2182
Synthesis of meso-phenyl-4,6-dipyrrins,
preparation of their Cu(II), Ni(II), and Zn(ll)
chelates, and structural characterization of
bis[meso-phenyl-4,6-d ipyrri nato] N i (II)
Christian Briickner, Veranja Karunaratne, Steven J. Rettig,
and David Dolphin
Abstract: meso-Phenyldipyrromethanes can be oxidized by 2,6-dicyano-3,5-dichloro-para-benzoquinone (DDQ) to the
corresponding meso-phenyldipyrrins. As expected, these novel, stable bipyrrolic pigments readily form metal chelates with
copper(II), nickel(II), and zinc(II). Their UV -VIS spectra are compared with a series of known alkyl-substituted dipyrrin
chelates and, based on the UV-VIS spectral analysis, the dihedral angle between the two ligands in the bis[mesophenyldipyrrinato]Ni(II) complex was calculated to be 42°. The molecular structure of this complex was determined by X-ray
crystallography, essentially confirming the calculation. Crystals of C 30H22N4Ni are orthorhombic, a = 17.156(3), b = 35.217( 1),
c = 7.886(1) A, Z = 8, space group Fddd. The structure was solved by direct methods and refined by full-matrix least-squares
procedures to R = 0.040 and Rw = 0.031 for 1058 reflections with I ~ 3u(F2 ). The central nickel is coordinated in a distorted
square-planar fashion by four nitrogens. The pair of the planar dipyrrinato ligands enclose a dihedral angle of 38.5°. This is the
lowest angle reported for nickel(II) complexes of this kind. As a result of this, and in sharp contrast to previously described
nickel(II) dipyrrin chelates, the central metal is diamagnetic.
Key words: meso-phenyldipyrromethanes, meso-phenyldipyrrins, meso-phenyldipyrrinato transition metal chelates,
X-ray crystallography.
Resume: Sous l'influence de la 2,6-dicyano-3,5-dichloro-para-benzoquinone (DDQ), on peut oxyder les mesophenyldipyrromethanes en meso-phenyldipyrrines correspond antes. Comme on pouvait s'y attendre, ces nouveaux pigments
bipyrroliques stables forment des chelates metalliques avec Ie cuivre(II), Ie nickel(II) et Ie zinc(II). On a compare leurs spectres
UV -VIS avec ceux d'une serie de chelates connus de dipyrrines substitutees par des groupes alkyles et, sur la base d'une analyse
des spectres UV-VIS, on a calcule que l'angle diedre entre les deux coordinats du complexe bis[meso-phenyldipyrrinato]Ni(II)
est de 42°. La structure moleculaire de ce complexe, telle que determinee par diffraction des rayons X, confirme essentiellement
les conclusions obtenues par calculs. Les cristaux du C3oH22N4Ni sont orthorhombiques, groupe d'espace Fddd, avec a =
17,156(3), b =35,217(1) et c =7,886(1) Aet Z =8. La structure a ete resolue par des methodes directes et affinee par la methode
des moindres carres jusqu' it des valeurs de R = 0,040 et Rw = 0,031 pour 1058 reflexions avec I ~ 3u(F2 ). Le nickel central est
coordine d'une fa~on plan carre deformee par les quatre azotes. La paire de coordinats dipyrrinato plans forme un angle diedrdre
de 38,5°. Cette valeur correspond it I' angle Ie plus faible rapporte pour des complexes de nickel(lII) de cette espece. II en resulte
que, par opposition it ce qui a ete decrit anterieurement pour les chelates de nickel(II) dipyrrine, Ie metal central est diamagnetique.
Mots cMs : meso-phenyldipyrromethanes, meso-phenyldipyrrines, meso-phenyldipyrrinato, chelates des metaux de transition,
diffraction des rayons X.
[Traduit par la redaction]
Introduction
Dipyrrins (1), also known as dipyrromethenes, are basic,
brightly colored, fully conjugated flat bipyrrolic molecules.
Received December 1,1995.
Their propensity to strongly chelate transition metals has long
been recognized (1, 2). Their structure, atom numbering
scheme, and the formal nomenclature for dipyrrins is shown
below. Positions I and 9 are also referred to as a positions,
positions 2, 3, 7, and 8 as 13 positions, and position 5 as the
meso position.
This paper is dedicated to Professor Howard C. Clark in
recognition of his contributions to Canadian chemistry.
C. Briickner, V. Karunaratne, S.J. Rettig, and D. Dolphin. l
Department of Chemistry, University British Columbia, 2036
Main Mall, Vancouver, BC V6T lZI, Canada.
1
Author to whom correspondence may be addressed.
Telephone: (604) 822-7881. Fax: (604) 822-9678. E-mail:
david@dolphin.chem.ubc.ca
Can. 1. Chern. 74: 2182-2193 (1996). Printed in Canada / Irnprirne au Canada
3
5
7
2~8
\""NHVNJ
1 10
11 9
1
4,6-Dipyrrin
2-(2-H-pyrrol-2-ylldenemethyl)pyrrole
2
5-Phenyl-4,6-dipyrrin
2-(2-H-pyrrol-2-ylidene-methylphenyl)pyrrole
Bruckner et al.
2183
Scheme 1.
