Iron(ii) tetrafluoroborate complexes of new tetradentate C-scorpionates as catalysts for the oxidative cleavage of trans-stilbene with H2O2.

Attachment of a 2-methylpyridyl group onto the unique 1-nitrogen atom on nitrogen-confused C-scorpionates with either pyrazol-1-yl or 3,5 dimethylpyrazol-1-yl donors gives two new cis-directing tetradentate-N4 ligands (L and L*). The complexes [(L or L*)Fe(CH3CN)2](BF4)2 (1 or 2) were prepared, fully characterized, and investigated for their ability to catalyse the oxidative cleaveage of trans-stilbene in CH3CN. Complexes 1 and 2 are capable of catalysing stilbene cleavage when H2O2 is used as an oxidant but up to six different products are formed, with C[double bond, length as m-dash]C cleavage products (benzaldehyde and benzoic acid) dominating over four products of oxygen transfer. Catalytic amounts of 1 or 2 enhance the ability for the organic photocatalyst riboflavin tetraacetate to use atmospheric oxygen and blue light irradation (450-460 nm) to selectively cleave stilbene to benzaldehyde. However, when benzaldehyde oxidizes further to benzoic acid, the iron species begin giving increasing amounts of stilbene oxygenation products.