NMR studies of the thermal and photochemical reactions of cyclopentadienyl ruthenium complexes

The research reported in this thesis primarily focuses on the thermal and photochemical reactions of half-sandwich ruthenium complexes. The photochemical reactions employ the use of ex situ and in situ UV irradiation of the complexes. The latter of these techniques allows for samples to be irradiated within an NMR spectrometer, the principal method used to monitor reactions when highly unstable products result.

The reactivity of [CpRu(PPh3)2Cl] towards a range of substrates is first described, where the thermal and photochemical reactions (applying the ex situ method) are contrasted. Replacement of PPh3 by a range of 2-electron donors, including CO, PEt3, ethene and tBuNC was achieved. Similar treatment is given to the complex, [CpRu(PPh3)2H]. However, this hydride complex proved to be slow to react and only minimal conversion to products was achieved, even using photochemical methods.

The reactivity of CpRu(PPh3)2Me toward a range of 2 electron donors was considered in greater detail, particularly its ability to activate Si-H, H-H and C-H adducts under photochemical conditions. Low temperature photochemical techniques, using the in situ method, were employed to determine that both Si-H and C-H bond activation is undertaken by the fragment [CpRu(κ2-2-C6H4PPh2)]. This fragment was shown to activate the C-H bonds of solvent molecules, and form Ru(IV) complexes [CpRu(PPh3)(sol)(SiEt3)H] (where sol = C-H activated solvent, e.g. THF), which were stable at room temperature. The substitution of PPh3 occurs in an analogous fashion to that of the chloride derivative. However, the rate of conversion was increased but no evidence for migration of either CO or ethene into the RuMe bond was observed.

The η3-coordinated complexes, [CpRu(PPh3)(η3-Si(Me2)-CH=CH2)], [CpRu(PPh3)(η3-CH2C2H3)], [CpRu(PPh3)(η3-CH2C6H5)] and [CpRu(PPh3)(η3-CH2C10H7)] were synthesised. In the cases of [CpRu(PPh3)(η3-CH2C2H3)] and [CpRu(PPh3)(η3-CH2C6H5)], thermal and photochemical reaction was initiated with substrates to generate the corresponding η1 substituted derivatives. These products were characterised by NMR techniques.

Finally, the ability of the fragment, [CpRh(NR3)], to C-H activate benzene was considered. NMR data were collected for the low stability products of the photochemical reaction which strongly indicated that this auxiliary is capable of C-H bond activation. Due to working at low temperatures (233 K) and the large amounts of amine required to generate [CpRh(NR3)], full characterisation by NMR of these species was not attained.