Carbonyl complexes of iron(II), ruthenium(II), and osmium(II) 5,10,15,20-tetraphenylporphyrinates: A comparative investigation by x-ray crystallography, solid-state NMR spectroscopy, and density functional theory

Article abstract of DOI:10.1021/ja9740069

We have synthesized and characterized via single-crystal X-ray diffraction methods iron(II), ruthenium(II), and osmium(II) carbonyl derivatives of (1-methylimidazole)(5,10,15,20- tetraphenylporphyrinate)[(5,10,15,20-tetraphenylporphyrinate = TPP)], Fe(TPP)(CO)(1-MeIm)·toluene, Ru(TPP)(CO)(1-MeIm)·chloroform, and Os(TPP)(CO)(1-MeIm)·chloroform, together with the osmium(II) pyridine adduct Os(TPP)-(CO)(py)·2benzene. The crystallographic results permit a detailed structural comparison between all of the six carbonyl metalloporphyrins which can be prepared from TPP, Fe, Ru, Os, and the two axial bases 1- methylimidazole and pyridine. The structures of all three (Fe, Ru, Os) 1- methylimidazole complexes display major saddle distortions, with the extent of the distortions being Fe > Ru ~ Os. For the pyridine complexes, deviations from planarity of the porphyrin ring are about an order of magnitude smaller than those for the 1-methylimidazole species. The M-C-O bond angles in all complexes are in the range 176.8-179.3°. We also determined the ¹³C and ¹⁷O NMR isotropic chemical shifts, the ¹³C NMR chemical shift tensor elements, and, for the three 1-MeIm adducts, the ¹⁷O nuclear quadruple coupling constants. We then used density functional theory (DFT) to relate the experimental spectroscopic results to the experimental structures. For the ¹³C and ¹⁷O isotropic shifts, there are excellent correlations between theory and experiment (¹³C, R² value = ~0.99; ¹⁷O, R² value = ~.99), although the slopes (¹³C, ~-0.97; ¹⁷O, ~-1.27) deviate somewhat from the ideal values. For the ¹⁷O nuclear quadruple coupling constant, our results indicate an rms error between theory and experiment of 0.20 MHz, for experimental values ranging from (+)1.0 to (- )0.40 MHz, where the signs are deduced from the calculations. The ability to predict spectroscopic observables in metalloporphyrin systems having relatively well characterized structures by using density functional theory provides additional confidence in the application of these theoretical methods to systems where structures are much less certain, such as heme proteins.

Full text of DOI:10.1021/ja9740069

J. Am. Chem. Soc. 1998, 120, 11323-11334
11323
Carbonyl Complexes of Iron(II), Ruthenium(II), and Osmium(II)
5,10,15,20-Tetraphenylporphyrinates: A Comparative Investigation by
X-ray Crystallography, Solid-State NMR Spectroscopy, and Density
Functional Theory
Renzo Salzmann, Christopher J. Ziegler, Nathalie Godbout, Michael T. McMahon,
Kenneth S. Suslick, and Eric Oldfield*
Contribution from the Department of Chemistry, UniVersity of Illinois at Urbana-Champaign, 600 South
Mathews AVenue, Urbana, Illinois 61801
ReceiVed NoVember 24, 1997
Abstract: We have synthesized and characterized via single-crystal X-ray diffraction methods iron(II),
ruthenium(II), and osmium(II) carbonyl derivatives of (1-methylimidazole)(5,10,15,20-tetraphenylporphyrinate)
[(5,10,15,20-tetraphenylporphyrinate ) TPP)], Fe(TPP)(CO)(1-MeIm)‚toluene, Ru(TPP)(CO)(1-MeIm)‚
chloroform, and Os(TPP)(CO)(1-MeIm)‚chloroform, together with the osmium(II) pyridine adduct Os(TPP)-
(CO)(py)‚2benzene. The crystallographic results permit a detailed structural comparison between all of the
six carbonyl metalloporphyrins which can be prepared from TPP, Fe, Ru, Os, and the two axial bases
1-methylimidazole and pyridine. The structures of all three (Fe, Ru, Os) 1-methylimidazole complexes display
major saddle distortions, with the extent of the distortions being Fe > Ru ∼ Os. For the pyridine complexes,
deviations from planarity of the porphyrin ring are about an order of magnitude smaller than those for the
1-methylimidazole species. The M-C-O bond angles in all complexes are in the range 176.8-179.3°. We
also determined the 13C and 17O NMR isotropic chemical shifts, the 13C NMR chemical shift tensor elements,
and, for the three 1-MeIm adducts, the 17O nuclear quadrupole coupling constants. We then used density
functional theory (DFT) to relate the experimental spectroscopic results to the experimental structures. For
the 13C and 17O isotropic shifts, there are excellent correlations between theory and experiment (13C, R2 value
) ∼0.99; 17O, R2 value ) ∼0.99), although the slopes (13C, ∼-0.97; 17O, ∼-1.27) deviate somewhat from
the ideal values. For the 17O nuclear quadrupole coupling constant, our results indicate an rms error between
theory and experiment of 0.20 MHz, for experimental values ranging from (+)1.0 to (-)0.40 MHz, where the
signs are deduced from the calculations. The ability to predict spectroscopic observables in metalloporphyrin
systems having relatively well characterized structures by using density functional theory provides additional
confidence in the application of these theoretical methods to systems where structures are much less certain,
such as heme proteins.
Introduction
ranging from essentially linear and untilted to highly bent, have
been reported.9-13 The results of several spectroscopic tech-
niques, such as extended X-ray absorption fine structure
(EXAFS)14 and X-ray absorption near edge spectroscopy
(XANES),15 have supported such bent geometries, while more
recent interpretations of infrared data, both in solution16 and in
the crystalline solid-state,17 have supported undistorted geom-
etries. There is thus interest in clarifying such questions by
using other spectroscopic techniques, such as nuclear magnetic
resonance spectroscopy18-20 and Mo¨ssbauer spectroscopy.21
Synthetic metalloporphyrin compounds can play an important
role in facilitating our understanding of heme protein structure,
Understanding how small ligand molecules, such as NO, CO,
O2, RNC, and RNO, bind to metal sites in metalloproteins has
been a topic of considerable interest for some time.1-8 In
principle, single-crystal X-ray crystallographic studies of pro-
teins should enable a determination of the local geometries of
metal-ligand interactions, but the relatively limited resolution
of protein crystal structures has resulted in some controversies
as to the actual geometries involved. The most studied system
is the Fe-CO interaction in heme proteins, where geometries
(1) Filehne, W. Arch. Exp. Pathol. Pharmakol. 1878, 9, 329-379.
(2) Warburg, O.; Kubouritz, T.; Christian, W. Biochem. Z. 1931, 242,
170-205.
(11) Kuriyan, J.; Wilz, S.; Karplus, M.; Petsko, G. A. J. Mol. Biol. 1986,
192, 133-154.
(12) Quillin, M. L.; Arduini, R. M.; Olson, J. S.; Phillips, G. N., Jr. J.
Mol. Biol. 1993, 234, 140-155.
(13) Yang, F.; Phillips, G. N., Jr. J. Mol. Biol. 1996, 256, 762-774.
(14) Ascone, I.; Bianconi, A.; Dartyge, E.; Della Longa, S.; Fontaine,
A.; Momentau, M. Biochim. Biophys. Acta 1987, 915, 168-171.
(15) Bianconi, A.; Congiu-Castellano, A.; Durham, P. J.; Hasnain, S.
S.; Phillips, S. Nature 1985, 318, 685-687.
(16) Lim, M.; Jackson, T. A.; Anfinrud, P. A. Science 1995, 269, 962-
965.
(17) Ivanov, D.; Sage, J. T.; Keim, M.; Powell, J. R.; Asher, S. A.;
Champion, P. M. J. Am. Chem. Soc. 1994, 116, 4139-4140.
(3) Jung, F. Naturwissenschaften 1940, 28, 264-265.
(4) Keilin, D.; Hartree, E. F. Nature 1943, 151, 390.
(5) Pauling, L.; Coryell, C. D. Proc. Natl. Acad. Sci. U.S.A. 1936, 22,
210-216.
(6) Pauling, L. Nature 1964, 203, 182-183.
(7) Weiss, J. J. Nature 1964, 203, 183.
(8) Perutz, M. Protein Structure. New Approaches to Disease and
Therapy; W. H. Freeman and Co.: New York, 1992.
(9) Steigemann, W.; Weber, E. In Hemoglobin and Oxygen Binding, Ho,
C., Ed.; Elsevier Biomedical: New York, 1982; pp 19-24.
(10) Norvell, J. C.; Nunes, A. C.; Schoenborn, B. P. Science 1975, 190,
568-570.
10.1021/ja9740069 CCC: $15.00 © 1998 American Chemical Society
Published on Web 10/27/1998

