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-(C 8 H 16 O 5 )C 6 H 3 C(Me)=NN-(H)C(=S)NHMe, 1 , containing the crown ether ring, with K 2 [PtCl 4 ], or alternatively with PtCl 2 (DMSO) 2 , and subsequent treatment with the diphosphanes Ph 2 PCH 2 PPh 2 (dppm) and Ph 2 PC(=CH 2 )PPh 2 (vdpp) produced the double nuclear platinacycles 3a , 3b , and 4 , probably via formation of the 2a and 2b intermediates. Complex 3a with the K + cation in a sandwich coordination was slightly mixed with 3b lacking any K + . Alternatively, reaction of 1 with K 2 [PtCl 4 ] or with PtCl 2 (DMSO) 2 followed by the diphosphane Ph 2 PC(=CH 2 )PPh 2 (vdpp) only gave the dinuclear phosphane-bridged compound 4 ; 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 3a and 4 .