Structural, computational, and 59Co NMR studies of primary and secondary amine complexes of Co(III) porphyrins

Article abstract of DOI:10.1021/ic000976c

Four novel low-spin bis(amine) Co(III) porphyrins [Co(TPP)(BzNH₂)₂](SbF₆), 1, [Co(TPP)(1-BuNH₂)₂](SbF₆), 2, [Co(TPP)(PhCH₂CH₂NH₂)₂] (SbF₆), 3, and [Co(TPP)(1-MePipz)₂](SbF⁶), 4, have been synthesized and characterized by low-temperature X-ray crystallography, IR, electronic, and NMR (¹H, ¹³C, and ⁵⁹Co) spectroscopy. The mean Co-N_p distance for the four structures is 1.986(1) . The Co-N_ax distances for the 1° amine derivatives average to 1.980(5) ; the axial bonds of the 2° amine derivative are significantly longer, averaging 2.040(1) . The porphyrin core conformation of 4 is significantly nonplanar (mixture of S₄-ruf and D_2d-sad distortions) due to a staggered arrangement of the axial ligands over the porphyrin core and meso-phenyl group orientations < 90°. The X-ray structures have been used with the coordinates for [Co(TPP)(Pip)₂](NO₃) (Scheidt et al. J. Am. Chem. Soc. 1973, 95, 8289-8294.) to parametrize a molecular mechanics (MM) force field for bis(amine) complexes of Co(III) porphyrins. The calculations show that two types of crystal packing interactions (van der Waals and hydrogen bonding) largely control the crystallographically observed conformations. Gas phase conformational energy surfaces have been computed for these complexes by dihedral angle driving methods and augmented with population distributions calculated by MD simulations at 298 K; the calculations demonstrate that the bis(1° amine) complexes are significantly more flexible than the bis(2° amine) analogues. ⁵⁹Co NMR spectra have been acquired for a range of [Co(TPP)(amine)₂]Cl derivatives as a function of temperature. The ⁵⁹Co chemical shifts increase linearly with increasing temperature due to population of thermally excited vibrational levels of the ¹A₁ ground state. Activation energies for molecular reorientation (tumbling) have been determined from an analysis of the ⁵⁹Co NMR line widths as a function of ¹/T; lower barriers exist for the conformationally rigid 2^° amine derivatives (2.6-3.8 kJ mol^-1). The ⁵⁹Co chemical shifts vary linearly with the DFT-calculated radial expectation values (r^-3)_3d for the Co(III) ion. The correlation leads to the following order for the σ-donor strengths of the axial ligands: BzNH₂ ≥ Cl^- > 1-BuNH₂ > PhCH₂CH₂NH₂ > 1-Bu₂NH > Et₂NH. The ⁵⁹Co NMR line widths are proportional to the square of the DFT-calculated valence electric field gradient at the Co nucleus. Importantly, this is the first computational rationalization of the ⁵⁹Co NMR spectra of Co(III) porphyrins.

Full text of DOI:10.1021/ic000976c

Inorg. Chem. 2001, 40, 3303-3317
3303
59
Structural, Computational, and Co NMR Studies of Primary and Secondary Amine
Complexes of Co(III) Porphyrins
Orde Q. Munro,* Sibongiseni C. Shabalala, and Nicola J. Brown
School of Chemical and Physical Sciences, University of Natal, Pietermaritzburg,
Private Bag X01, Scottsville, 3209, South Africa
ReceiVed August 28, 2000
Four novel low-spin bis(amine) Co(III) porphyrins [Co(TPP)(BzNH2)2](SbF6), 1, [Co(TPP)(1-BuNH2)2](SbF6),
2, [Co(TPP)(PhCH2CH2NH2)2](SbF6), 3, and [Co(TPP)(1-MePipz)2](SbF6), 4, have been synthesized and
characterized by low-temperature X-ray crystallography, IR, electronic, and NMR (1H, 13C, and 59Co) spectroscopy.
The mean Co-Np distance for the four structures is 1.986(1) Å. The Co-Nax distances for the 1° amine derivatives
average to 1.980(5) Å; the axial bonds of the 2° amine derivative are significantly longer, averaging 2.040(1) Å.
The porphyrin core conformation of 4 is significantly nonplanar (mixture of S4-ruf and D2d-sad distortions) due
to a staggered arrangement of the axial ligands over the porphyrin core and meso-phenyl group orientations
< 90°. The X-ray structures have been used with the coordinates for [Co(TPP)(Pip)2](NO3) (Scheidt et al. J. Am.
Chem. Soc. 1973, 95, 8289-8294.) to parametrize a molecular mechanics (MM) force field for bis(amine)
complexes of Co(III) porphyrins. The calculations show that two types of crystal packing interactions (van der
Waals and hydrogen bonding) largely control the crystallographically observed conformations. Gas phase
conformational energy surfaces have been computed for these complexes by dihedral angle driving methods and
augmented with population distributions calculated by MD simulations at 298 K; the calculations demonstrate
that the bis(1° amine) complexes are significantly more flexible than the bis(2° amine) analogues. 59Co NMR
spectra have been acquired for a range of [Co(TPP)(amine)2]Cl derivatives as a function of temperature. The
59Co chemical shifts increase linearly with increasing temperature due to population of thermally excited vibrational
1
levels of the A1 ground state. Activation energies for molecular reorientation (tumbling) have been determined
from an analysis of the 59Co NMR line widths as a function of 1/T; lower barriers exist for the conformationally
rigid 2° amine derivatives (2.6-3.8 kJ mol-1). The 59Co chemical shifts vary linearly with the DFT-calculated
radial expectation values r-3 for the Co(III) ion. The correlation leads to the following order for the σ-donor
3d
strengths of the axial ligands: BzNH2 g Cl- > 1-BuNH2 > PhCH2CH2NH2 > 1-Bu2NH > Et2NH. The 59Co
NMR line widths are proportional to the square of the DFT-calculated valence electric field gradient at the Co
nucleus. Importantly, this is the first computational rationalization of the 59Co NMR spectra of Co(III) porphyrins.
Introduction
ligands. Marchon and co-workers have, for example, shown that
selective binding of mainly one enantiomer from a racemic
Although Co(III) porphyrins are not naturally occurring, they
have become increasingly important as useful receptors for
amines, amino acids, and other ligands.1-3 Advantageous
physical properties such as slow axial ligand exchange on the
1H NMR time scale, a large diamagnetic ring current effect,4,5
and negligible line broadening have resulted in the use of Co(III)
porphyrins as NMR shift reagents for a range of ligand
systems.6-8 An interesting, recent development with analytical
applications is the use of chiral Co(III) porphyrins as enantio-
selective receptors for amino acids, their esters, and other chiral
mixture of a chiral ligand is possible when a chiral Co(III)
porphyrin receptor is used.2,3
Our interest in bis(amine) complexes of Co(III) porphyrins
stems from our work on the isoelectronic d6 Fe(II) complexes9
and fundamental questions which relate to the role of the
N-terminal amino group of Tyr-1 in the plant cytochromes-f10,11
as an axial ligand to the heme iron. In the case of Co(III)
porphyrins, the coordination of amine ligands has been studied
mainly by 1H NMR spectroscopy,12-14 particularly since these
kinetically inert diamagnetic complexes are useful as NMR shift
reagents.6-8,15,16 Although X-ray structures of [Co(TPP)(Pip)]-
(NO3),17,18 [Co(TPP)(PhCH(CH3)NH2)2]Br,19 [Co(TMCP)((R/
* To whom correspondence should be addressed. E-mail: MunroO@
nu.ac.za.
(1) Gouedard, M.; Gaudemer, F.; Gaudemer, A.; Riche, C. J. Chem. Res.,
Synop. 1978, 30-31.
(2) Simonato, J.-P., Pe´caut, J.; Marchon, J.-C. J. Am. Chem. Soc. 1998,
120, 7363-7364.
(3) Toronto, D.; Sarrazin, F.; Pe´caut, J.; Marchon, J.-C.; Shang, M.;
Scheidt, W. R. Inorg. Chem. 1998, 37, 526-532.
(4) Riche, C.; Gouedard, M.; Gaudemer, A. J. Chem. Res., Synop. 1978,
34-35.
(5) Abraham, R. J.; Marsden, I. Tetrahedron 1992, 48, 7489-7504.
(6) Abraham, R. J.; Medforth, C. J. Magn. Res. Chem. 1990, 28, 343.
(7) Abraham, R. J.; Medforth, C. J. Magn. Res. Chem. 1988, 26, 803.
(8) Abraham, R. J.; Medforth, C. J. J. Chem. Soc., Chem. Commun. 1987,
1637-1638.
(9) Munro, O. Q.; Madlala, P. S.; Warby, R. A. F.; Seda, T. B.; Hearne,
G. Inorg. Chem. 1999, 38, 4724-4736.
(10) Martinez, S. E.; Huang, D.; Szczepaniak, A.; Cramer, W. A.; Smith,
J. L. Structure 1994, 2, 95-105.
(11) Martinez, S. E.; Huang, D.; Ponomarev, M.; Cramer, W. A.; Smith,
J. L. Protein Sci. 1996, 5, 1081-1092.
(12) Choi, I.-K.; Liu, Y.; Wei, Z.; Ryan, M. D. Inorg. Chem. 1997, 36,
3113-3118.
(13) Gouedard, M.; Gaudemer, F.; Gaudemer, A. Tetrahedron Lett. 1973,
2257-2260.
(14) Mikros, E.; Gaudemer, F.; Gaudemer, A. Inorg. Chem. 1991, 30,
1806-1815.
10.1021/ic000976c CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/25/2001

