Reactions of nickel(II) 2-aza-5,10,15,20-tetraphenyl-21-carbaporphyrin with methyl iodide. The first structural characterization of a paramagnetic organometallic nickel(II) complex

Article abstract of DOI:10.1021/ja9527028

The methylation of a nickel(II) complex (CTPP)Ni(II) of 2-aza-5,10,15,20-tetraphenyl-21-carbaporphyrin (CTPPH₂) with the mild methylating agent methyl iodide yields novel stable organonickel(II) complexes: diamagnetic (21-CH₃TPP)Ni(I

Full text of DOI:10.1021/ja9527028

5690
J. Am. Chem. Soc. 1996, 118, 5690-5701
Reactions of Nickel(II) 2-Aza-5,10,15,20-tetraphenyl-21-
carbaporphyrin with Methyl Iodide. The First Structural
Characterization of a Paramagnetic Organometallic Nickel(II)
Complex†
Piotr J. Chmielewski, Lechosław Latos-Graz3yn´ski,* and Tadeusz Głowiak
Contribution from the Department of Chemistry, UniVersity of Wrocław, 50 383 Wrocław, Poland
ReceiVed August 9, 1995X
Abstract: The methylation of a nickel(II) complex (CTPP)NiII of 2-aza-5,10,15,20-tetraphenyl-21-carbaporphyrin
(CTPPH2) with the mild methylating agent methyl iodide yields novel stable organonickel(II) complexes: diamagnetic
(21-CH3TPP)NiII and two scarce paramagnetic species (2-NH-21-CH3CTPP)NiIIX and (2-NCH3-21-CH3CTPP)NiIIX
(X ) Cl, I). The demetalation procedure resulted in isolation of two 21-carbaporphyrin derivatives, methylated at
the internal C(21) carbon atom, i.e., 2-aza-5,10,15,20-tetraphenyl-21-methyl-21-carbaporphyrin (21-CH3-CTPPH2)
and 2-aza-2-methyl-5,10,15,20-tetraphenyl-21-methyl-21-carbaporphyrin (2-NCH3-21-CH3CTPPH). The methylation
mechanism involves the oxidative addition of the methyl cation to the carbaporphyrin C(21) activated due to Ni-C
coordination. These C-methylated macrocycles preserve their coordinating properties as the remetalation processes
have been carried out. The reversible concerted addition of HX converts the diamagnetic (21-CH3TPP)NiII into the
paramagnetic (2-NH-21-CH3CTPP)NiIIX. The axial coordination step is accompanied by a protonation of the peripheral
nitrogen. The structures of (21-CH3CTPP)NIII (monoclinic, P21/c; a ) 15.055(3) Å, b ) 15.795(3) Å, c ) 17.069(3)
Å, â ) 115.00(3)°, Z ) 4, least-square refinement of 476 parameters using 3622 reflections, R ) 0.069) and (2-
NCH3-21-CH3CTPP)NiIII (monoclinic, P21/n; a ) 12.946(3) Å, b ) 23.519(5) Å, c ) 13.945 Å; â ) 93.2(3)°, Z )
4, the least-square refinement of 502 parameters using 3257 reflections, R ) 0.0559) have been determined by
X-ray diffraction. In the first case the nickel(II) is four-coordinate with bonds to three pyrrole nitrogen atoms (Ni-N
distances 1.948(5); 1.955(5); 1.938(5) Å) and the pyrrole carbon (Ni-C 2.005(6) Å). The nickel lies in the plane
of the three nitrogens, while the methylated pyrrole is sharply tilted out of the plane with dihedral angle between the
plane of three nitrogens and the methylated pyrrole plane being -42.2°. The methylated pyrrole is bound to nickel
Via a pyramidal carbon in the η1-fashion. The first structurally characterized paramagnetic organonickel(II) complex
(2-NCH3-21-CH3CTPP)NiIII presents unique features related to its electronic structure. The nickel(II) is five-coordinate
with bonds to three pyrrole nitrogen atoms (Ni-N distances 2.032(8); 2.057(8); 1.979(8) Å) and to the pyrrole
C(21) carbon (Ni-C 2.406(9) Å). The nickel is moved out from the plane of the three nitrogen plane toward the
iodide ligand. The 21-CH3 group and iodide are located on the opposite sides of the macrocycle. The substituted
pyrrole is sharply tilted out of the plane with the dihedral angle between the three nitrogen plane and the methylated
pyrrole plane being -55.3°. The methylated pyrrole is bound to nickel in the η1-fashion but the coordinating C(21)
atom preserves features related to trigonal sp2 hybridization. The angle between the inverted pyrrole plane and the
Ni-C bond increases from 42.8° to 70.1° on moving from the diamagnetic to paramagnetic species. The 1H NMR
and 2H NMR spectra of paramagnetic (2-NH-21-CH3CTPP)NiIIX and (2-NCH3-21-CH3CTPP)NiIIX complexes have
been examined. Functional group assignments have been made with use of selective deuteration and 2D COSY
experiments. The characteristic patterns of six downfield shifted pyrrole resonances accompanied by upfield shifted
3-H and 2-NH resonances are diagnostic of C-methylation. The 21-CH3 resonance appears in a characteristic 90-
110 ppm region.
Introduction
transition metal intermediates.1-3 The metal-carbon bond can
be firmly held in the cavity of the multidentate ligand such that
the possible dissociation of the M-C bond will be impaired.
The potentially terdentate monoanionic ligands [(2,6-Me2NCH2)-
C6H3]- and R,R′-diphosphino-m-xylenes provide spectacular
examples of such chemistry.2,3 Intramolecular activation, which
results in cyclometalation, received considerable interest in this
respect.3 The formation of the stable organometallic compounds
may be supported by the prearranged structure of the macro-
cyclic ligand, for instance the introduction of a m-xylene group
into the crown thioether framework produced 2,6,10-trithia[11]-
m-cyclophane which acted as a tetradentate ligand toward
palladium. The precoordination by other donor centers of this
polydentate ligand enhances an activation of the C-H bond.
Thus this macrocycle coordinates through three S donors and
the C(2) carbon of the xylene moiety.4
The development of the polydentate ligands with the potential
donor carbon atom favorably oriented toward the transition metal
ion affords a new strategy for stabilization of organometallic
compounds including their atypical oxidation states or unusual
† Abbreviations used: CTPP (CTPPH2) 2-aza-5,10,15,20-tetraphenyl-
21-carbaporphyrin dianion; 2-NCH3CTPP (2-NCH3CTPPH) 2-aza-2-methyl-
5,10,15,20-tetraphenyl-21-carbaporphyrin dianion; 21-CH3CTPP (21-CH3-
CTPPH2) 2-aza-5,10,15,20-tetraphenyl-21-methyl-21-carbaporphyrin dianion;
2-NH-21-CH3CTPP (2-NH-21-CH3CTTPH) 2-aza-5,10,15,20-tetraphenyl-
21-methyl-21-carbaporphyrin monoanion; 2-NCH3-21-CH3CTTP (2-NCH3-
21-CH3CTPPH) 2-aza-2,21-dimethyl-5,10,15,20-tetraphenyl-21-carbapor-
phyrin monoanion; TPP (TPPH2), 5,10,15,20-tetraphenylporphyrin dianion,
NCH3TPP (NCH3TPPH), 5,10,15,20-tetraphenyl-21-methylporphyrin monoan-
ion; OEP (OEPH2) octaethylporphyrin dianion; NCH3OEP (NCH3OEPH)
N-methyloctaethylporphyrin monoanion. The abbreviations for the neutral
forms are given in parentheses.
X Abstract published in AdVance ACS Abstracts, May 15, 1996.
S0002-7863(95)02702-8 CCC: $12.00 © 1996 American Chemical Society

A Paramagnetic Organometallic Nickel(II) Complex
J. Am. Chem. Soc., Vol. 118, No. 24, 1996 5691
Van Koten et al. demonstrated that the [(2,6-Me2NCH2)-
C6H3]- ligand stabilized the unique organometallic Ni(III)
complex.1c-e The remarkably low NiII/NiIII redox potentials1c-e,k
of {[(2,6-Me2NCH2)C6H3]NiII}X originate catalytic reactivity
in the Kharasch addition reaction, i.e., the 1:1 addition of
polyhalogenated alkanes to alkenes with formation of new C-C
and C-X bonds. Homogenous catalysts related to heteroge-
neous ones based on soluble polymeric supports1j or silane
dendrimers11 functionalized with pendant arylnickel(II) com-
plexes have been explored as well.
