1-Methylimidazolin-2-yl functionalized cyclopentadienyl complexes of titanium and zirconium. Crystal structure of {[η:η-κN-C5H4CPh2CH2-(1-Me-C3H4N2)]ZrCl2}2(μ-Cl)2

The novel bidentate ligand, C₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂) (3), has been prepared and characterized as its lithium salt LiC₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂) (3-Li). Cyclopentadiene HC₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂) (3-H) has been obtained from 6,6-diphenylfulvene and 1,2-dimethylimidazoline (1). In THF-d₈ solution in the presence of 1, (1-methylimidazoline-2-yl)methyllithium (2) has been proved to undergo gradual conversion into a dilithium derivative of N¹-methyl-N²-[(1E,2E)-1-methyl-2-(1-methylimidazolidine-2-idene)ethylidene]ethane-1,2-diamine (2a). In a solution, cyclopentadiene 3-H has been shown to undergo isomerization into 3-{N-[2-(N-methylamino)ethyl]amino}-1,1-diphenyl-1,2-dihydropentalene (4) and, further, into a mixture of 4 and two rotameric 3-[N-(2-aminoethyl)-N-methylamino]-1,1-diphenyl-1,2-dihydropentalenes (5a) and (5b). Treatment of the lithium salt 3-Li with Me₃SiCl has lead to 3-{N-[2-(N-trimethylsilylamino)ethyl]amino}-1,1-diphenyl-1,2-dihydropentalene (6) as the dominant component in the reaction mixture. In the latter case the expected Me₃Si-C₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂) (3-Si) was not observed. Stannylation of 3-Li with 1 equiv. of Me₃SnCl has resulted in formation of a mixture of Me₃Sn-C₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂) (3-Sn), (Me₃Sn)₂-C₅H₃CPh₂CH₂-(1-Me-C₃H₄N₂) (3-Sn₂), and cyclopentadiene 3-H in a ca. 2:1:1 molar ratio. Monocyclopentadienyl complexes {[η⁵:η¹-κN-C₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂)]MCl₃ (M = Ti (7), Zr (8)) have been prepared starting from the organotin and organolithium compounds 3-Sn and 3-Li, respectively. The dynamic behavior of complexes 7 and 8 has been investigated by means of variable-temperature NMR spectroscopy in solutions. The molecular structures of the dihydropentalene 4, binuclear complex {[η⁵:η¹-κN-C₅H₄CPh₂CH₂-(1-Me-C₃H₄N₂)]ZrCl₂}₂(μ-Cl)₂8, and a coordination dimer of the dilithium salt 2a have been established by X-ray diffraction analysis. In the crystal structure of the 2a-dimer, the shortest known Li-Li contact has been found.     

A new synthetic route to optically active cyclomercurated ferrocenylimines

An adaptation of Kagan’s method for preparing 2-substituted ferrocenecarboxaldehydes has allowed us to directly prepare enantiopure (S_p)-2-chloromercurio-ferrocenecarboxaldehyde, (S_p)-3. Subsequent condensation of this aldehyde with (1R,2R)-(+)-1,2-diphenyl-1,2-ethanediamine ((R,R)-4) yielded a novel, enantiopure bis-cyclomercurated ferrocenylimine, (S_p,S_p,R_c,R_c)-N,N-bis(2-(chloromercurio)ferrocenylidene)-1,2-diphenylethane-1,2-diimine ((S_p,S_p,R_c,R_c)-5). In addition to the chiroptical data collected for both (S_p)-3 and (S_p,S_p,R_c,R_c)-5, the solid-state structure and absolute configuration of (S_p,S_p,R_c,R_c)-5 were confirmed by X-ray crystallography.     

