Hypervalent Organotin(IV) Compounds as Efficient Catalysts for the Knoevenagel Condensation of Aldehydes

We report the synthesis of six mononuclear organotin(IV) compounds, [R 2 Sn(L 1 )] [R = Ph ( 1 ), t‐ Bu ( 2 ), and Me ( 3 )] and [R 2 Sn(L 2 )] [R = Ph ( 4 ), t‐ Bu ( 5 ), and Me ( 6 )] supported by two polydentate pro‐ligands, ( E )‐2,4‐dichloro‐6‐(((2‐hydroxy‐5‐nitrophenyl)imino)methyl)phenol ( H 2 L 1 ) and ( E )‐2,4‐dichloro‐6‐(((2‐hydroxyphenyl)imino)methyl)phenol ( H 2 L 2 ). HR‐MS, multinuclear ( 1 H, 13 C, and 119 Sn) NMR spectroscopy, and FT‐IR spectroscopy were used to characterize all compounds ( 1 – 6 ). Structural investigation via single‐crystal X‐ray diffraction confirmed a mononuclear geometry for all compounds, each featuring a five‐coordinate tin(IV) center. The Lewis acidity of the compounds ( 1 – 6 ) was examined through the Gutmann–Beckett method. The effectiveness of all Sn(IV) compounds ( 1 – 6 ) as catalysts for the Knoevenagel condensation of various aldehydes with malononitrile was assessed. In addition, a plausible mechanism is proposed based on the mechanistic studies and theoretical calculations.