Chart 1
Organometallic chemistry of nickel is of current interest in
connection with mechanism of reactions of metalloenzymes
which contain the nickel ion, e.g., methyl-S-coenzyme-M
reductase and carbon monoxide dehydrogenase.5-9 Organo-
nickel complexes have been included as crucial intermediates
in both enzymatic cycles. In general organonickel(II) complexes
are diamagnetic including uncommon derivatives of nickel(II)
porphyrins.10 Paramagnetic organonickel(II) compounds are
extremely rare and for a very long period of time have been
exemplified by (σ-methyl)nickel(II)[(R,R,S,S)-N,N′,N′′,N′′′-tet-
ramethylcyclam].11 Recently a paramagnetic σ-methyl deriva-
tive of F430 (a nickel(II) tetrapyrrole whose structure corre-
sponds to that of hydrocorphin) was prepared by in situ
methylation.12 In the same time the axial coordination of
σ-phenyl to nickel(II) to produce paramagnetic complexes with
21-thiaporphyrin or 21-N-methylporphyrin as equatorial ligands
were demonstrated as well.13
In the context of organometallic chemistry of nickel(II)
facilitated by the appropriate construction of the polydentate
macrocycle, we have focused on porphyrin-related ligands, i.e.,
2-aza-5,10,15,20-tetraphenyl-21-carbaporphyrin and 2-N-methyl-
5,10,15,20-tetraphenyl-21-carbaporphyrin. These ligands are
isomers of their regular counterparts, i.e., of 5,10,15,20-
tetraphenylporphyrin and 5,10,15,20-tetraphenyl-21-N-meth-
ylporphyrin and are formed formally by an inversion of pyrrole
or N-methylated pyrrole rings.14-16 With the replacement of
the pyrrolenine nitrogen by a methine group, a carbaporphyrin
molecule retains coordination properties as demonstrated re-
cently by the formation of diamagnetic nickel(II) complexes,
i.e., (CTPP)NiII and (2-NCH3CTPP)NiII.14,16 CTPPH2 and
2-NCH3CTPPH are geometrically similar to TPPH2 and poten-
tially offer a suitable fit to a variety of metal ions. The structural
constraints typical for metalloporphyrins may be instrumental
in stabilization of their metallocarbaporphyrin counterparts
resulting in a peculiar stabilization of a σ-metal-carbon
bond.14,16 The unusual lability of the inner C-H bond is a
prerequisite of the 21-carbaporphyrin coordination to produce
the relatively robust NiII-C bond.
(1) (a) de Koster, A.; Kanters, J. A.; Spek, A. L.; van der Zeijden, A. A.
H.; van Koten, G.; Vrieze, K. Acta Crystallogr. 1985, C41, 893. (b) Grove,
D. M.; van Koten, G.; Ubbels, H. J. C.; Zoet, R.; Spek, A. L. Organome-
tallics 1984, 3, 1003. (c) Grove, D. M.; van Koten, G.; Zoet, R.; Murrall,
N. W.; Welch, A. J. J. Am. Chem. Soc. 1983, 105, 1379. (d) Grove, D.
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Schmitz, J. E. J.; Murrall, N. W.; Welch, A. J. Inorg. Chem. 1988, 27,
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In the course of the mild methylation of CTPPH2 we have
identified the derivative methylated exclusively at the ligand
periphery.16 Here we have sought to extend our investigation
from the methylation of 21-carbaporphyrin to its nickel(II)
complex.
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As a part of our continuing program of investigating the
general relationship between the isotropic shift pattern and the
molecular and electronic structures of paramagnetic nickel(II)
porphyrins13,17-19 we now report on the synthesis and charac-
terization of mono- and dimethylated nickel(II) carbaporphyrins.
In particular this work demonstrates that it is conceivable to
stabilize high-spin organonickel(II) macrocyclic complex with
(5) Jaun, B. HelV. Chim. Acta. 1990, 73, 2209.
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12th Summer School on Coordination Chemistry, Karpacz, Poland 1993.
(b) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Rachlewicz, K.; Głowiak, T.
Angew. Chem., Int. Ed. Engl. 1994, 33, 779.
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5692 J. Am. Chem. Soc., Vol. 118, No. 24, 1996
Chmielewski et al.
an equatorial nickel-carbon bond. The first structural charac-
terization of paramagnetic organonickel(II) complexes has been
also accomplished.
Results and Discussion
Formation of Mono- and Dimethylated Nickel(II) Car-
baporphyrins. Methylation of (CTPP)NiII has been performed
in chloroform or dichloromethane solution using methyl iodide.
In spite of the (CTPP)NiII reactivity toward methyl iodide its
stability in chlorinated solvents has been observed. Preliminary
studies involved introduction of methyl iodide into a chloro-
form-d solution of (CTPP)NiII (30:1 molar ratio). Since the
1H NMR spectra of nickel(II) porphyrins and heteroporphyrins
offer a sensitive technique for distinguishing between various
spin/oxidation/ligation states13,17-20 it has been used as the
principal method for following the methylation pattern and the
progress of the reaction. “Finger print” resonances of the 21-
CH3, 2-NH, and 2-N-CH3 groups are located out of the crowded
1
diamagnetic region and were readily detected. The H NMR
changes are consistent with the preference for methylation at
the internal C(21) position followed subsequently by the reaction
at the peripheral N(2) nitrogen. A variation in the relative
concentrations of monomethylated and dimethylated derivatives
has been observed over 7 days. The C-monomethylated species
dominated the reaction products after 24 h of the reaction.
Eventually the reaction resulted in complete conversion to a
dimethylated paramagnetic product. Concurrently the reaction
progress was followed by chromatographic separation. We have
found that the reaction route does not include the peripheral
methylation as the first step to form (2-NCH3CTPP)NiII in
measurable yield. Previously we have demonstrated that
methylation of CTPPH2 with methyl iodide proceeded exclu-
sively at the outer N(2) position and that insertion of the
nickel(II) in this macrocycle was readily achieved to produce
diamagnetic (2-NCH3CTPP)NiII.16 Furthermore, in an inde-
pendent experiment we have found that treatment of (2-NCH3-
CTPP)NiII with methyl iodide in chloroform (292 K, 1:50 molar
ratio) results in the methylation of the C(21) position, yielding
practically quantitatively as determined by the 1H NMR,
dimethylated paramagnetic nickel(II) complexes after 2 days
of reaction. Once the optimal conditions were determined the
way was open toward isolation of the new compounds.
Methylation of (CTPP)NiII carried out on the synthetic scale
lead to isolation of mono- and dimethylated species, i.e., (21-
CH3CTPP)NiII, (2-NH-21-CH3CTPP)NiIICl, and (2-NCH3-21-
CH3CTPP)NiIICl. The resulting complexes have good solubility
in dichloromethane, chloroform, and toluene. In the solid state
and in solution these complexes are air stable and can be
chromatographed. The feasible spontaneous demethylation
process to end up with (CTPP)NiII or (2-NCH3CTPP)NiII,
demonstrated previously for N-methylated analogue (NCH3-
TPP)NiIICl, has not been detected.17 It has ruled out the
possibility of the activation of a carbon-carbon bond by nickel
insertion2d,e even though C(21)-CH3 bond is favorably oriented
toward the NiII ion.
Figure 1. UV-vis spectra of the methylated nickel(II) carbaporphyrins
(dichloromethane, 293 K): solid line, (21-CH3CTPP)NiII; dashed line;
(2-NH-21-CH3CTPP)NiIICl; dotted line, (2-NCH3-21-CH3CTPP)NiIICl.
The electronic absorption spectra of (21-CH3CTPP)NiII, (2-
NH-21-CH3CTPP)NiIICl, and (2-NCH3-21-CH3CTPP)NiIICl are
presented in Figure 1. Methylated complexes have spectral
characteristics that resemble those of regular metalloporphyrins.
Thus the intense feature at ca. 450 nm corresponds to the
porphyrin Soret band, and the weaker features in the visible
region are related to the porphyrin Q-band absorption. The (2-
NH-21-CH3CTPP)NiIICl and (2-NCH3-21-CH3CTPP)NiIICl com-
plexes are paramagnetic as demonstrated by their distinctive
isotropic shift of pyrrole and phenyl resonances (vide infra).
Figure 2. UV-vis spectra of the methylated carbaporphyrins (dichlo-
romethane, 293 K): solid line, 21-CH3CTPPH2; dashed line, 2-NCH3-
21-CH3CTPPH.
The identification of ligands has been confirmed by the
parallel investigation of the acidic demetalation products of (21-
CH3CTPP)NiII and (2-NCH3-21-CH3CTPP)NiIICl to obtain 21-
CH3CTPPH2 and 2-NCH3-21-CH3CTPPH, respectively. The
electronic spectra of 21-CH3CTPPH2 and 2-NCH3-21-CH3-
CTPPH are porphyrin-like with the most intense bands at 445
and 455 nm, respectively, corresponding to the Soret band of
the regular porphyrin and are shown in Figure 2. The 1H NMR
(20) La Mar, G.; Walker, F. A. In Porphyrins; Dolphin, D., Ed.;
Academic Press: New York, 1979; Vol. IVB, p 61.

A Paramagnetic Organometallic Nickel(II) Complex
J. Am. Chem. Soc., Vol. 118, No. 24, 1996 5693
Both methylated carbaporphyrins preserve some degree of
aromaticity. All outer pyrrole and phenyl resonances demon-
strate downfield shifts due to ring current effect. The upfield
shifts have been determined for 21-CH3 and inner NH protons.
However, the ring current shifts decrease considerably on going
from 21-CH3CTPPH2 to 2-NCH3-21-CH3CTPPH or as previ-
ously found16 on going from CTPPH2 to 2-NCH3-CTPPH.
Accordingly the lowering of aromaticity is due to the external
methylation.
Different tautomeric forms may also be invoked to account
for the pyramidal coordination and the possible anionic nature
of the C(21) atom of methylated carbaporphyrin. Hypothetical
tautomers in Chart 2 are conveniently prearranged for coordina-
tion and demonstrate strongly marked pyramidal nature of the
C(21) carbon. Two inner protons, 21-CH and 23-NH of 21-
H-21-CH3CTPPH, are available for dissociation to create a
dianion. Only the inner 21-CH of 2-NH-21-CH3CTPP or
2-NCH3-21-H-21-CH3CTPP may dissociate to generate a monoan-
ionic environment. Such tautomers have not been experimen-
tally encountered as uncoordinated structures but represent the
useful presentation of the feasible coordination modes (Vide
infra).
