Palladium(II) complexes of oxybenziporphyrin

Article abstract of DOI:10.1021/ic010394a

8,19-Dimethyl-9,13,14,18-tetraethyloxybenziporphyrin coordinates palladium(II) to form the four-coordinate anionic complex [(OBP)Pd^II]^-. The NMR data provide evidence for the retention of macrocyclic aromaticity and coordination via a carbon σ-donor. Protonation of the external oxygen atom to give [(HOBP)Pd^II] switches the molecule to a less aromatic phenol-like state, which is manifested by a significant reduction of the macrocyclic ring current. [(AcOBP)Pd^II] and [(TsOBP)Pd^II], two ester derivatives of [(OBP)Pd^II]^-, are similar to the protonated species, and their benzenoid character is more pronounced. However, reaction of [(OBP)Pd^II]^- with methyl iodide leads to selective methylation of the coordinating C(22) atom to form a novel organopalladium complex (OBPMe)-Pd^II. The strong shielding of the inner Me(22) (δ(¹H) -2.00 ppm in CDCl₃) indicates that the aromaticity of the macrocycle has been retained. At the same time the ¹³C chemical shift of C(22) (44 ppm) shows that the palladium-bound carbon has undergone a drastic hybridization change. Alkylation with n-BuI yields a mixture of the O-substituted [(n-BuOBP)Pd^II] and the C-substituted [(OBP-n-Bu)pd^II], which confirms the ambident nucleophilicity of [(OBP)Pd^II]^-. DFT calculations carried out for six tautomers of oxybenziporphyrin and the 22-methylated palladium species provide further insight into the electronic structure of the ligand and its complexes. Relative energies of the tautomers, increasing in the order [CH,NH,N,NH,O] < [CH,N,NH,N,OH] < [CH₂,N,NH,N,O,] < [CH₂,N,N,N,OH], have been used to estimate the accessibility of four limiting delocalization modes postulated for oxybenziporphyrin and its derivatives. The state of macrocyclic aromaticity observed experimentally in the free base and the phenolic aromaticity of the O-protonated tautomer are the most favorable, and the latter has its energy higher by only 13 kcal/mol. The peculiar bonding situation in (OBPMe)Pd^II, which can be inferred from the NMR data, is also predicted by the DFT methods, which show a strongly distorted tetrahedral environment of C(22).

Full text of DOI:10.1021/ic010394a

6892
Inorg. Chem. 2001, 40, 6892-6900
Palladium(II) Complexes of Oxybenziporphyrin
Marcin Ste¸pien´,† Lechosław Latos-Graz3yn´ski,*,† Timothy D. Lash,‡ and Ludmiła Szterenberg†
Departments of Chemistry, University of Wrocław, 14 F. Joliot-Curie Street, Wrocław 50 383, Poland,
and Illinois State University, Normal, Illinois 61761
ReceiVed April 13, 2001
8,19-Dimethyl-9,13,14,18-tetraethyloxybenziporphyrin coordinates palladium(II) to form the four-coordinate anionic
complex [(OBP)PdII]-. The NMR data provide evidence for the retention of macrocyclic aromaticity and
coordination via a carbon σ-donor. Protonation of the external oxygen atom to give [(HOBP)PdII] switches the
molecule to a less aromatic phenol-like state, which is manifested by a significant reduction of the macrocyclic
ring current. [(AcOBP)PdII] and [(TsOBP)PdII], two ester derivatives of [(OBP)PdII]-, are similar to the protonated
species, and their benzenoid character is more pronounced. However, reaction of [(OBP)PdII]- with methyl iodide
leads to selective methylation of the coordinating C(22) atom to form a novel organopalladium complex (OBPMe)-
PdII. The strong shielding of the inner Me(22) (δ(1H) -2.00 ppm in CDCl3) indicates that the aromaticity of the
macrocycle has been retained. At the same time the 13C chemical shift of C(22) (44 ppm) shows that the palladium-
bound carbon has undergone a drastic hybridization change. Alkylation with n-BuI yields a mixture of the
O-substituted [(n-BuOBP)PdII] and the C-substituted [(OBP-n-Bu)PdII], which confirms the ambident nucleophilicity
of [(OBP)PdII]-. DFT calculations carried out for six tautomers of oxybenziporphyrin and the 22-methylated
palladium species provide further insight into the electronic structure of the ligand and its complexes. Relative
energies of the tautomers, increasing in the order [CH,NH,N,NH,O] < [CH,N,NH,N,OH] < [CH2,N,NH,N,O] <
[CH2,N,N,N,OH], have been used to estimate the accessibility of four limiting delocalization modes postulated
for oxybenziporphyrin and its derivatives. The state of macrocyclic aromaticity observed experimentally in the
free base and the phenolic aromaticity of the O-protonated tautomer are the most favorable, and the latter has its
energy higher by only 13 kcal/mol. The peculiar bonding situation in (OBPMe)PdII, which can be inferred from
the NMR data, is also predicted by the DFT methods, which show a strongly distorted tetrahedral environment
of C(22).
Introduction
their 2-N-methyl, 21-C-methyl, and 2-N-21-C-dimethyl deriva-
tives.6,7 Alternatively, the replacement of one pyrrole ring by
Recently a novel group of porphyrin-like macrocycles has
emerged, which can be generally classified as monocarbapor-
phyrinoids. Formally their formation requires a modification of
the porphyrin skeleton that would provide a CH unit in place
of one of the pyrrolenic nitrogens. Thus, the coordinating
(CH,N,N,N) core becomes the denominator of this class of
macrocycles.
By interchanging one of the nitrogens with a â-methine group
of the same pyrrole, one transforms 5,10,15,20-tetraarylpor-
phyrin (TPPH2) into 2-aza-21-carba-5,10,15,20-tetraarylpor-
phyrin (21-CTPPH2, inverted porphyrin), which, while porphyrin-
like in character, has fundamentally different electronic and
coordination properties.1-3 The peralkylated, meso-unsubstituted,
inverted porphyrin (CHAPH2) has been synthesized as well.4,5
Taking advantage of the peculiar reactivity of nickel carba-
porphyrin and free 21-carbaporphyrin, it was possible to generate
benzene,8 semiquinone,9,10 cycloheptatriene,11,12 indene,11,13
azulene,14 cyclopentadiene,15 aliphatic bicyclic alkene,16 or 2,4-
linked thiophene17 yielded a series of monocabaporphy-
rinoids.18,19
2-Aza-21-carba-23-oxaporphyrin, 2-aza-21-carba-23-thiapor-
phyrin, and 2-aza-21-carba-22-selenaporphyrin (i.e. “inverted”
isomers of 21-oxaporphyrin, 21-thiaporphyrin, and 21-selena-
porphyrin) combine features of both the inverted porphyrin and
a 21-heteroporphyrin leading to a new type of coordination core
(6) Chmielewski, P. J.; Latos-Graz˘yn´ski, L. J. Chem. Soc., Perkin Trans.2
1995, 503.
