Synthesis, structure, and unusual reactivity of β-halovinyl cobalt porphyrin complexes

Article abstract of DOI:10.1021/ic0518834

The preparation, structures, and reactivity of tetraphenylporphyrin (TPP) cobalt halovinyl complexes are reported. β-Halovinyl complexes of (TPP)Co(E-CHCHX) (X = Br and I) were prepared from the insertion of acetylene into the cobalt halide bonds of the corresponding halide complexes. The reactivity of these compounds and of the previously reported (TPP)Co(E-CHCHCl), was studied in depth, and it was found that complex reactivity increased with the leaving group ability of the halide. A trans-dichlorovinyl cobalt porphyrin complex, (TPP)Co(Z-CClCHCl), was also prepared through the reaction of (TPP)CoNa and TCE. The structures of (TPP)Co(E-CHCHBr), (TPP)-Co(Z-CClCHCl), and (TPP)Co(C₂H) are reported. The C-C bond length of the vinyl group was found to vary for the β-halovinyl complexes (TPP)Co(E-CHCHX) from 1.211 A for X = Br to 1.234 A for X = Cl and 1.320 A for (TPP)Co(Z-CClCHCl). A comparison of these structures to many chlorovinyl cobalt complexes shows that trans2-halo substitution results in a dramatically decreased vinyl C-C bond length. The mechanism of halide substitution for the β-halovinyl complexes was investigated with kinetic experiments that indicated a dissociative mechanism and supported the intermediacy of a cobalt acetylene complex.

Full text of DOI:10.1021/ic0518834

Inorg. Chem. 2006, 45, 2288−2295
Synthesis, Structure, and Unusual Reactivity of
Porphyrin Complexes
â-Halovinyl Cobalt
Joseph M. Fritsch, Noah D. Retka, and Kristopher McNeill*
Department of Chemistry, UniVersity of Minnesota, 225 Pleasant Street SE,
Minneapolis, Minnesota 55455
Received October 31, 2005
The preparation, structures, and reactivity of tetraphenylporphyrin (TPP) cobalt halovinyl complexes are reported.
-Halovinyl complexes of (TPP)Co(E-CHCHX) (X Br and I) were prepared from the insertion of acetylene into
â
)
the cobalt halide bonds of the corresponding halide complexes. The reactivity of these compounds and of the
previously reported (TPP)Co(E-CHCHCl), was studied in depth, and it was found that complex reactivity increased
with the leaving group ability of the halide. A trans-dichlorovinyl cobalt porphyrin complex, (TPP)Co(Z-CClCHCl),
was also prepared through the reaction of (TPP)CoNa and TCE. The structures of (TPP)Co(E-CHCHBr), (TPP)-
Co(Z-CClCHCl), and (TPP)Co(C2H) are reported. The C
the -halovinyl complexes (TPP)Co(E-CHCHX) from 1.211 Å for X
(TPP)Co(Z-CClCHCl). A comparison of these structures to many chlorovinyl cobalt complexes shows that trans-
2-halo substitution results in a dramatically decreased vinyl C C bond length. The mechanism of halide substitution
for the -halovinyl complexes was investigated with kinetic experiments that indicated a dissociative mechanism
and supported the intermediacy of a cobalt acetylene complex.
−C bond length of the vinyl group was found to vary for
â
)
Br to 1.234 Å for X Cl and 1.320 Å for
)
−
â
Introduction
apparent involvement of Co-C-bonded intermediates, par-
ticularly chlorovinyl complexes4-6,14-20 and, potentially,
chloroethyl complexes.6,21
Chlorovinyl organometallic cobalt complexes have been
synthesized in the native cobalamin and cobalamin model
systems.12,13,18,22-24 Many other cobalt vinyl compounds have
also been prepared with various substituents.25-30 Because
Chlorinated ethylenes are widespread groundwater con-
taminants listed on the US EPA’s priority pollutant list
because of their environmental presence and their adverse
toxicological profile.1-3 There has been much recent interest
in the catalytic reductive dehalogenation of these compounds
by cobalt catalysts, such as cyanocobalamin and tetrakis(4-
carboxyphenyl) porphyrin cobalt, (TCPP)Co).4-14 One of the
key distinguishing features of these catalyst systems is the
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* To whom correspondence should be addressed. Email: mcneill@
chem.umn.edu.
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2288 Inorganic Chemistry, Vol. 45, No. 5, 2006
10.1021/ic0518834 CCC: $33.50
© 2006 American Chemical Society
Published on Web 01/28/2006

â-HaloWinyl Cobalt Porphyrin Complexes
0.34 mmol) and Na35Cl (100 mg, 1.72 mmol) in methanol; the
resulting solid was 26 wt % 35Cl.
General Methods. H and 13C NMR spectra were collected at
300 and 75 MHz, respectively, on a Varian Inova Instrument. ESI-
TOF mass spectra were collected on a Bruker BioTOF II instrument.
UV-vis absorbance spectra were collected with a Jasco V530
spectrophotometer (300-700 nm) with a 4 mL septum-sealed quartz
cuvette. GC-MS data were collected with an Agilent 6890 GC
(column Phenomenex ZB-624, 60 m × 0.32 mm i.d., 1.8 µm film
thickness) and an Agilent 5973 Mass Selective detector.
of our studies of (TCPP)Co, we have had a continuing
interest in porphyrin cobalt chlorovinyl complexes including
one that has been previously reported.14,31 While the chem-
istry of halovinyl complexes of cobalt has only begun to be
explored in the past decade, halovinyl complexes of other
metals have been well studied. There appear to be numerous
differences between halovinyl complexes of cobalt and other
metal centers such as nickel, palladium, and platinum. For
example, trichlorovinylmetal complexes are readily prepared
for Group 10 metals, but they have remained elusive with
cobalt.32-38
In this study, we further explore the chemistry of halovinyl
cobalt complexes through the preparation of a series of
complexes, an examination of their structures, and an
investigation into the unusual lability of trans-â-halovinyl
cobalt porphyrin complexes.
