Cationic half-sandwich complexes (Rh, Ir, Ru) containing 2-substituted-1,8-naphthyridine chelating ligands: Syntheses, X-ray structure analyses and spectroscopic studies

Reactions of the dinuclear complexes [(η⁶-arene)Ru(μ-Cl)Cl]₂ (arene = C₆H₆, p-ⁱPrC₆H₄Me) and [(η⁵-C₅Me₅)M(μ-Cl)Cl]₂ (M = Rh, Ir) with 2-substituted-1,8-naphthyridine ligands, 2-(2-pyridyl)-1,8-naphthyridine (pyNp), 2-(2-thiazolyl)-1,8-naphthyridine (tzNp) and 2-(2-furyl)-1,8-naphthyridine (fuNp), lead to the formation of the mononuclear cationic complexes [(η⁶-C₆H₆)Ru(L)Cl]⁺ {L = pyNp (1); tzNp (2); fuNp (3)}, [(η⁶-p-ⁱPrC₆H₄Me)Ru(L)Cl]⁺ {L = pyNp (4); tzNp (5); fuNp (6)}, [(η⁵-C₅Me₅)Rh(L)Cl]⁺ {L = pyNp (7); tzNp (8); fuNp (9)} and [(η⁵-C₅Me₅)Ir(L)Cl]⁺ {L = pyNp (10); tzNp (11); fuNp (12)}. All these complexes are isolated as chloro or hexafluorophosphate salts and characterized by IR, NMR, mass spectrometry and UV/Vis spectroscopy. The molecular structures of [1]Cl, [2]PF₆, [4]PF₆, [5]PF₆ and [10]PF₆ have been established by single crystal X-ray structure analysis.     

Synthesis and characterization of half-sandwich Rh, Ir complexes containing mono-thiolate-ortho-carborane ligand

Two binuclear complexes [Cp^∗M(Cl)Carb^S]₂ (Cp^∗ = η⁵-C₅Me₅, M = Rh (1a), Carb^S = SC₂(H)B₁₀H₁₀, Ir (1b)) were synthesized by the reaction of LiCarb^S with the dimeric metal complexes [Cp^∗MCl(μ-Cl)]₂ (M = Rh, Ir). Four mononuclear complexes Cp^∗M(Cl)(L)Carb^S (L = BuⁿPPh₂, M = Rh (2a), Ir (2b); L = PPh₃, M = Rh (4a), Ir (4b)) were synthesized by reactions of 1a or 1b with L (L = BuⁿPPh₂ (2); PPh₃ (4)) in moderate yields, respectively. Complexes 3a, 3b, 5a, 5b were obtained by treatment of 2a, 2b, 4a, 4b with AgPF₆ in high yields, respectively. All of these compounds were fully characterized by IR, NMR, and elemental analysis, and the crystal structures of 1a, 1b, 2a, 2b, 4a, 4b were also confirmed by X-ray crystallography. Their structures showed 3a, 3b and 5a, 5b could be expected as good candidates for heterolytic dihydrogen activation. Preliminary experiments on the dihydrogen activation driven by these half-sandwich Rh, Ir complexes were done under mild conditions.     

Mono and dinuclear iridium, rhodium and ruthenium complexes containing chelating carboxylato pyrazine ligands: Synthesis, molecular structure and electrochemistry

The mononuclear complexes [(η⁵-C₅Me₅)IrCl(L¹)] (1), [(η⁵-C₅Me₅)RhCl(L¹)] (2), [(η⁶-p-PrⁱC₆H₄Me)RuCl(L¹)] (3) and [(η⁶-C₆Me₆)RuCl(L¹)] (4) have been synthesised from pyrazine-2-carboxylic acid (HL¹) and the corresponding complexes [{(η⁵-C₅Me₅)IrCl₂}₂], [{(η⁵-C₅Me₅)RhCl₂}₂], [{(η⁶-p-PrⁱC₆H₄Me)RuCl₂}₂], and [{(η⁶-C₆Me₆)RuCl₂}₂], respectively. The related dinuclear complexes [{(η⁵-C₅Me₅)IrCl}₂(μ-L²)] (5), [{(η⁵-C₅Me₅)RhCl}₂(μ-L²)] (6), [{(η⁶-p-PrⁱC₆H₄Me)RuCl}₂(μ-L²)] (7) and [{(η⁶-C₆Me₆)RuCl}₂(μ-L²)] (8) have been obtained in a similar manner from pyrazine-2,5-dicarboxylic acid (H₂L²). Compounds isomeric to the latter series, [{(η⁵-C₅Me₅)IrCl}₂(μ-L³)] (9), [{(η⁵-C₅Me₅)RhCl}₂(μ-L³)] (10), [{(p-PrⁱC₆H₄Me)RuCl}₂(μ-L³)] (11) and [{(η⁶-C₆Me₆)RuCl}₂(μ-L³)] (12), have been prepared by using pyrazine-2,3-dicarboxylic acid (H₂L³) instead of H₂L². The molecular structures of 2 and 3, determined by X-ray diffraction analysis, show the pyrazine-2-carboxylato moiety to act as an N,O-chelating ligand, while the structure analyses of 5-7, confirm that the pyrazine-2,5-dicarboxylato unit bridges two metal centres. The electrochemical behaviour of selected representatives has been studied by voltammetric techniques.     

