C O M M U N I C A T I O N S
days in toluene solution at 100 °C with only modest decomposition.
Moreover, the parent ion (M + H ) 850) can be observed by
electrospray MS. We also prepared an 15N-labeled phenyl complex,
[PhBP3]Co(15NPh) (5a), and its nonlabeled derivative, 5b, by an
analogous route. Difference IR spectra for 5a and 5b revealed a
band associated with coupled modes of the Co-NPh and the CoN-
References
(1) (a) Groves, J. T.; Takahashi, T. J. Am. Chem. Soc. 1983, 105, 2073. (b)
LaPointe, R. E.; Wolczanski, P. T.; Mitchell, J. F. J. Am. Chem. Soc.
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Ph linkages at 1340 cm-1. We have been unable to resolve the 15
NMR signal for 5a.
N
The solid-state structure of 4, its thermal stability, and its modest
reactivity (vide infra) are consistent with formulating the Co-N
interaction as a strong triple bond. This is plausible in view of
simple symmetry considerations and isolobal concepts.10 A preli-
mary DFT study on the geometry-optimized electronic structure
of 4 corroborated this suggestion and provided an orbital splitting
diagram consistent with the qualitative frontier orbital diagram
sketched in Figure 1c.11 The DFT study suggested the orbital of
2
predominantly dz parentage actually lies lower in energy than the
xy and x2 - y2 orbitals of the filled lower set. Two empty orbitals
of xz and yz parentage, strongly destabilized by a pair of orthogonal
π-bonds from the imido ligand, lie at higher energy.12,13
In a related reaction, we canvassed the ability of 3 to intercept
a diphenylcarbene unit from Ph2CN2. Rather than undergoing
carbene transfer and concomitant expulsion of N2, we found that 2
equiv of Ph2CN2 reacted with 3 to generate the phosphazine
Me3P(N2CPh2) and the thermally stable diazoalkane adduct com-
plex, [PhBP3]Co(N2CPh2) (6). Terminal diazoalkane adducts of
group 9 metals are very rare;14a,b the single cobalt diazoalkane
derivative previously reported exhibits side-on η2-coordination.14c
The X-ray structure of diamagnetic 6 was therefore of interest
(Figure 2b).15 Most prominent is that complex 6 features an η1-
ligated diazoalkane ligand.16 The Co-N bond length (1.667(2) Å)
is nearly as short as the Co-N distance observed in 4. This again
suggests strong multiple bond character at the Co-N linkage in 6
and perhaps explains the reluctance of this system to expel N2 under
mild conditions. The relatively short N1-N2 bond distance of
1.280(2) Å indicates there is still multiple bond character between
these two atoms. The two resonance contributors shown in Scheme
1 for 6 are emphasized.17
A cursory survey of the reactivity of 4 indicates that it is fairly
resistant to nitrene transfer chemistry. We did find that the imido
functionality can be transferred to carbon monoxide to produce the
isocyanate (OdCdN-p-tolyl), albeit sluggishly (14 equiv of CO,
70 °C, 12 days).18 The isolated cobalt(I) byproduct (90%) was the
diamagnetic dicarbonyl species [PhBP3]Co(CO)2 (7) (ν(CO) )
2008, 1932; KBr/THF).
The successive transformations 3 f 4 and 4 f 7 comprise a
system in which (i) a late first-row complex acts as an acceptor in
a high yielding, oxidative, two-electron-group-transfer process (3
f 4). The resulting species can then (ii) undergo a reductive two-
electron group-transfer process to deliver the accepted group to a
substrate (4 f 7). The method by which 4 is prepared suggests
that direct, two-electron group-transfer processes to cobalt, and
perhaps other later first-row metals, are possible. Maintaining
approximate 3-fold symmetry is a promising design strategy for
further developments in this area of synthesis.
(6) Hay-Motherwell, R. S.; Wilkinson, G.; Hussain-Bates, B.; Hursthouse,
M. B. Polyhedron 1993, 12, 2009.
(7) (a) Shapiro, I. R.; Jenkins, D. M.; Thomas, J. C.; Day, M. W.; Peters, J.
C. Chem. Commun. 2001, 2152. (b) Jenkins, D. M.; Di Bilio, A. J.; Allen,
M. J.; Betley, T.; Peters, J. C. 2002, submitted.
(8) [PhBP3] refers to anionic tridentate ligand [PhB(CH2PPh2)3]: (a) Peters,
J. C.; Feldman, J. D.; Tilley, T. D. J. Am. Chem. Soc. 1999, 121, 9871.
(b) Barney, A. A.; Heyduk, A. F.; Nocera, D. G. Chem. Commun. 1999,
2379.
