All-Carbon-Substituted Allenylidene and Related Cumulenylidene Ligands

Ruthenium(IV)-Catalyzed Markovnikov Addition of Carboxylic Acids to Terminal Alkynes in Aqueous Medium

“…In general, the catalytic activity of trans -[RuCl 2 (η 3 :η 3 -C 10 H 16 )(PPh 3 )] ( 6a ) turned out to be somewhat lower than that shown by the hydrophilic complex [RuCl 2 (η 6 -C 6 H 6 )(TPPMS)] . However, it is worth noting that the addition of benzoic acid to tertiary aromatic alkynols HCCC(OH)Ar 2 (Ar = 4-C 6 H 4 F ( 9m ), 4-C 6 H 4 Cl ( 9n )) gave rise to the β-oxo esters 10ma and 10na as the major reaction products (entries 13 and 14 of Table ), in contrast with the catalytic activity of [RuCl 2 (η 6 -C 6 H 6 )(TPPMS)], which resulted in the almost exclusive formation of the alkene products H 2 CCAr 2 via hydrolysis of the highly reactive allenylidene intermediate [Ru]CCCAr 2 generated by dehydration of the alkynol . However, we must note that formation of minor amounts of olefinic side products was observed in many of the reactions given in Table .…”

Osmium-Centered Oxetylidene: Formation and Cleavage

“…As a result, the heteroatom–H bonds of amines, alcohols, and water add across the highly polarized C α –C β double bond of electrophilic vinylidene compounds to afford Fischer-type carbene derivatives . γ-Hydroxyvinylidene complexes are transient species that dehydrate to give allenylidene and/or alkenylvinylidene derivatives or alternatively isomerize into hydroxyalkenylcarbene compounds, depending upon the electronic nature of the metal center. The isomerization is generally viewed as a two-step process involving the dehydration of the hydroxyvinylidene and the subsequent addition of water to the C α –C β double bond of the resulting cumulene .…”