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Article
Bonding and Structure of Copper Nitrenes
Thomas R. Cundari,*t Adriana Dinescu,t and Abul B. Kazit,*
Center for Advanced Scientific Computing and Modeling (CASCaM), Department of Chemistry,
University of North Texas, Box 305070, Denton, Texas 76203-5070, and Department of Chemistry
and Physics, University of Arkansas at Pine Bluff Pine Bluff, Arkansas 71601
Received July 17, 2008
Copper nitrenes are of interest as intermediates in the catalytic aziridination of olefins and the amination of C-H
bonds. However, despite advances in the isolation and study of late-transition-metal multiply bonded complexes,
a bona fide structurally characterized example of a terminal copper nitrene has, to our knowledge, not been reported.
In anticipation of such a report, terminal copper nitrenes are studied from a computational perspective. The nitrene
complexes studied here are of the form (P-diketiminate)Cu(NPh). Density functional theory (DFT), complete active
space self-consistent-field (CASSCF) electronic structure techniques, and hybrid quantum mechanical/molecular
mechanical (QM/MM) methods are employed to study such species. While DFT methods indicate that a triplet
(S = 1) is the ground state, CASSCF calculations indicate that a singlet (S = 0) is the ground state, with only a
small energy gap between the singlet and triplet. Moreover, the ground-state (open-shell) singlet copper nitrene is
found to be highly multiconfigurational (i.e., biradical) and to possess a bent geometry about the nitrene nitrogen,
contrasting with the linear nitrene geometry of the triplet copper nitrenes. CASSCF calculations also reveal the
existence of a closed-shell singlet state with some degree of multiple bonding character for the copper-nitrene
bond.Introduction
Copper catalysts are widely used for nitrene (NR, where
R is most often a hydrocarbyl or functionalized hydrocarbyl
group) transfer, most notably the aziridination of unsaturated
organic substrates such as olefins.' For example, Jacobsen
and co-workers have suggested that aziridination by copper
diimine catalysts involves a copper nitrene intermediate.2
Brandt et al. clarified the mechanism of the copper-catalyzed
aziridination of alkenes through a combination of density
functional theory (DFT) calculations and kinetics experi-
ments.3 In related chemistry, Perez and co-workers have
studied the mechanism of alkene aziridination and C-H bond
amination by copper scorpionate catalysts.4 While aziridi-
* To whom correspondence should be addressed. E-mail: tomc@unt.edu.
University of North Texas.
* University of Arkansas at Pine Bluff.
(1) (a) Muller, P.; Fruit, C. Chem. Rev. 2003, 103, 2905. (b) Vedernikov,
A. N.; Caulton, K. G. Chem. Commun. 2004, 2, 162. (c) Halfen, J. A.
Curr. Org. Chem. 2005, 9, 657.
(2) Li, Z.; Quan, R. W.; Jacobsen, E. N. J. Am. Chem. Soc. 1995, 117,
5889.
(3) Brandt, P.; Soldergren, M. J.; Andersson, P. G.; Norrby, P. O. J. Am.
Chem. Soc. 2000, 122, 8013.
(4) Fructos, M. R.; Trofimenko, S.; Diaz-Requejo, M. M.; Perez, P. J.
J. Am. Chem. Soc. 2006, 128, 11784.
10.1021/ic801337f CCC: $40.75 2008 American Chemical Society
Published on Web 10/04/2008nation has been widely studied from an experimental point
of view, another attractive target is nitrene transfer to CO to
yield isocyanates, which are widely used as intermediates
for the production of polymers.5 Several researchers have
demonstrated the feasibility of aryl isocyanate (ArNCO)
synthesis by the reaction of CO with structurally character-
ized arylimido/nitrene complexes of late transition metals.
For example, Mindiola and Hillhouse have reacted a bis-
(phosphine)nickel nitrene with CO to form ArNCO.6 Bart
et al.7 and Peters et al.8 have reported nitrene group transfer
from structurally characterized late-transition-metal nitrene
complexes (iron and cobalt, respectively) to CO to yield
ArNCO. There is considerable interest in phosgene-free
processes for the production of isocyanates from nitroaro-
matics (nitrenes are proposed as intermediates) using late-
transition-metal catalysts.5'9 For example, Moiseev et al.
(5) Tafesh, A. M.; Weiguny, J. Chem. Rev. 1996, 96, 2035.
(6) Mindiola, D. J.; Hillhouse, G. L. Chem. Commun. 2002, 1840.
(7) Bart, S. C.; Lobkovsky, E.; Bill, E.; Chirik, P. J. J. Am. Chem. Soc.
2006, 128, 5302.
(8) (a) Iron: Brown, S. D.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc.
2003, 125, 322-323. (b) Cobalt: Jenkins, D. M.; Betley, T. A.; Peters,
J. C. J. Am. Chem. Soc. 2002, 124, 11238-11239.
(9) Paul, P. Coord. Chem. Rev. 2000, 203, 269.
Inorganic Chemistry, Vol. 47, No. 21, 2008 10067
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Cundari, Thomas R., 1964- & Dinescu, Adriana. Bonding and Structure of Copper Nitrenes, article, October 4, 2008; [Washington, D.C.]. (https://digital.library.unt.edu/ark:/67531/metadc77132/m1/1/: accessed April 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Arts and Sciences.