Multisite Magnetization Transfer Studies of Metal Migration in (η³-C₇H₇)Re(CO)₄, (η³-C₇H₇)Os(CO)₃SnPh₃, (η³-C₇H₇)Re(CO)₃PMe₃, (η⁵-C₇H₇)Re(CO)₃, (η⁵-C₇H₇)Fe(CO)₂SnPh₃, (η⁵-C₇H₇)Os(CO)₂SnPh₃, and (η^5<

Abstract

Multisite magnetization transfer (MMT) studies of metal migration around the C7H7 rings in (η3-C7H7)Re(CO)4 (1), (η3-C7H7)Os(CO)3SnPh3 (2), (η3-C7H7)Re(CO)3PMe3 (3), (η5-C7H7)Re(CO)3 (4), (η5-C7H7)Fe(CO)2SnPh3 (5), (η5-C7H7)Os(CO)2SnPh3 (6), and (η5-C7H7)Ru(CO)2SnPh3 (7) are reported. The possible presence of 1,2-, 1,3-, and/or 1,4-metal shifts in the ring fluxionality was investigated in all compounds, and it was shown that both 1,2- and 1,3-shifts occur concurrently in 5 and 6, but that only 1,2-shifts occur in 1, 2, 3, and 4, and only 1,3-shifts in 7. Several of the compounds exist as mixtures of isomers, and the application of MMT was crucial in unraveling the fluxionality of one isomer in the presence of the other. Thus, MMT experiments allowed the study of the rate of metal migration in the symmetric isomer of 2, which occurs in the presence of more rapid exchange in the asymmetric isomer. The symmetric isomer of 3 was found to exchange faster than the asymmetric isomer. MMT study of the exchange between symmetric and asymmetric isomers of 7 at low temperatures showed that the two enantiomers of the asymmetric isomer exchange directly with the symmetric isomer, but not with each other. MMT experiments allowed the study of metal migration in 7 in the presence of the isomer interchange process. The rate constants and free energies of activation for the metal shifts and for the isomer interchange are reported. It was concluded that orbital symmetry considerations do not provide useful predictions about the mechanisms of metal migration in compounds containing η1-, η3-, or η5-C7H7 rings.

Elucidating the Mechanism of Reversible Oxiranations via Magnetization Transfer Spectroscopy

“…This one-dimensional NMR technique involves the monitoring of a nucleus undergoing chemical exchange as it relaxes from a selective 180° pulse. While magnetization transfer has been previously utilized in biological, organometallic, and other physical chemistry studies, it has not been employed to study C–C bond forming reactions to the best of our knowledge.…”