The first metal complexes of bis(diisopropylamino)carbene: synthesis, structure and ligand properties

The synthesis of rhodium(I) and iridium(I) complexes of the bis(diisopropylamino)carbene is described for the first time. The formamidinium chloride and the free bis(diisopropylamino)carbene (L) were used as consecutive precursor compounds to form the metal complexes. Spectroscopic and, for LRh(cod)Cl, crystallographic data are presented for the complexes LRh(cod)Cl and LIr(cod)Cl (L=bis(diisopropylamino)carbene). The ligand properties of the acyclic bis(diisopropylamino)carbene are compared with imidazolin-2-ylidenes and imidazolidin-2-ylidenes as ligands in related rhodium(I) carbonyl complexes. Bis(diisopropylamino)carbene is the most basic known carbene ligand to date.     

Carbonyl rhodium(I) complexes containing (H)PNX (X = O or N) ligands deriving from natural aminoacid–amides. Synthesis, X-ray structure and spectroscopic characterization

The polyfunctional (H)PNX (X = O or N) ligands 1 and 2 react with [Rh(CO)₂Cl]₂ to give the corresponding chloro carbonyl complexes {Rh[κ²-(H)PN](CO)Cl} (1a and 2a), where the neutral ligands coordinate in a κ²-PN bidentate fashion, the square planar coordination being completed by the CO trans to N and the chloride trans to P. In chloroform solution 1a maintains its original structure, while 2a partially transforms into the cationic species {Rh[κ³-(H)PNO](CO)}Cl. The chloroform solutions of 1a and 2a react with AgPF₆ to give the purely cationic species {Rh[κ³-(H)PNO](CO)}PF₆ ([1a]⁺ and [2a]⁺), while addition of Et₃N originates the neutral species {Rh[κ³-PNN′](CO)} (1b and 2b). All the complexes have been characterized by microanalysis, IR, ¹H NMR as well as ³¹P{¹H} NMR spectroscopy. The X-ray structures of ligand 1 and complex 1b are also reported.     

Investigation of the zinc(II) acetylacetonate/benzotriazole reaction system in the presence of bridging N,N′-ligands: Pentanuclear, enneanuclear and polymeric complexes

The reaction of Zn(acac)₂ with btaH (1,2,3-benzotriazole) in dmf yielded the pentanuclear complex [Zn₅(bta)₆(acac)₄(dmf)]·dmf (1·dmf). In the presence of pyrazine, the pentanuclear [Zn₅(bta)₆(acac)₄(dmf)]·3.7dmf (2·3.7dmf) and enneanuclear [Zn₉(bta)₁₂(acac)₆]·6dmf (3·6dmf) complexes were formed, whereas in the presence of 4,4′-bpy the 1D coordination polymer [Zn(acac)₂(4,4′-bpy)]_n (4) was isolated. The molecular structures of 1·dmf and 2·3.7dmf reveal that the [Zn₅] clusters consist of four Zn^II ions which span the corners of a tetrahedron and the fifth resides at its centre. The molecular structure of 3·6dmf reveals that the [Zn₉] clusters consist of two corner sharing tetrahedra and the structure can be described as the addition of two [Zn₅] clusters of 1·dmf and/or 2·3.7dmf followed by the simultaneous abstraction of [Zn(acac)₂] and dmf molecules; this alternative was accomplished by recrystallization of 1·dmf from dmf which yielded 3·6dmf. Each of the μ₃-κN:κN′:κN′′ benzotriazolate ligands in 1·dmf, 2·3.7dmf and 3·6dmf spans an edge of the tetrahedron. The molecular structure of 4 reveals mononuclear [Zn(acac)₂] units bridged via 4,4′-bpy molecules to 1D coordination polymer. Characteristic IR bands of the four complexes are discussed in terms of the coordination modes of the ligands and known structures.     

