Presentation Type
Oral Presentation
Category
STEM (science, technology, engineering, mathematics)
Abstract/Artist Statement
High-valent transition metal-oxo (TM-oxo) species have been ascertained to be key intermediates in the catalytic cycles of various metalloenzymes involved in C-H functionalization. Advances in the structural and mechanistic elucidation of these metalloenzymes have provided new rationale for designing biomimetic and bio-inspired systems that harness high-valent TM-oxo chemistry and in turn provide further insights into the electronic, structural and reactive properties of enzymatic TM-oxo intermediates. However, high-valent oxo complexes of late transition metals are less accessible due to electronic bonding restrictions. Synthetic efforts can be shifted toward developing high-valent late TM-non-oxo systems, which present electronic, structural and reactive properties similar to the natural metal-oxo moiety and pose as an accessible strategy for mapping out chemical space surrounding high-valent late transition metals.
In this research, we characterized the hydrogen atom transfer (HAT) reactivity of a series of bio-inspired complexes exhibiting nickel in its unusual +4 oxidation state obtained by one-electron oxidation of their Ni(III) precursors. UV-Vis spectroscopy was used to monitor the reaction between the Ni(IV) complex and sp3 C-H bond substrate under pseudo-first order conditions in acetonitrile at -40°C. Coordinating anions with higher basicity (azide, acetate, and hydroxide) to Ni(IV) enhanced HAT reactivity toward strong C-H bonds both thermodynamically and kinetically.
Cleavage of C-H bonds in HAT processes is driven by two components: basicity and redox potential of the oxidant. Our observations led us to conclude that basic anions and redox potentials allowing facile electron transfer combine to enable this Ni(IV) system to cleave strong C-H bonds. This evidence lands our system among the rare cases of a Ni(IV) species with such high HAT reactivity and complements observations of an analogous series of Co(IV) complexes previously described by our lab. These findings help map some chemical space around high-valent nickel and provide a foundation for bio-inspired C–H functionalization catalysts.
Mentor Name
Dong Wang
Coordinating Lewis bases to Ni(IV) enhances reactivity toward strong sp3 C-H bonds
UC 327
High-valent transition metal-oxo (TM-oxo) species have been ascertained to be key intermediates in the catalytic cycles of various metalloenzymes involved in C-H functionalization. Advances in the structural and mechanistic elucidation of these metalloenzymes have provided new rationale for designing biomimetic and bio-inspired systems that harness high-valent TM-oxo chemistry and in turn provide further insights into the electronic, structural and reactive properties of enzymatic TM-oxo intermediates. However, high-valent oxo complexes of late transition metals are less accessible due to electronic bonding restrictions. Synthetic efforts can be shifted toward developing high-valent late TM-non-oxo systems, which present electronic, structural and reactive properties similar to the natural metal-oxo moiety and pose as an accessible strategy for mapping out chemical space surrounding high-valent late transition metals.
In this research, we characterized the hydrogen atom transfer (HAT) reactivity of a series of bio-inspired complexes exhibiting nickel in its unusual +4 oxidation state obtained by one-electron oxidation of their Ni(III) precursors. UV-Vis spectroscopy was used to monitor the reaction between the Ni(IV) complex and sp3 C-H bond substrate under pseudo-first order conditions in acetonitrile at -40°C. Coordinating anions with higher basicity (azide, acetate, and hydroxide) to Ni(IV) enhanced HAT reactivity toward strong C-H bonds both thermodynamically and kinetically.
Cleavage of C-H bonds in HAT processes is driven by two components: basicity and redox potential of the oxidant. Our observations led us to conclude that basic anions and redox potentials allowing facile electron transfer combine to enable this Ni(IV) system to cleave strong C-H bonds. This evidence lands our system among the rare cases of a Ni(IV) species with such high HAT reactivity and complements observations of an analogous series of Co(IV) complexes previously described by our lab. These findings help map some chemical space around high-valent nickel and provide a foundation for bio-inspired C–H functionalization catalysts.