1
X-ray Structure Analysis. Diffraction data were collected using
crystals mounted on thin glass capillaries with oil on a Siemens
SMART Platform CCD diffractometer with Mo KR radiation
(graphite monochromator) at 173(2) K. The structures were solved
using direct and Patterson methods using SHELXS-97 and were
refined using SHELXL-97.39 Crystallographic data for (TPP)Co-
(E-CHCHBr), (TPP)Co(Z-CClCHCl), and (TPP)Co(C2H) are given
in Table 1. Additional crystallographic data including tables of bond
lengths and angles are presented in the Supporting Information.
(trans-2-Bromovinyl)(tetraphenylporphyrin) Cobalt(III),
(TPP)Co(E-CHCHBr), 1. The methods from Sakurai and Setsune
were adapted for the preparation of compound 1.14,31,40 (TPP)CoBr
was prepared by two methods. Method A. (TPP)CoBr was prepared
through reaction of (TPP)Co (300 mg, 0.45 mmol) with HBr (47-
49 wt %, 4 mL, 24 mmol) in methanol (300 mL) with 4 days of
stirring at room temperature. The solution was vacuum filtered,
and the solvent was removed from the filtrate in vacuo to near
dryness. The (TPP)CoBr solid was isolated with vacuum filtration
and washed with 2:1 H2O/MeOH. (TPP)CoBr was isolated in a
49% yield. Method B. (TPP)CoBr was also prepared from (TPP)-
CoCl through halide exchange; lithium bromide (10 equiv) was
added to (TPP)CoCl in THF, and then the mixture was washed
with H2O, and extracted into CHCl3. The combined extracts were
washed with H2O and dried over MgSO4. (TPP)CoBr was isolated
in a 95% yield.
Experimental Section
Materials. Trichloroethylene (TCE), tetraphenylporphyrin cobalt-
(II) ((TPP)Co), tetrabutylammonium fluoride hydrate (TBAF),
tetrabutylammonium bromide (TBABr), tetrabutylammonium iodide
n
(TBAI), hydrobromic acid (47-49 wt %), BuLi in hexanes (1.0
M), 1,1-dichloroethylene, vinyl chloride, 4-(dimethylamino)pyridine
(DMAP), 4-cyanopyridine (4-CN-py), sodium chloride (Na35Cl,
99%), lithium bromide, potassium hexamethyldisilazide (KHMDS),
aluminum trichloride, and benzophenone were purchased from
Aldrich. Tetrabutylammonium hexafluorophosphate (TBAPF6) and
tetrabutylammonium chloride (TBACl) were purchased from Fluka.
Hydroiodic acid (57 wt %) was purchased from J. T. Baker.
Acetylene was purchased from Minneapolis Oxygen Company
(Minneapolis, MN). Both cis-dichloroethylene (cDCE) and trans-
dichloroethylene (tDCE) and were purchased from TCI America.
Deuterated acetylene (C2D2) was purchased from Cambridge Isotope
Laboratories. Sodium benzophenone ketyl was prepared via the
addition of 0.9 equiv of sodium metal to benzophenone in THF.
Sodium mercury amalgam was prepared by dissolving up to 0.5%
sodium in mercury. tert-Butoxide (tBuOK) was prepared by reaction
of excess neat tert-butyl alcohol (tBuOH) with KH under an inert
atmosphere. TBA35Cl was prepared by mixing TBAPF6 (132 mg,
(TPP)Co(E-CHCHBr) was prepared from the reaction of (TPP)-
CoBr (100 mg, 0.14 mmol) and C2H2 (200 mL, 1 atm, 8 mmol) in
CH2Cl2 (30 mL) in a sealed tube with stirring for 4 days. The
solvent was removed in vacuo. Purification was performed by
column chromatography (SiO2, 60:40 hexane/CHCl3), and the yield
was 60%. X-ray quality crystals were obtained by slow cooling of
a saturated solution (4:1 hexane/CH2Cl2) to -35 °C. UV-vis (CH2-
(23) Rich, A. E.; DeGreeff, A. D.; McNeill, K. Chem. Comm. 2002, 234-
235.
(24) Jones, P. G.; Yang, L.; Steinborn, D. Acta Crystallogr. 1996, C52,
2399-2402.
(25) Meeks, B. S.; Johnson, M. D. J. Chem. Soc. B 1971, 185-189.
(26) Johnson, M. D.; Meeks, B. S. J. Chem. Soc. D 1970, 1027-1028.
(27) Stang, P. J.; Datta, A. K. J. Am. Chem. Soc. 1989, 111, 1358-1363.
(28) Pickin, K. A.; Welker, M. E. Organometallics 2000, 19, 3455-3458.
(29) Dodd, D.; Johnson, M. D.; Meeks, B. S.; Titchmarsh, D. M.; Nguyen
Van Duong, K.; Gaudemer, A. J. Chem. Soc., Perkin Trans. 2 1976,
1261-1267.
(30) Nguyen Van Duong, K.; Gaudemer, A. J. Organomet. Chem. 1970,
22, 473-481.
(31) Setsune, J.; Saito, Y.; Ishimaru, Y.; Ikeda, M.; Kitao, T. Bull. Chem.
Soc. Jpn. 1992, 65, 639-648.
(32) Coronas, J. M.; Muller, G.; Rocamora, M.; Miravitlles, C.; Solans,
X. J. Chem. Soc., Dalton Trans. 1985, 2333-2341.
(33) Fontaine, X. L. R.; Higgins, S. J.; Shaw, B. L.; Thornton-Pett, M.;
Su, Y. J. Chem. Soc. Dalton Trans. 1987, 1501-1507.
(34) Wada, M.; Kumazoe, M. J. Organomet. Chem. 1983, 259, 245-251.
(35) Wada, M.; Nishiwaki, K. J. Chem. Soc., Dalton Trans. 1983, 1841-
1844.
