Abstract

2,2’-bipyridines constitute an old and widely studied class of ligands whose most common bonding mode is as N,N neutral chelating donors. In contrast, the so called "rollover cyclometallation" is a rare and particular behaviour which entails a C(3)-H bond activation. This reaction proceeds, in the case of platinum(II), with a variety of 6-substituted 2,2’-bipyridines. We report here that under strictly controlled conditions and starting from [Pt(DMSO)2(Me)2] the reaction occurs also with the unsubstituted 2,2’-bipyridine to give both mono- and dinuclear rollover complexes. The study was articulated as follows: 1) Synthesis of mononuclear "rollover" species [Pt(X)(N’,C(3))(L’)]. (X= Me, Cl; L’ = neutral ligand).
2) Activation of a second C-H bond: synthesis of homo- and hetero-dinuclear species, symmetric and not-symmetric.
3) Synthesis of unusual mono- and polinuclear hydrides: [Pt(H)(N’,C(3))(L’)] and [Pt(H)(N’,C(3))]n.
4) Protonation with acids to yield cationic species containing a zwitterionic bipy ligand.
In addition, some results obtained in the course of the main study induced us to follow additional points: a) Sinthesis of hydrido complexes of platinum(II) with tridentate nitrogen ligands [Pt(H)(N,N,C)] (N,N,CH = 6-substituted 2,2’-bipy).
b) Insertion of CO into the Pd-C(3) bond of a palladium "rollover" derivative to give derivatives of nicotinic acid. c) Study of the organometallic behaviour of 6,6’-diphenyl-2,2’-bipyridine. d) Synthesis of platinum(II) cyclometalated NHC carbene complexes.

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