Cl 4a and 4b or CF₃ 5a and 5b. Single crystal X-ray diffraction studies of 1 to 5 exhibit a common pattern with an osmium center in a trigonal-bipyramidal coordination arrangement. The axial positions are occupied by mutually trans thiolate and phosphane ligands, while the remaining three equatorial positions are occupied by three thiolate ligands. The three pentafluorophenyl rings of the equatorial ligands are directed upwards, away from the axial phosphane ligand in the arrangement “3-up” (isomers a). On the other hand, ³¹P{¹H} and ¹⁹F NMR studies at room temperature reveal the presence of two isomers in solution: The “3-up” isomer (a) with the three C₆F₅-rings of the equatorial ligands directed towards the axial thiolate ligand, and the “2-up, 1-down” isomer (b) with two C₆F₅-rings of the equatorial ligands directed towards the axial thiolate and the C₆F₅-ring of the third equatorial ligand directed towards the axial phosphane. Bidimensional ¹⁹F–¹⁹F NMR studies encompass the two sub-spectra for the isomers a (“3-up”) and b (“2-up, 1-down”). Variable temperature ¹⁹F NMR experiments showed that these isomers are fluxional. Thus, the ¹⁹F NMR sub-spectra for the “2-up, 1-down” isomers (b) at room temperature indicate that the two S-C₆F₅ ligands in the 2-up equatorial positions have restricted rotation about their C–S bonds, but this rotation becomes free as the temperature increases. Room temperature ¹⁹F NMR spectra of 3 and 5 also indicate restricted rotation around the Os–P bonds in the “2-up, 1-down” isomers (b). In addition, as the temperature increases, the ¹⁹F NMR spectra tend to be consistent with an increased rate of the isomeric exchange. Variable temperature ³¹P{¹H} NMR studies also confirm that, as the temperature is increased, the a and b isomeric exchange becomes fast on the NMR time scale.     

Novel organotin antibacterial and anticancer drugs

From the reaction of 6-(p-methoxyphenyl) fulvene (1a), 6-(p-N,N-dimethylaminophenyl) fulvene (1b) and 6-(3,4-dimethoxyphenyl) fulvene (1c) with LiBEt₃H, lithiated cyclopentadienide intermediates (2a–c) were synthesised. These intermediates were then transmetallated to tin with SnCl₄ to yield tetra-substituted bis(cyclopentadienyl)tin dichloride complexes (3a–c). Further reaction with tin tetrachloride yielded the benzyl-substituted derivatives bis-[(p-methoxybenzyl)cyclopentadienyl] tin(IV) dichloride (4a), bis-[(p-N,N-dimethylaminobenzyl)cyclopentadienyl] tin(IV) dichloride (4b), and bis-[(3,4-dimethoxyphenyl)cyclopentadienyl] tin(IV) dichloride (4c). Preliminary antibacterial tests were carried out using the Kirby–Bauer disk-diffusion method, in which 4a–c showed little to no activity against the Gram-negative bacterium Escherichia coli, but medium activity against Gram-positive bacteria (MRSA, MSSA). In addition, the organotin complexes had their cytotoxicity investigated through preliminary in vitro testing on the LLC-PK (pig kidney epithelial) cell line in order to determine their IC50 values. Compound 4c showed no cytotoxic activity, while 4a and 4b were found to have IC50 values of 15 and 205 μM, respectively.     

Synthesis, photophysical properties and sugar-dependent in vitro photocytotoxicity of pyrrolidine-fused chlorins bearing S-glycosides

