Catalytic C−H Borylation Using Iron Complexes Bearing 4,5,6,7‐Tetrahydroisoindol‐2‐ide‐Based PNP‐Type Pincer Ligand

Abstract

Catalytic C−H borylation has been reported using newly designed iron complexes bearing a 4,5,6,7‐tetrahydroisoindol‐2‐ide‐based PNP pincer ligand. The reaction tolerated various five‐membered heteroarenes, such as pyrrole derivatives, as well as six‐membered aromatic compounds, such as toluene. Successful examples of the iron‐catalyzed sp3 C−H borylation of anisole derivatives were also presented.

Direct C−H Borylation of Arenes Catalyzed by Saturated Hydride‐Boryl‐Iridium‐POP Complexes: Kinetic Analysis of the Elemental Steps

“…However, they have been scarcely used for stabilizing C−H borylation catalysts. Three classes of pincers have received attention: neutral 6 e − donors, monoanionic 5 e − donors, and dianionic 4 e − donors . The first type has been employed by the groups of Chirik, Cui, and Kamitani.…”

“…Cui has synthesized a cobalt(II) compound stabilized by a silylene‐pyridine‐silylene pincer, which enables reactions of pyridines, furans, and fluorinated arenes, whereas Kamitani has achieved efficient C−H borylation of arenes and heteroarenes using an iron complex bearing a quinoline‐based PNN ligand. Pincers donating 5 e − and 4 e − have been mainly used to stabilize iridium catalysts, in addition to some examples of iron, rhodium, and platinum . Chianese's group has observed that, in combination with NaO t Bu, iridium(III) complexes containing CCC‐pincer N ‐heterocyclic carbene ligands form active species for C−H borylation of disubstituted substrates.…”

Synthesis and structures of anionic rhenium polyhydride complexes of boron–hydride ligands and their application in catalysis

“…To the best of our knowledge, this is the highest reported meta selectivity observed for the stoichiometric or catalytic C-H borylation of toluene. 23 This reaction is likely to proceed by a similar mechanism reported for [Ir(Bpin) 3 (L) 2 ] complexes (where L is a bisphosphine, bipyridine or phenanthroline ligand) which undergo s-CAM activation of the arene C-H bond. 24 This is the rst example of a high oxidation-state rhenium complex mediating C-H borylation, contrasting with previous examples that exploit complexes of lower oxidation-states.…”

Phosphines and N‐Heterocycles Joining Forces: an Emerging Structural Motif in PNP‐Pincer Chemistry

“…The iron derivative Pyr ( tBu PNP)Fe(N 2 ) 39‐Fe and the iron(II) hydride Pyr ( t BuPNP)Fe(H) 40 were both found to effectively catalyze the hydroboration of alkenes and alkynes with HBpin (see Scheme ) . Using catalytic amounts of the dimeric P i Pr 2 ‐substituted 4,5,6,7‐tetrahydroisoindol‐2‐ide‐hydridoiron(II) pincer complex 41 , catalytic C–H borylations of furans were also achieved (Scheme ) . For the C–H borylation of less activated arenes, B 2 Pin 2 has been used as a B‐transfer reagent, but these transformations are best carried out using the more reactive iron(II) methyl complexes Pyr ( R PNP)Fe(Me) as catalysts …”

“…Using catalytic amounts of the dimeric P i Pr 2 ‐substituted 4,5,6,7‐tetrahydroisoindol‐2‐ide‐hydridoiron(II) pincer complex 41 , catalytic C–H borylations of furans were also achieved (Scheme ) . For the C–H borylation of less activated arenes, B 2 Pin 2 has been used as a B‐transfer reagent, but these transformations are best carried out using the more reactive iron(II) methyl complexes Pyr ( R PNP)Fe(Me) as catalysts …”