[6+2]Cycloadditions catalyzed by titanium complexes

The Ziegler catalyst TiCl₄-Et₂AlCl and the arenetitanium(II) complex (η6-C₆H₆)Ti(II)(AlCl₄)₂ induce [6 + 2]cycloaddition reactions of cycloheptatriene with dienes and acetylenes. Addition to 1,3-butadiene affords 7 - endo - vinyl - bicyclo[4.2.1]nona - 2,4 - diene (main product) and bicyclo[4.4.1]- undeca - 2,4,8 - triene, a product of [6+4]cycloaddition. Isoprene reacts similarly, yielding mainly 7- endo - isopropenyl - bicyclo[4.2.1]nona - 2,4 - diene. 2,3 - Dimethyl - 1,3 - butadiene gives 8,9dimethylbicyclo [4.4.1]undeca - 2,4,8 - triene, a product of [6 + 4]cycloaddition, while [6 + 2]cross-adducts are minor products. The reaction of cycloheptatriene with norbornadiene gives mainly hexacyclo[6.5.1.0^2,7.0^3,12.^6,10.0^9,13]tetradec - 4 - ene via [6+2]cycloaddition followed by intramolecular Diels-Alder reaction. As a by-product, pentacyclo[7.5.0.0^2,7.0^3,5.0⁴⁸]tetradeca - 10,12 - diene is formed by a [2+2+2]mechanism. Addition of cycloheptatriene to diphenylacetylene and bis - (tri- methylsilyl)acetylene furnishes sustituted bicyclo[4.2.1]nona - 2,4,7 - trienes. Alkenes, E,E-2,4 - hexadiene and 1,3 - cyclooctadiene are unreactive. The [6+2]cycloaddition is made possible by coordination of cycloheptatriene to titanium, which changes the symmetry of the frontier orbitals in the triene. The reactivity of the trienophile is also enhanced by coordination to the catalyst.     

Fluorescence signaling of aromatic oxoanion inclusion within metal-ion activated molecular receptor complexes formed from 2-(9-anthracenylmethylamino)ethyl-appended cyclen

Our observations that 1-[2-[(9-anthracenylmethylamino)ethyl)-4,7,10-tris[(2S)-2-hydroxy-3-phenoxypropyl]-1,4,7,10-tetraazacyclododecane, L¹, complexes Cd(II) to form fluorescent [CdL¹]²⁺ which undergoes a fluorescence change when it acts as an aromatic anion receptor complex has caused us to explore further the potential development of an interesting sequestration/sensor system. Accordingly, three new, octadentate, fluorescent, macrocyclic ligands, 1-[2-[(9-anthracenylmethyl)((2S)-2-hydroxy-3-phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-3-phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L²), 1-[2-[(9-anthracenyl-methyl)((2S)-2-hydroxy-3-(4??-methyl)phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-3-(4??-methyl)phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L³), and 1-[2-[(9-anthracenylmethyl)((2S)-2-hydroxy-3-(4??-t-butyl)phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-3-(4??-t-butyl)phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L⁴), have been prepared with a view to using their metal complexes to study aromatic anion sequestration. The eight-coordinate Cd(II) complexes of L² and L³, [CdL²](ClO₄)₂·5H₂O and [CdL³](ClO₄)₂·2H₂O·2Et₂O are both capable of acting as receptors for a range of aromatic oxoanions. This is demonstrated by perturbation of the anthracene derived fluorescence emission intensity as the guest aromatic oxoanion and the receptor complex combine. In 20% aqueous 1,4-dioxane the receptor complex/aromatic oxoanion association constants are in the range of 10^3.2 M^?1 (guest = p-hydroxybenzoate) to 10^7.3 M^?1 (guest = 3,4,5-trihydroxybenzoate).     

