Classical vs. Non-Classical Cyclometalated Pt(II) Complexes

Abstract

Rollover cyclometalated complexes constitute a family of derivatives which differ from classical cyclometalated species in certain aspects. Various potential application fields have been developed for both classes of compounds, which have both similarities and differences. In order to uncover the relationships and distinctions between these two families of compounds, four Pt(II) cyclometalated complexes derived from 2-phenylpyridine (ppy) and 2,2′-bipyridine (bpy), assumed as prototypical ligands, were compared. For this study, an electron rich isostructural and isoelectronic pair of compounds, [Pt(N^C)Me(PPh3)], and an electron-poorer compound, [Pt(N^C)Cl(PPh3)] were chosen (N^C = ppy or bpy). DFT calculations, cyclic voltammetry, and UV-Vis spectra also helped to shed light into these species. Due to the presence of the more electronegative nitrogen in place of a C-H group, the rollover bpy-H ligand becomes a slightly weaker donor than the classical ppy-H ligand, and hence, generates (slightly) more stable cyclometalated complexes, lower energy frontier molecular orbitals, and electron-poorer platinum centers. On the whole, it was revealed that classical and rollover complexes have overall structural similarity, which contrasts to their somewhat different chemical behavior.

Regioselective C(sp2)-C(sp3) Coupling Mediated by Classical and Rollover Cyclometalation

“…The greater difficulty of the oxidative addition reaction on complex 2 may be explained by the donor properties of the rollover-coordinated 6-phenyl-2,2 ′ -bipyridine. As we recently reported [32], a good indicator of the donor properties of platinum(II) cyclometalated complexes is the direct 195 Pt-31 P coupling value revealed by 31 P NMR spectroscopy. In comparison with related cyclometalated ligands (Figure 2), 6-phenyl-2,2 ′ -bipyridine is a poorer donor than cyclometalated 2-phenylpyridine and rollover-coordinated 2,2 ′ -bipyridine, but better than the worst donor (6-CF 3 -2,2 ′ -bipyridine).…”

Synthesis and Biological Activities of Luminescent 5,6-Membered Bis(Metallacyclic) Platinum(II) Complexes

“…Due to chelating ring strain, Pt-C(aryl) bond lengths are close to Pt-N(trans position) distances. For complex (−)-3, two carbon atoms are located at a trans position, and Pt-C(aryl) distances (1.994( 9) and 1.986(9) Å) differ Pt-C(isocyanide) bonds (2.049(10) and 2.053(9) Å) by less than 0.05 Å, owing to a stronger ligand of the aryl carbon atom [9,24]. Both Pt atoms in complexes (−)-2 and (−)-3 reside in a distorted square-planar environment.…”