R'
R
R"
)Nj
R"
H
4
+
n
R"
OHC
N
H
HBr
.-
A
R'
R
HCOOH
5
n
R'
2
R
R'
Is
3
2. MXn,
C02C2Hs
6
0
R"
Br2
NH HN
7
\
1. C'O
2. MXn,
R"
R'~R
~
!J
R
N
R
~';d";,"
R"
~
.-
Br
R
R"
N
H
1. base
R'
R
~,w,
R"
R
.-
N-
/
M
1
R
2
10, M = Co2+, Ni 2+,
Cu 2+, Zn 2+
9, M = Ca 2+
H Br
R"
R'~R
~
!J
NH HN
R
8
R
Scheme 2.
12
COCI
6
cr
13
Scheme 1 outlines the principal pathways for the synthesis
of a- and l3-alkyldipyrrins (3) and their chelate-type mode of
metal complex formation. Four main synthetic pathways can
be distinguished:
A: The "classic" acid-catalyzed reaction of an a,l3-alkyl-a'free pyrrole (4) with a trialkylpyrrole-a-aldehyde (5) (1, 4);
B: The reaction of an a,l3-alkyl-a'-ethyloxycarbonylpyrrole
(6) in concentrated formic acid (5).
C: The oxidation of hexaalkyl-dipyrromethanes (7) by ferrous
chloride (1) or 2,3-dichloro-5,6-dicyano-l,4-benzoquinone
(DDQ) (6).
D: The meso-bromination of a dipyrromethane to yield the
meso-bromo-dipyrromethane 8, and subsequent reaction with
calcium oxide to form the calcium chelate (9), yields directly a
metal chelate. The calcium chelate can easily be transmetallated with a variety of transition metals (7-9).
In all other cases, reaction of dipyrrin (3) with a divalent transition metal salt yields the corresponding dipyrrinato complexes 10. None of the methods A, B, or D has the potential to
give access to meso-substituted, a,l3-free dipyrrins (2). Only
14
route C offers access to the title compounds by oxidation of a
meso-phenyldipyrromethane (10). As will be outlined later in
detail, this route was, indeed, successful in providing the title
compounds.
meso-Alkyl-substituted dipyrrins are less common (1, 1113) and the synthesis of meso-phenyl-substituted dipyrrins is
even rarer, in fact, we are only aware of four previous syntheses, two of them shown in Scheme 2. Rogers (14, 15) confirmed in 1943 a finding of Gabriel from 1908 (16) that
described the formation of 11 by reaction of 2,4-diphenylpyrrole (12) with in situ generated benzoyl chloride. In a similar
approach, Treibs et al. reacted pyrrole 13 with benzoyl chloride to yield the hexasubstituted meso-phenyldipyrrin hydrochloride 14 (5). It is noteworthy that in both instances the
pyrroles were substituted, particularly at one a and at least one
13 position. This prevents polymerization of the pyrroles during the harsh reaction conditions, consequently, these methods
are not options to synthesize meso-phenyl, a-unsubstituted
dipyrrins. A disadvantage of the protecting a-phenyl moieties
is that they introduce severe steric interligand interactions
2184
Can. J. Chem. Vol. 74, 1996
Scheme 3.
R
R
CHO
¢
..
TFA
DDQ
R
17, ~ = H
18, R = N02
19
15, R = H
16, R = N02
upon metal complex formation. Moreover, meso-phenyl substitution concomitant with [3-substituents also introduces
intra-ligand steric interactions that can, for instance in the case
of 14, lead to deviations from planarity and even chemical
instability (17). No reports were made on the metal complexation properties of either 11 or 14. In 1985 the X-ray structure
of bis[ 1-(2,6-dichlorobenzy1)-5-(2,6-dichloropheny l)-dipyrrinato]zinc(I1) was reported (18). This meso-phenyl and a-substituted dipyrrin complex was the kinetic product in the
Rothemund-type condensation of the sterically hindered 2,6dichlorobenzaldehyde with pyrrole, and its isolation was
unexpected and fortuitous. Similarly unanticipated, Cavaleiro
et al. isolated and crystallized meso-aryl-substituted dibenzofuranyldipyrrin in an attempted tetraarylporphyrin synthesis
from o-acetoxybenzaldehyde and pyrrole (19). These synthetic pathways towards meso-phenyl dipyrrins and their metal
complexes cannot be generalized. Recently two reports
appeared in the literature in which meso-phenyl-substituted
dipyrrin moieties were integral parts of larger molecules. The
BF2 complex of an a-methyl-meso-phenyldipyrrin unit was
the input unit of a molecular photonic wire (20) and an athiophenyl and [3-alkyl-substituted meso-phenyldipyrrin was
synthesized in the course of research towards poly heterocyclic
ligands; however, neither the complexing properties nor the
conformation of this compound were reported (21).
The stereochemistry of pyrrin ligands around the metal is
dependent on the bulkiness of the substituents in the a and a'
positions, and has found interest (22) since Porter (23) called
attention to this phenomenon; however, only a limited number
of structural data are available (18, 22, 24, 25). Few a-unsubstituted dipyrrinato complexes have been prepared (26, 27)
and in no case has a crystal structure been described. Therefore, it was interesting to investigate the complex geometry of
the a'-unsubstituted meso-phenyldipyrrin ligands of type 2
and to contrast these findings with published data. This and the
general interest for novel ligand classes for use in transition
metal catalysis (28), photometric metal detection (29), or biomedical purposes (30) prompted us to investigate the synthesis
and the metal complexing properties of a,[3-unsubstituted
meso- pheny Idipyrrins.