11324 J. Am. Chem. Soc., Vol. 120, No. 44, 1998
Table 1. Crystallographic Data Summary
Salzmann et al.
Fe(TPP)(CO)(1-MeIm) Ru(TPP)(CO)(1-MeIm) Ru(TPP)(CO)(1-MeIm)28 Os(TPP)(CO)(1-MeIm)
Os(TPP)(CO)(py)
formula
mol wt
color
C49H34N6OFe‚toluene
870.81
red
C49H34N6ORu‚CHCl3
943.26
purple
C49H34N6ORu‚toluene
916.03
C49H34N6O Os‚CHCl3
1032.39
purple
C49H34N6O Os‚2(benzene)
1066.23
black
crystal system
a (Å)
b (Å)
triclinic
orthorhombic
9.7228(2)
17.6641(3)
25.58000(10)
90
triclinic
orthorhombic
9.7179(2)
17.6120(4)
25.5891(6)
90
90
90
4379.6(2)
4
1.566
monoclinic
13.2059(2)
19.3726(4)
19.86200(10)
90
105.9950(10)
90
4884.63
4
9.76770(10)
13.28250(10)
17.6251(3)
74.7500(10)
88.3660(10)
83.7290(10)
2192.95(5)
2
9.7959(15)
13.3197(13)
17.6180(16)
74.881(9)
87.973(10)
83.229(10)
2203.8(5)
2
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
90
90
4393.22(12)
4
1.426
D
calc (g cm-3
)
1.319
1.380
1.450
space group
radiation,
P1h
P212121
Mo KR, 0. 710 73
P1h
P212121
Mo KR, 0. 710 73
P21/c
Mo KR, 0.710 73
Mo KR, 0.710 73
wavelength (Å)
µ (mm-1
)
0.392
0.585
3.140
2.659
crystal size (mm)
temperature (K)
diffractometer
no. of data points
collected
0.08 × 0.18 × 0.22
0.04 × 0.04 × 0.46
0.06 × 0.09 × 0.42
0.05 × 0.10 × 0.11
198(2)
198(2)
153(2)
9049
198(2)
198(2)
Siemens SMART/CCD Siemens SMART/CCD
6798
Siemens SMART/CCD Siemens SMART/CCD
10441
7699
7660
no. of data points
with I > 2σ(I)
abs min/max
R1
5516
5444
8361
5186
0.816/0.990
0.0430
0.0607
0.8654/1.000
0.0886
0.1444
0.1360/0.2196
0.0601
0.0906
0.0068/0.0233
0.0523
0.0964
0.0344
0.0939
wR2
GOF
1.175
1.181
1.204
1.154
since the structures of the smaller synthetic analogues generally
have smaller uncertainties than the protein crystal structures.22
Well-characterized model systems can then form a database for
interpreting the results of spectroscopic studies of the heme
proteins using modern quantum chemical techniques. Here, the
recent developments and applications of density functional
theory,23-25 together with recent improvements in computer
hardware, and the use of parallel processing26 show real promise
for relating the results of spectroscopic measurementsse.g.,
infrared24 and NMR27sto structure and, in the future, to
function.
There is, however, the need for more complete structural and
spectroscopic data on CO-, O2-, RNC-, RNO-, and R2S-
containing metalloporphyrins to serve as both the structural and
spectroscopic database for quantum chemical calculations. In
this paper, we describe the synthesis and characterization via
single-crystal X-ray diffraction of three meso-tetraphenylpor-
phyrin (TPP) systems: carbonyl(1-methylimidazole)(5,10,15,-
20-tetraphenylporphyrinato)iron(II), carbonyl(1-methylimidazole)-
(5,10,15,20-tetraphenylporphyrinato)osmium(II), and carbonyl
(pyridine)(5,10,15,20-tetraphenylporphyrinato)osmium(II). This
enables a comparative study of the six CO complexes which
can be made from TPP, Fe/Ru/Os, 1-methylimidazole, and
pyridine: Fe(TPP)(CO)(1-MeIm), Ru(TPP)(CO)(1-MeIm),28
Os(TPP)(CO)(1-MeIm), Fe(TPP)(CO)(py),29 Ru(TPP)(CO)-
(py),30 and Os(TPP)(CO)(py). In addition, we report the
structure of a second form of Ru(TPP)(CO)(1-MeIm), containing
a single CHCl3 solvate molecule, which crystallizes in a space
group different from that of the toluene solvate reported
previously28 and permits an estimate of the effects of crystal-
lattice or intermolecular interactions on structure in these
systems.
Experimental Section
(18) Scheidt, R. W.; Lee, J. Y. Struct. Bonding (Berlin) 1987, 64, 1-70.
(19) Park, K. D.; Guo, K.; Adebodun, F.; Chiu, M. L.; Sligar, S. G.;
Oldfield, E. Biochemistry 1991, 30, 2333-2347.
All compounds were fully characterized by elemental analysis, field
desorption mass spectrometry, UV-visible absorption spectroscopy,
and solution and solid-state NMR spectroscopy. Elemental analyses
were conducted at the University of Illinois School of Chemical
Sciences Microanalytical Laboratory. Field desorption mass spectrom-
etry measurements were made using a Finnigan-MAT (Bremen,
Germany) Model 731 instrument. Porphyrin UV-visible spectra were
measured using a Hitachi Ltd. (Tokyo, Japan) Model 3300 UV-visible
double-monochromator spectrophotometer. The single-crystal X-ray
measurements were made using a Siemens (Madison, WI) SMART
diffractometer. Solid-state NMR spectra were obtained on “home-built”
360 and 500 MHz spectrometers using Oxford magnets (Oxford
Instruments, Osney Mead, U.K.), Tecmag (Houston, TX) pulse
programmers, and Doty Scientific (Columbia, SC) probes.
(20) Barrie, P. J.; Gerothanassis, I. P.; Momentau, M.; Hawkes, G. E. J.
Magn. Reson., Ser. B 1995, 108, 185-188.
(21) Gerothanassis, I.; Barrie, P. J.; Momentau, M.; Hawkes, G. E. J.
Am. Chem. Soc. 1994, 116, 11944-11949.
(22) (a) Trautwein, A.; Maeda, Y.; Harris, F. E.; Formanek, H. Theor.
Chim. Acta 1974, 36, 67-76. (b) Trautwein, A. In Structure and Bonding;
Dunitz, J. D., Hemmerich, P., Holm, R. H., Ibers, J. A., Jørgensen, C. K.,
Neilands, J. B., Reinen, D., Williams, R. J. P., Eds.; Springer-Verlag: New
York, 1974; pp 101-167. (c) Case, D. A.; Huynh, B. H.; Karplus, M. J.
Am. Chem. Soc. 1979, 101, 4433-4453.
(23) Malkin, V. G.; Malkina, O. L.; Casida, M. E.; Salahub, D. R. J.
Am. Chem. Soc. 1994, 116, 5898-5908.
(24) Ghosh, A.; Bocian, D. F. J. Phys. Chem. 1996, 100, 6363-6367.
(25) Rovira, C.; Ballone, P.; Parrinello, M. Chem. Phys. Lett. 1997, 271,
247-250.
(26) Frisch, M. J.; Trucks, G. W.; Head-Gordon, M.; Gill, P. M. W.;
Wong, M. W.; Foresman, J. B.; Johnson, B. G.; Schlegel, H. B.; Robb, M.
A.; Repiogle, E. S.; Gomperts, R.; Andres, J. L.; Raghavachari, K.; Binkley,
J. S.; Gonzalez, C.; Martin, R. L.; Fox, D. J.; Defrees, D. J.; Baker, J.;
Stewart, J. J. P.; Pople, J. A. Gaussian 94/DFT; Gaussian, Inc.: Pittsburgh,
PA, 1994.
Synthetic Aspects. The syntheses of 5,10,15,20-tetraphenylpor-
phyrin (H2TPP) and of (5,10,15,20-tetraphenylporphyrinato)iron(III)
(28) Slebodnick, C.; Seok, W. K.; Kim, K.; Ibers, J. A. Inorg. Chim.
Acta 1996, 57, 243.
(29) Ping, S.-M.; Ibers, J. A. J. Am. Chem. Soc. 1976, 98, 8032-8036.
(30) Little, R. G.; Ibers, J. A. J. Am. Chem. Soc. 1973, 95, 8583-8596.
(27) Oldfield, E. J. Biomol. NMR 1995, 5, 217-225.

Metalloporphyrin Structures
J. Am. Chem. Soc., Vol. 120, No. 44, 1998 11325
Figure 1. ORTEP structures of (A) carbonyl(1-methylimidazole)(tetraphenylporphyrinato)iron(II)-toluene, (B) carbonyl(1-methylimidazole)-
(tetraphenylporphyrinato)ruthenium(II)-chloroform, (C) carbonyl(1-methylimidazole)(tetraphenylporphyrinato)osmium(II)-chloroform (disordered
solvent molecule), and (D) carbonyl(pyridine)(tetraphenylporphyrinato)osmium(II)-2(benzene).
chloride [Fe(TPP)(Cl)] were based on modifications of the work of
Adler and Dolphin.31-33
thaw cycles, 13CO or C17O gas (Isotec, Miamisburg, OH) was transferred
via a gastight syringe into the Schlenk flask. Careful layering of a
5-fold excess of pentane resulted in crystallization of carbonyl
(1-methylimidazole)(5,10,15,20-tetraphenylporphyrinato)iron(II) after
4 days at room temperature. Anal. Found (calcd) for Fe(TPP)(CO)-
(1-MeIm)‚toluene: C, 77.31 (77.24); H, 4.71 (4.86); N, 9.67 (9.65).
(a) Carbonyl(1-methylimidazole)(5,10,15,20-tetraphenylporphy-
rinato)iron(II). Reduced iron porphyrins are extremely sensitive to
air and solvent impurities. All solvents used in the reduction of Fe-
(TPP)(Cl) were therefore purified by distillation: benzene, over calcium
hydride; toluene and heptane, over sodium; and pentane, over sodium
benzophenone ketyl. Ethanol was used for the reduction of Fe(TPP)-
(Cl) without further purification and was purchased from the McCor-
mick Distillation Co. (Weston, MI). All solvents used in the reductions
were freeze/pump/thaw degassed prior to use. Fe(TPP) was generated
from Fe(TPP)(Cl) using Cr(acac)2 as the reductant. All syntheses and
manipulations of Fe(TPP) and reduced iron porphyrins were conducted
in a glovebox or in a Schlenk apparatus under rigorously anaerobic
and dry conditions. Cr(acac)2 was synthesized using a literature
technique,34 as modified by Chen.35
IR (νCO in CD2Cl2): 1969 cm-1 13C NMR (CO): 204.1 ppm.
.
(b) Carbonyl(1-methylimidazole)(5,10,15,20-tetraphenylporphy-
rinato)ruthenium(II). The ruthenium porphyrin complex was gener-
ated from the ethanol adduct Ru(TPP)(CO)(EtOH)36 as follows. First,
the 1-methylimidazole complex (Ru(TPP)(CO)(1-MeIm)) was isolated
from a solution of 50 mg of the ethanol complex in 5% v/v
1-methylimidazole in CHCl3 by addition of heptane. For isotopic
labeling, crystals were collected and redissolved in 50 mL of toluene.
This toluene solution was then placed in a water-cooled Schlenk flask
under 1 atm of either 13CO or C17O and irradiated with a 300 W xenon
arc lamp (filtered from IR and UV, 360 nm) for ∼30 min. FTIR
measurements indicated complete exchange of the unlabeled CO with
13CO or C17O. The toluene solution was then reduced in volume and
the resultant labeled compound crystallized by layering of heptane.
Yield: 40 mg of Ru(TPP)(CO)(1-MeIm)‚CHCl3 (77%). Anal. Found
(calcd) for Ru(TPP)(CO)(1-MeIm)‚CHCl3: C, 63.42 (63.66); H, 3.84
The Fe(TPP) so produced was then dissolved in toluene, a 2-fold
excess of 1-methylimidazole was added, and after three freeze/pump/
(31) Abbreviations used: TPP, 5,10,15,20-tetraphenylporphyrinate-
(2-); 1-MeIm, 1-methylimidazole; py, pyridine.
(32) (a) Adler, A. D.; Longo, F. R.; Finarelli, J. D.; Goldmacher, J.;
Assour, J.; Korsakoff, J. J. Org. Chem. 1967, 32, 476. (b) Adler, A. D.;
Longo, F. R.; Kampas, F.; Kim, J. J. Inorg. Nucl. Chem. 1970, 32, 2443-
2445.
(33) Rousseau, K.; Dolphin, D. Tetrahedron Lett. 1974, 48, 4251-4254.
(34) Ocone, L. R.; Block, B. P. Inorg. Synth. 1966, 8, 125-130.
(35) Chen, C. T. Ph.D. Thesis, University of Illinois at Urbana-
Champaign, 1992.
(3.74); N, 8.97 (8.91). IR (νCO in CD2Cl2): 1936 cm-1 13C NMR
.
(CO): 178.5 ppm.
(36) Barley, M.; Becker, J. Y.; Domazetis, G.; Dolphin, D.; James, B.
R. Can. J. Chem. 1983, 61, 2389-2396.

