Preparation and spectroscopic study of functionally substituted cyclopentadienides of thallium(I), potassium, rhodium(I), and iridium(I)

A 13C and 1H n.m.r. study has been carried out on a series of monosubstituted cyclopentadienide compounds of type MI(C5H4X)[M = K or Tl; X = Cl, COMe, CO2Me, CHO, Ph, COCO2Et, or C(CN)C(CN)2]. The different patterns observed for the ring nuclei reflect both the Lewis-acid character of the metal and the electronic effect of the substituent. Fluxional behaviour is observed for K(C5H4COMe). Pseudo-first-order rate constants have been evaluated for hydrogen–deuterium exchange in several of the potassium compounds. The thallium(I) compounds generally exhibit greater synthetic utility than their potassium analogues and several have been used in the synthesis of new [M(η5-C5H4X)(η2-C2H4)2](M = Rh or Ir) complexes. Activation barriers for alkene rotation and mass spectral fragmentation patterns are discussed for these compounds. The 1H n.m.r. spectra found for the cyclopentadienyl ring indicate that the M–ring bonding is not fully delocalised. Analysis of the products resulting from reaction between methyl chloroformate and cyclopentadienide ion confirms the strongly electrophilic character of the former reagent.