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

Treatment of the heterobimetallic iron(II) alkoxides [(THF)MFe-(OtBu)(3)](2) with p-tert-butylcalix[4]are-neH(4) ((LH4)-H-1) affords the oxo-bridged diiron(III) complexes (Fe[M-(NCMe)(x)](2)L-1}(2)(mu-O), M=Na, x=2 1.8-(CH3CN), M = K, x = 3 2.3.5(CH3CN); similar use of p-tert-butylcalix[6]are-neH(6) ((LH6)-H-2) afforded [{Fe-2(mu-O)Na-2 (OH2)(NCMe)(2)L-2}(2)[{Fe-2(mu-O)Na(OH2) (NCMe)(6)L-2}(2)](2-)[Na(NCMe)(5)](2)(2+) 3.9.46-(CH3CN) and [(Fe-2(mu-O)L-2 (K-(NCMe)(2))(2)}(2)] 4.10.8(MeCN), respectively. In the case of 4, a minor product {((L2Fe8O8)-Fe-2)[K(NCMe)(1.5)K(H2O)- (NCMe)(2.5)](2)} 5.6(CH3CN), which is comprised of chains of ((L2Fe8O8)-Fe-2) clusters bridged by K/MeCN fragments, is also isolated. Use of p-tert-butylcalix[8]areneH(8) ((LH8)-H-3) and two equivalents of [(THF)KFe(OtBU)(3)](2) affords [(K-2(mu-NCCH3)(4)(mu-OH2))(2)(Fe-2(mu-O)(LH2)-H-3)(2)(CH3CN)(2)] 6.9(CH3CN). In the case of p-tert-butyltetrahomodioxacalix[6]areneH(6) ((LH6)-H-4), reaction with [(THF)MFe(OtBu)(3)](2) (two equivalents) leads to isolation of the pseudoisomorphic complexes [M-2(CH3CN)(4)(LFe2)-Fe-4(mu-O)]center dot 4CH(3)CN M=Na 7.4(CH3CN), M=K 8.2(CH3CN); similar use of p-tert-butylhexahomotrioxacalix [3]areneH(3) ((LH3)-H-5) led to [Na2Fe2(mu-OH)(2)(L-5)(2)(CH3CN)(4)] 9.2(CH2Cl2). The complex [L-4(ZnEt)(4)Zn-2(CH3CN)(4)(mu-OEt)(2)], 10.2(CH3CN), isolated from the reaction of (LH6)-H-4 and ZnEt2 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.