Manganese coordination chemistry of bis(imino)phenoxide derived [2 + 2] Schiff-base macrocyclic ligands

Abstract

The [2 + 2] Schiff-base macrocycles [2,2′-(CH₂CH₂)(C₆H₄NCH)₂-2,6-(4-RC₆H₂OH)]₂ (I^RH₂), upon reaction with MnCl₂ (two equivalents) afforded the bimetallic complex [Cl₃Mn(μ-Cl)Mn(I^MeH₂)] (1) or the salt complex [Cl₃Mn(NCMe)][MnCl(I^tBuH₂)] (2). Under similar conditions, use of the related [2 + 2] oxy-bridged macrocycle [2,2′-O(C₆H₄NCH)₂-4-RC₆H₂OH] (II^RH₂), afforded the bimetallic complexes [(MnCl)₂II^R] (R = Me 3, tBu 4), whilst the macrocycle derived from 1,2-diaminobenzene and 5,5′-di-tert-butyl-2,2′-dihydroxy-3,3′-methylenedibenzaldehyde (IIIH₄) afforded the complex [(MnCl)₂(III)]·2MeCN (5·2MeCN). For comparative studies, the salt complexes [2,6-(ArNHCH)₂-4-MeC₆H₂O][MnCl₃(NCMe)] (Ar = 2,4-Me₂C₆H₃, 6) and {[(2-ArNCH),6-(ArNHCH)-4-Me-C₆H₂O]MnCl}₂[MnCl₄]·8CH₂Cl₂ (Ar = 4-MeC₆H₄, 7·8CH₂Cl₂) were prepared. The crystal structures of 1–7 are reported (synchrotron radiation was necessary for complexes 1, 3 and 5). Complexes 1–7 (not 5) were screened for their potential to act as pre-catalysts for the ring opening polymerization (ROP) of ε-caprolactone; 3, 4 and 6, 7 were inactive, whilst 1 and 2 exhibited only poor activity with low conversion (<15%) at temperatures above 60 °C.