1
Cl2): λmax 410, 527 nm. H NMR (CD2Cl2): δ 8.91 (s, 8H), 8.13
(d, J ) 6.3 Hz, 8H), 7.75 (m, 12H), -0.25 (d, J ) 11.7 Hz, 1H),
-0.97 (d, J ) 11.4 Hz, 1H). 13C NMR (CDCl3): δ 145.5, 141.4,
133.6, 133.3, 128.1, 127.1, 122.1, 82.9. ESI-TOF MS (MeOH):
m/z observed M+ ) 776.10, [M + K]+ ) 815.07. ESI-TOF high-
resolution mass spectrometry (HRMS) with polypropylene glycol
standard: m/z 776.098, -3.2 ppm error.
For compound 1 prepared with (TPP)CoBr from Method A, a
brominated porphyrin impurity, (Br1-TPP)Co(E-CHCHBr), was
identified with 1H NMR spectroscopy and mass spectrometry
analysis at approximately the 10% level. This was also observed
in the crystal structure of 1 which showed a single Br replacement
of H, modeled at 6% incorporation, at the â-pyrrole position on
the porphyrin ring. No bromoporphyrin impurity was observed with
(TPP)CoBr prepared by Method B.
(trans-2-Iodovinyl)(tetraphenylporphyrin) Cobalt(III), (TPP)-
Co(E-CHCHI), 2. The methods from Sakurai and Setsune were
(36) Wada, M.; Nishiwaki, K.; Kumazoe, M. Chem. Commun. 1984, 980-
981.
(37) Lewis, J.; Johnson, B. F. G.; Taylor, K. A.; Jones, J. D. J. Organomet.
Chem. 1971, 32, C62-C64.
(38) Hacker, M. J.; Littlecott, G. W.; Kemmitt, R. D. W. J. Organomet.
Chem. 1973, 47, 189-193.
(39) SHELXTL, version 6.14; Bruker-AXS: Madison, WI, 2000.
(40) Sakurai, T.; Yamamoto, K.; Naito, H.; Nakamoto, N. Bull. Chem. Soc.
Jpn. 1976, 49, 3042-3046.
Inorganic Chemistry, Vol. 45, No. 5, 2006 2289

Fritsch et al.
Table 1. Crystallographic Data and Details of the Structural Refinements for (TPP)Co(E-CHCHBr), 1, (TPP)Co(Z-CClCHCl), 3, and (TPP)Co(C2H), 4
1
3
4
empirical formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C
46 H29.94 Br1.06 Co N4
C
46 H29 Cl2 Co N4
C
46 H29 Co N4
777.58
triclinic
P1h
767.56
triclinic
P1h
696.17
tetragonal
I4/m
13.2500(9)
13.2500
9.7890(7)
90
11.251(2)
13.175(3)
14.369(3)
103.136(3)
107.623(3)
102.179(3)
1884.9(7)
2
12.2370(15)
12.3804(15)
13.7944(17)
67.209(2)
86.051(2)
66.063(2)
1751.3(4)
2
90
90
1789.3(13)
2
1.293
5.18
720
Z
F
calcd (g cm-1
)
1.370
15.53
792
1.456
6.84
788
µ (cm-1
F(000)
)
cryst color
ind. reflns
obsd reflns
Rint
red-purple
6642
5534
0.0284
1.076
purple
6184
5339
0.0232
1.064
3.91, 10.06
4.73, 10.52
purple
7990
820
0.0257
1.254
3.60, 11.26
3.70, 11.34
GOF on F2
R1a, wR2b(%) [I > 2σ(I)]
4.47, 11.91
5.32, 12.42
R1a, wR2b(%) all data
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑Fo. b wR2 ) [∑[w(Fo -Fc )2)]/∑w(Fo )2]1/2
.
Figure 2. ORTEP drawing of 3 with thermal ellipsoids drawn at the 50%
probability level. The disordered dichlorovinyl group was refined at an
occupancy of 77:23 into two conformers at 180° from one another. For
clarity, only the major conformer is shown.
Figure 1. ORTEP drawing of 1 with thermal ellipsoids drawn at the 50%
probability level. Porphyrin bromination refined to be present at 6% total
occupancy over two symmetric positions.
adapted for preparing compound 2.14,31,40 (TPP)CoI was prepared
by reaction of (TPP)Co (300 mg, 0.45 mmol) with HI (57 wt %, 5
mL, 22 mmol) in methanol (300 mL) with 4 days of stirring. The
solution was vacuum filtered, and the solvent was removed from
the filtrate in vacuo to near dryness. The (TPP)CoI solid was
isolated with vacuum filtration and washed with 2:1 H2O/MeOH.
(TPP)CoI was isolated in an 83% yield.
with sodium benzophenone ketyl (10 mL of a 69 mM THF solution)
under an inert atmosphere. (An alternate reduction method utilized
excess sodium amalgam with 4 h of stirring followed by decanting
the (TPP)CoINa solution from the amalgam.) The red porphyrin
solution turned dark green upon reduction. TCE (0.5 mL, 5 mmol)
was added to (TPP)CoINa. The mixture was stirred for 1 h, and
the solvent was removed in vacuo. The residue was extracted with
CH2Cl2 and purified by column chromatography (SiO2, 70:30
hexane/toluene); the yield was 23%. Method B. Chlorinated
ethylene deprotonation methods were adapted from Ko¨ebrich.41-43
TCE (100 µL, 1.4 mmol, dried over molecular sieves) was added
to a 100 mL Schlenk flask in 15 mL of 1:1:1 (v/v/v) THF/Et2O/
hexanes. The solution was cooled to -110 °C in a liquid nitrogen-
ethanol bath. Either nBuLi (500 µL, 1.25 mmol, 2.5 M in hexanes)
or KHMDS (70 mg, 0.33 mmol in THF solution) was added to the
Schlenk flask via syringe under a nitrogen atmosphere. The reaction
was allowed to proceed for 20 min. The reaction mixture was
transferred via cannula to a solution of (TPP)CoIIICl (50 mg, 0.072
mmol, cooled to -110 °C in a liquid nitrogen-ethanol bath) in 15
mL of THF. The reaction was held at -110 °C for 4 h, then slowly
warmed to -35 °C overnight. The solvent was removed in vacuo.
