Unusual C−H Allylic Activation in the {Pt^II(cod)} Fragment Bonded to a {Pt₂(μ-S)₂} Core

Complexes [{Pt2(μ3-S)2(dppp)2}Pt(cod)]Cl2 (1) and [{Pt2(μ3-S)2(cod)2}Pt(dppp)]Cl2 (3), where dppp = 1,3-bis(diphenylphosphino)propane and cod = 1,5-cyclooctadiene, have been synthesized by reacting [Pt2(μ-S)2(dppp)2] and [PtCl2(cod)] (1:1), and [Pt(SH)2(dppp)] and [PtCl2(cod)] (1:2), respectively. Complex 1 has not allowed substitution of cod by the chelating dppp ligand. Remarkably, the reaction of 1 with methoxide anion yields [{Pt2(μ3-S)2(dppp)2}Pt(C8H11)]Cl (2), which entails deprotonation of cod instead of the nucleophilic attack of CH3O- on the olefinic bond. In addition, replacement of the deprotonated cod ligand in 2 by dppp has not been achieved. A combination of experimental data and DFT calculations in 2 is consistent with the binding of C8H11- to platinum(II) by means of one η2-alkene and one η1-allyl bond. The structures of 1 and 2 have been confirmed by single-crystal X-ray diffraction. Analogous to 1, the reaction of 3 with sodium methoxide causes the subsequent deprotonation of the two cod ligands, yielding [{Pt2(μ3-S)2(cod)(C8H11)}Pt(dppp)]Cl (4) and [{Pt2(μ3-S)2(C8H11)2}Pt(dppp)] (5). In contrast to 1, replacement of cod by dppp in 3 and 4 leads to 1 and 2, respectively. Also, the substitution of one C8H11- ligand by dppp in 5 leads to 2. On the basis of DFT calculations, with inclusion of solvent effects, the factors governing the chemical behavior of the {Pt(cod)}2+ fragment bonded to a [Pt2(μ-S)2L4] (L2 = dppp, cod, or C8H11-) metalloligand are discussed.