11326 J. Am. Chem. Soc., Vol. 120, No. 44, 1998
Salzmann et al.
Table 2. Structural Summary for Fe, Ru, and Os Porphyrinsa
M(TPP)(CO)(1-MeIm)
M(TPP)(CO)(py)
M ) Fe29 M ) Ru30 M ) Os
M ) Fe
M ) Ru
2.063(7)
M ) Ru28
M ) Os
M-N(1)
M-N(2)
M-N(3)
M-N(4)
M-N(5)
M-C
2.009(2)
1.999(2)
2.006(2)
1.999(2)
2.071(2)
1.793(3)
1.061(3)
1.095
2.053(2)
2.060(2)
2.052(2)
2.066(2)
2.187(2)
1.828(2)
1.147(3)
2.054(6)
2.047(6)
2.060(6)
2.047(6)
2.175(7)
1.846(9)
1.150(10)
1.186
2.05(1)
1.99(1)
2.00(1)
2.02(1)
2.10(1)
1.77(2)
1.12(2)
2.057(6) 2.068(6)
2.055(6) 2.0676)
2.058(5) 2.054(6)
2.038(6) 2.060(6)
2.193(4) 2.194(6)
1.838(9) 1.817(9)
1.141(10) 1.190(9)
1.225
2.065(6)
2.051(7)
2.055(7)
2.185(8)
1.830(10)
1.142(10)
1.181
C-O
C-O, riding model52
N(1)-M-N(2)
N(1)-M-N(3)
N(1)-M-N(4)
N(2)-M-N(3)
N(2)-M-N(4)
N(3)-M-N(4)
C-M-N(1)
89.6(2)
179.2(2)
90.3(2)
90.6(2)
176.1(2)
89.4(2)
89.8(2)
91.9(2)
89.5(2)
92.0(2)
178.3(3)
179.3(3)
90.0(3)
175.8(3)
89.8(3)
90.0(3)
177.9(3)
90.4(3)
91.7(4)
90.0(3)
92.5(4)
92.0(3)
176.7(4)
178.6(8)
89.40(7)
175.26(7)
90.34(7)
90.84(7)
178.88(7)
89.33(7)
92.18(9)
90.42(9)
92.55(9)
90.68(9)
177.83(8)
179.3(2)
90.3(3)
174.9(3)
89.5(3)
89.8(3)
176.9(3)
90.1(3)
92.4(4)
91.3(3)
92.6(4)
91.7(5)
177.5(4)
176.8(9)
89.1(5)
89.8(2)
90.0(3)
179.4(6) 177.2(2) 175.2(3)
90.0(5)
91.3(5)
89.8(2)
89.8(2)
90.3(3)
89.7(3)
178.3(6) 175.2(2) 176.6(3)
89.7(5)
90.0(8)
89.4(7)
90.5(9)
92.0(7)
90.3(2)
92.3(3)
90.5(3)
92.7(3)
92.1(3)
89.7(3)
91.8(3)
91.2(3)
93.0(4)
92.2(4)
C-M-N(2)
C-M-N(3)
C-M-N(4)
C-M-N(5)
177.5(8) 178.9(3) 177.6(4)
179(2) 178.4(7) 178.3(7)
M-C-O
torsion amplitudes of TPP phenyl rings
angle between imidazole ring and porphyrin plane 83
1, 8, 10, 26 10, 12, 16, 30 10, 12, 16, 30 8, 12, 15, 28 3, 6, 9, 14 1, 2, 3, 8 4, 7, 14, 16
80 80 81 80 88 80
a Distances are given in angstroms; angles and torsion amplitudes are given in degrees.
(c) Carbonyl(1-methylimidazole)(5,10,15,20-tetraphenylporphy-
rinato)osmium(II). The osmium precursor was also generated using
a modified literature procedure,37 from H2TPP and osmium carbonyl.
Carbonyl(1-methylimidazole)(5,10,15,20-tetraphenylporphyrinato)-
osmium(II) and labeled samples were synthesized in the same manner
as the Ru analogues. Suitable crystals were obtained from slow
diffusion of pentane into a chloroform solution over 3 days. Anal.
Found (calcd) for Os(TPP)(CO)(1-MeIm)‚CHCl3: C, 58.09 (58.45);
method,38 using Becke’s exchange functional39 and Perdew and Wang’s
gradient-corrected correlation functional40 (“BPW91” exchange and
correlation functional). For both the shifts and the efg, we used a locally
dense approach41 in which the metal was represented by an effective
core potential (ECP), or an all-electron basis set, and two or three sets
of functions were employed for the other atoms.
In initial calculations, we carried out a constrained geometry
optimization of the Fe(TPP)(CO)(1-MeIm) model, in which only the
Fe-C and C-O bond lengths were allowed to change, by using Becke’s
three-parameter functional42 with the Lee, Parr, and Yang correlation
functional43 (“B3LYP” exchange and correlation functional). For this
calculation, we used Wachters’ (62111111/331211/3111/3) iron basis
set,44,45 which we modified to (62111111/3311111/3111) by decon-
tracting the p-type functions (to add flexibility) and removing the f-type
functions. The Wachters’ cobalt basis set was similarly modified and
used successfully in our previous study of cobalt-59 shielding.46 Other
basis sets were 6-31G* on the CO ligand and the nitrogen atoms
coordinated to iron and 3-21G on the remaining atoms (including the
phenyl groups). The shielding tensor calculations for the Fe(TPP)-
(CO)(1-MeIm) models were carried out by including phenyl groups
on the porphyrin ring and using the following basis set scheme:
Wachters’ iron basis set, 6-311++G(2d) on the CO ligand and the
nitrogen atoms coordinated to iron, 6-31G* on the carbons bonded to
H, 3.29 (3.42); N, 8.14 (8.01). IR (νCO in CD2Cl2): 1899 cm-1 13C
.
NMR (CO): 142.6 ppm.
(d) Carbonyl(pyridine)(5,10,15,20-tetraphenylporphyrinato)-
osmium(II). This compound was synthesized in the same manner as
Os(TPP)(CO)(1-MeIm), but employing pyridine as the axial base.
Suitable crystals were obtained from slow diffusion of pentane into a
benzene solution over 5 days. Anal. Found (calcd) for Os(TPP)(CO)-
(py)‚2(benzene): C, 69.79 (69.89); H, 4.13 (4.26); N, 6.47 (6.69). IR
(νCO in CD2Cl2): 1912 cm-1 13C NMR (CO): 142.9 ppm.
.
Crystallographic Aspects. Single-crystal data for the four systems
described above were collected on a Siemens (Madison, WI) SMART/
CCD diffractometer using MoKR radiation (λ ) 0.710 73 Å). The
structures were solved using the SHELXTL V5.0 (Siemens) system
and refined by full-matrix least-squares procedures on F2 using all
reflections. The data were corrected for Lorentz and polarization
effects, and an empirical absorption correction was applied.
The color and morphology of the crystals, the crystallographic
systems and space groups, and other information related to the crystal
structure determinations are summarized in Table 1. In general, from
6798 to 10 441 data points were collected using the area detector, and
from 5186 to 8361 data points having I > 2σ(I) were used in the
refinements. The final R1 values varied from 0.0430 to 0.0886 and
the GOF values from 1.154 to 1.204, Table 1. (See Supporting
Information.) Atomic coordinates, bond lengths angles, and thermal
parameters have also been deposited with the Cambridge Crystal-
lographic Data Centre (CCDC). Any request to the CCDC for this
material should quote the full literature citation and the reference
number.
(38) Cheesman, J. R.; Trucks, G. W.; Keith, T. A.; Frisch, J. J. Chem.
Phys. 1996, 104, 5497-5509.
(39) Becke, A. D. Phys. ReV. A 1988, 38, 3098-3100.
(40) Perdew, J. P.; Wang, Y. Phys. ReV. B 1992, 45, 13244-13249.
(41) Chesnut, D. B.; Moore, K. D. J. Comput. Chem. 1989, 10, 648-
659.
(42) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652.
(43) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785-
789. (b) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett.
1989, 157, 200-206.
(44) Wachters, A. J. H. J. Chem. Phys. 1970, 52, 1033-1036; IBM Tech.
Rept. RJ584 1969.
(45) Basis sets were obtained from the Extensible Computational
Chemistry Environment Basis Set Database, Version 1.0, as developed and
distributed by the Molecular Science Computing Facility, Environmental
and Molecular Sciences Laboratory, which is part of the Pacific Northwest
Laboratory, P.O. Box 999, Richland, WA 99352, and is funded by the U.S.
Department of Energy. The Pacific Northwest Laboratory is a multiprogram
laboratory operated by Battelle Memorial Institute for the U.S. Department
of Energy under Contract DE-AC06-76RLO 1830. Contact David Feller,
Karen Schuchardt, or Don Jones for further information.
(46) Godbout, N.; Oldfield, E. J. Am. Chem. Soc. 1997, 119, 8065-
8069.
Computations. The shielding tensor and electric field gradient (efg)
calculations were performed using density functional theory as imple-
mented in the Gaussian 94 program.26 The NMR shielding tensors
were calculated using the gauge-including atomic orbital (GIAO)
(37) Che, C. M.; Poon, C. K.; Chung, W. C.; Gray, H. B. Inorg. Chem.
1985, 24, 1277-1278.

