A Simple Synthetic Route to [Rh(acac)(CO)(NHC)] Complexes: Ligand Property Diagnostic Tools and Precatalysts

Abstract

An operationally simple, user and eco‐friendly synthetic protocol for the synthesis of [Rh(acac)(CO)(NHC)] complexes is described. Insights into the mechanism are provided using operando spectroscopy. The spectroscopic fingerprints of these complexes are correlated to NHCs reported electron‐donating descriptor values, highlighting a new strategy to evaluate carbenes’ electronic properties. An assessment of these complexes in catalytic applications is also reported, showing promising results in the catalytic hydrogenation of aromatic ketones.

Simple synthetic access to [Au(IBiox)Cl] complexes

“…Since 2013, when Nolan 17 and Gimeno 18 independently reported simple and efficient approaches to Au-NHC complexes using weak bases, this "weak base route" 19,20 has been extended to numerous metal-NHC syntheses. [21][22][23][24][25] We now extend the range of NHC ligands compatible with this weak base route to the IBiox ligand family with a focus on Au-IBiox complexes (Scheme 1). The classical synthetic route employed to access IBiox ligands usually leads to the isolation of triflate IBiox salts.…”

Mechanistic Insights into the Synthesis of [Rh(acac)(CO)(NHC)] (NHC=N‐heterocyclic carbene) Complexes Using a Weak Base

“…Data are in agreement with reported values. [6] Synthesis of [Rh(acac)(CO)(IPr*)] 1 c from [Rh(acac)(CO) 2 ]: In a 20 mL vial were mixed 100 mg of [Rh(acac)(CO) 2 ] (0.39 mmol, 1 equiv. ), 372 mg of IPr*•HCl (0.39 mmol, 1 eq) and 269 mg of K 2 CO 3 (1.95 mmol, 5 equiv.)…”

“…[3] Recently, the Glorius group successfully made use of the [RhCl(CAAC)(COD)] complex (CAAC = cyclic (alkyl)(amino)carbene, COD = cyclooctadiene) for chemoselective hydrogenation of fluoroarenes, fluoropyridine, silylarenes and aryl boronic esters. [4,5] In 2021, proof-of-concept was achieve in showcasing the potential of [Rh(acac)(CO)(NHC)] (1) (acac = acetylacetonato) complexes in selective hydrogenation of aryl ketones, [6] but this area remains underexplored.…”

“…If the synthetic access to [RhCl(cod)(NHC)] complexes through the weak base route has been known for years, [14] it was only recently confirmed that this pathway was also viable for [Rh(acac)(CO)(NHC)] systems. [6] This most recent work provided examples starting from the NHC * HBF 4 salts, and not from their more easily accessible NHC * HCl relatives. A mechanistic investigation of this reaction would lead to easier synthetic access to these complexes and to the further development of their catalytic/synthetic potential.…”

A green route to platinum N-heterocyclic carbene complexes: mechanism and expanded scope

“…11 The development of a protocol utilizing a weak base ( e.g. , K 2 CO 3 , NaOAc or NEt 3 ) and azolium NHC precursors has been a major advance in accessing ubiquitous well-defined NHC complexes, and has recently become the new standard in the synthesis of gold-, 12 copper-, 13 palladium-, 14 rhodium-, 15 iridium- 15 a and ruthenium-NHC 16 compounds.…”