Reactions of pentadienyl iron tricarbonyl complexes and related systems

Reactions of coordinated ligands in two organometallic systems are examined. Part I describes the work carried out on (diene)-, and (dienyl)-iron tricarbonyl complexes. Properties of [pi]-enyl palladium II compounds are described in Part II.In Part I, the preparation and properties of the open-chain (dienyl) iron tricarbonyl cations are examined using kinetic methods. The formation of (1-methyl, 5-phenyl) P. I. T. from the two diastereoisomers of (6-phenyl hexa-3,5-dien-2-ol) iron tricarbonyl is shown to be much slower with the endo isomer than with the exo isomer at room temperature. At low temperature, each isomer generates a different cationic species. The kinetic behaviour and products formed in this system are shown to be consistent with the involvement of trans ion intermediates.The significance of the trans ion species is also demonstrated in the reactions of a series of substituted P. I. T. cations with arenes and with alcohols. The rate law observed for each reaction is shown to be dependent on both the nature and position of substituents on the dienyl system as well as the nucleophile. A mechanism consistent with the kinetic behaviour is discussed in terms of the role of the trans ion.The (diene)- and (dienyl)-iron tricarbonyl systems are also examinedby use of H, and C nmr together with i. r. and Mossbauer spectroscopic techniques. It is suggested that the charge on the dienyl complex is delocalised throughout the molecule from a comparison of the two systems.In Part II, the stability of 4-substituted (but-2-enyl) palladium II complexes in acid solution is shown to be decreased if the chloro-bridge is replaced by a group V ligand. The decomposition is also controlled by the ease of departure of the leaving group at the 4-position. The nmr spectra of the [pi]-enyl compounds are temperature dependent and indicate that [pi],[sigma]-transitions can occur.