(7) Chmielewski, P. J., Latos-Graz˘yn´ski, L.; Głowiak, T. J. Am. Chem.
Soc. 1996, 118, 5690.
(8) Berlin, K.; Breitmaier, E. Angew. Chem., Int. Ed. Engl. 1994, 33, 1246.
(9) Lash, T. Angew. Chem., Int. Ed. Engl. 1995, 34, 2533.
(10) Lash, T. D. Chaney, S. T.; Richter, D. T. J. Org. Chem. 1998, 63,
9076.
* To whom correspondence should be addressed.
† University of Wrocław.
(11) Berlin, K.; Steinbeck, C.; Breitmaier, E. Synthesis 1996, 336.
(12) Lash, T. D.; Chaney, S. T. Tetrahedron Lett. 1996, 37, 8825.
(13) Lash, T. D.; Hayes, M. J. Angew. Chem., Int. Ed. Engl. 1997, 355,
841.
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(16) Hayes, M. J.; Lash, T. D. Chem. Eur. J. 1998, 4, 508.
(17) Sprutta, N.; Latos-Graz˘yn´ski, L. Tetrahedron Lett. 1999, 8457.
(18) Lash, T. Syntheses of Novel Porphyrinoid Chromophores. In The
Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press: New York, 2000; Vol. 2, p 125.
(19) Lash, T. D. Synlett. 1999, 279.
‡ Illinois State University.
(1) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Rachlewicz, K.; Głowiak,
T. Angew. Chem., Int. Ed. Eng. 1994, 33, 779.
(2) Furuta, H.; Asano, T.; Ogawa, T. J. Am. Chem. Soc. 1994, 116, 767.
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Metalloporphyrins. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: New York, 2000; Vol. 2,
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10.1021/ic010394a CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/27/2001

Palladium(II) Complexes of Oxybenziporphyrin
Inorganic Chemistry, Vol. 40, No. 27, 2001 6893
of the type (CH,N,X,N) with X ) O, S20-22 or (CH, X, N, N)
with X ) Se.23 The recent syntheses of dicarbaporphyrinoids
and a doubly confused porphyrin have further extended the class
of carbaporphyrinoid macrocycles.24,25
Chart 1
Inverted porphyrin and 21-methylated inverted porphyrin act
as mono- or dianionic ligands for nickel(II) and nickel-
(III).1,5,6,7,26,27 These macrocycles enforce the coordination of
the pyrrolic sp2 carbon to nickel(II).1,5,6 In the case of (21-CH3-
CTPP)NiII the nickel(II) is four-coordinate with bonds to the
three pyrrole nitrogens and the inner sp3 carbon.7 The methylated
pyrrole is bound to the nickel via a pyramidal carbon forming
a σ-bond. A similar mode of coordination can be expected in
nickel(II) heptaalkyl inverted porphyrin [(CHAPH)NiII]+ and
[2-N-CH3CTPPH)NiII]+ protonated at the C(21) carbon.5,28
In the paramagnetic (2-NCH3-21-CH3CTPP)NiIII the
methylated pyrrole is linked to nickel in the η1-fashion but the
coordinating C(21) carbon preserves the features related to the
trigonal sp2 hybridization.7 Addition of the phenyl Grignard
reagent to a toluene solution of the nickel(II) chloride complex
of dimethylated inverted porphyrin (2-NCH3-21-CH3CTPP)NiII-
Cl gave a rare paramagnetic (σ-phenyl)nickel(II) species (2-
NCH3-21-CH3CTPP)NiIIPh which contains simultaneously equa-
torial and apical NiII-carbon bonds.27 The inverted porphyrins
and their methylated derivatives stabilize the unusual organo-
copper(II) complexes (CTPP)CuII, (2-NCH3CTPP)CuII, (CTP-
PH)CuIIX, (2-NCH3CTPPH)CuIIX (X: Cl-, TFA-), and [(2-
NCH3-21-CH3CTPP)CuIICl.28 Recently Furuta and co-workers
have demonstrated that inverted porphyrin acts as a trianionic
ligand stabilizing silver(III).29 This brief overview demonstrates
that until now the coordination chemistry of monocarbapor-
phyrinoids has been narrowed to the derivatives of inverted
porphyrin.
The development of polydentate ligands with a potential
carbon donor favorably oriented toward the transition metal ion
offers a new general strategy to stabilize untypical oxidation
states and coordination geometries in organometallic com-
pounds.30-35 The metal-carbon bond can be firmly held in the
cavity of such a ligand so that the possible dissociation of the
M-C bond will be impaired. In light of these we have decided
to probe the coordination chemistry of carbaporphyrinoid
macrocycles other than inverted porphyrins. Here we present
our results on the coordination properties of 8,19-dimethyl-
9,13,14,18-tetraethyloxybenziporphyrin (OBPH)H2 (1). From
now on we will use the symbol OBP to denote the hypothetical
trianion obtained from the free base by abstraction of the two
pyrrolic protons and the C-bound proton H(22). The groups
attached to the O(2) atom will be indicated by a prefix (e.g.
AcOBP for O-acetyl derivative), while those bound to C(22)
will appear as suffixes (OBPMe for 22-methylation).
Oxybenziporphyrin is conceptually derived from benzipor-
phyrin,8,10 in which a benzene ring replaces one of the
porphyrinic pyrroles leading to a structure devoid of macrocyclic
aromaticity. However, 2-hydroxybenzoporphyrin 1-4 is found
to exist solely as its keto form 1-1-3 (oxybenziporphyrin), in
which the 18e porphyrinoid π-delocalization pathway is restored
(Chart 1).9,10 The hypothetical forms 1-5 and 1-6 will be of
significance in further discussion.
To explore the coordination of metal ions by oxybenzipor-
phyrin we decided to focus on the chemistry of palladium(II).
A variety of palladium(II) complexes with porphyrins,36 het-
eroporphyrins,37 and doubly-N-confused porphyrins25 have been
isolated and characterized. Importantly, the palladium(II) ion
is susceptible to phenyl coordination in a cyclopalladation
process.38-40 Once the carbon donor is built into macrocylic or
pincer ligands, the palladium(II) ion forms robust organometallic
compounds.30-32,35,38,41 These species, while sufficiently inert,
form more readily that their Pt(II) congeners.
(20) Heo, P.-Y.; Shin, K.; Lee, C.-H. Tetrahedron Lett. 1996, 37, 197.
(21) Lee, C.-H. Kim, H.-J. Tetrahedron Lett. 1997, 38, 3935.
(22) Lee, C.-H.; Kim, H.-J.; Yoo, D.-W. Bull. Korean Chem. Soc. 1999,
20, 276.
(23) Pacholska, E.; Latos-Graz˘yn´ski, L.; Szterenberg, L.; Ciunik, Z. J. Org.
Chem. 2000, 65, 8188.