Metalloporphyrin Structures
J. Am. Chem. Soc., Vol. 120, No. 44, 1998 11327
Figure 3. Plots showing the mean absolute deviations from planarity
(in mÅ) for iron, ruthenium, and osmium metalloporphyrins containing
1-methylimidazole (solid lines) and pyridine (dashed lines) as axial
bases.
in previous work49 we have found to give best accord between theory
and experiment, in metal-olefin complexes.49 Calculations here were
performed using modifications of the crystallographic structures in
which the phenyl groups were replaced by hydrogen atoms, an
approximation which again is discussed in more detail below. Calcula-
tions were performed on a cluster of Silicon Graphics/Cray (Mountain
View, CA) Origin-200 workstations in this laboratory and on Silicon
Graphics/Cray Origin-2000 and Power Challenge computers at the
National Center for Supercomputing Applications, located in Urbana,
IL.
Results and Discussion
We have synthesized and structurally characterized three new
porphyrin compounds, the Fe and Os complexes of TPP with
1-methylimidazole and CO as axial ligands, together with the
Os-CO-pyridine complex, in addition to determining the
structure of Ru(TPP)(CO)(1-MeIm)‚CHCl3 in the P212121 space
group. The ORTEP structures of these four molecules are
shown in Figure 1. The availability of these new structures
now permits a comparison of the structures of all six possible
pyridine and 1-methylimidazole adducts of Fe, Ru, and Os with
TPP and CO, and selected metric details are given in Table 2.
The most striking feature which can be seen from these results
is that all three 1-methylimidazole adducts have significant
saddle distortions, while all three pyridine adducts have much
smaller distortions. The deviations of each of the porphyrin
heavy atoms, as well as the central metal atoms, from the least-
squares plane of each macrocycle are shown in Figure 2.
The largest distortions seen are in the Fe(TPP)(CO)(1-MeIm)
complex, where the Câ atoms are on average ∼0.286 Å from
the mean plane, to be compared with only ∼0.049 Å in the
case of Fe(TPP)(CO)(py),29 Figure 2. In the Ru complexes,
the mean deviations are 0.196 Å (1-MeIm) versus 0.04 Å (py),
and in the Os complexes, 0.183 Å (1-MeIm) versus 0.055 Å,
Figure 2. This is shown graphically in Figure 3, together with
additional results for CR, the meso-carbons, as well as the metal
centers themselves.
Figure 2. Structures showing deviations from planarity of all of the
six carbonyl metalloporphyrins which can be prepared from tetraphe-
nylporphyrin, iron, ruthenium, osmium, 1-methylimidazole, pyridine,
and carbon monoxide. The numbers shown are the deviations (in mÅ)
from the least-squares porphyrin plane, and the positive numbers
indicate a displacement toward the CO ligand. The uncertainties vary
from ∼2 to 10 mÅ (Table 2).
the nitrogens, and 3-21G* on the remaining atoms (for a total of 797
basis functions). We then investigated shielding using a slightly
modified porphyrin, Fe(C2Cap)(CO)(1-MeIm), in which the phenyl
groups of the porphyrin ring were replaced by hydrogens, using
Wachters’ iron basis set, 6-311++G(2d) on the CO ligand, and 6-31G*
on the remaining atoms. These initial calculations gave useful
information on the sensitivity of the calculations to small structural
differences.
Several effective core potentials (ECPs) for the metals were also
considered. For iron, we used the Los Alamos (LANL2) ECP with
the double-ú (DZ) basis set,26,47 with a (42111/2111/311) basis set
decontracted from (441/311/41), while the Stuttgart ECP48 used a
(311111/22111/411) basis set. A variety of other basis set test schemes
were used on the main elements, and details are given under Results
and Discussion.
We then evaluated all of the Fe, Ru, and Os shielding and efg results
using a unified approach, based on these exploratory studies. Specif-
ically, we generated two sets of constrained geometry-optimized
structures (LANL2DZ ECPs on the metal and a locally dense scheme
for the light atoms) using either the BPW91 or B3LYP functional,
followed by property evaluations using the BPW91 functional, which
The observation that the smallest, iron-containing metallo-
cycle has the largest saddle distortion is not unreasonable, given
current ideas about the forces that influence porphyrin planarity.
The high charge density on the smaller Fe(II) results in shorter
metal (M)-N(porphyrin), M-N(ligand), and M-C bond lengths,
(47) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 284-298.
(48) Dolg, M.; Wedig, U.; Stoll, H.; Preuss, H. J. Chem. Phys. 1987,
86, 866-872.
(49) Havlin, R.; McMahon, M.; Srinivasan, R.; Le, H.; Oldfield, E. J.
Phys. Chem. A 1997, 101, 8908-8913.

11328 J. Am. Chem. Soc., Vol. 120, No. 44, 1998
Salzmann et al.
Table 3. Experimental 13C and 17O Shift Parameters and Infrared Vibrational Stretch Frequencies for Model Porphyrins
13C shifts (ppm)
17O δi
(ppm)
IR νCO
system
δi
δ11
δ22
δ33
|δ33 - δ11|
(cm-1
)
Fe(TPP)(CO)(1-MeIm)
Fe(TPP)(CO)(py)
Ru(TPP)(CO)(1-MeIm)
Ru(TPP)(CO)(py)
Os(TPP)(CO)(1-MeIm)
Os(TPP)(CO)(py)
205
205
178.7
179.7
142.2
144
370
386
334
338
299
300
342
328
334
338
299
300
-98
-100
-132
-136
-171
-168
468
486
466
474
470
468
372
369
305
320
235
254
1969
1975
1936
1943
1899
1912
Figure 4. Carbon-13 and oxygen-17 magic angle sample-spinning
NMR spectra of 13C- and 17O-labeled metalloporphyrins: (A) 13C MAS
NMR spectrum of carbonyl(1-methylimidazole)(5,10,15,20-tetraphe-
nylporphyrinato)ruthenium(II); (B) 17O MAS NMR spectrum of
carbonyl(1-methylimidazole)(5,10,15,20-tetraphenylporphyrinato)-
ruthenium(II).
Figure 5. Graphs showing correlations between the infrared vibrational
stretch frequencies, νCO, and the experimental carbon-13 and oxygen-
17 NMR chemical shifts, for metalloporphyrins and metalloproteins.
(A) correlations for carbon-13 shifts in proteins and metalloporphyrin
complexes: b, pyridine metalloporphyrin complexes; 2, 1-MeIm
metalloporphyrin complexes; O, heme metalloproteins. (B) As for (A)
but for oxygen-17. The metalloprotein data points are from ref 19.
which results in a saddle distortion. This can be clearly seen
in the M-N(1-5) and M-C bond lengths reported in Table 2.
For example, the average Fe-Np bond length in Fe(TPP)(CO)-
(1-MeIm) is 2.003 Å and the Fe-NIm bond length is 2.071 Å,
to be compared with average values for the Ru- and Os-1-
MeIm complexes of 2.056 Å and the much longer M-NIm
values of 2.182 Å, increases of between ∼0.05 and 0.10 Å. In
addition, the Fe-C bond is shorter, 1.793(3) Å versus 1.835
Å, a ∼0.04 Å difference. The increased saddle distortions can
thus be rationalized on the basis of a core contraction which
enables stronger Fe-C,N bonding.
differences between the Fe and the Ru and Os dh(M-Np) of
0.042 Å, essentially the same as the 0.053 Å seen for the
1-MeIm complexes. Thus, on the basis of the dh(M-Np) values,
the origins of the major changes in porphyrin distortion between
the Ru and Os 1-methylimidazole and pyridine complexes is
unclear. Similarly, the d(M-N5) differences between the Ru
and Os 1-MeIm/py complexes are only 0.01 Å, and the d(M-
C) differences are even less.
The picture becomes more complex, however, when the
structural results for the 1-MeIm complexes are compared with
those obtained for the pyridine adducts, Table 2. Here, there
appears to be no major difference in M-Np bond lengths
between the pyridine and 1-methylimidazole adducts. For
example, for the Ru and Os systems, we find mean bond lengths
of dh(M-Np) ) 2.056 Å for the 1-MeIm adducts versus dh(M-
Np) ) 2.057 Å for the pyridine complexes, Table 2, and
These results indicate that a simple model in which the M-N
bond lengths dominate the porphyrin distortions is likely to be
incomplete, since the Fe, Ru, and Os geometries about the
central metal atom are very similar in the 1-methylimidazole
and pyridine complexes. Either a more subtle steric or electronic
effect from the axial base plays a significant role in influencing
the porphyrin distortions, or crystal lattice packing effects are
important. Clearly, further work of a theoretical nature is needed

