The synthesis and reactivity of several nickel complexes supported by a tridentate pincer ligand scaffold or by two monodentate ligands are detailed in this thesis.

Chapter 3 investigates the reactivity of B-X bonds (X = H, Cl Bcat) at the Ni(II) precursors [Ni(iPrPNP*)X] (X = H (I), Cl (II)) and reports the formation of nickel(II) complexes supported by a dearomatised iPrPNP* or rearomatised iPrPNP scaffold characterised by structural and/or spectroscopic techniques. The direct addition of X-Bcat (X = H, Cl) to the Ni(II) precursors I and II resulted in the formation of the backbone borylated dearomatised complexes [Ni(iPrPNP*Bcat)X] (X = H (IV) or Cl (VI)) and the corresponding cationic rearomatised complexes [Ni(iPrPNP)X]+ (X = H (V) or Cl (VII)). In contrast, the direct addition of B2cat2 to I resulted in the non-selective formation of nickel-boryl complexes [Ni(iPrPNP*Bcat)Bcat] (VIII) and [Ni(iPrPNP)Bcat]+ (IX) as well as IV and [V]+. Additionally, [Ni(iPrPNP*BCF)H] (X) was prepared from the addition of BCF to I.

Chapter 4 reports the preparation and structural characterisation of nickel(II) complexes supported by two monodentate IMes ligands. The direct addition of chloroboranes ClBcat or ClBdan to the Ni(0) precursor [Ni(IMes)2] (III) resulted in B-Cl oxidative addition and formation of the corresponding unsupported nickel-boryl complexes [Ni(IMes)2(BR2)Cl] (R2 = cat (XIII), dan (XIV)). In contrast, the analogous B-H oxidative addition of hydridoboranes HBcat and HBdan was not observed. Computational investigations determined that B-Cl activation at III proceeds readily via nucleophilic displacement whereas B-H activation via a concerted mechanism is kinetically inaccessible.

The research detailed in Chapter 5 builds upon the previous chapter and investigates the reactivity of the unsupported nickel chloro boryl complex XIV. The direct addition of MeLi or Na[Et3BH] to XIV afforded the corresponding halide-substituted nickel complexes [Ni(IMes)2(Bdan)(X)] (X = Me (XVII), H (XVI)). XVII was shown to rapidly insert CO2 to form [Ni(IMes)2(Bdan)(OAc)] (XVIII). The instability of XVIII was apparent and onward reactivity led to the characterisation of further products in which B-O bond formation and C-O activation had occurred. XVII reacted with HBpin to generate XVI which led to preliminary investigations into the potential of XVI to facilitate the reduction of CO2 to CO with HBpin.