232929-75-8Relevant academic research and scientific papers
Synthesis and electrochemistry of platinum complexes of hydroquinon-2-ylmethyl- and p-benzoquinon-2-ylmethyldiphenylphosphine
Sembiring, Seri Bima,Colbran, Stephen B.,Craig, Donald C.
, p. 1543 - 1554 (2007/10/03)
Platinum(II) complexes of new (hydroquinon-2-ylmethyl)diphenylphosphine (PPh2thqH2) and diphenyl(quinon-2-ylmethyl)phosphine (PPh2tq) ligands have been studied. Reaction of (2,5-dimethoxybenzyl)diphenylphosphine (PPh2dmb) with [PtCl2(PhCN)2] afforded [PtCl2(PPh2dmb)2] 1a. Metathesis reactions gave the bromo (1b) and iodo (1c) congeners. Deprotection of the hydroquinone groups in 1a using boron tribromide followed by treatment with base produced the O,P-chelated hydroquinonate phosphine complex, cis-[Pt(O,P-PPh2thqH)2] 2. Reaction of 2 with hydrobromic acid afforded cis-[PtBr2(PPh2thqH)2] 3 which can be oxidised to give the quinone phosphine complex cis-[PtBr2(PPh2tq)2] 4. Unlike previously reported quinone phosphine complexes, 4 is robust and stable to hydrolysis; its reduction with excess of zinc and dilute hydrobromic acid produced cis-[Pt(O,P-PPh2thqH)2(ZnBr2)] 5. Crystal structure analyses of 2·2dmf, 4·0.5dcm and 5·2dmf were performed. The electrochemistries of 1b, 3, and 4 have been characterised by cyclic voltammetry and controlled potential electrolyses. Cyclic voltammograms of 4 in the presence of dilute hydrobromic acid exhibit a four-electron cathodic process, attributed to reduction to 3; those of 3 show an anodic process attributed to oxidation to 4. The electrochemistry of 4 under aprotic conditions is extraordinary. Although there are two well separated, pendant quinone substituents only a single one-electron reduction process is observed. The reduction affords a radical species (6?-) which has been characterised by cyclic voltammetry, and by EPR and UV/Vis/NIR spectroscopy. It is argued from the available data that 6?- is a novel platinum(IV) complex with bound hydroquinonate and semiquinonate (sq) groups, namely [PtBr2(O,P-PPh2thq)(O,P-PPh2tsq ?)]-, and a possible mechanism for its remarkable formation is discussed.