Synthesis and characterization of bis(2,2′-bipyridine) ruthenium complexes containing thiosemicarbazide ligands: unique redox series

Two series of heterochelates of ruthenium(II) containing two bipyridyl molecules and a bidentate chelating sulfur---nitrogen donor ligand in the form of 4-aryl substituted thiosemicarbazides have been synthesized and characterized. The first series of complexes are dicationic in which the ring substituted 4-aryl thiosemicarbazides (N---S) are chelated in the keto form through the hydrazinic nitrogen and the thione sulfur atom. They are of the [Ru(bpy)₂NS]⁺² type. The second series have the general formula [Ru(bpy)₂NS]⁺¹ in which the thiosemicarbazide moiety remains chelated to the Ru^II centre through the hydrazinic nitrogen and the deprotonated thiolato S-atom. All the complexes have been characterized by elemental analysis, UV-vis, IR and EPR spectroscopy. The complexes were found to constitute a three membered redox series which were investigated by cyclic voltammetry.     

Synthesis,characterization, and biological and anticancer studies of mixed ligand complexes with Schiff base and 2,2′‐bipyridine

New mixed ligand complexes of transition metals were synthesized from a Schiff base (L¹) obtained by the condensation reaction of oxamide and furfural as primary ligand and 2,2′‐bipyridine (L²) as secondary ligand. The ligands and their metal complexes were studied using various spectroscopic methods. Also thermal analyses were conducted. The mixed ligand complexes were found to have formulae [M(L¹)(L²)]Cl_m ⋅n H₂O (M = Cr(III) and Fe(III): m  = 3, n  = 0; M = Cu(II) and Cd(II): m  = 2, n  = 1; M = Mn(II), Co(II), Ni(II) and Zn(II): m  = 2, n  = 0). The resultant data revealed that the metal complexes have octahedral structure. Also, the mixed ligand complexes are electrolytic. The biological and anticancer activities of the new compounds were tested against breast cancer (MCF‐7) and colon cancer (HCT‐116) cell lines. The results showed high activity for the synthesized compounds.     

Cationic rhodium(I)–diolefin complexes containing an optically active C2-symmetric bis(sulfoximine) ligand: Synthesis and catalytic activity

A series of cationic rhodium(I) complexes [Rh(diene)(N^N)][BF₄] (diene = 1,5-cyclooctadiene (cod), norbornadiene (nbd), tetrafluorobenzobarralene (tfb)), containing the optically pure bis(sulfoximine) ligand 1,2-bis(S-methyl-S-phenylsulfonimidoyl)benzene, have been synthesized and fully characterized. The structure of the R,R enantiomer of the ligand, and that of its cyclooctadiene–Rh(I) complex, were confirmed by means of single-crystal X-ray diffraction techniques. Studies on the catalytic activity of these complexes in acetophenone hydrosilylation and dimethyl itaconate hydrogenation are also reported.     

Organometallic ruthenium, rhodium and iridium complexes containing a P-bound thiophene-2-(N-diphenylphosphino)methylamine ligand: Synthesis, molecular structure and catalytic activity

Reaction of Ph₂PNHCH₂-C₄H₃S with [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂, [Ru(η⁶-benzene)(μ-Cl)Cl]₂, [Rh(μ-Cl)(cod)]₂ and [Ir(η⁵-C₅Me₅)(μ-Cl)Cl]₂ yields complexes [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-p-cymene)Cl₂], 1, [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-benzene)Cl₂], 2, [Rh(Ph₂PNHCH₂-C₄H₃S)(cod)Cl], 3 and [Ir(Ph₂PNHCH₂-C₄H₃S)(η⁵-C₅Me₅)Cl₂], 4, respectively. All complexes were isolated from the reaction solution and fully characterized by analytical and spectroscopic methods. The structure of [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-benzene)Cl₂], 2 was also determined by single crystal X-ray diffraction. 1-4 are suitable precursors forming highly active catalyst in the transfer hydrogenation of a variety of simple ketones. Notably, the catalysts obtained by using the ruthenium complexes [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-p-cymene)Cl₂], 1 and [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-benzene)Cl₂], 2 are much more active in the transfer hydrogenation converting the carbonyls to the corresponding alcohols in 98-99% yields (TOF ≤ 200 h⁻¹) in comparison to analogous rhodium and iridium complexes.     