Results and discussion
Synthesis of 5-phenyldipyrromethanes 15 and 16
The meso-phenyldipyrromethanes 15 and 16 were synthesized
by the acid- catalyzed condensation of benzaldehyde (17) or pnitrobenzaldehyde (18), with pyrrole (19). Pyrrole was also
used as solvent according to a procedure of Lee and Lindsey
2, R = H
20, R = N02
(10) (see Scheme 3). The synthesis of 16 offers the great practical advantage over the synthesis of 15 or other dipyrromethanes described by Lee and Lindsey, in avoiding any
chromatography during the work-up or purification of the
compound; thus it is amenable to large-scale (2: 10.0 g product
per experiment) preparations. The higher electrophilicity of pnitrobenzaldehyde compared to benzaldehyde likely results in
a faster reaction rate and a stabilization of the resulting dipyrromethane towards acid-catalyzed decompositions. Both
these aspects in combination with the simple work-up explain
the high overall yield of 82% for 15 vs. the reported 49% (10)
for 16.
Preparation and characterization of mesophenyldipyrrins 2 and 20
Dehydrogenations with DDQ have found wide application in
the synthesis of pyrrolic pigments (31). In particular, DDQ is
useful in the conversion of any type of reduced porphyrins
(e.g., porphyrinogens or chlorins) to the corresponding fully
unsaturated porphyrins (32). Porphyrinogens are intermediates (33) in the synthesis of meso-tetraarylporphyrins according to the methods of Adler et al. (34) or Lindsey and Wagner
(35), i.e., the acid-catalyzed cyclization of pyrrole and benzaldehydes. Hence, it was not unexpected that the reaction of
meso-phenyldipyrromethanes 15 or 16 with one equivalent of
DDQ smoothly formed the desired dipyrrins 20 and 2
(Scheme 3). p- and o-Chloranil are equally well suited to perform the conversion. Reduction of 2 or 20 with NaBH4 in
MeOH regenerates the leuko form 16 or 15. In dilute solution,
the oxidation products are bright yellow in color. The optical
spectrum of 2 under acidic and basic conditions is shown in
Fig. I. The two-band pattern of the protonated species is analogous to that of I, 2, 3, 7, 8, 9-hexamethyldipyrrin hydrobromide (11), but ~ 14 nm hypsochromic ally shifted, with
slightly lower extinction coefficients. The bands have been
assigned to 'IT* f- 'IT transitions and are indicative of the
marked planarity of these fully conjugated aromatic systems.
Addition of acid protonates the basic imine-type nitrogen of
the 2H-pyrrole unit and this removal of non-degeneracy of the
linear resonator in combination with the presence of a positive
charge induces a bathochromic shift of 42 nm and a tripling of
the extinction coefficient (36). For steric reasons, it can be
inferred that the phenyl moiety is approximately perpendicular to the plane of the dipyrrin. Consequently, the phenyl
group is not in full conjugation with the pyrrolic system and
substituents on the phenyl group minimally influence the 'ITcloud of the dipyrrin. This explains the close similarity of the
optical spectrum of 2 and its p-nitro derivative 20; a similar
Bruckner et al.
2185
Fig. 1. Optical spectra of 2 in CH2CI 2 - 0.5% MeOH - trace
NHpH (broken line) and in CH zCI 2 - 0.5% MeOH - trace HCI
(dotted line), and of 20 in CH2Cl z - 0.5% MeOH - trace HCI
(solid line).
Scheme 4.
6E+04
2, R
20, R
:=-- 4E+04
E
o
=H
= N02
M(II)-acetate/
MeOH/base
~
W
23, R = N02 , M =Zn
24, R = N02 M = eu
21, R = N02 ' M = Ni
2E+04
22, R
300
400
500
= H, rvi = Ni
600
wavelength (nm)
situation is also found in variously phenyl-substituted mesotetraphenylporphyrins (37). The nitro compound 20, and its
metal complexes, exhibit a band at ~260 nm that we attribute
to the p-nitro moiety. The optical spectrum of2 is closer to that
of the hexamethyldipyrrin than to the spectrum of 11, which is
about 110 nm bathochromically shifted (17), possibly reflecting the extended conjugation (and distortion) of this system by
.
the a-phenyl groups.
The signals in the lH and l3C NMR of the meso-phenyldipyrrins indicate a plane of symmetry. This is consistent with
formulating the dipyrrins as adopting a planar conformation
and a rapid tautomeric exchange of the NH proton between the
two nitrogens. The lH NMR shifts for the ~-protons of 2 of
6.39 and 6.47 ppm and for the a-protons of7.78 ppm attest to
the aromatic character of these compounds.
Alkyldipyrrins of type 3 are, owing to their basicity, generally isolated and purified as their hydrobromide or hydrochloride salts (1). Although conditions for thin-layer and column
chromatography of dipyrrin hydrobromides have been
described (mixture of formic acid, methanol, and chloroform silica gel (38)), it is not common practice. Their free bases are
also reportedly less stable. We were surprised to find that in
case of the meso-phenyldipyrrins, column chromatography
(CH 2CI 2 - silica gel) of their free bases posed no difficulty.
