Selective dimerization of terminal acetylenes in the presence of PEPPSI precatalysts and relative chloro- and hydroxo-bridged N -heterocyclic carbene palladium dimers

Piano-Stool Iron Complexes as Precatalysts for gem-Specific Dimerization of Terminal Alkynes

“…The catalytic dimerization of terminal alkynes is an effective synthetic route for conjugated enynes, owing to its unity atom economy and the availability of various alkyne precursors. − The main challenge is to control the regio- and stereoselectivity. The homodimerization of a terminal alkyne may yield up to three isomeric enyne products, − whereas the cross-dimerization of two different terminal alkynes may result in an even more complicated mixture of products. − Moreover, the formations of cumulenes, higher oligomers, and polymers may further complicate the reaction outcome. − A large number of catalysts, mostly precious-metal catalysts and f-block elements, have been extensively investigated. − ,− Meanwhile, there have been increasing research endeavors toward the development of sustainable and environmentally benign alternatives to noble-metal catalysts for alkyne dimerization. − Such an effort is evidenced by the rapid development of iron-based catalysts. For example, a few iron-hydride complexes of P,N,P-pincer ligands have proven effective toward the Z -selective dimerization of arylacetylenes at room temperature without any additive. − The iron complex of a cyclic (alkyl)­aminocarbene ligand has been reported as an E -selective catalyst toward the dimerization of arylacetylenes in the presence of a large excess of KO t Bu at high temperatures .…”

Polymerization of 5-Alkylidene-2-norbornenes with Highly Active Pd–N-Heterocyclic Carbene Complex Catalysts: Catalyst Structure–Activity Relationships

“…A promising combination of catalytic activity, durability, and good tolerance to the functional groups was found in Pd catalysts. At the same time, it is well known that the introduction of an N-heterocyclic carbene (NHC) ligand into transition metal complexes leads to higher stability and improved catalytic properties. , Different Pd complexes with NHC ligands were developed as catalysts for cross-coupling reactions like C–C − and C–N bond − formation and others, , but their catalytic activity in the polymerization of alkenes is less known. It seems attractive to use Pd complexes bearing NHC ligands as (pre)­catalysts for the addition polymerization of norbornene derivatives.…”

Catalytic Alkyne Dimerization without Noble Metals

“…During the past few decades, impressive advances have been made to develop catalytic systems for the dimerization of alkynes with high activity and selectivity as well as functional group tolerance. ,, Some of these methods have been applied in the syntheses of natural products. − Most of the reported selective alkyne dimerization catalysts are based on noble metals. ,,,− In contrast, catalysts without noble metals are underdeveloped. There are some reports on early metal (e.g., groups 3 and 4 metals as well as f-block elements) − and main-group catalysts (e.g., Al and Ga) − toward alkyne dimerization, albeit with relatively limited substrate scopes.…”