Z-Selective alkyne semi-hydrogenation catalysed by piano-stool N-heterocyclic carbene iron complexes

Abstract

Piano-stool NHC iron complexes catalyze the selective semi-hydrogenation of alkynes without any over-reduction and with high selectivity towards Z-alkynes when starting from disubstituted alkynes.

Copper-NHC-Mediated Semihydrogenation and Hydroboration of Alkynes: Enhanced Catalytic Activity Using Ring-Expanded Carbenes

“…Recent years have witnessed a number of reports on homogeneous alkyne semihydrogenation catalysts, with the aim being to develop systems that alleviate some of the issues of selectivity and over-reduction associated with the well-known commercially used heterogeneous Lindlar catalyst . Much of the focus has been on cheap and sustainable metals, including Mn, Fe, Co, and Ni . Copper complexes have proved very versatile in preventing the over-reduction of typically challenging substrates such as aryl- and diaryl-substituted alkynes, especially ones containing functional groups.…”

Chiral Iron Complexes in Asymmetric Organic Transformations

“…A notable stereoselective behavior was observed with the N ‐heterocyclic carbene iron complex 52 by Albrecht and Johnson in 2018 [74] . Indeed, this half sandwich pre‐catalyst, whose structure was established by X‐Ray crystallographic analysis, [75] is able to convert internal alkyne to alkene with high Z ‐selectivity.…”

“…[73] A notable stereoselective behavior was observed with the N-heterocyclic carbene iron complex 52 by Albrecht and Johnson in 2018. [74] Indeed, this half sandwich pre-catalyst, whose structure was established by X-Ray crystallographic analysis, [75] is able to convert internal alkyne to alkene with high Zselectivity. As example, when 1-phenyl-1-hexyne was dissolved in 1,2-DCE, treated with 7 mol% of 52 and methyldiethoxysilane as hydrogen source for 24 hours at 60 °C, the respective olefin was isolated with 63% of conversion and with Z/E ratio of 99:1 (Scheme 29).…”

Catalytic, Z-Selective, Semi-Hydrogenation of Alkynes with a Zinc–Anilide Complex

“…The current industrial standard with regard to this process is the palladium based heterogeneous Lindlar catalyst, 17 however, in recent years many homogeneous transition metal systems have also been developed. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] Due to the current imperative to replace expensive and toxic transition metal catalyst systems, such as those based on palladium, rhodium, ruthenium or iridium, we were interested in the application of non-transition metal elements to this reaction. To date, the only homogeneous non-transition metal catalysts to successfully achieve selective semi-hydrogenation of internal alkynes are Frustrated Lewis Pair (FLP) systems, featuring boranes in combination with a Lewis basic moiety.…”