Mixed Metal Multinuclear Cr(III) Cage Compounds and Coordination Polymers Based on Unsubstituted Phenolate: Design, Synthesis, Mechanism, and Properties

Abstract

Oxidative substitution reactions of chromium(II) chloride with lithium phenoxide in the presence of water give access to new polynuclear chromium(III) aryloxide complexes and coordination polymers. While a one-dimensional coordination polymer based on chromium(III), [Cr 2 (μ 3 -OPh) 2 (μ-OPh) 6 (μ-OH)(μ 3 -Li) 4 (μ 3 -Cl) 2 Li(THF) 6 ] n , is first obtained by serendipity, the controlled addition of water to the initial Cr(II) complex as well as variation of the stoichiometry lead to three new discrete chromium(III) aggregates, namely, [Cr(OPh) The properties of such polymetallic compounds depend on (a) the types and proportions of metallic species, and (b) the use of ligands allowing the tuning of the properties. Indeed, depending of the ligand, we obtained a different configuration of complex which in the case of the bridging ligand, changes angles and distances between metals ions. The bulkiness of the ligand has a major role in the case where accessibility of metal center is necessary, e.g., in catalysis. 5,6 In our group, we have investigated alkali and alkaline earth metal compounds in order to study their behavior in nonaqueous solvents, their analogy to transition metals, and possible applications in oxide materials. 2,22−43 We have previously shown that group 2 metal halides may act as starting materials for both homometallic alkaline earth and mixed-metal alkali and alkaline earth aryl and alkoxide cage compounds obtained from (partial) abstraction of halide. 2,38,39,42−44 Depending on the bulk of the R group on the alkoxide or aryloxide reagent and the nature of the alkali metal and the solvent of crystallization, different structures were achieved. 36,37,43,44 In this context, we have also used calixarenes, which can be understood as cyclic polyphenols, to obtain lithium polyaryloxides. 22,23,37,40 This straightforward access to mixed metal aryl-and alkoxides inspired us to use this approach, replacing alkaline earth metal halides by chromium dihalides as starting compounds due to their better solubility and in spite of the sensitivity of such compounds to humidity. 45Very similar to a compound described by us, [Ca(OPh) 8 Li 6 -(THF) 6 ], 42 the literature reports on a Cr(II) compound,

Robust Chromium Precursors for Catalysis: Isolation and Structure of a Single-Component Ethylene Tetramerization Precatalyst

“…Significant efforts have identified ligands and cocatalysts to support ethylene tetramerization, but the pool of Cr precursors has remained small (Figure a). These are typically Cr­(III) or Cr­(II) salts: Cr­(acac) 3 , Cr­(ethylhexanoate) 3 , CrCl 3 (THF) 3 , and CrCl 2 (THF) 2 (acac = acetylacetonate, THF = tetrahydrofuran) . To generate a catalytically active species in situ, these precursors are typically mixed with alkylaluminum cocatalysts such as modified methylaluminoxane (MMAO) in the presence of an auxiliary ligand.…”

Compartmentalization of Alkaline-Earth Metals in Salen-Type Cu- and Ni-Complexes in Solution and in the Solid State

“…Interesting and enhanced properties for potential biological or physical applications can emanate from the combination and the complexation of specific metal ions − orderly placed in different compartments of one ligand entity, delivering various intriguing structural architectures. − For instance, aluminum–dipyrrin complexes able to selectively bind alkaline-earth ions in an aqueous mixed solvent have been recently synthesized and can be applied for colorimetric and/or fluorometric sensing applications. − …”

Threading Salen-type Cu- and Ni-Complexes into One-Dimensional Coordination Polymers: Solution versus Solid State and the Size Effect of the Alkali Metal Ion

“…Functional compartments can also be created by substitution of the ligand, allowing the coordination of two different metal ions ,− and originating macrocycle-type compounds. The latter combination can lead to new properties , in compounds such as coordination polymers, − mono- and multimetallic − complexes or oxide materials. − …”