3304 Inorganic Chemistry, Vol. 40, No. 14, 2001
Munro et al.
S)-prolinol-N)2]Cl,2 and [Co(TMCP)((S)-2-butylamine)2]Cl3 have
been reported, there have been no systematic structural, com-
putational, and spectroscopic studies of a carefully tailored range
of bis(amine) Co(III) porphyrin derivatives. The coordination
chemistry, conformational energetics, electronic structures, and
physical properties of this class of compounds have therefore
not been fully delineated. Moreover, there have been no 59Co
NMR studies of bis(amine) complexes of Co(III) porphyrins,
even though this technique has been applied to bis(imidazole)20-22
and bis(pyridine)23 complexes of Co(III) meso-tetraaryl por-
phyrins and is one of the few currently available direct
experimental probes of the metal center.
benzophenone. Dichloromethane, pyrrole, benzylamine, 1-butylamine,
phenethylamine, and 1-methylpiperazine (all from Aldrich) were
distilled over CaH2. Benzaldehyde (Merck) and silver hexafluoro-
antimonate(V) (Aldrich) were used as received. H2TPP was synthesized
using published procedures.24 [Co(TPP)Cl] was prepared by metalation
of H2TPP with cobalt(II) chloride hydrate in refluxing DMF.25
Instrumentation. Electronic spectra were recorded with a Shimadzu
UV-2101PC UV-vis scanning spectrophotometer using dry methylene
chloride solutions containing 0.1-0.5 M amine in 1.0 and 0.1 cm path
length cuvettes. Samples for IR spectroscopy were KBr mulls of
polycrystalline material. FT-IR spectra were recorded with a Perkin-
Elmer Spectrum One spectrometer (4 scans, spectral resolution ) 1.0
cm-1). Microanalytical data (3 measurements per sample) were obtained
with a Perkin-Elmer CHN 2400 Elemental Analyzer. 1H and 13C NMR
spectra of all [Co(TPP)(L)2]SbF6 species were recorded using saturated
solutions in CDCl3 with a 500 MHz Varian Unity Inova spectrometer
equipped with an Oxford magnet (11.744 T). Standard 1H and 13C pulse
sequences were used for 1D and 2D spectra. The probe and setting
temperatures of the instrument were calibrated using the chemical shift
difference between the methyl and hydroxyl resonances of methanol
for variable-temperature work.26 59Co NMR spectra were recorded for
several [Co(TPP)(L)2]Cl derivatives, where L ) 1-butylamine, 5,
benzylamine, 6, phenethylamine, 7, piperidine, 8, 1-methylpiperazine,
9, diethylamine, 10, and dibutylamine, 11, as a function of temperature.
Samples were prepared by dissolving ∼15-20 mg of [Co(TPP)Cl] in
300 µL of CDCl3 in thin-walled 5-mm diameter NMR tubes prior to
adding 300 µL of freshly distilled amine. A broad band probe with
three separate frequencies (76.750 MHz, deuterium lock; 499.982 MHz,
proton decoupler; and 119.533 MHz, 59Co observation frequency) was
used for all 59Co NMR spectra. The 59Co resonance frequency of a
saturated solution of K3[Co(CN)6] in D2O was used as an external
reference (eq 1),
In this paper, we present a general method for the synthesis
of bis(amine) complexes of low-spin cobalt(III) porphyrins. Four
complexes of the type [Co(TPP)(L)2](SbF6), where L ) benzyl-
amine, 1-butylamine, phenethylamine, and 1-methylpiperazine,
have been characterized by X-ray crystallography as well as
electronic, IR, and NMR (1H, 13C, and 59Co) spectroscopy.
Moreover, together with the atomic coordinates of [Co(TPP)-
(Pip)](NO3),18 the four X-ray structures of this study have been
used to parametrize a force field (MM+) for bis(amine)
derivatives of Co(III) porphyrins. The conformational energetics
of these complexes have been determined by a combination of
conventional dihedral angle mapping and MD simulations at
298 K. The force field has also been used to calculate accurate
input geometries for DFT calculations of the electronic structures
of a range of [Co(TPP)(amine)2]+ complexes. Importantly, this
is the first report on the use of MM, MD, and DFT methods to
delineate the fundamental factors which determine 59Co chemi-
cal shifts and line widths in Co(III) porphyrins. We have found
that the total 3d electron populations or, more fundamentally,
the radial expectation values r-3 3d reflect the σ-donor strengths
of the axial ligands coordinated to the Co(III) ion. Moreover, a
(νmeasured - νreference
)
sample
lock
reference
lock
δ
)
59Co
+ (δ
- δ
)
(1)
118.068
linear correlation exists between the 59Co NMR line width, ω1/2
,
where 118.068 MHz is the theoretical 59Co resonance frequency at
sample
lock
reference
are the lock solvent frequencies of the
lock
11.744 T; δ
and δ
and the square of the calculated valence electric field gradient,
sample (CDCl3) and reference (D2O), respectively.27,28 A pulse width
of 7.0 µs was used with an acquisition time of 0.5 s (full relaxation
was, however, evident after 0.01 s in all cases) and a spectral window
of 400 kHz. Between 5000 and 10 000 transients were accumulated
into 64 000 data points. Spectral singlets were fit to a single Voigt
amplitude function with a time index of 13.2, eq 2,
q2val, of the Co(III) ion.
Experimental Section
General Information. All manipulations were carried out under
nitrogen using a double manifold vacuum line, Schlenkware, and
cannula techniques. THF and hexane were distilled over sodium/
2
-1
exp(-t2)
νobs - a
exp(-t )
∞
∞
(15) Gaudemer, A.; Gaudemer, F.; Merienne, C. Org. Magn. Reson. 1983,
21, 83.
(16) Abraham, R. J.; Bedford, G. R.; Wright, B. Org. Magn. Reson. 1983,
21, 637-642.
I ) a0
2 dt ×
)
dt
(2)
∫
∫
a23 + t2
-∞
-∞
(
)
a23 +
1 - t
(
a2
(17) Abbreviations: 1-BuNH2, 1-butylamine; 1-MePipz, 1-methylpipera-
zine; 4σ, 4 standard deviations; BzNH2, benzylamine; Ca, Cb, Cm,
porphyrin alpha-, beta-, and meso-carbons; Cp and CL, phenyl and
ligand carbons; CSA, chemical shift anisotropy; DFT, density func-
tional theory; DMF, N,N-dimethylformamide; EFG, electric field
gradient; L, ligand in general; MD, molecular dynamics; MM,
molecular mechanics; Np, porphinato nitrogen; Nax, axial ligand
nitrogen; |Np|, |Ca|, |Cb|, and |Cm| are the mean absolute perpendicular
displacements of the porphyrin nitrogens, R-, â-, and meso-carbons
from the 24-atom porphyrin mean plane, respectively; PhCH2CH2-
NH2, phenethylamine; Pip, piperidine; THF, tetrahydrofuran; TMCP,
dianion of 5, 10, 15, 20-tetrakis(2-methoxycarbonyl-3,3-dimethylcyclo-
propyl)porphyrin; TPP, 5, 10, 15, 20-tetraphenylporphyrin dianion.
(18) Scheidt, W. R.; Cunningham, J. A.; Hoard, J. L. J. Am. Chem. Soc.
1973, 95, 8289-8294.
where the adjustable variables a0, a1, a2, and a3 are the amplitude,
resonance frequency, line width, and line shape, respectively.29 The
quintet spectra obtained for 6 were fit to the sum of five Voigt amplitude
functions with equivalent width and shape parameters. A linear
background was used for all line shape analyses. Because both 10 and
(24) Barnett, G. H.; Hudson, M. F.; Smith, K. M. J. Chem. Soc., Perkin
Trans. (1) 1975, 1401-1403.
(25) Adler, A. D.; Longo, F. R.; Kampas, F.; Kim, J. J. Inorg. Nucl. Chem.
1970, 32, 2443-2445.
(26) Braun, S.; Kalinowski, H.-O.; Berger, S. 150 and More Basic NMR
Experiments; Wiley-VCH: Weinheim, 1998; pp 136-139.
(27) Brevard, C.; Granger, P. Handbook of High-Resolution Multinuclear
NMR; John Wiley & Sons: New York, 1981; p 43.
(19) Riche, C.; Chiaroni, A.; Gouedard, M.; Gaudemer, A. J. Chem. Res.,
Synop. 1978, 32-33.
(28) The temperature-dependence of the 59Co resonance frequency of
K3[Co(CN)6], νreference, was established so that the correction could
be applied at all temperatures.
(20) Hagen, K. I.; Schwab, C. M.; Edwards, J. O.; Sweigart, D. A. Inorg.
Chem. 1986, 25, 978-983.
(21) Hagen, K. I.; Schwab, C. M.; Edwards, J. O.; Jones, J. G.; Lawler, R.
G.; Sweigart, D. A. J. Am. Chem. Soc. 1988, 110, 7024-7031.
(22) Bang, H.; Edwards, J. O.; Kim, J.; Lawler, R. G.; Reynolds, K.; Ryan,
W. J.; Sweigart, D. A. J. Am. Chem. Soc. 1992, 114, 2843-2852.
(23) Medek, A.; Frydman, V.; Frydman, L. J. Phys. Chem. B 1997, 101,
8959-8966.
(29) The program PeakFit 4.0 (SPSS Inc., 444 N. Michigan Avenue,
Chicago, IL 60611) was used for all line shape analyses. Equation 2
is written with integrals because the convolution integrals lack real
closed form solutions. The analytical closed form complex solutions
are, however, used during fitting to give exact Voigt functions to at
least 14 significant figures.

Co(III) Porphyrins
Inorganic Chemistry, Vol. 40, No. 14, 2001 3305
11 showed some CSA17 effects (slight to moderate line shape distortion),
Voigt amplitude functions with variable width and shape parameters
were used to fit the NMR data. The intrinsic line widths for these two
derivatives were taken as the average width of the three (resolved) center
lines of the quintet in each case.
134.29 (o-C, TPP); 134.41 (γ-C, PhCH2CH2NH2); 135.08 (Cb, TPP);
140.35 (Cphenyl-Cm, TPP); 143.77 (Ca, TPP).
Synthesis of [Co(TPP)(1-MePipz)2](SbF6), 4. [Co(TPP)Cl] (100
mg, 0.15 mmol), AgSbF6 (224 mg, 0.65 mmol), and 1-methylpiperazine
(330 µL, 3.0 mmol) were reacted as described above. X-ray quality
crystals of the monohydrate, [Co(TPP)(1-MePipz)2](SbF6)‚H2O, were
grown from CH2Cl2/hexane over a period of 5 days in five 15 × 150
mm test tubes. Isolated yield: 53 mg, 32%. Anal. Calcd for C54H54N6-
OCoSbF6: C, 57.6; H, 4.8; N, 10.0. Found: C, 57.1; H, 4.6; N, 9.8.
IR (KBr pellet): 3234 cm-1 (w, ν(N-H)), 660 cm-1 (s, ν(Sb-F)).
UV-vis (CH2Cl2) [λmax, nm (ꢀ, M-1cm-1)]: 430 (266 × 103), 544 (12.6
Synthesis of [Co(TPP)(BzNH2)2](SbF6), 1. To [Co(TPP)Cl] (100
mg, 0.15 mmol) and AgSbF6 (58 mg, 0.17 mmol) in a two-neck 100-
mL round-bottom flask under nitrogen was added 50 mL of freshly
distilled THF. The solution was allowed to stir for ∼24 h at room
temperature prior to removing the solvent in Vacuo. The red-brown
solid, [Co(TPP)(FSbF5)], was redissolved in dichloromethane (∼20 mL)
and filtered under nitrogen. Addition of benzylamine (0.5 mL, 4.6
mmol) changed the solution from red-brown to purple on swirling. The
solution was transferred (∼2-mL aliquots) into ten 15 × 150 mm test
tubes; each aliquot was layered with hexane. X-ray quality crystals
were obtained after 5 days. Crystals of 1 were collected by filtration
and washed with 40% ethanol in hexane to remove yellow-brown
crystals of benzylamine. Isolated yield: 72 mg, 46%. Anal. Calcd for
C58H46N6CoSbF6: C, 62.1; H, 4.1; N, 7.5. Found: C, 61.8; H, 3.7; N,
7.4. IR (KBr pellet): 3309 cm-1, 3254 cm-1 (w, ν(N-H)), 1588 cm-1
(m, δ(NH2)), 1165 cm-1 (m, Ft(NH2)), 658 cm-1 (s, ν(Sb-F)). UV-
vis (CH2Cl2) [λmax, nm (ꢀ, M-1cm-1)]: 431 (238 × 103), 546 (12.2 ×
103), 577 (5.71 × 103). 1H NMR (499.98 MHz, CDCl3) [δ, ppm]: 9.17
(s, 8H, pyrrole-H); 8.15 (d, 3J ) 7.0 Hz, 8H, TPP o-H); 7.80 (m, 12H,
1
× 103), 578 (5.48 × 103). H NMR (499.98 MHz, CDCl3) [δ, ppm]:
3
4
9.24 (s, 8H, pyrrole-H); 8.19 (dd, J ) 7.6 Hz, J ) 1.7 Hz, 8H, TPP
o-H); 7.83 (m, 12H, TPP m,p-H); 0.94 (s, 6H, N-CH3); 0.44 (d, J )
13.4 Hz, 4H, â-CH2); -0.98 (t, J ) 11.8 Hz, 4H, â-CH2); -3.76 (m,
4H, R-CH2); -4.52 (d, J ) 12.6 Hz, 4H, R-CH2); -6.89 (t, 3J ) 11.8
Hz, 2H, NH). 13C NMR (125.736 MHz, CDCl3) [δ, ppm]: 43.83 (N-
CH3, 1-MePipz); 43.93 (â-C, 1-MePipz); 53.25 (R-C, 1-MePipz);
120.40 (Cm, TPP); 127.44 (m-C, TPP); 128.77 (p-C, TPP); 134.34 (o-
C, TPP); 135.86 (Cb, TPP); 139.73 (Cphenyl-Cm, TPP); 143.77 (Ca, TPP).
X-ray Structure Determinations. Intensity measurements were
made on air-stable crystals of compounds 1-4 that were platelike
lustrous purple rhombs with the approximate dimensions 0.6 × 0.5 ×
0.4 mm3, 0.6 × 0.5 × 0.2 mm3, 0.4 × 0.4 × 0.3 mm3, and 0.8 × 0.3
× 0.2 mm3 (needlelike), respectively. The X-ray diffraction data were
collected with a Siemens SMART 1000 CCD area detector diffracto-
meter at -100 °C with graphite-monochromated Mo KR radiation
(λh ) 0.71703 Å). Data were corrected for Lorentz and polarization
factors but not for absorption (µ ∼0.9 mm-1 for all four compounds).
A total of 28 493, 46 199, 28 353, and 50 381 observed reflections
(Fo g 2.0σ(Fo)) were collected and averaged to 5760, 5947, 12 360,
and 12 264 unique reflections for 1-4, respectively.
3
3
TPP m,p-H); 6.67 (t, J ) 7.7 Hz, 2H, BzNH2 p-H); 6.46 (t, J ) 7.7
3
Hz, 4H, BzNH2 m-H); 4.58 (d, J ) 7.7 Hz, 4H, BzNH2 o-H); -2.78
(t, J ) 7.0 Hz, 4H, R-CH2); -5.50 (t, J ) 7.0 Hz, 4H, NH2). 13C
NMR (125.736 MHz, CDCl3) [δ, ppm]: 41.62 (R-C, BzNH2); 119.76
(Cm, TPP); 125.47 (o-C, BzNH2); 127.28 (m-C, TPP); 127.53 (p-C,
BzNH2); 128.09 (m-C, BzNH2); 128.45 (p-C, TPP); 133.53 (â-C,
BzNH2); 134.18 (o-C, TPP); 135.48 (Cb, TPP); 140.09 (C phenyl-Cm,
TPP); 143.47 (Ca, TPP).
3
3
Synthesis of [Co(TPP)(1-BuNH2)2](SbF6), 2. A similar procedure
to that described above was employed using [Co(TPP)Cl] (100 mg,
0.15 mmol), AgSbF6 (74 mg, 0.22 mmol), and 1-butylamine (300 µL,
2.9 mmol). The reaction mixture was transferred in equal aliquots to
four 25 × 180 mm Schlenk tubes and layered with hexane. X-ray
quality crystals were obtained from the CH2Cl2/hexane mixture after 4
days. Isolated yield: 77.6 mg, 50%. Anal. Calcd for C52H50N6CoSbF6:
C, 59.3; H, 4.8; N, 8.0. Found: C, 59.2; H, 4.7; N, 7.8. IR (KBr
pellet): 3302 cm-1, 3258 cm-1 (w, ν(N-H)), 1584 cm-1 (m, δ(NH2)),
1100 cm-1 (m, Ft(NH2)), 655 cm-1 (s, ν(Sb-F)). UV-vis (CH2Cl2)
[λmax, nm (ꢀ, M-1cm-1)]: 430 (534 × 103), 545 (24.1 × 103), 580
Direct methods (SHELXS-97, OSCAIL V8)30,31 were used to solve
the structures of 1 and 2 in the orthorhombic space group Pbcn. The
structures of 3 and 4 were similarly solved in the monoclinic space
groups P21 and P21/c, respectively. Difference Fourier syntheses were
used to locate the remaining non-hydrogen atoms in each case. The
structures were refined anisotropically against F2 with SHELXL-97.32
A final difference Fourier synthesis for 1 located all of the hydrogens
atoms, including those of the coordinated amine nitrogens. In the case
of 2, the final difference Fourier synthesis located most of the hydrogen
atoms and indicated that the axial ligand methyl group (C(34)) was
disordered about two positions. The latter were refined as separate parts
to a final site occupancy factor of 0.718. In the case of 3, the final
difference Fourier synthesis located all of the porphyrin hydrogens and
suggested that one of the axial phenethylamine ligands had two
conformations that were related by a 43.3° rotation about the Co-
N(6) bond (measured by the N(1)-Co-N(6)-C(61) dihedral angle).
Both conformations were refined as separate parts (the final dihedral
angle between the disordered phenyl groups measured 21.1(9)°) to a
final site occupancy factor of 0.527. The absolute configuration of 3
could not be determined unambiguously from the value of the Flack
parameter.33 The final difference Fourier synthesis for 4 located all of
the porphyrin hydrogens as well as an oxygen atom of a water molecule
2.93 Å from the methylated nitrogen, N(6), of one of the axial
1-methylpiperazine ligands. With the exception of the hydrogen atoms
belonging to the solvate water of 4, all hydrogen atoms for the four
structures were included as idealized contributors in the least-squares
process with standard SHELXL-97 idealization parameters. The final
refinements converged to the discrepancy indices listed below. The
maximum (and minimum) electron densities on the final difference
Fourier maps of 1-4 were 0.446 (-0.623), 0.590 (-0.645), 0.350
(-0.475), and 2.541 (-1.311) e/Å3, respectively. The maximum residual
electron density peak, Q(1), of 2.541 e/Å3 in the difference Fourier
map of 4 was located 1.14 Å from N(6) and 2.00 Å from the oxygen
1
(10.1 × 103). H NMR (499.98 MHz, CDCl3) [δ, ppm]: 9.18 (s, 8H,
3
4
pyrrole-H); 8.17 (dd, J ) 7.4 Hz, J ) 1.7 Hz, 8H, o-H); 7.80 (m,
12H, m,p-H); -0.37 (t, 3J ) 7.4 Hz, 6H, CH3); -0.89 (m, 4H, γ-CH2);
-1.66 (m, 4H, â-CH2); -4.00 (m, 4H, R-CH2); -5.93 (t, 3J ) 5.8 Hz,
4H, NH2). 13C NMR (125.736 MHz, CDCl3) [δ, ppm]: 11.90 (δ-C,
1-BuNH2); 17.48 (γ-C, 1-BuNH2); 28.64 (â-C, 1-BuNH2); 37.10 (R-
C, 1-BuNH2); 119.93 (Cm, TPP); 127.24 (m-C, TPP); 128.41 (p-C, TPP);
134.22 (o-C, TPP); 135.18 (Cb, TPP); 140.40 (Cphenyl-Cm, TPP); 143.73
(Ca, TPP).
Synthesis of [Co(TPP)(PhCH2CH2NH2)2](SbF6), 3. [Co(TPP)Cl]
(100 mg, 0.15 mmol), AgSbF6 (142 mg, 0.41 mmol), and phenethyl-
amine (400 µL, 3.2 mmol) were reacted as described above. Test tubes
(15 × 150 mm) were used for crystallization; X-ray quality crystals
were obtained from CH2Cl2/hexane after 5 days. Isolated yield: 126.4
mg, 75%. Anal. Calcd for C60H50N6CoSbF6: C, 62.7; H, 4.4; N, 7.3.
Found: C, 62.3; H, 4.2; N, 7.2. IR (KBr pellet): 3307 cm-1, 3252
cm-1 (w, ν(N-H)), 1587 cm-1 (m, δ(NH2)), 1145 cm-1 (m, Ft(NH2)),
654 cm-1 (s, ν(Sb-F)). UV-vis (CH2Cl2) [λmax, nm (ꢀ, M-1cm-1)]:
429 (363 × 103), 544 (17.3 × 103), 577 (8.67 × 103). 1H NMR (499.98
3
MHz, CDCl3) [δ, ppm]: 9.13 (s, 8H, pyrrole-H); 8.08 (dd, J ) 6.6
4
3
Hz, J ) 1.7 Hz, 8H, o-H); 7.80 (m, 12H, m,p-H); 6.81 (t, J ) 7.4
3
Hz, 2H, PhCH2CH2NH2 p-H); 6.64 (t, J ) 7.8 Hz, 4H, PhCH2CH2-
3
NH2 m-H); 5.08 (d, J ) 7.0 Hz, 4H, PhCH2CH2NH2 o-H); -0.23 (t,
3J ) 6.6 Hz, 4H, â-CH2); -3.74 (t, J ) 7.0 Hz, 4H, R-CH2); -5.99
3
(30) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, A46, 467-473.
(31) McArdle, P. J. Appl. Crystallogr. 1995, 28, 65.
(32) Sheldrick, G. M.; Schneider, T. R. Methods Enzymol. 1997, 277, 319-
343.
(t, 3J ) 6.2 Hz, 4H, NH2). 13C NMR (125.736 MHz, CDCl3) [δ, ppm]:
32.07 (â-C, PhCH2CH2NH2); 37.83 (R-C, PhCH2CH2NH2); 119.98 (Cm,
TPP); 126.23 (p-C, PhCH2CH2NH2); 126.54 (o-C, PhCH2CH2NH2);
127.11 (m-C, TPP); 128.12 (m-C, PhCH2CH2NH2); 128.37 (p-C, TPP);
(33) Flack, H. D. Acta Crystallogr., Sect. A 1983, A39, 876-881.