Formation and characterization of transition metal
chelates of the meso-phenyldipyrrins
General data and synthesis
A concentrated MeOH solution of the meso-phenylpyrrins 2 or
20, when mixed with a methanolic solution of the divalent
metal ions N?+, Cu 2+, and Zn2 +, as their acetates, yields the
corresponding highly colored metal complexes (Scheme 4).
The complexes are stable and do not require any special handling. Analyses confirmed the stoichiometry of the precipitates as M(ligandh. The metal complexes formed X-ray
quality dichroic (metallic green-red) crystals.
The vibrational spectra of the metal complexes are similar
to those of their ligands. This is not unexpected as conjugation
is already attained in the planar ligand moiety before coordination to a metal. Thus, intraligand vibrations will undergo
only minor shifts upon metal chelation. This has been ratio-
Fig. 2. Optical spectra of 21 in CHCl 3 (broken line) and 22 in
CHCI 3 (solid line).
6E+04
:=-- 4E+04
E
o
~
W 2E+04
OE+OO1---~--------r--------.----~~r---400
500
300
600
wavelength (nm)
nalized before for the metal complexes of hexaalkylpyrrins
(39).
UV-VIS spectra
The optical properties of the metal compounds are strongly
dependent on the central metal but the nickel chelates 21 and
22 are very similar (Fig. 2). This similarity, in particular with
respect to ~max and log E, is indicative of a very similar stereochemistry of these two compounds. The UV-VIS spectrum
of the zinc chelate 23 resembles that of the protonated ligand,
suggesting the absence of any metal f - metal transitions (see
Fig. 3). However, metal f - ligand charge transfer transitions
are generally observed in this energy region and they cannot
be excluded (27), though other authors have assigned this
band exclusively to intraligand 71"* f - 71" transitions and the
bands in the 320-350 nm region to charge transfer transitions
(40). The electronic spectra of the nickel and the copper chelates 20, 21, and 24 follow the same general pattern as that of
23 (see Figs. 2 and 3). The UV-VIS spectra of the metal chelates are nearly indistinguishable in non- or weakly coordinating solvents such as benzene, methanol, methylene chloride,
or chloroform but show changes in pyridine, most noticeable
for the zinc chelate, as also shown in Fig. 3. Table 1 lists
selected UV-VIS data of some known dipyrrinato-metal complexes (25-40) and of the novel compounds 21, 23, and 24.
When comparing the longest wavelength absorption of the
Zn-chelate 23 at 486 nm against the equivalent transitions of
2186
Can. J. Chem. Vol. 74, 1996
Fig. 3. Optical spectra of 23 in CH 2Cl 2 (dotted line) and
pyridine (dashed line), and 24 in CHCl 3 (solid line).
6E+04
E
u
:.w
4E+04
2E+04
.~....I""""'................
OE+OO~---r------~;=------~~~~~~---
300
600
500
400
wavelength (nm)
the alkyl-substituted analogues 25-32, it is remarkable that the
meso-phenylpyrrin chromophore is distinguished by the highest transition energy. An equivalent trend can be seen in the
nickel (22 vs. 33-36) and copper (24 vs. 37-40) chelate series.
Hyperconjugation effects have been suggested for the progressive bathochromic shift with increasing methyl substitution
(27). Extended 1T-conjugation can be evoked for the bathochromic ally shifted optical spectrum in case of dipyrrins 28
and 32. The absence of both effects in the zinc, nickel, and copper chelates 21-24 rationalize their relatively high transition
energies. The introduction of a meso-methyl substituent in chelates 29 and 30 leads, when compared to their meso-unsubstituted analogues 27 and 28, to a relatively small change in the
energy of the longest wavelength transition; however, their
extinction coefficients significantly decrease. This, based on
theoretical considerations, may be taken as a sign of distortion
from planarity (17). Based on the foregoing, the high extinction
coefficients of the metal chelates of the meso-phenyldipyrrins
seem to indicate that the ligands are flat. In the absence of any
l3-substituent and hence any intraligand steric crowding, and in
analogy to the conformation of meso-tetraphenylporphyrins
(42), this appears to be a reasonable assumption. As will be
detailed later, the single crystal X-ray structure of 22 shows
that the assumption of planarity is, in fact, valid.
The stereochemistry of the ligands around the central metal
is strongly dependent on the metal type. The preference of
zinc(lI) for a tetrahedral, and of nickel(II) and, even more so,
of copper(II) for a square-planar coordination sphere is well
documented (43). Regardless of the a substituents present in
the dipyrrin ligands, the realization of a tetrahedral coordination sphere poses no interligand steric interactions. Consequently, and in analogy to the stereochemistry of the zinc
chelates of alkyldipyrrins, compound 23 can be assigned a tetrahedral structure (9, 22, 27,40). The picture is more complex
for the nickel and copper chelates. It has been found in previous studies that a substituents prevent square-planar coordination due to interligand crowding. This forces the complex into
a distorted tetrahedral structure in which the two approximately planar a-methyldipyrrinato ligands are inclined (as
determined by X-ray crystal structure analysis) at an angle
(referred to as dihedral angle) of 76.3° for nickel chelate 33
(24) and 66° for copper chelate 39 (25). With hydrogen as the
sole a substituents no a priori statement can be made about the
stereochemistry around the metal. It has been suggested that
some electronic interaction exists between the 1T-systems of
the two dipyrrin units coordinated to the same metal ion in the
"tetrahedral" Co(ll) and Cu(I1) complexes (44). Motekaitis
and Martell presented an MO theory model and derived a relationship (eq. [I]) in which the intensity of the longest wavelength transition is assumed to change with the tetrahedral
angle e between the ligands:
(RWJ
R
\
/
~+
Compound no.
