LNL-Carbazole Pincer Ligand: More than the Sum of Its Parts

Abstract

The utility of carbazole in photo-, electro-, and medicinal applications has ensured its widespread use also as the backbone in tridentate pincer ligands. In this review, the aim is to identify and illustrate the key features of the LNL-carbazolide binding to transition metal centers (with L = flanking donor moieties, e.g., C, N, P, and O-groups) in a systematic bottom-up progression to illustrate the marked benefits attainable from (i) the rigid aromatic carbazole scaffold (modulable in both the 1,8-and 3,6-positions), (ii) the significant electronic effect of central carbazole-amido binding to a metal, and the tunable sterics and electronics of both the (iii) flanking donor L-moieties and (iv) the wingtip R-groups on the L-donors, with their corresponding influence on metal coordination geometry, d-electron configuration, and resultant reactivity. Systematic implementation of the ligand design strategies not in isolation, but in a combinatorial approach, is showcased to demonstrate the potential for functional molecules that are not only modulable but also adaptable for wide-ranging applications (e.g., stereoselective (photo)catalysis, challenging small molecule activation, SET and redox applications, and even applications in chemotherapeutics) as an indication of future research efforts anticipated to stem from this versatile pincer assembly, not only for the transition metals but also for s-, p-, and f-block elements.

Enhancing Precatalyst Performance and Robustness through Aromaticity: Insights from Iridaheteroaromatics

“…This distinction between NHCs and phosphines highlights the unique characteristics of NHC ligands in transition-metal coordination chemistry . Among the diverse range of NHCs, the chemistry of pyridine-derived carbenes (pyridylidene) has been relatively less explored compared to that of imidazolylidenes and triazolylidenes . This disparity can be attributed to the higher electron density of the pyridine heterocycle, which contains only one heteroatom, resulting in limited stabilization of the free carbene and the challenge in isolating a free pyridylidene .…”

Synthesis and Alkyne Metathesis Activity of Pincer Rhenium Carbyne Complexes

“…It is expected that the barrier for the cycloaddition-cycloreversion reaction is dependent on both the identity and the arrangement of the X-and L-type ligands. Considering the rigid nature of pincer ligands, 18 we envisioned that Re(V) carbyne complexes of pincer ligands are good candidates for studying this effect. For this reason, we have attempted to prepare Re(V) carbyne complexes bearing a labile ligand L′ and a pincer ligand of the types (1) 1 6 with bis(2-diphenylphosphino-4-tolyl)amine (PNHP) 19,20 in toluene at 100 °C for 4 h (Scheme 1).…”

Tandem Electrochemical Oxidation of Polycyclic Aromatic Amines Towards Carbazoles and Phenazine‐based Aza‐helicenes

“…Heteroatom (N, O, S)-fused helical polycyclic aromatic hydrocarbons (PAHs) with non-planar π-conjugated system and tunable electrochemical, charge carrier, and semiconducting nature have become the frontier of molecular materials science such as organic optoelectronics, photonics and spintronics. [1][2][3][4][5][6] Fused-ring carbazole and phenazine typed aza-helicenes are endowed with versatile functions in OLED, [7] photovoltaic, [8] pincer ligand, [9] pharmacophore, [10] and smart molecular materials. [11] Carbazoles are obtained through pyrrole annulation using polycyclic aromatic amines (PAAs), such as DDQ, [12] air-Rh/C, [13] or copper (II) mediated 2-anthracenamine oxidative coupling aromatization [14] (Scheme 1).…”