Honors Capstone Project
Date of Submission
Arts and Science
Capstone Prize Winner
Won Capstone Funding
Sciences and Engineering
Chemistry | Inorganic Chemistry | Materials Chemistry | Organic Chemistry
Acetylide complexes of the heavy alkaline-earth metals were first introduced by our group. With our group being interested in how the ligand and donor affect the structural chemistry of the resulting complexes, my project was focused on the detailed analysis of past work and the extension towards new ligand and donor sets. The work required the analysis and development of synthetic procedures towards these highly reactive species.
Past synthetic work in our group had established several synthetic routes towards the target compounds including transamination and toluene elimination. Using toluene elimination, I was able to reproduce the synthesis of M(C≡CSiPh3)2(18-crown-6) (M = Sr, Ba), a group of compounds previously only prepared by transamination. I was also able to reproduce the calcium compound using the original transamination route. Extension of toluene elimination to Ca(C≡CSiPh3)2(18-crown-6) compound has so far proven elusive due to the difficult preparation of the dibenzyl Ca(CH2Ph)2 starting material.
Acetylene ligand systems employed in my work included the commercially available compounds HC≡CR with R = SiPh3, SiMe3, 4-tBuC6H4, and t-Bu. Donor studies focused mainly on crown ethers, specifically 18-crown-6, which had been shown to bind favorably to calcium, strontium, and barium. Studies also included donors of lower hapticity including the monodentate tetrahydrofuran (THF) and the bidentate N,N,N',N'-tetramethylethylenediamine (TMEDA). To compare the chemistry of the highly reactive calcium, strontium, and barium acetylides with the more stable, lighter magnesium, a series of magnesium acetylides was also prepared: Mg(C≡CtBu)2(TMEDA)2, Mg(C≡CC6H4tBu)2(TMEDA)2, Mg(C≡CC6H4tBu)2(15-crown-5), Mg(C≡CSiMe3)2(TMEDA)2, and Mg(C≡CSiPh3)2(THF)4.
Overall, the molecular geometries of the magnesium compounds adhered to the predicted octahedral geometry for the 6-coordinate compounds and pentagonal bipyramidal geometry for the 7-coordinate compound. The Mg-C bond length was found to be slightly longer for the more sterically demanding ligands. However, this metal-ligand bond was not affected by coordination number or donor choice. The general trend in the alkaline earth metal acetylides, including magnesium compounds, shows a decrease in the C-M-C and C≡C-M angles as one descends group 2, as explained by the decreased covalent metal-ligand bond character.
Baker, Eva, "Synthesis of Novel Alkaline Earth Metal Acetylides" (2005). Syracuse University Honors Program Capstone Projects. 676.
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