Metalloporphyrin Structures
J. Am. Chem. Soc., Vol. 120, No. 44, 1998 11329
Table 4. Theoretical 13C and 17O Shifts (ppm) for Model Iron 1-Methylimidazole Porphyrins as a Function of the Structure, Basis Sets, and
Effective Core Potentials Useda
13C
17O
calculation no.
1
system
Fe(TPP)b
δi
δ11
δ22
δ33
δi
δ11
δ22
δ33
198.0
359.6
Structural Effects
385.2
359.3
344.4
382.6
356.7
-122.2
333.0
571.7
570.6
-143.2
2
3
4
5
Fe(TPP)b (g-opt)
Fe(P)b
215.2
196.9
186.8
211.9
382.5
356.0
341.2
380.1
-122.2
-124.5
-125.2
-126.9
378.7
333.0
309.7
368.1
639.1
573.1
538.7
623.6
637.6
571.6
537.8
622.2
-140.5
-145.6
-147.3
-141.4
Fe(P)b (X-ray)
Fe(C2Cap)
Basis Set Effects
6
7
8
9
10
11
Fe(P)c
Fe(P)d
Fe(P)e
Fe(P)f
Fe(P)g
Fe(P)h
197.0
167.6
170.2
187.1
198.8
200.2
359.5
356.2
307.1
309.7
332.6
356.1
359.1
-124.7
-116.3
-120.2
-115.5
-117.6
-118.8
333.0
320.6
313.5
323.1
333.3
332.4
573.2
548.4
541.8
551.8
564.4
563.6
571.5
544.5
536.5
547.0
563.6
562.8
-145.5
-131.1
-137.7
-129.4
-128.1
-129.1
312.1
320.9
344.2
358.0
360.2
exptl
205
370
342
-98
372
a Unless otherwise specified, riding model geometry and BPW91 XC functionals were employed. b Fe Wachters/6-311++G(2d) CO and N/6-
31G* C (bond to N)/3-21G* others. c Fe Wachters/6-311++G(2d) CO and N/6-31G* C (ring)/3-21G* H. d Fe Stuttgart ECP with (311111/22111/
411) basis set/6-311++G(2d) CO and N/6-31G* C (bond to N)/3-21G* others. e Fe LANL2 ECP with (42111/2111/311) basis set/6-311++G(2d)
CO and N/6-31G* C (bond to N)/3-21G* others. f Fe LANL2 ECP with DZ basis set/6-311++G(2d) CO and N/6-31G* C (bond to N)/3-21G*
others. g Fe LANL2 ECP with DZ basis set/6-311++G(2d) CO/6-31G*N and C (bond to N)/3-21G* others. h Fe LANL2 ECP with DZ basis
set/6-311++G(2d) CO/6-31G* N/3-21G* others
Table 5. Selected X-ray and Partial Geometry Optimizationa Structural Parameters of Model Porphyrins (Å)
X-ray
BPW91
B3LYP
system
d(M-C)
d(C-O)
d(M-C)
d(C-O)
d(M-C)
d(C-O)
Fe(P)(CO)(1-MeIm)
1.7929
1.061
1.7428
(1.7411)b
1.7444
1.8600
1.8628
1.8689
1.8686
1.1670
(1.1686)b
1.1664
1.1708
1.1703
1.1763
1.1754
1.8013
(1.8053)c
1.8009
1.8755
1.8779
1.8740
1.8731
1.1472
(1.1495)c
1.1470
1.1561
1.1555
1.1632
1.1624
Fe(P)(CO)(py)
Ru(P)(CO)(1-MeIm)
Ru(P)(CO)(py)
Os(P)(CO)(1-MeIm)
Os(P)(CO)(py)
1.7755
1.8311
1.8373
1.8453
1.8185
1.1285
1.1418
1.1423
1.1508
1.1897
a The partial geometry optimizations were done using the LANL2DZ ECP for the metals, 6-31G* for the CO ligand and the nitrogens, and
3-21G* on the remaining atoms. b This structure was obtained using the LANL2DZ ECP on Fe, 6-31G* on C, N, and O, and 3-21G* on H (and
shows the influence of a locally dense scheme on the geometry optimization). c This structure was obtained using the Wachters basis set on Fe,
6-31G* on CO and nitrogens, and 3-21G on the other atoms (and shows the effect of the ECP on the geometry optimization).
to quantitate such effects. Rovira et al.25 recently reported the
results of Carr-Parrinello molecular dynamics geometry opti-
mization studies on Fe(porphyrin)(CO)(imidazole), whose ex-
perimental structure is unfortunately not yet known, so that it
is reasonable to suppose that the structures of even larger
systems (whose structures are known) should become tractable
in the not-too-distant future. As for the effects of crystal lattice
packing, inspection of the 1-MeIm and py structures reveals
no dramatic changes in crystal packing, unlike the case with
e.g. nickel(II) octaethylporphyrin,50 where major porphyrin
distortions are associated with large changes in lattice packing.
Also of interest in Figures 2 and 3 is the observation that the
positions of the Cmeso are far less distorted from the mean plane
for Os vs Ru vs Fe, with the 1-methylimidazole and pyridine
values being remarkably similar. At the same time, the metal
atoms themselves become located higher above the mean plane
(toward CO), as noted previously for Ru by Ibers et al.51
We should also note at this point that the structural parameters
of the two Ru(TPP)(CO)(1-MeIm) molecules shown in Table
2, obtained by different groups on systems having different
solvent molecules (CHCl3, toluene) and crystallizing in different
space groups (P212121, P1h), are nevertheless very similar. On
average, there is a 0.005 Å difference in the key bond lengths
shown in Table 2 and a 0.7° difference in the key bond angles.
The agreement may be even closer though, since our standard
deviations are ∼3-4 times higher than those reported for the
toluene structure.28
In all seven structures, the mean M-C-O bond angle is
178.5° with a standard deviation of 0.8°. The C-O bond
lengths do, however, appear to vary. The shortest C-O bond
length seen is that in Fe(TPP)(CO)(1-MeIm), while the longest
is in Os(CO)(py)(TPP). The 1.061(3) Å value determined for
Fe(CO)(1-MeIm)(TPP) is surprisingly short, since most C-O
bond lengths in Fe porphyrins are in the range 1.107(13)-1.161-
(8) Å.28 We therefore selected a second crystal and carried out
a second independent structure determination, but with the same
result. Such apparent shortening of terminal groups may be
due to anisotropic thermal motions, and mathematical (so-called
“riding”) corrections have been used previously by Schomaker
and Trueblood52 and Mason et al.53 to account in part for such
effects. We therefore re-refined all four structures using a riding
correction for CO. In this case, the Fe(CO)(1-MeIm)(TPP)
C-O bond length increased to 1.095 Å, and this and the other
riding model corrected C-O bond lengths are shown in Table
2.
(50) (a) Cullen D. L.; Meyer, E. F., Jr. J. Am. Chem. Soc. 1974, 96,
2095-2102. (b) Scheidt, R. W.; Mondal, J. U.; Eigenbrot, C. W.; Adler,
A.; Radonovich, L. J.; Hoard, J. L. Inorg. Chem. 1986, 25, 795-799.
(51) Bonnet, J. J.; Eaton, S. S.; Eaton, G. R.; Holm, R. H.; Ibers, J. A.
J. Am. Chem. Soc. 1973, 95, 2141-2149.
(52) Schomaker, V.; Trueblood, K. N. Acta Crystallogr. 1968, B24, 63-
76.
(53) Groombridge, C. J.; Larkworthy, L. F.; Mason, J. Inorg. Chem. 1993,
32, 379-380.