(24) Lash, T. D.; Romanic, J. L.; Hayes, M. J.; Spence, J. D. Chem.
Commun. 1999, 819.
(25) Furuta, H.; Maeda, H.; Osuka, A. Yasutake, M.; Shinmyozu, T.;
Ishikawa Y. Chem. Comun. 2000, 1143.
(26) Chmielewski, P. J.; Latos-Graz˘yn´ski, L. Inorg. Chem. 1997, 36, 840.
(27) Chmielewski, P. J.; Latos-Graz˘yn´ski, L. Inorg. Chem. 2000, 39, 5639.
(28) Chmielewski, P. J.; Latos-Graz˘yn´ski, L, Schmidt, I. Inorg. Chem. 2000,
39, 5475.
Here we report on the synthesis and spectroscopic properties
of oxybenziporphyrin complexes with Pd(II). In particular we
(29) Furuta, H.; Ogawa, T.; Uwatoko, Y.; Araki, K. Inorg. Chem. 1999,
38, 2676.
(30) van Koten, G. Pure Appl. Chem. 1989, 61, 1681.
(31) Rietveld, M. H. P.; Grove, D. M.; Van Koten, G. New. J. Chem. 1997,
21, 751.
(32) Gossage, R. A.; van de Kuil, L. A.; van Koten, G. Acc. Chem. Res.
1998, 31, 423.
(36) Stolzenberg, A. M.; Schussel, L. J.; Summers, J. S.; Foxman, B. M.;
Petersen, J. L. Inorg. Chem. 1992, 31, 1678.
(37) Latos-Graz˘yn´ski, L.; Lisowski, J.; Chmielewski, P. J.; Grzeszczuk,
M.; Olmstead, M. M.; Balch, A. L. Inorg. Chem. 1994, 33, 192.
(38) Steenwinkel, P.; Gossage, R. A.; Grove, D. M.; van Koten, G. Chem.
Eur. J. 1998, 4, 759.
(33) Gozin, M.; Weisman, A.; Ben-David, Y.; Milstein, D. Nature 1993,
364, 699.
(34) Newkome, G. R.; Puckett, W. E.; Gupta, V. K.; V. K.; Kiefer, G. E.
Chem. ReV. 1986, 86, 451.
(35) Giesbrecht, G. R.; Hanan, G. S.; Kickham, J. E.; Loeb, S. J. Inorg.
Chem. 1992, 31, 3286.
(39) Steenwinkel, P.; Gossage, R. A.; Maunula, T.; Grove, D. M.; van
Koten, G. Chem. Eur. J. 1998, 4, 763.
(40) Jolliet, P.; Gianini, M.; von Zelewsky, A.; Bernardinelli, G.; Stoeckli-
Evans, H. Inorg. Chem. 1996, 35, 4883.
(41) van der Boom, M.; Liou, S.-Y.; Ben-David, Y.; Shimon, L. J. W.;
Milstein, D. J. Am. Chem. Soc. 1998, 120, 6531.

6894 Inorganic Chemistry, Vol. 40, No. 27, 2001
Ste¸pien´ et al.
Figure 1. Electronic spectra of 2 (s), 3 (---), and 5 (···, excess MeI
Figure 2. 1H NMR spectrum of 2 (298 K, MeCN-d3, trace A) and 3
(trace B, same conditions, obtained by addition of 1 equiv of TFAH to
the sample).
present) recorded at 298 K in MeCN.
Scheme 1
have focused on the effects of complexation and electrophile
addition on the aromaticity of the ligand.
Results and Discussion
Formation and Characterization of K[(OBP)PdII]. Reac-
tion of palladium(II) chloride with oxybenziporphyrin (1) in
acetonitrile in the presence of anhydrous K2CO3 results in the
formation of the four-coordinate K[(OBP)PdII] (2) in 96% yield
(Scheme 1). Potassium carbonate neutralizes HCl formed in the
course of insertion and provides the necessary countercation to
balance the charge of the anionic [(OBP)PdII]-. It is important
that the stoichiometric amount of metal carrier be used for the
reaction. The product obtained in the presence of excess PdCl2
quickly loses solubility after removal of the solvent and has
not been characterized. Probably the insertion process is
followed by coordination of palladium to the phenolic oxygen
and the resultant species oligomerize in the solid state.
Figure 3. 1H-15N correlation spectrum of 2 (298 K, CDCl3). The solid
line indicates the connectivity within the Hmeso-N coupling network.
(191 ppm) is fairly typical of a carbonyl fragment, while the
C(22) resonance, located at 139 ppm, is indicative of the sp2
1
hybridization. The H-15N HMQC experiment performed for
2 (Figure 3) provides an unambiguous assignment of the
coordinating nitrogens and, in addition, of the meso protons.
15N chemical shifts measured for 2 are in the range found for
porphyrins and their complexes (from -126 to -263 ppm).42
Thus, the NMR data provide evidence for the coordination of
the aromatic trianionic ligand derived from 1 after the dissocia-
tion of two NH protons and one CH proton.
The electronic absorption spectrum of K[(OBP)PdII] (2)
(Figure 1) with its intense Soret-like band (443 nm in MeCN)
and a set of bands in the Q region is similar to the spectrum of
the free ligand.9,10 The spectrum is slightly solvent-dependent.
Protonation of K[(OBP)PdII]. Addition of 1 equiv of TFAH
to the solution of 2 in acetonitrile transforms the green anion
[(OBP)PdII]- into its red-violet protonated form (HOBP)PdII
(3) (Scheme 2). Titration followed by UV-vis spectroscopy
proceeds with well-defined isosbestic points, and the final
spectrum of 3 is shown in Figure 1. The strong Soret band shifts
hypsochromically to 416 nm but is retained. This remains in
striking contrast with the spectrum of the O-protonated dication
(HOBPH)H32+, whose broadened features were explained in
terms of the loss of aromaticity.9,10,18 The phenolic moiety,
which in the case of 3 is held in the macrocyclic plane by the
coordinated metal atom, is conjugated with the tripyrrolic
subunit more strongly than in (HOBPH)H32+, where it may be
1
The H NMR spectrum of K[(OBP)PdII] resembles that of
(OBPH)H2 (Figure 2).9,10 The complete assignment of all
resonances (trace A, Figure 2) has been obtained from COSY
and NOESY experiments. For the sake of comparison we have
carried out parallel 2D experiments for (OBPH)H2 to confirm
that both patterns in the 10-7 ppm regions are alike. The most
notable feature of 2 is coordination of palladium(II) in the plane
of the C6 ring through the unprotonated trigonally hybridized
carbon(22) center. The H(22) resonance of (OBPH)H2, located
1
at -7.2 ppm, is absent in the H NMR spectrum of 2, and
consequently, the H(4) signal, which in 1 shows couplings to
H(3) and H(22), simplifies to a doublet. Partial assignment of
(42) Medforth, C. NMR Spectroscopy of Diamagnetic Porphyrins. In The
Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press: New York, 2000; Vol. 5, p 1.
