Biaryl formation in the synthesis of endo and exo-platinacycles

Abstract

The reactions of cis-[Pt₂(4-MeC₆H₄)₄(μ-SEt₂)₂] with bifunctional ligands ArCHNCH₂(2-XC₆H₄) containing a C–X bond at the ortho positions of the benzyl ring (Ar = 4-ClC₆H₄, X = Br (1d); Ar = 2,4,6-(CH₃)₃C₆H₂, X = Br (1e); Ar = 2,4,6-(CH₃)₃C₆H₂, X = Cl (1f); Ar = 2-CH₃C₆H₄, X = Br (1h); Ar = 2,6-F₂C₆H₃, X = Br (1i)) in refluxing toluene were studied. Several types of platinum(II) cyclometallated compounds containing a biaryl linkage were obtained: i) endo-five-membered with a Pt–C(sp²) bond (2d, 2h), ii) endo-six-membered with a Pt–C(sp³) bond (2e, 2f), and iii) exo-five membered with a Pt–C(sp²) bond (2i). The formed biaryl linkage involves the metallated ring for 2i and the non-metallated ring for the endo-metallacycles. The reaction of compounds 2 with PPh₃ produced the corresponding phosphine derivatives, some of which (3d, 3e, 3h and 3i) were characterised crystallographically. In addition, compound [PtBr{2-CH₃C₆H₃C₆H₄CHNCH₂(2-C₆H₄Br)}SEt₂] (2c) containing a seven-membered endo-metallacycle was also obtained and characterised crystallographically.