Studies of low oxidation state main group complexes : their syntheses and reactivities

• Main Author: Rose, Richard P.
• Published: Cardiff University 2006
• Subjects: 546
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.583926

The work presented in this thesis describes the synthesis, structure and reactivities of a range of low oxidation state main group metal complexes. The work upon this subject is divided into six chapters. Chapter 1 provides a general introduction to the group 13 elements, low oxidation state group 13 chemistry and group 13 diyls. This chapter also describes the synthesis, theoretical treatments and reactivities of N-heterocyclic carbenes and their main group 13, 14 and 15 analogues, with a focus on the group 13 N-heterocyclic carbene analogues. Chapter 2 describes an investigation into the formation of transition metal complexes of an anionic gallium(I) N-heterocyclic carbene analogue, K(tmeda) Ga{ N(Ar)C(H) 2} , Ar = 2,6- diisopropylphenyl. These studies highlighted three different mechanistic pathways by which complexes could be isolated. Initially, substitution of a carbonyl ligand by the gallium carbene analogue in transition metal half sandwich carbonyl complexes was investigated. This yielded, for example, the first structurally authenticated Ga-V bond in K(tmeda) CpV(CO)3 Ga{ N(Ar)C(H) 2} , Cp = cyclopentadienyl. Secondly, the direct donation of the gallium carbene analogues lone pair of electrons towards a manganese dialkyl fragment gave the complex K(tmeda) Mn{CH(SiMe3)2}2 Ga{ N(Ar)C(H) 2} . Finally, the salt metathesis reactions of the gallium carbene analogue with a series of Lewis base stabilised transition metal di-halides were explored. Results include, a series of complexes taking the structural form M(tmeda) Ga{ N(Ar)C(H) 2} 2 , M = Mn, Fe, Co, Ni, Zn and the first structurally authenticated Ga-Cu bond in Cu(dppe) Ga{N(Ar)C(H)}2 , dppe = Bis(diphenylphosphino)ethane-P,P Chapter 3 details a study into the reactions of a gallium(III) heterocycle, l2Ga{ N(Ar)C(H) 2'} , by the group 2 metals calcium or magnesium. A series of gallium-group 2 metal bonded complexes have been isolated including, for example the first structurally authenticated group 13-group 2 bond in the complex Ca{Ga (N(Ar)C(H))2 }2(THF)4 . Furthermore, a subsequent investigation into the reactivity of an anionic gallium(I) N-heterocyclic carbene analogue, K(tmeda) Ga{ N(Ar)C(H) 2} , towards N-heterocyclic carbenes and imidazolium cations gave, in one case, the novel group 13 hydride complex HGa{ N(Ar)C(H) 2}(IMes) , IMes = l,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene. Chapter 4 describes the reactions of a paramagnetic gallium(II) dimeric complex, {(Bul- DAB )GaI}2 , with the alkali metal pnictides, ME(SiMe3)2 (M = Li or Na E = N, P or As). These reactions have led to a series of paramagnetic gallium(III)-pnictide complexes, (Bul- DAB)Ga{E(SiMe3)2}I (E = N, P, As) and (Bul-DAB)Ga{E(SiMe3)2}2 (E = P, As). The complex (Bul-DAB)Ga{As(SiMe3)2}I possesses the shortest Ga-As single bond yet recorded. Chapter 5 details an investigation into the reactivity of a amidinato germanium chloride complex, (Cl)Ge{N(Ar)C(But)N(Ar)} . This complex has been shown to participate in a range of different reactions. These are, salt metathesis giving, for example, the complex {(CO)2Fe(n5- Cp)}Ge{N(Ar)C(Bul)N(Ar)} and donation of a lone pair of electrons giving {(CO)5W}(Cl)Ge{N(Ar)C(But)N(Ar)} . Furthermore, an investigation into the synthesis of a range of amidinato bismuth complexes by salt metathesis is described. The first structurally characterised amidinato bismuth complexes, for example (u2-Br)Bi(Br) {(2,6- 'Pr2C6H3)N}2C(H) (THF) 2 , have been isolated and subsequent reductions have been attempted in some cases. Finally, chapter 6 describes some aspects of group 13 hydride chemistry and details the attempted syntheses of group 13 metal(II)-metal(II) bonded species. Complexes, for example QuinAl(H)2 tempo , Quin = l-azabicyclo 2.2.2 octane, tempo = 2,2,6,6-Tetramethyl-l- piperidinyloxy were isolated from reactions of a radical abstraction agent with Lewis base adducts of group 13 trihydrides.