ic8b00618_si_001.pdf (1.5 MB)
Hydrogen-Atom Noninnocence of a Tridentate [SNS] Pincer Ligand
journal contribution
posted on 2018-07-03, 17:23 authored by Kyle E. Rosenkoetter, Michael K. Wojnar, Bronte J. Charette, Joseph W. Ziller, Alan F. HeydukDouble deprotonation
of bis(2-mercapto-4-methylphenyl)amine ([SNS]H3) followed
by addition to NiCl2(PR3)2 in air-free
conditions afforded [SN(H)S]Ni(PR3) (1a, R
= Cy; 1b, R = Ph) complexes, characterized as diamagnetic,
square-planar nickel(II) complexes. When the same reaction was conducted
with 3 equiv of KH, the diamagnetic anions K{[SNS]Ni(PR3)} were obtained (K[2a], R = Cy; K[2b],
R = Ph). In the presence of air, the reaction proceeds with a concomitant
one-electron oxidation. When R = Cy, a square-planar, S = 1/2 complex, [SNS]Ni(PCy3) (3a), was isolated. When R = Ph, the bimetallic complex {[SNS]Ni(PPh3)}2 ({3b}2) was obtained.
This bimetallic species is diamagnetic; however, in solution it dissociates
to give S = 1/2 monomers analogous
to 3a. Complexes 1–3 represent a hydrogen-atom-transfer series. The bond dissociation
free energies (BDFEs) for 1a and 1b were
calculated to be 63.9 ± 0.1 and 62.4 ± 0.2 kcal mol–1, respectively, using the corresponding pKa and E°′ values. Consistent
with these BDFE values, TEMPO• reacted with 1a and 1b, resulting in the abstraction of a
hydrogen atom to afford 3a and 3b, respectively.
