Facilitating the Ferration of Aromatic Substrates through Intramolecular Sodium Mediation

Abstract

Exploiting cooperative effects between Na and FeII centres present in tris(amide) ferrate complexes has led to the chemoselective ferration of pentafluorobenzene, benzene, toluene, anisole, and pyridine being realised at room temperature. The importance of this bimetallic partnership is demonstrated by neither the relevant sodium amide (NaHMDS or NaTMP) nor the FeII amide Fe(HMDS)2 efficiently metallating these substrates under the conditions of this study. By combining NMR studies with the isolation of key intermediates and DFT calculations, we offer a possible mechanism for how these reactions take place, uncovering a surprising reaction pathway in which the metals cooperate in a synchronised manner. Although the isolated products are formally the result of Fe‐H exchange, theoretical calculations indicate that the aromatic substrates undergo Na‐H exchange followed by fast intramolecular transmetallation to Fe, thus stabilizing the newly generated aryl fragment.

Building Square Planar Cobalt (II) Complexes via Sodium Mediated Cobaltation of Fluoroarenes

“…Under these conditions, we could isolate and structurally characterize the heteroleptic sodium cobaltate [NaCo(HMDS) 2 (C 6 F 5 )] ( 3 a ) in 86 % yield Figure 1a, iii). Complex 3 a displays a contacted ion‐pair structure and is isostructural to the ferration product obtained by reacting [NaFe(HMDS) 3 ] with pentafluorobenzene [11b] . The two retained HMDS ligands are bridging the two metal centers while pentafluorophenyl is coordinated to the Co II center in a terminal position (Co−C7, 2.0624(92) Å).…”

“…The resulting intermediate I3′ subsequently undergoes intermolecular transmetalation with 2 , furnishing 3 a and regenerating 2′ (Figure 4). While the mechanism of this transmetalation is not obvious, we envision this process to be kinetically feasible as a similar ligand exchange between [(toluene)NaFe( μ ‐benzyl)( μ ‐TMP)(TMP)] and [(toluene)NaFe(HMDS) 3 ] is known to be very fast [11b] . In an attempt to experimentally mimic such intermolecular transmetalation, we reacted NaC 6 F 5 with the tris(amide) complex 2 , but this resulted unsuccessful due to the fragility of this fluoroaryl sodium species at room temperature.…”

“…Recently, we reported that pairing sodium amides with the Fe II bis(amide) Fe(HMDS) 2 [HMDS=N(SiMe 3 ) 2 ] can promote regioselective Fe II −H exchange reactions of a series of aromatic substrates including fluoroarenes [11] . This special reactivity has been attributed to the cooperative behavior inherent in these heterobimetallic bases, wherein sodium triggers the initial metalation while both sodium and iron together contribute to stabilizing the fragile aryl anion produced [11b] …”