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Can. J. Chem. Vol. 87, 2009
Table 2. Preparation of Co(II) complexes.
Scheme 2. Synthesis of Co(II) complexes.
10 equiv.) at rt. After 15 h, the solution was concentrated
under reduced pressure. TLC showed that the residue
showed numerous spots. Flash chromatography over silica
gel (25% EtOAc/hexanes) allowed separation of at least six
distinct bands, one of which (Rf = 0.25, 40% EtOAc/hex-
anes) provided material that eventually crystallized. The
crystal for X-ray analysis was grown from a vapor diffusion
1
chamber containing EtOAc, toluene, and hexanes. H NMR
(600 MHz, C6D6) δ: 7.43 (d, J = 7.3 Hz, 4H), 7.24–7.20 (m,
8H), 7.15–7.08 (m, 8H), 7.00 (d, J = 7.1 Hz, 4H), 6.88–6.81
(m, 10H), 6.75 (t, J = 7.50, 4H), 6.53 (s, 2H), 6.34 (s, 2H),
6.26 (t, J = 7.3 Hz, 2H), 5.58 (d, J = 14.5 Hz, 2H), 5.29 (d,
J = 15.4 Hz, 2H), 5.20 (d, J = 14.1 Hz, 2H), 4.28 (d, J =
16.8 Hz, 2H), 3.44–3.38 (m, 6H), 3.02 (d, J = 16.5 Hz, 2H),
1.26 (s, 18H), 1.01 (s, 18H), –3.39 (s, 1H), –3.72 (s, 1H).
59Co NMR (144 MHz, C6D6) δ: 13364 (brs). Combustion
calcd.: C 67.28, H 6.31, N 3.62; found: C 68.03, H 6.36, N
3.62.
Note: The compounds shown are representative of the metal to ligand
stoichiometry only, and are not meant to imply structure.
aUnoptimized yields of complexation.
bPoor solubility.
Results and discussion
This modified procedure proved effective for the prepara-
tion of a variety of 2,4-dioxo amide complexes and these
results are summarized in Table 2. Replacement of the
morpholine with piperidine (3b), diethylamine (3c), or
dibenzyl amine (3d) gave complexes as microcrystalline
pink powders unsuitable for single crystal X-ray analysis. Of
these, the dibenzyl amide 3d displayed the most promising
crystalline character, and in entries 5–7 of Table 2 the
dibenzyl amide portion of the ligand was conserved while
substitutions were made in place of the tert-butyl group. The
methyl (4), isopropyl (5), and phenyl (6) analogs of 3d were
each prepared successfully, but they too failed to give crys-
tals suitable for X-ray analysis.
Cobalt(II) structures
Our initial efforts to employ the Mukaiyama oxidation in
synthesis were complicated by fickle oxidation results as a
consequence of inconsistent purity of the Co(II) complex.
The first reports on Co(II) 2,4-dioxo-alkanoic acid amide
complexes utilized CoCl2 under aqueous alkaline conditions,
but we found that such conditions caused decomposition of
the morpholine amide 2a (Scheme 2). The result was that
the preparation of catalyst 3a under the aqueous conditions
provided a highly contaminated amorphous brown solid and
attempts at purification proved fruitless. However, these dif-
ficulties were overcome by complexation under neutral con-
ditions in organic solvent. When a solution of the free ligand
2a in benzene was treated with 0.5 equiv. of Co(II)(2-ethyl
hexanoate)2, the initial dark blue color quickly dissipated
and the resulting red solution was treated with hexane to
precipitate the complex 3a.
A more substantial change was made by installing a
methyl group at C(3) and, gratifyingly, the complex 7 was
obtained as red crystals and the unusual X-ray structure of 7
is shown in Fig. 1.5 Selected bond lengths and angles are re-
ported in Table 3. There are three cobalt atoms present in the
5 Supplementary data for this article are available on the journal Web site (canjchem.nrc.ca) or may be purchased from the Depository of Un-
published Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 3859. For more in-
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ing.html (Or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033; or de-
posit@ccdc.cam.ac.uk).
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