(9) 4‚C6H6 (C55H51BCoNP3), MW ) 888.62, red plate, collection temperature
) 96(2) K, monoclinic, space group P21/c, a ) 14.1174(11) Å, b )
14.3252(11) Å, c ) 22.3306(18) Å, R ) 90°, â ) 96.202(1)°, γ ) 90°,
V ) 4489.6(6) Å3, Z ) 4, R1 ) 0.0415 [I > 2σ(I)], GOF ) 1.670.
(10) (a) Albright, T. A.; Burdett, J. K.; Whangbo, M. H. Orbital Interactions
in Chemistry; John Wiley and Sons: New York, 1985; Chapter 20. (b)
See also: Glueck, D. S.; Green, J. C.; Michelman, R. I.; Wright, I. N.
Organometallics 1992, 11, 4221.
(11) These studies will be elaborated in a forthcoming full paper. Briefly, a
geometry optimization was carried out with the program JAGUAR
(B3LYP/LACVP**) using the complete crystal coordinates of complex
4. Convergence was achieved, and the theoretical structure obtained for
4 was in fair agreement with that determined experimentally (Figure 2a).
(12) To correlate the frontier orbitals of [PhBP3]Co-Y fragments (Y ) PMe3,
I, or NR) to those of an octahedron, a redefinition of axes is required.
Using a notation in which the z-axis of an octahedral ML6 molecule
proceeds through the center of one triangular face of an octahedron, the
orbital parentages transform to the following: t2g set, z2; {(2/3)1/2(x2 - y2)
- (1/3)1/2yz}; {(2/3)1/2xy - (1/3)1/2xz}; eg set, {(1/3)1/2x2 - y2 + (2/3)1/2yz};
{(1/2)1/2xy + (2/3)1/2xz}. Under this notation, the ground-state electronic
configuration predicted for complex 4 is (z2)2 ({(2/3)1/2(x2 - y2) -
(1/3)1/2yz})2 ({(2/3)1/2xy - (1/3)1/2xz})2 ({(1/3)1/2x2 - y2 + (2/3)1/2yz})0
({(1/2)1/2xy + (2/3)1/2xz})0.
(13) Orgel, L. E. An Introduction to Transition-Metal Chemistry; Wiley: New
York, 1960; p 174.
(14) (a) Schramm, K. D.; Ibers, J. A. J. Am. Chem. Soc. 1978, 100, 2932. (b)
Werner, H.; Schneider, M. E.; Bosch, M.; Wolf, J.; Teuben, J. H.;
Meetsma, A.; Troyanov, S. I. Chem.-Eur. J. 2000, 6, 3052. (c) Klein, H.
F.; Ellrich, K.; Hammerschmitt, B.; Koch, U.; Cordier, G. Z. Naturforsch.,
B: Chem. Sci. 1990, 45, 1291.
(15) 6 (C58H51BCoN2P3), MW ) 938.66, red plate, collection temperature )
98(2) K, monoclinic, space group P21/n, a ) 13.1284(8) Å, b )
16.5975(11) Å, c ) 21.8205(14) Å, R ) 90°, â ) 97.168(1)°, γ ) 90°,
V ) 4717.5(5) Å3, Z ) 4, R1 ) 0.0466 [I > 2σ(I)], GOF ) 1.572.
(16) An η1-hydrazido Co complex has been prepared: Korner, V.; Huttner,
G.; Vogel, S.; Barth, A.; Zsolnai, L. Chem. Ber. Recl. 1997, 130, 489.
(17) Hillhouse, G. L.; Haymore, B. L. J. Am. Chem. Soc. 1982, 104, 1537.
(18) Free isocyanate was observed (30% by 1H NMR integration; GC/MS,
133 m/z). An additional product(s) was also observed by 1H NMR (∼45%),
which presumably arises from thermal isocyanate degradation during the
course of the reaction.
Acknowledgment. We thank the NSF (CHE-0132216), the ACS
PRF, and the Dreyfus Foundation for financial support. D.M.J. is
grateful for an NSF predoctoral fellowship. The authors acknowl-
edge J. Christopher Thomas for assistance with preliminary DFT
calculations and Dr. Daniel Mindiola for insightful discussions.
Supporting Information Available: Experimental procedures
(PDF), characterization data, and crystallographic information (CIF).
This material is available free of charge via the Internet at http://
pubs.acs.org.
JA026852B
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J. AM. CHEM. SOC. VOL. 124, NO. 38, 2002 11239