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

Treatment of the heterobimetallic iron(II) alkoxides [(THF)MFe(O t Bu) 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 (μ‐O), M=Na, x =2 1 ⋅8(CH 3 CN), M= K, x =3 2 ⋅3.5(CH 3 CN); similar use of p ‐ tert ‐butylcalix[6]areneH 6 (L 2 H 6 ) afforded [{Fe 2 (μ‐O)Na 2 (OH 2 )(NCMe) 2 L 2 } 2 ][{Fe 2 (μ‐O)Na(OH 2 )(NCMe) 6 L 2 } 2 ] 2− [Na(NCMe) 5 ] 2 2+ 3 ⋅9.46(CH 3 CN) and [{Fe 2 (μ‐O)L 2 (K(NCMe) 2 ) 2 } 2 ] 4 ⋅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 ⋅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(O t Bu) 3 ] 2 affords [(K 2 (μ‐NCCH 3 ) 4 (μ‐OH 2 )) 2 (Fe 2 (μ‐O)L 3 H 2 ) 2 (CH 3 CN) 2 ] 6 ⋅9(CH 3 CN). In the case of p ‐ tert ‐butyltetrahomodioxacalix[6]areneH 6 (L 4 H 6 ), reaction with [(THF)MFe(O t Bu) 3 ] 2 (two equivalents) leads to isolation of the pseudoisomorphic complexes [M 2 (CH 3 CN) 4 L 4 Fe 2 (μ‐O)].4CH 3 CN M=Na 7 ⋅4(CH 3 CN), M=K 8 ⋅2(CH 3 CN); similar use of p ‐ tert ‐butylhexahomotrioxacalix[3]areneH 3 (L 5 H 3 ) led to [Na 2 Fe 2 (μ‐OH) 2 (L 5 ) 2 (CH 3 CN) 4 ] 9 ⋅2(CH 2 Cl 2 ). The complex [L 4 (ZnEt) 4 Zn 2 (CH 3 CN) 4 (μ‐OEt) 2 ], 10 ⋅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 ε‐caprolactone.