Heterocyclic systems containing tin(IV) - XIII [1]. Possible ceasing or inversion of the structural trans influence during the course of a bimolecular nucleophilic attack of a donor group in a series of SnIV rings

Article abstract of DOI:10.1016/S0277-5387(97)00180-0

In the series of the heterocycles X[(CH₂)₃]₂SnR₂ (16 newly synthesized compounds and two taken from the literature) and in the germanium analog BuⁱN[(CH₂)₃]₂GeCl₂, the donor group X (= NMe, NBz, NBuⁱ, NPrⁱ, O, S) intramolecularly attacks the Lewis acidic atoms Sn or Ge. Eight structure determinations (and, in addition, 2 taken from the literature) are compared. The nucleophilic attack at Sn is stronger for the ligands R₂ = Cl₂ than for the more electronegative R₂ = (OSiPh₃)₂. Overall the familiar trans influence holds: simultaneous approach of X and weakening of the ligand R(trans). In three cases of subtly graded donor strength a slight inversion or ceasing is observed: shorter distances X...Sn and simultaneously shorter distances Sn - R(trans). Also in a series of 8 compounds with O...Si-(Hal) interaction, taken from the literature, the dominant trans influence ceases to zero in the central part of the oxygen approach. Actually, the discussed ranges of inversion or ceasing of the trans influence are small and in terms of e.s.d.s at the borderline of statistical significance. Despite this objection, the existence of four alike cases is noticeable. As an explanation for this secondary effect, a bonding scheme is discussed in which the electronegativity of the ligands inhibits the nucleophilic attack and in which its drive originates from the π-basicity of the ligands into a σ*-LUMO at Sn or Ge. This bonding scheme is supported by semi-empirical MO calculations on the extended Hueckel level for the Ge compound and its tetrahedral analogue Cl₂GeBuⁿ₂. In addition, a qualitative discussion of ¹¹⁹Sn NMR chemical shifts is given, which uses the same line of arguments as applied above on the basis of interactions of frontier Orbitals.