The transition metal complexes cyclopentadienylrhenium tricarbonyl [CpRe(CO)3, Cp = cyclopentadienyl] and (isopropylcyclopentadienyl)rhenium tricarbonyl [(i-PrCp)Re(CO)3, i-Pr = isopropyl] were photolysed in alkanes at low temperature and the resulting alkane complexes, of the general formula Cp'Re(CO)2(alkane) (Cp' = Cp or (i-PrCp)), were studied using NMR spectroscopy. Characteristic proton chemical shifts (δ) and couplings (3JHH) were observed for alkane complexes of several linear, branched and cyclic alkanes of up to eight carbons. Alkanes with chemically distinct methyl (CH3) and/or methylene (CH2) units were observed alternatively binding through each unit to rhenium. No bound methine unit was observed. Large C-H coupling constants (1JCH) were observed for protons of several bound CH3 and CH2 units, indicating the bound C-H is intact. These species are, thus, alkane sigma (σ) complexes, wherein the alkane has an agostic (M-H-C, 3 centre 2 electron) interaction with the rhenium centre. The CH3 binding mode of (i-PrCp)Re(CO)2(1-pentane) was elucidated; sequential deuteration in the bound CH3 revealed an equilibrium isotope effect (EIE) in the remaining proton/s, confirming that only one C-H has an agostic interaction with rhenium at any instant . NMR parameters δ(1H) (-8.22), δ(13C) ( 42.4) and 1JCH (85 Hz) for the complexed C-H reveal it is unequivocally intact and yet strongly interacting with the rhenium centre, hallmarks for the agostic interaction. Intramolecular exchange was identified between pentane complex isomers Cp'Re(CO)2(1-pentane), Cp'Re(CO)2(2-pentane) and Cp'Re(CO)2(3-pentane). Equilibrium constants were determined, revealing a preference for CH2 binding over CH3. The inequivalent hydrogens found in methylene groups of cyclohexane at low temperature permitted simultaneous observation of axial and equatorial C-H protons of a bound CH2 in CpRe(CO)2(cyclohexane); an EIE, upon deuteration, indicated rapid exchange between complexed C-H bonds in the bound CH2 unit. The rhenium centre was found to prefer complexation of the axial C-H bond, over the equatorial, with K ~2.9. Intermolecular exchange of alkane ligands with free solvent was directly observed, in the competitive complexation of the [CpRe(CO)2] fragment to different alkanes in binary mixtures. The preference cyclohexane > cyclopentane > pentane > isobutane was established and equilibrium constants determined. The kinetics were followed by NMR and modelled, revealing rate constants; decay rates were also determined.

The transition metal complexes cyclopentadienylrhenium tricarbonyl [CpRe(CO)3, Cp = cyclopentadienyl] and (isopropylcyclopentadienyl)rhenium tricarbonyl [(i-PrCp)Re(CO)3, i-Pr = isopropyl] were photolysed in alkanes at low temperature and the resulting alkane complexes, of the general formula Cp'Re(CO)2(alkane) (Cp' = Cp or (i-PrCp)), were studied using NMR spectroscopy. Characteristic proton chemical shifts (δ) and couplings (3JHH) were observed for alkane complexes of several linear, branched and cyclic alkanes of up to eight carbons. Alkanes with chemically distinct methyl (CH3) and/or methylene (CH2) units were observed alternatively binding through each unit to rhenium. No bound methine unit was observed. Large C-H coupling constants (1JCH) were observed for protons of several bound CH3 and CH2 units, indicating the bound C-H is intact. These species are, thus, alkane sigma (σ) complexes, wherein the alkane has an agostic (M-H-C, 3 centre 2 electron) interaction with the rhenium centre. The CH3 binding mode of (i-PrCp)Re(CO)2(1-pentane) was elucidated; sequential deuteration in the bound CH3 revealed an equilibrium isotope effect (EIE) in the remaining proton/s, confirming that only one C-H has an agostic interaction with rhenium at any instant . NMR parameters δ(1H) (-8.22), δ(13C) ( 42.4) and 1JCH (85 Hz) for the complexed C-H reveal it is unequivocally intact and yet strongly interacting with the rhenium centre, hallmarks for the agostic interaction. Intramolecular exchange was identified between pentane complex isomers Cp'Re(CO)2(1-pentane), Cp'Re(CO)2(2-pentane) and Cp'Re(CO)2(3-pentane). Equilibrium constants were determined, revealing a preference for CH2 binding over CH3. The inequivalent hydrogens found in methylene groups of cyclohexane at low temperature permitted simultaneous observation of axial and equatorial C-H protons of a bound CH2 in CpRe(CO)2(cyclohexane); an EIE, upon deuteration, indicated rapid exchange between complexed C-H bonds in the bound CH2 unit. The rhenium centre was found to prefer complexation of the axial C-H bond, over the equatorial, with K ~2.9. Intermolecular exchange of alkane ligands with free solvent was directly observed, in the competitive complexation of the [CpRe(CO)2] fragment to different alkanes in binary mixtures. The preference cyclohexane > cyclopentane > pentane > isobutane was established and equilibrium constants determined. The kinetics were followed by NMR and modelled, revealing rate constants; decay rates were also determined.

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 <b>Chapter 2</b> 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 [BAr^F4]^─ anion are produced by hydrogenation. A rare example of a sigma-alkane complex, [Rh(ⁱBu₂PCH₂CH₂PⁱBu₂)(eta²-_CH-eta²-_CH-NBA][BAr^F4]<sup>─</sup], is also formed in the solid-state, by a single crystal to single crystal transition driven by hydrogen. This complex is crystallographically characterised and displays two short Rh∙∙∙H−C sigma-interactions. Deuteration studies indicate that the agostic complex [Rh(ⁱBu₂PCH₂CH₂PⁱBu₂)(eta²-_CH-eta²-_CH-NBE][BAr^F4] 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 <b>Chapter 3</b> 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. <b>Chapter 4</b> 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][BAr^F4]. H/D exchange of NH3 can also occur in the solid state in the bis-ammonia complex [Rh(ⁱBu₂PCH₂CH₂PⁱBu₂)(NH₃)₂][BAr^F4]. A variety of rhodium complexes are tested as heterogeneous catalysts for the hydrogenation of ethene and the isomerisation of butene. In <b>Chapter 5</b> 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.