1
The H NMR spectrum of diamagnetic (21-CH3CTPP)NiII
(trace A in Figure 3) demonstrates the very characteristic feature
of the upfield shifted C-methyl resonances in close analogy to
diamagnetic N-methylated metalloporphyrin21 and provides
evidence for the structural formula as below:
1
Figure 3. 300 MHz H NMR spectra of (21-CH3CTPP)NiII (trace A,
dichloromethane-d2, 293 K), 21-CH3CTPPH2 (trace B, dichloromethane-
d2, 203 K), and 2-NCH3-21-CH3CTPPH (trace C, chloroform-d, 223
K). Peak labels follow systematic position numbering of the porphyrin
ring or denote proton groups: pyrr, regular pyrrole ring protons; o, m,
and psortho, meta, and para protons of meso-phenyl ring, respectively;
s, solvent. Asterisk mark solvents present in the crystal lattice of
2-NCH3-21-CH3CTPPH.
This structural formula favors the π delocalization Via the outer
porphyrin path as established also in the corresponding crystal
structure (vide infra), while in 21-CH3CTPPH2 the inner and
outer delocalization routes can act simultaneously. Conse-
quently the remarkable increase of the ring current effect in the
C-methylated pyrrolic fragment of (21-CH3CTPP)NiII, reflected
by the remarkable chemical shift of the 3-H resonance, has been
demonstrated. Finally, we have found that both isolated ligands
21-CH3CTPPH2 and 2-NCH3-21-CH3CTPPH are susceptible to
facile nickel(II) insertion giving as products (21-CH3CTPP)-
NiII and (2-NCH3-21-CH3CTPP)NiIICl, respectively.
Crystal and Molecular Structure of (21-CH3CTPP)NiII.
The structure of (21-CH3CTPP)NiII has been determined by
X-ray crystallography. Table 1 contains selected bond distances
and angles. The structure suffers from disorder that involves
the location of the peripheral nitrogen atom and the adjacent
carbon atom. Thus N(2) and C(3) share a common position. It
has been refined to give 50% occupancy. Figure 4 shows the
perspective view of the complex with the disorder removed.
The crystal contains also one disordered molecule of dichlo-
romethane. The Ni-N distances are comparable to those in
the nearly planar diamagnetic (OEP)NiII complex (1.958(2) Å)22
in the triclinic form and are consistent with the averaged
distances 1.955(3) Å and 1.963(3) Å determined for disordered
(CTTP)NiII.14 These distances are slightly longer than those
found for four-coordinate nickel(II) porphyrin, i.e., the tetragonal
modification of (OEP)NiII (1.929(3) Å);23 nickel(II) tetraphe-
spectrum of 21-CH3CTPPH2 shows three AB patterns of the
pyrrole protons (Figure 3). The fourth inverted C-methylated
pyrrole ring shows a CH3 singlet in the unique position of
-4.837 ppm. This shift is consistent with the position of the
N-methyl resonances of the regular N-methylated porphyrins.21
Thus the 21-CH3 upfield chemical shift is clearly associated
with its location in the inner core of the carbaporphyrin. The
methyl group is exposed to the strong shielding effect produced
by the ring current effect. The spectrum of 21-CH3CTPPH2
resembles one analyzed previously in detail for CTPPH2,
admitting the fact that the strongly upfield shifted 21-H
resonance has been replaced by the resonance with intensity of
three protons unambiguously assigned to 21-CH3.14-16 Two
resonances of deuterium exchangeable 22-NH and 24-NH
protons have been also identified at -3.02 and -3.20 ppm
(CD2Cl2, 203 K). The 1H NMR spectrum of 2-NCH3-21-CH3-
CTPPH is presented in trace C of Figure 3. In comparison to
21-CH3CTPPH2 we have observed considerable smaller values
of all chemical shifts including the 21-CH3 signal at -1.398
ppm. In addition we have identified only a single 23-NH
resonances at 4.18 ppm (CDCl3, 223 K). The peripheral
methylation resulted with the 2-NCH3 resonance at 2.972 ppm.
The tautomeric structures, shown in Chart 1, prevail in the
solution for the newly isolated ligands. The close similarities
(21) Lavallee, D. K. The Chemistry and Biochemistry of N-substituted
Porphyrins; VCH Publishers: New York, 1987.
(22) Cullen, D. R.; Meyer, E. F. Jr. J. Am. Chem. Soc. 1974, 96, 2095.
(23) Meyer, E. F., Jr. Acta Crystallogr. 1972, B28, 2162.
1
of the H NMR spectra have been observed in pairs between
CTPPH2 and 21-CH3CTPPH2 or 2-NCH3CTPPH and 2-NCH3-
21-CH3CTPPH, respectively.

5694 J. Am. Chem. Soc., Vol. 118, No. 24, 1996
Chmielewski et al.
Chart 2
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
(21-CH3CTPP)NiII and (2-NCH3-21-CH3CTPP)NiIII
Bond Lengths (Å)
slightly displaced from the N(22)N(23)N(24) plane in the same
direction. The shape of carbaporphyrin resembles that seen in
metal complexes of N-alkylporphyrins. Contrary to the coor-
dination center the macrocycle is far from being planar. The
inverted C-methylated pyrrole is sharply tipped out of the
N(22)N(23)N(24) plane. The cis and trans pyrrole rings are
tilted in the reverse direction. Thus deviation of the pyrrole
planes from the plane defined by N(22)N(23)N(24) are as
follows: C(21) -42.2°, N(22) 15.4; N(23) 3.1°; N(24) 15.8°.
Bending of the pyrrole ring allows this group to coordinate to
the nickel(II) ion in an η1 fashion through the C(21) carbon
which acquires a pyramidal (sp3-hybridized) geometry. Thus
the metal lies out of the inverted pyrrole plane. The angle
between the methylated pyrrole plane and the NiII-C(21) bond
equals 42.0° and between the same plane and the C(21)-C(25)
bond equals 52°. The perfect tetrahedral arrangement would
produce ca. 55° inclination of these bonds.
Comparison of bond distances within the pyrrole and inverted
methylated pyrrole portions demonstrates that extensive delo-
calization exists through the macrocycle and extends to the
inverted pyrrole fragment. Bond distances of the regular
pyrroles CR-Câ > CR-Cmeso > CR-CN > Câ-Câ reproduce
the pattern of the regular porphyrin ligands. There is appreciable
effect of the aromatic character of the macrocycle on the inverted
C-methylated pyrrole fragment. So N(2)-C(3), N(2)-C(1), and
C(3)-C(4) bond distances are markedly shorter than C(1)-
C(21) and C(4)-C(21). The C(21) atom approaches sp3
hybridization geometrical parameters as illustrated by respective
bond angles and distances presented in Table 1. The pattern
of bond lengths within this fragment of the macrocycle is
modified to allow π-delocalization Via the outer path. The
longer C(1)-C(21) and C(4)-C(21) bond distances are ac-
counted for by the sp2 f sp3 hybridization change due to
C-methylation. This type of coordination is related to that of
η1-cyclopentadienyl complexes in which the metal-carbon bond
displays a sp3 hybridization geometry and the angle between
the M-C bond and the C5 plane is ca. 50°. The structural
features of the inverted pyrrole ring are remarkably similar to
the corresponding ones for monohaptocyclopentadienyl ring(s)
in (C5H5)3MoNO, (C5H5)4Ti, and (C5H5)4Zr complexes.28 For
instance in the case of (C5H5)4Ti C-C bond length of η1-C5H5
vary systematically around the ring in a manner consistent with
the diene structure (starting at the carbon atom bound to Ti):
1.446(5), 1.360(6), 1.420(5), 1.355(6), and 1.442(5) Å. The
C(2)-C(1)-C(5) angle at the coordinating carbon C(1) is
105.2(2)°. The Ti-C(1)-C(2) and Ti-C(1)-C(5) angles are
equal 106.4(1)° and 114.1(1)°.28b No relevant nickel(II) por-
(21-CH3TPP)NiII
(2-NCH3-21-CH3TPP)NiIII
Ni-N(24)
Ni-N(22)
Ni-N(23)
Ni-C(21)
C(21)-C(25)
C(21)-C(4)
C(21)-C(1)
C(3)-C(4)
N(2)-C(3)
N(2)-C(1)
1.948(5)
1.955(5)
1.938(5)
2.005(6)
1.541(9)
1.468(9)
1.480(8)
1.392(9)
1.344(9)
1.372(9)
2.032(8)
2.057(8)
1.979(8)
2.406(9)
1.53(2)
1.41(2)
1.390(14)
1.407(14)
1.332(14)
1.406(14)
Bond Angles (deg)
(21-CH3CTPP)NiII (2-NCH3-21-CH3CTPP)NiIII
C(21)-Ni-N(23)
N(22)-Ni-N(24)
C(21)-Ni-N(24)
C(21)-Ni-N(22)
N(24)-Ni-N(23)
N(23)-Ni-N(22)
Ni-C(21)-C(25)
Ni-C(21)-C(1)
Ni-C(21)-C(4)
C(1)-C(21)-C(25)
C(4)-C(21)-C(25)
C(1)-C(21)-C(4)
N(2)-C(1)-C(21)
C(3)-N(2)-C(1)
C(4)-C(3)-N(2)
C(21)-C(4)-C(3)
176.6(2)
173.8(2)
88.8(2)
88.5(2)
91.4(2)
91.0(2)
94.8(4)
117.6(4)
118.2(4)
113.1(5)
113.8(5)
100.2(5)
111.5(6)
108.3(6)
110.5(6)
109.6(5)
154.2(4)
158.4(4)
84.8(4)
85.3(3)
90.9(3)
89.8(3)
87.2(6)
101.0(7)
101.4(7)
125.0(11)
125.0(9)
106.7(9)
107.8(10)
109.3(9)
108.7(10)
107.4(9)
nylporphyrin with ethoxycarbonylcarbene fragment inserted into
Ni-N bond (1.92(1) Å),10a N-tosylamino-5,10,15,20-tetraphe-
nylporphyrinatonickel(II) (1.920(3), 1.883(3), 1.920(3) Å),10b
and nickel(II) complexes of octaethylporphyrin N-oxide dianion
(1.922(4), 1.900(4), 1.929(5) Å).24
The Ni-C bond length 2.005(6) Å in (21-CH3CTPP)NiII is
in the upper limits of Ni(II)-C bond lengths (1.81-2.02
Å).1b,25-27 This bond is essentially longer than one determined
for the constrained van Koten’s nickel(II) system [(2,6-Me2-
NCH2)2C6H3]NiII(HCOO) 1.814(2) Å.1b The NiII-C bond
length suggests sp3 hybridization of the coordinating C(21)
carbon atom. The determined distance is in good agreement
with those found for the plain examples of the low spin
nickel(II)-sp3 hybridized carbon atom coordination, e.g., a
simple alkyl derivative in a square planar nickel(II) complex
(1.94(1) Å),26 and nickel(II) complexes derived from the
tripoidal ligands [(N(CH2CH2S-iso-C3H7)3NiII(CH3)]+ 1.94(2)
Å9 and [(N(CH2CH2P(C6H5)2)3NiII(CH3)]+ 2.02(2) Å.27
(25) Jolly, P. W. In ComprehensiVe Organometallic Chemistry; Wilkin-
son, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, 1982; Vol.
