title: Rollover cyclometalation with 2-(2'-pyridyl)quinoline.
abstract: Rollover cyclometalation of 2-(2'-pyridyl)quinoline, L, allowed the synthesis of the family of complexes [Pt(L-H)(X)(L')] and [Pt(L*)(X)(L')][BF4] (X = Me, Cl; L' = neutral ligand), the former being the first examples of Pt(II) rollover complexes derived from the ligand L. The ligand L* is a C,N cyclometalated, N-protonated isomer of L, and can also be described as an abnormal-remote pyridylene. The corresponding [Pt(L-H)(Me)(L')]/[Pt(L*)(Me)(L')](+) complexes constitute an uncommon Brønsted-Lowry acid-base conjugated couple. The species obtained were investigated in depth through NMR and UV-vis spectroscopy, cyclic voltammetry, and density functional theory (DFT) methods to correlate different chemico-physical properties with the nature of the cyclometalated ligand (e.g., L vs bipy or L* vs L) and of the neutral ligand (DMSO, CO, PPh3). The crystal structures of [Pt(L-H)(Me)(PPh3)], [Pt(L-H)(Me)(CO)] and [Pt(L*)(Me)(CO)][BF4] were determined by X-ray powder diffraction methods, the latter being the first structure of a Pt(II)-based, protonated, rollover complex to be unraveled. The isomerization of [Pt(L*)(Me)(PPh3)](+) in solution proceeds through a retro-rollover process to give the corresponding adduct [Pt(L)(Me)(PPh3)](+), where L acts as a classical N,N chelating ligand. Notably, the retro-rollover reaction is the first process, among the plethora of Pt-C bond protonolysis reactions reported in the literature, where a Pt-C(heteroaryl) bond is cleaved rather than a Pt-C(alkyl) one.
authors.affiliation: Dipartimento di Chimica e Farmacia, Università degli Studi di Sassari, via Vienna 2, 07100 Sassari, Italy. zucca@uniss.it
authors.forename: Antonio
authors.initials: A
authors.lastname: Zucca
authors.forename: Diletta
authors.initials: D
authors.lastname: Cordeschi
authors.forename: Luca
authors.initials: L
authors.lastname: Maidich
authors.forename: Maria Itria
authors.initials: MI
authors.lastname: Pilo
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Masolo
authors.forename: Sergio
authors.initials: S
authors.lastname: Stoccoro
authors.forename: Maria Agostina
authors.initials: MA
authors.lastname: Cinellu
authors.forename: Simona
authors.initials: S
authors.lastname: Galli
mesh_terms: D018360:Crystallography, X-Ray; D008958:Models, Molecular; D009944:Organoplatinum Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011725:Pyridines / Q000138:chemical synthesis / Q000737:chemistry*; D011804:Quinolines / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D009944:Organoplatinum Compounds; D011725:Pyridines; D011804:Quinolines; C037219:quinoline