Remarkable coordination variability of the P,C,P-pincer ligand in organotin(iv) compounds – a promising outlook for other p-block elements

Abstract

The coordination properties of the P,C,P-pincer ligand (Ar = 2,6-(tBu₂PO)₂C₆H₃) with organotin(IV) compounds were examined. For this purpose, a set of neutral compounds including ArSnPh₂Cl (1), ArSnPhCl₂ (2) and ArSnCl₃ (3), ArSnBu₃ (4) and the cations [ArSnPh₂][BArF] (1⁺[BArF]⁻), [ArSnPhCl][BArF] (2⁺[BArF]⁻), [ArSnCl₂][BArF] and (3⁺[BArF]⁻) ([BArF] = [3,5-(CF₃)₂C₆H₃]₄B) were prepared and characterized by multinuclear NMR spectroscopy and single-crystal (sc) X-ray diffraction analysis (2, 3, 1⁺[BArF]⁻ and 3⁺[BArF]⁻). This study revealed different types of ligand coordination, i.e. no P → Sn intramolecular interaction in 1 and 2, while one P atom is coordinated in 3 and both P atoms in tin cations 1⁺, 2⁺ and 3⁺. To further elucidate the strength of these P → Sn dative bonds, all compounds were reacted with [BH₃(SMe₂)] to prove whether it coordinates toward pendant P atoms or even de-coordinates those P atoms already connected to the tin atom. Thus, in 1, 2, and 4, both P atoms formed complexes with the borane, while in 3 only one phosphorus reacted with BH₃, because the second remained bonded to the tin atom. Finally, even in the cation 1⁺ one of the P atoms could be blocked by borane leaving the tin atom four-coordinated, while it was not possible for 2⁺ and 3⁺. DFT calculations were used to gain a deeper insight into the P → Sn bonding interaction in the studied compounds.