3306 Inorganic Chemistry, Vol. 40, No. 14, 2001
Munro et al.
atom, O(1), of the water molecule H-bonded to N(6). Since the angles
C(52)-N(6)-Q(1) (102.7°) and C(53)-N(6)-Q(1) (139.5°) were
inconsistent with those for an sp3-hybridized quaternary nitrogen (e.g.,
a protonated nitrogen), the peak was not assigned to any specific atom.
Complete crystallographic details, fractional atomic coordinates for
all non-hydrogen atoms, anisotropic thermal parameters, fixed hydrogen
atom coordinates, bond lengths, bond angles, and dihedral angles for
compounds 1-4 are given in the Supporting Information (Tables S1-
S28). Experimental lattice constants and SHELXL-97 refinement
parameters for the four compounds are given below.
[Co(TPP)(BzNH2)2](SbF6). C58H46N6CoSbF6, fw ) 1121.69 amu,
a ) 17.0323(8) Å, b ) 12.2935(6) Å, c ) 23.4079(11) Å, V ) 4901.3-
(4) Å3, orthorhombic, Pbcn, Z ) 4, Dc ) 1.520 g cm-3, µ ) 0.959
mm-1, T ) 173(2) K, R1 (wR2)34 ) 0.0342 (0.0759) for 4922 unique
data with I > 2σ(I), R1 (wR2) ) 0.0433 (0.0803) for all 5760 data (Rint
) 0.0347).
time steps. Data were collected at 7.5 fs intervals, affording 6.8 × 104
snapshots. At least four simulations, starting from unique input
coordinates, were used to check the generality of the results in each
case. The data were reduced for plotting by using a 75 fs sampling
interval for the analysis of each MD trajectory.
DFT Calculations. DFT calculations (pseudospectral method,44
B3LYP functional,45 LACVP basis set,46 medium grid) were performed
with Jaguar 4.047 running on a Compaq AlphaStation DS20e. The
LACVP basis set employs effective core potentials for the elements
K-Cu, Rb-Ag, Cs-La, and Hf-Au. Second and third row s- and
p-block elements are described by Pople’s 6-31G48 basis set. Input
coordinates for all [Co(TPP)(L)2]+ cations were energy minima obtained
from MM geometry optimizations in the gas phase. In the case of [Co-
(TPP)Cl], the X-ray coordinates49 were used as a starting structure for
a full geometry optimization at the B3LYP/LACVP level of theory.
The converged DFT wave functions for each complex were analyzed
with Weinhold’s NBO 4.M program50 which uses the first-order reduced
density matrix of the wave function to obtain natural atomic orbitals
(NAOs) and natural electron populations for the system.
[Co(TPP)(1-BuNH2)2](SbF6). C52H50N6CoSbF6, fw ) 1053.66 amu,
a ) 16.2614(9) Å, b ) 12.7546(7) Å, c ) 23.2873(12) Å, V )
4830.0(5) Å3, orthorhombic, Pbcn, Z ) 4, Dc ) 1.449 g cm-3, µ )
0.968 mm-1, T ) 173(2) K, R1 (wR2)34 ) 0.0593 (0.0857) for 4579
unique data with I > 2σ(I), R1 (wR2) ) 0.0868 (0.0930) for all 5947
data (Rint ) 0.0725).
Results
[Co(TPP)(PhCH2CH2NH2)2](SbF6). C60H50N6CoSbF6, fw ) 1149.74
amu, a ) 10.6378(5) Å, b ) 22.0466(11) Å, c ) 10.9585(5) Å, â )
94.2140(10)°, V ) 2563.1(2) Å3, monoclinic, P21, Z ) 2, Dc ) 1.490
g cm-3, µ ) 0.919 mm-1, T ) 173(2) K, R1 (wR2)34 ) 0.0334 (0.0708)
for 11393 unique data with I > 2σ(I), R1 (wR2) ) 0.0388 (0.0746) for
all 12360 data (Rint ) 0.0255).
Crystal Structures. The molecular structures of 2 and 4 are
shown in the ORTEP51 plots of Figure 1. Formal diagrams of
the porphinato cores of the two derivatives are shown in Figure
2; the perpendicular displacement of each crystallographically
(39) The following parameters were developed for bis(amine) Co(III)
porphyrins using the X-ray structures of 1-4 and [Co(TPP)(Pip)2]-
(NO3)18 for parametrization. Bond deformation: bond, ks (mdyn Å-1),
l0 (Å); Np-Co(III), 2.000, 1.892; Nax-Co(III), 2.650, 1.927. Bond
angle deformation: angle, kθ (mdyn Å rad-2), θ0 (deg); trans-Np-
Co(III)-Np, 0.005, 180.0; cis-Np-Co(III)-Np, 0.200, 90.0; Np-Co-
(III)-Nax, 1.250, 90.0; Nax-Co(III)-Nax, 1.000, 180.0; Ca-Np-
Co(III), 0.700, 126.8; C(sp3)-Nax-Co(III), 0.600, 124.0; H-Nax-
Co(III), 0.400, 109.47; C(sp3)-Nax-C(sp3), 0.630, 111.7. Dihedral
angle deformation: dihedral angle, V1, V2, V3 (kcal mol-1); Ca-Np-
Co(III)-Np (Np-Co(III)-Np trans), 0.000, 0.000, 0.000; Ca-Np-
Co(III)-Np (Np-Co(III)-Np cis), 0.000, 0.100, 0.000; Co(III)-Nax-
C(sp3)-H, 0.000, 0.000, 0.520; Co(III)-Nax-C(sp3)-C(sp3), -0.200,
0.730, 0.800; Co(III)-Nax-C(sp3)-C(sp2), 0.000, 0.000, 0.000; Np-
Co(III)-Nax-C(sp3), 0.000, 0.000, 0.000; Np-Co(III)-Nax-H, 0.000,
0.000, 0.000; Nax-Co(III)-Nax-H, 0.000, 0.000, 0.000; C(sp2)-
C(sp2)-C(sp3)-Nax, 0.000, 0.000, 0.000; Cb-Ca-Np-Co(III), 0.000,
0.100, 0.000; Cm-Ca-Np-Co(III), 0.000, 0.200, 0.000. Out-of-plane
deformation: sp2-hybridized-attached atom, koop (mdyn Å rad-2); Np-
Co(III), 0.050; Ca-Np, 0.050.
[Co(TPP)(1-MePipz)2](SbF6)‚H2O. C54H54N8OCoSbF6, fw ) 1125.70
amu, solvent/asymmetric unit ) H2O, a ) 13.4112(9) Å, b )
19.0611(12) Å, c ) 19.6630(13) Å, â ) 93.2450(10)°, V ) 5018.4(6)
Å3, monoclinic, P21/c, Z ) 4, Dc ) 1.487 g cm-3, µ ) 0.939 mm-1
,
T ) 173(2) K, R1 (wR2)34 ) 0.0951 (0.2360) for 7271 unique data
with I > 2σ(I), R1 (wR2) ) 0.1547 (0.2759) for all 12264 data (Rint
)
0.0868).
Molecular Mechanics Calculations. HyperChem 5.02 (MM+ force
field)35 was used for all calculations. Porphyrin core parameters were
taken from our published force field for iron porphyrins.36-38 New bond
stretching, angle bending, and dihedral angle parameters for bis(amine)
cobalt(III) derivatives were developed by fitting the structures of 1-4
and [Co(TPP)(Pip)2](NO3),18 calculated in the presence of all lattice
neighbors, to their X-ray structures.39 A root-mean-square gradient
termination cutoff of 0.005 kcal/(Å mol) was used for geometry
optimization with the Polak-Ribiere conjugate gradient algorithm. A
dielectric constant of 1.5 D was employed for all calculations. The
vacuum dielectric constant (1.0 D) was not used because even in the
gas-phase some screening of intramolecular dipolesdipole interactions
occurs.40,41 Partial atomic charges were not included in the calcula-
tions.38,42,43 Conformational surfaces for [Co(TPP)(1-BuNH2)2]+, [Co-
(TPP)(1-MePipz)2]+, and [Co(TPP)(Et2NH)2]+ were calculated as
described previously.9
Molecular Dynamics Simulations. HyperChem 5.02 was used for
gas-phase MD simulations of [Co(TPP)(1-BuNH2)2]+, [Co(TPP)-
(BzNH2)2]+, [Co(TPP)(PhCH2CH2NH2)2]+, [Co(TPP)(1-MePipz)2]+,
and [Co(TPP)(Et2NH)2]+ at a constant temperature of 298 K with a
bath relaxation constant of 0.1 ps. A heating time of 10 ps was used to
heat the system from 0 to 298 K in 5 K increments. This was followed
by a 500 ps simulation interval at the set temperature employing 0.5 fs
(40) (a) Allinger, N. L. J. Am. Chem. Soc. 1977, 99, 8127. (b) Allinger, N.
L.; Yuh, Y. MM2(87). Distributed to academic users by QCPE, under
special agreement with Molecular Design Ltd., San Leandro, CA. (c)
Sprague, J. T.; Tai, J. C.; Young, Y.; Allinger, N. L. J. Comput. Chem.
1987, 8, 581.
(41) Jensen, F. Introduction to Computational Chemistry; Wiley: New
York, 1999; pp 23-25.
(42) Shelnutt, J. A.; Medforth, C. J.; Berber, M. D.; Barkigia, K. M.; Smith,
K. M. J. Am. Chem. Soc. 1991, 113, 4077-4087.
(43) The force field includes the standard MM240 bond dipoles for the C-C
and C-N bonds. All M-L bond dipoles have an assigned value of
zero.
(44) Jaguar47 solves the Schro¨dinger equation iteratively using SCF methods
to calculate the lowest-energy wave function within the space spanned
by the basis set. The fundamental integrals are, however, computed
in physical space on a grid rather than in the spectral space defined
by the basis functions, affording a sizable speed increase for large
systems. (a) Friesner, R. A. Chem. Phys. Lett. 1985, 116, 39. (b)
Friesner, R. A. Annu. ReV. Phys. Chem. 1991, 42, 341.
(34) R1 ) ∑||Fo| - |Fc||/∑|Fo| and wR2 ) {∑[w(Fo2 - Fc )2]/∑[wFo ]}1/2
.
2
4
R factors R1 are based on F, with F set to zero for negative F2. The
criterion of F2 > 2σ(F2) was used only for calculating R1. R factors
based on F2 (wR2) are statistically about twice as large as those based
on F.
(45) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(46) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299-310.
(47) Jaguar, version 4.0; Schro¨dinger, Inc.: Portland, OR, 2000.
(48) (a) Rassolov, V. A.; Pople, J. A.; Ratner, M. A.; Windus, T. L. J.
Chem. Phys. 1998, 109, 1223. (b) Francl, M. M.; Pietro, W. J.; Hehre,
W. J.; Binkley, J. S.; Gordon, M. S.; DeFrees, D. J.; Pople, J. A. J.
Chem. Phys. 1982, 77, 3654-3665.
(49) Sakurai, T.; Yamamoto, K.; Naito, H.; Nakamoto, N. Bull. Chem. Soc.
Jpn. 1976, 49, 3042-3046.
(50) Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J. E.;
Weinhold, F. NBO 4.M; Theoretical Chemistry Institute, University
of Wisconsin: Madison, WI, 1999.
(35) HyperChem, version 5.02: Hypercube, Inc.: Gainsville, FL.
(36) Munro, O. Q.; Bradley, J. C.; Hancock, R. D.; Marques, H. M.;
Marsicano, F.; Wade, P. W. J. Am. Chem. Soc. 1992, 114, 7218-
7230.
(37) Marques, H. M.; Munro, O. Q.; Grimmer, N. E.; Levendis, D. C.;
Marsicano, F.; Pattrick, G.; Markoulides, T. J. Chem. Soc., Faraday
Trans. 1995, 91, 1741-1749.
(38) Munro, O. Q.; Marques, H. M.; Debrunner, P. G.; Mohanrao, K.;
Scheidt, W. R. J. Am. Chem. Soc. 1995, 117, 935-954.

