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

Abstract

A ¹³C and ¹H n.m.r. study has been carried out on a series of monosubstituted cyclopentadienide compounds of type M^I(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.