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
R
2
R
-H
-Me
-Me
-Me
-Me
-Me
-C02Et
-Ph
-Me
-Me
-Me
-Ph
-H
-Me
-Me
-Ph
R'
-Me
-H
-Me
-C02Et
-C02Et
-Me
-Cl
-H
-H
-Me
-C02Et
-H
-Me
-Me
-C02Et
-H
R"
R meso
M2+
-Me
-Me
-Me
-Me
-Me
-Me
-Cl
-H
-Me
-Me
-Me
-H
-Me
-Me
-Me
-H
-H
-H
-H
-H
-Me
-Me
-H
-H
-H
-H
-H
-H
-H
-H
-H
-H
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Ni
Ni
Ni
Ni
Cu
Cu
Cu
Cu
Bruckner et al.
2187
Table 1. Selected UV-VIS data and dihedral angles of
dipyrrinato chelates.
Compound
no.
Am" (log £)"
(nm)
Dihedral
angle CO)b
Reference
23
486 (4.97)d
90"
This work
25
500 (5.08/
483 (4.97)
488 (4.22)'
469, sh
505 (4.93)'
487 (5.07)
490 (5.33)'
446, sh
501 (5.051
505 (4.061
537 (5.13)'
552 (4.93)'
510 (5.06)
90"
27
9(F
27
90"
27
90"
22
26
27
28
29
30
31
32
II
11
90"
9,41
27
22
484 (4.63)d
42/' 3805'
This work
33
34
512 (4.85)'
531 (4.70)UIe
76.3'
24, 39
35
36
462 (4.57)
495 (4.99)'
540 (4.85)'
60! 66 h
40
26
24
474 (4.72)'
4810
This work
37
471
409
525
471
495
564
509
50,10 6Y
26
6Si
39
66'
25,40
26
39
38
39
40
(4.85)'
(4.61)
(4.65)'
(4.76)
(5.05)'
(4.93)'
(4.70)
90,h 7Y
"Longest wavelength n* (,-- n transition.
bBetween planes formed by the ligands.
'p-N02 -pheny \.
dIn CH,CI,.
'In CHCI 3 •
fSolvent not specifIed.
g Assumed angle.
"Calculated according to Motekaitis et al. (9).
'From X-ray single crystal structure.
iBased on ligand field transition analysis (26).
E8
[1]
. 2
-::-go = sm
e
E
e is the tetrahedral angle, E8 is the extinction coefficient of a
reference compound known to be tetrahedral, i.e., e = 90°,
and E8 is the extinction coefficient of a similar compound
whose geometry is to be determined. According to eq. [1], the
calculated tetrahedral angle in the meso-phenyldipyrrin nickel
complex 22 would be 42°, and in the copper complex 24, 48°.
There are, however, precautions to be taken when applying
Martell's methodology for determination of the interligand
dihedral angle. The prerequisite that the ligands are flat and
coordinate in exactly the same MN4 fashion to the complexes
to be compared must be strictly fullfilled. Fergusson and coworkers (22), for instance, published the crystal structure analysis of the palladium chelate of 3,3',5,5'-tetramethyl-4,4'diethoxycarbonyldipyrrin in which the dipyrrin unit was not
planar. The tendency for palladium to achieve square-planar
coordination geometry is strong enough to distort the planar
ligand and to enforce a stepped arrangement of the ligands
around the metal centre. With little change in transition
energy, the extinction coefficients were reduced compared to
the analogous tetrahedral cadmium, mercury, or zinc complexes. However, the application of eq. [I] gives incorrect
results when compared to the actual structures. A second
example can be derived from examination of the literature.
Based on the extinction coefficient of 31, Martell determined
the dihedral angle of the copper analogue to be 40° (9). However, considering the steric requirement of the ethoxycarbonyl
moiety and setting it against the crystallographically determined dihedral angle of 66° for 39 or values determined for
the complexes 37-40, this value appears to be considerably
too low. Murakami et al. investigated the IR spectrum and the
ligand-field bands of this complex and proposed the involvement of the carbonyl oxygen in this copper chelate, giving a
CuN40 2 coordination (41). In light of this it becomes apparent
that the dihedral angle predicted by Martell' smethod had to be
in error. In the present case, however, the prerequisites of similarly flat ligands forming in all cases a MN4 coordination
sphere are most likely fullfilled and, consequently, the theoretically determined values may be significant. Indeed, the X-ray
crystal structure analysis for nickel complex 22 proved the
value determined by Martell's method to be fairly accurate
(3.5° deviation, Table 1). As for the copper chelate, a final
experimental proof of the calculated value still awaits, but the
value of 48° is in agreement with the calculated value of one
other a-unsubstituted copper chelate 37 and, as expected, is
significantly smaller than for the a-alkyl-substituted chelates.
The calculated values for the copper chelates have to be taken
with some reservation as shown by the discrepancies of the
values determined by ligand field transition band analysis and
by Martell's method.
