Preparation, characterisation and reactivity of low oxidation state d-block metal complexes stabilised by extremely bulky amide ligands.

Chapter 1 gives a general introduction into d-block elements, including some of the fundamental concepts, such as the 18 electron rule and metal-metal bonding. It also includes an overview of low oxidation state metal complexes, in addition to some of the ligands that have been used to stabilize such complexes. Finally, dimeric magnesium(I) complexes are introduced showing their use as effective reducing agents in organic and inorganic synthesis. Chapter 2 focuses on the preparion of extrememly bulky amido d-block metal(II) halide complexes, including those of chromium, manganese, iron, cobalt, zinc, cadmium and mercury. The synthesis, structure and magnetic propreties of these complexes were explored and compared to related terphenyl d-block metal(II) halide complexes. These amido d-block metal(II) halide complexes could potentially serve as precursors for low coordinate, low oxidation state d-block chemistry. Low coordinate, low oxidation state manganese complexes are discussed in Chapter 3. These include the characterisation of the first two-coordinate manganese(I) dimer [{(Ar*(SiMe3)NMn}₂] (Ar* = 2,6-{Ph₂CH}₂-4-Me-C₆H₂), synthesised by the reduction of [Ar*(SiMe3)NMn(THF)(µ-Br)}₂] with the magnesium(I) reducing agent [{(MesNacnac)Mg}₂] (MesNacnac = [(MesNCMe)₂CH]–, Mes = mesityl). The reduction of the bulkier precursor complex [Ar†(SiⁱPr₃)NMn(THF)(µ-Br)}₂] (Ar† = 2,6-{Ph₂CH}₂-4-ⁱ Pr-C6H₂) with the same magnesium(I) reducing agent yielded the unprecedented Mn(0)Mg(II) heterobimetallic complex [Ar†(SiⁱPr₃)NMnMg(MesNacnac)] posessing an unsupported Mn-Mg bond. The complex was utilized as an “inorganic Grignard reagent”, in the prepaption of the asymmetric manganese(I) dimer [Ar†(SiⁱPr₃)NMnMn(SiMe₃)Ar*] and the related mixed valence, bis(amido)-heterobimetallic complex [CrMn{Ar†(SiⁱPr₃)N}{Ar*(SiMe₃)N}]. It is also shown to act as a two-electron reducing agent in reactions with unsaturated substrates. Chapter 4 concentrates on low oxidation state group 12 complexes with metal-metal bonds. This includes the synthesis and characterisation of a homologous series of two-coordinate amido group 12 metal(I) dimers [{(Ar†(SiMe₃)NM}₂] (M = Zn, Cd, Hg). The reduction of the extrememly bulky amido zinc(II) bromide complex [Ar*(SiⁱPr₃)NZnBr] with [{(MesNacnac)Mg}₂] gave the novel Zn(0)Mg(II) heterobimetallic complex [Ar*(SiⁱPr₃)NZnMg(MesNacnac)], which bears the first example of a Zn-Mg bond in a molecular complex. The complex was utilized as a transfer reagent in the preparation of the unprecendented trimetallic zinc complex [{Ar*(SiⁱPr₃)NZn}₂Zn], which bears a string of two-coordinate zinc atoms. The related group 12 trimetallic complexes [{Ar*(SiiPr₃)NZn}₂M] (M = Cd, Hg) were also isolated. Chapter 5 investigates the synthesis, structure and reactivity of low coordinate, low oxidation state cobalt complexes. A series of low coordinate, high-spin cobalt(I) complexes bearing the extremely bulky amide ligand Ar*(SiPh₃)N– are described. These include the benzene capped cobalt(I) complex [Ar*(SiPh₃)NCo(η⁶-benzene)], which readly looses its benzene ligand upon dissolution in THF or fluorobenzene, to give the dimeric cobalt(I) complex [{Ar*(SiPh₃)NCo}₂]. The first neutral two-coordinate cobalt(I) complex [Ar*(SiPh₃)NCo(IPriMe)] (IPriMe = :C{N(ⁱPr)C(Me)}₂) was also isolated by exchange of the benzene ligand with the N-heterocyclic carbene IPriMe. Finally, Chapter 6 discusses transition metal tetrelyne complexes, which are heavier group 14 analogues of transition metal carbyne complexes. The synthesis and structure of the two singly bonded Mo-Ge complexes [Cp(CO)₃Mo–GeN(Ph)Ar*] (Cp = η5-C₅H₅) and [Cp(CO)₃Mo–GeN(SiMe₃)Ar*] is discussed. The latter readily eliminates a molecule of CO when heated or irradiated with UV light to give the unprecedented amino-germylyne complex [Cp(CO)₃Mo≡GeN(SiMe₃)Ar*]. The spectroscopic and structural data for this complex, in combination with the results of computational studies, show that this compound is best viewed as having a bent Mo−Ge “triple” bond, with little multiple bond character to its Ge−N interaction.