Study of stereodynamics by variable-temperature ZVPt NMR spectroscopy. Diastereomerism in platinum(II) thioether complexes and solvent effects
New (PtCl3(thioether)) complexes have been synthesized with the following thioethers as unidentate ligands: N-formyl-DL-homomethionine (FHMetH), N-acetyl-L-methionine (AcMetH), N-acetyl-S-methyl-DL-cysteine (AcMeCysH), DL-3-(methylthio)-1,2-propanediol (MTPD), and DL-3-(methylthio)-2-butanone (MTB). These complexes constitute a series in which the length of the (CH2)/sub x/ chain connecting the chiral carbon and sulfur atoms is varied systematically: x = 3,2,1,1, and 0, respectively. Each of the complexes exists in two diastereomeric forms, which are related by intramolecular inversion of configuration at the coordinated sulfur atom. The diastereomers are clearly evident in the ZVPt NMR spectra, whose dependence on temperature yields the G/sup double dagger/ values for inversion. Stereodynamic processes involving all but the simplest thioether ligands and processes resulting in subtle changes in molecular structure proved intractable by the common H and TC NMR methods. The barrier to inversion depends on the solvating ability of the medium in an interesting way. Small amounts of diglyme in aqueous solution reduce the difference in chemical shifts between the ZVPt NMR peaks of the diastereomers and thus lower the coalescence temperature, but they do not affect the barrier significantly, Large amounts of diglyme, however, lessen the stabilizing effect of hydration upon the thioether complex and lower the barrier. In unidentate complexes, which have flexible structures, the chiral C atom provides virtually no discrimination between the two configurations of the chiral S atom irrespective of the length of the (CH2)/sub x/ chain between the two atoms. Significant discrimination is evident, however, in the bidentate complex cis-(PtCl2(MeCysH)). Steric constraint, such as that provided by chelation, seems to be a prerequisite for chiral discrimination.
- Research Organization:
- Iowa State Univ., Ames
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 6371957
- Journal Information:
- Inorg. Chem.; (United States), Vol. 26:13
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ETHERS
STEREOCHEMISTRY
SYNTHESIS
ORGANOMETALLIC COMPOUNDS
PLATINUM SULFIDES
EXPERIMENTAL DATA
NMR SPECTRA
PLATINUM 195
TEMPERATURE EFFECTS
CHALCOGENIDES
DATA
DAYS LIVING RADIOISOTOPES
EVEN-ODD NUCLEI
HEAVY NUCLEI
INFORMATION
INTERNAL CONVERSION RADIOISOTOPES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
NUCLEI
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PLATINUM COMPOUNDS
PLATINUM ISOTOPES
RADIOISOTOPES
SPECTRA
STABLE ISOTOPES
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
400201* - Chemical & Physicochemical Properties
400202 - Isotope Effects
Isotope Exchange
& Isotope Separation