Synthesis and crystal structures of the first C2-symmetric bis-aldimine NCN-pincer complexes of platinum and palladium

(S,S)-2,6-bis[(N-α-methylbenzyl)imino]phenylpalladium bromide was synthesised by oxidative addition of palladium(0) to (S,S)-1-bromo-2,6-bis[(N-α-methylbenzyl)imino]benzene. In contrast, (S,S)-2,6-bis[(N-α-methylbenzyl)imino]phenylplatinum chloride was synthesised by direct C-H activation from the reaction of potassium tetrachloroplatinate with (S,S)-1,3-bis[(N-α-methylbenzyl)imino]benzene. The X-ray crystal structures of both pincer complexes were obtained. Treatment of both complexes with silver hexafluoroanimonate gave effective but not stereoselective catalysts for a Michael reaction between methyl vinyl ketone and methyl 2-cyanopropanoate.     

Chiral bisphospholane ligands (Me-ketalphos): synthesis of their Rh(I) complexes and applications in asymmetric hydrogenation

Rhodium complexes of functionalized bisphospholane ligands (S,S,S,S-Me-ketalphos) 1 and (R,S,S,R-Me-ketalphos) 2 have been used as catalyst precursors for the asymmetric hydrogenation of several different types of functionalized olefins and have achieved high enantioselectivities.     

Synthesis, characterization and anticancer activity of new chiral Pd(II)-complexes derived from unsymmetrical α-diimine ligands

A set of new diastereopure unsymmetrical α-diimine ligands 2a-d derived from methylglyoxal and optically pure primary amines 1a-d afforded the new chiral Pd(II)-complexes (S,S)-3a, (S,S)-3b, (S,S)-3c, and (1S, 2S, 3S, 5R)-3d. All compounds have been characterized by IR, ¹H, and ¹³C NMR spectroscopies along with MS-FAB⁺ spectrometry. The crystal and molecular structure for the complexes 3a, 3b and 3d have been fully confirmed by single-crystal X-ray studies. Likewise, complexes 3a-d have also been screened for their in vitro cytotoxicity against different classes of cancer: leukemia (K-562 CML), colon cancer (HCT-15), human breast adenocarcinoma (MCF-7), central nervous system (U-251 Glio) and prostate cancer (PC-3) cell lines.     

Stereospecific ligands and their complexes. IV: Synthesis,characterization and cytotoxicity of novel platinum(IV) complexes with ethylenediamine-N,N′-di-S,S-2-propanoate and halogenido ligands: Crystal structure of s-cis-[Pt(S,S-eddp)Cl2]·4H2O and uns-cis-[Pt(S,S-eddp)Br2]

The syntheses of two novel platinum(IV) complexes of formula [PtX₂(S,S-eddp)]·nH₂O (S,S-eddp = ethylenediamine-N,N′-di-S,S-2-propanoate ion, X = chlorido (1) or bromido (2), n = 4, 0) are reported. The complexes have been obtained by direct reaction of corresponding potassium hexahalogenidoplatinate(IV) with neutralized ethylenediamine-N,N′-di-S,S-2-propanoic acid (H₂-S,S-eddp). The complexes were characterized by elemental analysis, infrared, ¹H and ¹³C NMR spectroscopy. The spectroscopically predicted geometrical configurations of the obtained complexes were confirmed by X-ray analyses of the crystal structures of the s-cis-[Pt(S,S-eddp)Cl₂]·4H₂O and uns-cis-[Pt(S,S-eddp)Br₂]. These complexes displayed significantly lower in vitro cytotoxicity in comparison to cisplatin.     