Coordination behaviour in transition metal complexes of asymmetric NPN ligands

Two bicyclic, chiral aminophosphine ligands, namely 4R, 9R-1,3-bis(pyridin-2-ylmethyl)-2-(2-propyl)octahydro-1H-1,3,2-benzodiazaphosphole (1) and 4R, 9R-1,3-bis(pyridin-2-ylmethyl)-2-(2-ethoxy)octahydro-1H-1,3,2-benzodiazaphosphole (2) have been prepared from 1R, 2R-diaminocyclohexane and the appropriate dichlorophosphine and the nature of their coordination to a number of transition metals explored. Ligand 1 coordinates to Pd(II) and Pt(II) as a terdentate donor to give complexes of the type [M(κ³-N,P,N-1)Cl]⁺ whereas ligand 2 favours bidentate κ²-P,N coordination to give the complexes M(κ²-P,N-2)Cl₂. The study of the coordination chemistry of the NPN ligand 1 is frustrated by its ready decomposition to an unknown species which appears to be promoted by transition metals. The ligand 2 does not undergo such a transformation and its metal chemistry is more readily examined. Aside from the Pt(II) and Pd(II) complexes above, 2 has been coordinated to Cr(0) and Mo(0) in the octahedral complexes M(κ²-P,N-2)(CO)₄ and Au(I) in linear Au(κ¹-P-2)Cl. All the complexes have been fully characterised by spectroscopic and analytical techniques including a single-crystal X-ray structure analysis of [Pt(κ³-N,P,N-1)Cl]Cl, 3.     

Synthetic access to optically active isoflavans by using allylic substitution

A general approach to the (S)- and (R)-isoflavans was invented, and efficiency of the method was demonstrated by the synthesis of (S)-equol ((S)-3), (R)-sativan ((R)-4), and (R)-vestitol ((R)-5). The key step is the allylic substitution of (S)-6a (Ar¹=2,4-(MeO)₂C₆H₃) and (R)-6b (Ar¹=2,4-(BnO)₂C₆H₃) with copper reagents derived from CuBr·Me₂S and Ar²-MgBr (7a, Ar²=4-MeOC₆H₄; 7b, 2,4-(MeO)₂C₆H₃; 7c, 2-MOMO-4-MeOC₆H₃), furnishing anti S_N2′ products (R)-8a and (S)-8b,c with 93-97% chirality transfer in 60-75% yields. The olefinic part of the products was oxidatively cleaved and the Me and Bn groups on the Ar¹ moieties was then removed. Finally, phenol bromide 9a and phenol alcohols 9b,c underwent cyclization with K₂CO₃ and the Mitsunobu reagent to afford (S)-3 and (R)-4 and -5, respectively.     

Liquid crystal behaviour of ionic allylpalladium complexes containing 2-pyrazolylpyridine as bidentate N,N′-ligand

Two types of Pd-complexes containing the new N,N′-ligands 2-[3-(4-alkyloxyphenyl)pyrazol-1-yl]pyridine (pz^Rpy; R = C₆H₄OC_nH_2n+1, n = 6 (hp), 10 (dp), 12 (ddp), 14 (tdp), 16 (hdp), 18 (odp)) (1-6), namely c-[Pd(Cl)₂(pz^Rpy)] (7-10) and c-[Pd(η³-C₃H₅)(pz^Rpy)]BF₄ (11-16), have been synthesised and characterised by different spectroscopic techniques. Those members of the second type containing the largest chains (R = ddp 13, tdp 14, hdp 15, odp 16) have been found to have liquid crystal properties showing smectic A mesophases. By contrast, neither the free ligands pz^Rpy nor their related c-[Pd(Cl)₂(pz^Rpy)] complexes exhibited mesomorphism. The new synthesised metallomesogens are mononuclear complexes with an unsymmetrical molecular shape as deduced from the X-ray structures of c-[Pd(η³-C₃H₅)(pz^Rpy)]BF₄ (R = hp, 11; dp, 12). Both compounds, which are isostructural, show a distorted square-planar environment on the palladium centres defined by the allyl and the bidentate pz^Rpy ligands. The crystal structure reveals that both the counteranion and the pz^Rpy ligand function as a source of hydrogen-bonding and intermolecular π?π contacts resulting in a ²D supramolecular assembly.     