6, p 37.
(26) Barnett, B. L.; Kruger, C. J. Organomet. Chem. 1972, 32, 1699.
(27) Sacconi, L.; Dapporto, P.; Stoppioni, P.; Innocenti, P.; Benneli, C.
Inorg. Chem. 1977, 16, 1669.
The coordination core of (21-CH3CTPP)NiII is essentially
planar. Nickel(II) (0.097(1) Å) and C(21) (0.074(5) Å) are
(28) (a) Calderon, J. L.; Cotton, F. A.; Legzdins, P. J. Am. Chem. Soc.
1969, 91, 2528. (b) Calderon, J. L.; Cotton, F. A.; DeBoer, B. G.; Takats,
J. J. Am. Chem. Soc. 1971, 93, 3592. (c) Rogers, R. D.; Bynum, R. V.;
Atwood, J. L. J. Am. Chem. Soc. 1978, 100, 5239.
(24) Balch, A. L.; Chan, Y.-W.; Olmstead, M. M. J. Am. Chem. Soc.
1985, 107, 6510.

A Paramagnetic Organometallic Nickel(II) Complex
J. Am. Chem. Soc., Vol. 118, No. 24, 1996 5695
Figure 4. The perspective drawing of (21-CH3CTPP)NiII showing one
of the two equally possible molecule orientation with respect to the
N(2)-C(3) permutation.
Figure 6. Comparison of nickel and C(21) environment geometry in
(21-CH3CTPP)NiII (upper drawing) and (2-NCH3-21-CH3CTPP)NiIII
(lower drawing).
raphenyl-21-thiaporphyrin 2.094(3), 1.963(3), 2.084(3) Å31 has
been also noted. The NiII-N distance of the Ni-N bond located
opposite to C(21) is the shortest in the set in analogy to the
(STPP)NiIICl structure where the bond length to the nitrogen
trans to the coordinating sulfur is the smallest.
The C-methylated carbaporphyrin has had to rearrange
profoundly in relation to (21-CH3CTPP)NiII in order to accom-
modate the high-spin nickel(II) ion in the coordination crevice.
The unprecedented structure demonstrates the methylated pyr-
role ring sharply bent from the core plane defined here by the
N(22)N(23)N(24) nitrogens, while the other pyrrole rings are
slightly bent in the opposite direction. The angle between the
C(1)C(21)C(4) and N(22)N(23)N(24) planes is -55.3° in the
high-spin complex but -42.2° in the low-spin one. The
methylated pyrrole ring is strongly bent out from the core plane
preserving the planarity of the C-methylated pyrrole. Thus the
N(2)-CH3 and C(21)-CH3 methyl groups lies near the meth-
ylated pyrrole plane with the angles between this plane and the
corresponding bonds being 17.1° and -11.0°, respectively. Such
an architecture allows coordination to the nickel(II) ion in an
η1 fashion through the C(21) carbon atom. Thus the metal lays
out of the pyrrole plane, with the angle between the methylated
pyrrole plane and the NiII-C(21) bond being 70.1° (Figure 6).
However the carbon atom does not acquire a pyramidal
geometry that is well defined for (21-CH3CTPP)NiII. The
coordinating carbon preserves planar trigonal geometry with
some degree of pyramidal distortion, pointing out the consider-
able preservation of sp2 hybridization. This suggests the bond
formation due to the σ-accepting properties of the NiII from
the pz orbital of the sp2 hybridized C(21) carbon. A comparison
of the bonding geometry between (21-CH3CTPP)NiII and (2-
NCH3-21-CH3CTPP)NiIII is clearly demonstrated in Figure 6
and in Table 1. In order to get a more quantitative measure of
the distortion we have decided to analyze the sum of the bond
angles ∑1 ) Ni-C(21)-C(1) + Ni-C(21)-C(4) + Ni-
C(21)-C(25) formed by the Ni-C(21) bond and ∑2 ) C(1)-
C(21)-C(4) + C(1)-C(21)-C(25) + C(4)-C(21)-C(25)
which describes the ligand planarity around the C(21) carbon.
The comparison of the idealized geometries with (21-CH3-
CTPP)NiII and (2-NCH3-21-CH3CTPP)NiIII structures is given
in Table 2.
Figure 5. The perspective drawing of (2-NCH3-21-CH3CTPP)NiIII
presenting the more abundant molecule orientation with respect to the
N(2)-C(3) disorder.
phyrin structure seems to be available for direct comparisons
with (21-CH3CTPP)NiII. However the geometry of (21-CH3-
CTPP)NiII bears some resemblance to the coordination mode
of N-methylated porphyrins where N-methylated pyrrole ring
is strongly tipped off to afford coordination of the sp3 hybridized
nitrogen atom of the N-methylated pyrrole ring.21
Crystal and Molecular Structure of (2-NCH3-21-CH3-
CTPP)NiIII. The structure of (2-NCH3-21-CH3CTPP)NiIII has
been studied by X-ray diffraction. The perspective view of the
complex which has no crystallographically imposed symmetry
is shown in Figure 5. A selection of important bond distances
and angles is included in Table 1 to compare with analogous
values of the diamagnetic (21-CH3CTPP)NiII species. The
structure displays disorder in the location of the 2-NCH3
fragment. The structure has been refined to give 65% oc-
cupancy with 2-NCH3 as shown in Figure 5 and 35% occupancy
with methyl group attached to the nitrogen atom replacing C(3)
of the major form. Figure 5 only shows the major form. The
unit cell also contains one molecule of benzene. The C-methyl
substituent lies on the face opposite to the iodide. The nickel is
displaced 0.375(2) Å out the N(22)N(23)N(24) plane toward
the axial iodide. The deviation of the pyrrole planes from the
plane defined by dihedral angles between the pyrrole and
N(22)N(23)N(24) planes are as follows: C(21) -55.3°, N(22)
14.3°, N(23) 0.9°, N(24) 14.4°. The Ni-N bond lengths are
longer than those found for (21-CH3CTPP)NiII or other dia-
magnetic nickel(II) porphyrins but are similar to that 2.038(4)
Å seen in a six-coordinate, high-spin nickel(II) porphyrin
complex29 or 2.09 Å in a six-coordinate high-spin nickel(II)
hydroporphyrin complex.30 The similarity of bond lengths to
those found for the five-coordinate, high-spin nickel(II) tet-
The observed tendency to shorten the C(1)-C(21) and C(4)-
C(21) bond distances within the inverted methylated pyrrole
on going from (21-CH3CTPP)NiII to (2-NCH3-21-CH3CTPP)-
NiIII (Table 1) reveals the extensive π delocalization in
(29) Kirner, J. F.; Garofolo, J. Jr.; Scheidt, W. R. Inorg. Nucl. Chem.
Lett. 1975, 11, 107.
(30) Kratky, C.; Fa¨ssler, A.; Pfaltz, A.; Kra¨utler, B.; Jaun, B.; Eschen-
moser, A. J. Chem. Soc., Chem. Commun. 1984, 1368.

5696 J. Am. Chem. Soc., Vol. 118, No. 24, 1996
Chmielewski et al.
