NMR Studies of Ruthenium and Rhodium Complexes. In-situ and Ex-situ Photochemistry

Catalytic processes often involve organometallic complexes, the aims of this thesis were to study some specific ruthenium and rhodium complexes using photochemistry. This allowed their behaviour towards small molecules to be investigated since the coordination and activation of small molecules are fundamental parts of catalytic cycles. A further aim was to study suitable complexs with parahydrogen using time-resolved NMR methods with the intention of measuring p-H2 addition and/or the evolution of the p-H2-derived singlet state
The photochemistry of CpRh(CH2CHSiMe3)2 (2.1), CpRh(COE)2 (2.2) and CpRh(COD) (2.3) with DMSO PhSOMe, trimethylvinylsilane and triethylsilane was probed. The photoactivity of 2.3 proved minimal with the main products being associated with the loss of the COD ligand. By contrast, 2.1 and 2.2 undergo the substitution of one or both of the alkene ligands, depending on the nature of the reacting ligand. Complexes 2.1, CpRh(CH2CHSiMe3)(DMSO) (2.4) and CpRh(P*Ph)(C2H4) (3.2) were deemed suitable for time-resolved studies with p-H2. 2.1 was found to form the expected dihydride (3.1) on a 50 ms timescale. 2.4 was also formed 3.1 but its PHIP enhancement was poor and whilst 3.1 did form the expected dihydride product PHIP was not observed.
[Ru(H)2(CO)(PPh3)(Xantphos)] 5.1 was also synthesised and its reactivity towards a range of small molecules, which included DMSO, CO, ethene and Et3SiH, investigated. These studies revealed that its H2, CO and PPh3 ligands could all be lost photochemically and that the xantphos ligand could switch between κ2-PP and κ3-POP coordination. Time-resolved NMR studies on 5.1, with p-H2, found the H2 addition to the intermediate to occur with a rate of the order of 0.5 s−1. cis-[Ru(H)2(dppp)2] 6.1 was also studied using time-resolved NMR, in this case the rate of H2 addition was faster than the NMR timescales. This allowed the evolution of the p-H2 singlet state to be probed and shown to be as a function of the difference in scalar coupling between the hydrides and the equatorial 31P nuclei.