Salen-ligands based on a planar-chiral hydroxyferrocene moiety: Synthesis, coordination chemistry and use in asymmetric silylcyanation

Condensation of the O-protected hydroxyferrocene carbaldehyde (S_p)-1 with suitable diamines, followed by liberation of the hydroxyferrocene moiety leads to a new type of ferrocene-based salen ligands (3). While the use of ethylenediamine in the condensation reaction yields the planar-chiral ethylene-bridged ligand [(S_p,S_p)-3a], reaction with the enantiomers of trans-1,2-cyclohexylendiamine gives rise to the corresponding diastereomeric cyclohexylene-bridged systems [(S,S,S_p,S_p)-3b and (R,R,S_p,S_p)-3c], which feature a combination of a planar-chiral ferrocene unit with a centrochiral diamine backbone. Starting with the ferrocene-aldehyde derivative (R_p)-1, the enantiomeric ligand series (3d/e/f) is accessible via the same synthetic route.The (S_p)-series of these newly developed N₂O₂-type ligands was used for the construction of the corresponding mononuclear bis(isopropoxy)titanium (4a/b/c), methylaluminum (5a/b/c) and chloroaluminum-complexes (6a/b/c), which were isolated in good yields and identified by X-ray diffraction in several cases. The aluminum complexes (5/6) were successfully used in the Lewis-acid catalyzed addition of trimethylsilylcyanide to benzaldehyde, yielding the corresponding cyanohydrins in 45-62% enantiomeric excess.     

Acid-catalyzed rearrangement of α-hydroxytrialkylsilanes

Cationic rearrangement of several α-hydroxysilanes is described. Treatment of both (1R,1′R,2′S)-α-hydroxycyclopropylsilane syn-9 and (1S,1′R,2′S)-anti-9 under aqueous H₂SO₄ underwent rearrangement via a common α-silyl cation intermediate A to give a mixture of the ring-opened (R)-vinylsilane 13, the tandem [1,2]-CC bond migration product (1R,2S,1′R)-14, and its 1′S isomer 15. On the other hand, the acidic treatment of (R,E)-α-hydroxyalkenylsilane 8 or (R,Z)-8 was each accompanied with partial racemization to give an enantiomeric isomer of allylic alcohol 23 via a preferential syn-facial S_N2′ reaction, respectively. Both α-hydroxyalkynylsilane 6 and α-hydroxyalkylsilane 12 were inert to the acidic conditions; however, treatment of (R)-α-mesyloxyalkynylsilane 26 under aqueous H₂SO₄ gave a mixture of the optically active rearranged allene 27, α,β-unsaturated ketone 28, and (S)-α-hydroxyalkynylsilane 6 with partial racemization. Comparisons of the reactivities of these α-hydroxysilanes under acidic conditions are also disclosed.     

Half-sandwich η-benzene Ru(II) complexes of phenolate-based pyridylalkylamine/alkylamine ligands: Synthesis, structure, and stabilization of one-electron oxidized species

