Recent Progress in the C−N Bond Formation via High‐Valent Group 9 Cp*M(III)‐Catalyzed Directed sp² C−H Activation

Abstract

The presence of nitrogen atom in a wide variety of organic compounds called for the use of powerful CÀ H activation strategy in the CÀ N bond formation. Pentamethylcyclopentadienyl (Cp*) based, high-valent, group 9 transition-metal complexes have shown a great potential as catalysts in the CÀ H activation/functionalization over the years. This minireview summarizes recent progress made in the context of CÀ N bond formation via catalytic (sp 2)CÀ H activation with Cp*M(III) (M = Co, Rh and Ir) catalysts. A general plausible mechanism is briefly discussed at the beginning, and then results are arranged according to metal cobalt, rhodium and iridium, respectively.

Pentacarboxycyclopentadienes in Organic Synthesis

“…According to the X-ray diffraction analysis (XRD), PCCP 1 exists in the crystalline state as 6-hydroxy-6-methoxy-1,2,3,4-tetrakis(methoxycarbonyl)fulvene [27], as well as other polycarbomethoxycyclopentadienes [43]. In a Cl 2 CDCDCl 2 solution, according to 1 H NMR data, PCCP 1 is also present in the fulvic form, which undergoes intramolecular prototropic tautomerism with an activation barrier of ~ 18-19 kcal/mol in the temperature range 60-90°C. At a concentration of PCCP 1 solutions of 0.51 M and higher, the dynamics of its 1 H NMR spectra are concentration-dependent, on account of the intermolecular proton transfer with ΔG ≠ 298 14.5 kcal/mol (in CD 2 Cl 2 ), and in the highly polar DMSO it completely dissociates to form an anion [44].…”

“…Pentasubstituted cyclopentadienes (Cp) with alkyl, aryl, benzyl, halogen-, cyano-, and other substituents in the fi ve-membered ring are popular organic ligands which form various metal complexes widely used as catalysts for C-H bond functionalization [1][2][3], cycloaddition reactions [4,5], olefi n polymerization [6,7], and other processes [8] and are also used to create materials for chemosensorics [9], molecular electronics [10][11][12], and spintronics [13,14]. Such compounds are more stable than unsubstituted Cp derivatives and have a wide range of useful properties [15][16][17][18][19][20][21][22][23][24][25].…”

“…Pentakis(methoxycarbonyl)cyclopentadiene (1) has been attracting close attention since 1942, when it was fi rst synthesized, and already in the 1960s, its main derivatives were obtained [26]. Due to the fact that 5 CO 2 Me substituents strongly stabilize the Cp anion, compound 1 is a strong organic acid, nearly as strong as HCl, and its stable anion forms salts that are stable in air and soluble in water.…”

Merging Directed C−H Activations with High-Throughput Experimentation: Development of Predictable Iridium-Catalyzed C−H Aminations Applicable to Late-Stage Functionalization

“…2 Directed C−H activations offer a means of introducing amine moieties in the vicinity of Lewis basic groups commonly present in drug-like molecules with high regioselectivity. Over the past decade a number of methodologies for C(sp 2 ) −H to C−N bond transformation have been developed, [10][11][12][13][14] utilizing among others Co, 15,16 Rh, [17][18][19] Ir [20][21][22][23][24] and Ru 25-28 catalysts. However, applicability for LSF in a drug discovery context remains challenging.…”

Rhodium-Catalyzed Directed C(sp2)–H Bond Addition of 2-Arylindazoles to N-Sulfonylformaldimines and Activated Aldehydes

“…Transition-metal-catalyzed C–H bond functionalization has emerged as a commanding tool, as it is more waste-reducing and step-economical route than the classical organic synthesis . In the past few years, illustrious success has been achieved on C–C or C–heteroatom bond forming reactions via C–H activation using various transition metal catalysts like Ir­(III), Ru­(II), Rh­(III), Co­(III), etc . Specifically, Rh­(III)-catalyzed functionalization of C–H bond has gained increasing attention due to their broad functional group tolerance, great efficiency, and high atom and step economy …”