title: Stereodynamics in eight-coordination; a 2D NMR spectroscopic and computational study of the exchange process in ThCl4(Me2NCH2CH2NMe2)2.
abstract: The (13)C{(1)H} NMR spectrum of eight-coordinate ThCl(4)(tmed)(2), where tmed = Me(2)NCH(2)CH(2)NMe(2), shows that two isomers are present at 219.8 K in a ratio of ≈8:1 and inversion of the five-membered Th-tmed ring is slow at this temperature in both isomers. The 2D (13)C{(1)H} exchange spectroscopy (EXSY) spectrum shows that each of the two inequivalent methyl groups of the major isomer does not exchange directly with each other but that they both exchange with both of the two inequivalent methyl groups found in the minor isomer. This implies that interconversion of the two enantiomers of the major isomer proceeds by a stepwise process that involves the minor isomer. The interconversion of the isomers involves a ring-inversion process that may proceed with or without Th-N bond breaking, and the NMR spectra cannot distinguish between these two processes nor can density functional theory (DFT) calculations (B3PW91 and M06 with consideration of dispersion effects and solvent) because these two possibilities proceed by way of transition states of similar energies in this case.
authors.affiliation: School of Chemistry, University of New South Wales (UNSW), Sydney, New South Wales 2052, Australia. g.ball@unsw.edu.au
authors.forename: Graham E
authors.initials: GE
authors.lastname: Ball
authors.forename: Richard A
authors.initials: RA
authors.lastname: Andersen