The change of the optical spectrum of 23 upon the addition
of pyridine (Fig. 3) results from an expansion of the Zn-coordination sphere from tetrahedral ZnN4 to a distorted tetragonal
pyramid ZnNs' This forces the dipyrrinato ligands to take up a
smaller dihedral angle, which probably accounts for the
observed spectrum. The nickel chelate UV-VIS spectrum
shows only a slight change upon addition of pyridine. This is
analogous to, for instance, the reluctance of the square- planar
nickel(II) porphyrins to expand their coordination sphere and
the small changes in their optical spectrum associated with
any additional coordination (45). This effect is even more pronounced in the case of the Jahn-Teller ion copper(II).
Magnetic properties
The magnetic properties of nickel (II) complexes with N-donor
ligands may permit conclusions regarding their coordination
geometry. Square-planar complexes are typically diamagnetic, and tetrahedral complexes paramagnetic (43). All
2188
Can. J. Chem. Vol. 74, 1996
Fig. 4. ORTEP plot (stereoview) of 22; 33% probability thennal ellipsoids are shown for
the non-hydrogen atoms.
22
41
nickel(II) chelates of dipyrrins have been described as paramagnetic and, therefore, their description as distorted tetrahedral rather than distorted square planar is plausible regardless
of the actual dihedral angle between the ligands. To our surprise, the nickel chelates 21 and 22, as judged by the sharp 1H
and l3C NMR, proved to be diamagnetic. This suggests that
they are (distorted) square planar. On the basis of a comparison of the steric interactions in the cyclic and planar [meso-tetraphenylporphyrinato]nickel(II) (41) or the cyclic and saddleshaped [5, 15-dimethyl-5, 15-dihydrooctaethylporphyrinato]nickel(II) (42) (46), it becomes clear that a planar coordination
can be excluded since the two a-hydrogens of the opposing
ligands would occupy the same space (given standard Ni-N
bond lengths) in case of square- planar coordination. To unambiguously answer the question about the dihedral angles in the
nickel chelate, an X-ray crystal structure analysis of a single
crystal of 22 was undertaken.
42
Crystal structure analysis
An ORTEP representation of 22 as it exists in the crystal
together with the numbering system employed in Tables 2 and
3 is shown in Fig. 4. Atom coordinates and Beq are listed in
Table 2. Selected bond parameters are listed in Table 3, and
the crystallographic data are listed in Table 4.
The molecule has D2 symmetry, which makes the two
ligands equivalent and endows a C2-axis passing through the
p-hydrogens of the meso substituent, the methine carbons, and
the central metal. The planes of the two essentially planar
dipyrrin ligands enclose a dihedral angle of 38.5°, in close
agreement with the calculated value of 42°. The equivalent
angle in [3,3',5,5'-tetramethylpyrrinato]nickel(II) (33) is, as
mentioned above, 76.3° (24). The small angle results directly
from the smaller size of the a-H as compared to the a-methyl
group. The bite angle N-Ni-Na of the ligand is 94.3°, which is,
within the experimental uncertainty, equal to the bite angle
Bruckner et al.
2189
Table 4. Crystallographic data for compound 22."
Table 2. Atom coordinates and BC'J° for 22.
Atom
x
Ni(l)
N(1)
0.12500
0.0990(1)
0.0985(1)
0.0592(2)
0.0340(2)
0.0592(2)
0.1250
0.1250
0.1658(2)
0.1666(2)
0.1250
C(l)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
"Beq
z
y
0.12500
0.16291(5)
0.20166(7)
0.21708(8)
0.18773(9)
0.15443(8)
0.22034(9)
0.26307(9)
0.28288(8)
0.32263(8)
0.3416(1)
Beq
3.07(1)
3.61(5)
3.91(6)
6.72(9)
8.0(1)
5.29(7)
3.50(7)
4.18(8)
5.70(8)
7.5(1)
8.6(2)
0.62500
0.4630(2)
0.4808(3)
0.3404(4)
0.2426(4)
0.3215(3)
0.6250
0.6250
0.5040(4)
0.5060(6)
0.6250
= 8/3rc'(,i,'·£'Uija;*a;*(a:a).
Table 3. Selected bond distances and bond angles for 22.0
Atoms
Distance (A)
Atoms
Ni(1)-N(l)
N(1)-C(4)
C(1)-C(5)
C(3)-C(4)
C(6)-C(7)
C(8)-C(9)
N(l)-C(1)
C(1)-C(2)
C(2)-C(3)
C(5)-C(6)
C(7)-C(8)
1.879(2)
1.336(3)
1.390(3)
1.396(4)
1.374(3)
1.355(4)
1.404(3)
1.405(4)
1.360(4)
1.505(4)
1.400(4)
N(1)-Ni(1)-N(1).
