Platinum-mediated oxidative P–O coupling of white phosphorus and alcohols: an ab initio study

Abstract

Ab initio quantum chemical investigations of the oxidative P–O coupling of white phosphorus and alcohol have been carried out by the model platinum complexes [PtCl 3(CH 3OH)(η 2-P 4)] + ( 1), [PtCl 3(CH 3OH)(η 2-P 4)] − ( 2), [PtBr 3(CH 3OH)(η 2-P 4)] + ( 3), [PtBr 3(CH 3OH)(η 2-P 4)] − ( 4) and [PtClBr 2(CH 3OH)(η 2-P 4)] + ( 5) applying the B3PW91 model of density functional theory. According to the performed geometry optimizations, both the tetrahedral P 4 and CH 3OH molecules are deformed and activated in complexes 1– 5. The results of the calculated total atomic charge (TAC) and overlap population (OP) show that the better conditions accounting for the nucleophilic attack of the P 4 molecule by the alkoxide ion, that is originated from the coordinated CH 3OH molecule, are found in the cationic Pt(IV) η 2-P 4 complexes 1, 3 and 5. In these molecules, the coordinated P 4 molecule acts as an electron-pair acceptor and easily reacts with the alkoxide ligand. The results of the present calculations agree with the experimental observation indicating that the P–O coupling reaction between P 4 and ROH, which affords trialkylphosphates, proceeds only in the presence of a Pt(IV)(η 2-P 4) intermediate complexes. The halide ligands, which complete the coordination sphere around Pt, do not directly participate in the reaction. However, they are active components of the catalytic cycle because they promote the reaction via nucleophilic assistance to the alcohol deprotonation step.