Purification was performed by column chromatography (SiO2, 60:
40 hexane/CHCl3); the yield was 85%.
(TPP)Co(E-CHCHI) was prepared by reaction of (TPP)CoI (100
mg, 0.13 mmol) and C2H2 (200 mL, 1 atm, 8 mmol) in CH2Cl2
(30 mL) in a sealed tube with stirring for 4 days. The solvent was
removed in vacuo. Purification was performed by column chro-
matography (SiO2, 60:40 hexane/CHCl3); the yield was 43%. UV-
1
vis (CH2Cl2): λmax 409, 527 nm. H NMR (CD2Cl2): δ 8.94 (s,
8H), 8.13 (d, J ) 6.9 Hz, 8H), 7.75 (m, 12H), -0.04 (d, J ) 11.4
Hz, 1H), -1.06 (d, J ) 11.4 Hz, 1H). 13C NMR (CDCl3): δ 145.6,
141.5, 133.7, 133.3, 128.1, 127.2, 122.1, 72.1, 52.4. ESI-TOF MS
(MeOH): m/z observed M+ ) 824.2. ESI-TOF HRMS with
polypropylene glycol standard: m/z 824.0839, 0.4 ppm error.
(trans-Dichlorovinyl)(tetraphenylporphyrin)
Cobalt(III),
(TPP)Co(Z-CClCHCl), 3. Compound 3 was prepared through
reaction of (TPP)CoINa with TCE (Method A) and via reaction of
(TPP)CoIIICl and the tDCE anion (Method B).41-43 Method A.
(TPP)Co (100 mg, 0.155 mmol) was dissolved in THF and reduced
X-ray quality crystals of 3 were obtained via slow evaporation
from a hexane/CH2Cl2 (5:1) mixture. UV-vis (CH2Cl2): λmax 393,
422, 531 nm. 1H NMR (CD2Cl2): δ 8.94 (s, 8H), 8.13 (d, J ) 5.7
Hz), 7.75 (m, 12H), 2.51 (s, 1H). 13C NMR (CDCl3): δ 146.0,
(41) Koebrich, G.; Flory, K. Tetrahedron Lett. 1964, 1137-1142.
(42) Koebrich, G.; Flory, K. Chem. Ber. 1966, 99, 1773-1781.
(43) Koebrich, G.; Trapp, H.; Hornke, I. Tetrahedron Lett. 1964, 1131-
1136.
2290 Inorganic Chemistry, Vol. 45, No. 5, 2006

â-HaloWinyl Cobalt Porphyrin Complexes
hold the ionic strength constant (0, 100, 150, 180, 195, 200, and
205 mg TBAPF6 in CDCl3, 0, 260, 400, 470, 500, 525, and 530
µmol). Total NMR solution volume was 700 µL in each tube. Time
points were collected at time ) 0, 2, 5, 12, 24, 36, 51, and 72 h.
The R-carbon proton peak areas of 1 and 5 were compared to
quantify the extent of conversion from 1 to 5.
Reaction with Pyridines. Approximately 10 mg of each
â-halovinyl complex was dissolved in CDCl3 for 1H NMR analysis.
A spectrum was collected and then 1 drop of pyridine (ap-
proximately 20 µL) was added to each tube. Spectra were collected
after the pyridine addition. In a similar manner, reactions between
5 with excess DMAP and 1 with excess 4-CN-py were monitored
Figure 3. ORTEP drawing of 4 with thermal ellipsoids drawn at the 50%
probability level. The acetylide moiety was refined with disordered partial
occupancy in “up” and “down” conformations in a 61:39 ratio.
1
with H NMR.
141.2, 133.4, 128.1, 127.2, 122.2, 122.1, 81.6, 29.9. ESI-TOF MS
(MeOH): m/z observed M+ ) 766.11, [M + Na]+ ) 789.10, [M
+ K]+ ) 805.20. ESI-TOF HRMS with polypropylene glycol
standard: m/z 766.1106, -1.3 ppm error.
Reaction with a Lewis Acid. Approximately 10 mg of 5 was
dissolved in C6D6 for 1H NMR analysis. Under an inert atmosphere,
excess AlCl3 was added to each tube. 1H NMR spectra were
collected before and after addition.
(Acetylide)(tetraphenylporphyrin) Cobalt(III), (TPP)Co-
(C2H), 4. Compound 4 was prepared through the reaction of (TPP)-
CoIIICl and the vinyl chloride anion generated with methods adapted
from Ko¨ebrich.41-43 Vinyl chloride (80 mL, 1 atm, 3.2 mmol) was
added via vacuum transfer to a 100 mL Schlenk flask containing
15 mL of 1:1:1 (v/v/v) THF/Et2O/hexanes. The solution was cooled
Reaction with Strong Bases. Approximately 10 mg of each
â-halovinyl complex was dissolved in C6D6 for 1H NMR analysis.
Under inert atmosphere, excess KHMDS was added to each tube.
To each â-halovinyl complex, excess tBuOK in tBuOH was added
to each tube. 1H NMR spectra were collected before and after
addition.
n
to -110 °C in a liquid nitrogen-ethanol bath. Either BuLi (500
Reactions with Aqueous Acid and Base Solutions. Ap-
proximately 10 mg of each â-halovinyl complex was utilized in
each experiment. For H2O, the â-halovinyl compounds were
dissolved in THF-d8. For HCl and NaOH, the â-halovinyl com-
plexes were dissolved in CDCl3 for 1H NMR analysis. Spectra were
collected before and after the addition of 1 drop of H2O, HCl (2
M), or NaOH (1 M) to each tube. Spectra were collected at regular
time intervals. In the case of HCl, the volatile materials were
isolated via vacuum transfer and characterized with GC-MS.