NCH3-21-CH3CTPP)NiIIX (X ) Cl-, I-) species investigated
in this work.13,17 It is truly remarkable that carbaporphyrin may
adopt different geometries to accommodate high-spin or low-
Table 2. Comparison of Geometry around the Coordinating
Carbon
sum of bond
angles (deg)
2
2
spin nickel(II) ions. The electron in the dx -y orbital greatly
increases the effective radius of the nickel(II) ion. This fact
easily accounts for the 0.05-0.1 Å increase of the NiII-N bond
length going from low-spin to the high-spin species. Likewise,
0.12 Å increase of the axial NiII-N bond distance was
determined for nickel(II) complexes with tripoidal ligands due
∑
1
∑
2
idealized geometrya tetrahedral
pz side-on-fashion
crystal structurea,b (21-CH3CTPP)NiII
(2-NCH3-21-CH3CTPP)NiIII
328.5 328.5
270 360
330.3 327.3
289.6 356.7
286.5 357.3
[IPtMeC6H3(CH2NMe2)2-2,6]+
to location of the unpaired electron at the dz orbital.9 Apart
2
[Pt(o-tolyl)MeC6H3(CH2NMe2)2-2,6]+ 277.5 359.4
from the modification of the NiII effective ionic radius the
dramatic change of the C(21) coordination mode is instrumental
as well. As already discussed the geometry of C(21) coordina-
tion in (21-CH3CTPP)NiII resembles a coordination of the
anionic sp3 hybridized alkyl ligand to the nickel(II) center. The
side-on coordination of the inverted pyrrole demonstrates the
novel type of coordination in the organometallic chemistry of
high-spin nickel(II) with aromatic ligands.
b
a ∑1, ∑2 of nickel(II) complexes defined in the text.
∑ ) Pt-
Cipso-Cortho + Pt-Cipso-Cortho′ + Pt-Cipso-CMe; ∑2 ) Cortho1-Cipso
-
Cortho′ + CMe-Cipso-Cortho + CMe-Cipso-Cortho′
.
(2-NCH3-21-CH3CTPP)NiIII Via the inner route contrary to the
(21-CH3CTPP)NiII case where the availability of this path is
limited.
The relevant structural rearrangement due to the methylation
was established for C-methylated trans-2,6-bis[(dimethylamino)-
methyl]phenyl-N,C,N′ complex of platinum(II) [PtI(MeC6H3-
(CH2NMe2)2-o,o′)]+ considered as an example of σ-metal
substituted arenonium ion, in which the methyl group of the
alkyl halide is bonded to the carbon atom of the aryl ring
originally σ-bonded (sp2-hybridized) to the platinum center.1f
The angles between the plane defined by the coordinating Cipso
and two ortho carbons of the phenyl ring and the C-CH3 and
Pt-C bonds equal 16.0° and 93.4°, respectively. The angle
between the Cipso-CH3 bond and the Pt-Cipso bond is 104.2°.
In the case of the [PtI(MeC6H3-(CH2NMe2)2-o,o′)]+ ([Pt(o-
tolyl)(MeC6H3-(CH2NMe2)2-o,o′)]+) the ∑1 and ∑2 parameters
suggest the relatively small tetrahedral distortion of Cipso from
the primary trigonal geometry and are rather consistent with
the side-on coordination of the platinum cation (Table 2).1f,m
The NiII-C(21) distance (2.406(9) Å) seems to be unusually
long, but we assume that it is still the bond distance. The
NiII-C interaction may result from the proximity effect due to
the location of the potential carbon donor at the macrocyclic
structure. It has seemed reasonable to consider an alternative
view of the bonding interaction which involves simultaneously
more than one carbon atom.36,37 The relevant relation of the
nickel-carbon distances for high-spin [(Ni-C(21) 2.406(9) Å,
Ni-C(25) 2.786 Å, Ni-C(4) 3.026 Å; Ni-C(1) 2.997 Å)] and
low-spin [Ni-C(21) 2.005(6) Å; Ni-C(25) 2.629 Å; Ni-C(1)
2.986 Å; Ni-C(4) 2.988 Å)] complexes unambigously identify
the C(21) atom as a center of the bonding interaction. The
bonding interaction is manifested by a strong downfield isotropic
Apart from the already mentioned σ-platinum substituted
arenonium ion1f,m such a bonding mode has been encountered
in the case of electrophilic interactions of silver salt with
arenes.33,34 An excellent example of η1-coordination was
offered by X-ray structure of a silver salt of the weakly
-
coordinating carborane anion B11CH12 containing benzene in
the lattice.34 One benzene molecule coordinates to silver in the
η1-mode with the Ag-CR distance of 2.400(7) Å and the Ag-
CR-Câ and Ag-CR-Câ′ bond angles equal 89.5° and 94.6°,
respectively (CRscoordinating atom of benzene, Câ or Câ′
adjacent carbon atoms).
The other example of the peculiar interaction between cationic
center and arene involves a structure of [Et3SiB(C6F5)4‚toluene]
where the silylium group is located directly above para-carbon
of toluene in the side-on-fashion.35 The description of the
electronic structure is the matter of controversy, but it is
considered in terms of an arenium cation [Et3Si‚toluene]+.35c
The existence of the covalent interaction between the Et3Si
group and the toluene has been recognized in spite of a long
Si-C distance (2.18 Å).35e
NMR Studies of Paramagnetic Nickel(II) Complexes of
Methylated Carbaporphyrin. The 1H NMR data of the
paramagnetic reaction products have been analyzed considering
their C1 symmetry which is adequate to described the methylated
complexes (2-NH-21-CH3CTPP)NiIICl and (2-NCH3-21-CH3-
CTPP)NiIICl. There are seven distinct pyrrole positions for (2-
NH-21-CH3CTPP)NiIICl, a 2-NH position analogous to the
2-CH of the regular porphyrin and four unequivalent meso
phenyl rings. Respective NMR data for (2-NH-21-CH3CTPP)-
NiIICl and (2-NCH3-21-CH3CTPP)NiIICl are presented in
Figures 7 and 8. The spectral parameters for these and other
relevant compounds have been gathered in Table 3. Resonance
assignments, which are given above each peak, have been made
on the basis of relative intensities, line widths, site specific
deuteration, and 2D COSY experiments. The most characteristic
feature, the downfield broad resonance (line width 1320 Hz) at
109.7 ppm has been identified as the 21-CH3 resonance. This
1
shift of the 21-CH3 group in the H NMR spectra (Vide infra).
To the best of our knowledge the structure discussed here
represents the very first structurally characterized case of high-
spin organometallic NiII species. Consequently, we are not
aware of any precedent for the typical high-spin NiII-C bond
length. In our opinion the situation bears some distant
resemblance, as far as bond lengths are concerned, to five-
coordinate N-methylated porphyrin complexes of the metals of
the first transition row. There, the N-methylated nitrogen-metal
bonds fall in the range 2.257(5)-2.530(7) Å when the other
regular M-N distances are markedly shorter.21,32 Generally
N-methylated porphyrins act as the monoanionic ligand stabiliz-
ing high-spin five coordinate complexes. The X-ray structure
of (NCH3TPP)NiIIX has not been determined. It was found by
means of 1H NMR that this compound is paramagnetic and five-
coordinate, similar to the (2-NH-21-CH3CTPP)NiIICl and (2-
1
resonance disappears in the H NMR spectrum of (2-NH-21-
(33) Turner, R. W.; Amma, E. L. J. Am. Chem. Soc. 1966, 88, 3243.
Hall Griffith, E. A.; Amma, E. L. J. Am. Chem. Soc. 1974, 96, 743.
(34) Shelly, K.; Finster, D. C.; Lee, Y. J.; Scheidt, W. R.; Reed, C. A.
J. Am. Chem. Soc. 1985, 107, 5995.
(35) (a) Lambert, J. B.; Zhang, S.; Stern, C. L.; Huffman, J. C. Science
1993, 260, 1917. (b) Lambert, J. B.; Zhang, S. Science 1995, 263, 984. (c)
von Rague´ Schleyer, P.; Buzek, P.; Muller, T.; Apeloig, Y.; Siehl, H.-U.
Angew. Chem., Int. Ed. Engl. 1993, 32, 1471. (d) Olah, G. A.; Rasul, G.;
Li, X.-Y.; Bucholz, A.; Sandford, G.; Prakash, G. K. S. Science 1995, 263,
983. (e) Pauling, L. Science 1995, 263, 983. (f) Reed, C. A.; Xie, Z.;
Bau, R.; Benesi, A. Science 1993, 260, 402. Reed, C. A.; Xie, Z. Science
1995, 263, 986. (g) Cacace, F.; Attina´, M.; Fornanrini, S. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 654.
(31) Latos-Graz˘yn´ski, L.; Lisowski, J.; Olmstead, M. M.; Balch, A. L.
Inorg. Chem. 1989, 28, 1184.
(32) (a) Bartczak, T.; Latos-Graz˘yn´ski, L.; Wysłouch, A. Inorg. Chim.
Acta 1990, 171, 205. (b) Balch, A. L.; Cornman, C. R.; Latos-Graz˘yn´ski,
L.; Olmstead, M. M. J. Am. Chem. Soc. 1990, 112, 7552.

A Paramagnetic Organometallic Nickel(II) Complex
J. Am. Chem. Soc., Vol. 118, No. 24, 1996 5697
Figure 7. NMR spectra of paramagnetic mono- and dimethylated
nickel(II) carbaporphyrin: (A) (2-NH-21-CH3CTPP)NiIICl (1H NMR,
CDCl3, 293 K); (B) (2-NH-21-CH3CTPP-d7)NiIICl (2H NMR, CHCl3,
293 K); (C) (2-NCH3-21-CH3CTPP)NiIICl; inset (2-NCD3-21-CD3-
CTPP)NiIICl (1H NMR, CDCl3, 293 K). Peak labels follow systematic
numbering of the porphyrin ring or denote proton groups: pyrr, regular
pyrrole ring protons; s, solvent. Asterisk marks traces of diamagnetic
(21-CH3CTPP)NiII found due to some 2-NH proton dissociation in
solution.
