Metal Complexes (M = Zn, Sn, and Pb) of 2‑Phosphinobenzenethiolates: Insights into Ligand Folding and Hemilability

The divalent metal complexes MII{(SC6H4-2-PR2)-κ2S,P}2 (3–7, and 9–11) (M = Zn, Sn, or Pb; R = iPr, tBu, or Ph), the Sn­(IV) complexes Sn­{(SC6H4-2-PR2)-κ2-S,P}­Ph2Cl (12 and 13) (R = iPr and tBu), and the ionic Sn­(IV) complexes [Sn­{(SC6H4-2-PR2)-κ2-S,P}­Ph2]­[BPh4] (14 and 15) (R = iPr and tBu) have been prepared and characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction when suitable crystals were afforded. The Sn­(II) and Pb­(II) complexes with R = Ph, iPr, or tBu (5, 6, 9, and 10) demonstrated ligand “folding” hinging on the P,S vectora behavior driven by the repulsions of the metal/phosphorus and metal/sulfur lone pairs and increased M-S sigma bonding strength. This phenomenon was examined by density functional theory (DFT) calculations for the compounds in both folded and unfolded states. The Sn­(IV) compound 13 (R = tBu) crystallized with the phosphine in an axial position of the pseudotrigonal bipyramidal complex and also exhibited hemilability in the Sn–P dative bond, while compound 12 (R = iPr), interestingly, crystallized with phosphine in an equatorial position and did not show hemilability. Finally, the crystal structure of 15 (R = tBu) revealed the presence of an uncommon, 4-coordinate, stable Sn­(IV) cation.