Amide-based atropisomers in tachykinin NK1-receptor antagonists: synthesis and antagonistic activity of axially chiral N-benzylcarboxamide derivatives of 2,3,4,5-tetrahydro-6H-pyrido[2,3-b][1,5]oxazocin-6-one

A series of novel N-benzylcarboxamide derivatives of bicyclic compounds, 3,4-dihydropyrido[3,2-f][1,4]oxazepin-5(2H)-one and 2,3,4,5-tetrahydro-6H-pyrido[2,3-b][1,5]oxazocin-6-one, were synthesized by cyclization of N-benzyl-2-chloro-N-(2-hydroxyethyl)- [and -(3-hydroxypropyl)-] nicotinamides, respectively. Atropisomerism was observed in 5-[3,5-bis(trifluoromethyl)benzyl]-7-phenyl-2,3,4,5-tetrahydro-6H-pyrido[2,3-b][1,5]oxazocin-6-ones due to steric hindrance of the carboxamide moiety and restriction of its rotation. Cyclization of N-[3,5-bis(trifluoromethyl)benzyl]-2-chloro-N-[(2S)-3-hydroxy-2-methylpropyl]-5-methyl-4-phenylnicotinamide gave (3S)-5-[3,5-bis(trifluoromethyl)benzyl]-3,8-dimethyl-7-phenyl-2,3,4,5-tetrahydro-6H-pyrido[2,3b][1,5]oxazocin-6-one, which exists predominantly in the thermodynamically stable aR-conformer in CDCl₃. This compound showed excellent NK₁-antagonistic activity with IC₅₀ value (in vitro inhibition of [¹²⁵I]-Bolton-Hunter-substance P binding in human IM-9 cells) of 0.47 nM, which is ca. 200-fold more potent than that of its enantiomer, indicating that the atropisomer chirality affects NK₁-receptor recognition.     

An investigation into the mechanism of conversion of fac-[Mn(CO)3{P(OMe)2Ph}2X] (X = Cl Br) into mer-cis-[MnCO2{P(OMe)2Ph}3X] in the presence of P(OMe)2Ph

The complex mer-trans-[Mn(CO)₃{P(OMe)₂Ph}₂X] (X = Cl, Br) is an intermediate in the conversion of fac-[Mn(CO)3{P(OMe)₂,Ph}₂,X] into mer- cis-[Mn(CO)₂{P(OMe)₂Ph}₃X] in the presence of P(OMe)₂Ph in benzene. No direct route between the latter two complexes could be detected kinetically. The results imply a trans carbonyl disposition as a prerequisite for higher carbonyl substitution in octahedral Mn¹ carbonyl complexes.     

The first stable examples of compounds containing both diazonium and acyl azide,and synthesis of a new pyrazino[2′,3′:3,4]pyrazolo[5,1-c][1,2,4]triazin-4(6H)-one heterocyclic system

The first stable compound containing both N₂⁺BF₄^? and CON₃ functional groups – 8-azidocarbonyl-3-(tert-butyl)-4-oxo-4,6-dihydropyrazolo[5,1-c][1,2,4]triazine-7-diazonium tetrafluoroborate was synthesized, and its stability and reactivity discussed. The Curtius rearrangement of 7-azido-3-(tert-butyl)-4-oxo-4,6-dihydropyrazolo[5,1-c][1,2,4]triazine-8-carbonylazide was investigated, and the synthesis of a novel heterocyclic system –pyrazino[2′,3′:3,4]pyrazolo[5,1-c][1,2,4]triazin-4(6H)-one is described.     

Polymerization of ethylene with self-immobilizing bis(phenoxyimine) catalytic systems

The kinetic features of polymerization of ethylene with five methylaluminoxane-activated selfim-mobilizing bis(phenoxyimine) complexes of titanium chloride, namely, bis{2-[(4-allyloxyphenylimino)methyl]-6-tert-butylphenoxy}TiCl₂, bis{2-[(4-allyloxyphenylimino)methyl]-4,6-di-tert-butylphenoxy}TiCl₂, bis{2-[(4-allyloxyphenylimino)methyl]-6-cumylphenoxy}TiCl₂, bis{2-[(4-allyloxyphenylimino)methyl]-4,6-dicumylphenoxy}TiCl₂, and bis{2-[(4-allyloxyphenylimino)methyl]-6-1-(4-tert-butylphenyl)ethylphenoxy}TiCl₂ have been studied. The activity of these complexes in the polymerization of ethylene in the temperature range 20–80°C and an ethylene pressure of 0.3 MPa has been investigated both in the homogeneous and polymer matrix-bound states. The self-immobilizing catalytic systems possess high activity (up to 40000 kg_PE/mol_cat MPa h) and give rise to ultrahigh-molecular-weight PE (M = (2–7) × 10⁶) with an improved morphology of polymer particles.     

