University of North Carolina at Chapel Hill Graduate School
Doi
Abstract
The synthesis and characterization of several new iridium(I) and iridium(III) carbonyl
complexes supported by aminophosphinite pincer ligands is reported. A surprising diversity
of reaction pathways were accessible upon treatment of Ir carbonyl complexes with salts of
redox-inactive alkali, alkaline earth, and lanthanide metal cations. Iridium(III)
hydridocarbonyl chloride complexes underwent either halide abstraction or halide
substitution reactions, whereas iridium(I) carbonyl complexes underwent protonative
oxidative addition reactions. When the nitrogen donor of the pincer ligand is an aza-crown
ether macrocycle, cation–macrocycle interactions can be supported, leading to divergent
reactivity in some cases.
New iridium and rhodium complexes supported by aminophosphinite pincer-crown
ether ligands were synthesized. Iridium-catalyzed hydroformylation of allylbenzene was
explored. Catalytic amounts of LiOTf (OTf = trifluoromethanesulfonate) doubled the rate of
hydrofunctionalization. The iridium pincer complexes were found to undergo remetallation
pathways under the conditions of catalysis. This guided the design of a new, more active
iridium catalyst supported by a pincer ligand with a methoxy substituent incorporated to
prevent remetallation. Rhodium-catalyzed hydroformylation of 1-octene was explored as
well. A systematic decrease in the n (linear) to iso (branched) aldehyde ratio was observed in the presence of increasingly bulky ammonium additives. However, catalyst stability studies showed that rhodium pincer complexes undergo decomposition under hydroformylation conditions and presumably simply act as pre-catalysts.
The first mononuclear gold(III) PNP pincer complexes (PNP = bis(2-
diisopropylphosphinophenyl)amide) are reported. The chloro complex [(PNP)Au(Cl)][OAcF]
(OAcF = OCOCF3) was synthesized by microwave irradiation of a tetrachloroaurate salt and
the neutral PNHP ligand. Dehalogenation with AgOAcF afforded the trifluoroacetate-bound
complex [(PNP)Au(OAcF)][OAcF]. Electronic absorption spectroscopy and time-dependent
density functional theory studies assigned the electronic transition that imbues the complexes with a deep royal blue color. The Au(III) trifluoroacetate complex is surprisingly stable, and no reactivity towards ethylene was observed, even under high pressures and at high temperatures. Density functional theory calculations suggest that the lack of reactivity is due to the high energy of the putative dicationic ethylene-bound intermediate invoked in a formal insertion reaction.Doctor of Philosoph
