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

Rh(II)-Catalyzed Si-H Insertion with Nosyl-hydrazone-Protected Aryl Donor Diazo Compounds

Dirhodium(II,II) paddlewheel catalysts were evaluated in silyl-hydrogen insertion reactions of aryl diazo compounds generated from o-nosyl hydrazones. The high reactivity of aryl diazo compounds necessitates their in situ generation from sulfonyl-protected hydrazones. Herein, we describe our efforts to evaluate this transformation utilizing Rh(II) catalysts, including those with tethered, axially coordinating ligands. The heteroleptic catalyst, Rh2(OAc)3(2-OX), provided the highest yield of silanes when dioxane was the solvent.

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

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.

Competition of Ester, Amide, Ether, Carbonate, Alcohol and Epoxide Ligands in the Dirhodium Experiment (Chiral Discrimination by NMR Spectroscopy) [1]

Thirty-eight derivatives of 3-hydroxy-2-methylpropanoic acid, each with two different oxygen functionalities, were synthesized and subjected to the standard dirhodium experiment (1H NMR in the presence of an equimolar amount of the chiral dirhodium tetracarboxylate complex Rh*). Their structures represent ester, amide, carbonate, ether, alcohol and/or epoxy groups. Significant selectivity in the binding of those oxygen groups to the complex were determined. From these results, a priority list in binding to a rhodium atom of Rh* was established:

epoxides > primary alcohols > ethers ≥ esters ≥ amides > carbonates > tertiary alcohols

This sequence allows the prediction of the preferred binding site of oxygen-containing groups in polyfunctional compounds, which frequently occur among natural products, and, particularly, in asymmetric synthesis of such compounds. Differentiation of the enantiomers by the dirhodium experiment is easily accomplished due to numerous signal dispersions in nearly all cases.

Adamantanes as spherical nanosondes in adducts with a chiral dirhodium complex-discriminating enantiomers and probing spatial proximities

Three different kinds of substituted chiral adamantane molecules-adamantanones, dioxolanoadamantanes and dithiolano-adamantanes-were studied in the dirhodium experiment (NMR measurement with 1:1 molar mixtures with Rh((II))(2)[(R)-(+)-MTPA](4) in CDCl(3)). Their different behavior in adduct formation is described, and the possibility of determining enantiomeric purities and absolute configurations is explored. Detailed inspection of one- and two-dimensional NMR experiments allowed for an interpretation of steric and electronic intra-adduct interaction showing that the phenyl groups of Rh* tend to enwrap the bound adamantane ligand so that through-space effects over a range of 6-7 Å away from the binding rhodium atom can be observed. Even slight differences in the relative orientation of phenyl groups can be monitored when comparing diastereomeric adducts via NMR signal dispersion.

Experimental verification of diverging mechanisms in the binding of ether, thioether, and sulfone ligands to a dirhodium tetracarboxylate

Complexation of the oxygen atom in 2-butylphenylethers and sulfur in 2-butylphenylthioethers to a rhodium atom in dirhodium tetracarboxylate Rh((II)) (2)[(R)-(+)-MTPA](4) is compared. Oxygen atoms complex via electrostatic attraction exclusively leading to an increase in alpha effects on C-2 complexation shifts in the sequence OCH(3) > F > Br > NO(2). However, that trend is opposite in thioethers. This can be rationalized by an additional highest occupied molecular orbital (HOMO)-LUMO interaction and the response of this interaction upon complex formation shifts. Thereby, an experimental evidence was found for the existence of the HOMO-LUMO binding mechanism which has been proposed previously based on theoretical considerations and indirect spectroscopic evidence. Sulfones hardly bind to Rh((II)) (2)[(R)-(+)-MTPA](4). Diastereomeric dispersion effects at (13)C and (1)H signals can be observed for all compounds indicating that enantiodifferentiation is easy in all classes of functionalities.