Synthesis, X-ray structural and DFT studies of n-membered ring P, C-chelated complexes of Pd(II) and Pt(II) derived from unsymmetrical phosphorus ylides and application of Pd(II) complexes as catalyst in Suzuki reaction

Abstract

The phosphonium salts [Ph₂P(CH₂)_nPPh₂CH₂C(O)C₆H₄-m-OMe]Br (n = 1 (S₁) and n = 2 (S₂)) were synthesized in the reaction of bis(diphenylphosphino)methane (dppm) and bis(diphenylphosphino)ethane (dppe) with 2-bromo-3ʹ-methoxy acetophenone, respectively. Further treatment with NEt₃ gave the phosphorus ylides Ph₂P(CH₂)_nPPh₂C(H)C(O)C₆H₄-m-OMe (n = 1 (Y₁) and n = 2 (Y₂)). These ligands were treated with [MCl₂(cod)] (M = Pd or Pt; cod = 1,5-cyclooctadiene) to give the P, C-chelated complexes, [MCl₂(Ph₂P(CH₂)_nPPh₂C(H)C(O)C₆H₄-m-OMe)] (n = 1, M = Pd (3), Pt (4), and n = 2, M = Pd (5), Pt (6)). These compounds were characterized by elemental analysis, spectroscopic methods, UV–visible, and fluorescence emission spectra. Further, the structures of complexes 3 and 6 were characterized crystallographically. The palladium complexes 3 and 5 proved to be excellent catalysts for the Suzuki reactions of various aryl chlorides. Also, a theoretical study on the structure of complexes 3–6 has been investigated at the BP86/def2-SVP level of theory. The strength and nature of donor−acceptor bonds between the phosphorus ylides (L) and MCl₂ fragment in the [LMCl₂] (M = Pd, Pt, L = Y₁, Y₂) were studied by NBO and energy decomposition analysis (EDA), as well as their natural orbitals for chemical valence variation (EDA-NOCV).

Keywords:

• Palladium and platinum
• ylide
• X-ray structure
• Suzuki reaction
• DFT, EDA analysis
• EDA-NOCV, nature of bond