Novel in situ manganese-promoted double-aldol addition

A novel in situ Mnn+-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 alpha,alpha 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. Crown Copyright (C) 2011 Published by Elsevier B. V. All rights reserved.