Biaryl formation in the synthesis of endo and exo-platinacycles

Abstract

The reactions of cis-[Pt2(4-MeC6H4)4(m-SEt2)2] with bifunctional ligands ArCH NCH2(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-CH3C6H3C6H4CH NCH2(2-C6H4Br)}SEt2] (2c) containing a seven-membered endo-metallacycle was also obtained and characterised crystallographically.