A series of cyclometallated phenylpyridine platinum(II) complexes have been synthesised with a systematic variation in both the phenylpyridine and the ancillary ligand. Oxidation of one of the cyclometallated species leads to a number of isomeric platinum(IV) complexes, all of which eventually isomerize to a single compound. The route to these new compounds has been demonstrated to involve an initial slow oxidation followed by a rapid C-H activation to give doubly cyclometallated complexes. The solid state structures of a number of both the platinum(II) and the platinum(IV) species have been solved; many of the structures exhibited extended interactions that result in complex three dimensional packing.

The use of (NHC)AgX salts as transmetallating agents for platinum can be tuned to introduce either one or two NHC ligands per platinum in high yield. Complexes with a single NHC ligand are prepared with an additional DMSO ligand, which can conVeniently be replaced by other ligands such as phosphines to giVe mixed cis NHC/phosphine complexes. Variable-temperature NMR and DFT haVe been used to probe the nature of the restricted rotation of the NHC ligand about the square planar platinum center: experimentally, the barrier has been established as at least 85 kJ mol -1 , and the computational Value has been determined to be 92 kJ mol -1 .

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The oxidation of square-planar cyclometalated Pt(II) phenylpyridine species using the electrophilic chlorine based oxidant PhICl2 has been studied. Rapid oxidations are observed in chloroform solvent at −40 °C leading to single products. In acetone solvent isomeric forms of the product are formed, and these are observed to isomerize at around −10 °C. The oxidation of a complex with an uncyclometalated pendant arm resulted in the very rapid cyclometalation of that arm by the resulting electrophilic Pt(IV) species.

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The reaction of a diphenylpyridine with one equivalent of potassium tetrachloroplatinate in ethanoic acid yields a cyclometallated species which can be induced to undergo a second cyclometallation to give a C ∧ N ∧ C tridentate species. Carbonyl derivatives of two such compounds have been structurally characterised. The X-ray structure of the complex [2,6-(4Ј-C 6 H 13 OC 6 H 3 ) 2 C 5 H 3 NPt(CO)], (1), obtained using 2,6-bis(4Ј-hexyloxyphenyl)pyridine, has no unusual features. In contrast, the structure of the complex [2,6-(C 6 H 4 ) 2 -4-(4Ј-C 8 H 17 OC 6 H 5 )C 5 H 2 NPt(CO)], (2), which results when using 4-(4Ј-octyloxy-phenyl)-2,6-diphenylpyridine, has close intermolecular contacts, with a Pt-Pt "bond" of 3.243(1) Å holding the molecules together as dimers. Compound 2 also exists in another form in the solid state, a form that does not appear to contain Pt-Pt bonds.

Oxidation of a square-planar platinum complex leads to a five coordinate cationic intermediate that can be stabilized and trapped out via an agostic interaction with the alkyl chain of a ligand. Subsequent reaction of this species leads to the formation of an alkyl-Pt bond at the expense of an aryl-Pt bond: an intramolecular transcyclometallation.

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