C O M M U N I C A T I O N S
transient cobalt nitride followed by C-H insertion. It is also possible
that the C-H bond activation event occurs prior to N2 loss from
the azide and avoids nitrido formation.25 We are currently unable
to distinguish between these two possibilities. Intramolecular C-H
bond activation following photolysis of bis(cyclopentadienyl)ura-
nium(IV) azide complexes has recently been postulated to proceed
through a terminal uranium(VI) nitride,26 and Berry and workers
have recently observed aryl C-H bond activation from a putative
terminal Ru nitride.27 If formed, the bis(imino)pyridine cobalt
nitrides, [(ArBPDI)CoN], are likely Co(III) compounds with unpaired
spin density on the nitrogen atom which promotes the C-H bond
activation event, possibly via H-atom abstraction. Such a postulate
is supported by Theopold’s observation of intramolecular C-H
activation by open-shell and likely isoeletronic Co(III) imido
complexes.28,29 In the case of isopropyl-substituted 1, the site of
C-H activation is the weak benzylic C-H bond of the methine
rather than the terminal methyl groups that are known in related
iron compounds to participate in oxidative addition28 and 1,2-
addition chemistry.31
Acknowledgment. We thank the Packard Foundation (Fellow-
ship in Science and Engineering to P. J. C.) and the National Science
Foundation and Deutsche Forschungsgemeinschaft for a Coopera-
tive Activities in Chemistry between U.S. and German Investigators
grant.
Supporting Information Available: Complete experimental pro-
cedures, electronic absorption spectra, and crystallographic data (PDF,
CIF). This material is available free of charge via the Internet at http://
pubs.acs.org.
References
(1) (a) Berry, J. F. Comments Inorg. Chem. 2009, 30, 28. (b) Eikey, R. A.;
Abu-Omar, M. M. Coord. Chem. ReV. 2003, 243, 83.
(2) (a) Seefeldt, L. C.; Hoffman, B. M.; Dean, D. R. Annu. ReV. Biochem.
2009, 78, 701. (b) Dance, I. Chem. Asian J. 2007, 2, 936. (c) Hinnemann,
B.; Norskov, J. K. Top. Catal. 2006, 37, 55.
(3) Ertl, G. Catalytic Ammonia Synthesis; Plenum: New York, 1991.
(4) DuBois, J.; Tomooka, C. S.; Hong, J.; Carriera, E. M. Acc. Chem. Res.
1997, 30, 364.
(5) Groves, J. T.; Takahaski, T. J. Am. Chem. Soc. 1983, 105, 2073.
(6) Schlangen, M. J.; Neugebauer, J.; Reiher, M.; Schroder, D.; Lopez, J. P.;
Haryono, M.; Heinemann, F. W.; Grohmann, A.; Schwarz, H. J. Am. Chem.
Soc. 2008, 130, 4285.
A possible mechanism to account for the formation of 2 is shown
in Figure 3. Following C-H bond activation by the putative cobalt
nitrido, the resulting cyclometalated cobalt amide complex under-
goes ꢀ-hydrogen elimination to form the coordinated imine and a
cobalt hydride. The lability of the metal hydride likely accounts
for the isotopic exchange with the glassware. Hydrogen migration
to the phenylated imine carbon position yields 2.
(7) Meyer, K.; Bill, E.; Mienert, B.; Weyhermu¨ller, T.; Wieghardt, K. J. Am.
Chem. Soc. 1999, 121, 4859.
(8) Grapperhaus, C. A.; Mienert, B.; Bill, E.; Weyhermu¨ller, T.; Wieghardt,
K. Inorg. Chem. 2000, 39, 5306.
(9) Aliaga-Alcade, N.; Debeer George, S.; Mienert, B.; Bill, E.; Wieghardt,
K.; Neese, F. Angew. Chem., Int. Ed. 2005, 44, 2908.
(10) Berry, J. F.; Bill, E.; Bothe, E.; Debeer George, S.; Mienert, B.; Neese, F.;
Wieghardt, K. Science 2006, 312, 1937.
Attempts to trap the cobalt nitrides with hydrogen gas,18 phos-
(11) Petrenko, T. S.; Debeer George, S.; Aliaga-Alcalde, N.; Bill, E.; Meinert,
B.; Xiao, Y.; Guo, Y.; Sturhahn, W.; Cramer, S. O.; Wieghardt, K.; Neese,
F. J. Am. Chem. Soc. 2007, 129, 11053.
18
phines, 1,4-cyclohexadiene, 9,10-dihydroanthracene, or ONMe3
were unsuccessful and yielded only the cyclometalated compounds
1 and 2. Performing the thermolysis of (iPrBPDI)CoN3 in toluene
solution at 100 °C for 4 h in the presence of 4 atm of carbon
monoxide cleanly furnished the bis(imino)pyridine cobalt isocyanate
complex, (iPrBPDI)CoNCO (eq 3). Similarly, (MesBPDI)CoNCO was
obtained following stirring a toluene solution of the azide complex
at 23 °C for 2 h in the presence of 4 atm of CO. Notably, photolysis
of (iPrPDI)CoN3 in the presence of 4 atm of CO cleanly yielded
the cobalt isocyanate complex, (iPrPDI)CoNCO, even though clean
cyclometalation chemistry was not observed in the absence of CO.
Each of the bis(imino)pyridine cobalt isocyanate complexes was
independently synthesized from treatment of the cobalt chloride
compounds with either KOCN or AgOCN.
