COMPLEXATION OF o-(ETHYLPHENYL-PHOSPHINO)(ETHYLTHIO)BENZENE TOWARDS NICKEL(II), PALLADIUM(II), AND PLATINUM(II) COMPLEXES

Abstract

Complexation of a hybrid P—S ligand o-(ethylphenylphosphino)(ethylthio)benzene (2) with NiCl₂. DME (DME = MeOCH₂CH₂OMe), (CH₃CN)₂PdCl₂, and (CH₃CN)₂PtCl₂ provided [o-C₆H₄(PEtPh)(SEt)-P,S)MCl₂ {3a, M = Ni; 3b, M = Pd, 3c, M = Pt) respectively. Due to the stereogenic center at phosphorus atoms, complexes 3a-c exist as a pair of geometrical isomers, which would interconvert to each other by inversion at the sulfur center. Substitution of chloride by triphenylphosphine occurs in complexes 3b-c to provide [{o-C₆H₄(PEtPh)(SEt)-P,S}M(PPh₃)Cl]Cl {4b, M = Pd; 4c, M = Pt}, but not in 3a. Both triphenylphosphine substituted complexes 4b and 4c readily undergo S-dealkylation to give {o-C₆H₄(PPhEt)(S)-P, S}MCl(PPh₃) {5b, M = Pd; 5c, M = Pt} respectively. The inversion barriers (kJ/mol) of coordinated sulfur centers were determined by NMR spectroscopy: 52 ± 2 for 3a, 60 ± 2 for 3b, 70 ± 2 for 3c, 53 ± 2 for 4b and 58 ± 3 for 4c. During dealkylation of [{o-C₆H₄(PEtPh)(SEt)-P, S}Pt(PPh₃)Cl]Cl (4c) with chloride in refluxing chloroform, side product cis-[o-C₆H₄(PPhEt)(S)]₂Pt (6c) was formed. Crystal structures of 3a-c, 5b-c, 6c and [{o-C₆H₄(PEtPh)(SEt)-P,S{Pd(PPh₃)Cl]PF₆ (4b') were determined.

Key Words:

• Phosphine complexes
• NMR spectra
• X-ray structures
• geometrical isomers
• P—S ligand