Novel in situ manganese-promoted double-aldol addition

Abstract

A novel in situ Mn n+-promoted double-aldol reaction is reported. Single crystal X-ray measurements confirm the addition of acetone to two o-vanillin molecules in an original in situ α,α double aldol reaction promoted by Mn ions in the presence of base. The newly formed ligands coordinate to four Mn III ions forming a defect-dicubane core structure (1) bridged exclusively by oxygen-based ligands. Other 3d metals were employed under the same reaction conditions, however no aldol addition occurred and tetranuclear cubane-like structures formed using Co II (2) and Ni II (3) ions. Magnetic measurements were carried out on all complexes using SQUID magnetometry. Dominant ferromagnetic interactions were observed for complexes 1 and 3 with J = 1.8 cm -1, J′ =-2.5 cm -1, g = 1.95 for 1 and J = 3.1 cm -1, g = 2.17 for 3 while complex 2 exhibited antiferromagnetic exchange interactions. Notably, complex 1 was shown to exhibit spin frustration rarely seen in {Mn III} 4 systems resulting in an intermediate spin ground state of S T = 6. © 2011 Elsevier B.V. All rights reserved.