Recent Mechanistic and Synthetic Developments in the Chemistry of Transition‐Metal Vinylidene Complexes

Abstract

Transition-metal vinylidene complexes are intermediates in a number of synthetically important transformations of alkynes. Underpinning these applications is the ability of various electron-rich transition-metal complexes to effectively facilitate the conversion of alkynes into their vinylidene tautomers. Recent experimental and theoretical studies have provided considerable insight into the mechanisms by which this process occurs and they are detailed herein. In particular, it has been demonstrated that different substituents on both the metal and the alkyne may have profound effects on both the kinetic and thermodynamic profiles of the alkyne/vinylidene tautomerisation. An important finding is that internal alkynes may be employed to prepare disubstituted vinylidene complexes under easily accessible conditions. This discovery brings to light a new facet of the potential synthetic applications of transition metal vinylidene complexes.

Solvent‐Promoted Regio‐ and Stereoselectivity in Ru‐Catalyzed Hydrocarboxylation of Terminal Alkynes: A DFT Study

“…Alkyne→vinylidene transformation : The conversion of η 2 ‐alkyne→η 1 ‐vinylidene, demonstrated in various experimental findings, is a well‐established route used for the synthesis of a wide range of vinylidene complexes . Numerous experimental and theoretical studies have been devoted to the investigation of the mechanism for this conversion to occur . As a result, several pathways have been suggested and the selection of a given route depends on the electronic property of the metal center and availability of a hydride ligand (Scheme ).…”

Syntheses, structural characterisation and electronic structures of some simple acyclic amino carbene complexes

“…19,21 For example, in the case of half-sandwich complexes MCl(L 2 )Cp′ (L = phosphine or L 2 = chelating bis( phosphine), Cp′ = Cp, Cp* etc. 19,21 For example, in the case of half-sandwich complexes MCl(L 2 )Cp′ (L = phosphine or L 2 = chelating bis( phosphine), Cp′ = Cp, Cp* etc.…”

The synthesis, molecular and electronic structure of cyanovinylidene complexes

“…The Group 6 metal carbonyl anions [M(CO) 3 Cp] -(M = Mo, W) reacted smoothly with Cl 2 C=C(CN) 2 to give 1-chloro-2,2-dicyanovinyl derivatives…”

“…Subsequent thermolysis of the vinyl compounds in the presence of trivalent phosphorus ligands resulted in carbonyl substitution and chloride migration to give a mixture of the cis-and transdicyanovinylidene complexes MCl{C=C(CN) 2 }(PR 3 ) 2 Cp [20 -22]; reactions of Mo{CCl=C(CN) 2 }(CO) 3 Cp with Bu t NC gave only the carbonyl substitution product Mo{CCl=C(CN) 2 }(CO) 2 (CNBu t )Cp, the chlorovinyl ligand remaining unchanged (Scheme 2) [23]. [24].…”