Diastereomers Of Complex Research Articles

Chiral Recognition of Diketopiperazine Cyclo(Pro-Gly) and Propranolol Using (-)-Epigallocatechin-3-O-gallate.

In the (1)H-NMR spectrum of a solution containing an equimolecular amount of cyclo(L-Pro-Gly), cyclo(D-Pro-Gly) and (-)-epigallocatechin-3-O-gallate (EGCg) in a D2O, a difference in the chemical shift of (1)H-NMR signal for H7α, H7β,8α of the Pro residue was observed. Judging from the crystal structures of the 2 : 2 complexes of EGCg and cyclo(L-Pro-Gly), cyclo(D-Pro-Gly), the difference in the chemical shift resulted mainly from a magnetic anisotropic shielding effect by the ring current from the B ring of EGCg. Therefore, it was considered that chirality of cyclo(Pro-Gly) was recognized by EGCg in the D2O solution. Furthermore, in the (1)H-NMR spectrum of a solution containing an equimolecular amount of racemic propranolol ((R)- and (S)-propranolols) and EGCg in D2O, the (1)H-NMR signal for H2 of the naphthalene group was observed as two doublets, suggesting that the racemic propranolol formed diastereomers of complexes with EGCg; as a result, chirality of propranolol was recognized by EGCg in the D2O solution.

Stereocontrolled monoalkylation of mixed-ring complex CpCp′ZrCl2 (Cp′ = 1-neomenthyl-4,5,6,7-tetrahydroindenyl) by lithium, magnesium and aluminum alkyls

The monoalkylation of mixed-ring complex η5-cyclopentadienyl-η5-(1-neomenthyl-4,5,6,7-tetrahydroindenyl)zirconium dichloride (CpCp′ZrCl2) by lithium, magnesium and aluminum alkyls has been studied by the means of NMR spectroscopy. It is shown the reaction of CpCp′ZrCl2 with 1 eq. of RLi (R = Et, nBu) at −78 °C in toluene gives the chiral-at-zirconium complexes CpCp′ZrRCl with epimer ratio 12:1. The use of Grignard reagent (EtMgBr) reduces the epimer ratio to 3:1. The reaction of CpCp′ZrCl2 with AlEt3 in the same conditions yields two diastereomers of complex [CpCp′ZrEt(μ-Cl)·AlEt3] in a ratio 1.6:1, followed by five-membered bimetallic hydride complex [CpCp′Zr(μ-H)(CH2CH2AlEt2] with diastereomeric ratio 10:1.Cyclohexyl isocyanide (CyNC) insertion into the Zr-R bond of CpCp′ZrRCl provides the corresponding η2-iminoacyl complexes CpCp′ZrC(R) = N(Cy)(Cl) (R = Et, nBu), which were characterized by NMR, IR spectroscopy and mass-spectrometry (MALDI/TOF).

Polymerization of ethene with zirconocene catalysts: an experimental and quantum chemical study of the influence of para-substituent in benzyl in bis{η 5-(1-benzyl)indenyl}zirconium dichlorides

The meso- and rac-like isomers of bis{η 5-(1-benzyl)indenyl}zirconium dichloride ( 5), bis{η 5-(1- para-methoxybenzyl)indenyl}zirconium dichloride ( 6), bis{η 5-(1- para-fluoro-benzyl)indenyl}zirconium dichloride ( 7) and bis{η 5-(1-phenylethyl)indenyl}zirconium dichloride ( 8) were synthesized and isolated. Solid-state structures of meso- and rac-like 5 were determined by X-ray structure analysis. Polymerization properties of the methylaluminoxane (MAO) activated diastereomers of complexes 5– 8 were studied in ethene polymerizations under different monomer concentrations. The rac-like isomer of 1-phenylethyl-substituted 8/MAO showed significantly higher activity than the 1-benzyl substituted analogs 5– 7/MAO. In addition, rac- 8/MAO behaves like a single center catalyst producing polyethene with narrow molar mass distribution (1.8–1.9), while diastereomers of 5– 7/MAO produce polymers with molar mass distributions varying from 2.7 up to 10.3. The rac and meso-like isomers of 5– 7/MAO have different response on the monomer concentration. Quantum chemical calculations suggest a strong interaction between the benzyl substituent and the electron deficient zirconium center. The phenyl metal coordination energies depend on the electronic properties of the para-substituent. In 8/MAO, due to the ethyl spacer, the coordination does not have a significant role and therefore much higher activity and single center polymerization behavior is observed.

