Autocatalysis for C–H Bond Activation by Ruthenium(II) Complexes in Catalytic Arylation of Functional Arenes

Abstract

Kinetic data for the C-H bond activation of 2-phenylpyridine by Ru(II)(carboxylate)(2)(p-cymene) I (acetate) and I' (pivalate) are available for the first time. They reveal an irreversible autocatalytic process catalyzed by the coproduct HOAc or HOPiv (acetonitrile, 27 °C). The overall reaction is indeed accelerated by the carboxylic acid coproduct and water. It is retarded by a base, in agreement with an autocatalytic process induced by HOAc or HOPiv that favors the dissociation of one carboxylate ligand from I and I' and consequently the ensuing complexation of 2-phenylpyridine (2-PhPy). The C-H bond activation initially delivers Ru(O(2)CR)(o-C(6)H(4)-Py)(p-cymene) A or A', containing one carboxylate ligand (OAc or OPiv, respectively). The overall reaction is accelerated by added acetates. Consequently, C-H bond activation (faster for acetate I than for pivalate I') proceeds via an intermolecular deprotonation of the C-H bond of the ligated 2-PhPy by the acetate or pivalate anion released from I or I', respectively. The 18e complexes A and A' easily dissociate, by displacement of the carboxylate by the solvent (also favored by the carboxylic acid), to give the same cationic complex B(+) {[Ru(o-C(6)H(4)-Py)(p-cymene)(MeCN)](+)}. Complex B(+) is reactive toward oxidative addition of phenyl iodide, leading to the diphenylated 2-pyridylbenzene.

A potential role of a substrate as a base for the deprotonation pathway in Rh-catalysed C–H amination of heteroarenes: DFT insights

“…Jutand et al suggested that intermolecular proton abstraction by an acetate ligand for the C-H bond activation of functional arenes by Ru(II) complexes is facilitated either by agostic M(C-H) bond or by the formation of a Wheland intermediate. 41,42 To validate this, we have conducted natural bond orbital (NBO) analysis and Bader's atoms in molecules (AIM) analysis of complexes a, b and TS1. 43,44 The possibility of an agostic Rh(C-H) bond is not observed in the above-mentioned complexes.…”

Cycloruthenation of aryl imines and N-heteroaryl benzenes via C–H bond activation with Ru(II) and acetate partners

“…13 C NMR spectra were obtained at 50, 75 and 100 MHz and referenced to the internal solvent signals (CDCl 3 , central peak at 77.2 ppm).…”

“…of KOAc at room temperature for 20 h led to the isolation of red complexes 3b (77%), 3c (52%), and 3d in 73% isolated yields (Scheme 1). The struture of 3a-3d was based on 1 H, 13 C NMR and the X-ray struture analysis of compounds 3a and 3b.…”

“…13 Thus the aryl imine 2a was reacted with Ru(OAc) 2 (p-cymene) in methanol but in the presence of one equiv. of KCl and then 66% yield of the complex 3a was isolated (Scheme 2).…”

Solvent‐Free Ruthenium(II)‐Catalyzed C–H Activation: Synthesis of Alkenylarylpyrazole Derivatives

“…In particular, deprotonation of C-H bonds assisted by carboxylates and a Ru II center proceeds through an autocatalytic process, in which the formed RCO 2 H acid plays a crucial role. [24,25] In contrast, both Miura and Ackermann recently reported the alkenylation of thiophene-2-carboxylic acid [26] and simple benzoic acid ditions or by using a user-friendly solvent system in which water was present as the major component. With less-reactive styrenes, monoalkenylation took place, whereas with alkyl acrylates ortho-dialkenylation occurred.…”