Co(III) Porphyrins
Inorganic Chemistry, Vol. 40, No. 14, 2001 3307
Figure 2. Formal diagrams of the porphyrin cores of (a) [Co(TPP)-
(1-BuNH2)2](SbF6) and (b) [Co(TPP)(1-MePipz)2](SbF6)‚H2O. Aver-
aged values (and their esd’s) of the chemically unique bond distances
(in Å) and angles (in degrees) are shown. The perpendicular displace-
ments (in units of 0.01 Å) of the cobalt and 24 porphyrin core atoms
from the porphyrin mean plane are also displayed. The dihedral angles
(deg) of the axial ligands (Np-Co-Nax-CR) are indicated by the solid
and dashed lines for the above- and below-plane ligands, respectively.
Figure 1. ORTEP diagrams (displaying selected atom labels) of the
low-temperature X-ray structures (-100 °C) of (a) [Co(TPP)(1-BuNH2)2]-
(SbF6) and (b) [Co(TPP)(1-MePipz)2](SbF6)‚H2O. Thermal ellipsoids
are drawn at the 50% probability level. Hydrogen atoms, SbF6- anions,
and a solvent water molecule in (b) have been omitted for clarity.
The crystal structure of 2 is centrosymmetric and, to a large
extent, representative of the conformations of the three bis(1°
amine) derivatives of this study; each has a relatively planar
porphyrin core conformation (Figures 2 and S2) and axial amine
orientations that reflect either the crystallographically required
center of inversion at the cobalt(III) ion or, in the case of 3, an
approximately centrosymmetric cation. The Co-Nax distance
in 2 is 1.980(2) Å; the Co-Np distances average to 1.987(4)
Å. The butylamine ligands exhibit an anti arrangement with a
symmetry-unique orientation of 30.2(2)° relative to the nearest
Co-Np vector (N(2)-Co-N(3)-C(31) dihedral angle). The two
Co-Nax vectors are slightly canted from the heme normal with
individual Np-Co-N(3) angles spanning the range 88.2(1)-
91.8(1)°. The Co-N(3)-C(31) angle measures 121.0(2)°. The
dihedral angles between the phenyl rings appended to C(m1)
and C(m2) and the 24-atom porphyrin mean plane are 69.4(1)°
and 73.3(1)°, respectively. As noted above, the structure of 2
is exemplary of the bis(1° amine) derivatives; the rather similar
coordination group distances and angles for 1 and 3 are therefore
given in Table 1 without further comment. One noteworthy
difference between the structure of 2 and the structures of
compounds 1 and 3 is the absence of H-bonding interactions
between the SbF6- anion and the axial ligand NH2 protons. As
unique atom from the 24-atom porphyrin mean plane and the
averaged values of the chemically unique bond distances and
angles are displayed in each case. The orientations of the axial
ligands relative to the Co-Np bonds are also shown. (Selected
bond distances and angles for compounds 1-4 are given in
Table 1; the average absolute perpendicular displacements of
the chemically unique atoms of the porphyrin core from the
24-atom mean plane are given in Table 2.) ORTEP plots and
formal diagrams of the porphinato cores of 1 and 3 are given
in the Supporting Information (Figures S1 and S2, respectively).
Complete listings of structural data (bond lengths, bond angles,
and dihedral angles) for compounds 1-4 are given in the
Supporting Information (Tables S3-S5, S10-S12, S17-S19,
and S24-S26).
(51) ORTEP-3 for Windows, v1.05. (Farrugia, L. J. J. Appl. Crystallogr.
1997, 30, 565.) This program is based on ORTEP-III, v1.02. (Burnett,
M. N.; Johnson, C. K. Oak Ridge National Laboratory report ORNL-
6895, 1996.)

3308 Inorganic Chemistry, Vol. 40, No. 14, 2001
Munro et al.
Table 1. Selected Bond Lengths and Bond Angles for [Co(TPP)(1-BuNH2)2](SbF6), [Co(TPP)(BzNH2)2](SbF6),
[Co(TPP)(PhCH2CH2NH2)2](SbF6), and [Co(TPP)(1-MePipz)2](SbF6)‚H2O
[Co(P)(L1)2]Xa,b
[Co(P)(L2)2]Xa,c
[Co(P)(L3)2]Xa,d
[Co(P)(L4)2]Xa,e
Co-N(1)
Co-N(2)
Co-N(3)
1.995(2)
1.979(2)
1.983(2)
1.986(2)
1.988(2)
1.982(2)
1.986(2)
1.972(2)
1.983(2)
1.994(5)
1.976(4)
1.971(4)
1.997(5)
2.039(5)
2.041(5)
(B) bond angles (deg)f
N(1)-Co-N(1)g
N(2)-Co-N(2)g
N(3)-Co-N(3)g
N(2)-Co-N(3)
N(2)g-Co-N(3)
N(2)-Co-N(3)g
N(2)g-Co-N(3)g
N(2)-Co-N(1)
N(2)g-Co-N(1)
N(2)-Co-N(1)g
N(2)g-Co-N(1)g
N(3)-Co-N(1)
N(3)g-Co-N(1)
N(3)-Co-N(1)g
N(3)g-Co-N(1)g
180.0(0)
180.0(0)
180.0(0)
88.7(1)
91.3(1)
91.3(1)
88.7(1)
89.8(1)
90.2(1)
90.2(1)
89.8(1)
91.3(1)
88.7(1)
88.7(1)
89.8(1)
180.0(1)
N(3)-Co-N(1)
N(4)-Co-N(2)
N(5)-Co-N(6)h
N(5)-Co-N(3)
N(3)-Co-N(6)h
N(5)-Co-N(1)
N(6)h-Co-N(1)
N(5)-Co-N(4)
N(3)-Co-N(4)
N(6)h-Co-N(4)
N(1)-Co-N(4)
N(5)-Co-N(2)
N(3)-Co-N(2)
N(6)h-Co-N(2)
N(1)-Co-N(2)
179.8(1)
179.8(1)
179.4(1)
94.0(1)
86.1(1)
85.9(1)
94.0(1)
90.0(1)
89.9(1)
89.4(1)
90.3(1)
89.9(1)
90.1(1)
90.7(1)
89.7(1)
179.7(2)
178.7(2)
177.5(2)
91.3(2)
91.1(2)
88.5(2)
89.1(2)
87.5(2)
90.2(2)
92.2(2)
90.1(2)
91.3(2)
89.6(2)
89.1(2)
90.1(2)
180.0(1)
180.0(2)
91.8(1)
88.2(1)
88.2(1)
91.8(1)
90.1(1)
89.9(1)
89.9(1)
90.1(1)
90.4(1)
89.6(1)
89.6(1)
90.4(1)
a X ) SbF6, P ) TPP. b L1 ) benzylamine. c L2 ) 1-butylamine. d L3 ) phenethylamine. e L4 ) 1-methylpiperazine. f The estimated standard
deviations of the least significant digits are given in parentheses. g Symmetry equivalent (-x,-y, -z). h N(7) in the case of [Co(TPP)(1-
MePipz)2](SbF6)‚H2O.
Table 2. Selected Crystallographic and MM-Calculated Conformational Data for Bis(amine)(meso-tetraphenylporphinato)Co(III) Derivatives
[Co(TPP)(L1)2]Xa
X-ray latticeb gasc
[Co(TPP)(L2)2]Xa
X-ray
latticeb gasc
[Co(TPP)(L3)2]Xa
X-ray latticeb gasc
[Co(TPP)(L4)2]X‚H2Oa
X-ray
latticeb gasc
[Co(TPP)(L5)2]Y‚Pipa
X-rayd latticeb gasc
e
Co-Nax 1.980(2) 1.976(0) 1.971(0) 1.983(2) 1.978(0) 1.969(0) 1.978(8) 1.975(1) 1.984(0) 2.040(1) 2.054(4) 2.028(0) 2.060(3) 2.061(2) 2.047(0)
f
Co-Np 1.987(4) 1.988(5) 1.986(3) 1.987(11) 1.986(5) 1.986(3) 1.986(3) 1.987(3) 1.987(4) 1.985(13) 1.982(7) 1.973(3) 1.979(6) 1.987(4) 1.987(0)
φg
30.2(2) 33.5(1) 0(0)
38.4(2) 33(1)
0(0)
28.7(8) 27.3(8) 8(2)
18.3(2) 19.7(0) 21.4(0) 23.1(2) 20(4)
46.1(2) 39.8(0) 21.2(0)
21.7(1)
h
|Co|
3
0
0
2
1
0
1
0
0
0
1
0
0
1
0
h
|Np|
2(2)
2(0)
1(1)
1(1)
2(1)
71(2)
3(2)
1(1)
2(1)
1(0)
2(1)
77(3)
0.054
0.266
0(0)
0(0)
1(0)
1(0)
1(0)
2(1)
2(1)
3(2)
3(3)
2(2)
6(4)
3(2)
5(4)
6(3)
5(3)
1(0)
0(0)
1(0)
1(0)
1(0)
2(2)
5(3)
11(3)
6(4)
6(5)
4(2)
3(1)
7(4)
4(2)
5(3)
81(4)
0.040
0.364
5(2)
2(2)
4(3)
5(4)
4(3)
87(1)
0.096
0.599
4(2)
6(5)
10(9)
28(10) 14(0)
19(4) 42(1)
16(12) 18(13) 5(3)
69(13) 89.9(0) 67(3)
0.068
0.194
0(0)
21(0)
3(3)
4(2)
6(2)
6(4)
3(2)
3(3)
5(3)
7(3)
4(3)
73(4)
0.032
0.163
0(0)
0(0)
0(0)
1(1)
0(0)
89.7(1)
0.056
0.475
h
|Ca|
|Cb|
|Cm|
11(7)
21(9)
20(2)
14(9)
67(11)
h
h
h
|Dav|
i
øav
89.4(1) 73.8(3) 78.8(6) 89.6(2) 68(6)
0.034
0.485
rmsd Aj
rmsd Bk
0.078
0.218
0.047
0.722
0.161
0.688
a L1 ) 1-butylamine, L2 ) benzylamine, L3 ) phenethylamine, L4 ) 1-methylpiperazine, L5 ) piperidine, X ) SbF6, Y ) NO3. b Calculation
f
on a single molecule with all nearest neighbors. c Gas-phase calculation. d Ref 18. e Mean axial Co-N distance (Å). Mean equatorial Co-N distance
(Å). g Mean axial ligand orientation (deg) defined as the dihedral angle between the axial ligand R-carbon and the closest porphyrin nitrogen.
h
|Co|, |Np|, |Ca|, |Cb|, and |Cm| are the mean absolute perpendicular displacements (in units of 0.01 Å) of the Co(III) ion, porphyrin nitrogens, R-,
i
â-, and meso-carbons, respectively, from the 24-atom porphyrin mean plane; |Dav| is the average for all atoms. øav, mean porphyrin core-phenyl
group dihedral angle (deg). j Root-mean-square difference (Å) for a fit of the calculated and observed structures (Co(III) ion, 24 porphyrin core
atoms, and axial nitrogens). k Root-mean-square difference (Å) for a fit of the calculated and observed structures (all atoms).
shown in the edge-on ORTEP diagram of Figure 3, both protons
of the NH2 group of the uppermost phenethylamine ligand of 3
(i.e., that coordinated to Co via N(5) in Figure S1) are hydrogen
bonded to a pair of cis fluorine atoms of the closely juxtaposed
SbF6 anion. Similar H-bonding interactions involving one of
the two NH2 protons are observed for 1 (Figure S3).
distances average to 2.040(1) Å, substantially longer than the
mean Co-Nax distances of the bis(1° amine) complexes. The
mean Co-Np distance is 1.985(13) Å. The Co-Nax vectors are
slightly tipped relative to the heme normal; individual Np-Co-
Nax angles span the range 87.5(2)-92.2(2)°. The modest off-
axis tilt of the axial donor atoms is also evident from the Nax-
Co-Nax angle of 177.5(2)°. The mean Co-Nax-CR angle is
116.8(5)°. The axial ligand orientations, measured by the Np-
Co-Nax-CR dihedral angles, are 7.1(4)° (N(4)-Co-N(7)-
C(61)), 43.5(5)° (N(3)-Co-N(7)-C(64)), 18.3(4)° (N(3)-Co-
N(5)-C(51)), and 21.7(4)° (N(2)-Co-N(5)-C(54)). The
dihedral angles between the four meso-phenyl groups and the
24-atom porphyrin mean plane measure 60.6(2), 82.8(2), 60.5(1),
and 64.2(2)° for the phenyl rings attached to Cm(1) through
Cm(4), respectively. Both the meso-carbons and the four pairs
of â-carbons of the porphyrin macrocycle are alternately
-
The noncentrosymmetric crystal structure of 4 is more
unusual. The axial 1-methylpiperazine ligands adopt a staggered
arrangement over the porphyrin core which is clearly nonplanar.
The NH proton of the uppermost ligand in Figure 1 is hydrogen
-
bonded to a fluorine atom of the SbF6 anion. The distances
and angle of the interaction are F(5)‚‚‚H(7) ) 2.258 Å, F(5)‚
‚‚N(7) ) 3.173 Å, and F(5)‚‚‚H(7)-N(7) ) 167.8° (Figure 3).
A solvate water molecule is hydrogen bonded to the noncoor-
dinated nitrogen atom, N(6), of the trans 1-methylpiperazine
ligand. The distance, N(6)‚‚‚O(1), is 2.928 Å. The Co-Nax

