Abstract:
A family of triphenylamido-amine ligands of the general stoichiometry
(LH3)-H-x=[R-NH-(2-C6H4)](3)N (R=4-t-BuPh ((LH3)-H-1), 3,5-t-BU2Ph
((LH3)-H-2), 3,5-(CF3)(2)Ph ((LH3)-H-3) CO-t-Bu ((LH3)-H-4), 3,5-Cl2Ph
((LH3)-H-5), COPh ((LH3)-H-6) CO-i-Pr ((LH3)-H-7), COCF3 ((LH3)-H-8),
and i-Pr ((LH3)-H-9)) has been synthesized and characterized, featuring
a rigid triphenylamido-amine scaffold and an array of
stereoelectronically diverse aryl, acyl, and alkyl substituents (R).
These ligands are deprotonated by potassium hydride in THF or DMA and
reacted with anhydrous FeCl2 to afford a series of ferrous complexes,
exhibiting stoichiometric variation and structural complexity. The
prevalent [(L-x)Fe(II)-solv](-) structures (L-x=L-1, L-2, L-3, L-5,
solv=THF; L-x=L-8, solv-DMA; L-x=L-6, L-8, solv=MeCN) reveal a distorted
trigonal bipyramidal geometry, featuring ligand-derived
[N3,amidoNamine] coordination and solvent attachment trans to the
N-amie atom. Specifically for [(L-8)Fe(II)-DMA](-), a N-amido residue
is coordinated as the corresponding N-imino moiety (Fe-N(Ar)=C(CF3)-O-).
In contrast, compounds [(L-4)Fe(II)](-), [(L-6)(2)Fe(II)(2)](2-),
[K(L-7)(2)Fe(II)(2)](2)(2-), and [K(L-9)Fe](2) are all solvent-free
in their coordination sphere and exhibit four-coordinate geometries of
significant diversity. In particular, [(L-4)Fe(II)](-) demonstrates
coordination of one amidato residue via the O-atom end
(Fe-O-C(t-Bu)=N(Ar)) Furthermore, [(L-6)(2)Fe(II)(2)](2-) and
[K(L-7)(2)Fe(II)(2)](2)(2-) are similar structures exhibiting bridging
amicato residues (Fe-N(Ar)-C(R)=O-Fe) in dimeric structural units,
Finally, the structure of [K(L-9)Fe](2) is the only example featuring
a minimal [N3.amidoNamine] coordination sphere around each Fe(II)
site. All compounds have been characterized by a variety of
physicocherrical techniques, including Mossbauer spectroscopy and
electrochemistry, to reveal electronic attributes that are responsible
for a range of Fe(II)/Fe(III) redox potentials exceeding 1.0 V.
