Reaction with 1,1-DCE also produced a clean, crystalline,
yellow product, (dmgH) (py)Co(CClNCH ) (3) in 48% yield.
The H NMR spectrum contains vinyl resonances with a small
geminal coupling constant (C , d 5.61, 5.95, J = 2.1 Hz).
The synthetic strategy for preparation of complexes 1–3
follows previous work in which nucleophilic Co( ) was used to
In the present case,
The authors thank Neil R. Brooks and Victor G. Young, Jr.
(Minnesota X-ray Crystallographic Laboratory), as well as
Carrie Buss for collection and analysis of the X-ray diffraction
data. Acknowledgment is made to the Donors of The Petroleum
Research Fund, administered by the American Chemical
Society for partial support of this research. The authors also
acknowledge support from the University of Minnesota.
2
2
1
6 6
D
I
prepare vinylcobalt complexes.2
substitution of cobalt for chlorine was accomplished. It is
4,27–30
notable that the stereochemical fidelity that has generally been
Notes and references
observed2
8–30
was also maintained in the preparation of 2 from
‡
Crystal data: C15
5 4
H21ClCoN O , M = 429.75, orthorhombic, a =
trans-DCE, and that cis-DCE did not react to give a chlorovinyl
complex under the same conditions.
3
9
.630(2), b = 12.377(2), c = 15.402(3) Å, U = 1835.8(6) Å , T = 173(2)
21
1 1 1 a
K, space group P2 2 2 (no. 19), Z = 4, m(Mo-K ) = 1.112 mm , 9319
Complexes 1–3 were subjected to acidic conditions to assess
whether protonolysis is a favorable pathway for the cleavage of
the Co–C bond. In separate protonolysis experiments the
reflections measured, 3259 unique (Rint = 0.037) which were used in all
2
calculations. The final wR(F ) was 0.0935. C2 of the vinyl ligand was
disordered over 2 sites, which were refined with 55+45 occupancy.CCDC
chlorovinyl complexes were dissolved in C
6 6
D with benzoic
1
72183. See http://www.rsc.org/suppdata/cc/b1/b109001a/ for crystallo-
acid, HCl and H SO . These solutions were placed into sealed
2
4
graphic files in .cif or other electronic format.
NMR tubes and heated incrementally to 135 °C. The reaction
progress was monitored by NMR spectroscopy. None of the
acids were observed to react with complexes 1–3 to produce a
free chlorinated ethylene or any other identifiable product.
Hydrogenolysis experiments were performed by exposing
1 P. J. Squillace, M. J. Moran, W. W. Lapham, C. V. Price, R. M. Clawges
and J. S. Zogorski, Environ. Sci. Technol., 1999, 33, 4176.
J. J. Westrick, J. W. Mello and R. F. Thomas, J. Am. Water Works
Assoc., 1984, 76, 52.
2
3
4
C. A. Schanke and L. P. Wackett, Environ. Sci. Technol., 1992, 26,
6 6 2
solutions of 1–3 dissolved in C D to relatively low H
8
30.
pressures ( ~ 200 mbar) in sealed NMR tubes and heating
incrementally to 135 °C. NMR spectroscopy was used to
monitor the reaction progress and identify the products. Only
C. Holliger, G. Schraa, E. Stupperich, A. J. M. Stams and A. J. B.
Zehnder, J. Bacteriol., 1992, 174, 4427.
5 C. J. Gantzer and L. P. Wackett, Environ. Sci. Technol., 1991, 25,
715.
6 U. E. Krone, K. Laufer, R. K. Thauer and H. P. C. Hogenkamp,
Biochemistry, 1989, 28, 10061.
the cis-dichlorovinyl complex, 1, reacted with H
2
after
prolonged heating at 135 °C to produce a small amount of free
cis-DCE (2% conversion after 2 d).
7
8
9
G. Glod, W. Angst, C. Holliger and R. P. Schwarzenbach, Environ. Sci.
Technol., 1997, 31, 253.
G. Glod, U. Brodmann, W. Angst, C. Holliger and R. P. Schwarzenbach,
Environ. Sci. Technol., 1997, 31, 3154.
The reactivity of 1 toward reducing agents was also
examined. Treatment of THF solutions of 1 with sodium
naphthalenide or sodium anthracenide at rt resulted in im-
mediate reaction. The volatile materials were transferred from
the reaction mixtures under vacuum and were analyzed by GC-
MS. It was found that chloroacetylene was the major volatile
product in both cases [eqn. (1)].
S. Lesage, S. Brown and K. Millar, Environ. Sci. Technol., 1998, 32,
2
264.
10 M. Semadeni, P.-C. Chiu and M. Reinhard, Environ. Sci. Technol.,
1998, 32, 1207.
1 J. K. Gotpagar, E. A. Grulke and D. Bhattacharyya, J. Hazard. Mater.,
1
1
1
1
1
998, 62, 243.
