Transition metal complexes of the PPO/POP ligand: variable coordination chemistry and photo-luminescence properties

Abstract

In the current work the tautomeric equilibrium between tetraphenyldiphosphoxane (Ph2P-O-PPh2, POP) and tetraphenyldiphosphine monoxide (Ph2P-P(=O)Ph2, PPO) in the absence and presence of transition metal precursors is investigated. Whereas with hard transition metal ions, such as Fe(ii) and Y(iii), PPO-type complexes, such as [FeCl2(PPO)2] (1) and [YCl3(THF)2(PPO)] (2), are formed, softer transition metals ions tend to form so-called coordination stabilised tautomers of the POP ligand form, such as [Cu2(MeCN)3(μ2-POP)2](PF6)2 (3), [Au2Cl2(μ2-POP)] (4), and [Au2(μ2-POP)2](OTf)2 (5). The photo-optical properties of the PPO- and POP-type transition metal complexes are investigated experimentally using photo-luminescence spectroscopy, whereby the presence of metallophillic interactions was found to play a crucial role. The dinuclear copper complex [Cu2(MeCN)3(μ2-POP)2](PF6)2 (3) shows a very interesting thermochromic behavior and intense photo-luminescence with remarkable phosphoresence lifetimes at 77 K, which can probably be attributed to short intramolecular Cu-Cu distances.