New chiral 2,2′:6′,2″-terpyridine ligands from the chiral pool: synthesis,crystal structure of a rhodium complex and uses in copper- and rhodium-catalyzed enantioselective cyclopropanation of styrene

A number of chiral C₂-symmetric 2,2′:6′,2″ terpyridines L₁–L₄ were synthesized in moderate to good yields from commercially available chiral materials. Copper(II) and rhodium(III) chloride complexes of these ligands were prepared in good yields. The Rh(L₂)Cl₃ complex was isolated as a yellow crystalline solid and characterized by X-ray crystallography. Both Cu(L)(OTf)₂ and Rh(L)(OTf)₃ were found to be active catalysts in the cyclopropanation of styrene with ethyl diazoacetate. Enantioselectivity up to 82% e.e. was observed.     

Reactivite des derives organomanganeux—VIII : Préparation de cétones par acylation d'organomanganeux. Influence de la nature de l'agent acylant,des solvants et des ligands

The influence of the nature of acylating reagents, solvents and ligands on the preparation of ketones by acylation of organomanganous reagents is studied. Thus acid chlorides in ether, symmetrical acid anhydrides in ether or THF and mixed carboxylic-carbonic anhydrides (R'COOCOOEt) in ether are compared, they lead to the corresponding ketones with good or excellent yields. Some problems of reproductibility are encountered and discussed when mixed anhydrides R'COOCOOEt are used in THF. The addition of a great variety of cosolvents (e.g. C₆H₆, AcOEt, CO₃Et₂, CH₂CN, CH₂CL₂, . .) to the reaction mixture before addition of the acylating reagent does not affect the yield of ketones. In comparison the complexation of organomanganous reagents by several ligands (e.g. Me₂S or Ph₃P) has no subsequent effect on their acylation. The main limitation for the choice of solvents or ligands is the use of amino derivatives which generally lead to a very low yield of ketones (e.g. C₅H₅N, TMEDA, Et₃N) or unreproducible yields (e.g. HMPA). Two applications of these studies are described:The stabilization of s or t-alkyl manganous derivatives by complexation which leads to the best yield of the corresponding ketonesThe use of a cosolvent in order to increase the yield when mixed anhydrides R'COOCOOEt are used in THF.     

Substituted salen–Ru(II) complexes as catalysts in the asymmetric cyclopropanation of styrene by ethyl diazoacetate: the influence of substituents and achiral additives on activity and enantioselectivity

A series of alkyl-, halogen- and nitro-substituted salen ligands, 1, have been employed in the asymmetric cyclopropanation of styrene with ethyl diazoacetate by its ruthenium(II) complex with [RuCl₂(p-cymene)]₂ or RuCl₂(PPh₃)₃ as precursors. The introduction of appropriate electron withdrawing groups in the salen ligands benefited the enantioselectivity of the reaction. Some additives, including O-donor, N-donor and P-donor ligands, were added to the reaction to improve the enantioselectivity and activity, and e.e.s of up to 80% were achieved. In the salen/[RuCl₂(p-cymene)]₂ system, the (1R,2S)-isomer was obtained in 80.2% e.e. by using the salen ligand 1f derived from 3,5-dibrominated salicylaldehyde with Et₃N as additive. E.e.s of up to 81.3% for (1S,2R)-isomers were achieved by using the complex 2 synthesized from the nitro-substituted ligand 1m and RuCl₂(PPh₃)₃. A possible mechanism was also discussed.     

Ein neuer koordinationstyp bei acyclischen phosphaalkenen: F3CPC(F)NMe2 als (η1-μ2) 4e-donator

The chromium complex Cr(CO)₅[F₃CPC(F)NMe₂] (2) in chloroform solution is slowly transformed at room temperature to give the binuclear system [(CO)₅Cr]₂[F₃CPC(F)NMe₂] (3) besides the C-amino substituted phosphaalkene F₃CPC(F)NMe₂ (1). The yield of this process amounts to 21% within 6 months. The X-ray diffraction analysis of 3 reveals a so far unknown coordination mode of acyclic phosphaalkenes: 1 operates as (η¹-μ₂) 4e donor.     

