Studies towards the Synthesis of a Heterobimetallic Zirconium Germanium Complex from Imidozirconocenes, Germanimines and Germylenes

Abstract

<p>Early-late transition metal heterobimetallic complexes with direct metal to metal interactions are desirable synthetic targets due to the complementary reactivity of the two different metals present in these compounds. The electron-rich late transition metal (often Rh, Ir, Fe, or Mo), and electron-poor early transition metal create an ideal environment for heterolytic bond cleavage in what is often termed ‘cooperative reactivity’. This project aimed to synthesise a zirconium-germanium heterobimetallic complex based on a known heterobimetallic ligand scaffold; 1. The synthesis of the desired heterobimetallic 1 was attempted using two different synthetic approaches. The first involved the investigating the reactivity between an unsaturated zirconium nitrogen bond (an imidozirconocene) and a germanium(II) source with a lone pair of electrons (known as a germylene). The second approach investigated the reactivity between an unsaturated germanium nitrogen bond (a germanimine) and a zirconium(II) source. In order to have the highest chance of success, a wide range of germanium and zirconium complexes were synthesised. The novel germylenes include [Ge(NAPHTMS)] (NAPHTMS = [1,8-((CH3)3Si)N)2C10H6]) and [Ge(BIANMes)] (BIANMes = [((2,4,6-Me(C6H2)N)2)C12H6)]). These proved to be unreactive towards the imidozirconium species [Cp2Zr(NAr*)(THF)] and [Cp2Zr(NDipp)(THF)] (Ar* = (2,6-(C6H5)2CH)-4-(tBu)C6H2), Dipp = (2,6-((CH3)2CH)C6H3)) as well as other amidozirconocenes. However, within these studies, the mixed coordination germanium species [[Ge(NAPHTMS)Ge(Bu)(NAPHTMS)]-[Li(THF4)]+] and [[Ge(NAPHTMS)Ge(Me)(NAPHTMS)]-[Li(THF4)]+]were synthesised. Density functional theory (DFT) molecular orbital calculations were used to help explain the observed reactivity. With regards to the second approach, routes to new germanimine complexes such as [(HMDS)2Ge(NMes)] ((HMDS) = ((CH3)3Si)2N), Mes = (2,4,6-CH3(C6H3))), were explored, and several methods for generating “Cp2Zr” were examined. Although these conditions proved unsuccessful for generating 1, the reaction between dialkyl zirconocene with azides to form novel zirconocene triazenido complexes was discovered and the sterics affecting the synthesis of new germanimine complexes was investigated.</p>