Selenofonsartan analogues: novel selenium-containing antihypertensive compounds

2-Butyl-4-(methylseleno)-1-[[2′-(1H-tetrazol-5-yl)-1,1′-biphenyl-4-yl]methyl]-1H-imidazole-5-carboxylic acid (4) and 2-butyl-4-(phenylseleno)-1-[[2′-(1H-tetrazol-5-yl)-1,1′-biphenyl-4-yl]methyl]-1H-imidazole-5-carboxylic acid (5) have been prepared and tested for AT₁ receptor antagonist properties. Both compounds proved to be potent AT₁ receptor antagonists, with pK_b estimates indicating that these selenides are very effective at blocking AT₁ receptor mediated responses.     

Diastereoselective addition of organozinc reagents to 2-alkyl-3-(arylsulfanyl)propanals

The preparation of compounds incorporating the 3-hydroxy-2-methyl-1-alkyl moiety of high diastereomeric purity is described. Such compounds can serve as potential building blocks for the preparation of several kinds of natural products. Diastereoselective synthesis of two potential pine sawfly pheromone components, one the pure racemic threo-isomer of 3-methylpentadecan-2-ol and the other the racemic erythro-isomer of 3-methyltridecan-2-ol are described. The diastereoselective addition of R₂Zn (R=Me, Et and n-Bu) to several 2-alkyl-3-(arylsulfanyl)propanals in the presence of a Lewis acid and CH₂Cl₂ as solvent was studied. An excellent diastereomeric ratio (95/5 anti-Cram/Cram) was obtained with 2-[(phenylsulfanyl)methyl]pentanal, 2-[(phenylsulfanyl)methyl]decanal and 2-[(phenylsulfanyl)methyl]dodecanal and Me₂Zn in the presence of TiCl₄.     

Structure,electrochemistry, spectroscopy,and magnetic resonance,including high-field EPR,of {(μ-abpy)[Re(CO)3X]2}o/•−, where abpy = 2,2′-azobispyridine and X = F,Cl, Br,I

Attempts to prepare and study the title complexes yielded the structurally characterized neutral compounds anti-{(μ-abpy)[Re(CO)₃X]₂}, X = Br (I4₁/a), I (C2/c), and two crystalline forms of anti-{(μ-abpy)[Re(CO)₃Cl]₂}. One of these forms (P2₁/c) has been reported before, the other (I4₁/a), obtained through crystallization in the presence of Zn, is isostructural to the form found for anti-{(μ-abpy)[Re(CO)₃Br]₂}. Syntheses of {(μ-abpy)[Re(CO)₃Cl]₂} at high or low temperatures yielded different compositions, the high temperature procedure led to partial formation of syn/anti mixtures and one-electron reduced species. The same was observed to a greater extent in the preparation of labile syn/anti-{(μ-abpy)[Re(CO)₃F]₂}^o/??. The identity of isolated species was investigated using ¹H NMR spectroscopy, variable frequency EPR spectroscopy, cyclic voltammetry, UV/Vis- and IR-spectroelectrochemistry. The effects of halide variation on structure, reduction potentials, isomerism and electronic situation are being discussed.     

