C-H and Si-H Activation Reactions at Ru/Ga Complexes: A Combined Experimental and Theoretical Case Study on the Ru-Ga Bond

Treatment of [Ru(COD)(MeAllyl)₂ ] and [Ru(COD)(COT)] with GaCp* under hydrogenolytic conditions leads to reactive intermediates which activate Si-H or C-H bonds, respectively. The product complexes [Ru(GaCp*)₃ (SiEt₃ )H₃ ] (1) and [Ru(GaCp*)₃ (C₇ H₇ )H₃ ] (2) are formed with HSiEt₃ or with toluene as the solvent, respectively. While 1 was isolated and fully characterized by NMR, MS, IR and SC-XRD, 2 was too labile to be isolated and was observed and characterized in situ by using mass spectrometry, including labelling experiments for the unambiguous assignment of the elemental composition. The structural assignment was confirmed by DFT calculations. The relative energies of the four isomers possible upon toluene activation at the ortho-, meta-, para- and CH₃ -positions have been determined and point to aromatic C-H activation. The Ru-Ga bond was analyzed by EDA and QTAIM and compared to the Ru-P bond in the analogue phosphine compound. Bonding analyses indicate that the Ru-GaCp* bond is weaker than the Ru-PR₃ bond.

Zinc-Promoted ZnMe/ZnPh Exchange in Eight-Coordinate [Ru(PPh3 )2 (ZnMe)4 H2 ]

The syntheses, reactivity and electronic structure analyses of [Ru(PPh₃)₂(ZnMe)₄H₂], 1 a, and [Ru(PPh₃)₂(ZnPh)₄H₂], 2 b, are reported. 1 a exhibits an 8‐coordinate Ru centre with axial phosphines and a symmetrical (2 : 2) arrangement of ZnMe ligands in the equatorial plane. The ZnMe ligands in 1 a undergo facile, sequential exchange with ZnPh₂ to give 2 b, which shows a 3 : 1 arrangement of ZnPh ligands. Both 1 a and 2 b exist in equilibrium with their respective 3 : 1 and 2 : 2 isomers. Mechanisms for ZnMe/ZnPh exchange and isomerisation are proposed using DFT calculations. The relationships of these {Ru(ZnR)₄H₂} species to isoelectronic Group 8 transition metal polyhydrides and related Schlenk equilibria in the Negishi reaction are discussed.

The synthesis of biphenyl through C–H bond activation in benzene over a Pd catalyst supported on graphene oxide

This is the first report on carbon–hydrogen (C–H) bond activation in benzene over a palladium catalyst supported on graphene oxide (GO) leading to the sole formation of biphenyl with a yield of 78%.