Four half-sandwich ruthenium(II) complexes [(η⁶-C₆H₆)Ru(L¹-O)][PF₆] (1), [(η⁶-C₆H₆)Ru(L²-O)][PF₆] (2), [(η⁶-C₆H₆)Ru(L³-O)][PF₆] (3), [(η⁶-C₆H₆)Ru(L⁴-O)][PF₆] (4a), and [(η⁶-C₆H₆)Ru(L⁴-O)][BPh₄] (4b) [L¹-OH, 4-nitro-6-{[(2′-(pyridin-2-yl)ethyl)methylamino]methyl}-phenol; L²-OH, 2,4-di-tert-butyl-6-{[(2′-(pyridin-2-yl)ethyl)methylamino]methyl}-phenol; L³-OH, 2,4-di-tert-butyl-6-{[2′-((pyridin-2-yl)benzylamino)methyl}-phenol; L⁴-OH, 2,4-di-tert-butyl-6-{[(2′-imethylaminoethyl)methylamino]methyl}-phenol (L⁴-OH)], supported by a systematically varied series of tridentate phenolate-based pyridylalkylamine and alkylamine ligands are reported. The molecular structures of 1-3, 4a, and 4b have been elucidated in solution using ¹H NMR spectroscopy and of 1, 3, and 4b in the solid state by X-ray crystallography. Notably, due to coordination by the ligands the Ru center assumes a chiral center and in turn the central amine nitrogen also becomes chiral. The ¹H NMR spectra exhibit only one set of signals, suggesting that the reaction is completely diastereoselective [1: S_Ru,S_N/R_Ru,R_N; 2: R_Ru,R_N/S_Ru,S_N; 3: S_Ru,R_N/R_Ru,S_N; 4b: S_Ru,R_N/R_Ru,S_N]. The crystal packing in 1 and 3 is stabilized by C-H^…O interactions, in 4b no meaningful secondary interactions are observed. From the standpoint of generating phenoxyl radical, as investigated by cyclic voltammetry (CV), complex 1 is redox-inactive in MeCN solution. However, 2, 3, and 4a generate a one-electron oxidized phenoxyl radical coordinated species [2]²⁺, [3]²⁺, and [4a]²⁺, respectively. The radical species are characterized by CV, UV-Vis, and EPR spectroscopy. The stability of the radical species has been determined by measuring the decay constant (UV-Vis spectroscopy).     

Synthesis, structure and photo-physical properties of phosphorus-supported fluorescent probes

Various phosphorus-supported fluorescent probes have been synthesized by the condensation reaction of multi-functional phosphorus hydrazides with various fluorophore-containing carboxaldehydes. Compounds, thus prepared, in this study are (PhO)₂P(O)[N(Me)-NCH-R] (1a, 1b), Ph₂P(O)[N(Me)-NCH-R] (2b, 2c, 2d), PhP(O)[N(Me)-NCH-R]₂ (3b, 3c), P(S)[N(Me)-NCH-R]₃ (4b, 4c), P(O)[N(Me)-NCH-R]₃ (5a, 5b, 5c), N₃P₃(O₂C₁₂H₈)₂[N(Me)-NCH-R]₂ (6a, 6b, 6c), N₃P₃(O₂C₁₂H₈)[N(Me)-NCH-R]₄ (7a, 7b, 7c, 7d) and N₃P₃[N(Me)-NCH-R]₆ (8b, 8c), where R=1-pyrenyl (a), 9-anthracenyl (b), 9-phenanthryl (c) and 7-(N,N′-diethylamino)-3-coumarinyl (d). All of these compounds have been characterized by various analytical techniques including ³¹P{¹H} NMR spectroscopy. Compounds 1b, 2b, 3b, 4b, 5b, 5c and 6d have also been characterized by single crystal X-ray analysis. All of these phosphorus-supported compounds exhibit excellent fluorescence properties in aqueous solution at near physiological conditions.     

Some new DTPA-N,N″-bis(amides) functionalized by alkyl carboxylates: Synthesis,complexation and stability properties

