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

<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>

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

<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>

Late Transition Metal (LTM)-NHC Catalyzed Transformations of Renewable Chemicals to Fine Chemicals, Fuels, and Intermediates

This title of the book chapter deals with the late transition metal-NHC (N-heterocyclic carbene) catalyzed transformations of renewable chemicals, i.e., bio-mass resources (carbohydrates/vegetable oils/natural products) into useful chemicals via oxidation, hydrogenation, dehydration, polymerization, hydrolysis, etc. along with brief introductory notes on late transition metals, carbenes, and renewable chemicals for better understanding to the reader.

Magnesium-Stabilised Transition Metal Formyl Complexes: Structures, Bonding, and Ethenediolate Formation

Herein we report the first comprehensive series of crystallographically characterised transition metal formyl complexes. In these complexes, the formyl ligand is trapped as part of a chelating structure between a transition metal (Cr, Mn, Fe, Co, Rh, W, and Ir) and a magnesium (Mg) cation. Calculations suggest that this bonding mode results in significant oxycarbene-character of the formyl ligand. Electron-rich late-transition metal complexes have the highest oxycarbene-character to the bonding and are the most stable in solution. Further reaction of a heterometallic Cr---Mg formyl complex results in a rare example of C–C coupling and formation of an ethenediolate complex. These results show that well-defined transition metal formyl complexes are potential intermediates in the homologation of carbon monoxide.

Factors Promoting Alkene Migratory Insertion into Metal-Nitrogen Bond during Hydroamination in Recent Studies

: Migratory insertion is a fundamental organometallic transformation that enables the functionalization of an unsaturated bond. Recent reports on catalytic hydroamination provide evidence that supports an intermolecular migratory insertion pathway featuring alkene insertion into metal-nitrogen (M-N) bonds. This article presents factors influencing the rate of migratory insertion in late-transition metal-catalyzed hydroamination, including steric and electronic effects from ligands, alkenes, and metal centers, along with stabilization from coordinated amine intermediates and ordered transition states.