Counteranion-Dependent Reaction Pathways in the Protonation of Cationic Ruthenium–Vinylidene Complexes

Abstract

The tetraphenylborate salts of the cationic vinylidene complexes [Cp*Ru═C═CHR(iPr2PNHPy)]+ (R = p-C6H4CF3 (1a-BPh4), Ph (1b-BPh4), p-C6H4CH3 (1c-BPh4), p-C6H4Br (1d-BPh4), tBu (1e-BPh4), H (1f-BPh4)) have been protonated using an excess of HBF4·OEt2 in CD2Cl2, furnishing the dicationic carbyne complexes [Cp*Ru≡CCH2R(iPr2PNHPy)]2+ (R = p-C6H4CF3 (2a), Ph (2b), p-C6H4CH3 (2c), p-C6H4Br (2d), tBu (2e), H (2f)), which were characterized in solution at low temperature by NMR spectroscopy. The corresponding reaction of the chloride salts 1a-Cl, 1b-Cl, 1c-Cl, and 1d-Cl followed a different pathway, instead affording the novel alkene complexes [Cp*RuCl(κ1(N),η2(C,C)-C5H4N-NHPiPr2CH═CHR)][BF4] (3a–d). In these species, the entering proton is located at the α-carbon atom of the former vinylidene ligand, which also forms a P–C bond with the phosphorus atom of the iPr2PNHPy ligand. To shed light on the reaction mechanism, DFT calculations have been performed by considering several protonation sites. The computational...