Ruthenium-based olefin metathesis catalysts are used in laboratory-scale organic synthesis across chemistry, largely thanks to their ease of handling and functional group tolerance. In spite of this robustness, these catalysts readily decompose, via little-understood pathways, to species that promote double-bond migration (isomerization) in both the 1-alkene reagents and the internal-alkene products. We have studied, using density functional theory (DFT), the reactivity of the Hoveyda–Grubbs second-generation catalyst 2 with allylbenzene, and discovered a facile new decomposition pathway. In this pathway, the alkylidene ligand is lost, via ring expansion of the metallacyclobutane intermediate, leading to the spin-triplet 12-electron complex (SIMes)RuCl₂ (³R21, SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene). DFT calculations predict ³R21 to be a very active alkene isomerization initiator, either operating as a catalyst itself, via a η³-allyl mechanism, or, after spin inversion to give R21 and formation of a cyclometalated Ru-hydride complex, via a hydride mechanism. The calculations also suggest that the alkylidene-free ruthenium complexes may regenerate alkylidene via dinuclear ruthenium activation of alkene. The predicted capacity to initiate isomerization is confirmed in catalytic tests using p-cymene-stabilized R21 (5), which promotes isomerization in particular under conditions favoring dissociation of p-cymene and disfavoring formation of aggregates of 5. The same qualitative trends in the relative metathesis and isomerization selectivities are observed in identical tests of 2, indicating that 5 and 2 share the same catalytic cycles for both metathesis and isomerization, consistent with the calculated reaction network covering metathesis, alkylidene loss, isomerization, and alkylidene regeneration.

A dimeric Zr₁₂ oxo cluster was used as new molecular building block in construction of metal–organic frameworks utilizing the precursor approach.

The crystal structure of hexylheptahydrooctasilasesquioxane C₆H₁₃(H₇Si₈O₁₂) has been determined by single-crystal X-ray diffraction and compared with the structures of H₈Si₈O₁₂, [Co(CO)₄(H₇Si₈O₁₂)] and (CH₃Si₈O₁₂. The monosubstituted Silasesquioxane molecules have a crystallographic C₁symmetry. The local symmetry of their octanuclear Si cage, however, is close to C_3v. They are closer to C_3v than H₈Si₈O₁₂ which has an effective molecular symmetry of T_h in the crystal. The major distortions originate in intermolecular O ⋯ Si contacts. The larger the number of such contacts per molecule, the larger is the distortion of the local symmetry of the cage. The structure of C₆H₁₃(H₇Si₈O₁₂) compares well with that of [Co(CO)₄(H₇Si₈O₁₂)], and it is clearly the least distorted of the two due to a reduced influence of the n-hexyl ligand on the cage geometry and due to a smaller number of intermolecular interactions. The IR spectrum of C₆H₁₃(H₇Si₈O₁₂) has been interpreted by correlating it with the three molecules H₈Si₈O₁₂, C₆H₁₃[Si(OSiMe₃)₃] and HSi(OSiMe₃)₃.

Pyridine as a stabilizing donor ligand drastically improves the performance of ruthenium monothiolate catalysts for olefin metathesis in comparison with previous versions based on a stabilizing benzylidene ether ligand. The new pyridine-stabilized ruthenium alkylidenes undergo fast initiation and reach appreciable yields combined with moderate to high Z selectivity in self-metathesis of terminal olefins after only a few minutes at room temperature. Moreover, they can be used with a variety of substrates, including acids, and promote self-metathesis of ω-alkenoic acids. The pyridine-stabilized ruthenium monothiolate catalysts are also efficient at the high substrate dilutions of macrocylic ring-closing metathesis and resist temperatures above 100 °C during catalysis.