alkyylikidinien

Alkyylikidinien, known in English as alkylidyne ligands, are a class of organometallic species in which a metal center is bonded to a carbon atom by a triple bond and that carbon bears an additional substituent, typically an alkyl or aryl group. The general motif is M≡C–R, with the triple bond to the metal and the R group modulating steric and electronic properties. These ligands are usually terminal, attaching to a single metal center, and they play an important role in several catalytic and synthetic applications.

Bonding and structure: The M≡C–R unit features a highly polarized triple bond. The carbon is sp-hybridized, and the interaction involves σ-donation from carbon to the metal along with π-back-donation from the metal to carbon. The electronic character and the bulky ligands surrounding the metal help stabilize the reactive M≡C core.

Synthesis and stabilization: Alkylidyne complexes are typically formed for high oxidation-state metals, such as molybdenum and tungsten, and are stabilized by bulky, electron-donating ligands (for example siloxide or aryloxide groups). Synthesis often requires rigorous, air-free techniques and carefully chosen precursors to prevent degradation of the sensitive M≡C unit.

Applications: The foremost significance of alkylidyne complexes lies in catalysis, especially alkyne metathesis. They serve as active catalysts and catalyst precursors for transformations involving alkynes, including cycloadditions and polymerization processes. They also function as key intermediates in the preparation of other carbynoid species.

Notable examples: Well-studied systems include Mo and W alkylidyne complexes bearing bulky supporting ligands, which have been extensively explored for their catalytic activity and mechanistic features.

See also: alkynyl, carbyne, alkyne metathesis.