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

May, Philip Scott (2010)

Permanent URL: https://etd.library.emory.edu/concern/etds/jm214p637?locale=en
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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 H3LiPr …………………………………………………….7

2.3. Electrochemistry of the LiPr complexes………………………………………...14

2.4. Cobalt chemistry with H3LtBu …………………………………………………...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] -
H3LiPr
…………………………………………………………………….23

4.2.4. 2,2'-Bistertpentylamidodiphenylamine [NH(o-PhNHC(O)tBu)2] -
H3LtBu
…………………………………………………………………….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(LiPr)2]……………………………………………………….24

4.3.2. 2:1 monomer (Et4N)2[Co(N(o-PhNC(O)iPr)(o-PhNHC(O)iPr))] -(Et4N)2[Co(HLiPr)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(LiPr)2]………………………………………30 Appendix B. Crystal Data for (Et4N)2 [Co(HLiPr)2] …………………………………….. 49

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