A new series of DTPA-N,N″-bis(amide) ligands functionalized by alkyl carboxylates on the amide side-arms (1a–1l) and their Gd(III) complexes of the type [Gd(1)(H₂O)] · xH₂O (2a–2l) were synthesized and characterized by analytical and spectroscopic techniques. Potentiality of 2a–2l as contrast agent for magnetic resonance imaging (MRI CA) was investigated by measuring some relevant physicochemical properties such as (i) the protonation constants of 1a–1l, (ii) thermodynamic and conditional stability constants of 2a–2l, (iii) the selectivity (pGd) of 1a–1l for the Gd(III) ion over the endogenous metal ions such as Zn(II), Ca(II), and Cu(II), and (iv) the relaxivities (R₁ and R₂) of 2a–2l in aqueous and aqueous HP-β-CD solutions. Comparative studies reveal that most of new Gd(III) complexes show enhanced thermodynamic stability and selectivity as compared with those of [Gd(DTPA-BMA)(H₂O)] (DTPA-BMA = N,N″-di(methylcarbamoylmethyl)diethylenetriamine-N,N′,N″-triacetate). Also enhanced with 1a–1l (except 1f and 1h) is affinity for Gd(III) as compared with [DTPA-BMA]³⁻ under physiological conditions. The relaxivities (R₁ and R₂) of aqueous solutions of 2a–2l, on the other hand, drop significantly as compared with [Gd(DTPA-BMA)(H₂O)] although they increase dramatically (6–10 fold) in aqueous hydroxypropyl-β-cyclodextrin (HP-β-CD) solutions.     

Synthesis and structure of new palladium complexes with the ligand 2-(diphenylphosphino)-1-methylimidazole: Evidence of hemilability

Several Pd(II) complexes containing the potentially bidentate ligand 2-(diphenylphosphino)-1-methylimidazole, dpim, have been synthesized and characterized: [PdCl₂(dpim)]_n (1), [PdCl₂(H₂O)(dpim-κP)] (2), [PdClMe(μ-dpim-κP,κN)]₂ (3) (previously described), [PdClMe(dpim-κP)₂] (4), [Pd(C₆F₅)₂(dpim-κP)₂] (5) and [Pd(η³-2-Me-C₃H₄)(μ-dpim-κP,κN)]₂[PF₆]₂ (6). The highly insoluble complex 1 dissolves in wet DMSO-d₆ to give the water adduct 2 in which a hydrogen bond is established between one of the water hydrogens and the imidazolyl nitrogen. Two types of coordination mode have been found for the dpim ligand in these derivatives, with the ligand behaving as P monodentate and also as a P,N bridge. The transformations between 3 and 4 demonstrate the hemilability of the dpim ligand. Complex 6 was obtained as a mixture of two pairs of enantiomers (R,S)/(S,R) and (R,R)/(S,S). Analysis of the fluxional behaviour of 6, in which the allyl group acts as a “reporter ligand”, indicates that Pd-N bond rupture takes place - again providing evidence of the hemilabile character of the dpim ligand.     

Supramolecular nanostructured assemblies of different types of porphyrins with fullerene using TiO2 nanoparticles for light energy conversion

TiO₂ nanoparticles were modified with porphyrin derivatives, 5-[4-benzoic acid]-10,15,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (Ar-H₂P-COOH), 5-[4-benzoic acid]-10,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (H-H₂P-COOH), and 5,10,15,20-tetra[4-benzoic acid]-21H,23H-porphyrin (H₂P-4COOH). The porphyrin-modified TiO₂ nanoparticles were deposited on nanostructured OTE/SnO₂ electrode together with nanoclusters of fullerene (C₆₀) in acetonitrile-toluene (3/1, v/v) using an electrophoretic deposition technique to afford the porphyrin-modified TiO₂ composite electrode denoted as OTE/SnO₂/(porphyrin-modified TiO₂ nanoparticle+C₆₀)_n. The porphyrin-modified TiO₂ composite electrodes have efficient light absorbing properties in the visible region, exhibiting the photoactive response under visible light excitation using redox couple. The incident photon-to-photocurrent efficiency (IPCE) values of supramolecular nanostructured electrodes of porphyrin-modified TiO₂ nanoparticles with fullerene [OTE/SnO₂/(Ar-H₂P-COO-TiO₂+C₆₀)_n, OTE/SnO₂/(H-H₂P-COO-TiO₂+C₆₀)_n, and OTE/SnO₂/(H₂P-4COO-TiO₂+C₆₀)_n] are much larger than those of the reference systems of porphyrin-modified TiO₂ nanoparticles without C₆₀ [OTE/SnO₂/(Ar-H₂P-COO-TiO₂)_n, OTE/SnO₂/(H-H₂P-COO-TiO₂)_n, and OTE/SnO₂/(H₂P-4COO-TiO₂)_n]. In particular, the maximum IPCE value (41%) is obtained for OTE/SnO₂/(H-H₂P-COO-TiO₂+C₆₀)_n under the bias potential of 0.2 V versus SCE. This indicates that the formation of supramolecular complexes between porphyrins and fullerene on TiO₂ nanoparticles plays an important role in improvement of the light energy conversion properties.     

