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 α,α double aldol reaction promoted by Mn ions in the presence of base. The newly formed ligands coordinate to four MnIII 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 CoII (2) and NiII (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 {MnIII}4 systems resulting in an intermediate spin ground state of ST = 6.