Synthesis and characterization of a N-salicylaldimine ligand and its vanadium(V) complex

The reduction of 2-nitro-1,3-di(pyridin-2-yl)-1,3-di(tert -butyldimethylsilyloxy)propane 1 with sodium borohydride affords 2-amino-1,3-di(pyridin-2-yl)-1,3-di(tert-butyldimethylsilyloxy)propane 2 which was subsequently reacted with salicyl aldehyde yielding rac-((2,2,3,3,9,9,10,10-octamethyl-5,7-di(pyridin-2-yl)-4,8-dioxa-3,9-disilaundecan-6-ylimino)methyl)phenol (Proligand 3 = HL(SiMe2tBu)2), with excellent yield. Reaction of 3 with vanadyl acetylacetonate followed by aerial oxidation diastereoselectively led to the octahedral coordinated vanadium(V) complex 4([VO(OMe)L(SiMe2t Bu)]). Compound 3 together with vanadyl acetylacetonate as well as with molybdenyl acetylacetonate shows catalytic activity in the sulfoxidation of (methylsulfanyl)benzene I, which was followed by NMR spectroscopy. The vanadium complex 4 was also able to catalyze the sulfoxidation but was considerably slower. All three tested catalytic systems lead to almost quantitative formation of the sulfoxide with only minor formation of the respective sulfone.