An expedient approach to tetrahydrofuro[3,2-b]pyridine-2(3H)-ones via activation of pyridine N-oxide by triflic anhydride

The double addition of bis(trimethylsilyl) ketene acetals [R₁, R₂ = CH₃, -(CH₂)₅-] to pyridine N-oxide promoted by triflic anhydride under mild conditions generates N-[(trifluoromethane)sulfonyl-1,2-dihydropyridine-2,4-dicarboxylic acids 2a-b. Subsequent reaction of these acids upon iodolactonization conditions affords tetrahydrofuro[3,2-b]pyridine-2(3H)-ones 3a-b containing an exo-insaturation on the products as a result of an unexpected decarboxylation.     

Practical and highly stereoselective method for the preparation of several chiral arylsulfinamides and arylsulfinates based on the spontaneous crystallization of diastereomerically pure N-benzyl-N-(1-phenylethyl)-arylsulfinamides

A novel and simple process for the preparation of enantiomerically pure (S_S)-benzenesulfinamide (S_S)-3a, (S_S)-p-toluenesulfinamide (S_S)-3b, (S_S)-p-chloro-benzenesulfinamide (S_S)-3c and (S_S)-p-fluorobenzenesulfinamide (S_S)-3d has been developed. The treatment of arylsulfinyl chlorides with (R)-N-benzyl-1-phenylethanamine in the presence of excess triethylamine gave diastereomeric mixtures of N-benzyl-N-(1-phenylethyl)-arylsulfinamides 1, which underwent spontaneous crystallization to furnish diastereomerically pure (R,S_S)-N-benzyl-N-(1-phenylethyl)-arylsulfinamides (R,S_S)-1a-1d in 28%, 29%, 27% and 31% yields, respectively. The diastereomerically pure compounds (R,S_S)-1 were then converted into four enantiopure (R_S)-methyl arylsulfinates (R_S)-2, and finally into four enantiopure (S_S)-arylsulfinamides (S_S)-3 in good yields.     

Rhodium complexes with chiral counterions: achiral catalysts in chiral matrices

The neutral complexes [Rh(I)(NBD)((1S)-10-camphorsulfonate)] (2) and [Rh(I)((R)-N-acetylphenylalanate)] (4) reacted with bis-(diphenylphosphino)ethane (dppe) to form the cationic Rh(I)(NBD)(dppe) complexes, 5 and 6, respectively, accompanied by their corresponding chiral counteranions. Analogously, 4 reacted with 4,4^′-dimethylbipyridine to yield complex 7. Complexes 5 and 6 disproportionated in aprotic solvents to form the corresponding bis-diphosphine complexes 8 and 9, respectively. 8 was characterized by an X-ray crystal structure analysis. In order to form achiral Rh(I) complexes bearing chiral countercations new sulfonated monophosphines 13-16 with chiral ammonium cations were synthesized. Tris-triphenylphosphinosulfonic acid (H₃TPPS, 11) was used to protonate chiral amines to yield chiral ammonium phosphines 14-16. Thallium-tris-triphenylphosphinosulfonate (Tl₃TPPS, 12) underwent metathesis with a chiral quartenary ammonium iodide to yield the proton free chiral ammonium phosphine 13. Phosphines 15 and 16 reacted with [Rh(NBD)₂]BF₄ to afford the highly charged chiral zwitterionic complexes [Rh(NBD)(TPPS)₂][(R)-N,N-dimethyl-1-(naphtyl)ethylammonium]₅ (17) and [Rh(NBD)(TPPS)₂][BF₄][(R)-N,N-dimethyl-phenethylammonium]₆ (18), respectively. Complexes 5, 6, and 18 were tested as precatalysts for the hydrogenation of de-hydro-N-acetylphenylalanine (19) and methyl-(Z)-(α)-acetoamidocinnamate (MAC, 20) under homogeneous and heterogeneous (silica-supported and self-supported) conditions. None of the reactions was enantioselective.     