N(1)-Ni(l)-N(1\
Ni(1)-N(1)-C(4)
N(1)-C(1)-C(2)
C(2)-C(1)-C(5)
C(2)-C(3)-C(4)
C(1)-C(5)-C(1)e
C(5)-C(6)-C(7)
C(6)-C(7)-C(8)
C(8)-C(9)-C(8\
N(1)-Ni(1)-N(1)b
Ni(1)-N(l)-C(l)
C(1)-N(1)-C(4)
N(1)-C(1)-C(5)
C(1)-C(2)-C(3)
N(1)-C(4)-C(3)
C(1)-C(5)-C(6)
C(7)-C(6)-C(7)e
C(7)-C(8)-C(9)
94.3(1)
92.1(1)
123.4(2)
108.0(2)
128.2(2)
106.7(3)
123.5(3)
120.5(2)
120.3(3)
120.9(4)
152.5(1)
128.6(2)
106.2(2)
123.4(2)
107.8(2)
111.3(3)
118.2(1)
118.9(3)
119.7(3)
"Symmetry operations: (a) 114 - x, 114 - y, z; (b) x, 114 - y, 5/4 - z;
(c) 114 - x, y, 5/4 - z.
observed for 33. The N-Ni-Nb angle is 152.5°. Unlike in the
latter structure, no distortion in the sense of a deviation of
colinearity of the two local twofold axes of each Ni-ligand
group can be detected. The four Ni-N distances are equal
(1.879(2) A), and unusually short for complexes of this kind.
We regard this effect to be partially due to the reduced ionic
radius of the d 8 low spin ion vs. the high-spin congener in 33
(47) and partially due to the reduced interligand steric interactions. The extent of the steric effect becomes perceptible if the
bond length is compared to those in related nickel complexes
33, nickel porphyrin (41), a ruffled nickel porphyrin (42), and
a 5,1O-dihydroporphyrin system (43) as listed in Table 5. The
quasi-rigid porphyrin core (in complex 41) resists undue radial
expansions or contractions in the equatorial plane of the core.
Therefore, the metal - porphyrin nitrogen bond lengths are
Formula
fw
Crystal system
Space group
a, A
b, A
c, A
v,N
z
3
Dead' g/cm
F(OOO)
j..l. cm- 1
Crystal size, mm
Transmission factors
Scan type
Scan range, deg in 0)
Scan speed, deg/min
Data collected
28 max , deg
Crystal decay, %
Total reflections
Total unique reflections
Reflections with I :;; 3cr(F2)
No. of variables
R
Rw
gof
Max /!Jcr (final cycle)
Residual density e/A3
C JoH22N.Ni
497.23
Orthorhombic
Fddd
17.156(3)
35.217(1)
7.886(1)
4764.4(9)
8
1.386
2964
8.41
0.20 x 0.30 x 0.40
0.877-1.000
0>-28
0.94 + 0.35 tan 8
16 (up to 8 rescans)
+h, +k, +1
70
2.3
2874
2874
1058
82
0.040
0.031
2.00
0.0002
-0.44 to 0.42
"Temperature 294 K, Rigaku AFC6S diffractometer, Mo Ko: radiation
(A = 0.71069 A), graphite monochromator, takeoff angle 6.0°, aperture 6.0
x 6.0 mm at a distance of 285 mm from the crystal, stationary background
counts at each end of the scan (scan/background time ratio 2: I); cr'(F2) =
[S,(C + 4B)]lLp, (S = scan rate, C = scan count, B = normalized
background count), function minimized ~w (lFol - IF,I), where w =
4Fo'/cr'(Fo'), R = ~IIFol - IF,II~IFol, R" = (~w(lFo - IF,I)'~wIFi)ll2, and
gof = [~w(IFol - IF,I)2/(m - n)]II2. Values given for R, R", and gof are
based on those reflections with I S; 3cr(F').
Table S. Ni-N bond lengths of selected tetrapyrrolic nickel
complexes.
Compound
no.
Ni-N bond
length (A)
Reference
22
27
42
1.879(2)
1.952(7) (averaged)
1.904(5) (3 out of 4)
1.929
1.960
This work
24
46
48
49, 51
43
41
"Typical value for nickel porphyrins.
restricted relative to the normal range of values that are found
in metal - monodentate nitrogen ligand bond lengths, which
results in a "stretched" bond length of ~ 1.96 A. Ruffled nickel
porphyrins can reduce the bond length by about 0.03 A; in the
saddle-shaped 42, which is essentially a strapped bisdipyrri-
2190
Fig. 5. Intraligand bond lengths, and limiting resonance structures
of the dipyrrinato ligand.
nato nickel(II) compound, the bond length is a further 0.025 A
shorter. The removal of the ligand strap concomitant with the
introduction of a-methyl groups introduces severe steric interactions in 33 but allows for a large dihedral angle, nonetheless,
a long Ni-N bond length is recorded for this class of complexes. Removal of a large portion of this interaction by the
replacement of the methyl groups with hydrogens in 22 allows
the two ligands to achieve "pseudo-planarity" and results in
the shortest Ni-N bond length of its class.
Inspection of the intraligand bond lengths reveals that two
types of C-N bonds exist, a short Crt -N bond and a long
Crt,-N bond. The differences can be accounted for in terms of
a resonance description of the 'IT-electrons in the ligand molecule. Figure 5 shows the two limiting resonance structures and
the associated bond lengths. According to this simplified picture, the Crt -N bond would receive partial 'IT-contribution,
the Crt,-N bond would not. The difference in double bond
character of these bonds explains the observed bond length
differences in a qualitative way. The deviation of the Crt,-N
bond length from the expected 1.42 A for a C-N single bond
reflects the aromatic character of the pyrrole unit itself, albeit
the analogous bond length in pyrrole is about 0.04 A shorter
(50). The Crt,-Cmeso bond and the Crt -Ci3 bond have a formal bond order of 1.5, and hence their bond lengths are as
expected. The mean plane of the meso-phenyl group is tilted
58.1 ° with respect to the mean plane of the dipyrrin unit. This
deviation from the, perhaps, expected orthogonal finds its parallels in the structure of meso-tetraphenylporphyrins (38, 51).