Reaction of complex ligands: Part 95. Chromium tricarbonyl complexes of polysubstituted naphthohydroquinones: regioselective synthesis via [3+2+1]-benzannulation and haptotropic rearrangement

A series of polysubstituted naphthohydroquinoid tricarbonyl chromium complexes were prepared by chromium mediated [3+2+1]-benzannulation of Fischer-type carbene complexes with alkynes. The kinetics and the thermodynamic data of the η 6-η 6-haptotropic rearrangements were investigated by in-situ NMR spectroscopy. The free activation energies Δ G # range from 23 to 26 kcal mol −1 and only slightly depend on the bulk and the donor/acceptor properties of the substituents. Equilibrium of metal migration was observed for naphthohydroquinone complexes bearing methoxy substituents at the non-hyroquinoid ring (ring A). In complexes bearing methyl groups or only hydrogen substituents at ring A the haptotropic rearrangement is irreversible. An NMR study suggests that the rearrangements of menthyloxy substituted tricarbonyl chromium complexes in hexafluorobenzene occurs intramolecularly. The two diastereomers of complex 19 show different rate constants for the metal shift which is the first example of kinetic data differing for the rearrangement of a ML n -fragment in two diastereomeric compounds.

Synthesis, properties, stereochemistry and crystal structures of diastereomeric benzene–ruthenium(II) complexes with a chiral salicylideneaminato ligand

The reaction of [{Ru(η6-C6H6)Cl2}2] with the sodium salt of (S)-N-(1-phenylethyl)salicylideneamine (HL–L) in CH2Cl2 led to a diastereomer mixture of (RRu,SC)- and (SRu,SC)-[Ru(η6-C6H6)(L–L)Cl]1a and 1b, in a ratio of 86 : 14. Mediated by AgPF6 in acetone at –30 to –35 °C, the chloride ligand in 1a/1b was substituted by 4-methylpyridine (4Me-py), 2-methylpyridine (2Me-py) or triphenylphosphane (PPh3) to give the two diastereomers 2a/2b of [Ru(η6-C6H6)(L–L)(4Me-py)]PF6, the pure diastereomer 3 of [Ru(η6-C6H6)-(L–L)(2Me-py)]PF6 and the two diastereomers 4a/4b of [Ru(η6-C6H6)(L–L)(PPh3)]PF6. At room temperature in [2H6]acetone, under equilibrium conditions, the diastereomer ratio 2a : 2b was 67 : 33, 3 was diastereomerically pure and the ratio 4a : 4b was 93.4 : 6.6. Variable-temperature 1H NMR spectroscopy of complexes 2a/2b and 4a/4b from –80 °C to room temperature demonstrated configurational lability of the ruthenium configuration. Since equilibration occurred during reaction and work-up, the ruthenium configuration was not retained in the substitution reactions. Diastereomer 2a was obtained diastereomerically pure by crystallisation. The diastereomers 4a and 4b were separated and examined by variable-temperature NMR spectroscopy. The crystal structures of the (RRu,SC) diastereomer of complex 1 and of the thermodynamically more stable (RRu,SC) diastereomers 2a and 4a″ were determined by X-ray analysis. A conformational analysis based on the NMR spectroscopic results showed that two main factors govern the orientation of the 1-phenylethyl group relative to the [Ru(η6-C6H6)(L–L)L′] moiety (L′= Cl, 4Me-py, 2Me-py or PPh3): (i) the face-on orientation of the phenyl substituent with respect to the π-bonded aromatic benzene ligand and (ii) the steric demand of the unidentate ligands with respect to the 1-phenylethyl group.

