Mechanochemical Synthesis and Computational Investigation of Organo-Main Group Species with Delocalized Ligands

Abstract

Conventional synthetic chemistry is generally facilitated by solvents that dissolve reagents and allow controlled interaction in a controlled manner, in addition to playing many other roles. However, in some cases, common solvents used can have a significant impact on the reaction outcome or the isolated products. This is especially true for main-group organometallics, where metal-carbon bonds are often ionic and easily interrupted by metal-heteroatom interactions that arise from the strongly coordinating solvents needed to dissolve polar metal starting materials. Surprisingly, these difficulties can be overcome by simply grinding reagents together using ball bearings in a ball mill. This is known as mechanochemistry, where reactions are driven or initiated by mechanical energy. This dissertation describes its application to main group synthesis, which has resulted in contributions to our understanding of structure and bonding, differences between solid-state and solution-phase reactivity, and inter- and intra-molecular interactions that are easily interrupted and consequently overlooked in solution. This is exemplified by work involving bulky allyl ligands and electropositive s-block elements. By grinding the potassium salt of the [1,3-(SiMe3)2C3H3]- allyl anion (known as A´) with metal halide precursors, a variety of unique compounds can be produced. Notable examples include [K2MgA´4], which contains the first example of an η3-coordinated allyl on magnesium, and [KCaA´3], the most active calcium isoprene polymerization initiator known, which forms from a puzzling meta-stable intermediate that can only be handled in arene solutions. The investigation of less polar systems is also described. This includes the synthesis of dispersion-stabilized tin allyls and a description of unique beryllium indenyl compounds.