Factors influencing cyclometalations in platinum(II) complexes with tertiary phosphine ligands.

Martin Sojka* ^a,b , Jaromír Toušek ^b, Marek Nečas ^a,b


 ^a Department of Chemistry,  Masaryk University, Kotlářská 2, 61137 Brno, and ^b CEITEC – Central
             European Institute of Technology, Kamenice 5, 62500 Brno, Czech Republic

* martin.sojka@mail.muni.cz

Intramolecular activation reactions of C-H bonds on aromatic rings are frequently studied in
transition metal complexes since resulting cyclometalated  complexes are tested and applied in
variable areas of research.^[1,2] However, factors influencing proclivity of single complex for
cyclometallation are far from being fully understood. We recently performed study of
cyclometallations in Pt(II) complexes with phosphinoamine and phosphinophenol ligands via C-H
thermal activation to evaluate the importance of ligand substitution on the reactivity of the
starting compounds. The presence and positioning (ortho and para) of the substituents combined with
intramolecular hydrogen interactions were found to be crucial for a successful cyclometalation. We
have therefore prepared a series of organophosphorus ligands and synthesized their cis-Pt(II)
complexes from PtCl[2](cod). By means of ^31P NMR spectroscopy we investigated their propensity for
cyclometalation via thermal C-H bond activation on aromatic moieties as well as possible
isomerization of cis complexes into trans isomers. We support our experimental findings by single
crystal X-ray diffraction and quantum-mechanical calculations.

Figure 1 Synthetic route to cyclometalated Pt(II) complexes

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1 M. Beller, H. Fischer, W. A. Herrmann, K. Öfele, C. Brossmer,  Angew. Chemie Int. Ed. English
1995, 34, 1848.

2 M. Albrecht, Chem. Rev. 2010, 110, 576.