Iron(III) and Zinc(II) Calixarene Complexes: Synthesis, Structural Studies, and Use as Procatalysts for ε‐Caprolactone Polymerization

Abstract

Treatment of the heterobimetallic iron(II) alkoxides [(THF)MFe(OtBu)(3)](2) with p-tert-butylcalix[4]areneH(4) (L(1)H(4)) affords the oxo-bridged diiron(III) complexes {Fe[M(NCMe)(x)](2)L(1)}(2)(mu-O), M = Na, x = 2 1 x 8(CH(3)CN), M = K, x = 3 2 x 3.5(CH(3)CN); similar use of p-tert-butylcalix[6]areneH(6) (L(2)H(6)) afforded [{Fe(2)(mu-O)Na(2)(OH(2))(NCMe)(2)L(2)}(2)][{Fe(2)(mu-O)Na(OH(2))(NCMe)(6)L(2)}(2)](2-)[Na(NCMe)(5)](2)(2+) 3 x 9.46(CH(3)CN) and [{Fe(2)(mu-O)L(2)(K(NCMe)(2))(2)}(2)] 4 x 10.8(MeCN), respectively. In the case of 4, a minor product {(L(2)(2)Fe(8)O(8))[K(NCMe)(1.5)K(H(2)O)(NCMe)(2.5)](2)} 5 x 6(CH(3)CN), which is comprised of chains of (L(2)(2)Fe(8)O(8)) clusters bridged by K/MeCN fragments, is also isolated. Use of p-tert-butylcalix[8]areneH(8) (L(3)H(8)) and two equivalents of [(THF)KFe(OtBu)(3)](2) affords [(K(2)(mu-NCCH(3))(4)(mu-OH(2)))(2)(Fe(2)(mu-O)L(3)H(2))(2)(CH(3)CN)(2)] 6 x 9(CH(3)CN). In the case of p-tert-butyltetrahomodioxacalix[6]areneH(6) (L(4)H(6)), reaction with [(THF)MFe(OtBu)(3)](2) (two equivalents) leads to isolation of the pseudoisomorphic complexes [M(2)(CH(3)CN)(4)L(4)Fe(2)(mu-O)] x 4 CH(3)CN M = Na 7 x 4(CH(3)CN), M = K 8 x 2(CH(3)CN); similar use of p-tert-butylhexahomotrioxacalix[3]areneH(3) (L(5)H(3)) led to [Na(2)Fe(2)(mu-OH)(2)(L(5))(2)(CH(3)CN)(4)] 9 x 2(CH(2)Cl(2)). The complex [L(4)(ZnEt)(4)Zn(2)(CH(3)CN)(4)(mu-OEt)(2)], 10 x 2(CH(3)CN), isolated from the reaction of L(4)H(6) and ZnEt(2) is also reported. Complexes 1-10 are structurally characterized (partially in the case of 4) and screened (not 5) as catalysts for the ring opening polymerization of epsilon-caprolactone.

A multimetallic iron(ii)–lithium complex as a catalyst for ε-caprolactone polymerization

“…6 The only examples we are aware of are heteromultimetallic calixarene iron(III) aryloxides, which are mostly showing very low catalytic activity towards ε-caprolactone polymerization. 7 In summary in most of the cases, the resulting PCL, initiated by the above mentioned iron-based complexes, have a broad molecular weight distribution, especially when the polymerization was carried out at high temperatures or without co-initiators. The catalytic activities of the metal-based complexes are affected by the metals as well as by the supporting ligands.…”

Dehydrocoelenterazine is the Organic Substance Constituting the Prosthetic Group of Pholasin

“…The synthesis of the single‐molecule‐like [(thf)NaFe(O t Bu) 3 ] 2 19 has been evaluated to be a good initiator for controlled ring‐opening polymerization of rac ‐lactide. As cited before, iron alkoxide/aryloxide complexes have particularly been shown to be interesting for several applications such as precursors for iron oxide nanoparticles,15,21 or as catalysts 10,12,13,19…”

“…For several decades, intensive research in the chemistry of metal alkoxides or aryloxides1–8 has developed, because of their interesting potential to serve many different applications for precursors of oxide materials such as LiCoO 2 ,7,9 as catalysts,10–13 or as conducting materials 9,14,15. Metal alkoxides have also been proposed as good precursors for ceramic materials based on high‐purity metal oxides, because of their high solubility, low decomposition temperatures,16 cross linking ability, and ease of modification 6,17.…”

Synthesis and Characterization of New Pentacoordinate Iron‐Based Aryloxide Complexes

“…For several decades, intensive research in the chemistry of metal alkoxides or aryloxides [1][2][3][4][5][6][7][8] has developed, because of their interesting potential to serve many different applications for precursors of oxide materials such as LiCoO 2 , [7,9] as catalysts, [10][11][12][13] or as conducting materials. [9,14,15] Metal alkoxides have also been proposed as good precursors for ceramic materials based on high-purity metal oxides, because of their high solubility, low decomposition temperatures, [16] cross linking ability, and ease of modification.…”

“…As cited before, iron alkoxide/ aryloxide complexes have particularly been shown to be interesting for several applications such as precursors for iron oxide nanoparticles, [15,21] or as catalysts. [10,12,13,19] For several years, we have been studying the synthesis of mixed metal compounds [22][23][24] containing alkali or alkaline earth and transition metal ions in order to generate mixed metal oxides with the intent of making these at much lower temperatures than those employed in the classical solid state synthesis. [15,24] Our general reaction scheme involves a M II halide, which is reacted with an alkali alkoxide or aryloxide in a dry solvent such as thf.…”