1
13C resonances has been carried out using H-13C correlation
techniques (HMQC, HMBC). The chemical shift found for C(2)

Palladium(II) Complexes of Oxybenziporphyrin
Inorganic Chemistry, Vol. 40, No. 27, 2001 6895
Scheme 2
nounced. 13C chemical shifts of C(22) and C(2) in 4-Ac are
142 and 156 ppm, respectively.
Alkylation of K[(OBP)PdII]. Of particular importance is the
observation that 2 is susceptible to methylation at the C(22)
atom. Thus, [(OBP)PdII]- rapidly reacts with methyl iodide to
yield a novel organopalladium(II) complex (OBPMe)PdII (5,
1
Scheme 3). Judging by the H NMR spectrum of the reaction
mixture, the process is nearly quantitative. Such a reactivity
resembles that of (CTPP)NiII, (2-NCH3CTPP)NiII, and (2-NCH3-
CTPP)CuII and C-methylation of trans-2,6-bis[(dimethylamino)-
methyl]phenyl-N,C,N′ complex of platinum(II), [PtI(C6H3-
(CH2NMe2)2-o,o′)]+.7,28,43
Scheme 3
The electronic absorption spectrum of 5 is broadened and
less intense compared to the spectra of 2 or 3 (Figure 1), which
might indicate that the aromaticity of the macrocycle is disrupted
upon methylation. Contrarily, the 1H NMR spectrum of 5
indicates the presence of a strong aromatic ring current (Figure
4, trace A). Thus, the meso resonances are detected practically
in the same positions as those of 2. However, the H(3) and H(4)
signals are displaced further downfield, by 0.8 and 0.3 ppm,
respectively. The Me(22) group gives rise to a singlet at -2.00
ppm (CDCl3), which shows dipolar couplings to H(6) and H(21)
in the NOESY map. This upfield shift is diagnostic for methyl
groups located in the center of aromatic macrocycles as found
for diamagnetic N-methyl porphyrins44 and particularly for 21-
C-methylated inverted porphyrins and their complexes (21-CH3-
CTPPH2, -4.84 ppm; 2-NCH3-21-CH3CTPPH, 1.58 ppm; (21-
CH3CTPP)NiII, -3.15 ppm).7 The 13C chemical shift of C(22)
is 44 ppm (98 ppm upfield with respect to 2), which can only
be rationalized by assuming a pesudotetrahedral geometry at
this carbon atom. C(2) resonates at 184.3 ppm, which corre-
sponds to a carbonyl group.
The macrocyclic aromaticity observed in 5 is apparently at
variance with the assumed simultaneous presence of an sp3
center and a carbonyl unit, both of which put an obstacle in the
delocalization pathways. This problem will be discussed later
in conjunction with DFT calculations.
tilted out of the macrocyclic plane. Stirring the solution of 3
with anhydrous K2CO3 regenerates the anion. However, when
dissolved in pyridine, 3 does not undergo deprotonation, which
sets the other limit of its acidity.
The result of an 1H NMR spectroscopic titration carried out
by addition of TFAH to a solution of 2 in acetonitrile-d3 at 293
K is shown in Figure 2 (trace B). Under these conditions proton
exchange rates involving 2 and 3 are fast on the NMR time
scale and consequently only a smooth change of the chemical
shifts can be observed in the whole titration range. Addition of
more than 1 equiv of TFAH does not cause further changes in
the spectrum apart from progressive broadening of the signals.
The macrocyclic ring current effect is markedly reduced in 3
as can be inferred from the more upfield shifts of the meso and
alkyl resonances. The effect of protonation upon the positions
of signals H(3) and H(4) is certainly more complex, presumably
involving the diamagnetic current induced in the six-membered
ring as well as a change in the anisotropy of the C-O bond.
Systematic titration of 5 with TFAH monitored by 1H NMR
results in a smooth although relatively small increase of the
chemical shifts, so the effect of protonation on aromaticity is
moderate. The difference between the shifts of H(3) and H(4)
is reduced, and almost certainly proton addition takes place at
the O(2) atom. Surprisingly, after addition of more than 1 equiv
of acid the signals begin to move in the reverse direction, i.e.,
upfield. Possibly TFAH associates to 5-H+ through hydrogen
bonding although coordination to palladium cannot be ruled out.
The selectivity of the alkylation reaction heavily depends on
the alkylating agent being used. n-Butyl iodide produces a
roughly equimolar mixture of the O(2)- and C(22)-butylated
species, 4-Bu and 5-Bu, respectively. Their spectral character-
istics compare well with those of other O- and C-substituted
1
Cyclic voltammetry of K[(OBP)PdII] in acetonitrile solution
shows a reversible oxidation at 0.32 V (vs AgCl/Ag). For
(HOBP)PdII the oxidation wave shifts to 0.43 V.
derivatives 4-R and 5-R (the H NMR spectrum of 4-Bu is
shown in Figure 4, trace B). An additional feature seen in the
1H NMR spectrum of 5-Bu is the diastereotopic differentiation
of the 22-Bu methylene resonances (especially strong for the
R-Bu signal, Figure 4, trace C). This reflects the fact that
addition to C(22) removes the unique symmetry plane of the
macrocycle. Accordingly, all species 5-R are chiral in a similar
way as described for complexes of N-methylporphyrins and
carbaporphyrin.7,45 The behavior of butyl iodide shows that there
Esterification of K[(OBP)PdII]. In contrast with the free
base, known to be fairly unreactive,10 [(OBP)PdII]- readily reacts
with a variety of electrophiles. Application of two typical
esterification reagents, acetic anhydride or p-toluenesulfonyl
chloride, yielded the respective ester derivatives of palladium-
(II) hydroxybenziporphyrin (3), i.e., (AcOBP)PdII and (TsOBP)-
PdII (4-Ac and 4-Ts, Scheme 3), whose electronic spectra are
almost identical with the spectrum of 3. The changes observed
(43) Grove, D. M.; van Koten, G.; Louwen, J. N.; Noltes, J. G.; Spek, A.
L.; Ubbels, H. J. C. J. Am. Chem. Soc. 1982, 104, 6609.
(44) Lavallee, D. K. The Chemistry and Biochemistry of N-substituted
Porphyrins; VCH Publishers: New York, 1987.
1
in their H NMR spectra follow the pattern already described
for 3, although the general upfield trend is now more pro-

6896 Inorganic Chemistry, Vol. 40, No. 27, 2001
Ste¸pien´ et al.
Figure 4. 1H NMR spectra of 5-Me (298 K, MeCN-d3, trace A) and 4-Bu (298 K, CDCl3, trace B). Trace C shows the 22-R-Bu signal of 5-Bu.
Table 1. Feasible Delocalization Modes within the Six-Membered
Ring of Oxybenziporphyrin and Its Complexes
tetrahedral C(22) atom (C). Moreover charge-separated contri-
butions of type B can accompany state A and, by analogy, there
may be D-type admixtures present in C (Chart 2).
