Tuning the Catalytic Activity of a Pincer Complex of Rhodium(I) by Supramolecular and Redox Stimuli

Abstract

We report a rhodium (I) complex [Rh(CNC‐NDI)(CO)]+, in which CNC‐NDI refers to a pincer‐CNC ligand decorated with a naphthalenediimide moiety. Due to the presence of the planar CNC ligand, and the naphthalenediimide moiety, the electronic nature of the complex can be modulated by means of supramolecular and redox stimuli, respectively. The metal complex shows a strong π−π‐stacking interaction with coronene. This interaction has an impact on the electronrichness of the metal, as demonstrated by the shifting of the ν(CO) stretching band to a lower frequency. The addition of tetrabutylammonium fluoride facilitates the sequential one‐ and two‐electron reduction of the NDI moiety of the ligand, thus rendering a situation in which the ligand can increase its electrondonor strength in two levels. The nature of the interaction with the fluoride anion was studied computationally. The catalytic activity of the [Rh(CNC‐NDI)(CO)]+ complex was tested in the cycloisomerization of alkynoic acids, where it is observed that the activity of the catalyst can be modulated between four levels of activity, which correspond to i) the use of the unmodified catalyst, ii) catalyst + coronene, iii) catalyst + 2 equivalents of fluoride, and iv) catalyst + 5 equivalents of fluoride.

“Anion-Switchable” Pincer-Mn(I) Catalyst for the Reductive N-Methylation of Amines with Formic Acid and CO2

“…The NDI-pincer Mn(I) complex 2 was prepared by reacting the NDI-functionalized bis-imidazolium salt [1](I) 2 22 with Ag 2 O in CH 2 Cl 2 , and then by transmetallating the in situ generated silver-NHC complex with [Mn(CO) 5 Br] in the presence of Na(BAr F 4 ), as shown in Scheme 1. For comparative purposes and following the same synthetic route, we also prepared complex 4, lacking the NDI functionalization, starting from [3](Br) 2 .…”

“…More recently, we showed how a rhodium(I) complex with an NDIfunctionalized NHC-based pincer ligand could improve its catalytic activity by adding fluoride, which turned out to behave as a very effective redox stimulus. 22 Building on these grounds, we herein report the preparation of a Mn(I) complex supported by an NDI-functionalized NHC-based pincer CNC ligand and the study of its catalytic performance in the reductive N-methylation of a series of secondary amines using formic acid or CO 2 . The effect of modulating the electronic properties of the NDI-functionalized pincer Mn(I) complex by the addition of chloride will be described and discussed.…”

“…Our studies revealed that the NDI moiety behaved as a redox-switchable tag that allowed modification of the electron-donating strength of the ligands in a controlled and reversible manner. More recently, we showed how a rhodium(I) complex with an NDI-functionalized NHC-based pincer ligand could improve its catalytic activity by adding fluoride, which turned out to behave as a very effective redox stimulus …”

Lone‐Pair‐π Bond Strength Unveiled by a Combined Experimental and Computational Study

“…[10] We also contributed to the field, by showing how the addition of fluoride to a Rh(I) complex bearing a CNC pincer ligand functionalized with a NDI moiety facilitates the sequential one-and two-electron reduction of the NDI moiety of the ligand, thus rendering a situation in which the ligand can increase its electrondonor strength in two levels. [11] This effect had an important impact on the catalytic performance of the complex, thus revealing a new application of anion-NDI interactions to the field of homogeneous catalysis.…”

Azobenzene-Integrated NHC Ligands: A Versatile Platform for Visible-Light-Switchable Metal Catalysis

“…As one of the most powerful ligand classes in catalysis, − N -heterocyclic carbenes (NHCs) have emerged as privileged candidates for implementing switchable functionality. − By incorporating azobenzene into the cyclic­(alkyl)­(amino)­carbene (CAAC) ligand of a ruthenium-based catalyst, Hong and co-workers demonstrated ON/OFF photoswitching of catalytic activity in ring-closing metathesis (Figure A) . In this system, the E isomer of the carbene ligand defines the catalyst’s ON state, while the Z -form is vaguely assumed to deactivate the catalyst.…”