Cyclization Accompanied with 1,2-Phenyl Migration in the Protonation of Ruthenium Acetylide Complex Containing an Allenyl Group

Reaction of the ruthenium allenylidene complex [Ru]CCCPh2 (1, [Ru] = Cp(PPh3)2Ru) with the propargylic Grignard reagent R-CCCH2MgBr (R = CH3, CH2CH3, Ph) yielded a mixture of two acetylide complexes. The major products, [Ru]CCCPh2C(R)CCH2 (2a, R = CH3; 2b, R = CH2CH3; 2c, R = Ph), have an allenyne moiety, and the minor ones, [Ru]CCCPh2CH2CCR (3a, R = CH3; 3b, R = CH2CH3; 3c, R = Ph), have a diyne ligand. The reaction of similar propargyl Grignard reagent HCCCH2MgBr with 1 yielded only the diyne complex 3d. Treatment of complexes 2a−2c with HBF4 afforded the cyclization complexes 5a−5c, respectively, proceeding via a vinylidene intermediate. The cyclization of the allenyl and the vinylidene groups is accompanied with a phenyl group migration. Complex 5b is fully characterized by a single-crystal X-ray diffraction analysis. Similar cyclization of complexes 2a and 2b, catalyzed by a Au phosphine complex, gave the ruthenium vinylidene complexes 6a and 6b, respectively, with different selectivity from that of the protonation reaction. Au-catalyzed cyclization of the diyne complex 3d yielded 6d, which is fully characterized by a single-crystal X-ray diffraction analysis

Probe the Dynamic Adsorption and Phase Transition of Underpotential Deposition Processes at Electrode–Electrolyte Interfaces

Electrochemical scanning tunneling microscopy (EC-STM) and electrochemical quartz crystal microbalance (E-QCM) techniques in combination with DFT calculations have been applied to reveal the static phase and the phase transition of copper underpotential deposition (UPD) on a gold electrode surface. EC-STM demonstrated, for the first time, the direct visualization of the disintegration of (√3 × √3)R30° copper UPD adlayer with coadsorbed SO42– while changing sample potential (ES) toward the redox Pa2/Pc2 peaks, which are associated with the phase transition between the Cu UPD (√3 × √3)R30° phase II and disordered randomly adsorbed phase III. DFT calculations show that SO42– binds via three oxygens to the bridge sites of the copper with sulfate being located directly above the copper vacancy in the (√3 × √3)R30° adlayer, whereas the remaining oxygen of the sulfate points away from the surface. E-QCM measurement of the change of the electric charge due to Cu UPD Faradaic processes, the change of the interfacial mass due to the adsorption and desorption of Cu(II) and SO42–, and the formation and stripping of UPD copper on the gold surface provide complementary information that validates the EC-STM and DFT results. This work demonstrated the advantage of using complementary in situ experimental techniques (E-QCM and EC-STM) combined with simulations to obtain an accurate and complete picture of the dynamic interfacial adsorption and UPD processes at the electrode/electrolyte interface