Enantiodifferentiation of polyethers by the dirhodium method. Part 2: Cyclotriveratrylenes and cryptophanes

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Complexation of the oxygen atom in 2-butyl phenyl ethers to a rhodium atom of the dirhodium tetracarboxylate Rh(II) 2[(R)-(+)-MTPA]4(Rh*, MTPA-H = methoxytrifluoromethylphenylacetic acid identical with Mosher's acid) deshields an sp3-hybridized 13C nucleus directly bonded to the ether oxygen; apparently, the inductive effect of the oxygen is enhanced when it is complexed to the rhodium atom. On the other hand, deshielding complexation shifts of aromatic ipso-carbons (alpha-positioned) are minute but ortho- and para-carbon signals are influenced by the resonance effect of oxygen. This effect can be modulated by further substituents at the benzene ring. In turn, this modulation of the resonance correlates linearly ith the magnitude of the inductive effect exerted on the aliphatic alpha-carbon atoms. Diastereomeric dispersion effects at 13C signals can be observed for most compounds, indicating that enantiodifferentiation is possible in this class of ethers.

“…[5,18] As tested for 1, other molar ratios, e.g. 2.5 : 1, afford practically the same NMR spectroscopic results.…”

Section: Complexation Shifts ( δ) Of the 2-butyl Phenyl Ethers 1-4csupporting

confidence: 54%

Section: Introductionmentioning

confidence: 90%

Section: Enantiodifferentiation By 13 C and 1 H Signal Dispersion ( ν)mentioning

confidence: 99%

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Origin of ¹³C complexation shifts in the adduct formation of 2‐butyl phenyl ethers with a dirhodium tetracarboxylate complex

Gómez

Duddeck

2007

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“…These salts act as chiral recognition agents. By this, one could determine either the optical purity of a compound or, in certain cases, its absolute configuration . For the proper application of dirhodium methods, it is essential to know the plausible adduct structures and the details of complexation processes.…”

Section: Introductionmentioning

confidence: 99%

Complexation of rhodium(II) tetracarboxylates with aliphatic diamines in solution: ¹H and ¹³C NMR and DFT investigations

Jaźwiński

Sadlej

2013

The complexation of rhodium(II) tetraacetate, tetrakistrifluoroaceate and tetrakisoctanoate with a set of diamines (ethane-1,diamine, propane-1,3-diamine and nonane-1,9-diamine) and their N,N'-dimethyl and N,N,N',N'-tetramethyl derivatives in chloroform solution has been investigated by (1) H and (13) C NMR spectroscopy and density functional theory (DFT) modelling. A combination of two bifunctional reagents, diamines and rhodium(II) tetracarboxylates, yielded insoluble coordination polymers as main products of complexation and various adducts in the solution, being in equilibrium with insoluble material. All diamines initially formed the 2 : 1 (blue), (1 : 1)n oligomeric (red) and 1 : 2 (red) axial adducts in solution, depending on the reagents' molar ratio. Adducts of primary and secondary diamines decomposed in the presence of ligand excess, the former via unstable equatorial complexes. The complexation of secondary diamines slowed down the inversion at nitrogen atoms in NH(CH3 ) functional groups and resulted in the formation of nitrogenous stereogenic centres, detectable by NMR. Axial adducts of tertiary diamines appeared to be relatively stable. The presence of long aliphatic chains in molecules (adducts of nonane-1,9-diamines or rhodium(II) tetrakisoctanoate) increased adduct solubility. Hypothetical structures of the equatorial adduct of rhodium(II) tetraacetate with ethane-1,2-diamine and their NMR parameters were explored by means of DFT calculations.

“…There are two NMR methods based on the ability of dirhodium salts to the formation of axial adducts. The first method makes use of optically pure rhodium(II) tetracarboxylates (usually Mosher's acid salts) as chiral recognition agent and is designed to the determination of optical purity of chiral compounds by NMR methods . The second application allows one to establish the compound configuration ( R or S ) by NMR spectroscopy .…”

Section: Introductionmentioning

confidence: 99%

Adducts of nitrogenous ligands with rhodium(II) tetracarboxylates and tetraformamidinate: NMR spectroscopy and density functional theory calculations

Cmoch

Głaszczka

Jaźwiński

et al. 2013

Complexation of tetrakis(μ2-N,N'-diphenylformamidinato-N,N')-di-rhodium(II) with ligands containing nitrile, isonitrile, amine, hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups has been studied in liquid and solid phases using (1)H, (13)C and (15)N NMR, (13)C and (15)N cross polarisation-magic angle spinning NMR, and absorption spectroscopy in the visible range. The complexation was monitored using various NMR physicochemical parameters, such as chemical shifts, longitudinal relaxation times T1 , and NOE enhancements. Rhodium(II) tetraformamidinate selectively bonded only unbranched amine (propan-1-amine), pentanenitrile, and (1-isocyanoethyl)benzene. No complexation occurred in the case of ligands having hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups, and more expanded amine molecules such as butan-2-amine and 1-azabicyclo[2.2.2]octane. Such features were opposite to those observed in rhodium(II) tetracarboxylates, forming adducts with all kind of ligands. Special attention was focused on the analysis of Δδ parameters, defined as a chemical shift difference between signal in adduct and corresponding signal in free ligand. In the case of (1)H NMR, Δδ values were either negative in adducts of rhodium(II) tetraformamidinate or positive in adducts of rhodium(II) tetracarboxylates. Experimental findings were supported by density functional theory molecular modelling and gauge independent atomic orbitals chemical shift calculations. The calculation of chemical shifts combined with scaling procedure allowed to reproduce qualitatively Δδ parameters.