11330 J. Am. Chem. Soc., Vol. 120, No. 44, 1998
Salzmann et al.
Table 6. G94/DFT BPW91a Calculated 13C and 17O Shieldings (ppm) for Fe, Ru, and Os Carbonyl Metalloporphyrins Containing
1-Methylimidazole or Pyridine at the X-ray, Riding, and Geometry-Optimized Structures
13C shieldings
17O shieldings
system
σi
σ11
σ22
σ33
|σ33 - σ11|
σi
σ11
σ22
σ33
|σ33 - σ11|
Fe(P)(CO)(1-MeIm) X-ray
-2.49 -156.9 -155.0 304.5
461.4
475.6
501.3
506.3
509.3
500.3
489.9
505.4
499.4
539.5
553.8
551.2
546.2
534.9
546.1
540.8
587.0
600.9
597.5
592.9
579.2
590.5
577.1
572.6
-4.40 -224.7 -224.4 435.9
660.6
692.5
755.2
760.5
759.6
752.0
723.3
758.9
749.9
785.8
824.5
822.5
811.6
778.7
813.2
801.8
928.4
967.6
957.8
945.0
915.5
951.4
910.9
898.7
X-ray riding -12.8
-172.0 -170.1 303.6
-197.6 -196.1 303.7
-203.1 -200.9 303.2
-204.9 -203.5 304.4
-196.6 -194.9 303.7
-188.4 -185.1 301.5
-204.1 -201.0 301.3
-197.9 -194.5 301.5
-179.1 -176.1 360.4
-27.3
-71.6
-74.6
-73.3
-68.9
-54.6
-79.5
-73.8
23.9
-258.4 -257.6 434.1
-323.6 -322.8 431.6
-328.8 -326.8 431.7
-327.2 -325.2 432.4
-320.0 -318.7 432.0
-296.6 -294.0 426.7
-333.7 -330.0 425.2
-324.7 -322.0 425.2
-239.3 -235.3 546.5
optb
opt BPW91
-30.0
-33.6
opt BPW91c -34.7
opt B3LYP
X-ray
opt BPW91
opt B3LYP
-29.2
-24.0
-34.6
-30.3
1.7
Fe(P)(CO)(py)
Ru(P)(CO)(1-MeIm) X-ray
X-ray riding
-8.10 -193.7 -190.6 360.1
-1.53 -277.9 -273.3 546.6
-2.2
3.8
opt BPW91
opt B3LYP
X-ray
opt BPW91
opt B3LYP
-6.3
-3.0
0.1
-191.0 -188.0 360.2
-186.0 -183.1 360.2
-178.5 -177.6 356.4
-190.0 -189.1 356.1
-184.9 -183.9 355.9
-160.2 -157.3 426.8
-171.8 -168.8 429.1
-169.5 -166.7 428.0
-165.3 -162.5 427.6
-172.2 -171.6 407.0
-183.9 -183.2 406.6
-169.5 -169.1 407.6
-165.2 -164.9 407.4
-277.8 -273.4 544.7
-268.2 -263.9 543.4
-243.8 -242.3 534.9
-280.0 -278.4 533.2
-270.0 -268.5 531.8
-195.5 -189.6 732.9
-224.9 -218.6 742.7
-225.8 -219.5 732.0
-216.4 -210.3 728.6
-225.2 -220.4 690.3
-257.4 -252.2 694.0
-232.3 -228.3 678.6
-222.6 -218.7 676.1
Ru(P)(CO)(py)
16.3
-8.4
-2.2
115.9
99.8
95.6
100.6
81.6
61.4
72.7
78.3
-7.7
-4.3
36.4
29.5
30.6
33.3
21.0
13.2
23.0
25.7
Os(P)(CO)(1-MeIm) X-ray
X-ray riding
opt BPW91
opt B3LYP
X-ray
X-ray riding
opt BPW91
opt B3LYP
Os(P)(CO)(py)
a The basis set schemes used were LANL2DZ ECP on the metal, 6-311++G(2d) on the CO ligand, 6-31G* on the five nitrogen atoms bound
to the metal, and 3-21G* on the remaining atoms. b Structure optimized at the DFT/B3LYP level with the Fe Wachters basis set (see text). c The
basis sets used were LANL2DZ ECP on Fe, 6-311++G(2d) on the CO ligand, and 6-31G* on the remaining atoms (this calculation shows the
effect of using a locally dense scheme on the chemical shielding).
We next carried out a 13C and 17O nuclear magnetic resonance
spectroscopic investigation of both 13CO- and C17O-labeled
metalloporphyrins, using “magic-angle” sample spinning (MAS),
to deduce the principal components of the 13C shielding tensor,
the solid-state 17O chemical shift, and the absolute magnitude
of the 17O nuclear quadrupole coupling constant, e2qQ/h. In
addition, we used density functional theory (DFT) to predict
these same parameters, which provides an important test of our
ability to predict spectroscopic observables in relatively well
characterized materials.
In Figure 4 we show representative 13C and 17O MAS NMR
spectra, in this case of Ru(TPP)(13CO)(1-MeIm) and Ru(TPP)-
(C17O)(1-MeIm). Numerous additional 13C NMR spectra at
different spinning speeds were obtained on each of the six
systems of interest, and the principal components of the chemical
shift tensor, δii, were derived by using the Bayesian probability/
Herzfeld-Berger method54 described elsewhere.49 A compila-
tion of the experimental results is given in Table 3. We also
determined the isotropic chemical shifts for 17O, together with
estimates of the 17O nuclear quadrupole coupling (e2qQ/h), using
in this case a nutation method.55 For 17O, the relatively long
T1 values and only moderate spectral signal-to-noise ratios made
combined CSA-e2qQ/h determinations using other methods,
such as satellite transition spectroscopy,56 less practical, and
since signal-to-noise ratios in proteinssthe main long-term
targets of our researchsare far worse, this approach was not
pursued.
and 17O shieldings as one goes from Fe to Ru to Os. These
increases correlate in a remarkably linear fashion with the
infrared vibrational stretch frequency, νCO, as shown in Figure
5, especially for 17O, where an R2 value for the IR-NMR
correlation of 0.992 is obtained. These correlations are very
different from those seen in Fe-CO-containing metalloproteins,
where the chemical shift changes seen over the same 100 cm-1
νCO range are much smaller, Figure 5, and for 13C have the
opposite sign. In these systems, electrostatic polarization and
not “back-bonding” seems to be a more reasonable description
of the spectroscopic changes seen experimentally, and indeed
the inclusion of weak electrical perturbations in DFT calculations
has recently permitted the relatively accurate description of the
experimental shielding/νCO relationships seen in proteins.57
The second point of note in Table 3 is that the 13C shielding
tensors have remarkably similar breadths, about 470 ppm,
independent of metal or axial base, and all are axially symmetric
or close to axially symmetric, given a ∼15 ppm experimental
uncertainty in each tensor element determination. As we show
below and elsewhere,58 the small asymmetries observed in the
Fe compounds arise, we believe, primarily from experimental
errors, since we have been unable to reproduce them in any
calculations, even though the 13C tensor breadths or spans and
the 13C and 17O isotropic shifts as well as the 17O e2qQ/h values
are well reproduced.
We therefore next investigated to what extent the experi-
mental shifts and shift (or shielding) tensor elements for the
Fe, Ru, and Os systems can be predicted theoretically by using
density functional theory, as embodied in the Gaussian 94
program, using the six experimental metalloporphyrin structures.
To do so, we first examined the calculated 13C and 17O shifts
of the CO ligand in the Fe(TPP)(CO)(1-MeIm) system. We
(57) deDios, A.; Earle, E. J. Phys. Chem. 1997, 101, 8132-8134.
(58) McMahon, M.; deDios, A.; Godbout, N.; Salzmann, R.; Laws, D.
D.; Le, H.; Havlin, R. H.; Oldfield, E. J. Am. Chem. Soc. 1998, 120, 4784-
4797.
The first observation to be made from the results shown in
Table 3 is that there are very pronounced increases in both 13
C
(54) Herzfeld, J.; Berger, A. J. Chem. Phys. 1980, 73, 6021-6030.
(55) Freude, D.; Haase J. In NMR Basic Principles and Progress; Fluck,
E., Gu¨nther, H., Kosfeld, R., Seelig, J., Eds.; Springer-Verlag: Berlin, 1993;
Vol. 29, pp 3-90.
(56) Ja¨ger, C. In NMR Basic Principles and Progress; Fluck, E., Gu¨nther,
H., Kosfeld, R., Seelig, J. Eds.; Springer-Verlag: Berlin, 1994; Vol. 31,
pp 133-170.

Metalloporphyrin Structures
J. Am. Chem. Soc., Vol. 120, No. 44, 1998 11331
Table 7. Summary of Theory-versus-Experiment Slope and R2
Values for 13C and 17O Isotropic Shifts and 17O Nuclear Quadrupole
Coupling Constant (NQCC) Results for X-ray and DFT
Geometry-Optimized Structuresa
structures
X-ray
slope
R2
δi 13C
-0.6870
-1.0220
2.0180
-0.5972
-0.9022
1.4933
-0.9822
-1.2727
0.6083
-0.9562
-1.2689
0.8590
0.840
0.910
0.653
0.841
0.908
0.623
0.994
0.995
0.980
0.994
0.995
0.949
δi 17O
NQCC 17
δi 13C
O
O
O
O
X-ray riding
BPW91
δi 17O
NQCC 17
δi 13C
δi 17O
NQCC 17
δi 13C
B3LYP
δi 17O
NQCC 17
a Properties evaluted with the BPW91 exchange-correlation func-
tional, as discussed in the text.
Figure 6. Graphs showing correlations between experimental chemical
shifts and theoretical shieldings for carbon-13 and oxygen-17 nuclei
in carbonyl metalloporphyrin model systems. (A) Carbon-13 NMR
correlations. The R2 value is 0.994, and the slope is -0.956. (B)
Oxygen-17 NMR correlations. The R2 value is 0.995, and the slope is
-1.27. Calculations were carried out using the BPW91 functional in
Gaussian 94, as described in the text, using the B3LYP locally dense/
ECP structures having the Fe-C and C-O bond lengths given in Table
5.
Figure 7. Experimental and theoretical 17O NMR nutation plots. The
open circles represent data points for carbonyl(1-methylimidazole)-
(5,10,15,20-tetraphenylporphyrinato)osmium(II) while the asterisks
represent nutation data for carbonyl(1-methylimidazole)(5,10,15,20-
tetraphenylporphyrinato)iron(II). The solid lines represent theoretical
nutation plots, and representative quadrupole coupling constants (in
MHz) are indicated. In the nutation calculations, an asymmetry
parameter of 0 was used.
investigated the effects on shielding of (i) the structure of the
model porphyrin, (ii) the use of all-electron basis sets versus
effective core potentials for the metal, and (iii) the use of various
locally dense basis set schemes. The use of ECPs in ligand
shift calculations is supported by the work of Kutzelnigg,59 who
has shown that contributions from core electrons on one center
to the shielding tensors on neighboring nuclei are negligible.
There are also several reports in the literature of ligand 13C and
17O chemical shifts in transition-metal carbonyls60,61 and
oxo-anions62 using quasirelativistic ECPs and density functional
theory. For 13C, good overall agreement with experiment was
found using sum-over-states density functional perturbation
theory with individual gauges for localized orbitals, even for
third-row transition-metal complexes, and in previous work49
we have found for metal-olefin complexes that combined use
of LANL2DZ metal ECPs and the BPW91 functional39,40
permits good predictions of olefin ligand shieldings, even with
second and third row metals.
We therefore first consider the effects of structure, basis set,
and the choice of ECP on shielding in Fe-porphyrin systems
and then explore to what extent ligand shieldings can be
predicted for the heavier elements, using ECPs. Results are
presented in Table 4. For the metalloporphyrins listed, we find
that replacement of phenyl groups by hydrogen atoms leads to
no significant change in the calculated shifts (calculations 1 and
3 in Table 4), permitting a significant savings in computing
time. The increasing C-O bond lengths from X-ray to riding
model to DFT geometry-optimized structures are reflected in a
maximum change in isotropic shift of 28.3 and 69.0 ppm for
13C and 17O, respectively, Table 4. We also find that using a
locally dense basis set scheme on the porphyrin ring (calcula-
tions 3 and 6) is a reasonable approximation and again represents
a useful time-savings. The replacement of the Wachters iron
basis set with the Stuttgart ECP or the LANL2 ECP (with the
modified, decontracted basis set) decreases the shifts by about
30 ppm (calculations 7 and 8). Calculation 9 indicates that the
LANL2 is best used with the DZ basis set without modification.
With the LANL2DZ ECP/basis set, calculations 10 and 11 show
(59) Kutzelnigg, W.; Fleischer, U.; Schindler, M. in NMR Basic
Principles and Progress; Springer-Verlag: Berlin, 1990; Vol. 29, pp 165-
262.
(60) Kaupp, M.; Malkin, V. G.; Malkina, O. L.; Salahub, D. R. Chem.
Phys. Lett. 1995, 235, 382-388.
(61) Kaupp, M.; Malkin, V. G.; Malkina, O. L.; Salahub, D. R. Chem.s
Eur. J. 1996, 2, 24-30.
(62) Kaupp, M.; Malkin, V. G.; Malkina, O. L.; Salahub, D. R. J. Am.
Chem. Soc. 1995, 117, 1851-1852.

