ABSTRACTPART A: IRIDIUM CATALYZED C-H BORYLATION OF ARENES; ENGINEERING SELECTIVITY BY LIGAND DESIGN.By Susanne L. MillerIridium catalyzed C-H borylation has gained popularity as a means to functionalize simple aromatic and heterocyclic substrates under mild conditions which tolerate a variety of functional groups. Initial efforts to develop this chemistry made use of sterically driven selectivity to achieve contra-electronic substitution patterns of aromatic and heterocyclic building blocks that were not easily obtainable by conventional organic chemistry prevalent before the discovery of this chemistry in 1999. As methodology and substrate scope rapidly expanded, steric selectivity became a limitation, as more diverse substitution patterns and higher selectivities were sought. These limitations were partially overcome by the extensive development of directing groups which enabled more traditional ortho substitution patterns to be accessed by the same mild conditions that made Ir-C-H borylation popular. While steric limitations that result in mixtures by the standard borylation protocols can now be overcome by directing groups, a serious challenge remains for the meta-functionalization of substrates which lack common directing groups or have small substituents. This work seeks to address this limitation by ligand-directed selectivity which can be instituted by the rational design of catalysts and ligands to achieve different selectivity outcomes depending on the desired product. The design and development of ligands which make use of either steric or electronic properties to achieve a given outcome was realized, and borylation meta to fluorine in simple arenes which lack directing groups was achieved. By varying the substituents on this ligand framework, the selectivity of the borylation can be shifted from steric to electronic selectivity.PART B: Z-SELECTIVE PALLADIUM CATALYZED CROSS COUPLING OF E-VINYL GERMANES.Germanium cross coupling reactions were born out of efforts to replace toxic organo-tin reagents used in the Stille cross coupling reaction for the construction of C-C bonds. Initial interest in germanium as a transmetalation partner peaked in the mid to late 1990s, but eventually waned due to poor reactivity of organo-germanium reagents and the harsh conditions needed to activate Ge-C bonds towards cross coupling. One such effort from the Maleczka group in the early 2000s, although suffering from poor conversion and unreliable results, gained modest attention by displaying a reactivity distinct from typical Stille coupling selectivity. Instead of retention of geometry, the major product of the E-vinyl germanium coupling reaction exhibited inverted Z- olefin geometry. In the reverse case, Z-vinylgermanes likewise gave inverted E-olefins as the major coupling products. Early studies of the reaction led to the hypothesis of a Heck-like insertion with subsequent germyl elimination to form the inverted product. The proposed mechanism featured a palladium-germyl elimination in preference to a possible b-H elimination. Based on the substrate scope and the organo-germane's required possession of a tertiary allylic alcohol, the Pd- Ge elimination theory was discarded in favor of the formation of a reactive epoxide intermediate, which eliminated germanium upon carbopalladation. The observation of the unactivated cross coupling of allylic germanium epoxides with iodo-arenes supported this hypothesis. Expansion of this chemistry was hampered by inconsistent results and a very narrow substrate scope. Further investigation suggested involvement of Pd nanoparticles.
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