Obviously the electronic structure of (OBPH)H2 and its
derivatives cannot be unraveled in terms of A-D relying solely
on the quantitative information provided by NMR. One can note,
however, that each of tautomers 1-1-6 is a realization of some
C(22)/O(2) substitution pattern and thus may closely approach
the limit of the corresponding delocalization state. Therefore a
theoretical treatment of the tautomers of 1 may provide
additional insight into the feasibility of states A-D.
To estimate the relative stability of the six tautomers we have
applied the density functional theory (DFT) in a similar way as
previously described for inverted porphyrins, sapphyrin, diheter-
osapphyrins, and inverted selenaporphyrin.23,47-49 DFT methods
and high-level ab initio calculations have recently been applied
to porphyrins, porphyrin isomers, metalloporphyrins, and related
systems.47-52 These theoretical investigations addressed prob-
lems of molecular geometry, NH tautomerization, electronic
spectra, and effects of substitution on electronic structure.
The optimized geometries of the representative tautomers of
1′ (1 with peripheral alkyls replaced by hydrogens) and the
corresponding relative energies (B3LYP/6-31G**//B3LYP/6-
31*G) are shown in Figure 5. In each case the macrocycle
remains virtually planar irrespective of the protonation state.
Root-mean-square deviations of bond lengths along the three
predicted delocalization pathways are given for the relevant
tautomers in Table 2. Inspection of these values leads to the
conclusion that the postulated delocalization modes A-D are
indeed realized by the theoretical model. In 1′-1 and 1′-6 the
two types of macrocyclic aromaticity A and D are present, as
indicated by the CsC distances along the respective deloca-
lization paths (21-1-22-5-6 and 21-1-2-3-4-5-6),
which approach the value of 1.40 Å. In 1′-5 localization of
double bonds can be seen, which agrees with the assumed state
C. Interestingly, bond lengths within the C6 ring of tautomer
1′-4 do not completely average out. It is conceivable that the
presence of the 2-hydroxyl substituent suffices to impart some
A-type aromatic character to the basically benzene-like structure.
is no sharp distinction between the O- and C-nucleophilicity of
2, and the selectivity of different electrophiles may depend on
both their steric demands and electronic characteristics (such
as polarizability46).
Tautomers of (OBPH)H2. DFT Calculations. It could be
seen from the preceding discussion that appropriate substitution
of atoms O(2) and C(22) can strongly influence the electronic
structure of oxybenziporphyrin and its complexes. Crucial in
this respect are the properties of the C6O unit, which participates
in the macrocyclic delocalization in a manner determined by
the internal/external substitution pattern. In principle, four
limiting delocalization routes can be distinguished, as shown
in Table 1. States A and D, with the conjugation pathways
passing respectively through the C(22) atom and around it, will
contribute to the macrocyclic aromaticity. On the other hand,
state B, known to prevail in the 2-unsubstituted benziporphyrin,8
will favor the [6]annulene aromaticity, while state C, in which
a keto function and an sp3 carbon are simultaneously present,
disables all delocalization routes involving the C6O fragment.
As indicated in Table 1, for certain of the species 1-5 several
delocalization states are potentially accessible. For instance states
A and C may be required to describe the 22-alkylated complex
5 to account for the macrocyclic aromaticity (A) and the
(47) Szterenberg, L.; Latos-Graz˘yn´ski, L. Inorg. Chem. 1997, 36, 6291.
(48) Szterenberg, L.; Latos-Graz˘yn´ski, J. Phys. Chem. A 1999, 103, 3302.
(49) Szterenberg, L.; Latos-Graz˘yn´ski, L. THEOCHEM 1999, 490, 33.
(50) Ghosh, A. Quantum Chemical Studies of Molecular Structures and
Potential Energy Surfaces of Porphyrins and Hemes. In The Porphyrin
Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic
Press: New York, 2000; Vol. 7, p 1.
(45) Kubo, H.; Aida, T.; Inoue, S.; Okamoto, Y. Chem. Comun. 1988, 1015.
(46) March, J. AdVanced Organic Chemistry, 4th ed.; Wiley and Sons: New
York, 1992; pp 365-368.
(51) Ghosh, A. Angew. Chem., Int. Ed. Engl. 1995, 34, 1028.
(52) Vanber, T.; Ghosh, A. J. Am. Chem. Soc. 1999, 121, 12154.

Palladium(II) Complexes of Oxybenziporphyrin
Inorganic Chemistry, Vol. 40, No. 27, 2001 6897
Chart 2
between the cis and trans tautomers of porphyrin, for which a
value of 6-11 kcal/mol was calculated).53,54
The energy differences obtained for the tautomers provide a
tentative measure of the π-electron effects caused by the
redistribution of protons among the potentially nucleophilic sites
in 1, showing that they are generally small. It is reasonable to
expect that these effects should be of comparable magnitude in
metal complexes of oxybenziporphyrin even in the presence of
back-donation, which in the case of Pd(II) interferes with the
π-system of the ligand.
The analysis of the calculated relative stability of oxybenzi-
porphyrin tautomers may provide additional insight into the
coordinating properties of oxybenziporphyrin. Considering the
mechanism of metal ion insertion into the coordination core of
inverted porphyrin, we included a preorganization step into the
mechanistic route.47 To satisfy the requirements imposed by the
inserted metal ion the molecular and electronic structures of
the ligand have to be prearranged. A preorganization may
contribute to the overall activation energy of metal insertion.
Energies of preorganization for 1′-1 f 1′-4 (12.74 kcal/mol,
oxybenziporphyrin f 2-hydroxybenziporphyrin) and 1′-1 f 1′-5
(18.07 kcal/mol, change in hybridization of C(22)) are compa-
rable with activation energies determined for metal ion insertion
to porphyrins and N-methylporphrins.55-58 However, mecha-
nistic factors that influence the value of activation enthalpy may
be essentially different for regular porphyrins and oxybenzi-
porphyrin. The relatively small calculated ligand preorganization
energy leads to an expectation that oxybenziporphyrin will
coordinate using several different coordination modes depending
on peripheral modifications and, presumably, on the nature of
the central atom. The very large energy difference between 1-1
and 1-6 (54.66 kcal/mol) excludes the contribution of 1-6 in
tautomeric equilibria of oxybenziporphyrin. However, as shown
experimentally, once the palladium(II) ion binds to the three
pyrrolic nitrogen atoms, both coordination modes of the C(22)
atom (trigonal and tetrahedral) are achievable. Thus, the aromatic
structure found for (OBPMe)PdII does not result from the
energetic preferences of the ligand but rather from the coordina-
tion of the palladium(II) ion.
Figure 5. DFT-optimized structures of 1′-1-6 (relative energies in
kcal/mol). The relevant bond distances are given in Å.