Co(III) Porphyrins
Inorganic Chemistry, Vol. 40, No. 14, 2001 3309
ppm), and 3.17(4) ppm/°C (8586(1) ppm) for [Co(TPP)Cl], 6,
5, 7, 10, and 11, respectively. As shown in Figures 4 and 5, the
59Co line widths also decrease rather markedly with increasing
temperature. The narrowest lines were observed for 10 (3.9(6)-
6.5(9) × 102 Hz over the temperature range 55.1-1.4 °C). Line
widths for 7 were the broadest, ranging from 3.3(0) × 103 Hz
at 37.2 °C to 1.3(2) × 104 Hz at -34.5 °C. Both 8 and 9 were
NMR-silent on the 59Co NMR time scale, irrespective of the
width of the spectral window used for data acquisition or the
solution temperature. The 1H and 13C spectra of these derivatives
were, however, normal. The complexes with intrinsically narrow
line widths, namely 6, 10, and 11, showed strong 59Co-14N
spinsspin coupling between the cobalt and axially coordinated
nitrogen nuclei, as evidenced by the emerging quintet pattern
at higher temperatures for the 59Co resonance of 6 in Figure 4.
1
The value of JCo-N measured 600(5) Hz in each case. The
sterically hindered secondary amine derivatives 10 and 11 each
showed an additional signal due to the mixed-ligand intermedi-
ate, [Co(TPP)(R2NH)Cl], even with a large excess of ligand
present.
Molecular Mechanics Calculations. New M-L force field
parameters were developed for bis(amine) complexes of Co(III)
porphyrins using the four X-ray structures of this study and that
of [Co(TPP)(Pip)2](NO3)18 for parametrization. Two types of
calculation were performed for each complex: (1) a gas-phase
geometry optimization on the isolated [Co(TPP)(L)2]+ cation;
(2) a geometry optimization on a single [Co(TPP)(L)2]+ cation
within its lattice environment. In the latter case, the lattice subset
modeled comprised all neighboring cations, anions, and solvate
molecules (when present). Since these calculations were com-
putationally expensive (>5000 atoms), an initial parameter set
was developed by comparison of the calculated gas phase
conformations with the X-ray structures. Final adjustments to
the M-L interaction parameters of the force field were made
by comparing the structures calculated in the presence of all
lattice neighbors with those observed crystallographically.
Metrical data comparing the calculated and X-ray coordina-
tion sphere geometries, ligand orientations, porphyrin core
conformations, and meso-phenyl group orientations of 1-4 and
[Co(TPP)(Pip)2](NO3) are given in Table 2. Figure 6 depicts
these data more graphically for one of the five compounds by
showing least-squares fits of the MM-calculated (gas phase and
solid state) and crystallographically observed structures of 4.
The results collectively demonstrate that the calculated gas phase
structures fit the X-ray structures poorly on the whole. The best
(rmsd ) 0.034 Å) and poorest (rmsd ) 0.161 Å) fits were for
[Co(TPP)(1-BuNH2)2]+ and [Co(TPP)(1-MePipz)2]+, respec-
tively. The largest deviations between theory and experiment
are for the Co-Nax distances, axial ligand and meso-phenyl
group orientations, and, in the case of the nonplanar derivative
4, the porphyrin core conformation. Significantly improved fits
of the X-ray structures were obtained when a full set of nearest
neighbors to the [Co(TPP)(L)2]+ cation selected for geometry
optimization were included in the calculation; rmsd’s ranged
from 0.032 Å for [Co(TPP)(Pip)2](NO3) to 0.078 Å for 1.
Figure 3. ORTEP diagrams (50% probability surfaces for all non-H
atoms) showing the intermolecular hydrogen bonding interactions in
edge-on views (parallel to the N(1)-Co-N(2) planes) of (a) [Co(TPP)-
(PhCH2CH2NH2)2](SbF6) and (b) [Co(TPP)(1-MePipz)2](SbF6)‚H2O.
displaced above and below the porphyrin mean plane (Figure
2, Table 2).
1
NMR Spectroscopy. The H and 13C NMR spectra of 1-4
were consistent with the NMR spectra reported for other bis-
(amine) low-spin d6 Co(III) porphyrins.12-14 (Assigned high-
resolution 1H and 13C spectra of 1 are illustrated for complete-
ness in Figure S4.) The narrow line widths and resolved triplet
patterns observed for the NH2 protons of 1-3 (3JNH -CH ) 5.8-
2
2
7.0 Hz) and the NH proton of 4 (3JNH-CH ) 11.8 Hz) indicate
2
that both the spin-spin relaxation rate and the rate of axial
ligand exchange are slow on the 500 MHz NMR time scale for
this class of compounds.
Figure 7 compares gas phase conformational energy surfaces
for [Co(TPP)(1-BuNH2)2]+ and [Co(TPP)(Et2NH)2]+ as plots
of the change in total steric energy with axial ligand orientation.
Similar plots for [Co(TPP)(1-MePipz)2]+ are given in the
Supporting Information (Figure S5). The data for [Co(TPP)-
(Et2NH)2]+ are included in Figure 7 even though we have not
determined the X-ray structure of this complex because the
conformational surface, population distribution, and energy
minima are directly relevant to our interpretation of the 59Co
Figure 4 shows selected 59Co NMR spectra for compound 6
as a function of temperature. The 59Co chemical shifts of 5-7,
10, and 11 all exhibit a linear increase (decrease in shielding)
with increasing temperature (Figure 5, Table S29). The temp-
erature coefficients (and intercepts) are 3.50(4) ppm/°C (8163(2)
ppm), 3.72(2) ppm/°C (8132.6(7) ppm), 2.75(5) ppm/°C (8322(1)
ppm), 3.21(6) ppm/°C (8383(2) ppm), 2.88(1) ppm/°C (8623.6(5)

3310 Inorganic Chemistry, Vol. 40, No. 14, 2001
Munro et al.
Figure 4. Selected 59Co NMR spectra of [Co(TPP)(BzNH2)2]Cl at different temperatures in 50% (v/v) ligand/CDCl3 solution.
axial ligands adopt an anti arrangement (∆φ ) 180°) over a
trans pair of Co-Np bonds (e.g., φ1, φ2 ) 0°, 180°; ∆UT )
0.03 kcal/mol) and (2) when the axial ligands are exactly
eclipsed (∆φ ) 0°) and lie directly over a single Co-Np bond,
e.g., φ1, φ2 ) 0°, 0° (∆UT ) 0.16 kcal/mol). In each case, the
R-CH2 protons of the ligands are staggered relative to the pyrrole
nitrogens (H‚‚‚Np ∼2.8 Å).53
The steric energy changes for [Co(TPP)(Et2NH)2]+ are ∼7.5
times larger (∆UTmax ∼7.5 kcal/mol) than those for [Co(TPP)-
(1-BuNH2)2]+ (Figure 7), consistent with the increased steric
bulk of the axial ligands. Three types of low-energy conforma-
tions exist for the Et2NH derivative. The N-H bonds of the
axial ligands are staggered (90° apart) and are positioned over
the bisectors of adjacent cis-Np-Co-Np angles in the lowest-
energy S4-ruffled conformations (∆UT ) 0 kcal/mol, e.g., φ1,
φ2 ) 121°, 344°). The first type of local minimum (∆UT ∼3.2
kcal/mol, e.g., φ1, φ2 ) 209°, 344°) has a planar porphyrin core
conformation and exact inversion symmetry (Ci); the N-H
bonds of the axial ligands adopt an anti arrangement (180° apart)
and lie over the bisector of a cis-Np-Co-Np angle. In the
second type of local minimum (∆UT ∼3.3 kcal/mol, e.g., φ1,
φ2 ) 210°, 165°) the N-H bonds of the axial ligands are
eclipsed and lie over the bisector of a cis-Np-Co-Np angle
(planar porphyrin core). For all low-energy conformations, the
axial pairs of R-CH2 protons of the ligands point toward a pair
of cis porphyrin nitrogens, favoring longer nonbonded contacts
(H‚‚‚Np ∼2.7 Å) than for the higher energy conformations.54
Molecular Dynamics Calculations. Scatter plots showing
the axial ligand orientations, φ1 and φ2, for 6800 snapshots
(0.075 ps sampling interval) taken during a typical 500 ps
constant temperature (298 K) MD simulation for [Co(TPP)(1-
BuNH2)2]+ and [Co(TPP)(Et2NH)2]+ are given in Figure 7. For
Figure 5. Plot of the variation of 59Co chemical shift with temperature
(top) and the log of the 59Co line width, log(ω1/2), with reciprocal
temperature (bottom) for five [Co(TPP)(amine)2]Cl derivatives.
(52) Scheidt, W. R.; Lee, Y. J. Struct. Bonding 1987, 64, 1-70.
(53) Three unique types of high-energy conformation (energy differences
> 0.02 kcal/mol) exist for [Co(TPP)(1-BuNH2)2]+: (1) conformations
with staggered axial ligands (relative orientations, ∆φ, of 90°)
positioned approximately over adjacent porphyrin meso-carbons, e.g.,
φ1, φ2 ) 45°, 225° (∆UT ) 0.96 kcal/mol), (2) conformations with
an anti axial ligand arrangement (∆φ ) 180°) over the bisector of a
cis-Np-Co-Np angle, e.g., φ1, φ2 ) 45°, 135° (∆UT ) 1.05 kcal/
mol), and (3) conformations with an eclipsed axial ligand arrangement
(∆φ ) 0°) over the bisector of a cis-Np-Co-Np angle, e.g., φ1, φ2 )
45°, 315° (∆UT ) 1.23 kcal/mol). In each case, the R-CH2 protons of
the butylamine ligands point at adjacent pyrrole nitrogens (H‚‚‚Np ∼2.6
Å).
NMR spectra of [Co(TPP)(Et2NH)2]Cl and the other bis(amine)
derivatives of this study.
Three types of low-energy conformation were found for [Co-
(TPP)(1-BuNH2)2]+. The lowest energy conformers (∆UT ) 0
kcal/mol) have staggered axial ligands (∆φ ) 90°) positioned
directly over a cis pair of Co-Np bonds, e.g., φ1, φ2 ) 0°, 90°.
The remaining two types of local minimum occur (1) when the