11332 J. Am. Chem. Soc., Vol. 120, No. 44, 1998
Salzmann et al.
Table 8. G94/DFT BPW91a Oxygen-17 Electric Field Gradient Tensor Elements and Theoretical and Experimental Quadrupolar Coupling
Constants for CO and Model Porphyrins
e2qQ/h (MHz)
system
V11 (au)
V22 (au)
V33 (au)
calc
expt
free CO
Fe(TPP)(CO)(1-MeIm)
-0.3534
-0.2743
-0.1275
-0.0733
-0.0167
-0.0155
-0.0852
-0.0439
-0.1062
-0.0335
-0.0378
-0.0386
-0.1905
-0.1274
-0.0661
-0.1182
-0.0184
-0.0845
-0.0528
-0.0242
-0.0378
-0.2198
-0.3868
-0.1138
-0.0503
-0.3534
-0.2655
-0.1178
-0.0578
-0.0041
-0.0007
-0.0726
-0.0373
0.0492
0.0130
-0.0227
0.0065
0.0862
0.0542
0.0227
-0.1100
-0.0097
-0.0763
-0.0379
0.0050
-0.0227
0.0939
0.1768
0.0416
0.0108
0.7068
0.5398
0.2452
0.1311
0.0208
0.0163
0.1578
0.0812
0.0569
0.0205
0.0606
0.0321
0.1043
0.0730
0.0434
0.2282
0.0281
0.1608
0.0907
0.0192
0.0606
0.1259
0.2100
0.0723
0.0400
4.25
3.24
1.5
0.78
0.12
0.10
0.91
0.49
-0.64
-0.20
0.35
-0.23
-1.1
-0.77
-0.38
1.37
0.17
0.97
0.54
-0.14
0.36
-1.32
-2.32
-0.68
-0.30
(+)4.40
X-ray
X-ray riding
optb
(+)1.0
opt BPW91
opt BPW91c
opt B3LYP
X-ray
X-ray riding
opt BPW91
opt B3LYP
X-ray
X-ray riding
opt BPW91
opt B3LYP
X-ray
opt BPW91
opt B3LYP
X-ray
opt BPW91
opt B3LYP
X-ray
X-ray riding
opt BPW91
opt B3LYP
}
Ru(TPP)(CO)(1-MeIm)
Os(TPP)(CO)(1-MeIm)
(+)0.68
(-)0.40
}
}
Fe(TPP)(CO)(py)
Ru(TPP)(CO)(py)
Os(TPP)(CO)(py)
NM
NM
}
}
}
NM
a The basis set schemes used were LANL2DZ on the metals, 6-311++G(2d) on the CO ligand, 6-31G* on the nitrogens bound to the metal, and
3-21G* on the remaining atoms. b Structure optimized at the DFT/B3LYP level with the Fe Wachters basis set (see text). c LANL2DZ on Fe,
6-311++G(2d) on CO, and 6-31G* on the remaining atoms.
Table 9. G94/DFT BPW91a Calculated 13C and 17O Shieldings for Fe(P)(CO)(1-MeIm) as a Function of M-C and C-O Bond Lengths
13C shielding (ppm)
17O shielding (ppm)
r(M-C) (Å)
r(C-O) (Å)
σ11
σ22
σ33
δi
σ11
σ22
σ33
δi
1.74
1.77
1.80
1.74
1.77
1.80
1.74
1.77
1.80
1.10
1.10
1.10
1.13
1.13
1.13
1.16
1.16
1.16
-173.6
-174.2
-174.6
-186.8
-187.8
-188.6
-199.9
-201.2
-202.4
-171.3
-172.1
-172.8
-184.6
-185.7
-186.7
-197.7
-199.2
-200.6
303.6
303.7
303.6
303.3
303.6
303.6
303.2
303.5
303.6
199.8
200.2
200.6
208.7
209.3
209.9
217.5
218.3
219.1
-252.9
-259.7
-265.9
-285.1
-292.6
-299.6
-319.6
-328.0
-335.8
-251.6
-258.6
-265.0
-283.5
-291.2
-298.5
-317.6
-326.3
-334.4
435.5
434.6
433.6
433.9
433.2
432.5
432.2
431.7
431.2
331.0
335.9
340.4
352.9
358.2
363.2
376.3
382.2
387.6
a The basis set schemes used were LANL2DZ ECP on the metal, 6-311++G(2d) on the CO ligand, 6-31G* on the five nitrogen atoms bound
to the metal, and 3-21G* on the remaining atoms.
that the size of the calculation can again be reduced by using
6-31G* basis sets on the metal-coordinated nitrogen atoms and
a locally dense scheme for the porphyrin ring. Calculations on
the Fe, Ru, and Os systems were therefore carried out as in
calculation 11: the metals were represented by the LANL2DZ
ECP/basis sets (as found in Gaussian 94), 6-311++G(2d) basis
sets were used for the CO ligand, 6-31G* for the metal-
coordinated nitrogen atoms, and 3-21G* for the remaining
atoms.
As can be seen in Table 4, closest accord with experiment is
obtained when an all-electron basis set and either the geometry-
optimized Fe(TPP)(CO)(1-MeIm) (calculation 2) or C2Cap
structure (calculation 5) are used. The riding model is close to
these results, but the 17O shift is almost 40 ppm in error
(calculation 1) and the X-ray geometry is even more in error
(calculation 4). Also notable is the close similarity in 13C and
17O shieldings between the all-electron calculation (1) and the
much smaller ECP calculation (11).
To test whether the choice of functional might also be important
in the optimization, we investigated both BPW91 and B3LYP
functionals, and results for the M-C and C-O bond lengths
are shown in Table 5. On the basis of previous geometry
optimizations of tilted and bent Fe-C-O systems both by
ourselves63 and others,24,25 a linear geometry was retained, since
the global energy minimum occurs at this geometry.24,25,63 As
can be seen in Table 5, there is generally good agreement
between the B3LYP and BPW91 optimizations and the X-ray
values. The only exception is in the case of the Fe(P)(CO)-
(MeIm) optimization, which at both B3LYP and BPW91 has a
significantly longer C-O bond than the X-ray or riding
geometry refinement. As for the M-C bond, the optimized
BPW91 and B3LYP bond lengths are in agreement and are
longer than the corresponding X-ray values, except for those
of the Fe compounds with the BPW91 functional. The use of
a locally dense basis set scheme and that of an effective core
potential versus an all-electron basis set for the metal were found
to cause no significant differences in the optimized structures.
Moreover, as may be seen in Table 5 (footnotes b and c), the
The fact that the all-electron and LANL2 ECP calculations
both show good agreement with experiment, using a geometry-
optimized structure, then led us to carry out similar restrained
geometry optimizations on each of the Ru and Os complexes.
(63) Havlin, R. H.; Godbout, N.; Salzmann, R.; Wojdelski, M.; Arnold,
W.; Schulz, C. E.; Oldfield, E. J. Am. Chem. Soc. 1998, 120, 3144-3151.

