Cyclometallated Platinum(II) Complexes with Small Crown Ether Rings: Appropriate Choice of the Bridging Diphosphane to Coordinate Potassium Cations.

This account reports the synthesis and structural characterization of the first cyclometallated platinum(II) complex that coordinates a potassium cation in a sandwich arrangement via two 15-crown-5 ether rings within the same molecule. The cooperation of the two small crown ether moieties allows the entrapment of the non-ideal potassium ion. The reaction of the parent thiosemicarbazone ligand 3,4-(CHO)CHC(Me)=NN-(H)C(=S)NHMe, , containing the crown ether ring, with K[PtCl], or alternatively with PtCl(DMSO), and subsequent treatment with the diphosphanes PhPCHPPh (dppm) and PhPC(=CH)PPh (vdpp) produced the double nuclear platinacycles , , and , probably via formation of the and intermediates. Complex with the K cation in a sandwich coordination was slightly mixed with lacking any K. Alternatively, reaction of 1 with K[PtCl] or with PtCl(DMSO) followed by the diphosphane PhPC(=CH)PPh (vdpp) only gave the dinuclear phosphane-bridged compound ; this highlights the importance of choosing the right diphosphane ligand. Density functional theory calculations (B3LYP-D3/LANL2DZ-ECP-6.311++G**) revealed similar affinities for both dppm and vdpp derivatives to coordinate potassium cations. Crystal structure analysis was performed for compounds and .