The bond distances within the tripyrrolic framework (given
in the Supporting Information) indicate that this part of the
macrocycle is highly conjugated in all the forms 1-1-6. In all
cases they are comparable to the corresponding distances
calculated for porphine and inverted porphine.47 In 1-5 and 1-6
the C(22) atom shows a slight distortion from the perfect
tetrahedral geometry. The expanded C(1)-C(22)-C(5) angle
(117° in 1-5 and 116° in 1-6) and the compressed H-C(22)-H
(102 and 100°, respectively) indicate that the macrocyclic
framework imposes certain strain on the 22-methylene moiety.
22-Methylated Complexes. DFT Calculations. DFT calcu-
lations have also been carried out for (OBPMe)PdII and
[(HOBPMe)PdII]+. The optimized geometries of 5′ and 5′-H+
(with alkyl groups removed as before) are shown in Figure 6.
The six-membered ring in 5′ is tipped out of the macrocyclic
Comparison of the energy values calculated for 1′-1-3 shows
that, as expected, they are the most stable tautomers and the
effect of reshuffling the NH protons does not exceed 5 kcal/
mol. The energies obtained for 1′-4 and 1′-5 are slightly higher
than those determined for A-type tautomers but still within
acceptable limits. The calculations suggest that the D-type
delocalization, exemplified by 1′-6, will be relatively disfavored.
However, modes B and C should be considered seriously
whenever they may contribute to the electronic structure. Finally
it should be noted that repulsion between the protons inside
the macrocyclic core, which varies from tautomer to tautomer,
also affects the predicted energy gaps (cf. the energy difference
(53) Ghosh, A.; Almlo¨f, J. Chem. Phys. Lett. 1993, 213, 519.
(54) Reimers, J. R.; Lu¨, T. X.; Crossley, M. J.; Hush, N. S. J. Am. Chem.
Soc. 1995, 117, 2855.
(55) Hambright, P.; Chock, P. B. J. Am. Chem. Soc. 1974, 96, 3123.
(56) Longo, R. F.; Brown, E. M.; Quimby, D. J.; Adler, A. D.; Meot-Ner,
M. Ann. N.Y. Acad. Sci. 1973, 206, 420.
(57) Longo, R. F.; Brown, E. M.; Rau, G. W.; Adler, A. D. In The
Porphyrins; Dolphin, D., Ed.; Academic Press: New York, 1978; Vol.
5, p 459.
(58) Bain-Ackerman, M. J.; Lavallee, D. K. Inorg. Chem. 1979, 18, 3358.

6898 Inorganic Chemistry, Vol. 40, No. 27, 2001
Ste¸pien´ et al.
5-H+
Table 2. Bonding Distances and Their Mean Standard Deviations along the Three Possible Delocalization Pathways
1′-1
1′-4
1′-5
1′-6
5′
C(6)-C(5)
C(21)-C(1)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(1)-C(22)
C(22)-C(5)
1.409
1.411
1.504
1.465
1.351
1.457
1.399
1.409
0.005
0.050
0.049
1.444
1.444
1.426
1.398
1.383
1.416
1.407
1.407
0.018
0.014
0.023
1.373
1.363
1.495
1.465
1.356
1.439
1.507
1.505
0.069
0.053
0.054
1.401
1.394
1.419
1.399
1.388
1.404
1.522
1.516
0.061
0.056
0.010
1.391
1.382
1.508
1.458
1.365
1.453
1.496
1.494
0.054
0.048
0.051
1.424
1.420
1.430
1.407
1.392
1.421
1.479
1.476
0.028
0.033
0.013
σ
σ
σ
21-1-22-5-6 (A)
1-2-3-4-5-22 (B)
21-1-2-3-4-5-6 (D)
(0.054). This corresponds to a nonplanar C(22) atom and the
localized structure C. However, predominance of the C structure
implies switching off the aromaticity of the system (both
benzenoid and macrocyclic) and, as stated before, it contradicts
the strong ring current observed for 5 in solution.
Two explanations of this discrepancy can be proposed. First,
the electronic structure of 5 may easily be affected by hydrogen
bonding to O(2) or interaction with solvent (through the Pd ion).
The dominant form of 5 in solution may therefore differ from
the isolated molecule used for calculations. On the other hand,
the bond length criterion used here to assess aromaticity is not
strictly applicable in the case of 5′ with a quadruply bound
C(22). The C(1)-C(22) and C(5)-C(22) distances cannot be
expected to approach the normal value for an “aromatic” C-C
bond (∼1.40 Å) even when the three atoms are included in a
delocalization pathway.
In the protonated form 5′-H+ the benzene ring is more tilted
(35°), but angle Pd-C(22)-C(Me) is still close to 90°. The
C(22) atom is now more pyramidal, the C-C(22)-C angles
being in the range 111-115°. Notably, except for the degree
of tilt of the six-membered ring the conformations of 5′-H+ and
1-6 are very similar. Bond averaging is more apparent than in
5′ and one might expect that 5′-H+ should be more aromatic.
Bond length pattern in 5′-H+ most closely approaches delocal-
ization mode D, although most of the pertinent distances are
longer than expected.
The predictions of DFT methods correspond to the side-on
coordination modes reported for N-alkyl porphyrins44 and in
particular for (21-CH3CTPP)NiII and ((N2CP-Tol)PdII.7,25 In
these complexes regular C-coordination is only possible with
concomitant reduction of macrocyclic aromaticity and the
observed geometry results from balancing two opposite effects.
Van Koten’s group provided an important precedent for this
type of coordination.43 In [PtI((CH3C6H3-(CH2NMe2)2-o,o′)]+
the Pt(II) ion was encapsulated by a pincer ligand and
coordinated to the methylated carbon of the benzene ring (Pt-C
) 2.183(7) Å). The environment of the coordinating carbon
was slightly distorted toward pyramidal but the structural
parameters and NMR data confirmed that the [6]annulene
aromaticity was retained. In a later study Milstein and co-
workers used a diphosphine pincer ligand to stabilize a η2 agostic
interaction between an arene C-H bond and rhodium(I).59 The
coordinated benzene ring remained aromatic, as evidenced by
NMR and X-ray data, despite the strong interaction with the
metal center.
Figure 6. DFT-optimized structures of 5′ and 5′-H+ (selected bond
distances in Å). Selected angles for 5′ (5′-H+): C(1)-C(22)-Me 108.6°
(111.8°), C(1)-C(22)-C(5) 113.8° (115.0°), C(5)-C(22)-Me 108.2°
(111.3°), C(1)-C(22)-Pd 116.0° (113.2°), C(5)-C(22)-Pd 115.6°
(113.6°), Pd-C(22)-Me 91.9° (89.2°). The interplanar angle between
(C(1)C(2)C(3)C(4)C(5)C(22)) and (PdC(22)N(23)N(24)N(25)) is 25.0°
(34.9°). Numbering of atoms corresponds to Chart 1.
plane by 25°. The methyl group is bound almost perpendicular
to the CN3 coordination square, and the C(22)-Me and C(22)-
Pd bond distances are remarkably large.