Application of α-chloroaldoxime O-methanesulfonates to one-pot synthesis of N,N′,N″-substituted guanidines via Tiemann rearrangement

A practical one-pot synthesis of N,N′,N″-trisubstituted guanidines via Tiemann rearrangement involving the reaction of α-chloroaldoxime O-methanesulfonates with alkyl amines is disclosed.     

Synthesis and spectroscopic studies of CoII, NiII, FeIII and ThIV complexes derived from 2,2'-dihydroxy-3,3'-di(carboxymethyl)-1,1'-binaphthyl

The synthesis of 2,2'-dihydroxy-3,3'-di(carboxymethyl)-1,1'-binaphthyl (H2L) and its novel metal complexes with Co(II), Ni(II), Fe(III) and Th(IV) salts are reported. The ligand and its metal complexes have been characterized on the basis of analytical, conductance, spectral (IR, UV-vis, 1H NMR, mass) and magnetic susceptibility measurements. The M?ssbauer spectrum of the Fe(III) complex indicates a low-spin octahedral geometry around the Fe(III) ion. The IR and 1H NMR spectral data show that the ligand behaves in a dibasic bidentate fashion coordinating to two metal atoms through the two deprotonated naphthyl OH groups and acts in a dibasic tetradentate manner using both carbonyl oxygen's and the deprotonated naphthyl OH groups coordinating to two metal ions. Thermal studies (TGA, DTA) confirm the presence of solvents either inside or outside the coordination sphere and support the mechanism of the decomposition process. The value of [alpha]D20 for the ligand has been determined in DMSO.     

Synthesis,spectroscopic, thermal analyses,biological activity and molecular docking studies on mixed ligand complexes derived from Schiff base ligands and 2,6‐pyridine dicarboxylic acid

Two novel Schiff base ligands (L^a and L^b) were prepared from the condensation of quinoline 2‐aldehyde with 2‐aminopyridine (ligand L^a) and from the condensation of oxamide with furfural (ligand L^b). Mixed ligand complexes of the type M⁺²L^a/b L^c were prepared, where (L^a and L^b) the primary ligands and L^c was 2,6‐pyridinedicarboxylic acid as secondary ligand. Metal ions used were Fe(II), Co(II), Ni(II) and Zn(II) for mixed ligands L^a L^c and Fe(II), Co(II), Ni(II), Cu(II), Hg(II) and Zn(II) for L^bL^c mixed ligands. L^a and L^b Schiff base ligands were both characterized using elemental analyses, molar conductance, IR, ¹H and ¹³C NMR. Mass spectra for L^b, [Zn(L^a)L^cCl]Cl and [Cu(L^b)L^cCl]Cl were also studied. ESR spectrum of the [Cu(L^b) L^cCl]Cl complex was also recorded The metal complexes were synthesized and characterized using elemental analyses, spectroscopic (IR, ¹H NMR, UV‐visible, diffused reflectance), molar conductance, magnetic moment and thermal studies. The IR and ¹H NMR spectral data revealed that 2,6‐pyridinedicarboxalic acid ligand coordinated to the metal ions via pyridyl N and carboxylate O without proton displacement. In addition, the IR data showed that L^a and L^b ligands behaved as neutral bidentate ligands with N₂ donation sites (quinoline N and azomethine N for L^a and two azomethine N for L^b). Based on spectroscopic studies, an octahedral geometry was proposed for the complexes. The thermal stability and degradation of the metal complexes were investigated by thermogravimetric analysis. The binding modes and affinities of L^a, L^b and Zn(II) complexes towards receptors of crystal structure of E. coli (PDB ID: 3 t88) and mutant oxidoreductase of breast cancer (PDB ID: 3 hb5) receptors were also studied. The antimicrobial activity against two species of Gram positive, Gram negative bacteria and fungi were tested for the Schiff base ligands, 2,6‐pyridinedicarboxylic acid and the mixed ligand complexes and revealed that the synthesized mixed ligand complexes exhibited higher antimicrobial activity than their free Schiff base ligands.     

