Macrocyclic Complexes Derived from Four cis ‐L 2 Pt Corners and Four Butadiynediyl Linkers; Syntheses, Electronic Structures, and Square versus Skew Rhombus Geometries

The dialkyl malonate derived 1,3‐diphosphines R 2 C(CH 2 PPh 2 ) 2 (R= a , Me; b , Et; c , n ‐Bu; d , n ‐Dec; e , Bn; f , p ‐tolCH 2 ) are combined with ( p ‐tol 3 P) 2 PtCl 2 or trans ‐( p‐ tol 3 P) 2 Pt((C≡C) 2 H) 2 to give the chelates cis ‐(R 2 C(CH 2 PPh 2 ) 2 )PtCl 2 ( 2 a – f , 94–69 %) or cis ‐(R 2 C(CH 2 PPh 2 ) 2 )Pt((C≡C) 2 H) 2 ( 3 a – f , 97–54 %). Complexes 3 a – d are also available from 2 a – d and excess 1,3‐butadiyne in the presence of CuI (cat.) and excess HNEt 2 (87–65 %). Under similar conditions, 2 and 3 react to give the title compounds [(R 2 C(CH 2 PPh 2 ) 2 )[Pt(C≡C) 2 ] 4 ( 4 a – f ; 89–14 % (64 % avg)), from which ammonium salts such as the co‐product [H 2 NEt 2 ] + Cl − are challenging to remove. Crystal structures of 4 a , b show skew rhombus as opposed to square Pt 4 geometries. The NMR and IR properties of 4 a – f are similar to those of mono‐ or diplatinum model compounds. However, cyclic voltammetry gives only irreversible oxidations. As compared to mono‐platinum or Pt(C≡C) 2 Pt species, the UV‐visible spectra show much more intense and red‐shifted bands. Time dependent DFT calculations define the transitions and principal orbitals involved. Electrostatic potential surface maps reveal strongly negative Pt 4 C 16 cores that likely facilitate ammonium cation binding. Analogous electronic properties of Pt 3 C 12 and Pt 5 C 20 homologs and selected equilibria are explored computationally.