Inorganic Chemistry Seminar: Professor Kiyoung Park, KAIST (Host: Ed Solomon)
**This seminar is available for virtual attendance.**
About the Seminar
"Lessons from Electronic Structures: Light and O2 Utilization for Organonickel Chemistry"
Organonickel complexes are the key intermediates of Ni-catalyzed cross-coupling reactions, and their reductive elimination (RE) activities often determine the rate of overall reaction. We have used diverse transition-metal based spectroscopic techniques, such as magnetic circular dichroism, electron paramagnetic resonance, resonance Raman, and X-ray absorption spectroscopies, to define the electronic structures of nickelacycle compounds and correlate to their RE activities. From high-valent cycloneophyl (-CH2C(CH3)2-o-C6H4-) NiIII and NiIV complexes, strong correlations between C-C bond-forming RE rates and C-to-Ni charge-transfer (CT) transition energies have been discovered. The result suggests that the kinetic barrier of the RE reaction is determined by energy cost for internal CT from the coordinated carbon moiety to the Ni center. In combination with density functional theory computations, the frontier molecular orbitals of the RE reaction turned out to be identical to those of the C-to-Ni CT electronic transitions. Thus, the cross-coupling activity of the C-to-Ni CT excited states have been examined, exhibiting significantly accelerated C-C bond formation by up to five orders of magnitude, compared to the ground-state chemistry.
The strong covalency of the Ni-C bonds observed from the above study has led us to test the O2 reactivity of organonickel complexes. While metalloenzymes can fully activate and utilize O2 for diverse chemistries, a rather limited O2 reactivity has been reported for organometallic chemistry, showing O2 serving mostly as an electron acceptor but not as an oxygen atom donor. We have discovered that the strong s donation of the carbon moiety can assist the reductive O2 activation and stabilize high-valent Ni intermediates resulting from the O-O bond cleavage. This full-extent O2 activation could be achieved in a similar manner as binuclear oxygenases, yielding the oxygenation of organonickel complexes. This finding well demonstrates that the electronic-structure level understanding can provide insights for developing new chemistry.
About the Speaker
Kiyoung Park is an associate professor in the Department of Chemistry at Korea Advanced Institute of Science and Technology (KAIST). Her research group has focused on the electronic structure level understanding of organometallic reactions such as reductive elimination reactions for determining rate-determining factors and harnessing photoactivation. Kiyoung attended Seoul National University for her undergraduate degree and worked for Prof. Myunhyun P. Suh to synthesize cyclam-based MOFs. She obtained her Ph.D. degree in 2010 from University of Wisconsin-Madison under the supervision of Prof. Thomas C. Brunold, where she researched the mechanism of Co-C bond formation during coenzyme B12 biosynthesis. Afterward, until 2014 prior to her independent career, she was a postdoctoral researcher for Prof. Edward I. Solomon at Stanford University, utilizing nuclear resonance vibrational spectroscopy to define the oxygenated intermediates of binuclear non-heme Fe enzymes.
IMAGE COURTESY OF KAIST