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The isomerization of internal alkynes Ar1C≡CAr2 within the coordination environment of low‐valent half‐sandwich [Ru(dppe)Cp]+ complexes via a 1,2‐migration process affords vinylidene species [Ru{=C=C(Ar1)Ar2}(dppe)Cp]+. The rearrangement reactions of symmetrically and asymmetrically substituted substrates featuring different electron‐donating and ‐withdrawing groups and of varying steric bulk were modelled using density functional theory (DFT), and the conclusions supported by experimental observations. Examination of the reaction pathway and associated activation barriers reveal a high solvent dependency for the generation of the key intermediate species [Ru(dppe)Cp]+ from [RuCl(dppe)Cp] by halide dissociation in the presence of Na+ salts of weakly coordinating anions, with the lattice enthalpy of the NaCl by‐product playing a critical role in the overall thermochemical balance of the reaction. The activation barriers associated with the reaction of [Ru(dppe)Cp]+ with Ar1C≡CAr2, and the relative energies of the alkyne complexes [Ru(η2‐Ar1C≡CAr2)(dppe)Cp]+, are sensitive to the electron density of the alkyne and conformational changes associated with the ‘bend‐back’ of the substrate. The latter differs by up to 66.1 kJ/mol, which in turn impacts the barrier height of the subsequent 1,2‐migration step involved in the rearrangement process and ultimately the overall thermochemical nature of the complete reaction. The relative importance of these factors is evinced by the successful rearrangement of the very sterically congested 1(9‐anthryl)‐2(9‐phenanthryl) acetylene into the fully characterized diaryl vinylidene complex, which was isolated in 89 % yield. [ABSTRACT FROM AUTHOR]

Three ferrocene analogues, D (η-CBH)M (M = Fe, Co, and Ni), with triplet aromatic CBH ligands have been predicted at TPSSh/6-311+G(d,p) level. We find that the M atom interacts drastically with the two CBH ligands through a nearly fully-filled 3d subshell, which is different from (η-CH)Fe. The natural population analyses suggest that (η-CBH)M have an unconventional charge distribution, i.e., the M atom is negatively charged, while the two boron rings are positively charged. The analyses of the electronic and dynamic stabilities indicate that (η-CBH)Co is the most stable among (η-CBH)M. Thus, we theoretically confirm that the triplet aromatic CBH cluster can be regarded as a potential new ligand. Our theoretical predictions are awaiting future experimental verification. [ABSTRACT FROM AUTHOR]

The first derivative of the methylium cation with the triple-decker substituent, [CpCo(C3B2Me5)RuC5Me4CH2]PF6 ( 2PF6), was synthesized from the reaction of the triple-decker complex CpCo(C3B2Me5)RuCp* ( 1) with the salt of the trityl cation [CPh3]+. The X-ray crystal structure of 2PF6 reveals that the methylium carbon is bound to the ruthenium with Ru−C bond length of 2.259 Å and corresponds to the description of its structure as η6-fulvene-ruthenium. Reactions of 2PF6 with nucleophiles OH−, Ph3P, Et3N led to the corresponding derivatives of 1 in high yields. Aromatic amines PhNEt2 and 4-MeC6H4NH2 react with 2PF6 to give the electrophilic aromatic substitution products quantitatively. Chemical reduction of 2PF6 with Zn powder in tetrahydrofuran leads to the formation of the bis(triple-decker) derivative (CpCo(C3B2Me5)RuC5Me4CH2)2 ( 10) with a CH2CH2-bridge. The structures of complexes 4, 7 - 10 were determined by X-ray diffraction. Density functional calculations support the crystallographically determined geometry of 2 and allow rationalization of some characteristics of its structure, spectroscopy, and reactivity. [ABSTRACT FROM AUTHOR]