Synthesis, characterization and crystal structure determination of platinum(IV) complexes containing, bipyridine derivatives and chloride, [Pt(5,5′-dmbipy)Cl4] and [Pt(6-mbipy)Cl4]

The complex [Pt(5,5′-dmbipy)Cl₄] (1) (5,5′-dmbipy is 5,5′-dimethyl-2,2′-bipyridine) was prepared from the reaction of H₂PtCl₆·6H₂O with 5,5′-dimethyl-2,2′-bipyridine in methanol. The same method was employed to make [Pt(6-mbipy)Cl₄] (2) (6-mbipy is 6-methyl-2,2′-bipyridine). Both complexes were characterized by elemental analysis, IR, UV–Vis, ¹H NMR, ¹³C NMR and ¹⁹⁵Pt NMR spectroscopy. Their solid state structures were determined by the X-ray diffraction method.     

Ruthenium-based bioconjugates: Synthesis and X-ray structure of the mixed ligand sandwich compound RuCp(p-(CO2H)C6H4Tp) and labelling of amino acids and the neuropeptide enkephalin

Four differently substituted mixed ligand sandwich complexes CpRu(p-BrC₆H₄)Tp (3), CpRu(p-BrC₆H₄)Tp^Me (4), Cp^∗Ru(p-BrC₆H₄)Tp (5), Cp^iPrRu(p-BrC₆H₄)Tp (6), incorporating cyclopentadienyl (Cp) and functionalized tris(pyrazolyl)borate (Tp) ligands, have been synthesized and characterized. Air-stable 6 has been converted to benzoic acid-functionalized Cp^iPrRu(p-(CO₂H)C₆H₄)Tp (7), which has been structurally characterized in the solid state by X-ray diffraction. Compound 7 may be readily coupled to biomolecules as exemplified by the coupling to phenylalanine-methylester to give Cp^iPrRu(p-(CO-Phe-OMe)C₆H₄Tp) (8). In a solid phase peptide synthesis (SPPS), 7 has been coupled to the pentapeptide Enkephalin, to provide Cp^iPrRu(p-(CO-Tyr-Gly-Gly-Phe-Leu-OH)C₆H₄Tp) (9) as the first example of a mixed ligand sandwich ruthenium bioconjugate.     

The crystal and molecular structure of potassium aquapentachloroiridate(III) and the H, C, N NMR coordination shifts in iridium(III) chloride complexes with 2,2′-bipyridine or 1,10-phenanthroline

The crystal and molecular structure of potassium aquapentachloroiridate(III) (K₂[Ir(H₂O)Cl₅]) was reported. The [Ir(H₂O)Cl₅]²⁻ anions are nearly octahedral, the axial Ir–Cl bond (2.322(2) Å) being shorter than the equatorial ones (2.346(2)–2.360(2) Å); the Ir–O bond length is 2.090(4) Å. Ir(III) chloride complexes with 2,2′-bipyridine (LL = bpy) or 1,10-phenanthroline (LL = phen), of the general formulae K[Ir(LL)Cl₄] and cis-[Ir(LL)₂Cl₂]Cl, were studied by far-IR and ¹H–¹³C, ¹H–¹⁵N HMBC/HMQC/HSQC–NMR. High-frequency ¹H NMR coordination shifts (Δ^1H_coord = δ^1H_complex − δ^1H_ligand; max. ca. +1 ppm) were noted for [Ir(LL)Cl₄]⁻ anions, while for cis-[Ir(LL)₂Cl₂]⁺ cations they had variable sign and magnitude (max. ca. ±1 ppm); they were dependent on the proton position, being mostly expressed for the nitrogen-adjacent hydrogens (H(6) for bpy, H(2) for phen). ¹³C NMR signals were high-frequency shifted (by max. ca. 8 ppm), whereas all ¹⁵N nuclei were shifted to the lower frequency (by ca. 105–120 ppm). The experimental ¹H, ¹³C, ¹⁵N NMR chemical shifts were reproduced by semi-empirical quantum-chemical calculations (B3LYP/LanL2DZ+6-31G^**//B3LYP/LanL2DZ+6-31G*).     