Synthesis and stereochemical resolution of functional [5]pericyclynes

Three different kinds of ring carbo-mers of [5]cyclitol ethers were targeted as challenging examples of functional [5]pericyclynes. Three tertiary pentaaryl-carbo-[5]cyclitol methyl ethers were synthesized through a [11+4] ring-closing double addition of triphenyl- and tri-p-anisyl-undecatetrayn-diides to dibenzoylacetylene. These compounds, obtained as oily mixtures of stereoisomers, are stable and can behave as acetylenic ligands of one or two Co₂(CO)₆ units. NMR analysis reveals that the broad diasteroisomeric dispersity of a triether, is consistently reduced in the symmetrized pentaether. Three bis-secondary triaryl-carbo-[5]cyclitol methyl ethers with adjacent CH(OR) vertices were synthesized through a similar [11+4] ring-closing process, where the same tetrayn-diides add to both the carbaldehyde ends of the (η²-OCH-CC-CHO)Co₂(CO)₆ complex. Despite the possibility of tautomeric isomerization, the occurrence of two adjacent bis-propargylic carbinol vertices does not diminish the stability of the [5]pericyclyne framework. Finally, two bis-secondary carbo-[5]cyclitol methyl ethers with non-adjacent CH(OH) vertices were synthesized through an alternative [10+5] ring-closing process. The bis-secondary carbo-[5]cyclitols are regarded as isohypsic equivalents of the challenging [C,C]₅carbo-cyclopentadienyl cation. A diphenyl-hexaoxy-[5]pericyclyne with two non-adjacent secondary carbinol vertices was also prepared through a [10+5] ring-closing strategy: this molecule is an isohypsic equivalent of the previously calculated zwitterionic carbo-cyclopentadienone, which could be observed as a DCI/NH₃-MS fragment after treatment with SnCl₂/HCl. Analytical HPLC showed that the C₁₁ triphenyl-undecatetrayne precursor of the [11+4] strategy was obtained as a statistical 1:2:1 mixture of the three possible diastereoisomers. Semi-preparative HPLC allowed for the resolution of this mixture. The pure major diastereoisomer was employed to prepare a partly resolved sample of pentamethoxy-pentaphenyl-[5]pericyclyne. Analytical HPLC showed that the latter corresponds to the statistical distribution of the expected three residual diastereoisomers. Semi-preparative HPLC finally afforded samples of diastereoisomerically pure pentamethoxy-[5]pericyclyne as crystalline solids.     

Dinuclear formamidino and triazenido compounds [{2,6-(Me2NCH2)2C6H3} (p-tolylNYNR)PtHgBrCl] (Y  CH,N) containing a platinum-to-mercury donor bond

Complexes [{2,6-(Me₂NCH₂)₂C₆H₃} (p-tolylNYNR)PtHgBrCl] (Y  CH, N; R  Me, Et, i-Pr) have been prepared by the reaction of [{2,6-(Me₂NCH₂)₂C₆H₃}-PtBr] with [Hg(p-tolylNYNR)Cl]. Similar complexes were obtained, although in lower yields, from exchange reactions of [{2,6-(Me₂NCH₂)₂C₆H₃} (RCO₂)-PtHg(O₂CR)Br] with p-tolylNNN(H)-p-tolyl and p-tolylNC(H)N(H)Et.The proposed structure for these heterodinuclear compounds involves a Pt-to-Hg donor bond which is bridged by a triazenido (Y  N) or a formamidino (Y  CH) group, the five-membered ring thus formed acting as a stabilizing factor. The absence of a subsequent electron transfer reaction is ascribed to the constraints of the terdentate 2,6-(Me₂NCH₂)₂C₆H₃ ligand, which fixes the N-donor atoms in mutual trans-positions.The use of p-tolylNYNR, where R is an alkyl group, results in the formation of two isomers of [{2,6-(Me₂NCH₂)₂C₆H₃} (p-tolylNYNR)PtHgBrCl] with p-tolyl-N and alkyl-N sites bonded either to Pt or Hg. The relative abundance of these isomers varies systematically with the nature of the group R. It is suggested that the ratio is determined during the formation of the complexes and that both steric and electronic factors are important.     

Diels–Alder reactions of enantiopure [(1S)-isoborneol-10-sulfinyl]- and [(1S-exo)-2-bornylsulfinyl]vinylcyclohexenes with maleimides

Uncatalyzed cycloadditions of enantiopure [(1S)-isoborneol-10-sulfinyl]- and [(1S-exo)-2-bornylsulfinyl]vinylcyclohexenes with N-phenylmaleimide occur with good facial diastereoselectivity, controlled by the sulfur configuration, even if the extent of this stereoselection appears influenced by the structural features of the terpene residue directly linked to the sulfoxide moiety. Complete endo diastereoselectivity is observed in LiClO₄ catalyzed cycloadditions of (R_S)-1-{1-[(1S)-isoborneol-10-sulfinyl]- and (S_S)-1-{1-[(1S-exo)-2-bornylsulfinyl]vinyl}cyclohexenes 4 and 5, respectively. The Diels–Alder reactivity of 5 and (S_S,E)-1-{2-[(1S-exo)-2-bornylsulfinyl]vinyl}cyclohexene 7, with the chiral auxiliary being in a different position with respect to the diene moiety, is also compared, and the results obtained comfirm that 1-sulfinyldienes are less reactive than 2-sulfinyldienes. SnCl₄ catalyzed cycloaddition of 7 with N-methylmaleimide is also performed.     