(12) Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2004, 126, 6252.
(13) Vogel, C.; Heinemann, F. W.; Sutter, J.; Anthon, C.; Meyer, K. Angew.
Chem., Int. Ed. 2008, 47, 2681.
(14) Scepaniak, J. J.; Fulton, M. D.; Bontchev, R. P.; Duesler, E. N.; Kirk, M. L.;
Smith, J. M. J. Am. Chem. Soc. 2008, 130, 10515.
(15) For application of this concept in group 6 metal chemistry see: Sarkar, S.;
Abboud, K. A.; Veige, A. S. J. Am. Chem. Soc. 2008, 130, 16128.
(16) Adhikari, D.; Basuli, F.; Fan, H.; Huffman, J. C.; Pink, M.; Mindiola, D. J.
Inorg. Chem. 2008, 47, 4439.
(17) Walstrom, A.; Pink, M.; Yang, X. F.; Tomaszewski, J.; Baik, M. H.;
Caulton, K. G. J. Am. Chem. Soc. 2005, 127, 5330.
(18) Scho¨ffel, J.; Rogachev, A. Y.; Debeer George, S.; Burger, P. Angew. Chem.,
Int. Ed. 2009, 48, 4734.
(19) Bart, S. C.; Chlopek, K.; Bill, E.; Bouwkamp, M. W.; Lobkovsky, E.; Neese,
F.; Wieghardt, K.; Chirik, P. J. J. Am. Chem. Soc. 2006, 128, 13901.
(20) Knijnenburg, Q.; Gambarotta, S.; Budzelaar, P. H. M. Dalton Trans. 2006,
5442.
(21) Chirik, P. J.; Wieghardt, K. Science 2010, 327, 794.
(22) Knijnenburg, Q.; Hetterscheid, D.; Kooistra, T. M.; Budzelaar, P. H. M.
Eur. J. Inorg. Chem. 2004, 1204.
(23) Kleigrewe, N.; Steffen, W.; Blo¨mker, T.; Kehr, G.; Fro¨hlich, R.; Wibbeling,
B.; Erker, G.; Wasilke, J.-C.; Wu, G.; Bazan, G. C. J. Am. Chem. Soc.
2005, 127, 13955.
(24) Bowman, A. C.; Milsmann, C.; Atienza, C. C. H.; Lobkovsky, E.;
Wieghardt, K.; Chirik, P. J. J. Am. Chem. Soc. 2010, 132, 1676.
(25) For C-H activation from a uranium diazoalkane complex prior to N2 loss,
see: Lam, O. P.; Feng, P. L.; Heinemann, F. W.; O’Connor, J. M.; Meyer,
K. J. Am. Chem. Soc. 2008, 130, 2806.
(26) Thomson, R. K.; Cantat, T.; Scott, B. L.; Morris, D. E.; Batista, E. R.;
Kiplinger, J. L. Nat. Chem. 2010, 2, 723.
(27) Long, A. K. M.; Yu, R. P.; Timmer, G. H.; Berry, J. H. J. Am. Chem. Soc.
2010, 132, 12228–12230.
Although carbonylation of both terminal32,33 and bridging34 metal
nitrides has precedent, it is more likely that the formation of the
bis(imino)pyridine cobalt isocyanate complexes proceeds through
direct insertion of CO into the azide35 rather than nitride carbo-
nylation. Experimental support for this hypothesis is derived from
the significantly lower temperatures (e.g., 23 °C versus 205 °C for
(28) Shay, D. T.; Yap, G. P. A.; Zakharov, L. N.; Rheingold, A. L.; Theopold,
K. H. Angew. Chem., Int. Ed. 2005, 44, 1508.
(29) Thyagarajan, S.; Shay, D. T.; Incarvito, C. D.; Rheingold, A. L.; Theopold,
K. H. J. Am. Chem. Soc. 2003, 125, 4440.
(30) Bart, S. C.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem. Soc. 2004, 126,
13794.
(31) Bart, S. C.; Bowman, A. C.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem.
Soc. 2007, 129, 7212.
(32) Tran, B. L.; Pink, M.; Gao, X.; Park, H.; Mindiola, D. J. J. Am. Chem.
Soc. 2010, 132, 1458.
(33) Silvia, J. S.; Cummins, C. C. J. Am. Chem. Soc. 2009, 131, 446.
(34) Knobloch, D. J.; Lobkovsky, E.; Chirik, P. J. Nat. Chem. 2010, 2, 30.
(35) For synthesis of isocyanate complexes from CO and azide, see: (a) Lorkovic´,
I. M.; Wrighton, M. S.; Davis, W. M. J. Am. Chem. Soc. 1994, 116, 6220.
(b) Graziani, M.; Busetto, L.; Palazzi, A. J. Organomet. Chem. 1971, 26,
261. (c) Werner, H.; Beck, W.; Engelmann, H. Inorg. Chim. Acta 1969, 3,
331. (d) Beck, W.; Smedal, H. S. Angew. Chem., Int. Ed. 1966, 5, 253.
(
MesBPDI)CoN3) needed to promote the carbonylation versus the
intramolecular C-H activation reaction.
In summary, thermolysis and photolysis of bis(imino)pyridine
cobalt azide complexes resulted in intramolecular C-H activation
chemistry to furnish cyclometalated amide complexes. These
products are in stark contrast to the previously reported isolable
bis(imino)pyridine iridium nitride18 and suggest formation of a more
reactive, likely open-shell first-row congener.
JA107288X
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