2 A. M. A. Aisa, F. W. Heinemann and D. Steinborn, Z. Anorg. Allg.
Chem., 1996, 622, 1946.
3 P. G. Jones, L. Yang and D. Steinborn, Acta Crystallogr., Sect. C: Cryst.
Struct. Commun., 1996, C52, 2399.
4 X. L. R. Fontaine, S. J. Higgins, B. L. Shaw, M. Thornton-Pett and W.
Yichang, J. Chem. Soc., Dalton Trans., 1987, 1501.
(
1)
Treatment of a THF solution of 1 with NaBH
4
also resulted
in reduction of the complex and the formation of volatile
products. After transferring the volatile materials from the
reaction mixture under vacuum, GC-MS analysis showed that
both chloroacetylene and vinyl chloride were recovered in a 1+1
ratio. Relevant to the wide use of Ti(III)citrate as a bulk electron
15 J. M. Coronas, G. Muller, M. Rocamora, C. Miravitlles and X. Solans,
J. Chem. Soc., Dalton Trans., 1985, 2333.
16 M. Wada, K. Nishiwaki and M. Kumazoe, J. Chem. Soc., Chem.
Commun., 1984, 980.
1
7 M. Wada and M. Kumazoe, J. Organomet. Chem., 1983, 259, 245.
1
8 M. Wada and K. Nishiwaki, J. Chem. Soc., Dalton Trans., 1983,
donor in the study of B12-catalyzed dechlorination reac-
1
841.
tions,4
,6–10
the reaction of 1 with Ti(III)citrate was also
1
2
9 B. F. G. Johnson, J. Lewis, J. D. Jones and K. A. Taylor, J. Chem. Soc.,
Dalton Trans., 1974, 34.
0 M. J. Hacker, G. W. Littlecott and R. D. W. Kemmitt, J. Organometal.
Chem., 1973, 47, 189.
investigated. The reduction performed in MeOH gave cis-DCE
as the major volatile product, while no chloroacetylene or vinyl
chloride was observed.
If (chlorovinyl)cobalt complexes are indeed intermediates in
the dechlorination of chlorinated ethylenes by B12, the reactivity
studies with models 1–3 indicate that protonolysis and hydro-
genolysis mechanisms are not likely candidates for their
decomposition. Instead, reduction appears to be a much more
favorable pathway for the cleavage of the Co–C bond to yield
dechlorinated products. Reduction of 1 by the radical anions of
naphthalene and anthracene (2.26 and 1.76 V vs. NHE,
respectively)31 in THF yields chloroacetylene as the major
volatile product. This is a potentially important result in light of
21 J. Lewis, B. F. G. Johnson, K. A. Taylor and J. D. Jones, J. Organomet.
Chem., 1971, 32, C62.
2
2
2 M. D. Johnson and B. S. Meeks, J. Chem. Soc. B, 1971, 185.
3 J. Shey and W. A. van der Donk, J. Am. Chem. Soc., 2000, 122,
1
2403.
2
4 K. A. Pickin and M. E. Welker, Organometallics, 2000, 19, 3455.
2
5 W. A. Arnold and A. L. Roberts, Environ. Sci. Technol., 1998, 32,
3
017.
2
6 A. L. Roberts, L. A. Totten, W. A. Arnold, D. R. Burris and T. J.
Campbell, Environ. Sci. Technol., 1996, 30, 2654.
27 P. J. Stang and A. K. Datta, J. Am. Chem. Soc., 1989, 111, 1358.
28 D. Dodd, M. D. Johnson, B. S. Meeks, D. M. Titchmarsh, K. N. V.
Duong and A. Gaudemer, J. Chem. Soc., Perkin Trans. 2, 1976,
the results of Burris et al.32 and Semadeni et al.10 that indicate
that the acetylene produced in the dechlorination of trichloro-
ethylene is derived from chloroacetylene. The results of this
study suggest that a (cis-dichlorovinyl)cobalamin complex may
be the direct precursor to chloroacetylene. The different product
1
261.
2
3
9 M. D. Johnson and B. S. Meeks, J. Chem. Soc. D, 1970, 1027.
0 K. N. V. Duong and A. Gaudemer, J. Organomet. Chem., 1970, 22,
4
73.
4
distributions obtained from NaBH and Ti(III)citrate indicate
3
1 L. Eberson, Electron Transfer Reactions in Organic Chemistry,
that the products generated are likely sensitive to the nature of
the reducing agent and possibly the solvent. A systematic
investigation of these effects is underway.
Springer-Verlag, 1987.
32 D. R. Burris, C. A. Delcomyn, B. Deng, L. E. Buck and K. Hatfield,
Environ. Toxicol. Chem., 1998, 17, 1681.
CHEM. COMMUN., 2002, 234–235
235