Pt(II) Derivatives with Rollover-Coordinated 6-substituted 2,2′-bipyridines: Ligands with Multiple Personalities
Source abstract
Abstract
We report here the synthesis, characterization and behavior of a series of Pt(II) cyclometalated rollover complexes with two substituted bipyridines, 6-ethyl-2,2′-bipyridine (bpy6Et) and 6-methoxy-2,2′-bipyridine (bpy6OMe), in comparison with previously studied 2,2′-bipyridine complexes. The two ligands have similar steric hindrance but different electronic properties. As a result, the reactivity of the two series of complexes follows very different routes. In particular, the new complexes behave differently towards protonation reactions, differences given by substituents and ancillary ligands, added to the presence of several nucleophilic centers. Reaction of complex [Pt(bpy6OMe-H)(PPh3)Me)] with [H3O⋅18-crown-6][BF4] results in a retro-rollover reaction whose final product is the cationic adduct [Pt(bpy6OMe)(PPh3)Me)]+. Surprisingly, only the isomer with the cis-PPh3-OMe geometry is formed; in spite of an expected instability due to steric hindrance, Density-Functional theory (DFT) calculations showed that this isomer is the most stable. This result shows that the cone angle is far from being a real “solid cone” and should lead to a different interpretation of well-known concepts concerning steric bulk of ligands, such as cone angle. Proton affinity values of ligands, neutral complexes and their protonated counterparts were analyzed by means of DFT calculations, allowing a comparison of their properties.
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Research context
OpenAlex topics: N-Heterocyclic Carbenes in Organic and Inorganic Chemistry · Metal complexes synthesis and properties · Organometallic Complex Synthesis and Catalysis
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Affiliations
Dipartimento di Chimica e Farmacia, Università degli Studi di Sassari, via Vienna 2, 07100 Sassari, Italy
Consorzio Interuniversitario Reattività Chimica e Catalisi (CIRCC), 70126 Bari, Italy
Funding
Regione Autonoma della Sardegna · Università degli Studi di Sassari
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