Luminescent activity of metallosupramolecular Cd(II) complexes containing dimethylterpyridine ligand

Four complexes of different Cd(II) salts with 6,6″-dimethyl-2,2′:6′,2″-terpyridine L have been synthesized of the following structural formulae: [CdL(CH₃OH)(ClO₄)₂] (1) [CdL(Cl/Br)₂] (2) [CdLCl₂] (2a) [CdL(CH₃CO₂)₂] (3). Their properties have been established through analytical and spectroscopic (ESI-MS, IR, ¹H NMR and UV–Visible absorption and emission) methods as well as by X-ray structure determinations. Quite high quantum yield values were obtained for the solution luminescence, despite the fact that presented compounds are ‘open species’ i.e. are susceptible to the effect of external environment. Titration experiments proved speciation i.e. formation of both 2:1 and 1:1 (L:Cd²⁺) species in MeCN, yet only the latter ones can be isolated in their crystalline form. In the solid state, there appears to be a correlation between the emission intensity and the stacking arrays in the lattice. There is no evidence that the methyl substituents exert a major influence upon the properties of the complexes, and it is implied however that they might also be responsible for preferential formation of 1:1 complexes in the solid state due to observed intermolecular packing lattices.     

1,2,4,6-Cycloheptatetraenes racemizations: substituent effects via ab initio

Racemizations of three series of non-planar 1-, 4- and 5-X-C₇H₅ cyclic conjugated allenes (1_x, 2_x, and 3_x to 1′_x, 2′_x and 3′_x, respectively) are investigated using ab initio HF, B3LYB and MP2 methods with a 6-31G* basis set (X=H, F, Cl, Br, I, OH, NH₂, CN and NO₂). These three topologically different series of allenes are found to go through their corresponding planar 2-, 3- and 4-X-C₇H₅ singlet carbenic transition states, 1_x–TS, 2_x–TS and 3_x–TS (Series 1: 1_x1_x–TS1′_x; Series 2: 2_x2_x–TS2′_x; Series 3: 3_x3_x–TS3′_x).Frequency calculations show negative force constants for all planar and singlet carbeneic transition states: 1_x–TS, 2_x–TS and 3_x–TS.Based on HF/6-31G*, B3LYP/6-31G* and MP2/6-31g* calculations, the order of substituent effects on energy barrier (ΔG^#) of racemization, increase in the order of: NO₂>CN>H>I>ClBr>OH>F>NH₂ for all three Series 1–3. The height of the energy barrier related to each substituent (X) is highest in Series 3 and lowest in Series 1.Hammet free energy relationships (ρ) found via B3LYP, for Series 1, 2 and 3, are −5.8, −3.4 and −4.1, respectively. Rather similar ρ values are found using HF (−4.3, −4.4 and −4.3). These data indicate that electron-releasing groups highly increase the rate of enantiomeric interconversions.Linearity of the free energy relationships is found to be a function of steric effects. Hence, higher correlation coefficients (R) are found for Hammet free energy relationships for Series 3. This is followed by Series 2, which in turn has a more linear free energy relationship than Series 1 (Series 3>Series 2>Series 1).     

Synthesis,structure and bonding situation of [(dcpe)Pt(InCp*)2] and {(dcpe)Pt[GaC(SiMe3)3]2}—two novel examples of platinum complexes of low valent Group 13 metal species

In analogy to the corresponding Cp*Al- and Cp*Ga-compounds two further bis(phosphine)platinum complexes [(dcpe)Pt(InCp*)₂] (1(In)) and {(dcpe)Pt[GaC(SiMe₃)₃]₂} (2(Ga)) containing monovalent Group 13 metal species as ligands are accessible by thermal activation of [(dcpe)Pt(H)(CH₂t-Bu)] (dcpe=bis(dicyclohexylphosphino)ethane) followed by the reaction with 2 equiv. of InCp* (Cp*=pentamethylcyclopentadienyl) or GaC(SiMe₃)₃. The crystal structure analysis reveals a distorted tetrahedral coordination of the platinum center for both compounds. The PtIn distances in 1(In) amount to 2.569(1) and 2.556(1) Å. The PtGa distances in 2(Ga) are exceptionally short and amount to 2.315(1) and 2.318(1) Å. Comparative theoretical investigations have been performed on this type of complexes and allow a deeper insight in the bonding situation. The NBO analysis reveals a significantly larger Pt→Ga π-back-donation for the model compound {(dhpe)Pt[GaC(SiH₃)₃]₂} (2M(Ga)) (0.44 e; dhpe=1,2-diphosphinoethane) in comparison with the related model compound [(dhpe)Pt(GaCp)₂] (1M(Ga)) (0.29 e) bearing a strong π-donating organic ligand at the Ga center. A similar trend is observed for the PtGa bond dissociation energies (D_e=33.0 kcal mol⁻¹ for 2M(Ga), D_e=18.3 kcal mol⁻¹ for 1M(Ga)). For the model compound [(dhpe)Pt(InCp)₂] (1M(In)) a value of D_e=19.1 kcal mol⁻¹ has been calculated.     

