A one-pot synthesis
of various 5,10-diaryl-5,10-dihydrophenazines
(DADHPs) from diarylamines has been achieved by using an iron-catalyzed
C–F amination. Homodimerization of magnesium diarylamides,
followed by defluorinative intramolecular cyclization (double ortho C–F amination) in the presence of catalytic
FeCl2 and stoichiometric 1,2-dibromoethane, affords the
corresponding DADHPs with complete regiocontrol. The unique high reactivity
of fluorine over other halogens indicates that amination proceeds
via an SNAr mechanism facilitated by iron.
As a measure of d-π* back-donation, IR stretching modes are, in general, used for metal carbonyl compounds. Once the ligand is replaced with olefins (metal−arene complexes), it can be analyzed crystallographically unless otherwise the C−C bond length falls into values within standard deviation. Herein, we propose a novel measure using an η 2 -(H 2 O@C 60 ) ligand in group 9 metal− fullerene complexes, in which the stronger d-π* backbonding causes enhanced sp 3character on the coordinated olefinic bond and consequently leads to the restricted rotation for the H 2 O molecule as detectable by the 1 H NMR relaxation time. The π-backbonding strengths were, therefore, found to follow the ascending order of atomic numbers (Co < Rh < Ir) in CpM(CO)(η 2 -H 2 O@C 60 ) (Cp = cyclopentadienyl), associated with the anodic shift on oxidation potentials and hypsochromic shift on absorption edges.
A chemoselective C−N coupling (Buchwald‐Hartwig‐type) reaction of diarylamines with aryl halides bearing non‐protected amino or hydroxy groups proceeds in the presence of a simple iron catalyst. Upon treatment with Grignard reagents, various diarylamines can be cross‐coupled with halocarbazoles, haloindoles, haloanilines, and halophenols to afford the corresponding triarylamines, without the undesired dimerization or oligomerization of the starting aryl halides. DFT studies on the dimeric iron amide intermediates reveal that the reductive elimination can be the selectivity determining step. Finally, a short‐step synthesis of a thermally activated delayed‐fluorescence emitter, DACT‐II, demonstrates the synthetic utility of the present method.
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