[4+2] Cycloaddition of 1-aminodienes and 2-substituted vinylphosphonates: application to asymmetric synthesis of 3-amino-5-phosphono-1-cyclohexene derivatives

N-Butadienylsuccinimide (1), iso-propyl N-butadienyl-(S)-pyroglutamate (5) and N-butadienyl-(R)-4-phenyloxazolidin-2-one (6) reacted with vinylphosphonates, vicinally-substituted (2) by electronwithdrawing groups (CO₂Me, CN, COMe), to furnish [4+2] cycloadducts (3-4,7-10, and 11-14) in moderate to good yields (40-88%). The reactions were highly selective: regioselectivity of 95-100%, endoselectivity of 75-92% and facial selectivity of 80-95%. The major diastereoisomers were fully characterized by ¹H and ¹³C NMR spectroscopy.     

Transition-metal complexes of phenoxy-imine ligands modified with pendant imidazolium salts: Synthesis, characterisation and testing as ethylene polymerisation catalysts

Reaction between 3-((1R,2R)-2-{[1-(3,5-di-tert-butyl-2-hydroxy-phenyl)-meth-(E)-ylidene]-amino}-cyclohexyl)-1-isopropyl-4-phenyl-3H-imidazol-1-ium bromide (1a) or the derivative 3-((1R,2R)-2-{[1-(2-hydroxy-5-nitro-phenyl)-meth-(E)-ylidene]-amino}-cyclohexyl)-1-isopropyl-4-phenyl-3H-imidazol-1-ium bromide (1b) and metal halides MCl_x.yTHF (M = Zr, x = 4, y = 2; M = V, x = y = 3; M = Cr, x = y = 3), in THF, at −78 °C gives the metal complexes of general formula [MCl_x(κ²-N,O-OC₆H₂R¹R²C(H)N-C₆H₁₀-Im)₂][Br]₂ (where M = Zr, x = 2, R¹ = R² = ^tBu, 2; M = Zr, x = 2, R¹ = H, R² = NO₂, 3; M = V, x = 1, R¹ = R² = ^tBu, 4; M = Cr, x = 1, R¹ = R² = ^tBu, 5; M = Fe, x = 0, R¹ = R² = ^tBu, 6; Im = 1-isopropyl-4-phenyl-3H-imidazol-1-ium-3-yl). ¹H and ¹³C NMR spectroscopy of 2 and 3 indicate κ²-N,O-ligand coordination via the phenoxy-imine moiety with pendant imidazolium salt that is corroborated by a single crystal structure of 6. Compounds 2, 3, 4 and 5 were tested as precatalysts for ethylene polymerisation in the presence of methylaluminoxane (MAO) cocatalyst, showing low activity. Selected polymer samples were characterised by GPC showing multimodal molecular weight distributions.     

Preparation and structures of 6- and 7-coordinate salen-type zirconium complexes and their catalytic properties for oligomerization of ethylene