Imidazolium-based chiral ionic liquids: synthesis and application

Synthesis of chiral ionic liquids containing an imidazole nucleus and chiral centers on N-substituents is reported. [(2S,3S)-2,3-Dihydroxybutane-1,4-bis(3-butylimidazolium)]-[bis(trifluoromethanesulfonyl)amide]₂ and [(4S,5S)-2-phenyl-1,3-dioxolane-4,5-bis(1-methylimidazolium)]-[bis(trifluoromethanesulfonyl)amide]₂ induced enantioselectivity in the Michael addition of malonic esters to chalcones.     

anti-Markovnikov addition of tellurium tetrachloride to trimethyl ethynyl silane

An investigation of the TeCl₄ interaction with trimethyl ethynyl silane 1 in CHCl₃ has shown that anti-Markovnikov adduct [Z-1-(trimethylsilyl)-2-chlorovinyl]tellurium trichloride is formed as the only product. In time, it is hydrolyzed to give [Z-1-(trimethylsilyl)-2-chlorovinyl]tellurium (hydroxy) dichloride which, in turn, is dehydrated to afford bis[(2-chloro-1-trimethyl-silylvinyl)dichlorotellurium]oxide. These data revealed that the reaction studied was the first example of anti-Markovnikov syn-addition of TeCl₄ to terminal acetylenes. A computed simulation of the TeCl₄ interaction with ethynyl silane 1 in a gas state using PES method did not reveal dominating orientation of the addition but showed the conditions at which anti-Markovnikov addition can occur and which were probably met in carrying out the reaction in CHCl₃.     

Solid-state electrolytes based on ionic network polymers

Interpenetrating and semi-interpenetrating polymer networks are synthesized with the use of cationic and anionic ionic monomers: N-[3-(methacryloyloxy)propyl]-N-methylpyrrolidinium bis(trifluoromethane-sulfonyl)imide, N-[2-(2-(2-(methacryloyloxy)ethoxy)ethoxy)ethyl]-N-methylpyrrolidinium bis(fluorosulfonyl)imide, and (N-butyl-N-methylpyrrolidinium 1-[3-(methacryloyloxy)propylsulfonyl] (trifluoromethanesulfonyl) imide. Their ionic conductivities, electrochemical stabilities, heat resistances, thermal stabilities, and mechanical properties and the swelling of the films in ionic liquid/lithium salt mixtures were studied. The copolymerization of N-[2-(2-(2-(methacryloyloxy)ethoxy)ethoxy)ethyl]-N-methylpyrrolidinium bis(fluorosulfonyl)imide and poly(ethylene glycol dimethacrylate) and poly(ethylene glycol methacrylate) in the presence of butadiene-acrylonitrile rubber and a solution of Li(CF₃SO₂)₂N in N-(methoxymethyl)-N-methylpyrrolidinium bis(fluorosulfonyl)imide yielded a solid-state electrolyte with a set of properties optimum among the studied films: an ionic conductivity of 1.3 × 10^?4S/cm (25°C), a tensile strength of 80 kPa, and an elongation at break of 60%.     

Fluorene-based oligomers as red light-emitting materials: a density functional theory study

The electronic structures, charge injection and transport, absorption and emission spectra, properties of two series of fluorene-based oligomers {2-[2-{2-[5-(9H-Fluoren-3-yl)-thiophen-2-yl]-vinyl}-6-(2-thiophen-2-yl-vinyl)-pyran- 4-ylidene]-malononitrile} _n (FTPM) _n and {2-{2-{2-[5-(9H-Fluoren-2-yl)-2-hydroxy- 3-methoxy-phenyl]-vinyl}-6-[2-(2-hydroxy-3-methoxy-phenyl)-vinyl]-pyran-4- ylidene}-malononitrile} _n (FOOPM) _n (n = 1–4) have been investigated by the density functional theory (DFT) approach. The ground-state geometries of (FTPM)₄ and (FOOPM)₄ optimized at B3LYP/6-31G(d) level exhibited zigzag arrangements. The energies of HOMO and LUMO, HOMO–LUMO energy gaps (ΔE _H–L ) of (FTPM) _n and (FOOPM) _n (n = ∞) were obtained by linear extrapolation method. Moreover, the calculations of ionization potential (IP), electronic affinity (EA), and reorganization energy (λ) were used to evaluate the charge injection and transport abilities. For (FTPM)₄ and (FOOPM)₄, the TDDFT calculations revealed that the absorption peaks can be characterized as π–π* transition and couple with the location of electron density distribution changes in different repeat units. All the earlier theoretical investigations are intended to establish the structure–property relationships, which can provide guidance to design the organic light-emitting diodes (OLEDs) with high performance.     

