Synthesis, reactivity and crystal structures of platinum (II) and platinum (IV) cyclometallated compounds derived from 2- and 4-biphenylimines

The reaction of [Pt2Me4(μ-SMe2)2] with ligands 4-C6H5C6H4CHNCH2CH2NMe2 (1a) and 2-C6H5C6H4CHNCH2CH2NMe2 (1b) carried out in acetone at room temperature produced compounds [PtMe2{4-C6H5C6H4CHNCH2CH2NMe2}] (2a) and [PtMe2{2-C6H5C6H4CHNCH2CH2NMe2}] (2b), respectively, in which the imines act as bidentate [N,N′] ligands. Cyclometallated [C,N,N′] compounds [PtMe{4-C6H5C6H3CHNCH2CH2NMe2}] (3a) and [PtMe{2-C6H5C6H3CHNCH2CH2NMe2}] (3b), were obtained by refluxing toluene solutions of compounds 2a or 2b. Reaction of [Pt2Me4(μ-SMe2)2] with ligands 4-C6H5C6H4CHNCH2Ph (1c) and 2-C6H5C6H4CHNCH2Ph (1d) produced compounds [PtMe{4-C6H5C6H3CHNCH2Ph}SMe2] (5c) and [PtMe{2-C6H5C6H3CHNCH2Ph}SMe2] (5d) containing a [C,N] ligand, from which triphenylphosphine derivatives 6c and 6d were also prepared. In all cases, metallation took place to yield five-membered endo-metallacycles and formation of seven-membered or of exo-metallacycles was not observed. The reactions of 3a, 3b, 6c and 6d with methyl iodide were studied in acetone and gave the corresponding cyclometallated platinum (IV) compounds. All compounds were characterised by NMR spectroscopy and compounds 3b, 4a, 6c and 6d were also characterised crystallographically.