Approximately 10 mg of compound 4 was dissolved in CDCl3
µL, 1.25 mmol, 2.5 M in hexanes) or KHMDS (70 mg, 0.33 mmol
in THF solution) was added to the Schlenk flask via syringe under
a nitrogen atmosphere. The reaction was allowed to proceed for
70 min. The reaction mixture was transferred via cannula to a
solution of (TPP)CoIIICl (50 mg, 0.072 mmol, cooled to -110 °C)
in 15 mL THF. The reaction was held at -110 °C for 4 h, then
slowly warmed to -35 °C overnight. The solvent was removed in
vacuo. Purification was performed by column chromatography
(SiO2, 60:40 hexane/CHCl3); the yield was 42%. X-ray quality
crystals were obtained by slow diffusion of hexane/CH2Cl2 (5:1).
1
for H NMR analysis. Spectra were collected before and after the
1
UV-vis (CH2Cl2): λmax 377, 421, 526 nm. H NMR (CDCl3): δ
addition of 1 drop of HCl (2 M). The volatile materials were isolated
via vacuum transfer and characterized with GC-MS.
8.97 (d, J ) 2.0, 8H), 8.20 (dm, J ) 7 Hz, 8H), 7.75 (m, 12H),
-1.67 (s, 1H). 13C NMR (CDCl3): δ 146.0, 141.4, 133.53, 133.51,
128.2, 127.24, 122.9, 92.10. ESI-TOF MS (MeOH): m/z observed
M+ ) 696.17, [M + Na]+ ) 719.3. ESI-TOF HRMS with
polypropylene glycol standard: m/z 696.1713, 0.8 ppm error.
Solution Stability. The stability of the â-halovinyl complexes
to the loss of C2H2 was tested by sparging halovinyl complex
solutions in p-xylenes with N2. Approximately 10 mg of each
â-halovinyl in CDCl3 was diluted into 50 mL of p-xylene. The
solutions were N2-sparged for various time intervals and monitored
with 1H NMR. The xylenes were removed in Vacuo, and the residue
dissolved in CDCl3.
C2D2 Replacement of C2H2. Approximately 10 mg of iodovinyl
2 (12 µmol) was dissolved into CDCl3 and transferred to an NMR
tube. A known volume bulb was used for quantitative gas transfer
of 25 µmol C2D2. The NMR tubes were flame-sealed and the
reaction mixture was analyzed by 1H NMR spectroscopy at regular
time intervals. At the completion of the experiment, the solution
was analyzed with ESI-TOF MS.
Halogen Substitution. Approximately 10 mg (∼10 µmol) of
each â-halovinyl complex was dissolved in CDCl3 and transferred
to an NMR tube. Excess TBAX (X) F, Cl, Br, I) was added to the
tube, dissolved, and mixed. Spectral features of interest are the
R-carbon vinyl proton doublet at -0.1 ppm for the iodovinyl
complex, 2, -0.25 ppm for the bromovinyl complex, 1, and -0.4
ppm for the chlorovinyl complex (TPP)Co(E-CHCHCl), 5 (previ-
ously reported).14 Halogen substitution was carried out at room
1
temperature and was monitored at regular intervals by H NMR
spectroscopy for 72 h.
Compound 5 (10 mg, 13 µmol) was treated with a TBA35Cl/
NaPF6 mixture (33.1 mg, 26 wt % Cl, 230 µmol) in refluxing CHCl3
for 5 days. In separate trials, the reaction was heated to reflux both
Results
1
Preparation of Halovinyl and Acetylide Cobalt Com-
plexes. An acetylene insertion reaction (eq 1) was used to
prepare the halovinyl compounds (TPP)Co(E-CHCHX) (X
) Cl, Br, I) 5, 1, and 2 in good yields.14,31
with an open condenser and in a sealed tube, monitored with H
NMR, purified by column chromatography (SiO2, 70:30 hexane/
CHCl3), and analyzed with ESI-TOF MS.
Kinetic Halogen Substitution Experiments. The kinetics of the
conversion of 1 (8 mg, 10 µmol) to 5 at 35 °C were monitored by
1H NMR spectroscopy in CDCl3. The reaction proceeded with a
constant amount of TBACl (25 µL of 0.5 M TBACl in CDCl3,
13.5 µmol) and varying amounts of TBABr (12.5, 25, 50, 125, and
250 µL of 0.5 M TBABr in CDCl3, 6.8, 13.5, 27, 54, and 135
µmol; 85 and 183 mg TBABr, 270 and 570 µmol) and TBAPF6 to
Inorganic Chemistry, Vol. 45, No. 5, 2006 2291

Fritsch et al.
Scheme 1. Reactivity Summary for the â-Halovinyl
Acetylene insertion into M-Cl bonds yielding chlorovi-
nylmetal complexes has been observed in a number of
systems including metal chlorides (M ) As, Sb, Pt, Hg)44-51
and transition metal porphyrin complexes (M ) Co, Rh).14,31,52
All three â-halovinyl complexes are air stable and were
handled on the benchtop. In the case of 1, it was prepared
in a 60% yield with a 6-10% (Br1-TPP)Co(E-CHCHBr)
impurity. This impurity resulted from the bromination of the
porphyrin during the (TPP)CoII oxidation to (TPP)CoIIIBr
with HBr. The replacement of â-pyrrole H atoms by Br has
been previously reported for bromination with Br2 (a possible
contaminant in HBr or generated under the reaction condi-
tions) and N-bromosuccinimide.53,54 The presence of (Br1-
TPP)CoBr in (TPP)CoBr was observed with ESI-TOF MS.
X-ray quality crystals of 1 were isolated, and during the
refinement, the (Br1-TPP)Co(E-CHCHBr) impurity, which
cocrystallized, was modeled as disorder and found to be
present at a 6% level (see Supporting Information). Com-
pound 1 was also prepared free of the bromoporphyrin
impurity by bromide exchange of the chloride in (TPP)CoCl,
followed by acetylene insertion.
Tetraphenylporphyrin Cobalt Complexes
The tetraphenylporphyrin ligand is symbolized by brackets.
Compound 2 was prepared from (TPP)CoI in a 43% yield
cDCE is the major observed product.14 The crystal structure
of 3 was modeled with disorder at the vinyl group resulting
in two conformations oriented at 180° from one another in
a ratio of 77:23 (see Supporting Information).
