Yu. K. Grishin

ortho-palladated α-phenylalkylamines for enantiomeric purity determination of monodentate P∗-chiral phosphines

Abstract Three ortho-palladated complexes were tested as chiral derivatizing agents for enantiomeric excess determination of monodentate P∗-chiral phosphines by 31P NMR analysis. The complexes containing a bulky substituent at the α-C∗- 1e or an N∗-stereocentre 1d are shown to be more efficient as compared to known N-achiral α-methyl substituted analogues. The structure and stereochemistry of the new dimeric complex (S C )- 1 e was established by X-ray analysis.

Nuclear magnetic resonance spectroscopy of metal cyclopentadienyls IV.13C NMR spectra of σ-cyclopentadienyl compounds of silicon, germanium and tin

Abstract 13 C NMR spectra of silicon, germanium and tin cyclopentadienyl compounds have been studied. 13 C chemical shifts and J ( 13 C H) constants verify the σ-structure of the compounds. The variation of the 13 C NMR spectrum of C 5 H 5 Ge(CH 3 ) 3 with temperature shows that a fast metallotropic rearrangement occurs in this compound at as low a temperature as 20° 13 C NMR data are discussed with reference to the structure of metal cyclopentadienyls.

Dynamic 13C N.M.R. studies

The 13C nuclear magnetic resonance technique has been applied to dynamical processes occurring in a number of compounds for which a 1H study would be difficult, owing to complications in the proton spectra. Simple 13C signals in the proton-decoupled spectra are very convenient. The 13C line shapes at various temperatures have been analysed, to give the activation barriers to rotation around the C-N bond in stereoisomeric 2-phenylcyclopropanecarboxylic acid N,N-diethylamides (ΔH ‡ = 16·7 ± 0·5 kcal/mole, ΔS ‡ = -0·6 ± 1·6 e.u. for the trans isomer; ΔH ‡ = 18·4 ± 0·6 kcal/mole, ΔS ‡ = 2·8 ± 1·9 e.u. for the cis isomer), around the Ar-N(O) bond in p-nitroso-N,N-dimethylaniline (ΔH ‡ = 14·5 ± 0·6 kcal/mole, ΔS ‡ = 4·0 ± 2·0 e.u.), around the C-C bond in 9-chloromethyltriptycene (ΔH ‡ = 13·5 ± 0·7 kcal/mole, ΔS ‡ = -1·8 ± 2·5 e.u.) and to the nitrogen inversion in N-(1,2-dicarbomethoxyethyl)-aziridine (ΔH ‡ = 21·8 ± 0·9 kcal/mole, ΔS ‡ = 10·6 ± 3·6 e.u.).

The alkoxides of zirconium and hafnium: direct electrochemical synthesis and mass-spectral study. Do “M(OR)4”, where M=Zr, Hf, Sn, really exist?

The direct electrochemical synthesis of zirconium (1a) and hafnium (1b) alkoxides, M(OPri)4·PriOH, Zr(OBui)4·BuiOH (4a) and M(OR)4, where R=Et (2a,b), Bun (3a), Bus (5a), C2H4OMe (6a,b) has been carried out by anodic oxidation of metals in anhydrous alcohols in the presence of LiCl as a conductive additive to give quantitative yields. The solubility polytherms and dissociation pressure of1a,b have been investigated. It has been proved by means of chemical analysis, X-ray powder, and IR spectral studies that the desolvation of 1a,b and Sn(OPri)4·PriOH (1c) is accompanied by the formation of amorphous oxocompounds M3O(OPri)10. On the basis of1H NMR data it has been proved that the structure of the latter is analogous to that of known triangular cluster molecules M3(μ3-O)(μ3-OR)(μ-OR)3(OR)6, where M=Mo, W, U. Mass-spectral data and the determined physicochemical characteristics of1–5 permit to conclude that the samples of composition M(OR)4, where M=Zr, Hf, and2,3,5 contain tri- and tetranuclear oxocomplexes M3O(OR)10 and M4O(OR)14 respectively, along with Zr(OR)4 oligomers of different molecular complexity.

Stereospecific co-crystallization of reactant and palladium complex in the resolution of stilbendiamine using N*-chiral ortho-palladated matrix

Abstract Resolution of racemic 1,2-diphenyl-1,2-ethanediamine was performed through recrystallization of its diastereomeric adducts 2a , b with N*-chiral ortho -palladated complex ( S C R N )- 1 . The structure and absolute configuration of the less soluble ( S C R N , SS )- 2a diastereomer was determined by X-ray diffraction. The complex has an unusual dimeric structure with a palladacycle:diamine ratio of 2:3; the association of 2a with an additional diamine molecule of the same ( SS ) absolute configuration is achieved due to hydrogen bonds between the coordinated and solvate diamine.

Nuclear magnetic resonance spectroscopy of metal cyclopentadienyls VII. A criterion for distinguishing the π- and σ-structures based on an analysis of 13CH satellites in the PMR spectra

The 13CH satellite magnetic resonance spectrum of cyclopentadienyltrimethyltin has been obtained. Its analysis enables the two J(HH) coupling constants J1 and J2 to be determined. If it is assumed that this molecule is fluxional, these two experimentally measured constants may be averaged over six independent constants in a rigid AA′BB′X(C5H5) system. By taking four coupling constants, averaged from the literature data, it is possible to estimate the two most important constants J(AX) and J(BX). On the other hand, comparing the values J1 and J2 for the compound C5H5Sn(CH3)3 with the respective values for other fluxional σ-cyclopentadienyls, taking averaged values of the appropriate couplings in rigid systems together with the values of J1 and J2 in π-complexes, it is possible to choose a criterion for distinguishing between π- and σ-structures. Other criteria (1H and 13C chemical shifts, H13C, M-H coupling constants where M is magnetic isotope of a metal) are discussed.

Proton-coupled 13C NMR spectra of cyclopentadiene

Abstract The complete high-precision analysis of proton-coupled 13C NMR spectra of cyclopentadiene is presente. The coupling constants J( 13 CH ) in cyclopentadiene are discussed in comparison with the data previously reported for five-membered heterocycles.

Phosphonium-iodonim ylides in nucleophilic substitution reactions

Properties of mixed phosphonium-iodonium ylides were investigated, and the compounds were shown to be capable to behave as O-nucleophiles in nucleophilic substitution reactions.

NEW HOMOCHIRAL ORTHO-PALLADATED MATRIX BEARING A BULKY SUBSTITUENT AT THE CARBON STEREOCENTER

A new homochiral dimericortho-palladated complex bearing a bulkytert-butyl substituent at the carbon stereocenter was synthesized from optically activeN,N-dimethyl-α-tert-butylbenzylamine. Regioselective activation of only the aromatic C−H bond was shown to occur during the cyclometallation process proceeding under very mild conditions due to steric effects. Spectral characteristics of mononuclear derivatives of the new dimeric complex indicate that the five-membered palladacycle exists predominantly in one of two possible chiral conformations with the axial position of thetert-butyl substituent.

Synthesis and structure of mixed phosphonium-iodonium ylide

A mixed phosphonium-iodonium ylide, phenyliodoniumethoxycarbonylmethylenetriphenylphosphorane borofluoride, was synthesized. Its structure was established by means of X-ray diffraction analysis. Temperature dependence of 1H, 13C, and 31P spectra of the ylide synthesized was investigated. A dynamic equilibrium between Z and E-isomers was observed.