Intramolecular hydroamination/cyclization of aminoalkenes catalyzed by diamidobinaphthyl magnesium- and zinc-complexes

Reaction of 2 equiv of n-Bu₂Mg and Et₂Zn with the chiral l-proline-derived axial chiral tetraamines (S,S,S)-1 and (R,S,S)-1 gave the chiral bimetallic complexes [M₂{(S,S,S)-DABN(MeProline)₂}{R}₂] (M=Mg, R=n-Bu ((S,S,S)-2); M=Zn, R=Et ((S,S,S)-3)) and [M₂{(R,S,S)-DABN(MeProline)₂}{R}₂] (M=Mg, R=n-Bu ((R,S,S)-2)); M=Zn, R=Et ((R,S,S)-3)). The magnesium complexes showed moderate to high catalytic activity in the intramolecular hydroamination/cyclization of aminoalkenes, though enantiomeric excess was limited to 14% ee due to protolytic ligand exchange processes. The zinc complexes were less reactive and generally required higher reaction temperatures of 60-100 °C, but achieved slightly higher enantiomeric excess of up to 29% ee.     

Synthesis,Characterization, and Antiproliferative Activity of Novel Chiral [QuinoxP*AuCl2]+ Complexes

Herein is reported the synthesis of two Au(III) complexes bearing the (R,R)-(–)-2,3-Bis(tert-butylmethylphosphino)quinoxaline (R,R-QuinoxP*) or (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxaline (S,S-QuinoxP*) ligands. By reacting two stoichiometric equivalents of HAuCl₄.3H₂O to one equivalent of the corresponding QuinoxP* ligand, (R,R)-(–)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (1) and (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (2) were formed, respectively, in moderate yields. The structure of (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (2) was further confirmed by X-ray crystallography. The antiproliferative activities of the two compounds were evaluated in a panel of cell lines and exhibited promising results comparable to auranofin and cisplatin with IC₅₀ values between 1.08 and 4.83 µM. It is noteworthy that in comparison to other platinum and ruthenium enantiomeric complexes, the two enantiomers (1 and 2) do not exhibit different cytotoxic effects. The compounds exhibited stability in biologically relevant media over 48 h as well as inert reactivity to excess glutathione at 37 °C. These results demonstrate that the Au(III) atom, stabilized by the QuinoxP* ligand, can provide exciting compounds for novel anticancer drugs. These complexes provide a new scaffold to further develop a robust and diverse library of chiral phosphorus Au(III) complexes.     

Syntheses and characterization of copper(II) complexes with Schiff-base ligands derived from ethylenediamine,diphenylethylenediamine and nitro,bromo and methoxy salicylaldehyde

Copper(II) quelates with Schiff bases derived from ethylenediamine, 1R,2R-(+)- or 1S,2S-(−)-1,2-diphenylethylenediamine and 5-X-salicylaldehyde (X=OCH₃, H, Br, NO₂) have been synthesized and characterized by elemental analysis and IR and UV-visible spectroscopies. The ORD and CD spectra of the chiral ligands and their related complexes have also been measured. The absorption and CD spectra of the metal complexes in the visible region are consistent with near square planar coordination geometries. Trends in absorption spectra over the series of complexes can be correlated with electronic effects of the substituents at position 5 of the salicylaldehyde. The sign patterns of the CD spectra in both UV and visible regions suggest the prevalence of δ and λ conformations for the chelate ring in the complexes of Schiff bases derived, respectively, from R,R- and S,S-diamines. Specific features of the CD spectra of the metal complexes are discussed in terms of the exciton chirality method.     

Chiral 1,4-bis-diphosphine ligands from optically active (Z)-olefines

The catalytic asymmetric hydrogenation of prochiral ketones was carried out with Ru(II) complexes prepared from new chiral diphosphine ligands, cis-(R,R)-2,5-bis[(diarylphosphino)]-3-hexenes. These new ligands were prepared from enantiomerically pure (R,R) or (S,S)-(Z)-3-hexene-2,5 diol and enantiomeric excesses up to 85% were obtained in the reduction of 2-benzamidomethyl-3-oxobutanoate, starting material for the synthesis of 4-acetoxy-2-azetidinone.     

