Studying reaction intermediates using IR spectroscopy

• Main Author: Batool, Madeeha
• Published: University of Nottingham 2011
• Subjects: 541.39
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555702

Chapter 1: Introduction A brief introduction to TRIR spectroscopy and its application to the study of reactive intermediates of organometallic complexes are provided. Chapter 2: The Photochemistry of Group VII NHC and Phosphine Complexes An introduction to the photochemistry of organometallic N-heterocyclic carbene complexes of the Group VII metals Mn and Re and a comparison with the analogous phosphine complexes is described. The photochemistry of the complexes has been studied using fast time resolved infrared spectroscopy (ns to IlS timescales). This Chapter explains the stability of metal-NHC bonds compared with metal-phosphine. The nature and reactivity of the intermediates of these complexes with alkanes in the presence of CO has been explained by analyzing a range of sterically different NHC complexes. Their rate constants have been determined in different alkane solvents to compare the reactivity of the phosphine and carbene complexes towards different alkanes. Evidence for the formation of agostic complexes is given. Chapter 3: Photochemical and Photophysical Investigation of fac-[Re(L)(COh( u- diimine)]" Complexes (where L = PPh3 or NHC) Rel( c-diimine) carbonyl complexes have great potential to act as infrared probes of DNA. The photophysics and photochemistry of fac-[Re(NHC)(CO))(a-diimine)t III complexes have been investigated by ps- and ns- TRIR spectroscopy. A comparison between both NHC and phosphine substituted Re(a-diimine) complexes is carried out. Moreover, the nature of the solvent and the substituent at the a-diimine has also been altered to study their effects on the energy of the excited states by emission and ns- and ps- TRIR spectroscopies. The 3MLCT excited state is found to be the lowest in energy in the fac-[Re(Iipr2Me2)(CO)3(dppz-F2)t complexes whilst the 3IL remains dominant for the other fac-[Re(Iipr2Me2)(CO)3(dppz)t complexes studied. A theoretical investigation using TD-DFT calculations into these complexes has been performed. Chapter 4: Investigation into the Photochemistry M«CF3hbpy)(COhX (M = Mn, Re and X = Br, Cl) This chapter focuses on the study of isomerization in M«CF3)2bpy)(CO)3X (M = Mn, Re and X = Br, Cl). The mer to fac isomerisation of Mn«CF3)2bpy)(CO)3Br in CH2Cb is investigated at room temperature using FTIR spectroscopy. The use of liquid CO2 at low temperature increases the life time of the intermediate and allows for the characterisation of a CO2-bound dicarbonyl species to be made. For the analogous Re complex, fac-Re«CF3)2bpy)(CO)3Cl, experiments were performed at low temperature in liquid CO2 and liquid CH2F2. Again,fac to mer isomerisation is observed.