10.1021/acs.organomet.8b00013.s001
James R. Gardinier
James R.
Gardinier
Jeewantha S. Hewage
Jeewantha S.
Hewage
Brian Bennett
Brian
Bennett
Denan Wang
Denan
Wang
Sergey V. Lindeman
Sergey V.
Lindeman
Tricarbonylrhenium(I) Complexes of Dinucleating Redox-Active
Pincer Ligands
American Chemical Society
2018
EPR
single-crystal X-ray diffraction
electrolyte
NNN
pincer ligands feature
DMF
complexes 1 n
Complex 1 exhibits
H 2
Dinucleating Redox-Active Pincer Ligands
UV
one-electron oxidations
oxidation potentials
CH 2 Cl 2
CO
DFT
III
II
NBu 4 PF 6
redox-active dinucleating pincer ligands
2018-03-08 18:52:59
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Tricarbonylrhenium_I_Complexes_of_Dinucleating_Redox-Active_Pincer_Ligands/5965084
Two homobimetallic tricarbonylrhenium(I)
complexes of new redox-active
dinucleating pincer ligands have been prepared to assess the impact
of spacer size on the first oxidation potentials with respect to mononucleating
analogues and on intramolecular electronic communication. The new
pincer ligands feature two tridentate <i>NNN</i>- sites
each composed of two pyrazolyl flanking donors and a diarylamido anchor
that are either directly linked (to form a central benzidene core,
H<sub>2</sub>(L1)) or linked via a <i>para</i>-phenylene
group (to form a <i>para</i>-terphenyldiamine core, H<sub>2</sub>(L2)). The bimetallic complexes of the deprotonated ligands,
[<i>fac</i>-Re(CO)<sub>3</sub>]<sub>2</sub>(μ-L1), <b>1</b>, and [<i>fac</i>-Re(CO)<sub>3</sub>]<sub>2</sub>(μ-L2), <b>2</b>, were fully characterized in solution
and the solid state including by single-crystal X-ray diffraction
for <b>1</b>. The electrochemical properties of each depended
strongly on solvent and electrolyte. Complex <b>1</b> exhibits
two one-electron oxidations in all electrolyte-containing solutions
but with separations between first and second oxidation potentials,
Δ<i>E</i><sub>1/2</sub>, between 119 and 316 mV depending
on conditions. On the other hand, cyclic voltammetry of <b>2</b> showed one two-electron oxidation in DMF with NBu<sub>4</sub>PF<sub>6</sub> as an electrolyte but two one-electron oxidations with a
maximal separation in Δ<i>E</i><sub>1/2</sub> of 96
mV in CH<sub>2</sub>Cl<sub>2</sub> with NBu<sub>4</sub>B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub> as an electrolyte. The oxidized complexes <b>1</b><sup><b>n+</b></sup> and <b>2</b><sup><b>n+</b></sup> (<i>n</i> = 1, 2) were
prepared by chemical oxidation and were studied spectroscopically
(UV–vis/NIR, EPR). The mono-oxidized complex <b>1</b><sup><b>+</b></sup> behaves as a Robin–Day Class III
species, while <b>2</b><sup><b>+</b></sup> is a Robin–Day
Class II species that shows thermal valence trapping at 77 K by EPR
spectroscopy. As suggested from theoretical studies using DFT methods,
the oxidized complexes maintain considerable ligand radical character,
so their electronic structures can be formulated as (CO)<sub>3</sub>Re<sup>I</sup>(μ-L<sup><i>n</i>+</sup>)Re<sup>I</sup>(CO)<sub>3</sub> (<i>n</i> = 1 or 2).