Dalton Transactions
Communication
approach iron(IV)–imido species with modified bis(anilido)imi-
nophosphorane ligands is under way in our laboratory.
This work was supported by the National Natural Science
Foundation of China (nos. 20923005, 21121062, and
21222208) and the Science and Technology Commission of
Shanghai Municipality (no. 11PJ1412100).
Notes and references
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Fig. 3 Molecular structures of 3a (left) and 3b (right), showing 30% proba-
bility ellipsoids and the partial atom numbering scheme. For clarity a mesityl
group on each structure has been omitted. Selected distances (Å) and angles (°)
for 3a: Fe(1)–N(3) 2.144(3), Fe(1)–N(1) 2.022(3), Fe(1)–N(2) 2.009(3), Fe(1)–N(5)
1.982(2), P(1)–N(1) 1.591(3), N(5)–Fe(1)–N(2) 111.1(1), N(1)–Fe(1)–N(3) 122.5(1);
for 3b: Fe(1)–N(3) 2.109(3), Fe(1)–N(4) 2.044(2), Fe(1)–N(1) 2.062(2), Fe(1)–N(2)
1.962(2), P(1)–N(4) 1.617(2), N(1)–Fe(1)–N(2) 105.6(1), N(3)–Fe(1)–N(4) 145.7(1).
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The isolation of 3a and 3b suggests that iron-mediated
C(sp3)–H bond amination reactions have occurred on the tripo-
dal ligand platform, which represents a rare example of
C(sp3)–H bond amination facilitated by non-heme iron after
Betley’s benzylic C–H bond amination reactions from (dipyrro-
methene)iron–imido complexes,26,27 and Che’s intramolecular
amidation of sulfamate esters catalyzed by iron–pyridyl com-
plexes.38 Besides these, Que,39 Latour,40 and Jensen41 have
reported non-heme iron complex-mediated and -catalyzed aro-
matic substitution reactions with tosyliminoiodane as the
nitrene precursor, and Borovik,42 Peters,43 and Holland22,23
have demonstrated the hydrogen-atom-abstraction reactivity by
iron–imido species toward C–H bonds but without C–N bond
formation. Accordingly, we propose that the formation of 3a
and 3b might involve iron(IV)–imido intermediates (MesN2NAd
)
Fe(NR) generated by the interaction of 2 with the alkyl azides.
Once formed, the iron(IV)–imido moiety could then perform
hydrogen-atom-abstraction followed by a radical-rebound step
to produce iron(II) complexes with appended amine side arms.
The whole process should be similar to the mechanism of iron(IV)–
oxo mediated C–H bond hydroxylation reactions.44,45 The
success of C–N bond formation in our system implies greater
reactivity of iron(IV)–imido species versus that of the iron(III)
imides.9,22 However, the proximity of benzylic C–H bonds to
the iron center should also play a role as we found that in the
presence of an excess of indene, 9,10-dihydroanthracene, or
1,4-cyclohexadiene the reactions of 2 with n-C8H17N3 in C6D6
still afforded 3a with the retention of all external hydrogen-
donors although the α-C–H bonds of these substrates are
much weaker than benzyl C–Hs.46
13 J. England, Y. Guo, E. R. Farquhar, V. G. Young Jr.,
E. Münck and L. Que Jr., J. Am. Chem. Soc., 2010, 132,
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14 Y. Morimoto, H. Kotani, J. Park, Y.-M. Lee, W. Nam and
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15 H. Kotani, T. Suenobu, Y.-M. Lee, W. Nam and
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M. P. Hendrich and A. S. Borovik, J. Am. Chem. Soc., 2010,
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18 O. Pestovsky, S. Stoian, E. L. Bominaar, X. Shan, E. Münck,
L. Que Jr. and A. Bakac, Angew. Chem., Int. Ed., 2005, 44,
6871–6874.
In conclusion, high-spin iron(II) complexes supported by
dianionic tridentate ligands, bis(anilido)phosphine and bis-
(anilido)iminophosphorane, have been synthesized and struc-
turally characterized. The reactions of the bis(anilido)imino-
phosphorane–iron(II) complex with alkyl azides afforded
ligand-based C–H bond amination products, demonstrating
the high reactivity of iron–imido intermediates supported by
the dianionic tripodal platform. Further exploration to
19 S. Shaik, H. Hirao and D. Kumar, Acc. Chem. Res., 2007, 40,
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20 S. Ye and F. Neese, Curr. Opin. Chem. Biol., 2009, 13, 89–98.
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T. R. Cundari and P. L. Holland, Angew. Chem., Int. Ed.,
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Dalton Trans., 2013, 42, 5607–5610 | 5609