Development of redox-active pincer ligands for Co(II) that display base-dependent nuclearity Open Access

Abstract

Pincer ligands offer an opportunity for exploring coordination geometry due to the
extreme variability in ligand design. Past research with amidate ligands has focused on
tripodal tetradentate ligand systems, and this work investigates the coordination
chemistry of the pincer analogs of these systems. The NNN pincer ligands reported here
are of the form NH(o-PhNHC(O)R)2 (R = ⁱPr, ^tBu) and have been complexed with Co(II)
metal ions. Structures for experiments involving the ligand when R = ^tBu have yet to be
obtained. When R = ⁱPr, the complexes produced have been a dinuclear dimeric complex
with a Co2N2 diamond-core structure when the ligand is treated with 3.1 equivalents of
base, and a monomeric complex with a 2:1 ligand:metal ration when the ligand is treated
with 2.1 equivalents of base. The dimeric complex has a relatively rare geometry, as the
Co2N2 diamond-core is not often seen with amidate ligands. The monomeric complex
has unique electrochemical properties, demonstrating four electrochemical events with
only one cobalt center. These complexes offer great opportunities and possibilities in the
area of coordination chemistry and catalysis.

Table of Contents

1. Introduction……………………………………………………………………………1

2. Results and Discussion………………………………………………………………...6

2.1. Ligand synthesis …………………………………………………………………6

2.2. Cobalt chemistry with H3L^iPr …………………………………………………….7

2.3. Electrochemistry of the L^iPr complexes………………………………………...14

2.4. Cobalt chemistry with H3L^tBu …………………………………………………...16 3. Conclusion and Future Direction…………………………………………………….19 4. Experimental…………………………………………………………………………21 4.1. General consideration….………………………………………………………..21 4.2. Ligand syntheses………………………………………………………………..22

4.2.1. Bis(2-nitrophenyl)amine [NH(o-PhNO2)2]………………………………22

4.2.2. Bis(2-aminophenyl)amine [NH(o-PhNH2)2]……………………………..22

4.2.3. 2,2'-Bisisobutylamidodiphenylamine [NH(o-PhNHC(O)ⁱPr)2] -
H3L^iPr …………………………………………………………………….23

4.2.4. 2,2'-Bistertpentylamidodiphenylamine [NH(o-PhNHC(O)^tBu)2] -
H3L^tBu …………………………………………………………………….24

4.3. Metal complexes………………………………………………………………...24

4.3.1. Diamond-core dimer (Et4N)2[Co2(N(o-PhNC(O)ⁱPr)2)2] -
(Et4N)2[Co2(L^iPr)2]……………………………………………………….24

4.3.2. 2:1 monomer (Et4N)2[Co(N(o-PhNC(O)ⁱPr)(o-PhNHC(O)ⁱPr))] -(Et4N)2[Co(HL^iPr)2]……………………………………………………...25

4.3.3. Proposed K2[Co(N(o-PhNC(O)^tBu)2)]…………………………………...26

4.3.4. Proposed K2[Co(N(o-PhNC(O)^tBu)(o-PhNHC(O)^tBu))]………………..26

5. References…………………………………………………………………………… 27

Appendix A. Crystal Data for (Et4N)2[Co2(L^iPr)2]………………………………………30 Appendix B. Crystal Data for (Et4N)2 [Co(HL^iPr)2] …………………………………….. 49

About this Honors Thesis

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School	Emory College
Department	Chemistry
Degree	BS
Submission	Honors Thesis
Language	English
Research Field	Chemistry, Inorganic Chemistry, General
Keyword	coordination chemistry inorganic chemistry pincer ligand base-dependent nuclearity redox-active ligand diamond core NNN pincer electrochemistry
Committee Chair / Thesis Advisor	MacBeth, Cora, Emory University
Committee Members	Lynn, David, Emory University Arp, Meggan J, Emory University

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