transfer. Also noteworthy are (a) the use of non-sulfonyl
organic azides as the nitrene sources for the group-transfer
chemistry, as opposed to the more common Bromamine-T and
PhIQNTs,20 and (b) the atom-economical nature of this
nitrene transfer reaction, which has only N2 as a byproduct.
We thank the University of Rochester (N.A.E., Weissberger
Fellowship), the National Science Foundation (P.L.H.,
CHE-0134658; R.E.C., Graduate Research Fellowship), and
the Petroleum Research Fund (44942-AC) for funding, and
William Brennessel for assistance with crystallography.
Scheme 2
Notes and references
z LtBuFeNAd: Yield 88% based on 1H NMR integration; 1H NMR
(400 MHz, C6D6): d 77 (6H, Ad-a), 43 (1H, backbone a-H), 38
(3H, Ad-b or Ad-g), 33 (3H, Ad-b or Ad-g), 23 (3H, Ad-b or Ad-g),
20 (18H, C(CH3)3), ꢀ9 (4H, m-Ar or CH(CH3)2), ꢀ13 (12H,
CH(CH3)2), ꢀ38 (2H, p-Ar), ꢀ57 (12H, CH(CH3)2), ꢀ59 (4, m-Ar
or CH(CH3)2); UV/vis (toluene, l (nm), e (mMꢀ1 cmꢀ1)): 335 (18),
435 (3.5), 530(sh), 660(sh); geff (toluene, 8 K, 9.414 GHz): 7.0, 1.8, 1.3.
y C50H80FeN5,
a = 13.1565(17), b = 19.524(2), c = 18.978(2), b = 100.703(3),
U = 4790.0(10) A3, T = 100.0(1) K, Z = 4, m(Mo-Ka) = 0.352 mmꢀ1
M = 807.04, monoclinic, space group P21/c,
t
Fig. 3 1H NMR spectra of the reaction between BuNC and N3Ad
with 10 mol% iron(I) (from LtBuFeNNFetBu).
,
31952 reflections measured, 4636 unique (Rint = 0.1721), R1 = 0.0609,
wR2 = 0.0999 [I 4 2s(I)]. CCDC 710042.
Table 1 Summary of catalytic reactions in C6D6
1 K. L. Carraway and D. E. Koshland, Methods Enzymol., 1972, 25,
616.
Azide ERC Fe (%) t/min T/1C Conv. (%) TON TOF/hꢀ1
2 Z. Li, S. T. Barry and R. G. Gordon, Inorg. Chem., 2005, 44, 1728.
3 (a) G. Tian, Y. Lu and B. M. Novak, J. Am. Chem. Soc., 2004, 126,
4082; (b) H.-Z. Tang, E. R. Garland, B. M. Novak, J. He,
P. L. Polavarapu, F. C. Sun and S. S. Sheiko, Macromolecules,
2007, 40, 3575.
AdN3 CO
AdN3 tBuNC 10
AdN3 tBuNC
AdN3 CyNC 10
TolN3 tBuNC
10
185
60
60
75
60
60
60
60
25
495
495
65
495
495
9.5
9.5
16
9.5
47
3.1
9.5
16
4
7.6
4 (a) H. L. M. van Gaal and J. P. J. Verlaan, J. Organomet. Chem.,
1977, 133, 93; (b) E. T. Hessell and W. D. Jones, Organometallics,
2
o2
41500
1992, 11, 1496; (c) G. Horlin, N. Mahr and H. Werner,
¨
Organometallics, 1993, 12, 1775.
is performed on a 2 mmol scale. Control experiments show
t
5 N. A. Eckert, S. Vaddadi, S. Stoian, R. J. Lachicotte,
T. R. Cundari and P. L. Holland, Angew. Chem., Int. Ed., 2006,
45, 6868.
that N3Ad and BuNC do not react with each other in the
absence of LtBuFeNNFeLtBu, at 60 1C in C6D6 for 5 d. Also,
LtBuFeCl18 and Rieke iron19 do not catalyze the formation of
tBuNQCQNAd, suggesting that iron(II) and iron(0) are not
capable of effecting the observed reactivity, and verifying that
these potential trace contaminants are not responsible for the
catalytic reaction.
