DIRECT OBSERVATION OF LOW-SPIN HIGH-SPIN ELECTRONIC GROUND-STATES AND CROSSOVER EXCHANGE IN MANGANOCENE DERIVATIVES, (ETA5-C5H4H)2MN, (ETA5-C5H4CH3)2MN, (ETA5-C5H4C2H5)2MN BY PARAMAGNETIC NUCLEAR-MAGNETIC-RESONANCE

The paramagnetic 1H nmr spectra for manganocene (1) and 1, 1′-dimethylmanganocene (2), and the 13C nmr spectra for 1, 1′-diethylmanganocene (3) have been recorded in toluene solvent over a - 90 to 90°C temperature range. 1 shows a low field and a high field ring proton resonance in its spectrum near - 59°C. At higher temperatures the low field resonance is prevalent and becomes gradually averaged due to a fast spin exchange process that dominates the spectrum at 90°C. For the ring substituted derivatives 2 and 3, resonances due to only one paramagnetic species were detected in the low temperature range. Above ambient temperature a new spectrum due to rapid spin exchange averaging is observed for these complexes. Results are readily interpreted in terms of ground state molecular cross-over exchanges between the 2E2g, 6A1g, and 2A1g spin states of the complexes.