Conformational equilibria in N-chloropiperidines

Nitrogen inversion equilibria in the anancomeric piperidines 3–6, 8 and 9 have been studied by variable temperature ¹H NMR in order to determine free energy differences ΔG_e→a⁰ for one class of N-substituted piperidines by an unequivocal method, i.e. direct integration of separate NMR signals for conformers whose interconversion is slow on the NMR timescale at an easily accessible temperature. Using 6 as a model ΔG_e→a⁰ (N-chloropiperidine) has been found to be 5·3±0·1 kJ mol^-1 at 193 K; similarly a study of 10 leads to ΔG_e→a⁰ (N-chloromorpholine) = 4·2±0·1 kJ mol^-1 at 203 K.     

Fine structures of 8-G-1-(arylethynylselanyl)naphthalenes (G = H, Cl, Br): Factors to control the linear alignment of five GSe–CC–CAr atoms in crystals and the behavior in solution

8-G-1-(p-YC₆H₄CCSe)C₁₀H₆ [2 (G = Cl) and 3 (G = Br): Y = H (a), OMe (b), Me (c), F (d), Cl (e), CN (f) and NO₂ (g)] have been prepared and the NMR spectra measured, in addition to 1 (G = H). Structures have been determined by X-ray crystallographic analysis for 2b, 2e and 2g, which are all type B (B), where the Se–C_sp bond is placed in the naphthyl plane in B. The type is classified as A if the Se–C_sp bond is perpendicular to the naphthyl plane. Structures around the p-YC₆H₄ (Ar) group are pd (perpendicular) for Y = OMe (2b) and Cl (2e) and pl (planar) for Y = NO₂ (2g), where the Se–C_Nap bond is placed in the aryl plane in pl and perpendicular to the plane in pd. The 1b (A: pd) structure changes dramatically on going to 2b (B: pd) with G = Cl at the 8-position. The effect is called the G-dependence in 2. The G-dependence arises from the energy lowering effect of the n_p(Cl)σ^*(Se–C_sp) 3c–4e interaction. Structures are both (B: pd) for 1e and 2e and both (B: pl) for 1g and 2g. One may realize that the structures are unchanged by G = Cl in place of G = H for Y = Cl and NO₂ at a first glance. However, the B structures in 2e and 2g must be much more stabilized by the G-dependence of the n_p(Cl)σ^*(Se–C_sp) 3c–4e interaction or the GSe–C_sp–C_sp–C_sp2 5c–6e type interaction. The structures of 2 and 3 are examined in solution based on the NMR parameters. The results show that 2 and 3 behave very similarly to each other and the structures are predominantly B, with some equilibrium between pd and pl around the aryl groups in solution. Quantum chemical calculations support the observations.     

Silylation as a protective method in acetylene chemistry. : Syntheses in the polyeneyne series,R3Si(CC)n(CHCH)4(CC)nSiR3 and H(CC)n(CHCH)4(CC)nH (n = 1, 2)

The Grignard reagents R₃Si(CC)_nMgBr (R = Me, n = 1; R = Et, n = 1,2) couple with cyclooctatetraene dibromide 1 in THF to give, as major products, the silyl-stabilised E, Z, Z, E-polyeneynes, Me₃SiCC(CHCH)₄CCSiMe₃3a, Et₃SiCC(CHCH)₄CCSiEt₃4a and Et₃Si(CC)₂(CHCH)₄(CC)₂SiEt₃6a together with minor proportions of configurational isomers Z, E, Z, Z 3c, all -E 3b, 4b, 6b and compounds in which a bicyclo-octadiene structure 2, 5 and 7 is retained. Irradiation converts the cis(Z)-rich isomers e.g. 3c into the all-trans(E) products. Treatment of the bissilyl compounds 3, 4 and 6 with aqueous base liberates the respective parent polyeneynes, H(CC)_n(CHCH)₄(CC)_nH, in each case.     

1,1′-Binaphthylazepine-based ligands for asymmetric catalysis. Part 2: New aminoalcohols as chiral ligands in the enantioselective addition of ZnEt2 to aromatic aldehydes

The new enantiopure 1,2-aminoalcohols 1b–1h having 1,1′-binaphthylazepine skeleton have been tested as catalytic precursors in the enantioselective addition of ZnEt₂ to benzaldehyde. The best results were seen with ligand 1d, which owes its chirality only to the atropisomerism of the binaphthyl nucleus and does not have any stereogenic carbon atom. In the presence of 1d benzaldehyde was quickly and cleanly transformed to (S)-1-phenylpropanol in 99% yield and 87% e.e. The same ligand was also used in the asymmetric ZnEt₂ addition to other aryl aldehydes giving rise to (S)-1-arylpropanols in almost quantitative yields and e.e.s up to 90%.     

