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

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.