Expanded ring carbenes - Synthesis, coordination and catalysis

• Main Author: Alonso, Manuel Iglesias
• Published: Cardiff University 2008
• Subjects: 547.59
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.584318

The work presented in this thesis is mainly concerned with the synthesis, metal coordination and applications of expanded (larger than five-membered) N-heterocyclic carbenes. Chapter two describes the spectroscopic and solid state properties of novel 7-membered carbenes and their parent azolium salts bearing a simple or substituted butane backbone with Cy, /-Pr, DIPP, Mes, Xyl and o-Tol N-substituents. A new method for the synthesis of saturated azolium salts, using K2CO3 as a mild base for the deprotonation of the corresponding formamidines, reacted with di-electrophiles under aerobic conditions, is also presented. In chapters three and four the syntheses, solid-state and solution studies of their silver, rhodium, iridium and platinum complexes are discussed. Expansion of the ring provides carbenes with N-Cnhc-N angles close to the sp2 angle (120 ), which consequently forces the N-substituents to bend towards the metal centre. Additionally, expanded carbenes were found to be more basic than their five-membered analogues. Chapter five describes the synthesis of seven-membered azolium salts with an alkenic function in the C(5)-C(6) position. The olefinic backbone was further functionalised by Diels-Alder reaction with cyclopentadiene. The rhodium complexes, Rh(NHC)(CO)acac , of these carbenes are also presented in this chapter. The greater donor abilities and wide NCN angles of the expanded carbenes make them interesting candidates for the study of their catalytic applications. In the sixth chapter results are presented from the catalytic performance of 7-NHC rhodium and iridium complexes in the transfer hydrogenation of ketones. The rhodium complexes of 5-, 6- and 7-membered carbenes were also tested as catalysts in olefin hydrogenation reactions with molecular hydrogen.