Figure 8. 1H NMR spectra of the meso-phenyl region of (2-NH-21-
CH3CTPP)NiIICl in CDCl3 at various temperatures. Peak labels denote
respective ortho, meta, or para protons of unequivalent phenyl rings;
s, solvent.
at 273 K. Cross-peaks reveal pairwise coupling among six
downfield pyrrole resonances. As expected no cross-peak has
been seen for the upfield pyrrole resonance but this can be
assigned to the 3-H position by default. Characteristic sets of
cross-peaks due to coupling between five protons of a phenyl
ring have been established and located in the COSY map for
the four nonequivalent phenyls of (2-NCH3-21-CH3CTPP)NiIICl.
The results of these assignments were used to identify the
individual resonances in Figures 8 and 9, and the resonance
positions are given in Table 3 together with analogous data for
(2-H-21-CH3CTPP)NiIICl. The two ortho and meta protons on
each of the meso-phenyl rings are inequivalent since the
porphyrin plane bears different substituents on the opposite sides
and the rotation about the meso carbon-phenyl bond may be
restricted. However, onset rotation about this bond will cause
an exchange of these positions. Since all meso phenyl rings
are structurally different and exposed to different steric hin-
drances, it is anticipated that there will be some differences in
the rate of phenyl rotation for each ring type. The representative
temperature dependence of the phenyl region for (2-H-21-CH3-
CTPP)NiIICl is shown in Figure 8. Two phenyls, labeled B
and C demonstrated a set of five resonances typical for the slow
rotation limit even at 293 K. The averaged features of three
phenyl resonances have been seen for two other phenyls A and
D. As the temperature lowered these meta and ortho resonances
of A and D split due to slower rotation rate. At this stage we
cannot assign the phenyls to the specific meso positions although
the larger shift differences of the ortho resonances favor the
tentative assignment of the B and C phenyls to the 5,20 positions
which are close to the inverted pyrrole ring. The temperature
dependent rotation of the meso phenyls have been observed for
diamagnetic (21-CH3CTPP)NiII as well.
CD3CTPP)NiIICl. A resonance at -23.07 ppm (293 K) has been
assigned to the 2-NH proton. This resonance is absent in the
spectrum of (2-NCH3-21-CH3CTPP)NiIICl. When chloroform-d
saturated with deuterium oxide was added to the solution of
(2-NH-21-CH3CTPP)NiIICl, the 2-NH resonance disappeared
due to formation of (2-ND-21-CH3CTPP)NiIICl. In order to
2
distinguish the pyrrole and phenyl resonances the H NMR
spectrum of (2-NH-21-CH3CTPP-d7)NiIICl has been obtained
and is shown in trace B of Figure 7. The six pyrrole resonances
are in the 60-20 ppm region. The single slightly upfield shifted
pyrrole resonances at 2.04 ppm has been assigned to the 3-D
position by analogy to (NCH3TPP)NiIICl.13,17 The additional
resonances, presented in detail in Figure 8, come from the meso
phenyl protons. The resonance assignments of (2-NCH3-21-
CH3CTPP)NiIICl follow that of (2-NH-21-CH3CTPP)NiIICl. The
2-NCH3 resonance has been unambiguously identified since it
is missing in the spectra of (2-NH-21-CH3CTPP)NiIICl and (2-
NCD3-21-CD3CTPP)NiIICl (Figure 8, Table 3).
The two-dimensional COSY experiment has been effective
in connecting protons within pyrrole moieties and meso phenyl
groups.38 Figure 9 shows the representative COSY data of (2-
NCH3-21-CH3CTPP)NiIICl gathered in chloroform-d solution
(36) Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1993, 32, 654 and
references cited therein.
(37) Kretz, C. M.; Gallo, E.; Sollari, E.; Floriani, C.; Chiesi-Villa, A.;
Rizzoli, C. J. Am. Chem. Soc. 1994, 116, 10775 and references cited therein.
(38) Keating, K. A.; de Ropp, J. S.; La Mar, G. N.; Balch, A. L.; Shiau,
F.-Y.; Smith, K. M. Inorg. Chem. 1991, 30, 3258.

5698 J. Am. Chem. Soc., Vol. 118, No. 24, 1996
Chmielewski et al.
Table 4. Crystallographic Data for (21-CH3CTPP)NiII‚CH2Cl2 and
(2-NCH3-21-CH3CTPP)NiIII‚C6H6
(21-CH3CTPP)NiII‚ (2-NCH3-21-CH3CTPP)NiIII‚
compound
CH2Cl2
C6H6
empirical formula
color, habit
fw
C46H32N4Cl2Ni
brown prism
770.38
C52H39N4INi
green prism
905.50
crystal system
space group
a, Å
b, Å
c, Å
monoclinic
P21/c
monoclinic
P21/n
15.055(3)
15.795(3)
17.069(3)
115.00(3)
3679(1)
12.946(3)
23.519(5)
13.945(3)
93.20(3)
4239(2)
293(2)
â, deg
V, Å3
T, K
293(2)
Z
4
4
crystal size, mm
d
0.05 × 0.1 × 0.20
0.08 × 0.1 × 0.12
calcd, g/cm-3
1.391
1.419
radiation λ, Å
1.54180
2.402
0.0691
1.54180
6.685
0.0559
µ (Cu KR), mm-1
a
R1
b
wR2
0.1849
0.1433
2
a R1 ) ∑||Fo - Fc||/∑|Fo|. b wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo )2]]1/2
.
Analysis of Hyperfine Shifts. The Curie plots of the
temperature dependencies of the chemical shifts of the pyrrole
and methyl resonances of (2-NCH3-21-CH3CTPP)NiIICl and (2-
NH-21-CH3CTPP)NiIICl (not shown) demonstrate linear be-
havior with extrapolated intercepts that do not correspond to
the suitable diamagnetic references (21-CH3CTPP)NiII or rel-
evant carbaporphyrin, indicating small contribution of the dipolar
shift due to the anisotropy of zero-field splitting. The ZFS
contribution presents the T-2 dependent curvature.39,40 How-
ever, the alternate directions of phenyl shifts in (2-NH-21-CH3-
CTPP)NiIICl or (2-NCH3-21-CH3CTPP)NiIICl are compatible
with the dominant π-contact contribution and negligible of the
dipolar one. Analysis of the temperature dependence and of
the phenyl isotropic shifts are in accord with dominance of
contact contribution at the pyrrole positions. The dipolar
mechanism in NiII(NCH3TPP)Cl also contributed less than 10%
to the pyrrole shifts.17 The downfield shift of pyrrole and
C-methyl resonances indicates a σ-delocalization of spin density.
This is consistent with the ground state of NiII which has two
1
1
2
2
2
unpaired electrons in the σ-symmetry orbitals (dx -y ) (dz ) .
The isotropic shift of the inverted C-methylated pyrrole ring
is of a significant importance with respect to the nature of the
interaction in this paramagnetic organometallic NiII complex
and requires a special comment. The considerable downfield
C-CH3 shift can be accounted for by the direct σ-delocalization
Via three single bonds in the Ni-C(21)-C-H fragment. The
directions and magnitudes of the shifts are close to those
reported for (NCH3TPP)NiIICl and (NCH3OEP)NiIICl com-
plexes.13,17 The tilt of the inverted C-methylated ring changes
the geometry of the spin density delocalization path as compared
to the regular pyrrole rings. The unpaired spin density is
localized on the molecular orbital dominated by the pz compo-
nent which can transfer the σ-spin density but simultaneously
contributes to π-orbitals of the inverted pyrrole ring. Such an
overlap within the inverted ring will permit the direct transfer
of unpaired spin density of the C(21) pz into the π system
without any π M-L bonding.17-19 The side-on-coordination
of the C-methylated moiety folds the pathways of the spin
delocalization. This should reduce the σ-effect for the 2-NH
and 3-H hydrogens since the σ-mechanism is strongly dependent
(39) La Mar, G. N.; Horrocks, W. D.; Holm, R. H. Eds. In NMR of
Paramagnetic Molecules; Academic Press: New York, 1974.
(40) (a) Kurland, R. J.; Mc Garvey, B. R. J. Magn. Reson. 1970, 2, 286.
(b) Bleaney, B. J. J. Magn. Reson. 1972, 8, 91.

A Paramagnetic Organometallic Nickel(II) Complex
J. Am. Chem. Soc., Vol. 118, No. 24, 1996 5699
fer.13,16,17 The considerable differences of the spin densities at
the particular pyrrole carbons were related to the pattern of the
occupied π and unoccupied π* molecular orbitals.
