posted on 2020-01-17, 21:44authored byFabian
A. Watt, Athul Krishna, Grigoriy Golovanov, Holger Ott, Roland Schoch, Christoph Wölper, Adam G. Neuba, Stephan Hohloch
We present the synthesis of a series
of new lanthanide(III) complexes
supported by a monoanionic bidentate anilidophosphine ligand (N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide,
short PN–). The work comprises the characterization
of a variety of heteroleptic complexes containing either one or two
PN ligands as well as a study on further functionalization possibilities.
The new heteroleptic complexes cover selected examples over the whole
lanthanide(III) series including lanthanum, cerium, neodymium, gadolinium,
terbium, dysprosium, and lutetium. In case of the two diamagnetic
metal cations lanthanum(III) and lutetium(III), we have furthermore
studied the influence of the lanthanide ion (early vs. late) on the
reactivity of these complexes. Thereby we found that the radius of
the lanthanide ion has a major influence on the reactivity. Using
sterically demanding, multidentate ligand systems, e.g., cyclopentadienide
(Cp–), we found that the lanthanum complex La(PN)2Cl (1-La) reacts well to the corresponding cyclopentadienide complex, while
for Lu(PN)2Cl (1-Lu) no reaction was observed under any conditions tested.
On the contrary, employing monodentate ligands such as mesitolate,
thiomesitolate, 2,4,6-trimethylanilide or 2,4,6-trimethylphenylphosphide,
results in the clean formation of the desired complexes for both lanthanum
and lutetium. All complexes have been studied by various techniques,
including multi nuclear NMR spectroscopy and X-ray crystallography. 31P NMR spectroscopy was furthermore used to evaluate the presence
of open coordination sites on the complexes using coordinating and
noncoordinating solvents, and as a probe for estimating the Ce–P
distance in the corresponding complexes. Additionally, we present
cyclic voltammetry (CV) data for Ce(PN)2Cl (1-Ce), La(PN)2Cl (1-La), Ce(PN)(HMDS)2 (8-Ce) and La(PN)(HMDS)2 (8-La) (with HMDS = hexamethyldisilazide,
(Me3Si)2N–) exploring the
potential of the anilidophosphane ligand framework to stabilize a
potential Ce(IV) ion.