A study of M–X–BR3 (M = Pt, Pd or Rh; X = Cl or I) interactions in square planar ambiphilic ligand complexes: structural, spectroscopic, electrochemical and computational comparisons with borane-free analogues

Abstract

Reaction of [PtCl₂(COD)] and [PtI₂(COD)] with 2,7-di-tert-butyl-5-diphenylboryl-4-diphenylphosphino-9,9-dimethylthioxanthene (TXPB) afforded square planar [PtCl₂(TXPB)] (1B) and [PtI₂(TXPB)] (4B), both of which were crystallographically characterized. Single-crystal X-ray quality crystals were also obtained for [PdCl₂(TXPB)] (2B; Emslie et al., Organometallics, 2008, 27, 5317) as 2B·2CH₂Cl₂ and solvent-free 2B. Both the chloro and iodo TXPB complexes exhibit metal–halide–borane bridging interactions similar to those in previously reported [RhCl(CO)(TXPB)] (3B) and [RhI(CO)(TXPB)] (5B) (Emslie et al., Organometallics, 2006, 25, 583 and Inorg. Chem., 2010, 49, 4060). To facilitate a more detailed analysis of M–X–BR₃ (X = Cl and I) interactions, a borane-free analogue of the TXPB ligand, 2,7-di-tert-butyl-4-diphenylphosphino-9,9-dimethylthioxanthene (TXPH), was prepared. Reaction with [PtX₂(COD)] (X = Cl or I), [PdCl₂(COD)] and 0.5 [{RhCl(CO)₂}₂] provided square planar [PtCl₂(TXPH)] (1H), [PdCl₂(TXPH)] (2H), [RhCl(CO)(TXPH)] (3H) and [PtI₂(TXPH)] (4H). M–Cl–BR₃ and M–I–BR₃ bonding in 1B–5B was then probed through the use of structural comparisons, IR and NMR spectroscopy, cyclic voltammetry, and DFT calculations (Slater-type orbitals, Mayer bond orders, Hirshfeld charges, fragment analysis, SCF deformation density isosurfaces, and energy decomposition analysis).