Molybdenum(II)-catalyzed alkylation of electron-rich aromatics with allylic acetates

The molybdenum(II) complex [Mo(CO)₄Br₂]₂ has been found to catalyze allylic substitution with aromatic ethers, e.g., anisole (7), as nucleophiles. The reaction is remarkably para-selective (e.g., 7 + 8 → 11).     

Role of ligand conformation in the structural diversity of copper(II) and silver(I) coordination polymers containing the angular dipyridyl ligand bearing amide spacer

The new dipyridyl ligands N,N′-(methylenedi-p-phenylene)bis(pyridine-4-carboxamide), L1, and N,N′-(methylenedi-p-phenylene)bis(pyridine-3-carboxamide), L2, incorporating amide spacers have been synthesized and reacted with metal salts to give complexes of the types [Cu(L1)₂X₂]_∞ (X = Cl, 1 and X = Br, 2), {[Cu(L1)₂(DMF)](NO₃)₂}_∞, 3, {[Ag₂(L1)₂](SO₄)}_∞, 4, and {[Cu(L2)(DMSO)₂(NO₃)](NO₃)}_∞, 5. All compounds have been characterized by spectroscopic methods and their structures determined by X-ray crystallography.Complexes 1, 2 and 3 form 1-D double-stranded polymeric chains showing rhombic molecular squares with approximate dimensions of 16.95 × 19.13 Å² for 1, 17.03 × 19.06 Å² for 2 and 16.66 × 19.94 Å² for 3. Complex 4 forms infinite 1-D zigzag polymeric chains, which are interlinked through a series of Ag–O interactions to form wavy 1-D ladder like chains, and complex 5 forms 1-D sinusoidal chains. While the L1 ligands in complexes 1, 2 and 3 adopt the cis conformation and that in complex 4 adopts trans conformation, the L2 ligand in complex 5 adopts the trans-anti conformation. The ligand conformations also differ in the dihedral angles between the pyridyl and phenyl rings. All complexes exhibit emissions which may be tentatively assigned as intraligand (IL) π → π* transition.     

A scalable synthesis of (R)-3-(2-aminopropyl)-7-benzyloxyindole via resolution

(±)-3-(2-Aminopropyl)-7-benzyloxyindole 1, assembled from 7-benzyloxyindole 3 in 59% overall yield, is resolved with O,O′-di-p-toluoyl l-(2R,3R)-tartaric acid 7 into (R)-1, a key intermediate of AJ-9677 2 (selective adrenaline β₃-agonist) in 99.5% e.e. and 36% overall yield. The unwanted enantiomer (S)-1 (61.9% e.e.; recovered in 57% yield from the crystallization filtrate) can be reused in another round of resolution after its enantiomeric purity is lowered to 3.7% by Raney Co treatment under a hydrogen atmosphere.     

Interacting blends of Styrenated unsaturated poly (ester–amide)s with commercial unsaturated polyester resin (o-phthalic anhydride based)

Unsaturated poly (ester–amide)s resins (UPEAs) were prepared by the reaction between an epoxy resin, namely diglycidyl ether of bisphenol-A (DGEBA) and unsaturated aliphatic bisamic acids (B_1–4) using a base catalyst. These UPEAs were then diluted by styrene and blended with commercial unsaturated polyester resin (o-phthalic anhydride based) to produce a homogeneous resin. The curing of these Styrenated UPEAs–UPR blends was carried out using Benzoyl peroxide (BPO) as a catalyst and N,N′-Dimethyl aniline (DMA) as a promoter. The glass fiber reinforced composites (i.e. laminates) of these Styrenated UPEAs–UPR (o-phthalic anhydride based) blends were fabricated. The mechanical and chemical resistance properties of the glass fiber composites have also been evaluated. The unreinforced cured samples of the Styrenated UPEAs–UPR (o-phthalic anhydride based) blends were also analyzed by thermogravimetry (TGA).     