N,N′-Bis(aryl)pyridine-2,6-dicarboxamide complexes of ruthenium: Synthesis,structure and redox properties

Reaction of five N,N′-bis(aryl)pyridine-2,6-dicarboxamides (H₂L-R, where H₂ denotes the two acidic protons and R (R = OCH₃, CH₃, H, Cl and NO₂) the para substituent in the aryl fragment) with [Ru(trpy)Cl₃](trpy = 2,2′,2″-terpyridine) in refluxing ethanol in the presence of a base (NEt₃) affords a group of complexes of the type [Ru^II(trpy)(L-R)], each of which contains an amide ligand coordinated to the metal center as a dianionic tridentate N,N,N-donor along with a terpyridine ligand. Structure of the [Ru^II(trpy)(L-Cl)] complex has been determined by X-ray crystallography. All the Ru(II) complexes are diamagnetic, and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on the [Ru^II(trpy)(L-R)] complexes shows a Ru(II)–Ru(III) oxidation within 0.16–0.33 V versus SCE. An oxidation of the coordinated amide ligand is also observed within 0.94–1.33 V versus SCE and a reduction of coordinated terpyridine ligand within −1.10 to −1.15 V versus SCE. Constant potential coulometric oxidation of the [Ru^II(trpy)(L-R)] complexes produces the corresponding [Ru^III(trpy)(L-R)]⁺ complexes, which have been isolated as the perchlorate salts. Structure of the [Ru^III(trpy)(L-CH₃)]ClO₄ complex has been determined by X-ray crystallography. All the Ru(III) complexes are one-electron paramagnetic, and show anisotropic ESR spectra at 77 K and intense LMCT transitions in the visible region. A weak ligand-field band has also been shown by all the [Ru^III(trpy)(L-R)]ClO₄ complexes near 1600 nm.     

The crystal structure, vibrational spectra, and thermal behavior of dilithium piperazinium(2+) selenate tetrahydrate and dilithium N,N′-dimethylpiperazinium(2+) selenate tetrahydrate

The crystal structure of dilithium piperazinium(2+) selenate tetrahydrate has been solved; this substance crystallizes in the triclinic space group , a=7.931(2) Å, b=7.974(2) Å, c=7.991(2) Å, α=106.99(2)°, β=101.83(2)°, γ=119.28(2)° Z=1, R=0.0280 for 1489 observed reflections. A similar compound, dilithium N,N′-dimethylpiperazinium(2+) selenate tetrahydrate crystallizes in a monoclinic system with space group P2₁/c and lattice parameters a=7.338(1) Å, b=8.792(2) Å, c=12.856(1) Å, β=92.04(2)°, Z=2, R=0.0334 for 1462 observed reflections. Both structures are centrosymmetric with center of symmetry in the center of eight membered ring formed with two SeO₄ tetrahedra and two LiO₄ tetrahedra connected through tops. The two remaining oxygens on each Li atom come from water molecules. The FTIR and FT Raman spectra of both natural and N,O-deuterated substances have been measured and studied. The thermoanalytical properties were studied using TG, DTG and DTA methods in the temperature range 293–873 K for piperazinium derivative and in the range 293–523 K for dimethylpiperazinium derivative. DSC measurements were carried out in the temperature range 95–343 K. No phase transition was found in this temperature region for either of the compounds.     

Stereoselective total synthesis of (+)-(6R,2′S)-cryptocaryalactone and (−)-(6S,2′S)-epi cryptocaryalactone

The total synthesis of (+)-(6R,2′S)-cryptocaryalactone and (−)-(6S,2′S)-epi cryptocaryalactone is reported based on stereoselective reduction of δ-hydroxy β-keto ester to install 1,3-polyol system, cis Wittig olefination, and lactonization as the key steps. The synthesis of (−)-(6S,2′S)-epi cryptocaryalactone is also reported using syn-benzylidene acetal formation and a preferential Z-Wittig olefination reaction and lactonization as the key steps.     

First examples of neutral rhenium(V) complexes with a novel semi-rigid ligand containing a P,N,N,S donor atom set: Synthesis,characterisation and crystal structure

A new PN₂S ligand, N-[2-(diphenylphosphino)phenyl]-2-[(S-trityl)acetylamino]ethanamide [Ph-P(Ph₂)N₂S(Trt)], was synthesised and reacted with Re^V precursors. The reaction of both tritylated and detritylated ligands with ReOCl₃(PPh₃)₂ gave the same expected neutral complex [ReO{Ph-P(Ph₂)N₂S}] (4) in good yield. An unexpected neutral and diamagnetic species, [ReN{Ph-P(Ph₂)N₂S(Trt)}] (5), has been isolated during the complexation of the tritylated ligand with ReNCl₂(PPh₃)₂. The complexes, characterized by classical spectroscopic methods and X-ray analysis for 4, are the first examples of neutral semi-rigid-PN₂S rhenium(V) complexes.