Structural characterization of triorganotin(IV) complexes with sodium fusidate and DFT calculations

Three new complexes of the steroid sodium fusidate (sodium 2-[(1S,2S,5R,6S,7S,10S,11S,13S, 14Z,15R,17R)-13-(acetyloxy)-5,17-dihydroxy-2,6,10,11-tetramethyl tetracyclo[8.7.0.0^2,7.0^11,15] heptadecan-14-ylidene]-6-methylhept-5-enoate = (NaFusidate, NaFA)]), with triorganotin(IV) moieties have been prepared and investigated by conventional techniques as FTIR, Mössbauer, ESI-MS and NMR spectroscopy. The isolated compounds showed stoichiometries organotin(IV)/fusidate 1/1, R₃Sn(IV)FA (R = Me, FA1; Bu, FA2; Ph, FA3). The ligand coordination sites were determined by FTIR spectroscopic measurements. In the complexes, the carboxylate group of the fusidate ligand behaves as monodentate monoanionic donor, binding the Sn(IV) through one oxygen atom.On the basis of C-Sn-O_COO angles, calculated through the rationalization of the ¹¹⁹Sn Mössbauer parameter nuclear quadrupole splitting, it has been confirmed that, in all the solid state complexes, the Sn(IV) was tetracoordinated in a distorted tetrahedral structure.Further data from ¹¹⁹Sn CP-MAS spectra confirmed the distorted tetrahedral arrangement.In MeOH solution, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy showed monomeric complexes, where the carboxylate group mainly acts as monodentate ester-type ligand, and the occurrence of a coordinated solvent molecule to the tin center, as validated by non-relativistic NMR DFT study.     

Synthesis of platinum-iodo-alkyl/aryl complexes in ligand-exchange reactions: Determination of the structure of Pt{(S,S)-bdpp}(X)I complexes (X = Me, I) by X-ray crystallography

Pt{(S,S)-bdpp}(R)I (bdpp = 2,4-bis(diphenylphosphino)pentane; R = Me, Ph, Bz, 2-Tioph) complexes were formed in alkyl/aryl ligand - iodide ligand-exchange reactions by reacting the corresponding Pt{(S,S)-bdpp}R₂ complexes with methyl iodide. The Pt{(S,S)-bdpp}(Me)I complex was isolated and fully characterised. The influence of the X ligand on the platinum-bdpp chelate conformation was investigated in Pt{(S,S)-bdpp}(X)I (X = I, SnCl₃, Me) complex series by means of X-ray crystallography.     

Synthesis and properties of alkylruthenium complexes bearing primary and secondary amine ligands

A series of 18-electron alkylruthenium complexes, RuR[κ²(N,N′)-(S,S)-R′SO₂NCHPhCHPhNH₂](η⁶-arene) (Ph = C₆H₅, R′ = p-CH₃C₆H₄ and CH₃), bearing a N-sulfonylated diamine ligand was synthesized from the reaction of RuCl[κ²(N, N′)-(S,S)-R′SO₂NCHPhCHPhNH₂](η⁶-arene) with alkylzinc reagents, in which transmetalation proceeded smoothly to give the desired alkyl complexes in good yield and selectivity. Although the isolable amine Ru complexes bearing functionalized alkyl ligands were thermally stable, the simple methyl and ethyl Ru complexes underwent intramolecular deprotonation from NH protons to give the amido Ru complexes with release of the alkanes. The reactivity of the alkyl Ru complexes is highly affected by the structures of the arene ligands.     

Asymmetric synthesis of anti-diastereoisomers of β-heterocycle substituted (S)-α-aminobutyric acids

A new efficient method for the asymmetric synthesis of β-heterocycle substituted (2S,3S)-α-aminobutyric acids through the diastereoselective addition of 5-thioxo-4-allyl-1,2,4-triazoles, containing various substituents at the 3-position, to the CC double bond of (E)- and (Z)-dehydroaminobutyric acid in the Ni^II complexes of their Schiff base with chiral auxiliaries (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide [(S)-BPB], (S)-N-(2-benzoylphenyl)-1-(3,4-dichlorobenzyl)pyrrolidine-2-carboxamide [(S)-3,4-DCBPB], (S)-N-(2-benzoylphenyl)-1-(3,4-dimethylbenzyl)pyrrolidine-2-carboxamide [(S)-3,4-DMBPB], and (S)-N-(2-benzoylphenyl)-1-(2-chlorobenzyl)pyrrolidine-2-carboxamide [(S)-2-CBPB] has been elaborated upon. The nucleophilic addition proceeds with high diastereoselectivity with a preferential formation of (S,S,S)-diastereoisomers. After decomposition of a mixture of diastereomeric complexes, optically active β-heterocycle substituted (2S,3S)-α-aminobutyric acids with high diastereomeric purity (de >98%) were isolated.     

