13C NMR Chemical Shifts and Coupling Constants of Organometallic Compounds

Abstract

Publisher Summary From the time of the first direct observation of a 13 C nuclear magnetic resonance (NMR) signal in 1957 until about 1968, the use of 13 C NMR spectroscopy was in the hands of the few specialists who were prepared to build their own spectrometers. To maximize sensitivity, it is usual to measure 13 C NMR spectra with complete proton decoupling. Correlations in 13 C chemical shifts found for methyl derivatives of organic compounds may apply to organometallic compounds. A number of workers have reported the 13 C NMR spectra of monosubstituted phenyl groups and correlated the shifts with molecular parameters. The large low-field chemical shifts of 362.3 to 253.7 ppm found for metal–carbene complexes are in the region where signals due to carbonium ions are found. The variation in Z eff can account for only a very small fraction of the total change and may even be neglected in most cases. l J( 13 C – l H) has also been related to the C–H bond length and the C–H stretching force constant. The magnitude of the olefin coordination shift appears to approximately correspond to the strength of the olefin–metal interaction, with the smallest coordination shifts being found for the weak silver–olefin complexes, and the largest coordination shift being found for the very strong rhodium–norbornadiene complex [(norbornadiene)Rh(C 5 H 5 )].