Six-membered cyclometallated derivatives of platinum(II) derived from 2-benzylpyridines. Crystal and molecular structure of [Pt(L)(Ph 3P)Cl] (HL = 2-(1-methylbenzyl)pyridine)

The reaction of K 2[PtCl 4] with 2-(1-methylbenzyl)pyridine, HL, and 2-benzylpyridine, HL', affords the cyclometallated species [{Pt(L)Cl} 2] ( 1) and [{Pt(L')Cl} 2] ( 2), respectively. The chloride bridge in complex 1 can be split by neutral or anionic species to give the monomeric, [Pt(L)(Ph 3P)Cl], as two isomers, trans-P-Pt-C ( 3) and trans-P-Pt-N, ( 4), [Pt(L)(py)Cl] ( 5), [Pt(L)(CO)Cl] ( 6), [Pt(L)(CNCH 2SO 2C 6H 4CH 3-4)Cl] ( 7), [Pt(L)(acac)] (Hacac = 2,4-pentanedione) ( 8), [Pt(L)(dppm)][BF 4] (dppm = bis(diphenyl-phosphino)methane) ( 9), [Pt(L)(dppe)][BF 4] (dppe = bis(diphenylphosphino)ethane) ( 10) and [Pt(L)(dipy)][BF 4](dipy = 2,2'-dipyridine) ( 11). Similarly, compound 2, by reaction with Ph 3P, affords [Pt(L')(Ph 3P)Cl], as two isomers, trans-P-Pt-C ( 12) and trans-P-Pt-N ( 13). Reaction of compounds 1 or 4 with AgBF 4 in acetonitrile affords [Pt(L)(CH 3CN) 2 IBF 4] ( 14) or [Pt(L)(Ph 3P)-(CH 3CN)][BF 4] ( 15). From these, [Pt(L)(Ph 3P) 2][BF 4] ( 16), [Pt(L)(Ph 3P)(CO)][BF 4] ( 17) and [Pt(L)(Ph 3P)(py)][BF 4] ( 18), can be obtained by displacement of the coordinated acetonitrile. The new complexes were characterized by IR, 1H and 31P NMR and FAB-MS spectroscopic techniques. The NMR spectra at room temperature of most of the species derived from HL give evidence for the presence in solution of two diastereomers a and b. The structure of one diastereomer of complex 4 has been solved by single crystal X-ray diffraction, 4b. The platinum atom is in an almost square planar geometry with a P-Pt-N trans arrangement: Pt-N = 2.095(3), Pt-C = 1.998(4), Pt-P = 2.226(1) and Pt-Cl = 2.400(1) Å. The six-membered cyclometallated ring is in a boat conformation, with the CH 3 group in an equatorial position, i.e pointing away from the metal. Attempts to obtain [{Pt(L″)Cl} 2] (HL″ = 2-(dimethylbenzyl)pyridine), afforded an insoluble product heavily contaminated by platinum metal; treatment of this crude material with Ph 3P gave [Pt(L″)(Ph 3P)Cl] ( 19).

Reactions of coordinated phosphines and arsines. Stereoselective reactions at the fluoroarsine-as stereocentre in the complex [(R*),(R*,R*)]-(±)-[(η 5- C 5H 5) {1,2-C 6H 4(PMePh) 2} Fe(AsFMePh)]PF 6 · CH 2Cl 2

The reaction of (±)-AsFMePh, freshly prepared from (±)-AsBrMePh and AgF in acetone, with ( R*, R*)-(±)-[η 5-C 5H 5){ 1,2-C 6H 4 (PMePh) 2}Fe(NCMe)]PF 6 in boiling dichloromethane affords a separable mixture of two diastereomeric iron complexes, epimeric at arsenic, viz. [( R*),( R*, R*)]-(±)- and [( S*),( R*, R*)]-(±)-[(η 5-C 5H 5-{1,2-C 6H 4 (PMePh) 2}Fe(AsFMePh)]PF 6, with the diastereomeric ratio( R*),( R*, R*)/( S*), ( R*, R*) = 3:1. The major diastereomer of the complex crystallizes as a 1 : 1-dichloromethane solvate, the crystal structure of which has been determined. The minor ( S*),( R*, R*) diastereomer crystallizes from acetone/diethyl ether as a 1 : 1 acetone solvate. Reactions of the two diastereomers with RMgBr (R=1cr; Bn or Et) are stereospecific giving the corresponding tertiary arsenic complexes with predominant inversion of configuration at arsenic. Hydrolysis of either diastereomer of the fluoroarsine complex affords the corresponding hydroxyarsine (arsinous acid) derivative stereospecifically with complete inversion at arsenic.