Metalloporphyrin Structures
J. Am. Chem. Soc., Vol. 120, No. 44, 1998 11333
in good accord with experiment, there is a fairly uniform
overestimation of the span of the 13C shielding tensor over that
seen experimentally, Tables 3 and 6. In the future, it seems
likely that the overall accord between theory and experiment
may be improved somewhat from the current results, for
example by using all-electron metal representations for the
heavier elements. However, the current R2 values for the
isotropic shift/shielding correlation are already excellent and
support the idea that DFT geometry optimization more ac-
curately represents the real Fe-C and C-O bond lengths for
Fe(TPP)(CO)(1-MeIm), since only the shieldings of the opti-
mized structure are close to the correlation line (Figure 6). And,
as we show below, the same improvement is also observed for
the 17O e2qQ/h as well.
Finally, we have investigated the 17O nuclear quadrupole
coupling constants in the three 1-methylimidazole complexes.
Because of limited signal-to-noise ratios, we used a pulse
nutation technique on the central transition. Nutation plots and
simulations are shown in Figure 7, and the e2qQ/h results
obtained from the simulations are presented in Table 8, together
with the results of Gaussian 94 electric field gradient tensor
and e2qQ/h calculations at a variety of geometries.
Figure 8. Graph showing correlation between experimental oxygen-
17 nuclear quadrupole coupling constants and those computed theoreti-
cally. The crosses indicate data for simple metal carbonyls and metal
clusters.64 The solid circles represent data for the three carbonyl
1-methylimidazole metalloporphyrins. The signs of the experimental
nuclear quadrupole coupling constants were taken from the theoretical
calculations. The solid line shows the ideal 1:1 experiment-versus-theory
correlation line.
In previous work,64 we found that the 17O nuclear quadrupole
coupling constants in four metal carbonyls, Fe(CO)5, Fe2(CO)9,
Ni2(η5-C5H5)2(CO)2, and Rh6(CO)16, could be measured ex-
perimentally and predicted theoretically (using the deMon/DFT
approach) with an rms error of 0.37 MHz (for a total of seven
points), a theory-versus-experiment slope of 1.09, and an R2
value of 0.959,64 which gives some idea as to the combined
accuracy of e2qQ/h nutation measurements and DFT calcula-
tions. These points are shown in Figure 8 (+) together with
the Gaussian 94 Fe, Ru, and Os C17O-TPP complex e2qQ/h
results (b), obtained using the B3LYP geometry-optimized
structure. Here, we must note that the signs of all experimental
e2qQ/h results are taken from the calculations, as we have done
previously with the simpler model systems,64 since the signs
cannot be determined from the nutation experiment. As can
be seen from Table 8 and Figure 8, there is good agreement
between the experimental and theoretical results when the
B3LYP DFT geometry-optimized structure is used, with an rms
error between theory and experiment of only 0.20 MHz, well
within the 0.37 MHz rmsd found previously (which derived from
a much larger range of nuclear quadrupole coupling constants
and a broader variety of compounds). For calculations per-
formed at the X-ray geometries (Table 5), there is also good
accord with experiment, but there are noticeable deviations for
the BPW91 optimized structures, Table 8, an effect which can
be attributed to the uniformly longer C-O bond lengths in the
BPW91 structures, Table 5. We show each of these correlations
in Table 7, together with the 13C and 17O shielding results, from
which it can be seen that we obtain the best, overall, description
of the 13C and 17O shifts and the 17O electric field gradient tensor
by use of B3LYP geometry-optimized structures, which are also
those which are closest to the conventional X-ray structures
(except in the case of Fe(TPP)(CO)(1-MeIm)). However, it is
not immediately obvious from the results obtained so far just
which bond lengths, metal-carbon (r(M-C)) or carbon-
oxygen (r(C-O)), dominate the shielding and electric field
gradient results observed. We therefore computed the 13C and
17O shieldings and 17O electric field gradients as a function of
r(M-C) and r(C-O) for the nine selected geometries given in
Tables 9 and 10. These parameter calculations were then
converted into the three corresponding property surfaces for the
Fe(P)(CO)(1-MeIm) complex: δO (r(M-C),r(C-O)), δC (r(M-
differences between using locally dense and more uniform basis
sets (footnote b, BPW91 calculation) and between the use of
the Wachters all-electron basis and the use of the LANL2DZ
ECP basis are essentially zero. In what follows, we therefore
use the locally dense/ECP optimized structures, for property
predictions.
We show in Table 6 the results of DFT shielding tensor
calculations for both crystallographic and DFT geometry-
optimized structures, the latter having the M-C and C-O bond
lengths shown in Table 5. There is very good overall agreement
between the computed and experimental results when DFT
optimized structures are used, and a typical set of 13C and 17O
isotropic shift results are shown in Figure 6. The slope of the
shift/shielding correlation using the B3LYP optimized structure
is -0.956 for 13C with an R2 value of 0.994, to be compared
with the ideal values of -1 and 1, respectively. For 17O, we
find a slope of -1.269 and an R2 value of 0.995, a slightly
worse slope than with 13C, but nevertheless the R2 value is
extremely high. Basically similar results are obtained when the
BPW91 geometry-optimized structures are used, as shown in
Table 7, although, as expected, results determined for the X-ray
structure are slightly worse, with a 13C slope of -0.69 and an
R2 value of 0.84, as shown in Table 7. For the iron-containing
systems, there is relatively good agreement between calculated
and experimental values of the shift anisotropies or tensor spans.
The average computed |σ33 - σ11| for the two bases is
comparable to an experimental value of ∼468 ppm. It is
interesting that in none of our shielding calculations is there
any appreciable asymmetry in the 13C shielding tensor, even
though a wide variety of metalloporphyrin/base orientations were
investigated, indicating that “proximal side” effects do not
change the symmetry of the tensor. Both carbon and oxygen
shieldings evaluated using the LANL2DZ iron basis, with or
without porphyrin phenyl groups, give results that are too
shielded when the shorter C-O bond lengths are used, Tables
4 and 5.
(64) Salzmann, R.; Kaupp, M.; McMahon, M.; Oldfield, E. J. Am. Chem.
Soc. 1998, 120, 4771-4783.
For Ru and Os, while the isotropic shieldings computed are

11334 J. Am. Chem. Soc., Vol. 120, No. 44, 1998
Salzmann et al.
Table 10. G94/DFT BPW91aCalculated 17O Electric Field
Gradient and Nuclear Quadrupole Coupling Constants in
Fe(P)(CO)(1-MeIm) as a Function of M-C and C-O Bond Lengths
1-methylimidazole complexessabout an order of a magnitude
larger than those for the three corresponding pyridine systems.
Second, we have determined the solid-state 13C NMR chemical
shifts and shift tensors, as well as the 17O NMR isotropic
chemical shifts, for all six systems. We find remarkably good
empirical correlations between the isotropic chemical shifts and
the vibrational stretch frequency, νCO, trends which are quite
different from those seen previously in metalloproteins, which
appear to be dominated by electrostatic field effects.57,58 Third,
we have used density functional theory to begin to investigate
the experimental shifts. We find a very good correlation
between theory and experiment, with R2 values of >0.99 being
found for both 13C and 17O NMR. Fourth, we have used a
nutation method to determine the overall magnitude of the
nuclear quadrupole coupling constant. There is very good
agreement (rmsd ) 0.20 MHz) between these results and those
of the DFT calculations, when DFT geometry-optimized
structures are employed.
electric field gradient
r(M-C) r(C-O)
(Å)
(Å)
V11 (au) V22 (au) V33 (au) NQCC (MHz)
1.74
1.77
1.80
1.74
1.77
1.80
1.74
1.77
1.80
1.10
1.10
1.10
1.13
1.13
1.13
1.16
1.16
1.16
-0.1714 -0.1601 0.3316
-0.1824 -0.1710 0.3534
-0.1931 -0.1816 0.3746
-0.1022 -0.0900 0.1922
-0.1135 -0.1012 0.2148
-0.1246 -0.1122 0.2368
-0.0320 -0.0191 0.0511
-0.0441 -0.0310 0.0751
-0.0559 -0.0425 0.0984
1.99
2.12
2.25
1.16
1.29
1.42
0.31
0.45
0.59
a The basis set schemes used were LANL2DZ ECP on the metal,
6-311++G(2d) on the CO ligand, 6-31G* on the five nitrogen atoms
bound to the metal, and 3-21G* on the remaining atoms.
The ability to predict the 13C and 17O NMR spectroscopic
observables in metalloporphyrins is an important first step in
using NMR and quantum chemistry to predict, refine, and
determine molecular structures in metalloproteins, where knowl-
edge of structural-spectroscopic correlations can help answer
long-standing questions about metal-ligand interactions.58,63,65
Acknowledgment. We thank Dr. H. Le for his Bayesian
spinning-sideband analysis program, Dr. J. Haase for providing
his nutation program, Dr. Scott R. Wilson and Teresa Prussak-
Wieckowska for extensive help with the crystallographic work,
and Professor Todd Martinez for helpful comments. This work
was supported in part by the U.S. Public Health Service
(National Heart, Lung and Blood Institute Grants HL-19481
and HL-25934). R.S. was a Swiss National Science Foundation
Postdoctoral Fellow, 1996-1997, and an American Heart
Association, Inc., Illinois Affiliate, Postdoctoral Fellow, 1997-
1998. C.J.Z. was a U.S. National Science Foundation Predoctoral
Fellow, 1994-1996, and M.M. was a National Institutes of
Health, Cellular and Molecular Biophysics Training Grant
Trainee (Grant GM-08276). This work used SGI/Cray Origin-
2000 and Power Challenge clusters at the National Center for
Supercomputing Applications (funded in part by the U.S.
National Science Foundation, Grant CHE 97-002ON). The
X-ray crystallographic facilities were supported by the National
Science Foundation (Grant CHE 95-01345). Solution NMR
spectra were obtained at the Varian-Oxford Instrument Center
for Excellence in NMR laboratory. Funding for this instrumen-
tation was provided in part from the W. M. Keck Foundation,
the National Institutes of Health (Grant RR-10444), and the
National Science Foundation (grant CHE 96-10502). High-
resolution mass spectra were obtained in the Mass Spectrometry
Laboratory, School of Chemical Sciences, University of Illinois,
supported in part by a grant from the National Institute of
General Medical Sciences (Grant GM-27029). The 70-VSE mass
spectrometer was purchased in part with a grant from the
Division of Research Resources, National Institutes of Health
(Grant RR-04648).
Figure 9. Property surfaces as a function of M-C and C-O bond
lengths: (A) 13C shift surface; (B) 17O shift surface; (C) 17O nuclear
quadrupole coupling constant surface. The calculations are for Fe(P)-
(CO)(1-MeIm) so M ) Fe; the axes are in Å.
C),r(C-O)) and NQCC (r(M-C),r(C-O)). These surfaces are
shown in Figure 9. As may be seen from the figure, all
properties are overwhelmingly dominated by changes in r(C-
O), the ligand bond length. Thus, any inaccuracies in the
crystallographic determinations of C-O bond lengths are
predicted to have a major influence on the computed ligand
properties, but the effect is much smaller for changes in M-C
bonding. More quantitatively, we can deduce metric shielding
derivatives, ∂σ/∂r, for both 13C and 17O in the Fe(TPP) species.
We find ∂σC/∂rCdO ∼ -300 ppm/Å and ∂σO/∂rCdO ∼ -800
ppm/Å, values which are to be compared with ∂σC/∂rCdO
)
-418 ppm/Å and ∂σO/∂rCdO ) -900 ppm/Å for free CO gas
(data not shown), while the Fe-C shielding derivatives are much
smaller, about -20 ppm/Å for 13C and about -190 ppm/Å for
17O, at the optimized geometry.
Supporting Information Available: Tables of crystal data,
structure solution and refinement details, atomic coordinates,
anisotropic displacement parameters, hydrogen coordinates,
bond lengths and angles, and torsion angles (60 pages, print/
PDF). X-ray crystallographic files, in CIF format, are available
on the Internet only. See any current masthead page for ordering
information and Web access instructions.
Conclusions
First, we have described the synthesis and structural charac-
terization of three new metalloporphyrins in the Fe, Ru, Os
series, which permits a structural comparison of all of the six
CO complexes which can be prepared from TPP, 1-MeIm, and
pyridine. The results indicate large saddle distortions in all three
JA9740069
(65) Godbout, N.; Havlin, R.; Salzmann, R.; Debrunner, P. G.; Oldfield,
E. J. Phys. Chem. A 1998, 102, 2342-2350.