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.

Good donor ligands react with an sp 2 cyclometalated complex of platinum containing an agostic interaction, initially causing displacement of the agostic interaction and decyclometalation. Eventually, these complexes rearrange to give sterically less congested complexes containing an sp 3 cyclometalated group. The same end products are observed even with poor donor ligands that do not displace the agostic interaction, and this, together with other results, suggests to us that the route to the end products goes via a different agostic species. These sp 3 cyclometalated complexes can be made to dicyclometalate via the simple expedient of adding water/base. Finally, dissolution of the agostic complex in DMSO results in a reversible "rollover" reaction, giving a C ∧ C chelated ligand.

2-tert-Butyl-6-(4-fluorophenyl)pyridine reacts with K(2)PtCl(4) via the activation of an sp(2) C-H bond to give a cyclometalated complex that contains a bifurcated agostic interaction. Rearrangement of this complex results in the activation of an sp(3) C-H bond, and reaction eventually leads to a doubly cyclometalated complex where both sp(2) and sp(3) C-H bonds have been activated. Deuterium exchange studies show that a delicate balance exists between the two cyclometalations.

Oxidation of cyclometalated Pt(II) complexes with S-bound DMSO ligands initially results in Pt(IV) complexes that retain the S-bound DMSO ligands in the same relative position. Isomerization reactions result in a rearrangement of the ligands to give O-bound DMSO complexes, with the DMSO trans to a cyclometalated carbon. X-ray structures representing the only two known examples of Pt(IV) complexes with O-bound DMSO ligands have been solved. The rate of isomerization of complexes without a pendant alkyl chain is strongly solvent dependent, consistent with the need to stabilize a coordinatively unsaturated intermediate. Pt(IV) complexes with a pendant alkyl chain show little dependence on isomerization rate with solvent, with solution NMR data strongly suggesting the presence of agostic complexes. DFT calculations provide support for the presence of agostic complexes, with the same interactions being used to account for the loss of DMSO from the O-bound DMSO complexes.

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