New chiral ligands and iron(III) complexes based on 2,6-bis(1-benzyl-4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-on-2-yl)pyridines

New ligands and their complexes with iron(III) chloride have been suggested and prepared: (R,S)-, (R,R)- and (S,S)-2,6-bis(1-benzyl-4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-on-2-yl) pyridines. Both the ligands and their complexes were characterised by ¹H and ¹³C NMR spectroscopy, optical rotation and X-ray diffraction.     

TpRu complexes as recoverable Lewis acid catalysts for enantioselective solvent-free cycloaddition reactions (Tp = hydrotris(pyrazolyl)borate)

The enantiomerically and diastereomerically pure dinitrogen-bridged complexes [{TpRu(L)}₂(μ-N₂)][PF₆]₂ (L = R,R- or S,S-1,2-bis(diphenylphosphinoamino)cyclohexane (R,R- or S,S-dppach)) were prepared by reaction of the corresponding chloro-complexes [TpRuCl(L)] with NaPF₆ in dichloromethane under dinitrogen. The dinitrogen adducts react with neat methacrolein furnishing the labile complexes [TpRu(methacrolein)(L)][PF₆] (L = R,R- or S,S-dppach). Both the dinitrogen and methacrolein derivatives are catalysts for the solvent-free regio- and enantioselective Diels–Alder reactions between methacrolein and cyclopentadiene or pentamethylcyclopentadiene, with moderate enantiomeric excesses ranging from 36 to ca. 70%. The metal complex can be easily recovered and re-utilised for further reactions. The dinitrogen complexes also catalyse the 1,3-dipolar cycloaddition reaction between methacrolein and benzylidenephenylamine N-oxide to yield 5-methyl-2-N-3-diphenyl-isoxazolidine-5-carbaldehyde with very high regioselectivity and 32% enantiomeric excess.     

Resonant two-photon ionization spectra of o,p, m-xylene...Ar n (n = 1, 2)

The resonant two-photon ionization technique (R2PI) is used to study jet-cooled van der Waals (vdW) complexes o, p, m-xylene...Ar _n (n = 1, 2) through the S ₁ ← S ₀ transition around the origin band. We have tentatively assigned the main spectral features of these vdW complexes. The transitions of these complexes are red-shifted from those of the monomers. The influence of the substituent positions on the vdW vibrations is investigated.     

Stereoselective synthesis of cationic heterobidentate C(NHC)/SR rhodium(I) complexes using stereodirecting N,N-dialkylamino groups

The synthesis of two different types of chiral C/S ligands based upon N-(N,N-dialkylamino)-substituted N-heterocyclic carbenes and thioether functionalities, along with their neutral [RhCl(CNH)(COD)] and cationic [Rh(I)(NHC/S)(COD)]⁺ complexes, has been accomplished. (S)-2-[(Phenylthio)methyl]pyrrolidine, carrying the thioether moiety, and (2S,5S)-2,5-diphenylpyrrolidine, combined with a thioether functionalized side chain, were studied as potential stereodirecting groups. Only the latter provided high selectivity in the formation of the neutral complex, leading to a single atropoisomer (de >98%) of the newly formed, configurationally stable C(NHC)–Rh bond. The synthesis of the corresponding cationic [Rh(I)(NHC/S)(COD)]⁺ complexes, however, resulted in the formation of single (R_a,S_S) and (S_a,S_S) diastereomers, respectively, of the four possible complexes in each case [combinations of the (R_a/S_a) C(NHC)–Rh axis and the (S_s/R_s) stereogenic S center formed upon coordination]. For the proline derivative, the resolution of the mixture of (R_a/S_a)-[RhCl(CNH)(COD)] neutral complexes proceeds via dynamic kinetic resolution through coordinatively unsaturated Rh(I) intermediates formed after halide abstraction. The absolute configurations of both types of cationic complexes were unequivocally assigned on the basis of X-ray diffraction analysis.     