Eight S-glycosylated 5,10,15,20-tetrakis(tetrafluorophenyl)porphyrins (1a′, 1b′, 1a and 1b (a: S-glucosylated, b: S-galactosylated)) and their 1,3-dipolar cycloadducts, i.e. chlorins 2a′, 2b′, 2a and 2b were prepared by nucleophilic substitution of the pentafluorophenyl groups with S-glycoside. These photosensitizers were characterized by ¹H, ¹³C and ¹⁹F NMR spectroscopies and elemental analysis. The photocytotoxicity of the S-glycosylated photosensitizers and the parent porphyrin (1) and chlorin (2) was examined in HeLa cells. Photosensitizers 1, 2, 1a′, 1b′, 2a′ and 2b′ showed no significant photocytotoxicity at the concentration of 0.5 μM, while the deprotected photosensitizers 1a, 1b, 2a and 2b were photocytotoxic. The strong inhibition by sodium azide of the photocytotoxicity of these photosensitizers suggested that ¹O₂ is the main mediator. The S-glucosylated photosensitizers 1a and 2a showed higher photocytotoxicity than S-galactosylated 1b and 2b, respectively. The cellular uptake of 1a and 2a increased up to 24 h, while that of 1b and 2b was saturated by 12 h.     

Synthesis, characterization, and cyclometalation studies of benzo[1,2-h: 5,4-h′]diquinolines with palladium and platinum

Benzo[1,2-h: 5,4-h′]diquinoline(1a) represents a new family of tridentate NCN pincer ligand. We report the synthesis of the parent ligand (1a) and its derivatives (1b R = Me, 1c R = t-Butyl, 1d R = Phenyl). The ligands were characterized by ¹H and ¹³C NMR, as well as mass spectral analysis, and X-ray structural determination. They readily undergo cyclometalation with LiPdCl₄, Pd(OAc)₂, and K₂PtCl₄ to form the cyclometalated Pd(NCN)Cl (2a-c, 3a), and Pt(NCN)Cl (4a) pincer complexes. These complexes have been characterized through NMR, and mass spectrometry. PdNCNCl (2a) structure was determined by single crystal X-ray diffraction. Complex 2a has shown to catalyze the Heck coupling reaction between bromobenzene and n-butylacyrlate in NMP at 140 °C, TON of 2506 were observed.     

Syntheses and pharmacological characterization of achiral and chiral enantiopure C/Si/Ge-analogous derivatives of the muscarinic antagonist cycrimine: a study on C/Si/Ge bioisosterism

The C/Si/Ge-analogous compounds rac-Ph(c-C₅H₉)El(CH₂OH)CH₂CH₂NR₂ (NR₂=piperidino; El=C, rac-3a; El=Si, rac-3b; El=Ge, rac-3c) and (c-C₅H₉)₂El(CH₂OH)CH₂CH₂NR₂ (NR₂=piperidino; El=C, 5a; El=Si, 5b; El=Ge, 5c) were prepared in multi-step syntheses. The (R)- and (S)-enantiomers of 3a–c were obtained by resolution of the respective racemates using the antipodes of O,O′-dibenzoyltartaric acid (resolution of rac-3a), O,O′-di-p-toluoyltartaric acid (resolution of rac-3b), or 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate (resolution of rac-3c). The enantiomeric purities of (R)-3a–c and (S)-3a–c were ≥98% ee (determined by ¹H-NMR spectroscopy using a chiral solvating agent). Reaction of rac-3a–c, (R)-3a–c, (S)-3a–c, and 5a–c with methyl iodide gave the corresponding methylammonium iodides rac-4a–c, (R)-4a–c, (S)-4a–c, and 6a–c (3a–c→4a–c; 5a–c→6a–c). The absolute configuration of (S)-3a was determined by a single-crystal X-ray diffraction analysis of its (R,R)-O,O′-dibenzoyltartrate. The absolute configurations of the silicon analog (R)-4b and germanium analog (R)-4c were also determined by single-crystal X-ray diffraction. The chiroptical properties of the (R)- and (S)-enantiomers of 3a–c, 3a–c·HCl, and 4a–c were studied by ORD measurements. In addition, the C/Si/Ge analogs (R)-3a–c, (S)-3a–c, (R)-4a–c, (S)-4a–c, 5a–c, and 6a–c were studied for their affinities at recombinant human muscarinic M₁, M₂, M₃, M₄, and M₅ receptors stably expressed in CHO-K1 cells (radioligand binding experiments with [³H]N-methylscopolamine as the radioligand). For reasons of comparison, the known C/Si/Ge analogs Ph₂El(CH₂OH)CH₂CH₂NR₂ (NR₂=piperidino; El=C, 7a; El=Si, 7b; El=Ge, 7c) and the corresponding methylammonium iodides 8a–c were included in these studies. According to these experiments, all the C/Si/Ge analogs behaved as simple competitive antagonists at M₁–M₅ receptors. The receptor subtype affinities of the individual carbon, silicon, and germanium analogs 3a–8a, 3b–8b, and 3c–8c were similar, indicating a strongly pronounced C/Si/Ge bioisosterism. The (R)-enantiomers (eutomers) of 3a–c and 4a–c exhibited higher affinities (up to 22.4 fold) for M₁–M₅ receptors than their corresponding (S)-antipodes (distomers), the stereoselectivity ratios being higher at M₁, M₃, M₄, and M₅ than at M₂ receptors, and higher for the methylammonium compounds (4a–c) than for the amines (3a–c). With a few exceptions, compounds 5a–c, 6a–c, 7a–c, and 8a–c displayed lower affinities for M₁–M₅ receptors than the related (R)-enantiomers of 3a–c and 4a–c. The stereoselective interaction of the enantiomers of 3a–c and 4a–c with M₁–M₅ receptors is best explained in terms of opposite binding of the phenyl and cyclopentyl ring of the (R)- and (S)-enantiomers. The highest receptor subtype selectivity was observed for the germanium compound (R)-4c at M₁/M₂ receptors (12.9-fold).     

