An experimental and a DFT study on the synthesis, spectroscopic characterization, and reactivity of the adducts of dimethyl- and diphenyltin(IV) dichlorides with γ-pyrones [4 H-pyran-4-one (PYR) and 2,6-dimethyl-4 H-pyran-4-one (DMP)]: Crystal structure of Ph 2SnCl 2(PYR)

Abstract

The Sn(IV) R 2SnCl 2(γ-pyrone) n [R = Me or Ph; γ-pyrone = 4 H-pyran-4-one (PYR) or 2,6-dimethyl-4 H-pyran-4-one (DMP); n = 1 or 2] adducts have been synthesized and investigated. The adducts Ph 2SnCl 2(PYR) ( 1), Me 2SnCl 2(PYR) 2 ( 2), Ph 2SnCl 2(DMP) ( 3) and Me 2SnCl 2(PYR)(PNO) ( 4), (PNO = 4-methylpyridine N-oxide) have been prepared by the addition of the corresponding γ-pyrone to chloroform solution of R 2SnCl 2. The new compounds have been characterized by elemental analysis and spectroscopic (IR, 1H, 13C NMR and Mössbauer) means. The single-crystal diffraction study of 1 shows the Sn(IV) to be five-coordinate, [Sn–O and Sn–Cl(1), Sn–Cl(2) distances of 2.3190(13) and 2.4312(6), 2.3653(7), respectively], and the Cl–Sn–Cl bond angle to be 91.17°. The reactivity of 2 towards bipy, Ph 3PO, QNO (Q = quinoline) resulted in complete displacement of PYR and formation of already known compounds whereas, the PNO displaced only one equivalent of PYR, causing the preparation of the new mixed complex 4, possibly through a S N 1 formation mechanism. DFT/B3LYP molecular orbital calculations were carried out for the 1– 4 complexes, their precursors, Ph 2SnCl 2, ( 5) and Me 2SnCl 2, ( 6) and the ligands, PYR, DMP and PNO in an attempt to explain the structures and reactivity of the complexes. Optimized resulting geometries, vibrational frequencies, and the electron-accepting ability of the complexes and the precursors towards nucleophiles are discussed.