In the calculated structure of 5′ one would expect deloca-
lization modes A and C to be the main contributors, in
proportions dependent on the nature of the C(22)-Pd interac-
tion. (Structures B and D should be disfavored because of charge
separation, Chart 2). Indeed, the external part of the six-
membered ring shows an enone-type localization of bonds (Od
C(2)-C(3)dC(4)), characteristic of both A and C. The C(1)-
C(22) and C(5)-C(22) bonds, which belong to the inner part
of the benzenoid ring, are very long (1.496, 1.494 Å, respec-
tively), which is reflected by the high value of σ21-1-22-5-6
Conclusions
In the present work we have described the synthesis and
reactivity of K[(OBP)PdII], an organometallic complex of
(59) Vigalok, A.; Uzan, O.; Shimon, L. J. W.; Ben-David, Y.; Martin, J.
M. L.; Milstein, D. J. Am. Chem. Soc. 1998, 120, 12539.

Palladium(II) Complexes of Oxybenziporphyrin
Inorganic Chemistry, Vol. 40, No. 27, 2001 6899
(AB, 4-H, 3-H, 3JAB ) 8.8 Hz); ∼3.78 (m, 8 H, 9,13,14,18-R-Et); 3.32,
3.29 (2×s, 6 H, 8,19-Me); ∼1.75 (m, 12 H, 9,13,14,18-â-Et). 13C NMR
(partial data; CDCl3, 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]-
hexacosane (Aldrich) added to improve solubility): 191 (2-C); 151
(4-C); 139 (22-C); 124 (3-C); 121 (6-C); 117 (21-C); 94, 95 (11,16-
C); 20 (9,13,14,18-R-Et); 18 (9,13,14,18-â-Et); 11 (8,19-Me). 15N NMR
(same conditions as 13C NMR): -212 (24-N); -225 (23-N); -226 (25-
N); -352 (cryptate). UV-vis (MeCN, λmax (nm) (log ꢀ)): 443 (4.63),
338 (4.32), 601 (4.17), 588 (4.17), 642(3.98). HRMS (ESI, m/z, negative
ions): 580.1604 (580.1587 for C32H32N3O106Pd-).
oxybenziporphyrin, showing that the ability of carbaporphy-
rinoids to coordinate metal ions and form metal-carbon bonds
extends beyond the family of inverted porphyrin. The anionic
[(OBP)PdII]- is conspicuous for the plasticity of its electronic
structure, which is easily modified by addition of an electrophile.
Depending on its nature, the electrophile reacts selectively at
the O(2) atom (e.g. proton or acetyl) or is added to the internal
carbon C(22) (methyl). O-addition results in structures with
phenolic aromaticity, whereas the C(22)-substituted species
retain their macrocyclic aromaticity despite the apparent inter-
ruption of the delocalization pathway by a pseudotetrahedral
center. The internal alkylation is particularly important as it leads
to a coordination mode that is drastically different from the in-
plane coordination seen for [(OBP)PdII]-.
The easy accessibility of the several delocalization patterns
observed for oxybenziporphyrin and its complexes has been
qualitatively explained through DFT studies. In most cases
energy differences between possible tautomers of the free base
are small suggesting that the π-electron density may be
reorganized without significant destabilization of the molecule.
This rationalizes the facile formation of oxybenziporphyrin
complexes with both macrocyclic and phenolic aromaticity.
Calculations carried out for the 22-substituted species predict a
markedly distorted environment of the coordinating internal
carbon leading to a structure that is difficult to describe in terms
of a simple valence-bond model.
(OBPMe)PdII. Solid 2 (5 mg) is placed in a small vial, and methyl
iodide (1 mL) is added. The reaction mixture is stirred until the starting
compound has dissolved. The brownish solution is evaporated in a
stream of nitrogen and the residue dried under vacuum. The product
does not require further purification. 1H NMR (CDCl3): 10.40 (s, 21-
H); 9.25 (s, 6-H); 9.22, 9.20 (2 × s, 11,16-H); 9.10, 7.84 (AB, 4-H,
3
3-H, JAB ) 9.3 Hz); ∼3.52 (m, 8 H, 9,13,14,18-R-Et); 3.09, 3.03 (2
× s, 6 H, 8,19-Me); ∼1.60 (m,12 H, 9,13,14,18-â-Et); -2.00 (s, 3 H,
22-Me). 13C NMR (CDCl3): 184.3 (2-C); 157.9 (1-C); 157.2 (5-C);
151.6, 150.1 (7-C, 20-C); 146.5 (×2, 9-C, 18-C); 145.4 (4-C); 143.6,
143.3 (×2), 143.1 (10-C, 12-C, 15-C, 17-C); 142.2, 142.1 (13-C, 14-
C); 136.0, 134.7 (8-C, 19-C); 130.8 (3-C); 122.6 (6-C); 121.0 (21-C);
108.2, 108.0 (11-C, 16-C); 44.3 (22-C); 30.0 (22-Me); 19.4 (×2), 19.1
(×2) (9,13,14,18-R-Et); 18.0 (×2), 17.1 (×2) (9,13,14,18-â-Et); 11.4,
11.1 (8,19-Me). MS (ESI, m/z): 595.2 (595.18 calculated for
C33H35N3O106Pd+).
(OBP-n-Bu)PdII and (n-BuOBP)PdII. The synthesis is carried out
analogously, n-BuI replacing methyl iodide. Gentle heating (50-60
°C, 1 h) is necessary to speed up the reaction. A mixture of the O- and
C-substituted compounds 4-Bu and 5-Bu is obtained. Only 4-Bu
survives chromatographic workup (silica gel/CH2Cl2), and thus, 5-Bu
has only been characterized in the reaction mixture. Data for 4-Bu are
The coordinating environment provided by all carbaporphy-
rins offers a unique opportunity to create novel organometallic
compounds and to control their reactivity. The additional feature
of oxybenziporphyrin, its expanded π-system, has enabled us
to investigate and eventually to control the subtle interplay
between coordination, tautomerism, and aromaticity.
1
as follows. H NMR (CDCl3): 9.04 (s, 21-H); 7.82 (s, 6-H); 7.62 (s,
3
2 H, 11,16-H); 8.16, 7.20 (AB, 4-H, 3-H, JAB ) 9.5 Hz); ∼3.10 (m,
8 H, 9,13,14,18-R-Et); 2.71, 2.70 (2 × s, 6 H, 8,19-Me); ∼1.44 (m,12
H, 9,13,14,18-â-Et); 4.38 (t, 2 H, 2-R-Bu); ∼2.06 (m, 2 H, 2-â-Bu);
∼1.74 (m, 2 H, 2-γ-Bu); 1.11 (t, 3 H, 2-δ-Bu). Data for 5-Bu are as
Experimental Section
1
follows. H NMR (MeCN-d3, partial data): 10.25 (s, 21-H); 9.35 (s,
3
Materials. 8,19-Dimethyl-9,13,14,18-tetraethyloxybenziporphyrin
was synthesized as described before.9,10 Solvents used in the syntheses
were purified by standard methods. Deuterated solvents (CIL) were
used as received, except for chloroform, which was deacidified by
passing down a basic alumina column. Palladium chloride and
trifluoroacetic acid (both from Aldrich) were used as received.
