The synthesis and reactivity of calcium salicylaldimine complexes have been explored. Utilizing 5-iodosalicylaldimine, the synthesis and purification of a novel calcium dimer and calcium trimer were developed. The solid state structure of the calcium dimer was determined to be a bridged calcium dimer bound to three salicylaldimine ligands, one HMDS ligand, and a molecule of THF. The calcium trimer was found to be a homoleptic complex with six salicylaldimine ligands huddled around the metal centers. The Schlenk redistribution of these complexes was studied and calcium trimer was found to be more kinetically stable than the calcium dimer.
The use of calcium salicylaldimine complexes in intramolecular hydroamination reactions was investigated. The calcium dimer was found to be catalytically active,while the calcium trimer was inactive. The dimer was able to form a variety of pyrrolidines with geminal substitution from both primary and secondary aminoalkenes. The catalytic activity of Ca[N(SiMe3)2]2THF2 was explored as well. This complex was also found to catalyze the formation of pyrrolidines,typically with lower catalyst loadings and reaction times compared to the calcium dimer. Analyses to determine possible decomposition of the calcium dimer to Ca[N(SiMe3)2]2THF2 under the hydroamination reaction conditions were inconclusive.
Palladium-mediated cross-coupling of zinc reagents with aryl thioesters and aryl sulfides was explored. An extension of the Fukuyama reaction to form diaryl ketones was developed using remarkably low loadings of the Pd(dba)2. A chemoselective cross-coupling of aryl thioesters in the presence of aryl halides was alsodiscovered. The order of reactivity was found to be aryl iodides > aryl thioesters > aryl bromides. The synthesis of polyoxazoles through the cross-coupling of thiooxazoles was also studied. Steric hindrance of the heterocyclic sulfide was insufficient to obtain selectivity in the cross-coupling of two oxazoles. Utilizing an electron-rich oxazole, selectivity in cross-coupling could be obtained.
The palladium-mediated allylic oxidation of terminal olefins with sulfide ligands promotes the formation of linear allylic acetates. Surveying monodentate and bidentate sulfide ligands, electron-rich, sterically unencumbered ligands were found to give the highest diastereo- and regioselectivity in allylic oxidation reactions. The intermolecular allylic etherification of cis-vinylsilanes utilizing Pd(OAc)2, PIDA (bisacetoxy iodobenzene), and methanol to form the trans-allylic ether product was also discovered. The reaction is proposed to proceed through a Pd(IV) intermediate.