1
and was characterized with H NMR, 13C NMR, UV-vis,
and ESI-TOF HRMS. Attempts to obtain crystals suitable
for X-ray analysis were unsuccessful. Compound 2 is
unstable toward acetylene deinsertion in solution over several
days under ambient conditions, but is stable as a solid under
inert atmosphere at -35 °C. A â-fluorovinyl cobalt porphyrin
complex could not be prepared through an acetylene insertion
reaction from either (TPP)CoF, prepared with HF, or by F-
exchange with (TPP)CoCl. The product isolated from the
reaction of (TPP)CoF and C2H2 was compound 4, the
acetylide.
Compound 3, (TPP)Co(Z-CClCHCl), was the only ha-
lovinyl complex isolated from the reaction of (TPP)CoINa
and chlorinated ethylenes (TCE, cDCE, tDCE, CH2CCl2, or
CH2CHCl). Compound 3 was isolated from the reaction of
(TPP)CoINa and TCE in a 23% yield. The 1H NMR spectrum
of this complex gives little stereochemical information, but
X-ray crystallography indicates a Z configuration, with the
two chlorine substituents trans to one another. The stereo-
chemistry of 3 as the product of reaction of CoI and TCE
was surprising. This complex has trans-dichloro stereochem-
istry in stark contrast to the observed products in the aqueous
phase reductive dehalogenation of TCE by (TCPP)Co, where
Another synthetic route to chlorovinyl cobalt complexes
was also explored through the deprotonation of chlorinated
ethylene substrates and reaction with (TPP)CoIIICl. Com-
pound 3 was the only chlorovinyl complex isolated from this
synthetic procedure and was isolated in an 85% yield from
the reaction of (TPP)CoIIICl and the anion derived from
tDCE. The characterization of 3 was consistent with the
isolated products of (TPP)CoINa and TCE. Also, through
the deprotonation reaction procedure, compound 4 was
obtained through of the reaction of deprotonated vinyl
chloride and (TPP)CoIII
Cl (compound 4 has been previously
1
reported).55 It was characterized with H NMR, 13C NMR,
UV-vis, and ESI-TOF HRMS.
The structure of 4 was solved in the space group I4/m, but
suitable solutions were also obtained with I4 and I-4. This
space group was chosen because it yielded the most
reasonable solution for the acetylide C-C and C-H bond
distances and for the thermal parameters of the ellipsoids.
Although there were favorable structure solutions for a
diacetylide complex based on symmetry operations, we do
not think this is the case because CoIV is not a viable
oxidation state and no lithium counterion was observed in
the structure; therefore we believe the compound to be a
monoacetylide. This is also supported by 1H NMR and ESI-
TOF MS data and in comparison to available literature data.55
The acetylide moiety was refined for partial occupancy and
found to be present in a 61:39 ratio of the two conformations
(see Supporting Information).
(44) Nesmeyanov, A. N. Bull. Acad. Sci. U. S. S. R. 1945, 239-250.
(45) Nesmeyanov, A. N.; Borisov, A. E. Bull. Acad. Sci. U. S. S. R. 1945,
251-260.
(46) Freidlina, R. K. Bull. Acad. Sci. U. S. S. R. 1942, 14-20.
(47) Freidlina, R. K.; Nesmeyanov, A. N. Dokl. Akad. Nauk 1940, 26, 60-
64.
(48) Chapman, D. L.; Jenkins, W. J. J. Chem. Soc., Trans. 1919, 115, 847-
849.
(49) Lewis, W. L.; Perkins, G. A. J. Ind. Eng. Chem. 1923, 15, 290-295.
(50) Dafert, O. A. Manatsh 1919, 40, 313-323.
(51) Shubin, A. A.; Nechitailova, R. S.; Bezbozhnaya, T. V.; Mitchenko,
S. A.; Beletskaya, I. P. Russ. J. Org. Chem. 2002, 38, 1693-1695.
(52) Ogoshi, I.; Setsune, J.; Nanbo, Y.; Yoshida, Z. J. Organomet. Chem.
1978, 159, 329-339.
(53) D’Souza, F.; Villard, A.; Van Caemelbecke, E.; Franzen, M.; Boschi,
T.; Tagliatesta, P.; Kadish, K. M. Inorg. Chem. 1993, 32, 4042-4048.
(54) D’Souza, F.; Deviprasad, G. R.; Hsieh, Y.-Y. J. Electroanal. Chem.
1996, 411, 167-171.
â-Halovinyl Cobalt complex Reactivity. The reactivity
of the â-halovinyl complexes was explored (Scheme 1) and
(55) Krattinger, B.; Callot, H. J. Bull. Soc. Chim. Fr. 1996, 133, 721-
724.
2292 Inorganic Chemistry, Vol. 45, No. 5, 2006

â-HaloWinyl Cobalt Porphyrin Complexes
contributes to previous work regarding the reactivity of
â-chlorovinylmetal complexes.47,56 Aspects of the observed
reactivity can be understood by considering the equilibrium
described by Setsune31 (eq 2) which includes a coordinated
acetylene π complex previously proposed in a number of
transition metal systems.31,51,52,57-60
The bromovinyl 1 and iodovinyl 2 complexes were found
to be much more reactive than the chlorovinyl 5. Both 1
and 2 were converted to 5 by reaction with excess TBACl.
In contrast, 5 could not be converted to either 1 or 2 through
the addition of excess TBABr or TBAI, respectively.
Preparation of the analogous â-fluorovinyl cobalt complex
through halide exchange with 1, 2, or 5 and TBAF was not
successful. When 5 was treated with TBA35Cl, no changes
in the M+ ion isotope pattern of 5 were observed. A
decomposition product, (TPP)CoCl, was formed after pro-
longed heating of 5 at 60 °C, indicating that acetylene
deinsertion is possible at higher temperature.