Instrumentation. NMR spectra were recorded at room temperature
on a Bruker AMX 300 (1H) and Bruker Avance 500 spectrometers (all
heteronuclear experiments). Proton-detected 13C and 15N gradient-
selected correlation spectra were measured using a 5 mm broad-band
inverse gradient probehead. All 2D spectra were recorded with a
resolution of 2048 data points in t2 and up to 256 points in t1 and
6-H); 9.25, 9.20 (2 × s, 11,16-H); 9.14, 7.56 (AB, 4-H, 3-H, JAB
)
9.2 Hz); ∼2.40 (m, 2 H, 22-R-Bu).
(AcOBP)Pd and (TsOBP)Pd. Solid 2 (5 mg) is dissolved in a small
volume of pyridine, and Ac2O (4 µL, ∼5 equiv) or TsCl (3 mg, 2 equiv)
is added. After 0.5 h of stirring, the solvent is removed in a stream of
nitrogen. The residue is recrystallized from CH2Cl2/hexane. Data for
4-Ac are as follows. 1H NMR (CDCl3): 8.03 (s, 21-H); 7.52 (s, 6-H);
7.24, 7.22 (2 × s, 11,16-H); 8.00, 7.37 (AB, 4-H, 3-H, 3JAB ) 8.2 Hz);
∼2.93 (m, 8 H, 9,13,14,18-R-Et); 2.56, 2.54 (2 × s, 6 H, 8,19-Me);
∼1.37 (m,12 H, 9,13,14,18-â-Et); 2.54 (s, 3 H, 2-Ac). 13C NMR
(CDCl3): 156 (2-C); 142 (4-C); 142 (22-C); 120 (3-C); 127 (6-C); 116
(21-C); 96, 95 (11,16-C); 21 (2-Ac); 19 (9,13,14,18-R-Et); 15, 16 (9,-
1
processed in the standard way. The H and 13C shifts were referenced
1
13,14,18-â-Et); 10 (8,19-Me). Data for 4-Ts are as follows. H NMR
vs the residual solvent signal and the 15N shifts vs neat nitromethane
(external reference). Chemical shifts extracted directly from HMQC
and HMBC maps are given without decimal digits. UV-vis spectra
were recorded on a Hewlett-Packard 8435 diode-array spectrophoto-
meter. The mass spectra were obtained on an AMD-604 spectrometer
using EI and LSIMS ionization techniques or on a Finnigan MAT TSQ
700 spectrometer by means of the ESI method. The electrochemical
measurements (MeCN, 0.1 M TBAP) were performed on an EA9C
Multifunctional Electrochemical Analyzer using a glassy-carbon work-
ing electrode and platinum wire as the auxiliary electrode and referenced
with a silver chloride electrode, which contacted the solution by a liquid
junction.
(CDCl3): 7.70 (s, 21-H); 7.41 (s, 6-H); 7.14, 7.10 (2 × s, 11,16-H);
3
7.91, 7.54 (AB, 4-H, 3-H, JAB ) 8.3 Hz); ∼2.88 (m, 8 H, 9,13,14,-
18-R-Et); 2.52, 2.25 (2 × s, 6 H, 8,19-Me); ∼1.31 (m,12 H, 9,13,14,-
3
18-â-Et); 7.70, 7.14 (A2B2, 2-Ts, JAB ) 8.2 Hz), 2.32 (s, 3 H, 2-Ts).
Calculation Method. The calculations were carried out with the
GAUSSIAN94 program.60 All structures were optimized within un-
constrained C1 symmetry of the system using the density functional
theory (DFT) with Becke’s three-parameter exchange functionals and
the gradient-corrected functionals of Lee, Yang, and Parr (DFT(B3-
LYP)).61-64 The final estimations of the total energies were performed
(60) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.; Johnson,
B. G.; Robb, M. A.; Cheeseman, J. R.; Keith, T.; Petersson, G. A.;
Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski,
V. G.; Ortiz, J. V.; Foresman, J. B.; Cioslowski, J.; Stefanov, B. B.;
Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen,
W.; Wong, M. W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.;
Martin, R. L.; Fox, D. J.; Binkley, J. S.; Defrees, D. J.; Baker, J.;
Stewart, J. P.; Head-Gordon, M.; Gonzales C.; Pople, J. A. GAUS-
SIAN94; Gaussian, Inc.: Pittsburgh, PA, 1995.
K[(OBP)PdII]. A suspension of (OBPH)H2 (20 mg, 42 µmol), PdCl2
(7.5 mg, 42 µmol), and anhydrous K2CO3 (excess) in dry MeCN (40
mL) is refluxed for 5 h under nitrogen. The bright green solution is
strongly concentrated (but not evaporated to dryness) and diluted with
a small volume of CH2Cl2, and the complex is precipitated with hexane
(recrystallization is repeated). The product is filtered out and dried
1
overnight under vacuum. Yield: 25 mg (96%). H NMR (MeCN-d3):
10.37 (s, 21-H); 9.08 (s, 6-H); 9.22, 9.17 (2×s, 11,16-H); 8.62, 6.96
(61) Becke, A. D. Phys. ReV. A 1988, 38, 3098.

6900 Inorganic Chemistry, Vol. 40, No. 27, 2001
Ste¸pien´ et al.
at the B3LYP level with the 6-31**G basis set (structures 1′-1-6) or
the LANL2DZ basis set (5′ and 5′-H+) using the B3LYP/6-31*G fully
optimized structures. The harmonic vibrational frequencies were
calculated using analytical second derivatives and zero-point vibrational
energies (ZPVE) were derived.
155 15), the Foundation for Polish Science (M.S., L.S., and
L.L.-G.), and the National Science Foundation (Grant CHE-
9732054, T.L.) is kindly acknowledged. The quantum calcula-
tions have been carried out at the Poznan´ Supercomputer Center
(Poznan´) and the Wrocław Supercomputer Center (Wrocław).
Acknowledgment. Financial support from the State Com-
mittee for Scientific Research KBN of Poland (Grant 3 T09A
Supporting Information Available: Tables of total energies,
bonding distances between heavy atoms, and optimized geometries (in
xyz format) for structures 1′-1-6, 5′, and 5′-H+. This material is
available free of charge via the Internet at http://pubs.acs.org.
(62) Lee, C.; Yang W.; Parr, R. G. Phys. ReV. B 1988, 37, 785.
(63) Johnson, B. G.; Gill, P. M. W.; Pople, J. A. J. Chem. Phys. 1993, 98,
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(64) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
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