Co(III) Porphyrins
Inorganic Chemistry, Vol. 40, No. 14, 2001 3311
(e.g., φ1, φ2 ) 90°, 135°). High energy conformations of [Co-
(TPP)(1-BuNH2)2]+ (e.g., φ1, φ2 ) 45°, 225°) are only oc-
casionally populated. In marked contrast, only one of several
possible low-energy S4-ruffled conformations of [Co(TPP)(Et2-
NH)2]+ is significantly populated (φ1, φ2 ) 121, 344°) through-
out the MD simulation period. The adjacent local minimum with
Ci symmetry (φ1, φ2 ) 209, 344°) and a planar porphyrin core
geometry is also partially populated at 298 K during the
simulation. From Figure 7, high-energy conformations of [Co-
(TPP)(Et2NH)2]+ are clearly not populated during the 500-ps
interval. A similar MD trajectory was obtained for the related
bis(secondary amine) derivative [Co(TPP)(1-MePipz)2]+ (Figure
S5).
DFT Calculations. Valence orbital (4s, 4p, and 3d) electron
populations computed at the B3LYP/LACVP level of theory
are given in Table 3 along with values of the electric field
gradient, qval, calculated from the Townes-Dailey approxima-
tion (eq 3),55-57
4
5
1
2
qval
)
r-3 -Np + (Np + Np ) +
4p
{
}
z
x
y
4
7
1
2
r-3 Ndx2-y2 - N 2 + N - (Nd + Nd ) (3)
3d
dz
dxy
{
}
xz
yz
where Np and Nd are the calculated electron populations of the
individual 4p and 3d orbitals. r-3 and r-3
are the
3d
4p
expectation values of 1/r3 taken over the 3d and 4p radial
functions, respectively. The value of r-3 3d was determined for
each complex from the total 3d electron population by interpola-
tion between the following estimated expectation values: 5.36
au for Co configuration 3d7, 6.08 au for 3d6, and 6.84 au for
3d5. These estimates are based on those reported by Weissbluth
and Maling58 for iron, but are corrected for the well-known
variation of r with atomic number.59,60 The value of r-3
4p
61
was taken as 1/3 r-3
.
3d
The total 3d electron population varies from 7.6189 for the
Ci symmetry conformation of [Co(TPP)(Et2NH)2]+ to 7.6731
for [Co(TPP)Cl]. The electron populations of individual 3d
orbitals vary considerably with the nature of the axial ligand
Figure 6. Comparison of MM-calculated (solid lines) and crystallo-
graphically observed (broken lines) structures of [Co(TPP)(1-MePipz)2]-
(SbF6)‚H2O. The gas-phase MM-calculated structure is shown in (a);
the structure calculated in the presence of all lattice neighbors is shown
in (b). Two rmsd’s (in Å) are shown for each fit. The first is for the
Co(III) ion, the 24 porphyrin core atoms, and the two axial nitrogens.
The second (in parentheses) is for all non-hydrogen atoms. Hydrogen
atoms have been omitted for clarity.
2
and the porphyrin core conformation; the 3dz orbital shows the
largest population variation from 0.3853 in [Co(TPP)Cl] to
1.6820 in [Co(TPP)(1-BuNH2)2]+. A significant increase in the
3d population from 0.9377 in [Co(TPP)(1-BuNH2)2]+ to 1.9821
yz
in the Ci symmetry conformation of [Co(TPP)(Et2NH)2]+ is also
evident. The 4p electron populations are similar for the [Co-
(TPP)(L)2]+ derivatives listed in Table 3 and show very minor
changes with axial ligand orientation in the case of [Co(TPP)-
(Et2NH)2]+. The electric field gradient, qval, is smallest for the
Ci symmetry conformation of [Co(TPP)(Et2NH)2]+ (0.0209) and
largest for [Co(TPP)(PhCH2CH2NH2)2]+ (0.1060). The sign of
qval is negative for the S4-ruffled conformations of [Co(TPP)-
(Et2NH)2]+ and [Co(TPP)(1-Bu2NH)2]+ and the local minimum
conformation of [Co(TPP)(Et2NH)2]+ in which the axial ligand
N-H groups are eclipsed and oriented over a Cm-Co vector
(Cs symmetry). The natural atomic charges of the Co(III) ion
vary from +1.0014 in [Co(TPP)(BzNH2)2]+ to +1.0823 in the
[Co(TPP)(1-BuNH2)2]+, all minima on the potential energy
surface have a high population frequency. However, the global
minima (e.g., φ1, φ2 ) 90°, 90°) show a slightly higher
population density than the local minima (e.g., φ1, φ2 ) 90°,
180°). The pathway from one minimum to the next occurs
mainly through the saddle points on the surface, as evidenced
by the relatively high population densities linking the minima
(54) As with [Co(TPP)(1-BuNH2)2]+, three types of high-energy conforma-
tions exist for [Co(TPP)(Et2NH)2]+. In the highest energy conforma-
tions (∆UT ∼7.5 kcal/mol, e.g., φ1, φ2 ) 85°, 100°), the N-H bonds
of the axial ligands adopt an anti arrangement (180° apart over a planar
porphyrin core) and lie approximately over a pair of trans-Co-Np
bonds (within 15°). The next highest energy maxima (∆UT ∼5.8 kcal/
mol) are slightly S4-ruffled and occur when the N-H bonds of the
axial ligands are eclipsed (< 20° apart) and lie over a single Co-Np
bond, e.g., φ1, φ2 ) 177°, 200°. The least strained high-energy
structures have slightly saddled porphyrin cores and arise when the
axial ligand N-H bonds are staggered (∼60° apart) and lie within
20° of an orthogonal pair of Co-Np bonds (∆UT ∼5.4 kcal/mol, e.g.,
φ1, φ2 ) 177°, 122°). In each case, the R-CH2 groups of the ligands
come close to eclipsing a pair of trans porphyrin nitrogens, leading to
short nonbonded contacts (H‚‚‚Np ∼2.4 Å) and a high steric energy.
(55) Townes, C. H.; Dailey, B. P. J. Chem. Phys. 1949, 17, 782-796.
(56) Bancroft, G. M.; Mays, M. J.; Prater, B. E. J. Chem. Soc. A 1970,
956-968.
(57) Grodzicki, M.; Ma¨nning, V.; Trautwein, A. X.; Friedt, J. M. J. Phys.
B: At. Mol. Phys. 1987, 20, 5595-5625.
(58) Weissbluth, M.; Maling, J. E. J. Chem. Phys. 1967, 47, 4166-4172.
(59) Cowan, R. D. The Theory of Atomic Structure and Spectra; University
of California Press: Berkley, 1981; p 236.
(60) Mason, J. Chem. ReV. 1987, 87, 1299-1312.
(61) Trautwein, A. Struct. Bonding 1974, 20, 101-167.

3312 Inorganic Chemistry, Vol. 40, No. 14, 2001
Munro et al.
Figure 7. Surface plot of the change in steric energy (∆UT) as a function of axial amine orientation for [Co(TPP)(1-BuNH2)2]+ and [Co(TPP)-
(Et2NH)2]+ (top). The center plots are contour maps of the three-dimensional surfaces; broken lines indicate regions encompassing minima on each
surface. The bottom graphs are scatter plots showing 6800 out of a total of 68 000 sampled conformations during a 500 ps MD simulation for each
complex at 298 K in the gas phase. In each plot, φ1 and φ2 correspond to the dihedral angles Np-Co(III)-Nax-CR for the top and bottom ligands,
respectively.
Cs symmetry conformation of [Co(TPP)(Et2NH)2]+. The primary
amine complexes exhibit higher axial nitrogen charge densities
(ranging from -0.7806 in the 1-BuNH2 derivative to -0.7870
in the PhCH2CH2NH2 derivative) than the secondary amine
Discussion
Molecular and Crystal Structures. The X-ray structures of
1-3 are the first examples of R-unsubstituted primary amine
complexes of Co(III) porphyrins. They are also isoelectronic,
but not isomorphous, with the structurally analogous Fe(II)
complexes;9 each has an essentially planar porphyrin core
complexes where qN varies from -0.6025 in [Co(TPP)(1-Bu2-
ax
NH)2]+ to -0.6080 in the Cs symmetry conformation of [Co-
(TPP)(Et2NH)2]+.

Co(III) Porphyrins
Inorganic Chemistry, Vol. 40, No. 14, 2001 3313
Table 3. DFT-Calculated d-Orbital Electron Populations and Selected Mean Atomic Charges for [Co(TPP)(L)2]+ Complexesa,b
1-BuNH2
BzNH2
PhCH2CH2NH2
Et2NHc
Et2NHd
Et2NHe
1-Bu2NHc
[Co(TPP)Cl]f
4s
0.0035
0.0008
0.0012
0.0012
1.3624
0.0038
0.0011
0.0012
0.0012
1.1965
0.0036
0.0010
0.0010
0.0011
1.7841
0.0039
0.0013
0.0017
0.0013
0.9132
0.2592
0.0011
0.0015
0.0012
0.9176
0.2589
0.0011
0.0015
0.0011
0.9035
0.2538
0.0016
0.0015
0.0016
0.9512
0.2826
0.0036
0.0036
0.0027
1.5483
4px
4py
4pz
3dx -y
3dz
2
2
2
1.6820
1.5817
1.5894
1.0844
1.0632
1.0658
1.1360
0.3853
3dyz
3dxz
3dxy
0.9377
1.9073
1.7723
7.6617
1.0662
1.9312
1.8933
7.6689
1.5442
1.4220
1.3266
7.6663
1.9758
1.6922
1.9781
7.6437
1.9821
1.6868
1.9785
7.6372
1.9790
1.6927
1.9779
7.6189
1.9470
1.6477
1.9650
7.6469
1.9639
1.9639
1.8117
7.6731
Total (3d)
r-3
4.8636
4.8583
4.8602
4.8770
4.8818
4.8953
4.8746
4.8552
3d
Total (val)
EFG, qval
qCo
7.6653
0.0837
1.0093
-0.5309(11)
-0.7806(1)
7.6706
0.0260
1.0014
-0.5308(61)
-0.7769(0)
7.6698
0.1060
1.0091
-0.5304(26)
-0.7870(2)
7.6475
-0.0753
1.0561
-0.5327(71)
-0.6054(5)
7.8964
0.0209
1.0635
-0.498(29)
-0.6067(0)
7.8777
-0.0564
1.0823
-0.537(11)
-0.6080(1)
7.9006
-0.0478
1.0547
-0.5329(79)
-0.6025(41)
7.9556
2.8055
1.0222
qN
-0.4984(0)
p
qN
-0.6152(0)g
ax
a All geometries, except that of [Co(TPP)Cl], were energy minima derived from MM calculations. DFT calculations were single point calculations
on the S ) 1 ground-state configurations with the LACVP basis set (B3LYP method). b Populations and charges in electronic charge units. c S4-
ruf52 porphyrin core conformation. d Ci-symmetry local minimum (∆UT ) 3.149 kcal/mol; φ1 ) 70°, φ2 ) 20°). e Local minimum (∆UT ) 3.864
kcal/mol; φ1 ) 70°, φ2 ) 290°). f DFT-optimized geometry (C4 symmetry). g Charge on axial chloride ligand.
conformation. The X-ray structure of 4, although not the only
structure of a bis(secondary amine) Co(III) porphyrin,2,18 is
nonetheless remarkable because hydrogen bonding interactions
within the lattice which involve the axial piperazine ligands
render the structure noncentrosymmetric. Moreover, the partly
staggered relative orientations of the axial ligands lead to a
significantly nonplanar conformation for the tetrapyrrole ligand
(Vide infra), a phenomenon more commonly observed with
sterically hindered porphyrin ligands.2,3,38,62,63
The Co-Nax bonds of 1-3 average 1.980(5) Å and compare
favorably with the axial bond distance reported for [Co(TPP)-
(PhCH(CH3)NH2)2]Br (1.983 Å),19 even though the axial ligands
in the latter complex are substituted at the R-carbon. The Co-
Nax distances of the R-unsubstituted primary amines of this study
are also equivalent (within 4σ) to those reported for [Co(TMCP)-
((S)-2-butylamine)2]+ (1.985(10) and 2.023(10) Å).3 This is
somewhat unexpected since the chiral porphyrin ligand in the
latter complex is strongly S4-ruffled and provides an orthogonal
pair of ligand binding cavities above and below the porphyrin
ring. The rather similar Co-Nax distances of the available
crystallographically characterized bis(1° amine) Co(III) por-
phyrins suggest that primary amines bind in a sterically efficient
manner. This conclusion is verified by the conformational energy
surface for [Co(TPP)(1-BuNH2)2]+ (Figure 7) which shows that
the coordination of primary amines by sterically unhindered Co-
(III) porphyrins is characterized by steric strain energies < 1.2
kcal/mol.
The mean Co-Nax distance of 4 (2.040(2)°) is significantly
longer than that observed for the bis(1° amine) derivatives,
consistent with a larger steric bulk for the secondary amine
ligands and an attendant increase in van der Waals repulsion
between the porphyrin core atoms and the axial ligand R-CH2
hydrogens. Interestingly, the Co-Nax distances for the 1-MePipz
derivative are somewhat shorter than those reported for [Co-
(TPP)(Pip)2](NO3) (2.060(3) Å), although they may be regarded
as being equivalent within 4σ. The main difference in the
structures of these two secondary amine derivatives is that the
porphyrin core conformation of 4 is a mixture of two types of
distortion (S4-ruf and D2d-sad),52,64 whereas the porphyrin core
of [Co(TPP)(Pip)2](NO3) is effectively planar (Ci symmetry).
The S4-ruf perturbation in 4 clearly favors a sterically efficient
approach of the axial ligands and thus shorter Co-Nax distances.
The modest distortion from planarity in the bis(1-MePipz)
complex is brought about by a noncentrosymmetric arrangement
of the axial ligands above and below the porphyrin core (Figures
1-3) and significant tilting (by up to 30° from the heme normal)
of the meso-phenyl groups.65 The unusual axial ligand arrange-
ment primarily reflects the H-bonding interactions within the
lattice while the canted meso-phenyl substituents are consistent
with crystal packing interactions, a well documented9,52,66
phenomenon that is clearly demonstrated by the MM-calculated
conformations of Figure 6 and Table 2.
The mean Co-Np distances of compounds 1 (1.987(11) Å),
2 (1.987(4) Å), 3 (1.986(3) Å), and 4 (1.985(13) Å) are
equivalent and compare favorably with the mean Co-Np
distance of 1.985(3) Å reported for [Co(TPP)(PhCH(CH3)NH2)2]-
Br.19 The sizable dispersion in the Co-Np distances of the
BzNH2 and 1-MePipz derivatives indicates that the equatorial
coordination group distances are asymmetric; the shorter Co-
Np distances are to the porphinato nitrogens that are within 40°
of the planes containing the ligand R-carbons (Table 1). We
attribute most, but not all, of the in-plane asymmetry of the
Co-Np bonds to crystal packing effects because the MM-
calculated structures only begin to reproduce (∼50-60%) the
dispersion in the Co-Np bond distances when carried out in
the presence of all lattice neighbors (Table 2).
Finally, the axial ligand orientations (measured by the Np-
Co-Nax-CR dihedral angles) vary markedly from 0° for the
(64) Shelnutt, J. A. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic: New York, 2000; Vol. 7, pp
167-223.
(65) Although nonplanar, the structure of 4 is considerably less distorted
than that of [Co(TMCP)((S)-2-butylamine)2]+.3 The mean absolute
perpendicular displacement of the meso-carbons of the chiroporphyrin
derivative measures 0.63(4) Å;3 the equivalent parameter for 4 is only
∼30% of this value (0.20(2) Å). The large S4-ruf distortion for [Co-
(TMCP)((S)-2-butylamine)2]+ results from the presence of four
sterically bulky R,â,R,â-meso-cyclopropyl substituents rather than the
steric bulk of the axial ligands, as is the case for 4. The marked S4-
ruffling of the chiroporphyrin macrocycle also leads to compression
of the Co-Np bonds to a rather short mean distance of 1.949(11) Å.
(66) Scheidt, W. R. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic: New York, 2000; Vol. 3, pp
49-112.
(62) Munro, O. Q.; Serth-Guzzo, J. A.; Turowska-Tyrk, I.; Mohanrao, K.;
Shokhireva, T. Kh.; Walker, F. A.; Debrunner, P. G.; Scheidt, W. R.
J. Am. Chem. Soc. 1999, 121, 11144-11155.
(63) Senge, M. O. In The Porphyrin Handbook; Kadish, K. M., Smith, K.
M., Guilard, R., Eds.; Academic: New York, 2000; Vol. 1, pp 239-
347.