Electrochemical study of catechol and some of 3-substituted catechols in the presence of 1,3-diethyl-2-thio-barbituric acid. Application to the electro-organic synthesis of new dispirothiopyrimidine derivatives

Electrochemical oxidation of catechol (1a), 3-methylcatechol (1b) and 3-methoxycatechol (1c) in the presence of 1,3-diethyl-2-thiobarbituric acid (3) as a nucleophile in aqueous solution has been studied using cyclic voltammetry and controlled-potential coulometry. The results indicate that (1a–1c) participating in a 1,4 (Michael) addition reaction converts to dispirothiopyrimidine derivatives (6a–6c). The electrochemical synthesis of 6a–6c has been successfully performed in an undivided cell in good yield and purity.     

Use of bis-aminoalcohol benzoquinones and dihydroxybenzoquinones in the formation of mono and polymeric structures of diorganotin(IV) derivatives

Reaction of three hexadentate ligands (L1-L3) derived from 1,4-benzoquinone bis(aminoalcohols) with diorganotin oxides (R₂Sn-O)_n (with R = Me, nBu, Ph) in 1:2 stoichiometric proportions lead to the formation of dinuclear tin compounds of the composition [(R₂Sn)₂(L)], wherein the five-coordinate metal centers are embedded in distorted trigonal-bipyramidal polyhedra. X-ray diffraction analysis revealed that diorganotin complexes carrying n-butyl groups tend to associate further through intermolecular O?Sn interactions to give 1D polymeric chains, while diphenyltin analogues tend to be monomeric. On the other hand, using 2,5-dihydroxy-3,6-dichloro-1,4-benzoquinone as ligand (L4) in 1:1 reactions with the diorganotin oxide derivatives, 1D polymeric complexes of the composition [R₂Sn(L4)(DMSO)]_n with seven-coordinate metal centers in distorted pentagonal-bipyramidal coordination polyhedra were obtained. In this case, the presence of different substituents attached to the tin atoms (Me, nBu, Ph) had no influence on the molecular composition of the products, but on the conformation of the polymeric chain, which was either planar (R = Me), slightly distorted from planarity (R = nBu) or ondulated (R = Ph).     

