New stibines containing acetal and formyl group: Platinum complex and unexpected oxastibol derivative

Abstract

A new tertiary stibine ligand ( 1) containing acetal group at the ortho-position has been synthesized. This new stibine was then complexed with PtCl 4 2 - to obtain trans-PtCl 2L 2 ( 2) where stibine acts as a monodentate ligand. The acetal was hydrolyzed in a slightly acidic medium and forms a very new stibine ( 3) containing formyl group at the ortho-position. When ( 3) was reduced with NaBH 4 an unusual oxastibol ( 4) derivative was obtained under the experimental conditions used. All the compounds were characterized by IR, mass, 1H, 13C, COSY and HETCOR NMR spectroscopy. The molecular structures of ( 2), ( 3) and ( 4) were determined. Compound ( 3) crystallizes in two different polymorphs ( 3a) and ( 3b) and both the polymorphs show hypervalent antimony with three Sb⋯O interactions and the molecule exists in O-cis-exo configuration. Compound ( 4) shows intramolecular Sb⋯O interactions. To the best of our knowledge this is the first report on organoantimony compounds containing carbonyl groups though their phosphorus and bismuth analogues are well known. Compound ( 2) shows helicoidal chirality, which is a very new concept in antimony chemistry