3314 Inorganic Chemistry, Vol. 40, No. 14, 2001
Munro et al.
four X-ray structures (Table 2). The conformation observed in
each crystal structure is therefore significantly different from a
local or global minimum on the conformational energy surface
for the molecule in the gas phase (Figure 7). The dominant role
of intermolecular interactions in controlling the conformations
of simple bis(amine) Co(III) porphyrins reflects two main
factors. (1) π-Bonding between the axial ligands and the dπ
orbitals is not possible for alkylamines since π-symmetry MOs
with nonvanishing amplitude on the N-donor atom are absent.
(2) The steric energy penalties to rotation of the axial ligands,
particularly in the bis(1° amine) derivatives, are relatively small.
59Co Chemical Shifts. The 59Co chemical shifts of [Co(TPP)-
Cl], 5-7, 10, and 11 all increase linearly with increasing
temperature (Figure 5 and Table S29). The extent of nuclear
shielding in diamagnetic Co(III) complexes and its temperature
dependence is usually interpreted with Ramsey’s magnetic
shielding theory (vide infra).67 The nuclear screening constant,
σCo, in the Larmor frequency equation (eq 4)
γ
νCo
)
CoB0(1 - σCo)
(4)
2π
where νCo, γCo, and B0 are the Larmor frequency, the magne-
togyric ratio, and the applied magnetic field, respectively, is
given by
σCo ) A - B/∆E
(5)
The two terms A and B/∆E in eq 5 correspond to the
diamagnetic (σd) and paramagnetic (σp) contributions to the
shielding, respectively (i.e., σCo ) σd + σp). Because the
magnitude of A is determined by the core electrons of the
nucleus in question,68,69 it is independent of both the ligand field
environment and the temperature of the system for a constant
spin and oxidation state. The magnitude of the paramagnetic
term B/∆E is, however, governed by the symmetry and nature
of the coordination sphere of the metal ion. For simple Oh Co-
(III) coordination complexes, ∆E is the energy difference
Figure 8. Plot of the relationship between the 59Co chemical shift and
the radial expectation value r-3 for the Co(III) ion (top) and the
3d
dependence of the 59Co line width, ω1/2, on the square of the electric
field gradient, q2val, (bottom) for several low-spin Co(III) porphyrins.
The 95% confidence interval is shown in the lower plot.
1
1
between the A1g (ground) and T1g terms for the low-spin d6
η(1A2), η(1B1), and η(1B2) are covalency (nephelauxetic)
parameters for the three excited-state terms.70-72 The decrease
in shielding with increasing temperature for [Co(TPP)Cl] and
the five bis(amine) complexes of Figure 5 therefore reflects an
increase in the population of the higher-lying vibrational levels
of the 1A1 ground state. This lowers the 1A1 f 1A2, 1A1 f 1B1,
and 1A1 f 1B2 transition frequencies and increases the contribu-
tion (deshielding) of the paramagnetic term in eq 6 to the
shielding of the Co(III) nucleus.
ion. A linear relationship is observed between the 59Co chemical
1
shift and the wavelength of the A1g
f
1T1g transition in
complexes with unobscured d-d transitions.70 For a complex
with effective C2v symmetry (the Co(III) derivatives of this study
have nondegenerate porphyrin and metal π-symmetry orbitals,
consistent with < 4-fold symmetry), the 1T1g term will be split
1
1
1
into its subterms A2, B1, and B2. The paramagnetic term of
eq 5 is thus inversely proportional to the mean energy of the
1
1
1
1
1
1A1 f A2, A1 f B1, and A1 f B2 transitions, eq 6,
A second, often overlooked factor is the variable nature of
r-3
for the complex.70 Specifically, as the mean Co-N
3d
2
-8µ0µB
distance increases with the heightened vibrational amplitude of
the M-L bonds at higher temperatures, a decrease in the total
3d electron population from poorer σ-donation is to be expected.
Depopulation of the 3d orbitals, even if slight, will lead to an
σp(C2v) )
r-3
×
3d
π
η(1A2)
η(1B1)
η(1B2)
+
+
(6)
3∆E( A2) 3∆E(1B1) 3∆E( B2)
1
1
increase in the magnitude of r-3
and thus the relative
[
]
3d
importance of σp to the nuclear shielding. As shown in Figure
8, a good linear correlation between the 59Co shift and r-3
where µ0, µB, and r-3 3d are the vacuum permeability, the Bohr
magneton, and the expectation value of 1/r3 taken over the 3d
radial function for the Co3+ ion, respectively. The parameters
3d
exists, confirming the relationship of eq 6. Interestingly, the
calculated values of r-3
appear to be sensitive to the
3d
conformation of the complex. This is illustrated for 10 in Table
(67) Ramsey, N. F. Phys. ReV. 1950, 78, 699-703.
(68) Freeman, R.; Murray, G. R.; Richards, R. E. Proc. R. Soc. London
1957, A242, 455-466.
3. The S4-ruf conformation (Co-Np ) 1.969(3) Å, Co-Nax )
2.057(0) Å, Figure S6) has a smaller value of r-3 than the
3d
(69) Kidd, R. G.; Goodfellow, R. J. In NMR and the Periodic Table; Harris,
R. K., Mann, B. E., Eds.; Academic: New York, 1978; pp. 195-
278.
(71) Juranic´, N. Inorg. Chem. 1980, 19, 1093-1095.
(72) Eichele, K.; Chan, J. C. C.; Wasylishen, R. E.; Britten, J. F. J. Phys.
Chem. A 1997, 101, 5423-5430.
(70) Juranic´, N. J. Chem. Phys. 1981, 74, 3690-3693.

Co(III) Porphyrins
Inorganic Chemistry, Vol. 40, No. 14, 2001 3315
time, τc, is temperature-dependent (eq 9),77
Ci symmetry planar conformation (Co-Np ) 1.989(2) Å, Co-
Nax ) 2.078(0) Å), consistent with somewhat shorter M-L
distances and a commensurate increase in total 3d electron
density due to better σ donation. The conformation dependent
spread in r-3 3d values for each derivative in Table 3 and Figure
8 is estimated to be about 0.0025 au. It follows that a large
Vc
τ ) τ0 exp
(9)
( )
c
c
RT
and proportional to the hydrodynamic volume, a3, of the solute
and the viscosity, ú, of the solvent:78,79
change in r-3 (of the order of 0.005-0.010 au) is required
3d
before a statistically significant difference in the 59Co chemical
shift can be predicted from the calculated r-3 3d values for this
class of Co(III) complexes. Several other important factors may
also contribute to the magnitude of the 59Co chemical shift
observed for a particular complex. These include variations in
τc ) (4π/3)(a3ú/kT)
(10)
The activation energy for tumbling, Vc, is therefore dependent
on both a and ú. Importantly, a plot of the log of the line width
against reciprocal temperature may be used to determine the
activation energy Vc for a range of related Co(III) complexes
(eq 11):77
1
1
1
1
1
1
the mean energy of the A1 f A2, A1 f B1, and A1 f B2
transitions for the different Co(III) derivatives as well as
variations in the solvent dielectric constant, particularly since
50% (v/v) amine/CDCl3 solutions were used to acquire the 59Co
NMR spectra of each derivative. Significant solvent and
counterion effects on 59Co chemical shifts have in fact been
reported by Edwards and co-workers20-22 for bis(imidazole)
complexes of Co(III) meso-tetraarylporphyrins.
Vc 1
R T
log(ω1/2) ) log A +
(11)
( )
Equation 11 therefore permits straightforward quantification of
the effect that the reduction in solvent viscosity with increasing
temperature has on the tumbling rate and rotational correlation
time through the variation in line width. From the fitted data in
Figure 5, the following activation energies (and intercepts) were
obtained for the six Co(III) complexes: 11, 2.6(1) kJ mol-1
(1.77(5)); 10, 3.12(6) kJ mol-1 (1.45(2)); [Co(TPP)Cl], 3.8(2)
kJ mol-1 (2.08(7)); 5, 5.3(2) kJ mol-1 (1.29(7)); 6, 6.0(2) kJ
mol-1 (0.34(7)); and 7, 6.3(2) kJ mol-1 (1.09(8)). Interestingly,
there is no obvious correlation between the measured values of
Vc and the calculated35 van der Waals volumes of the molecules,
as might have been expected from eq 10. However, the
viscosities of the CDCl3/amine mixtures used for acquisition
of the 59Co NMR spectra are probably not constant across the
series and this is likely to have contributed in part to the
observed order of Vc values. Perhaps more interesting from a
structural standpoint is the fact that the nonplanar complexes
11 (S4-ruf), 10 (S4-ruf), and [Co(TPP)Cl] (C4V dome) all have
relatively small activation energies for molecular reorientation,
while those that are conformationally flexible exhibit signifi-
cantly higher activation energies. The marked difference in
conformational flexibility between [Co(TPP)(1-BuNH2)2]+ and
[Co(TPP)(Et2NH)2]+ is strikingly demonstrated in the plots of
the MD trajectories of these two systems at 298 K in Figure 7.
Provided that the solvent viscosities and hydrodynamic radii
of the species being compared are reasonably similar, it is not
untenable to suggest from the gas phase MD data in Figure 7
that a spread in conformational isomers in solution may lead to
a mean activation energy barrier for molecular reorientation that
is overall higher than that for a system which largely populates
a single type of conformation in solution.
A significant outcome of the relationship between the 59Co
chemical shifts and the total 3d electron population, or r-3
,
3d
is that a quantitative measure of the σ-donor strengths of the
axial ligands is immediately apparent. From Figure 8, the
σ-donor power of the ligands in this series of [Co(TPP)(L)2]+
derivatives follows the following order: BzNH2 g Cl-
>
1-BuNH2 > PhCH2CH2NH2 > 1-Bu2NH > Et2NH. Importantly,
this order cannot be predicted from the pKas of the ligands73 or
the Mulliken populations of the free ligand donor atoms. Since
the d-d absorption bands of the low-spin d6 ion are completely
obscured by bands from the strongly allowed porphyrin π f
π* transitions, electronic spectroscopy cannot be used to gauge
the ligand field strength at the metal either. Thus, when
combined with an accurate calculation of the total 3d electron
population for the metal, 59Co NMR spectroscopy is the only
reliable method for measuring the axial ligand field strength in
Co(III) porphyrins.
59Co Line Widths and Electric Field Gradients. In addition
to changes in nuclear shielding, there are marked changes in
the 59Co line widths with temperature. Figure 5 shows that the
line widths decrease linearly with increasing temperature. For
a single quadrupolar nucleus of spin I, for which quadrupole
relaxation is the dominant spin relaxation mechanism, and for
which molecular motion is characterized by an isotropic
tumbling correlation time τc, the line width is given by eq 7,
(2I + 3)
3π
10
1
3
ω1/2
)
ø2 1 + η2 τc
(7)
(
)
2
I (2I - 1)
where ø and η are the nuclear quadrupole coupling constant
and asymmetry parameter, respectively.69 The nuclear quadru-
pole coupling constant is given by eq 8,
For a constant temperature, e.g., 24 °C, the NMR data in
Figure 5 and Table S29 show that the 59Co line widths follow
the order 10 < 6 < 11 < 5 < [Co(TPP)Cl] < 7. Any attempt
to explain this trend must also account for the fact that neither
8 nor 9 showed a 59Co resonance. Equations 7 and 8 indicate
that the line width, ω1/2, is proportional to the square of the
e2qzzQ
ø )
(8)
h
where e is the charge on the electron, qzz the principal component
of the EFG at the nucleus, and Q the nuclear electric quadrupole
moment.69 The asymmetry parameter lies in the range 0 < η <
1 and is given as η ) (qyy - qxx)/qzz. The rotational correlation
(74) Christensen, J. J.; Izatt, R. M.; Wrathall, D. P.; Hansen, L. D. J. Chem.
Soc. A 1969, 1212-1223.
(75) Bunting, J. W.; Stefanidis, D. J. Am. Chem. Soc. 1990, 112, 779-
786.
(76) Cox, M. C.; Everett, D. H.; Landsman, D. A.; Munn, R. J. J. Chem.
Soc. B 1968, 1373-1379.
(73) For example, the pKas of benzylamine,74 phenethylamine,75 buty-
lamine,76 diethylamine,74 and dibutylamine74 are 9.40(8), 9.92(4),
10.66(2), 10.92, and 11.25, respectively, at 25 °C and ionic strengths
of 0.0-0.1 M.
(77) Bernheim, R. A.; Brown, T. H.; Gutowski, H. S.; Woessner, D. E. J.
Chem. Phys. 1959, 30, 950-956.
(78) Obermyer, R. T.; Jones, E. P. J. Chem. Phys. 1973, 58, 1677-1679.
(79) Fury, M.; Jones, E. P. J. Chem. Phys. 1976, 65, 2206-2210.

