Activation of Dioxygen by Dimethylplatinum(II) Complexes

The ligands RN­(CH₂-2-C₅H₄N)₂ (<b>L1</b>, R = CH₂CH₂OH; <b>L2</b>, R = CH₂CH₂CH₂OH; <b>L3</b>, R = 2-C₆H₄OH) have been designed to give dimethylplatinum­(II) complexes that can activate dioxygen in the absence of a protic solvent. The ligands react with [Pt₂Me₄(SMe₂)₂] to give an equilibrium mixture, with the major constituent being [PtMe₂(κ²-N,N′-<b>L</b>)] (<b>1a</b>, <b>L</b> = <b>L1</b>; <b>1b</b>, <b>L</b> = <b>L2</b>; <b>1c</b>, <b>L</b> = <b>L3</b>). In the absence of air, <b>1a</b> reacts with solvent CH₂Cl₂ to give [PtMe₂(CH₂Cl)­(κ³-<i>N</i>,<i>N</i>′,<i>N</i>″-<b>L1</b>]­Cl, while <b>1c</b> decomposes with loss of methane to give [PtMe­(κ³-<i>N</i>,<i>N</i>′,<i>N</i>″-<b>L3</b>-H)] and then, by reaction with solvent, the binuclear complex [{PtMe­(κ³-<i>N</i>,<i>N</i>′,<i>N</i>″-<b>L3</b>-H)}₂(μ-H)]­Cl. In the presence of oxygen the complexes <b>1</b> in CH₂Cl₂ solution react to give [Pt­(OH)­Me₂(κ³-<i>N</i>,<i>N</i>′,<i>N</i>″-<b>L</b>)]­Cl, when <b>L</b> = <b>L1</b> or <b>L2</b>, or [Pt­(OH)­Me₂(κ³-<i>N</i>,<i>N</i>′,<i>O</i>-<b>L</b>-H)], when <b>L</b> = <b>L3</b>. The complex [Pt­(OH)­Me₂(κ³-<i>N</i>,<i>N</i>′,<i>N</i>″-<b>L2</b>)]Cl decomposed in the presence of air to give the binuclear complex [{PtMe₂(2-C₅H₄NCO₂)­(μ-OH)}₂]. The factors influencing reactivity and mechanism in these reactions are elucidated, and the presence of both a free pyridyl donor (push group) and a free hydroxyl (pull group) is suggested to give a synergy for dioxygen activation by dimethylplatinum­(II) complexes

Activation of Dioxygen by Dimethylplatinum(II) Complexes

The ligands RN­(CH₂-2-C₅H₄N)₂ (<b>L1</b>, R = CH₂CH₂OH; <b>L2</b>, R = CH₂CH₂CH₂OH; <b>L3</b>, R = 2-C₆H₄OH) have been designed to give dimethylplatinum­(II) complexes that can activate dioxygen in the absence of a protic solvent. The ligands react with [Pt₂Me₄(SMe₂)₂] to give an equilibrium mixture, with the major constituent being [PtMe₂(κ²-N,N′-<b>L</b>)] (<b>1a</b>, <b>L</b> = <b>L1</b>; <b>1b</b>, <b>L</b> = <b>L2</b>; <b>1c</b>, <b>L</b> = <b>L3</b>). In the absence of air, <b>1a</b> reacts with solvent CH₂Cl₂ to give [PtMe₂(CH₂Cl)­(κ³-<i>N</i>,<i>N</i>′,<i>N</i>″-<b>L1</b>]­Cl, while <b>1c</b> decomposes with loss of methane to give [PtMe­(κ³-<i>N</i>,<i>N</i>′,<i>N</i>″-<b>L3</b>-H)] and then, by reaction with solvent, the binuclear complex [{PtMe­(κ³-<i>N</i>,<i>N</i>′,<i>N</i>″-<b>L3</b>-H)}₂(μ-H)]­Cl. In the presence of oxygen the complexes <b>1</b> in CH₂Cl₂ solution react to give [Pt­(OH)­Me₂(κ³-<i>N</i>,<i>N</i>′,<i>N</i>″-<b>L</b>)]­Cl, when <b>L</b> = <b>L1</b> or <b>L2</b>, or [Pt­(OH)­Me₂(κ³-<i>N</i>,<i>N</i>′,<i>O</i>-<b>L</b>-H)], when <b>L</b> = <b>L3</b>. The complex [Pt­(OH)­Me₂(κ³-<i>N</i>,<i>N</i>′,<i>N</i>″-<b>L2</b>)]Cl decomposed in the presence of air to give the binuclear complex [{PtMe₂(2-C₅H₄NCO₂)­(μ-OH)}₂]. The factors influencing reactivity and mechanism in these reactions are elucidated, and the presence of both a free pyridyl donor (push group) and a free hydroxyl (pull group) is suggested to give a synergy for dioxygen activation by dimethylplatinum­(II) complexes