Mechanism of ethylene hydroformylation on platinum complexes with hydrophosphoryl ligands: a DFT study

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The mechanism of ethylene hydroformylation on model organoplatinum hydrides [(R2PO)2H]Pt(PR3)(H)] (R = H, Me, CF3) was studied within the framework of the density functional theory with the PBE gradient-corrected functional and the TZ2p basis set. The presence of a free coordination site in these square-planar 16-electron platinum complexes provides the possibility of alkene coordination in the first step without energetically unfavorable dissociation of one of the metal-ligand bonds. High strength of the —PR2O—H....O—R2 hydrogen bond results in the formation of a bidentate ligand in the coordination sphere of the metal atom. This ligand makes the geometry of the catalytic center rigid, thus enhancing the regioselectivity of the process. The proton can reversibly migrate with ease within the —PR2O—H... O—R2 hydrogen bond, thus providing fine adjustment of the electron density in the catalytic center in each reaction step and acting as a molecular switch. The rate-limiting step in the hydroformylation is the CO insertion into the Pt-Et σ-bond. Electron-donating Me groups at the phosphorous atoms hamper, while electron-withdrawing CF3 groups facilitate, the process.