A series of salen-type zirconium complexes of the general formula LZrCl₂ (L = N,N′-ethylenebis(salicylideneiminate), 3a; N,N′-ethylenebis(3,5-di-tert-butylsalicylideneiminate), 3b; N,N′-ethylenebis(5-methoxysalicylideneiminate), 3c; N,N′-ethylenebis(5-chlorosalicylideneiminate), 3d; N,N′-ethylenebis(5-nitrosalicylideneiminate), 3e; N,N′-o-phenylenebis(salicylideneiminate), 4a; N,N′-o-phenylenebis(3,5-di-tert-butylsalicylideneiminate), 4b; N,N′-o-phenylenebis(5-methoxysalicylideneiminate), 4c; N,N′-o-phenylenebis(5-chloro-salicylideneiminate), 4d) were prepared. The crystal structures of 6- and 7-coordinate zirconium complexes 4b and [4b · OCMe₂] were determined by X-ray crystallography, which reveals that a salen-type zirconium complex possesses a labile coordination site on the Zr center with a relatively stable framework and that the coordination and the dissociation of O-donor molecules occur readily at this site. The catalytic properties of 3(a-e) and 4(a-d) were studied for ethylene oligomerization in combination with Et₂AlCl as co-catalyst. Complex 3c featuring a methoxy-substituted salen ligand displayed higher activity than its analogous precursors having chloro and nitro groups as substituents. The catalytic reactions by 3(a-e) and 4(a-d) gave C₄-C₁₀ olefins and low-carbon linear α-olefins in good selectivity.     

Trifluoroethanol: key solvent for palladium-catalyzed polymerization reactions

A series of cationic palladium complexes of general formula [Pd(CH₃)(NCCH₃)(N-N)][X] (N-N = phen 1, 3-sec-butyl-1,10-phenanthroline (3-sBu-phen) 2, bpy 3, (−)-(S,S)-3,3′-(1,2-dimethylethylenedioxy)-2,2′-bipyridine (bbpy) 4, (+)-(R)-3,3′-(1-methylethylenedioxy)-2,2′-bipyridine (pbpy) 5, N,N′-bis(2,6-diisopropylphenyl)-2,3-butanediimine (iso-DAB) 6; , OTf (OTf = triflate) b) containing different nitrogen-donor ligands were prepared from the corresponding neutral chloro derivatives [Pd(CH₃)(Cl)(N-N)] (1c-6c). They were characterized by ¹H NMR spectroscopy and elemental analysis. Single crystals suitable for X-ray determination were obtained for complexes [Pd(CH₃)(NCCH₃)(bbpy)][PF₆] (4a), [Pd(CH₃)(NCCH₃)(iso-DAB)][PF₆] (6a) and [Pd(Cl)₂(bbpy)] (4c′). The latter is the result of an exchange reaction of the methyl group, present in complex 4c, with a chloride, that occurred after dissolution of 4c in CDCl₃, for 1 week at 0 °C. The catalytic behavior of complexes 1a-5a and 1b-5b in the CO/styrene copolymerization was studied in CH₂Cl₂ and 2,2,2-trifluoroethanol (TFE) evidencing the positive effect of the fluorinated alcohol both in terms of productivity and molecular weight values of the polymers obtained. Influence of the nitrogen ligand, the anion and the reaction time in both solvents were investigated and is discussed in detail. Encouraging preliminary results were also obtained in the synthesis of polyethylene, in TFE, catalyzed by [Pd(CH₃)(NCCH₃)(iso-DAB)][PF₆] (6a).     

Regioselective rearrangement of 7-azabicyclo[2.2.1]hept-2-aminyl radicals: first synthesis of 2,8-diazabicyclo[3.2.1]oct-2-enes and their conversion into 5-(2-aminoethyl)-2,3,4-trihydroxypyrrolidines, new inhibitors of α-mannosidases

Enantiomerically pure 2,8-diazabicyclo[3.2.1]oct-2-ene derivatives (+)-5 and (−)-5 have been obtained from 2-azido-3-tosyl-7-azabicyclo[2.2.1]heptanes (+)-1 and (−)-2 and their enantiomers, by ring expansion under radical conditions. Compounds (+)-5 and (−)-5 were transformed into hemiaminals 9 ((3S,4R,5R)- and 10 ((3R,4S,5S)-5-(2-aminoethyl)-2,3,4-trihydroxypyrrolidine) that are good inhibitors of α-mannosidases.