6 R. E. Cowley, J. Elhaık, N. A. Eckert, W. W. Brennessel, E. Bill
¨
and P. L. Holland, J. Am. Chem. Soc., 2008, 130, 6074.
7 J. M. Smith, A. R. Sadique, T. R. Cundari, K. R. Rodgers,
G. Lukat-Rodgers, R. J. Lachicotte, C. J. Flaschenriem, J. Vela
and P. L. Holland, J. Am. Chem. Soc., 2006, 128, 756.
8 Y. Yu, A. R. Sadique, J. M. Smith, T. R. Dugan, R. E. Cowley,
W. W. Brennessel, C. J. Flaschenriem, E. Bill, T. R. Cundari and
P. L. Holland, J. Am. Chem. Soc., 2008, 130, 6624.
9 A. R. Sadique, W. W. Brennessel and P. L. Holland, Inorg. Chem.,
2008, 47, 784.
10 E. Kogut, H. L. Wiencko, L. Zhang, D. E. Cordeau and
T. H. Warren, J. Am. Chem. Soc., 2005, 127, 11248.
11 Y. M. Badiei, A. Krishnaswamy, M. M. Melzer and T. H. Warren,
J. Am. Chem. Soc., 2006, 128, 15056.
12 D. J. Mindiola and G. L. Hillhouse, Chem. Commun., 2002, 1840.
13 S. D. Brown, T. A. Betley and J. C. Peters, J. Am. Chem. Soc.,
2003, 125, 322.
14 S. C. Bart, E. Lobkovsky, E. Bill and P. J. Chirik, J. Am. Chem.
Soc., 2006, 128, 5302.
15 (a) T. H. Warren, PCT patent publication number WO2008/
073781, 18 June 2008; (b) Y. M. Badiei, A. Dinescu, X. Dai,
R. M. Palomino, F. W. Heinemann, T. R. Cundari and
T. H. Warren, Angew. Chem., Int. Ed., 2008, 47, 9961.
16 H. Lebel and O. Leogane, Org. Lett., 2005, 7, 4107.
17 R. P. Bennett and W. B. Hardy, J. Am. Chem. Soc., 1968, 90, 3295.
18 J. M. Smith, R. J. Lachicotte and P. L. Holland, Chem. Commun.,
2001, 1542.
To briefly examine the scope of the carbodiimide forma-
tion we tested several azides and isocyanides (Table 1).
For example, AdNQCQNCy and TolNQCQNtBu are
formed in 495% yield from AdN3 + CyNC (60 1C, 1 h)
and TolN3
+
tBuNC (25 1C, o2 min) using 5 mol%
LtBuFeNNFeLtBu as a precatalyst. Of particular note is the
especially facile coupling of tBuNC with p-tolyl azide, in which
495% yield of TolNQCQNtBu was formed within minutes
at room temperature, giving a turnover frequency (TOF) of
41500 hꢀ1. Without iron, the background reaction is much
slower, with only a trace (o0.5%) of carbodiimide formed
after 3 d at 80 1C.
In summary, it is possible to generate a three-coordinate
imidoiron(III) complex from adamantyl azide and an iron(I)
precursor. The formation of this metal-bound nitrene enables
rapid, clean nitrene transfer reactions. Importantly, nitrene
transfer to CO and to isocyanides is catalytic, indicating that
the metal–nitrogen bond has an appropriate balance where it
is stable enough to be formed, yet reactive enough for nitrene
19 A. V. Kavaliunas, A. Taylor and R. D. Rieke, Organometallics,
1983, 2, 377.
20 J. B. Sweeney, Chem. Soc. Rev., 2002, 31, 247.
ꢁc
This journal is The Royal Society of Chemistry 2009
1762 | Chem. Commun., 2009, 1760–1762