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.

The synthesis and reactivity of a number of mixed transition metal-aluminium and σ-alane complexes are detailed in this thesis. Chapter III reports on the formation and structural characterisation of N,N'-chelated aluminium dihalide precursors featuring amidinate and guanidinate substituents. These precursors of the type RC(R'N)₂AlX₂ (R = ⁱPr₂N or Ph; R' = Cy or ⁱPr or Dipp; X = hal), readily react with Na[CpFe(CO)₂] via salt elimination to form the corresponding mixed iron-aluminium complexes CpFe(CO)2[(X)Al(NR')2CR] which have been characterised both spectroscopically and by X-ray diffraction. The reactivity of the novel mixed aluminium-iron complexes towards halide abstraction agents has been investigated and a propensity for augmented coordination at the aluminium centre observed. Furthermore, complementary syntheses of the methyl substituted complex CpFe(CO)₂[(Me)Al(NCy)₂CNⁱPr₂] have been developed. This can be achieved either via the reaction between the related chloride complex and MeLi, or from the reaction between ⁱPr₂C(CyN)₂Al(Me)Cl and Na[CpFe(CO)₂]. The research detailed in Chapter IV builds on the previous chapter and is focussed on the use of more sterically demanding substituents at both aluminium and transition metal, as well as more electron rich transition metal fragments. The transition metal anions Na[Cp*Fe(CO)₂] and Na[Cp^SiFe(CO)(PPh₃)] react with the aluminium precursors forming related mixed iron-aluminium complexes which have been structurally characterised. The Dipp₂NacNacAlCl₂ precursor has been shown to undergo reaction with both Na[CpFe(CO)₂] and Na[Cp*Fe(CO)₂]. The halide abstraction chemistry of the latter utilising both Lewis acid and salt metathesis based abstraction approaches has been investigated. The dehydrohalogenation chemistry of the Dipp₂NacNacAlCl₂ precursor was investigated and the ligand activated products of reactions with both alkyl lithium and alkyl potassium reagents characterised. Chapter V reports the extension of salt metathesis for the formation of an Al-H-Mn interaction, and the product has been fully characterised. In addition, the coordination of Al-H bonds from a number of alane precursors to in situ generated 16-electron fragments has allowed the structural characterisation of a number of novel σ-alane complexes. The incorporation of the transition metal fragments [Cp'Mn(CO)₂] and [W(CO)₅] permit comparison to archetypal borane and silane σ-complexes. Quantum chemical calculations suggest that the alane ligand has a binding energy close to that of dihydrogen but significantly less than that of CO, consistent with a predominant σ-donor role of the Al-H bond. The formation and structural characterisation of the κ²-complexes (OC)₄M[κ²-H₂AlDipp₂NacNac] (M = Cr, Mo or W) define an unprecedented binding motif for the alane ligand. In the cases of chromium and molybdenum the κ²-complexes can be prepared either photolytically or via alkene displacement from the corresponding (OC)₄M(cod) reagent. In the case of tungsten the alkene displacement route yields the desired product, but only under more forcing conditions. Spectroscopic characterisation of the related κ¹-complex (OC)₅Cr[κ¹-H₂AlDipp₂NacNac], which readily forms the κ²-complex in solution without photolysis, has enabled the kinetics of chelate ring closure to be investigated. This analysis further characterises the formation of the unprecedented κ²-binding motif for the alane ligand.