Figure 4. Concentration of 1 at time points along the kinetic time course
for the conversion of 1 to 5 at different [Cl-]/[Br-] ratios. Curve fits
represent an exponential fitting of the concentration data yielding the
observed rate constant (kobs) for each experiment. Time points were collected
at 2, 5, 12, 24, 36, 51, and 72 h.
the halovinyl compounds was observed after 2 days. In the
case of HCl addition, within 1 day the halovinyl complexes
were completely degraded, and the emergence of vinyl halide
peaks consistent with vinyl chloride, vinyl bromide, and vinyl
1
iodide were observed by H NMR spectroscopy. Isolation
To determine the mechanism of halide exchange among
the â-halovinyl complexes, the conversion of 1 to 5, using
varying amounts of bromide (TBABr) in the presence of
constant chloride (TBACl) concentration, was monitored with
1H NMR through integration of their respective vinyl proton
signals. The loss of 1 was correlated to an increase in 5.
Slower rates of conversion from 1 to 5 were observed with
increasing bromide concentration (Figure 4).
of the volatile materials via vacuum transfer followed by
1H NMR and GC-MS analysis identified the products as
(TPP)CoCl and the corresponding vinyl halide (i.e., vinyl
chloride, vinyl bromide, or vinyl iodide). In the case of NaOH
addition, no changes to the halovinyl protons were observed
within 2 days. Compound 4 was also treated with HCl and
yielded vinyl chloride as the major product.
The reaction of â-chlorovinyl complex 5 with AlCl3 was
explored. Upon addition of AlCl3 to a benzene-d6 solution
of 5, an immediate color change from red to green-black
was observed. The resulting 1H NMR spectrum was consis-
tent with [(TPP)CoIII][AlCl4]. Subsequent treatment of the
reaction mixture with pyridine yielded (TPP)Co(py)+ and
The reaction of â-halovinyl complexes with pyridine had
varied results depending on the â-halogen substitution.
Simple complexation of pyridine to 5 giving a 6-coordinate
1
complex was observed by H NMR spectroscopy and ESI-
TOF MS. The vinyl proton resonances shifted downfield
from -0.46 and -1.00 ppm to 0.14 and -0.96 ppm (where
the signal at -0.46 ppm corresponds to the proton bound to
the R-carbon and the resonance at -1.00 ppm is the proton
on the â-carbon). In the case of 1 and 2, no vinyl group
+
(TPP)Co(py)2 , on the basis of mass spectrometry results,
confirming the loss of the chlorovinyl group.
The reaction of â-halovinyl complexes with strong bases
was also explored. All of the â-halovinyl complexes were
determined to be unreactive toward KHMDS as there were
no observed changes to the halovinyl proton signals. Treat-
1
signals were observed in the H NMR spectrum following
pyridine addition, and mass spectrometry data indicated the
loss of acetylene and formation of a mixture of (TPP)(py)-
CoX and (TPP)(py)2Co+ in both reactions. In the reaction
of 5 with DMAP, a 6-coordinate complex was observed with
t
ment with BuOK yielded no reaction with 5, but it reacted
with both 1 and 2 slowly to yield the acetylide complex, 4.
The lability of the C2H2 moiety was also investigated.
Sparging solutions of the â-halovinyl complexes with N2
yielded no change in 5 after several days, complete loss of
acetylene from 1 in 6 days, and complete loss of acetylene
from 2 in 1 day. Further evidence of the lability of the C2H2
component of the â-halovinyl complexes was the replace-
ment of C2H2 with C2D2. Complete replacement for complex
1
a similar shift in the H NMR as described above for
pyridine. Simple coordination to give a 6-coordinate â-bro-
movinyl cobalt complex was achieved through the reaction
of 1 with the more weakly donating 4-cyanopyridine.
The reactivity of the halovinyl complexes with H2O, H+,
and OH- was tested. In the case of H2O, no degradation of
1
2 was observed within 2 days as observed by H NMR
(56) Setsune, J.; Ikeda, M.; Kishimoto, Y.; Ishimaru, Y.; Fukuhara, K.;
Kitao, T. Organometallics 1991, 10, 1099-1107.
spectroscopy and confirmed with ESI-TOF MS, which had
an increase of two mass units for the M+ ion.
(57) Treichel, P. M.; Komar, D. A. Inorg. Chim. Acta 1980, 42, 277-80.
(58) Chisholm, M. H.; Clark, H. C. Inorg. Chem. 1971, 10, 2557-2563.
(59) Setsune, J.-i.; Ito, S.; Takeda, H.; Ishimaru, Y.; Kitao, T.; Sato, M.;
Ohya-Nishiguchi, H. Organometallics 1997, 16, 597-605.
(60) Setsune, J.-i.; Takeda, H.; Ito, S.; Saito, Y.; Ishimaru, Y.; Fukuhara,
K.; Saito, Y.; Kitao, T.; Adachi, T. Inorg. Chem. 1998, 37, 2235-
2246.
Discussion
â-Halovinyl Complex Structures. Characterization of the
halovinyl cobalt complexes identified new complexes with
Inorganic Chemistry, Vol. 45, No. 5, 2006 2293

Fritsch et al.
Table 2. Halovinyl Bond Lengths and Angles of Interest for (TPP)CoR
(1, R ) E-CHCHBr; 3, R ) Z-CClCHCl; 5, R ) E-CHCHCl)
metric
1
3
5a
Co-C (Å)
CdC (Å)
C-X (Å)
1.925(4)
1.211(6)
1.927(4)
1.929(4)
1.320(7)
1.757(7)b
1.735(4)c
1.9246(4)
1.234(5)
1.752(4)
Co-CdC (deg)
126.9(3)
134.0(5)
126.7(3)
a Ref 14. b C45-Cl1 c C46-Cl2.
Scheme 2. General Summary of the Reactivity of â-Halovinyl
Complexes
Figure 5. Comparison of C-C vinyl bond distances in angstroms for
selected Co vinyl complexes with corrin, dimethylglyoximate, and porphyrin
ligand sets.
varying stability. The crystallographic data shows the C-C
bond of the vinyl group to be very short in the â-halovinyl
complexes (see Table 2); the bond distance for the vinyl
carbons of â-halovinyl cobalt complexes (compound 1 )
1.211 Å, compound 5 ) 1.234 Å) strongly resembles that
measured for acetylene with a C-C bond distance of 1.181
Å.61 It is interesting to compare the metrical parameters for
the trans-â-halovinyl complexes and the dichlorovinyl
complex 3, in which the Cl substituents are trans, as the
C-C bond distances are very different (Table 2).
