Unusual C - H allylic activation in the {PtII(cod)} fragment bonded to a {Pt2(μ-S)2} core

Complexes [{Pt 2 (μ 3 -S) 2 (dppp) 2 }Pt(cod)]Cl 2 (1) and [{Pt 2 (μ 3 -S) 2 (cod) 2 }Pt(dppp)]Cl 2 (3), where dppp = 1,3-bis(diphenylphosphino)propane and cod = 1,5-cyclooctadiene, have been synthesized by reacting [Pt 2 (μ-S) 2 (dppp) 2 ] and [PtCl 2 (cod)] (1:1), and [Pt(SH) 2 (dppp)] and [PtCl 2 -(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 [{Pt 2 (μ 3 -S) 2 (dppp) 2 }-Pt(C 8 H 1 1 )]Cl (2), which entails deprotonation of cod instead of the nucleophilic attack of CH 3 O - 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 C 8 H 1 1 - to platinum(II) by means of one η 2 -alkene and one η 1 -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 [{Pt 2 (μ 3 -S) 2 (cod)(C 8 H 1 1 )}Pt(dppp)]Cl (4) and [{Pt 2 (μ 3 -S) 2 (C 8 H 1 1 ) 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 C 8 H 1 1 - 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 [Pt 2 (μ-S) 2 L 4 ] (L 2 = dppp, cod, or C 8 H 1 1 -) metalloligand are discussed.