Metallation of sensitive fluoroarenes using a potassium TMP-zincate supported by a silyl(bis)amido ligand

Abstract

Combining a bulky bis(amide) and a reactive one-coordinate TMP (2,2,6,6-tetramethylpiperidide) ligand, a new mixed K/Zn heteroleptic base has been developed for regioselective zincation of fluoroarenes. This special ligand set allows...

Alkali‐Metal‐Alkoxide Powered Zincation of Fluoroarenes Employing Zinc Bis‐Amide Zn(TMP)2

“…[19] For example, using a TMP-based potassium zincate supported by a bulky bis(amide) ligand Ph 2 Si(NAr*) 2 (Ar* = 2,6-diisopropylpheny), we reported zincation of 1 required 3 h at refluxing temperatures in THF or three days at room temperature. [28] The efficient metalation of 1 under mild reaction conditions aligns better with the reactivities previously described using [NaM(HMDS) 3 ] (M = Fe, Co) for the ferration (or cobaltation) of 1. Mechanistic studies for these reactions have revealed that initial NaÀ H exchange takes place followed by trapping of the trisfluorophenyl fragment by the divalent transition metal.…”

“…[42][43][44] Significantly less activated substrates such as fluorobenzene and 1-fluoronaphthalene are also quantitatively zincated in 24 h at room temperature to give products 2 d and 2 e. This is striking as previous approaches using alternative zincating reagents mentioned above fail to metalate these substrates in reasonable yields even when harsh reaction conditions are employed. [28,45] Bromo and chloro para-substituted arenes are zincated easily in 1 h to give zincates 2 f and 2 g. Ortho, meta, and para fluorotoluene can be regioselectively zincated ortho to the fluorine substituent to give products 2 h-2 j avoiding any competing lateral metalation of the methyl substituent as reported for 2-fluorotoluene using the aforementioned LiNK superbase, which favors the benzylic metalation product. [7] Reactivity studies with 2-and 4-fluoroanisole revealed that acidifying effects take prevalence over coordination effects, thus favoring quantitative zincation at the ortho-position to the F substituent furnishing 2 k and 2 l (Figure 3).…”

“…Rapid zincation of 1 with this bimetallic combination under extremely mild reaction conditions contrasts with previous studies on the zincation of fluoroarenes that require the use of sterically demanding ligands, higher temperatures, longer reaction times and in some cases the use of Pd catalysis [19] . For example, using a TMP‐based potassium zincate supported by a bulky bis(amide) ligand Ph 2 Si(NAr*) 2 (Ar*=2,6‐diisopropylpheny), we reported zincation of 1 required 3 h at refluxing temperatures in THF or three days at room temperature [28] . The efficient metalation of 1 under mild reaction conditions aligns better with the reactivities previously described using [NaM(HMDS) 3 ] (M=Fe, Co) for the ferration (or cobaltation) of 1 .…”

Synthesis and Catalysis of Anionic Amido Iron(II) Complexes

“…A very similar deprotonative complexation was utilized by Hevia et al in the syntheses of potassium amido metalates of Zn, Mg, and Mn. [26,28] A third synthesis attempt involving trans-amination of the homoleptic triamido ferrate K(Et 2 O) 2 [Fe(hmds) 3 ] (3) with the rac Ph LH 2 showed no conversion by 1 H NMR despite a closely literature precedent. [29,30] Crystalline rac-1 was isolated as THFmonosolvate (by EA; Mp 176 °C, decomp.…”

Applying Na/Co(ii) bimetallic partnerships to promote multiple Co–H exchanges in polyfluoroarenes

“…In this case the bulky ligand was proposed to be key, providing steric protection for the trapping of the C 6 F 4 dianion, although forcing reaction conditions were required (16 h, 70 °C). 9 Sodium ferrate [(dioxane)NaFe(HMDS) 3 ] can also promote the di-ferration of activated fluoroarenes, although the scope of this reactivity has not been fully investigated. 5 a Opening new ground in this area, building on the mechanistic understanding acquired in sodium-mediated cobaltations here we evaluate the potential of 1 to promote dimetalations of fluoro- and chloro-arenes.…”