Conversion of indole into 3-s-(cysteinyl)indoles and 2-s-(cysteinyl) tryptophans. an approach to tryptathionines

The 3-S-(cysteinyl)indoles 8a and 8b, easily derived (ca 95% yield) from indole and the sulfenyl chlorides 7a and 7b, respectively, have been converted (ca 50%) into oximino derivatives of tryptophan 9a,b. Reduction gave a mixture of two diastereomeric 2-S-(cysteinyl)tryptophan derivatives - i.e. 10 and its H₂N-C(α)epimer - which could be separated. One of these is a derivative of tryptathionine, the characteristic structural element of toxic principles (e.g. Phalloin (5)) of members of the genus Amanita.     

Mono and dinuclear hydrotris(3,5-dimethylpyrazolyl)borato tantalum complexes

In an effort to obtain suitable starting materials, the synthesis and crystal structure of hydrotris(3,5-dimethylpyrazolyl)borato (Tp^Me2) tantalum(III) complexes are reported. Reaction of KTp^Me2 with [TaCl₂(tht)]₂(μ-Cl)₂(μ-tht) (1) (tht=tetrahydrothiophene) gives the X-ray characterized unsymmetrical (Tp^Me2Ta)(TaCl₃)(μ-Cl₂)(μ-tht) (2) in fair yield. This doubly bonded TaTa complex [2.6791(5) Å, diamagnetic, 18e per Ta] is a rare example of an unsymmetrical Ta₂X₆L₃ complex. The X-ray structure of Tp^Me2TaCl₂(PhCCMe) (3) is also reported. It has the (4e)-alkyne in the symmetry plane of the molecule. The trans effects of tht and phenylpropyne are discussed. 1 is inert towards the reaction with a second equivalent of KTp^Me2.     

Selectivite de la reduction de cyclohexen-2 ones par NBu4BH4 dans divers solvants et par NaBH4 dans des conditions de transfert de phase

The 2-cyclohexenone 1 and isophorone 2 reductions with NBu₄BH₄ in aprotic solvents lead to a highly preferential 1–4 attack; i.e. 85% with 1 and 96% with 2 in THF. These regioselectivities are nearly the same as those observed with LiBH₄ in the presence of[2.1.1) cryptand confirming thus the cation influence. This method which is inexpensive and easy to work up, seems to constitute a general way to reduction of α-enones to saturate alcohols while other reagents such as K(sec Bu)₃BH are not able to reduce the carbon-carbon double bond of isophoron.Phase transfer catalysis conditions are not useful for selective reduction: large amounts of allylic alcohols are formed in liquid-liquid phase transfer conditions (60% in toluene-water); a good regioselectivity is only obtained when a cryptand is used as a transfer agent in solid-liquid conditions.     

8-phosphabicyclo[3.2.1]octanes—II: The synthesis and stereochemistry of 8-phosphabicyclo[3.2.1]oct-6-enes

Several new 8-phosphabicyclo[3.2.1]oct-6-enes and -6-en-3-yl acetates were prepared by the alkyl (or aryl)dihalophosphane addition to cyclohepta -1,3-diene and 1-acetoxy cyclohepta-3,5-diene. The P-configuration in two P-epimer pairs (3, 4 and 5, 6) and three other compounds which were each obtained as a single isomer (1, 2 and 7) was determined by investigation of the NMR spectra, i.e. by complexation of the compounds with Eu(dpm)₃ as well as from the various phosphorus-hydrogen coupling constants. Compounds possessing the same P-substituent were correlated among themselves and in the case of the PPh bearing compounds (1 and 7) further correlation to a known compound (8a) was established. The chemical behaviour of the C₆C₇ double bond is discussed and compared with the corresponding behaviour in trop-6-enes. Great steric hindrance was found for this bond, for which the following sequence is suggested:

The synthesis of a phosphaatropine analog is described.     

Dihypersilylstannylene and dihypersilylplumbylene—two Lewis-amphoteric carbene homologues

Dihypersilylstannylene [(Me₃Si)₃Si]₂Sn (1) and dihypersilylplumbylene [(Me₃Si)₃Si]₂Pb (2) are Lewis-amphoteric compounds, i.e. they may behave as Lewis-acid and/or as Lewis-base. Quantum-chemical calculations indicate that their Lewis-acidity is strongly enhanced compared with their diorganyl substituted relatives by the electropositive silyl substituents present. Furthermore silyl substituents are expected to migrate more easily than organyl groups, due to relatively weak ESi bonds formed to the heavier Group 14 congeners (tetrels) leading to different reaction patterns. Here I will give a brief report about our recent investigations on the chemical behavior of the title compounds towards other Lewis-acidic or Lewis-basic or Lewis-amphoteric species.