Continuous Flow Synthesis of Sulfur‐ and Selenium−NHC Compounds (NHC=N‐Heterocyclic Carbene)

Abstract

The first continuous flow syntheses of sulfur‐ and selenium−NHC (NHC=N‐heterocyclic carbene) adducts in unprecedented short reaction times and high yields are reported. The importance of these species in coordination chemistry or as efficient tools for determining the π‐acceptor character of NHC ligands make any improvement in their synthesis a worthy goal. Thiourea derivatives bearing both saturated and unsaturated NHCs were obtained using NEt3 as a weak base (homogeneous setup) in conjunction with a bed of elemental sulfur (S8). The synthetic route proving optimal for selenoureas involves the use of a simple Se/K2CO3 heterogeneous microreactor design.

“Green Is the Color”: An Update on Ecofriendly Aspects of Organoselenium Chemistry

“…In 2021, Nolan and colleagues [ 128 ] reported the first synthesis of selenoureas using a continuous flow system. Unlike their sulfur isosteres, selenium- N -heterocyclic carbene compounds 99 were obtained using a heterogeneous Se/K 2 CO 3 microreactor ( Scheme 48 ).…”

“…Diphenyl diselenide 6b was used in the reaction with different alkenes 75 in the presence of nucleophiles using a graphite electrode as the anode, a platinum electrode as the cathode and Bu4NI as electrolyte. Later, the same group [127] applied a similar approach to synthesizing chalcogenophosphites 58 in a fast, inexpensive, metal-free, environmentally friendly and In 2021, Nolan and colleagues [128] reported the first synthesis of selenoureas using a continuous flow system. Unlike their sulfur isosteres, selenium-N-heterocyclic carbene compounds 99 were obtained using a heterogeneous Se/K2CO3 microreactor (Scheme 48).…”

“…Unlike their sulfur isosteres, selenium-N-heterocyclic carbene compounds 99 were obtained using a heterogeneous Se/K2CO3 microreactor (Scheme 48). From different ligands 98, it was possible to synthesize three selenoureas, even on a large In 2021, Nolan and colleagues [128] reported the first synthesis of selenoureas using a continuous flow system. Unlike their sulfur isosteres, selenium-N-heterocyclic carbene compounds 99 were obtained using a heterogeneous Se/K2CO3 microreactor (Scheme 48).…”

Advances in the Synthesis and Applications of N-Heterocyclic Carbene Metal Complexes with a Focus on the Weak Base Route

“…Inspired by their recent exploration of the synthesis of metal-NHC complexes in flow, the Nolan and Stevens groups have developed an efficient and simple microreactor for the preparation of thioureas and selenoureas . These NHC and chalcogen adducts have been widely studied for their properties and coordination chemistry with different transition metals.…”

“…Inspired by their recent exploration of the synthesis of metal-NHC complexes in flow, 82 the Nolan and Stevens groups have developed an efficient and simple microreactor for the preparation of thioureas and selenoureas. 83 These NHC and chalcogen adducts have been widely studied for their properties and coordination chemistry with different transition metals. Thioureas are considered as strong donor ligands due to the high polarity of the carbon−sulfur bond, which proved to be advantageous in many palladium-catalyzed processes.…”