Investigating the chemistry of cationic rhodium bisphosphine complexes: comparing reactivity in the solid state with solution

This thesis describes the synthesis and characterisation of a series of cationic rhodium bis-phosphine complexes. The reactivity of these new complexes in the solid-state and in solution is reported. In Chapter 2 the synthesis of a series of rhodium bis-phosphine diene complexes is presented and the reactions of these complexes with hydrogen in the solid-state are investigated. Several examples of zwitterionic complexes coordinating the [BArF4]─ anion are produced by hydrogenation. A rare example of a sigma-alkane complex, [Rh(iBu2PCH2CH2PiBu2)(eta2-CH-eta2-CH-NBA][BArF4]─iBu2PCH2CH2PiBu2)(eta2-CH-eta2-CH-NBE][BArF4] may form as a short lived intermediate prior to the formation of the sigma-alkane complex. The temporal evolution of the solid-state hydrogenation reactions is monitored by powder X-ray diffraction methods. In Chapter 3 the C−X activation of various aryl halides using the [Rh(iBu2PCH2CH2PiBu2)]+ fragment is reported. The 'ligand innocence' of the phosphine with respect to intramolecular C−H activation is also discussed. A rare example of C−X activation in the solid-state is presented, which shows the formation of an isomer that is not observed by analogous solution routes. Chapter 4 investigates solid-state ligand exchange reactions using ethene, butadiene, CO and NH3 gases. A solid-state transfer dehydrogenation reaction is reported within single crystals of [Rh(iBu2PCH2CH2PiBu2)(C2H4)2][BArF4]. H/D exchange of NH3 can also occur in the solid state in the bis-ammonia complex [Rh(iBu2PCH2CH2PiBu2)(NH3)2][BArF4]. A variety of rhodium complexes are tested as heterogeneous catalysts for the hydrogenation of ethene and the isomerisation of butene. In Chapter 5 the binding affinity of a variety of fluorinated arenes to rhodium bis-phosphine fragments is presented using ESI-MS methods. The dependence upon the arene substituents, phosphine substituents and phosphine bite angle are discussed.