Author

Joshua Woods

Bound Volume Number

Volume III

Document Type

Honors Capstone Project

Date of Submission

Spring 5-2016

Capstone Advisor

Karin Ruhlandt

Capstone Major

Chemistry

Capstone College

Engineering and Computer Science

Audio/Visual Component

no

Keywords

Alkali and alkaline earth metal organometallics, novel metal organic chemical vapor deposition precursors, catalysts and as synthetic reagents

Capstone Prize Winner

no

Won Capstone Funding

yes

Honors Categories

Sciences and Engineering

Subject Categories

Chemistry

Abstract

Alkali and alkaline earth metal organometallics have been sought after for a variety of applications such as in electronic devices produced by novel metal organic chemical vapor deposition precursors, catalysts and as synthetic reagents. Despite significant advances in synthetic techniques, the chemistry of the highly reactive s-block metals is still relatively unexplored. It is difficult to predict properties, structure and binding modes of these compounds due to a number of factors including enhanced reactivity and tendency to aggregation due to the large metal diameter. On the other hand, many of the s-block metals are earth abundant and environmentally friendly, making them highly attractive reagents.

The use of bulky ligands has propelled the chemistry of the metals, as the large ligands have a unique capability to suppress aggregation. The use of bulky ligand capable of participating in secondary metal-ligand π (M-π) interactions enables further control of metal coordination environment and has allowed for the synthesis of a variety of novel s-block compounds of low nuclearity, while introducing the capacity of fine-tuning reactivity, a necessary requirement for the use of these compounds for the above mentioned applications. However, not much is know about M-ligand π interactions, as such, their impact is difficult to predict. Early studies suggest a direct dependency on metal size and character.

The first part of this work focuses on developing synthetic schemes for the formation of novel heavy alkali metal pyrazolates (pz). Pyrazolates of the lighter alkali metals, lithium and sodium, have been well explored, yet there are no literature examples involving the heavier congeners rubidium or cesium.

The second part of this work explores the synthesis and characterization of novel heteroleptic alkaline earth pyrazolate tetraarylborates. This new family of bisarenes of the form [M(thf)2(tBu2pz)(B((3,5-Me2)C6H3)4)] (M= Sr, Ba) reveal the increased tendency of the heavy alkaline earth metals towards M-π interactions, whereas the lighter metals afforded monocationic species of the type [M(thf)2(Et2O)2(tBu2pz)][B((3,5-Me2)C6H3)4] (M = Mg, Ca) where predominant metal-donor interactions, rather than M-ligand π interactions are observed. Furthermore, the use of bulky tBu2pzH ligand reveals how ligand steric demand can be used to circumvent cluster or aggregate formation, which are typically observed when using less sterically hindered systems.

In summary, the results presented here provide a seminal understanding on how M-ligand π interactions can be used purposefully to control the structure and thus the function of the heavy s-block metals. This will ultimately help in the construction of highly selective catalysts.

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