Synthesis of N-Aryloxy-β-diketiminate Ligands and Coordination to Zirconium, Ytterbium, Thorium, and Uranium

Abstract

Two examples of N-aryloxy-β-diketiminate dianions (11a,b) have been synthesized on a multigram scale, in four steps, from commercially available chemicals. The synthetic scheme relies on the sequential addition of 2,6diisopropylaniline and 2-amino-4-tert-butylphenol (1a) (or 2amino-4,6-di-tert-butylphenol (1b)) to acetylacetone, using Et 3 OBF 4 as an activation reagent. Both the nature of the activation reagent and the order of addition of the primary amines have a major impact on the outcome of the reaction, and acid catalysts (such as sulfuric acid or p-toluenesulfonic acid) lead to decomposition of the β-diketiminate backbone via formation of a benzoxazole derivative (3a,b). Using dianions 11a,b, mono-and bis(N-aryloxy-β-diketiminate) complexes of zirconium(IV), ytterbium(III), thorium(IV), and uranium(IV) have been synthesized (12−18), by salt metathesis reactions, and characterized by a combination of 1 H/ 13 C NMR spectroscopy, elemental analysis, and X-ray crystallography. The two ligands differ in their steric bulk and exhibit different coordination behaviors, which were rationalized on the basis of geometric considerations.

Tuning steric and electronic effects in transition-metal β-diketiminate complexes

“…N -Aryloxy-β-diketiminate zirconium complexes also showed a different orientation depending on steric bulk (Scheme 3.1.1). 95 Bridged aryloxides were observed with one meta-t Bu on the N -aryl, but the presence of a second meta - t Bu group gave steric conflict that resulted in the isolation of a [LZrCl 2 ] 2 dimer instead. In the same system, the L 2 Zr complexes also showed conformational differences where the bulkier ligand adopted a trigonal prismatic geometry (Figure 3.1.2).…”

Werner-Type Complexes of Uranium(III) and (IV)

“…Lappert’s {Me 3 SiNC­(Ph)} 2 CH – chelate ensues from reactions of ligand cannibalization, forming complexes with 1,3-diaza-allyl ligands . Other examples of uranium complexes using β-diketiminate-like scaffolds include a macrocycle tetramethyltetraazaannulene, − a dianionic and a tridentate N -aryloxy-β-diketiminate, a cyanopentadienyl dianion, and an aza β-diketiminate ligand 2-(4-tolyl)-1,3-bis­(quinolyl)­malondiiminate) …”

Improved Synthesis of Unsymmetrical N‐Aryl‐N′‐alkylpyridyl ß‐Diketimines Using Molecular Sieves and their Lithium Complexes

“…β‐Diketiminato Li complexes are often used as ligand transfer reagents in the preparation of transition‐metal coordination complexes because of their high yield lithiation and transmetalation activities , . For example, metal β‐diketiminate complexes with rare‐earth or d‐block transition metals can be synthesized by the reaction of β‐diketiminato Li complexes with their corresponding metal halides , , . Indeed, there are few studies describing the preparation of Li complexes bearing unsymmetrical N ‐aryl‐ N′ ‐alkyl β‐diketimines (UNAAD) , .…”

“…[6,[31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] For example, metal -diketiminate complexes with rare-earth or d-block transition metals can be synthesized by the reaction of -diketiminato Li complexes with their corresponding metal halides. [1,5,[46][47][48][49][50][51] Indeed, there are few studies describing the preparation of Li complexes bearing unsymmetrical N-aryl-N′-alkyl -diketimines (UNAAD). [52,53] In order to explore the lithiation chemistry of UNAADpy, we synthesized four UNAADpy Li complexes (LiL1, LiL2, LiL3 , and LiL4) and investigated their binding modes in solution as well as in the solid state.…”