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Monoanionic Anilidophosphine Ligand in Lanthanide Chemistry: Scope, Reactivity, and Electrochemistry

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posted on 17.01.2020, 21:44 authored by Fabian 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.