Reaction Mechanism. Reaction of methyl iodide with
(CTPP)NiII results in formation of (21-CH3CTPP)NiII ac-
companied by formation of two paramagnetic derivatives (2-
NH-21-CH3CTPP)NiIIX and (2-NCH3-21-CH3CTPP)NiIIX. The
remarkable modification of the organometallic substrate results
from the methylation of the inner σ-coordinating sp2 hybridized
21-carbon atom. This transformation changes the pattern of
the C(21) coordination from planar to the pyramidal one owing
to the sp3 hybridization in the C-methylated diamagnetic product
(21-CH3CTPP)NiII. The coordination of this carbon corresponds
formally to the formation of a tertiary alkyl complex.42 The
unusual side-on coordination preserving strongly sp2 trigonal
geometry of 21-C has been found appropriate to describe the
bonding in the paramagnetic (2-NH-21-CH3CTPP)NiIIX and (2-
NCH3-21-CH3CTPP)NiIIX complexes. These are the principal
structural features determining the properties of these com-
pounds which should be taken into account in the reaction
mechanism. Usually, the NiII-C configuration observed in this
work would be expected to be unstable, but firm restraints
imposed by the location of a coordinating center inside the
macrocycle provide a reason for the extraordinary stability. The
first methylation step may involve either nickel(II) or negative
charged nucleophilic carbon atom. Accordingly two reaction
mechanisms can be suggested. Scheme 1 considers the situation
that, in the transient state, the σ-methylation of nickel(II) has
taken place to generate formally σ-methylated nickel(IV)
species. The formation of the intermediate may be preceded
2
by the SN displacement of the iodide by the nickel(II)
nucleophilic of the methyl iodide as suggested for methylation
of [(2,6-Me2NCH2)C6H3]PtII}+.1o The transients will undergo
1,2-methyl shift between nickel and C-coordinated pyrrole to
produce a nickel(II) complex of C-methylated carbaporphyrin.
The reaction intermediate presents an oxidation state of the
nickel rarely found in coordination complexes. Moreover a
stabilization of NiIV with alkyl-substituted diphosphine and
diarsine ligands is well established.43 Recently (alkyl radical)-
organonickel(III) complexes, formally two electrons oxidized
with respect to the ground state, were considered as the plausible
transient intermediates in addition to reaction of polyhalogenoal-
kanes to olefin catalyzed by arylnickel(II) complexes.1h-1l
Alternatively the methyl iodide molecules interacts directly with
the substrate (Scheme 2), and the oxidative addition of the
methyl cation to the carbaporphyrin at the C(21) will take place.
The redundant positive charge from the macrocycle may be
removed by the dissociation of 2-NH proton. Coordination of
iodide, which in this mechanism accompanies the bond cleavage
in methyl iodide, would result in formation of the sterically
unfavorable arrangement of C-methyl and axially coordinated
iodide on the same side of the macrocycle. In structurally
similar N-methylporphyrin complexes the coordination of an
anion usually takes place at the opposite to N-methyl side of
the equatorial plane unless low temperature conditions are
generated.44 For this reason we have suggested the concerted
dissociation of the HX (HI, HCl) molecule to produce the
diamagnetic (21-CH3CTPP)NiII complex. We have found
however that concerted HX dissociation/association is reversible
according to the mechanism presented in Scheme 3. Finally
as the reaction proceeds, the N(2) methylation takes place as
1
Figure 9. The 2D H COSY spectrum of (2-NCH3-21-CH3CTPP)-
NiIICl (CDCl3, 273K). Upper map, low field region showing spin-
spin coupling of regular pyrrole protons; lower map, meso-phenyl
region; peak labels denote respective ortho, meta, or para protons of
unequivalent phenyl rings; s, solvent.
on geometry.41 The replacement of the upfield shifted 2-NH
proton of (2-NH-21-CH3CTPP)NiIICl with the methyl group of
(2-NCH3-21-CH3CTPP)NiIICl results in the downfield shift of
2-NCH3 with the similar absolute value of the isotropic shift.
This demonstrates a dominance of the π-transfer mechanism at
this fragment of C-methylated nickel(II) carbaporphyrin. The
pattern of the six downfield pyrrole resonance shows the
domination of the σ-mechanism. However a large difference
in contact shifts of pyrrole resonances is seen even for protons
located on the same pyrrole ring. These differences result from
the π-spin density delocalized by the porphyrin framework and
originating from the peculiar spin density transfer within the
inverted pyrrole ring. Previously we have observed and
discussed the similar π delocalization of unpaired spin density
in nickel(II) heteroporphyrins and nickel(II) N-methylporphyrins
in terms of ligand-to-metal and metal-to-ligand charge trans-
(42) Balch, A. L.; Hart, R.; Latos-Graz˘yn´ski, L.; Traylor, T. G. J. Am.
Chem. Soc. 1990, 112, 7382.
(43) (a) Higgins, S.; Levason, W.; Feiters, M. C.; Steel, A. T. J. Chem.
Soc., Dalton Trans. 1986, 317. (b) Hanton, L. R.; Evans, J.; Levason, W.;
Perry, R. J.; Webster, M. J. Chem. Soc., Dalton Trans. 1991, 2039.
(44) Balch, A. L.; Cornman, C. R.; Latos-Graz˘yn´ski, L.; Olmstead, M.
M. J. Am. Chem. Soc. 1990, 112, 7552.
(41) Bertini, I.; Luchinat, C. In NMR of Paramagnetic Molecules in
Biological Systems; The Benjamin/Cumming Publishing Co. Inc.: Menlo
Park, CA, 1986.

5700 J. Am. Chem. Soc., Vol. 118, No. 24, 1996
Chmielewski et al.
Scheme 1
Scheme 2
Scheme 3
ylated complexes, considered here as two likely stages in the
full sequence of the process (Scheme 4).
Experimental Section
Solvents and Reagents. All solvents were purified by standard
procedures. Chloroform-d (CDCl3, Glaser AG) was dried before use
by passing through activated basic alumina.
Preparation of Compounds. CTPP, 2-NCH3CTPP, and their
nickel(II) complexes were synthesized as previously described.14,16
CTPPH2-d7 was obtained in the identical procedure as CTPPH2, but
the regular pyrrole was replaced with pyrrole-d5 (Aldrich).
well. In this case the positive charge in the system is
compensated by the strong tendency to axially coordinate of
an anionic ligand.
Synthesis of 2-Aza-5,10,15,20-tetraphenyl-21-methyl-21-carba-
porphyrinatonickel(II) ((21-CH3CTPP)NiII) and 2-Aza-2,21-di-
methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinatonickel(II) Chlo-
ride ((2-NCH3-21-CH3CTPP)NiIICl). CH3I (1 mL, 8 mmol) was
added to a solution of (CTPP)NiII (100 mg, 0.15 mmol) in dichlo-
romethane and stirred for 24 h at 293 K. The mixture was then taken
to dryness under reduced pressure. The product was dissolved in
dichloromethane and chromatographed on the silica gel column with
dichloromethane as an eluent. The fastest moving green band consisted
of starting material (21-CH3CTPP)NiII, the second olive band contained
(21-CH3CTPP)NiII, and the third brown band (eluted with 10% solution
of chloroform in dichloromethane) was a mixture of (2-NCH3-21-CH3-
CTPP)NiIICl and (2-NCH3-21-CH3CTPP)NiIII. From the fraction
containing monomethylated species (brown solution) the brown solid
was obtained by addition of n-hexane and dried in Vacuo for 5 days.
Yield: 34 mg (33%). 1H NMR (300 MHz, 293 K, CDCl3) δ 9.898
(3-H), 8.633 (m, overlapping parts of two AB systems, two pyrrole
protons), 8.49 (m, overlapping parts of two AB systems, two pyrrole
protons, 8.452, 8.415 (AB, 3J ) 4.5 Hz), 8.18 (b, ortho), 8.06 (b, ortho),
7.77 (m, meta), 7.69 (m, para), -3.154 (21-CH3). UV-vis λmax/nm
(log ꢀ) 430 (4.59), 550 (sh), 610 (sh), 735 (2.72); MS (EI, 70 eV) 684
([M - H]+, 100%), 670 (M - CH3, 30%). Anal. Calcd for C45H30N4-
Ni: C, 78.93; H, 4.42; N, 8.19. Found: C, 78.46; H, 4.22; N, 7.78.
Chloroform solution containing dimethylated species (the third
fraction) was shaken with 5% hydrochloric acid, and organic phase
was then evaporated and dried. The oily product was dissolved in
dichloromethane and precipitated with hexane giving 10 mg of dark
green solid. 1H NMR still revealed presence of about 10% of (2-NCH3-
21-CH3CTPP)NiIII. The full in situ conversion to the chloride salt was
accomplished by addition of 2-fold excess of tetraethylammonium
chloride: UV-vis λmax/nm (log ꢀ) 465 (4.26), 580 (sh), 730 (3.80),
820 (sh); MS (LSIMS) 699 (M - Cl - 1). Syntheses of (21-CD3-
CTPP)NiII and (2-NCD3-21-CD3CTPP)NiIICl were performed analo-
gously using CD3I (POCh).
The ionic charge of the coordination center determines the
spin state of their nickel(II) complexes. The monoanionic
coordination supports the paramagnetic S ) 1 electronic state.
Dianionic coordination results in the diamagnetic complexes.
To the best of our knowledge this is the very first example of
the control of the spin state in the organometallic nickel(II)
complexes by the concerted reversible addition of the HX
molecule.
Conclusions
The present work offers conclusive evidence for the stabiliza-
tion of paramagnetic organometallic nickel(II) complexes Via
the very efficient protection of the nickel-carbon bond by
encapsulating the coordinating carbon center in the structure
of the porphyrin macrocycle. The general overview of the
reactivity pattern emphasizes the unusual methylation route
which includes methylation of the sp2 hybridized coordinated
C(21) atom to end up with its pyramidal or pyramidally distorted
trigonal geometry for this center in the methylated species. The
viability of C-methylated ligands for reversible nickel removal/
insertion processes demonstrates the spectacular flexibility of
the ligand electronic/molecular structure accompanied by the
appropriate reversible hybridization change sp3 h sp2.
