Synthesis and structure of 4,6-disubstituted dibenzothiophenes and their use in the preparation of binuclear platinum(ii) complexes

The reaction of two equivalents of [Pt(PEt3)4] with 4,6-dibromodibenzothiophene (DBT-Br2) afforded trans,trans-[(μ-DBT-1κC4:2κC6){PtBr(PEt3)2}2] (5), a unique example of double oxidative addition of a heteroaromatic substrate to Pt(0). The related bimetallic Pt(II) complex, cis,cis-[(μ-DBT-1κC4:2κC6){Pt(η4-cod)Cl}2] (6), was isolated via a double transmetallation of 4,6-bis(trimethylstannyl)dibenzothiophene with [Pt(η4-cod)Cl2], where cod is 1,5-cyclooctadiene. The new complexes were characterised by spectroscopic techniques. The disubstituted dibenzothiophene compounds were prepared by dilithiation of dibenzothiophene, followed by quenching with chlorotrimethylsilane and chlorotrimethylstannane, to give 4,6-(SiMe3)2(SC12H6) (2) and 4,6-(SnMe3)2(SC12H6) (4), respectively. Treatment of 4,6-(SiMe3)2(SC12H6) with bromine produced 4,6-Br2(SC12H6) (3). The X-ray crystal structures of 2 and 3 were determined. An improved method of synthesis of 2,8-dibromodibenzothiophene (1) was also developed.