3316 Inorganic Chemistry, Vol. 40, No. 14, 2001
Munro et al.
principal component of the EFG, qzz. Clearly, a quantitative
explanation of the line width variation from one Co(III) complex
to the next requires determination of the EFG at the nucleus.
We have used DFT methods to calculate the valence shell
electron populations for all of the bis(amine) Co(III) porphy-
rinates of this study. The task of obtaining reliable ground state
wave functions was simplified by using accurate input geom-
etries derived from MM calculations. As shown in Table 3, the
electric field gradients calculated from the Co(III) valence
electron populations vary significantly depending on the type
of ligand coordinated to the Co(III) ion and the conformation
of the complex. More importantly, the 59Co line widths increase
linearly with the square of the valence EFG, qval (Figure 8).
This relationship holds well for the bis(amine) complexes listed
in Table 3 but does not extend to the parent derivative [Co-
(TPP)Cl]. Thus, provided one is dealing with a class of Co(III)
porphyrins with relatively similar axial ligands, it is possible
to quantitatively account for the 59Co line widths in terms of
the magnitude of the EFG due to the valence electrons of the
metal. Moreover, the good correlation of ω1/2 with q2val in
Figure 8 indicates that the contribution to the EFG from the
ligand electrons is insignificant and may be neglected.
in-plane coupling constant (roughly < 100 Hz) is close in
1
magnitude to the reported JCo-N value of 45 Hz for [Co-
(NH3)6]+.81
MM, MD, and DFT Calculations. One of our main
objectives has been to use MM, MD, and DFT calculations to
help delineate the fundamental factors affecting the crystal-
lographic conformations and 59Co NMR spectra of bis(amine)
complexes of Co(III) porphyrins (vide supra). An accurate force
field, even if specific for metalloporphyrins, therefore underpins
the theoretical work in this report. As shown in Figure 6 and
Table 2, the force field parameters that we have developed
provide an acceptable level of accuracy for the calculation of
[Co(TPP)(amine)2]+ structures in the solid state. When the
results of a “lattice” calculation are compared with a calculated
gas phase conformation of the same molecule, the effects of
crystal packing interactions on the molecular conformation are
readily identified and indeed proven. The present force field
has also allowed the calculation of accurate gas phase and
solution phase conformations82 of [Co(TPP)(amine)2]+ deriva-
tives for which X-ray data are lacking. This has been essential
for obtaining suitable input coordinates for DFT calculations
(Table 3) and for predicting the low energy conformations of
[Co(TPP)(1-Bu2NH)2]+ and [Co(TPP)(Et2NH)2]+. A challenging
test of the force field parametrization is whether Marchon’s
highly distorted X-ray structure2 of [Co(TMCP)((S)-prolinol-
N)2]+ can be suitably matched by an MM-calculated structure.
The predicted conformation is summarized by the following
parameters: Co-Np ) 1.951(3) Å, Co-Nax ) 2.058(0) Å, |Np|
) 0.03(3) Å, |Ca| ) 0.31(2) Å, |Cb| ) 0.17(4) Å, and |Cm| )
0.65(3) Å. The data for the X-ray structure are as follows: Co-
Np ) 1.951(4) Å, Co-Nax ) 2.046(1) Å, |Np| ) 0.02(1) Å,
|Ca| ) 0.35(2) Å, |Cb| ) 0.24(3) Å, and |Cm| ) 0.65(3) Å. The
rmsd for a least-squares fit of the calculated structure to the
X-ray structure is 0.074 Å. This level of agreement clearly
indicates that the force field is capable of predicting accurate
structures for bis(amine) Co(III) porphyrins that are fairly remote
from those used for parametrization.
The conformational energy surface for [Co(TPP)(1-BuNH2)2]+
shown in Figure 7 is representative of the type of surface
obtained for the bis(1° amine) complexes of this study. It is
also identical in symmetry to that calculated for [Fe(TPP)(1-
BuNH2)2].9 However, the steric energy changes are up to ∼1.5
times larger for the Co(III) derivative due to the fact that the
Co-Nax force constant (2.65 mdyn Å-1) is ∼1.4 times larger
than that used for the FeII-Nax interaction (1.90 mdyn Å-1).9,83
Although empirically derived, these force constants do take into
account the enhanced electrostatic M-L attractions in the Co-
(III) derivatives and thus offer a qualitatively correct picture of
the energetics of axial ligand rotation for this class of com-
pounds. Interestingly, the conformational energy surface for [Co-
(TPP)(Et2NH)2]+ is significantly different to that calculated for
[Co(TPP)(1-MePipz)2]+ (Figure S5). In addition to a lower
symmetry, the changes in steric energy for [Co(TPP)(Et2NH)2]+
are more marked; the highest energy conformations for the Et2-
NH derivative lie ∼2 kcal/mol above the analogous maxima
for [Co(TPP)(1-MePipz)2]+. This mainly reflects the wider CR-
The fact that neither 8 nor 9 afforded a 59Co NMR spectrum
is indicative of a large nuclear quadrupole coupling constant
(i.e., a large EFG) and a very short T2q. The crucial test of the
combined MM/DFT approach to delineating the electronic
structures of these complexes is whether an unusually large EFG
is predicted for these secondary amine derivatives. A DFT
calculation (B3LYP/LACVP) on the S4-ruffled global minimum
conformation of 9 gave the following relevant Co(III) valence
orbital electron populations (in units of e) and parameters: 4s,
2
2
0.0042; 4px, 0.0015; 4py, 0.0050; 4pz, 0.0013; 3dx -y , 0.8556;
-3
2
3dz , 0.8883; 3dyz, 1.9623; 3dxz, 1.9672; 3dxy, 1.9750; r
,
3d
4.8736; r-3 4p, 1.6245; qval, 10.883. The value of qval calculated
for 9 is 2 orders of magnitude larger than that calculated for 7
(Table 3). This unusually large EFG for 9 is suggestive of a
very short relaxation time, T2q, and infinitely broad 59Co line
width, consistent with the experimental fact that no 59Co
resonance could be detected for this complex and the related
bis(piperidine) derivative.
59Co-14N Coupling Constants. The 1JCo-N coupling con-
ax
stants for 6, 10, and 11 measured 600(5) Hz, as evidenced by
the well resolved quintet spectrum for 6 at elevated temperatures
1
(Figure 4). More recently, we have determined a JCo-N
ax
coupling constant of 615 Hz for [Co(TPP)(i-PrNH2)2]Cl.80
Importantly, this is the first direct observation of 14N-59Co
spin-spin coupling for Co(III) porphyrins. An intriguing
question is why coupling to only the axially coordinated 14N
spins is observed for a select few of the Co(III) derivatives
studied. The key requirement for the observation of 59Co spin-
spin coupling is that the complex has a relatively small electric
field gradient and thus an intrinsically narrow 59Co line width.
If at a given temperature ω1/2 e 1JCo-N , then resolution of the
ax
spin-spin coupling is possible. This is readily seen from the
line width data for 6, 10, and 11 in Table S29. The fact that
spin-spin coupling between the cobalt nucleus and the por-
phyrin 14N nuclei is not observed strongly suggests that 1JCo-N
p
is significantly smaller than ∼390 Hz, the narrowest line width
(81) Jordan, R. B. J. Magn. Reson. 1980, 38, 267.
measured in Table S29 (compound 10 at 55.1 °C). This result
(82) The difference between a gas phase and solution phase structure is
negligibly small for a solute in a nonpolar solvent and manily reflects
the choice of dielectric constant for the calculation.41
1
is consistent with Edward’s estimate of 40 Hz for JCo-N for
p
bis(imidazole) complexes of Co(III) meso-tetraarylporphyrins.21
The porphyrin 14N nuclei are therefore similar in nature to the
14N nuclei of simple ammine ligands since the intrinsically small
(83) The conformational energy surface for [Co(TPP)(1-MePipz)2]+ (Figure
S5) is very similar to that calculated previously9 for [Fe(TPP)(Pip)2]+
and also shows an increase in the magnitude of the strain energy
maxima by a factor of ∼1.4 relative to the surface for the Fe(II)
derivative.
(80) Jamieson, S.; Munro, O. Q. Unpublished work.

Co(III) Porphyrins
Inorganic Chemistry, Vol. 40, No. 14, 2001 3317
However, the line widths narrow significantly upon on warming
so that the multiplets from the two conformers are sufficiently
resolved at 37.2 °C. We speculate that the lower intensity signal
is due to the less frequently populated local minimum with
approximate Ci symmetry and a planar porphyrin core confor-
mation (Figure S6). The total 3d electron population (7.637 e)
for this conformer is marginally smaller than that for the S4-
ruffled conformation (7.644 e). From the correlation between
the 59Co chemical shift and r-3 3d in Figure 8, one would predict
similar, probably unresolvable, chemical shifts for these two
species. However, the 4s electron population calculated for the
planar conformer (0.259 e) is significantly larger than that
calculated for the S4-ruffled conformer (0.004 e); the higher
s-electron density clearly accounts for the upfield chemical shift
of the 59Co resonance from the planar conformation.
Conclusions
Figure 9. Selected 59Co NMR spectra of [Co(TPP)(Et2NH2)2]Cl at
different temperatures in 50% (v/v) ligand/CDCl3 solution. The
downfield multiplet from the major conformational isomer (∼78% at
37.2 °C) is assigned to the ensemble of lowest-energy S4-ruf confor-
mational isomers of [Co(TPP)(Et2NH2)2]Cl; the upfield multiplet is
assigned to the higher-energy planar conformations of [Co(TPP)(Et2-
NH2)2]Cl.
Four new low-spin bis(amine) Co(III) porphyrins have been
synthesized and structurally characterized. The X-ray data have
been used in the parametrization of a molecular mechanics force
field (MM+) for this class of metalloporphyrins. Together with
MD and DFT calculations we have been able to show (1) that
bis(1° amine) complexes are inherently more flexible than their
secondary amine counterparts, (2) crystal packing interactions
have a significant impact on the crystallographically observed
conformations of these complexes, (3) the 59Co chemical shifts
depend directly on the total 3d electron population (or, more
fundamentally, the radial expectation value r-3 3d), (4) the 59Co
NMR line widths are proportional to the square of the calculated
electric field gradient at the cobalt nucleus, and (5) that the
calculated conformational populations in the gas-phase correlate
well with those observed in solution by 59Co NMR spectroscopy,
particularly in the case of sterically hindered bis(secondary
amine) complexes. Importantly, this paper describes the un-
precedented use of electronic structure theory calculations to
rationalize the 59Co NMR spectra of diamagnetic Co(III)
porphyrins.
N-CR angles in the bis(Et2NH) complex (111.6°), relative to
those of the bis(1-MePipz) complex (107.8°), and the attendant
increase in axial ligand-porphyrin core nonbonded repulsion.
The latter effect is also consistent with the longer Co-Nax
distances for the lowest-energy gas phase conformation of [Co-
(TPP)(Et2NH)2]+ (2.057(0) Å) relative to those calculated for
[Co(TPP)(1-MePipz)2]+ (2.028(0) Å). The lower symmetry of
the surface for [Co(TPP)(Et2NH)2]+ reflects the partly staggered
ethyl group configuration for the axial ligands (Figure S6); this
is absent in [Co(TPP)(1-MePipz)2]+ since the chair conforma-
tions of the piperazine rings are rigorously maintained, favoring
eclipsed Nax-CR-Câ-N torsion angles.
As noted above, the conformational energy surfaces are useful
when combined with scatter plots of the MD trajectories for
the [Co(TPP)(amine)2]+ derivatives for interpreting some of the
59Co NMR data for these compounds. In particular, Figure 7
clearly shows that bis(2° amine) complexes of Co(III) porphyrins
are considerably less flexible than the analogous bis(1° amine)
derivatives. This difference in flexibility appears to directly
affect the activation energies for molecular reorientation and
hence the rotational correlation times for these complexes. One
main concern is whether the calculated gas phase MM and MD
data actually reflect the conformational behavior of these
complexes in solution. From the calculated gas-phase population
distribution for [Co(TPP)(Et2NH)2]+ in Figure 7, the global
minimum (S4-ruffled porphyrin core; ∆UT ) 0 kcal/mol; φ1,
φ2 ) 121°, 344°) is largely populated at all times. However,
the scatter plot also shows that the system spends part of the
time in the adjacent local minimum (planar porphyrin core; ∆UT
∼3.2 kcal/mol; φ1, φ2 ) 209°, 344°). As shown by the 59Co
NMR spectra for 10 in Figure 9, two conformations with
different chemical shifts do indeed coexist in solution. At 1.4
°C, the line widths of the resonances from the two conformations
are broad and the separate signals cannot be distinguished.
Acknowledgment. We thank the University of Natal (Uni-
versity Research Fund) and the National Research Foundation
(Pretoria) for generous financial support. We would also like
to express our gratitude to Leanne Cooke (University of the
Witwatersrand, Johannesburg) for the low-temperature X-ray
data collections and Martin C. Watson (University of Natal,
Pietermaritzburg) for recording our NMR spectra and suggesting
the 59Co experiments.
Supporting Information Available: Crystallographic details,
atomic coordinates, bond distances, bond angles, torsion angles,
anisotropic thermal parameters, and hydrogen atom coordinates for
compounds 1-4 (Tables S1-S28), 59Co NMR data (Table S29), X-ray
crystallographic files in CIF format, labeled ORTEP diagrams of 1 and
3, formal diagrams of the porphyrin cores of 1 and 3, ORTEP diagram
1
of the H-bonding interactions in 1, H and 13C NMR spectra for 1,
surface plots of the change in steric energy with axial ligand orientation
for [Co(TPP)(1-MePipz)2]+, and MM-calculated conformations (S4-ruf
and planar) of [Co(TPP)(Et2NH)2]+ (Figures S1-S6). This material is
available free of charge via the Internet at http://pubs.acs.org.
IC000976C