[W(CO)(dppe)2] Cumulenylidene and Acetylide Complexes Accessed via Stannylated Acetylenes and Butadiynes

Low-valent group 6 metals/Al(C6F5)3 donor-acceptor systems for CO2 activation and cleavage

Donor-acceptor systems for CO2 activation combining a formally zero-valent group 6 metal as the donor with the Lewis acid Al(C6F5)3 (AlCF) are reported. They were obtained from AlCF adducts of N2-complexes by N2-to-CO2 substitution. One species was capable of C-O cleavage. The boron analogues led to intractable mixtures.

Migration of Condensed Aromatic Hydrocarbons During Alkyne-Vinylidene Rearrangements

Diarylacetylenes ArC≡CAr featuring condensed aromatic hydrocarbon fragments (Ar) such as naphthalene, anthracene, phenanthrene and pyrene were converted into vinylidene ligands by 1,2-migration reactions within the coordination sphere of half-sandwich complexes [MII(dppe)Cp]+ (MII = RuII, FeII). Comparison of the extent of conversion of the alkyne substrates to the vinylidene complexes [Ru{=C=CAr2}(dppe)Cp]+ with those obtained from acetylenes functionalized by smaller groups (H, CH3, Ph) show that the molecular volume (VM) of the migrating group and relief of steric congestion plays a role during the rearrangement process. Conversely, the H-atoms from the larger condensed ring aryl groups that are in close proximity to the migrating sites also have a significant influence on the efficacy and extent of the reaction by restricting access of the alkyne to the metal center, resulting in a less effective migration reaction. This combination of competing steric factors (acceleration due to relief of steric congestion and restricted access of the alkyne moiety to the reaction site) is exemplified by the facile migration of 1-pyryl entities and the low yields of vinylidene products formed from 1,2-bis(9-anthryl)acetylene.