Synthesis of ACAT inhibitors through substitution using allylic picolinate and copper reagent

Amide of an octanoic acid possessing an aryl group at C3 position is a highly potent ACAT inhibitor. In this paper, we describe a synthetic access to this class of compounds as optically active forms. The key reaction is substitution of the allylic picolinate of (S,Z)-8-(benzyloxy)oct-5-en-4-ol with a copper reagent derived from (benzo[d][1,3]dioxol-4-yl)MgBr and CuBr·Me₂S to produce anti S_N2′ product regio- and stereo-selectively. The product was hydrogenated to afford (S)-3-benzo[d][1,3]dioxol-4-yloctan-1-ol, which upon oxidation furnished the octanoic acid. Finally, the acid was converted with 2,6-(i-Pr)₂C₆H₃NH₂ to the target amide via acid chloride. In a similar way, the one-carbon long homolog was synthesized.     

Synthesis of the dibenzo[f,h]phthalazine and dibenzo[f,h]cinnoline skeleton via a ‘Suzuki-Pd-catalyzed intramolecular arylation’ and a ‘Suzuki-Pschorr’ approach

Palladium-catalyzed intramolecular arylation of 2-benzyl-5-(2-bromophenyl)-4-phenylpyridazin-3(2H)-one yielded hitherto unknown 2-benzyldibenzo[f,h]phthalazin-1(2H)-one. The synthesis of this new tetracyclic pyridazinone from 2-benzyl-5-(2-aminophenyl)-4-phenylpyridazin-3(2H)-one via a Pschorr type reaction was also investigated. Similarly, the construction of 2-methyldibenzo[f,h]cinnolin-3(2H)-one from 2-methyl-5-(2-bromophenyl)-6-phenylpyridazin-3(2H)-one and 2-methyl-5-(2-aminophenyl)-6-phenylpyridazin-3(2H)-one is also reported. Removal of the N-benzyl protective group of 2-benzyl-dibenzo[f,h]phthalazin-1(2H)-one with AlCl₃ yielded unsubstituted dibenzo[f,h]phthalazin-1(2H)-one.     

The reactions of 2-[(dimethylamino)methyl]phenylcopper and -lithium tetramer with cuprous and cupric halides

2-[(Dimethylamino)methyl]phenylcopper tetramer (R₄Cu₄) forms a red $\text{1}\text{1}$ complex (RCu - CuBr)_n with cuprous bromide. The $\text{1}\text{1}$ interaction of 2-[(dimethylamino)methyl]phenylcopper with cupric halides results in the formation of the dimer RR, the 2-halo-substituted benzylamine R—Halide and minor amounts of N,N-dimethylbenzylamine RH. The formation of these products can be explained on the basis of an intramolecular electron-transfer redox reaction taking place in innersphere activated complexes of the type R₄Cu₃Cu - - - X - - - Cu^IIX(Cu^IIX₂)_n-1. The course of the metathesis reaction of 2-[(dimethylamino)methyl]phenyllithium with cuprous bromide depends on the order of addition of the reactants. Reversed addition (RLi to CuBr) results in the formation of an inseparable mixture of complexes of the type (RCu)_x- (CuBr)_y. Upon addition of CuBr to RLi the uncomplexed organocopper compound R₄Cu₄ is formed.     

Synthesis of iridium complexes with new planar chiral chelating phosphinyl-imidazolylidene ligands and their application in asymmetric hydrogenation

The synthesis of planar chiral phosphinoimidazolium salts such as (R_p)-3-(4-diphenyl-phosphino[2.2]paracyclophan-12-ylmethyl)-1-(2,6-diisopropylphenyl)imidazolium bromide (R_p)-11c starting from enantiopure 4,12-dibromo[2.2]paracyclophane (R_p)-6 is reported. After deprotonation of these salts and a subsequent reaction with [Ir(COD)Cl]₂, chelating iridium imidazolylidene complexes (R_p)-5a–c are obtained. These complexes catalyze the asymmetric hydrogenation of functionalized and simple alkenes with up to 89% ee.