59Co second-order quadrupolar effects in the13C cross-polarization magic angle spinning NMR spectra of the cobaltocenium salts [Cp*2Co]+[PF6]− and [Cp*CpCo]+[PF6

Abstract

The cobaltocenium ions [Cp*2Co]+, [Cp*CpCo]+, [Cp2Co]+ and [(EtC5H4)2Co]+ (Cp* = C5Me5; Cp = C5H5) were studied by 13C cross-polarization magic angle spinning NMR spectroscopy. The ring carbon signals of [Cp*2Co]+[PF6]− and [Cp*CpCo]+[PF6]− showed splitting patterns which are a signature of the hitherto unknown 59Co, 13C dipolar coupling. In contrast, a unique signal was found for the remaining cations. The dependence of the patterns on the field, the rotor spinning rate and the temperature was investigated, and full-matrix diagonalization treatment was used to fit the spectra. The patterns were better resolved at lower fields and to some extent at lower spinning rates. Self-decoupling was observed for [Cp*CpCo]+[PF6]− above 360 K. Visual fitting yielded dipolar and indirect isotropic 59Co, 13C coupling constants of 530 and 40 Hz, respectively. When the counter ion of [Cp*CpCo]+ was changed from [PF6]− to Cl− or [TCNE]2− the dipolar coupling pattern was not present, probably because of self-decoupling. Copyright © 1999 John Wiley & Sons, Ltd.