In complex 3, the Co-C and C-Cl bond distances are
also consistent with the chlorovinyl bond distances for other
complexes (see Supporting Information), but the Co-CdC
(134°) is significantly distorted from an idealized sp2 carbon
bond angle presumably because of steric interactions between
Cl2 and the porphyrin ring.
Figure 6. Contributing resonance structures for E-â-halovinyl complexes.
and these structural trends are reflected in the reactivity of
the â-halovinyl complexes.
Reactivity of trans-â-Halovinyl Complexes. The reactiv-
ity of â-halovinyl complexes can largely be summarized by
the equilibrium shown in Scheme 2.
Evidence for this equilibrium was obtained through the
kinetics of the halogen substitution experiments. In these
experiments, support for a dissociative substitution mecha-
nism was obtained through inhibition of the conversion of 1
to 5 by added bromide ion (eq 3).
A number of cobalt halovinyl structures have appeared
recently. It is instructive to compare the C-C bond distance
results across the ligand sets and halogen substitution patterns
for the chlorovinyl and vinyl complexes (see Figure 5).
Such comparison emphasizes that trans-â-halo substitution
leads to a very short CdC bond, consistent with the
resonance structures shown in Figure 6.
This resonance model is not new. Indeed, it was put forth
65 years ago to explain infrared absorbance data for
â-halovinyl Hg complexes that were consistent with inter-
mediate bonding between double and triple.47 While the short
vinyl C-C bonding was inferred for complexes of this type
on the basis of spectroscopic and reactivity data, the
crystallographic data presented here give the first structural
support for this model.
The diminished rate constant for the conversion to 5 in
the presence of increasing Br- concentrations is consistent
with a competition between Br- and Cl- for addition to the
coordinated acetylene. The kinetic data were interpreted using
the scheme presented in eqs 3-5. The rate constants at
[Cl-]
[Br-]
k1
kobs
)
(4)
[Cl-]
[Br-]
k-1
k2
+
-d[1]
dt
) kobs [1]
(5)
35 °C for Br- loss (k1) and the ratio of Cl- and Br-
attachment (k2/k-1) were determined to be 1.39 × 10-5 s-1
and 11.6, respectively (see Figure 7). The intermediacy of
the cobalt-coordinated C2H2 has been previously invoked and
our results support the existence of such a complex.31,59,60
In general, 5 appears to be very stable on the basis of the
inability to yield halogen substitution with excess Br-, I-,
or 35Cl-. Chloride loss could only be observed with
Unsubstituted cobalt vinyl complexes have intermediate
bond lengths, while other chlorovinyl complexes have C-C
bond lengths approaching those of ethylene. It is apparent
that the location of the halogen substituents plays an
important role in the C-C bond length of the vinyl group,
(61) McMullan, R. K.; Kvick, A.; Popelier, P. Acta Crystallogr. 1992, B48,
726-731.
(62) Van Nes, G. J. H.; Vos, A. Acta Crystallogr. 1979, B35, 2593-2601.
2294 Inorganic Chemistry, Vol. 45, No. 5, 2006

â-HaloWinyl Cobalt Porphyrin Complexes
the halide could be replaced and the C2H2 could be displaced
with N2 sparging. The iodovinyl complex 2 complex was
found to be the most reactive since the halide could be
replaced, C2H2 could be removed by the sparging in 1 day,
and C2H2 could be replaced with C2D2. This observed
complex instability provides a rationale for the inability to
obtain suitable crystals of 2.
Conclusions
This study furthers our understanding of cobalt halovinyl
complexes, demonstrating that the trans-â-halovinyl substitu-
tion pattern leads to an unusual reactivity pattern. This work
confirms and amplifies Setsune and co-workers view that
â-halo substituents are susceptible to dissociation, leading
to overall lability of the C2H2 moiety. The reactivity trend
follows the leaving group ability: I > Br . Cl. Finally, the
distinct reactivity of â-halovinyl cobalt complexes is reflected
in their structures, which display significantly shortened vinyl
C-C bonds.
Figure 7. Observed rate constants for the conversion of 1 to 5 at different
ratios of [Cl-]/[Br-]. The curve fit represents a saturation fit of kobs, eq 4.
Error bars represent the error of the exponential fit of [1] vs time plots.
prolonged heating or following the addition of AlCl3, yielding
[(TPP)Co][AlCl4].
The reactivity of the â-halovinyl complexes was further
explored, and 1 and 2 shared many properties. On the basis
of the reactions, the stability of the complexes follows the
trend 5 . 1 > 2 and agrees with each halide’s propensity to
act as a leaving group. Acid hydrolysis of the Co-C bond
in â-halovinyl compounds yielding (TPP)CoCl and the
corresponding vinyl halide was a different result than that
observed in the chlorovinyl cobaloximes, which were shown
to be stable to acid.23
The lability of acetylene varied across the â-halovinyl
complexes. Since halide substitution was not possible for 5,
it was expected that the acetylene would not be displaced
by sparging with N2. The results with bromovinyl complex
1 demonstrated a trend toward increasing reactivity in that
Acknowledgment. This work was funded in part by the
EPA STAR Fellowship program (U-91610701-1) and the
National Science Foundation (CHE-0239461). We thank
Victor G. Young, Jr. and Ben Kucera from the X-ray
Crystallographic Laboratory for help solving the crystal
structures.
Supporting Information Available: Table comparing structure
details for many vinyl and halovinyl cobalt complexes of porphyrin,
dimethylglyoximate, and corrin ligands and crystallographic infor-
mation for (TPP)Co(E-CHCHBr), 1, (TPP)Co(Z-CClCHCl), 3, and
(TPP)Co(C2H), 4. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC0518834
Inorganic Chemistry, Vol. 45, No. 5, 2006 2295