Formally the methylated pyrrolic fragments of both com-
pounds i.e., (21-CH3CTPP)NiII and (2-NCH3-21-CH3CTPP)-
NiIIX may be treated as structural models of the hypothetical
reductive-elimination process assuming the C-methylated pyrrole
as a leaving group. The macrocyclic restraints stop the process
at the stage just preceeding the elimination of the methylated
organic fragment. The smooth structural rearrangements, inher-
ent to reductive-elimination, seem to be appropriately visualized
by the respective “snapshot” structures of mono- and dimeth-
Synthesis of 2-Aza-2-hydro-5,10,15,20-tetraphenyl-21-methyl-21-
carbaporphyrinatonickel(II) Chloride ((2-NH-21-CH3CTPP)NiIICl).
Solution of 2-aza-21-methyl-21-carbatetraphenylporphyrinatonickel(II)
(20 mg, 0.029 mmol) in 50 mL of chloroform was stirred with 10 mL

A Paramagnetic Organometallic Nickel(II) Complex
J. Am. Chem. Soc., Vol. 118, No. 24, 1996 5701
Scheme 4
of 1% solution of hydrochloric acid until brown solution turned green.
The organic layer was then separated, dried, dissolved in dichlo-
romethane, and precipitated with hexane. Yield: 10 mg (48%). UV-
vis λmax/nm (log ꢀ) 455 (4.54), 580 (3.35), 730 (3.88), 820 (sh). Anal.
Calcd for C45H31N4NiCl‚CH2Cl2: C, 71.77; H, 4.32; N, 7.28. Found:
C, 72.00; H, 4.25; N, 6.94.
Synthesis of 2-Aza-2,21-dimethyl-5,10,15,20-tetraphenyl-21-car-
baporphyrinatonickel(II) Iodide ((2-NCH3-21-CH3CTPP)NiIII). So-
lution containg (2-NCH3CTPP)NiII (20 mg, 0.029 mmol) and methyl
iodide (8 mmol) in 50 mL of dichloromethane was stirred for 48 h.
After that time the green solution turned brown. Reaction mixture was
then taken to dryness, dissolved in dichloromethane, and precipitated
with n-hexane. Yield: 19 mg (79%). UV-vis λmax/nm (log ꢀ) 435
(4.26), 465 (4.27), 575 (sh), 670 (sh), 735 (3.85). Anal. Calcd for
C46H33N4NiI‚CH2Cl2: C, 61.88; H, 3.87; N, 6.14. Found: C, 62.32;
H, 4.15; N, 6.29.
broadening. The residual 1H NMR resonances of the deuterated
solvents were used as a secondary reference. The H NMR spectra
2
were collected using a Bruker AMX instrument operating at 46.1 MHz.
A spectral width of 20 kHz was typical, and 16 K points were used. A
pulse delay of 50 ms was applied. The signal-to-noise ratio was
improved similarly as in proton spectra. The residual 2H NMR
resonances of the solvents were used as a secondary reference.
The 2D COSY spectra were obtained after collecting a standard 1D
reference spectrum. The 2D spectra were collected by use of 2048
points in t2 over the desired bandwidth (to include all desired peaks)
with 512 t1 blocks and 320 scans per block. All experiments included
four dummy scans prior to the collection of the first block. Absorption
spectra were recorded on a Spekord M-42 spectrometer and diode array
Beckman 7500 spectrometer. Mass spectra were recorded on a ADM-
604 spectrometer using the liquid matrix secondary ion mass spectros-
copy (8 keV Cs+ ions) or electron impact techniques.
Synthesis of 2-Aza-5,10,15,20-tetraphenyl-21-methyl-21-carba-
porphyrin (21-CH3CTPPH2). Solution of (21-CH3CTPP)NiII (20 mg,
0.029 mmol) in 50 mL of dichloromethane was shaken with 10%
hydrochloric acid. After solution color turned green, the water layer
was removed, and organic layer was washed with water and dried with
sodium carbonate. Chromatography on a basic alumina column with
dichloromethane as an eluent (brown-green band was collected) and
crystallization from dichloromethane/ethanol gave 10 mg (55%) of the
free carbaporphyrin: 1H NMR (300 MHz, CD2Cl2, 203 K) δ 8.979,
X-ray Data Collection and Refinement (21-CH3CTPP)NiII‚CH2-
Cl2. Crystals of (21-CH3CTPP)NiII were prepared by diffusion of
n-hexane into the dichloromethane solution contained in a thin tube.
Data were collected at 293 K on a Kuma KM-4 diffractometer. The
stability of intensities was monitored by the measurement of three
standards every 100 reflections. The data were corrected for Lorentz
and polarization effects. No absorption correction was applied. Crystal
data are compiled in Table 4.
The structure was solved by the direct methods with SHELXS-86
and refined by full-matrix least square method using SHELX-93 with
anisotropic thermal parameters for non-H atoms. Scattering factors
were those incorporated in SHELXS-93.
The disorder at the N(2)-C(3) positions was treated by examining
several different models which exchange N(2) and C(3) atoms. The
last cycles of refinement include N(2) and N(3′) at 50% occupancy.
The positional parameters of these atoms were fixed and their isotropic
thermal parameters allowed to vary. A molecule of dichloromethane
in the lattice exhibits a disorder.
3
3
8.490 (AB, J ) 4.6 Hz), 8.821, 8.418 (AB, J ) 4.7 Hz), 8.463 (m,
2H) (regular pyrrole protons), 8.664 (d), 8.274 (d), 8.202 (d), 8.55 (b),
8.32 (b), 8.002 (d) (ortho), 8.06-7.75soverlapping multiplets of meta
and para protons, 7.113 (3-H), -3.014, -3.195 (22, 24-NH), -4.837
(3H, 21-CH3). Assignments were made on the basis of 2D COSY
experiment: UV-vis λmax/nm (log ꢀ) 445 (4.96), 515 (3.72), 550 (3.94),
590 (4.02), 740 (3.95); MS (EI, 70 eV) 630 (100%, M + 1). Anal.
Calcd for C45H32N4‚CH2Cl2‚C2H5OH (the presence of solvents detected
1
in the H NMR spectrum): C, 79.60; H, 5.57; N, 7.74. Found: C,
79.77; H, 5.19; N, 7.85.
(2-NCH3-21-CH3CTPP)NiIII‚C6H6. The suitable crystals of (2-
NCH3-21-CH3CTPP)NiIII were prepared by diffusion of n-hexane into
the benzene solution contained in a thin tube. Data were collected at
293 K on a Kuma KM-4 diffractometer. The stability of intensities
was monitored by the measurement of three standards every 100
reflections. The data were corrected for Lorentz and polarization
effects. No absorption correction was applied. Crystal data are
compiled in Table 4.
The structure was solved by the direct methods with SHELXS-86
and refined by full-matrix least square method using SHELX-93 with
anisotropic thermal parameters for non-H atoms. Scattering factors
were those incorporated in SHELXS-93. The disorder at the N(2)-
CH3 positions was treated by examining several different models which
exchange N(2)-CH3 and C(3)-H groups. The last cycles of refinement
include N(2)-C(26) at 65% occupancy and N(3′)-C(27) at 35%
occupancy.
Synthesis of 2-Aza-2,21-dimethyl-5,10,15,20-tetraphenyl-21-car-
baporphyrin (2-NCH3-21-CH3CTPPH). Solution of (2-CH3-21-CH3-
CTPP)NiIII (20 mg, 0.024 mmol) in 50 mL of dichloromethane was
stirred with concentrated hydrochloric acid for 1 h. Acid was then
removed and organic phase was washed with water and dried with
sodium carbonate. Product was chromatographed on a basic alumina
column with dichloromethane as an eluent. The fastest moving green
band was collected. Addition of ethanol to the solution and reduction
of solvents volume resulted in deep green precipitate. Yield: 8 mg
(51%). 1H NMR (300 MHz, CD2Cl2, 203 K) δ 7.910, 7.27 (AB, 3J )
3
4.4 Hz), 7.845, 7.27 (AB, J ) 4.4 Hz), 7.59 (m, 12,13-H) (regular
pyrrole protons), 8.06 (m, 2H), 8.00 (m, 2H) (ortho protons), 7.79-
7.54 (overlapping multiplets of meso-phenyl protons), 5.647 (3-H),
3.824 (23-NH), 2.905 (2-CH3), -1.584 (21-CH3). Assignments based
on selective proton-decoupling: UV-vis λmax/nm (log ꢀ) 455 (4.90),
600 (sh), 655 (4.15), 710 (4.25); MS (EI, 70 eV) 644 (100%, M + 1).
Anal. Calcd for C46H34N4‚CH2Cl2‚C2H5OH (the presence of solvents
detected in the 1H NMR spectrum): C, 76.06; H, 5.47; N, 7.24.
Found: C, 76.45; H, 5.13; N, 7.31.
Acknowledgment. The financial support of the State Com-
mittee for Scientific Research KBN (Grant 3 T09A 14309) is
kindly acknowledged.
Instrumentation. 1H NMR spectra were recorded on a Bruker
AMX spectrometer operating in the quadrature mode at 300 MHz. A
typical spectrum was collected over 45 000 Hz (paramagnetic systems)
or 4500 Hz (diamagnetic compounds) spectral window with 32 K data
points with 100-5000 transients for the experiment and 50 ms
(paramagnetic) or 2 s (diamagnetic samples) prepulse delay. The free
induction decay (FID) was apodized using exponential multiplication
depending on the natural line width. This induced 0.2-30 Hz
Supporting Information Available: Crystal data, atom
coordinates, complete listings of bond lengths, anisotropic
displacement coefficients, and calculated hydrogen parameters
(20 pages). Ordering information is given on any current
masthead page.
JA9527028