Enantiodifferentiation of a silane and the analogous hydrocarbon by the dirhodium method—silane⋯dirhodium complex interaction

Magnetic Reson in Chemistry

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.

Section: Introductionmentioning

confidence: 99%

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

Magnetic Reson in Chemistry

Sadlej

2013

“…[38][39][40][41][42][43] Chiral, optically pure rhodium tetracarboxylates, usually Mosher's acid derivatives, were used in nuclear magnetic resonance (NMR) spectroscopy as chiral discrimination agents, allowing determining the optical purity of organic ligands. [44][45][46][47][48][49][50][51][52] In some cases, the dirhodium method enabled to determine the configuration, R or S, of a ligand. 53,54 For the above two methods, the sample preparation consists of adding a substrate to the solution of the ligand in question.…”

Section: Introductionmentioning

confidence: 99%

Complexation in situ of 1‐methylpiperidine, 1,2‐dimethylpyrrolidin, and 1,2‐dimethylpiperidine with rhodium(II) tetracarboxylates: Nuclear magnetic resonance spectroscopy, chiral recognition, and density functional theory studies

Sadlej

2021

Chirality

Complexation in situ of 1-methylpiperidine, racemic 1,2-dimethylpyrrolidin, and racemic 1,2-dimethylpiperidine with rhodium(II) tetracarboxylates in chloroform was studied by 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) methods. As substrates, three dirhodium(II) compounds were applied, tetraacetate, tetrakistrifluoroacetate, and a derivative of optically pure Mosher's acid. Due to conformational flexibility, free and complexed ligands can adopt potentially various conformations. The NMR titration experiments revealed the subsequent formation of 1:1 and 1:2 complexes, depending on the molar ratio of substrate to ligand. Conformations of free and complexed ligands were examined by the comparison of experimental and DFT gauge-independent atomic orbital (GIAO) calculated chemical shifts and by the analysis of the internal energy of the compounds. For some ligand and substrate combinations, a mixture of complexes differing in ligand conformations was formed. Complexes of Mosher's acid derivative of rhodium(II) with racemic 1,2-dimethylpyrrolidin and 1,2-dimethylpiperidine exhibited NMR chiral recognition phenomenon, manifested by splitting of signals in 13 C NMR and 1 H, 13 C HSQC spectra.

“…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

Magnetic Reson in Chemistry

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.