Synthesis, characterization of novel half-sandwich iridium and rhodium complexes containing pyridine-based organochalcogen ligands

A series of neutral pyridine-based organochalcogen ligands, 2,6-bis(1-methylimidazole-2-thione)pyridine (Bmtp), 2,6-bis(1-isopropylimidazole-2-thione)pyridine (Bptp), and 2,6-bis(1-tert-butylimidazole-2-thione)pyridine (Bbtp) have been synthesized and characterized. Reactions of [Cp*M(μ-Cl)Cl]₂ (Cp* = η⁵-pentamethylcyclopentadienyl, M = Ir, Rh) with three pyridine-based organochalcogen ligands result in the formation of the complexes Cp*M(L)Cl₂ (M = Ir, L = Bmtp, 1a·Cl₂; M = Rh, L = Bmtp, 1b·Cl₂; M = Ir, L = Bptp, 2a·Cl₂; M = Rh, L = Bptp, 2b·Cl₂; M = Ir, L = Bbtp, 3a·Cl₂; M = Rh, L = Bbtp, 3b·Cl₂), respectively. All compounds have been characterized by elemental analysis, NMR and IR spectra. The molecular structures of Bbtp, 1a·Cl₂, 1b·Cl₂, 2b·Cl₂ and 3b·Cl₂ have been determined by X-ray crystallography.     

Stereo-controlled approach to pyrrolidine iminosugar C-glycosides and 1,4-dideoxy-1,4-imino-l-allitol using a d-mannose-derived cyclic nitrone

Intramolecular N-alkylation of 2,3-O-isopropylidene-5-O-methanesulfonyl-6-O-t-butyldimethylsilyl-d-mannofuranose-oxime 7 afforded a five-membered cyclic nitrone 9, which on N–O bond reductive cleavage followed by deprotection of –OTBS and acetonide functionalities gave 1,4-dideoxy-1,4-imino-l-allitol (DIA) 3. Addition of allylmagnesium chloride to nitrone 9 afforded α-allylated product 10a in high diastereoselectivity providing an easy entry to N-hydroxy-C1-α-allyl-substituted pyrrolidine iminosugar 4a after removal of protecting group, while N–O bond reductive cleavage in 10a afforded C1-α-allyl-pyrrolidine iminosugar 4b.     

Effect of substituents on the photoluminescence performance of Ir(III) complexes: Synthesis, electrochemistry and photophysical properties

We have prepared and characterized a series of substituted imidazole ligands namely dmmppi, dmmpfpi, dmdmppi and dmdmpfpi. These compounds will readily undergo cyclometalation with iridium trichloride and form di-irrido and the six coordinated iridium(III) dopants of the substituted imidazole ligands. They emit green colour both in solid and in solution phase. The peak emission wavelength of the dopants (λ_max = 428–497 nm) can be finely tuned depending upon the electronic properties of the phenyl, fluorophyenyl, methoxy phenyl and dimethoxyphenyl substituents as well as their positions in the imidazole ring. These iridium complexes namely Ir(dmmppi)₂(pic) 1a, Ir(dmmpfpi)₂(pic) 1b, Ir(dmdmppi)₂(pic) 1c and Ir(dmdmpfpi)₂(pic) 1d were characterized by ¹H NMR, MS and elemental analysis. All these iridium complexes 1a–1d show unusual high HOMO levels (E_HOMO = 5.21–5.41 eV) and high phosphorescence. These complexes emit green light with exceedingly high efficiency.     

Selective oxidation of acetylenic 1,4-diols with dioxiranes in comparison with the methyltrioxorhenium-hydrogen peroxide oxidant

Dimethyldioxirane (1a) and its trifluoro analog (1b) were employed to achieve selectively the direct transformation of hex-3-yne-2,5-diol 3a and 1,4-diphenyl-but-2yne-1,4-diol 3b (two representative acetylenic 1,4-diols) into the corresponding carbonyls, leaving the carbon-carbon triple bond moiety untouched. The results are compared with those recorded in the analogous oxidation using the methyltrioxorhenium (MTO)/85% H₂O₂ homogeneous system. The powerful methyl(trifluoromethyl)dioxirane (1b) is the reagent of choice to achieve optimum yields of the target alkyne-1,4-diones, which are extremely versatile synthons.