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 (η5-C7H7)Ru(CO)2SnPh3

Elucidating the mechanism of reversible oxiranations via magnetization transfer spectroscopy

The reversible [2 + 1] cycloadditions between an N,N'-diamidocarbene (DAC) and eight aldehydes were examined using NMR spectroscopy. Variable temperature magnetization transfer experiments revealed higher exchange rates and lower activation barriers when electron-deficient aldehydes were employed. Likewise, competitive equilibrium studies indicated a thermodynamic preference for electron-deficient aryl and sterically unhindered alkyl aldehydes compared to more electron-rich or bulkier substrates. Collectively, these and other data collected were consistent with the oxiranation process proceeding in an asynchronous manner.