Synthesis and structural characterization of platinum(II) bis(chelate) complexes derived from the ligand system meso/rac-Ph(O)HPCH2CH2PH(O)Ph

Abstract

The ligand (R,S)-Ph(O)HPCH₂CH₂PH(O)Ph reacted with [Pt(PPh₃)₄] to give the complex syn-[Pt{(R,S)-Ph(O)P(CH₂)₂P(OH)Ph}₂]3. In this reaction a long-lived intermediate was observed and spectroscopically characterized as the six-co-ordinate platinum(IV)trans-dihydride complex syn-[PtH₂{(R,S)-Ph(O)P(CH₂)₂P(OH)Ph}₂]4. Complex 4 exhibits fluxional behaviour in CD₂Cl₂ solution at 20 °C as a result of a rapid proton exchange between the OH protons and the hydride ligand that is syn with respect to these groups. Mechanistic proposals were made to account for the OH proton–hydride exchange process and for the decomposition of the dihydride complex 4 to complex 3. Treatment of 3 with dry HCl afforded the monoprotonated complex syn-[Pt{(R,S)Ph(O)P(CH₂)₂P(OH)Ph}{(R,S)-Ph(OH)P(CH₂)₂P(OH)Ph}]Cl 12. The diprotonated complex anti[Pt{(R,S)-Ph(OH)P(CH₂)₂P(OH)Ph}₂]Cl₂9 was obtained by the reaction of [{PtCl₂(C₂H₄)}₂] with (R,S)-Ph(O)HPCH₂CH₂PH(O)Ph. Reaction of BF₃·Et₂O with 3 gave the macrocyclic complex syn-[Pt{[(R,S)-Ph(O)P(CH₂)₂P(O)Ph]BF₂}₂]·CH₂Cl₂13. Treatment of [Pt(PPh₃)₄] with the racemic ligand (RR,SS)-Ph(O)HPCH₂CH₂PH(O)Ph afforded a white insoluble solid composed of the polymeric complexes meso-[{Pt[(R,R)-Ph(O)P(CH₂)₂P(OH)Ph][(S,S)-Ph(O)P(CH₂)₂P(OH)Ph]}_n]15 and rac-[{Pt[(RR,SS)-Ph(O)P(CH₂)₂P(OH)Ph]₂}_n]16. Addition of HCl to this solid in CH₂Cl₂ led to the isolation of a mixture of the dicationic complexes meso-[Pt{(R,R)-Ph(OH)P(CH₂)₂P(OH)Ph}{(S,S)-Ph(OH)P(CH₂)₂P(OH)Ph}]Cl₂17 and rac-[Pt{(RR,SS)-Ph(OH)P(CH₂)₂P(OH)Ph}₂]Cl₂18. The structures of complexes 3, 9, 12, 13, 15, 17 and 18 have been determined by single-crystal X-ray diffraction studies.