Interaction of chiral bis-distamycin derivatives with DNAs: electronic circular dichroism study

The new diastereomeric complexes of two oligo-N-methylpyrrole peptides, linked by a methano[1,5]-diazocin scaffold with DNA, were prepared. The specificity of the binding modes of (4S,9S)- and (4R,9R)-bis-distamycins derivative with ct-DNA explains the observed optical activity of the racemic mixture of distamycin if DNA is present. The bis-distamycin derivative possesses a clear sequence selectivity for A-T rich sequences of DNA, although a nonspecific binding mode with low affinity was also seen for G-C rich sequences. The reversibility of ECD spectra at 5 °C after heating to 90 °C was established.     

The synthesis,characterization and melting properties of thiophene-containing dithiocarboxylate complexes of nickel(II)

The reactions of a series of 5-alkyl-2-thiophenedithiocarboxylates with nickel(II) chloride afforded two types of complexes, blue nickel(II) complexes with two terminal dithiocarboxylate ligands, [Ni(S₂CTR)₂] and violet nickel(II) complexes with perthio- and dithiocarboxylate ligands, [Ni(S₂CTR)(S₃CTR)] (where T = 2,5-disubstituted thiophene, R = C_nH_2n+1, n = 4, 6, 8, 12, 16). The blue monomers are preferred for the shorter chains (C₄ and C₆) and the violet compounds form exclusively for the longer chains (C₈, C₁₂, and C₁₆) in the alkylthiophene complexes. In addition to the above series, [Ni(S₂CTCH₃)₂], was prepared in a one-pot reaction in THF and both the blue and violet products were isolated. It was possible to convert the blue complexes [Ni(S₂CTR)₂] (R = butyl, hexyl) into the corresponding violet complexes [Ni(S₂CTR)(S₃CTR)] after stirring in THF solutions for prolonged periods of time. Liquid-crystalline properties of these complexes were examined by DSC and POM. The violet complexes with C₈ and C₁₂ alkyl chains showed liquid-crystalline properties.     

Synthesis of (-)-2s,3s, 11s,12r-2,3,11,12-tetraphenyl[18]crown-6

The synthesis of ( - ) 2S,3S,11S,12R-2, 3,11,12-tetraphenyl [18]-crown-6 from (-)-1S,2S-hydrobenzoin and meso-hydrobenzoin is described. Chemical shifts and vicinal coupling constants of the benzylic protons in the 2 S, 3 S and 11 S,12 R substructures in the free ligands and in complexes with KSCN and 1-phenylethylammonium bromides and a brief discussion of the related conformational changes are also presented. A detailed procedure for the resolution of racemic hydrobenzoin is given.     

Four-coordinated palladium(II) and platinum(II) complexes containing the Lewis-acid {M(S2CNHR)(PR3′)} group combined with a variety of other ligands

A new series of four-coordinated Pd(II) and Pt(II) complexes in which the Lewis-acid (14-electron) {M(S₂CNHR)(PR₃′)} group is combined with a variety of other ligands (such as RHNCS₂^?, I^?, SCN^?, SnCl₂I^?) has been synthesised and studied. The structures of the new compounds are discussed in relation to their specroscopic, magnetic and thermal properties. In the case of [M(S₂CNHR)₂(PR₃′)] complexes both the spectroscopic data (IR, ¹H NMR, UV-Vis) and their thermal behaviour strongly suggest the coexistence of two kinds of gem-disulphide ligands, one acting as a bidentate ligand and the other one as a unidentate. Also it was confirmed that the chemical behaviour of the bis(N-alkyldithiocarbamato) complexes of Pd(II) and Pt(II) towards tertiary phosphines is similar to that of the isoelectronic xanthate complexes rathe than to the bis(N,N-dialkyldithiocarbamato) complexes.