Azido-Functionalized Aromatic Phosphonate Esters in ^RPOSS-Cage-Supported Lanthanide Ion (Ln = La, Nd, Dy, Er) Coordination

Abstract

Within this work, a modified preparation of diethyl 4-azidobenzylphosphonate (L1) is presented and the family of 4-or 4′-azido-substituted aromatic phosphonate esters is increased by three new ligand platforms: diisopropyl 4-azidobenzylphosphonate (L2), diisopropyl ((4′-azido-[1,1′-biphenyl]-4-yl)methyl)phosphonate (L3), and diisopropyl 4-azido-2,3,5,6-tetrafluorobenzylphosphonate (L4), which exhibit an anomalous splitting of the N 3 stretching vibrations. Subsequent coordination to the in situ generated R POSS (polyhedral oligomeric silsesquioxane)-cage-supported lanthanide precursors [(Ln{ R POSS}) 2 (THF) m ] (P1−P6) (Ln = La, Nd, Dy, Er; R = iBu, Ph; m = 0, 1) yields complexes of the general formula [Ln{ R POSS}(L1−L4) n (S1) x (THF) m ] (1−30) (n = 2, 3; x = 0, 1; m = 0−2) retaining the azide unit for future semiconductor surface immobilization. Because the latter compounds are mostly oils or viscous waxes, preliminary solution-state structure elucidations via DOSY-ECC-MW estimations have been carried out which are in accordance with 1 H NMR integral ratios as well as solidstate structures, where available. Moreover, the optical properties of the Nd, Dy, and Er derivatives of complexes 1−30 are examined in the visible and NIR spectral regions, where applicable.

Synthesis of Geminal Bis‐ and Tetrakisphosphonate Ester Derivatives and Their Coordination Behavior Towards Ca(II) Ions

“…At the same time, a solvent‐separated ion pair is formed, which probably best reflects the presence of dissolved calcium chloride or BP‐supported calcium complexes in the human body that are expected to show a solvation by ubiquitous water molecules. Despite of being formally hexadentate chelate ligands, the geminal BP esters of this study show an exclusive bidentate coordination via the P + −O − oxygen atoms which was already observed for the corresponding monophosphonate ester derivatives [14,15] . Additionally, weak intermolecular hydrogen bonds of 2.490(2) Å are formed in [Ca(H 2 O) 2 ( L1 ) 2 ]Cl 2 ( C1 ) between O6 and the aromatic para hydrogen atom (H20) of adjacent molecules forming infinite hydrogen bonded strands (SI, Figure S40).…”

“…Additionally, in the reaction of mono phosphonate S4, the para protonated derivative tetraethyl ((2,3,5,6-tetrafluorophenyl)methylene)bis(phosphonate) (L4) is obtained instead of the expected para bromide derivative tetraethyl ((4-bromo-2,3,5,6tetrafluorophenyl)methylene)bis(phosphonate). Similar behavior was observed to a minor extend for the related compound diisopropyl (4-bromo-2,3,5,6-tetrafluorobenzyl)-phosphonate [15] when introducing an azido substituent at the 4-position of the aryl ring tagging these species to be highly available for modifications at their aromatic periphery. In addition to the above mentioned phosphonic esters, the tetrakisphosphonate ester ligand octaethyl propane-1,1,3,3tetrayltetrakis(phosphonate) (L8) is prepared according to a literature procedure, providing four phosphonate ester units at once (see Scheme 3).…”

“…Despite of being formally hexadentate chelate ligands, the geminal BP esters of this study show an exclusive bidentate coordination via the P + À O À oxygen atoms which was already observed for the corresponding monophosphonate ester derivatives. [14,15] Additionally, weak intermolecular hydrogen bonds of 2.490(2) Å are formed in [Ca(H 2 O) 2 (L1) 2 ]Cl 2 (C1) between O6 and the aromatic para hydrogen atom (H20) of adjacent molecules forming infinite hydrogen bonded strands (SI, Figure S40). Complex [Ca(L8)Cl 2 ] n (C4) crystallizes in the monoclinic space group P2 1 /c containing 1.5 molecules of C4 as well as four co-crystallized lattice CDCl 3 molecules in the asymmetric unit.…”

Synthesis and Characterization of Solvated Lanthanide Tris(trimethylsilyl)siloxides

“…), we were interested in the production of LnSiO x materials for radiation shielding applications. While a number of lanthanide siloxides ([Ln­(OSiR 3 ) 3 ]) have been reported, − all attempts in our hands to exploit these types of precursors for production of LnSiO x materials yielded only LnO x products; therefore, alternative Ln–O–Si-bearing precursors attracted interest.…”

Keggin-Type Tridecanuclear Europium-Oxo Nanocluster Protected by Silsesquioxanes

“…Oligosiloxanes, derived from the hydrolysis and condensation of alkoxysilanes, have proved to be effective ligands for metallasilsesquioxanes (including clusters or cages containing the M–O–Si bond, M = metal ion), providing ideal molecular model compounds for deep insights into the scenarios occurring on silica-supported metal species. − However, in most cases, the reaction was performed in an inert atmosphere, impeding their practical applications. Recently, our group has made use of oligosiloxane ligands and successfully constructed several oligosiloxane-based transition-metal nanocages under an atmospheric environment. − To our knowledge, there is no report as yet on oligosiloxane-protected Ln clusters isolated under air.…”