NMR spectroscopy
The IH and l3C NMR data of the diamagnetic metal chelates
21-23 are largely as expected, and similar to the spectra of the
protonated ligands. One noticeable exception is a large low
field shift of the a-protons in the nickel chelates 21 and 22, i.e.,
a shift of +2.48 ppm for 22 as compared to the zinc analog 23.
This also is evidence of the small dihedral angle of the ligand
mean planes in the nickel complex. The a-protons experience
shielding effects of both the aromatic dipyrrinato systems and
thus are more shielded than in the tetrahedral zinc complex,
where such "double" shielding cannot occur.
Conclusion
The meso-phenyl-4,6-pyrrins can be conveniently prepared
from the corresponding dipyrromethanes. They exhibit properties similar to previously described alkyl-substituted dipyrrins with the exception that they exhibit a significantly higher
'IT* f-- 'IT transition energy as judged by their hypsochromically
shifted UV-VIS spectra. The meso-phenyldipyrrins fonn
Can. J. Chem. Vol. 74,1996
metal complexes with nickel(II), copper(II), and zinc(II).
Their spectroscopic data can be rationalized in the context of
the previously described dipyrrinato complexes; however, the
lack of a bulky a-substituent allows unique properties to this
class of ligands. Based on optical and IH NMR data, the zinc
complex can be assigned a tetrahedral structure. Both the
nickel and the copper complex can be described as distorted
square-planar complexes. The distortion from planarity of the
nickel complex was predicted to be 42°, based on UV-VIS
data analysis. An X-ray crystal structure analysis determined
the angle to be 38S and the Ni-N distance to be 1.879(2) A.
This is the smallest angle and the shortest Ni-N bond length
recorded for dipyrrinato complexes. As a consequence of this,
and in contrast to previously described [dipyrrinato ]nickel(II)
complexes, the [meso-phenyldipyrrinato ]nickel(II) complexes
are diamagnetic. The stereochemistry of the copper complex
is assumed to be similar to that of the nickel complex. Studies
to utilize the unique steric requirement of the meso-phenyldipyrrin ligand, e.g., to form coordination polyhedra with no
precedent in the dipyrrinato field, such as octahedral
M(III)(ligand)3 complexes, are currently under way in our laboratories.
Experimental section
Instrumentation and materials
Melting points were determined on a Thomas model 40 Micro
Hot Stage and are uncorrected. The infrared spectra were measured with a Perkin-Elmer model 834 FT-IR instrument. The
NMR spectra were measured with a Bruker AC 200 FT spectrometer and are expressed in parts per million (0) relative to
the external standard TMS. The low- and high-resolution mass
spectra were obtained by Dr. G. Eigendorf and co-workers of
this department using an AEI MS9 and a Kratos MS50 spectrometer, respectively. The electronic spectra were measured
on a HP 8452A photodiode array spectrophotometer. Elemental analyses were performed by Mr. P. Borda of this department on a Fisons CHN/O Analyzer, model 1108.
meso-Phenyldipyrromethane 15 was synthesized according
to the procedure of Lee and Lindsey (10). All other reagents
and solvents were commercially available and of reagent
grade or higher, and were, unless otherwise specified, used as
recieved. The silica gel used in flash chromatographies was
Merck Silica Gel 60, 230-400 mesh.
5-( 4-Nitrophenyl)dipyrromethane (16)
Nitrobenzaldehyde (18) (3.0 g, 19.87 mmol) was dissolved in
freshly distilled pyrrole (19) (44.0 g, 0.66 mol). The mixture
was degassed by bubbling with Nz for 10 min. TFA (0.15 mL,
0.1 equiv based on the benzaldehyde) was added and the mixture was stirred under Nz until no starting aldehyde could be
detected by TLC (ca. 15 min). The volume of the slightly yellow mixture was reduced under high vacuum at 50°C to a viscous oil. This oil was dissolved in CHzCl z (100 mL) and
cyclohexane (50 mL) was added. Without heating, the mixture
was reduced on the rotary evaporator until precipitation just
began. Scratching with a glass rod caused rapid crystallization
of an slightly greenish solid which, after drying at 50°C/0.2
Torr (1 Torr = 133.3 Pa) for 24 h gave 3.85 g (71.2%) of analytically pure compound 16. A second crop of lesser purity
was obtained from the mother liquor upon further evaporation
Bruckner et al.
(0.55 g, 10.3%); mp 158°C; UV-VIS (MeOH) Amax nm (reI.
intensity): 222 (1.0), 266 (0.77); IH NMR (200 MHz) 0: 5.58
(s, lH), 5.87 (m, 2H), 6.18 (dd, J = 11.8,2.5 Hz, 2H), 6.74 (m,
2H), 7.37 (d, J = 11.8 Hz, 2H), 7.95 (br s, 2H), 8.14 (d, J = 11.8
Hz, 2H); l3C NMR (50 MHz) 0: 43.8, 107.8, 108.8, 118.0,
123.8, 129.2, 130.8, 146.9, 149.7; LR-MS(EI) mle: 267
(100.0, M+), 220 (9.7, MW - N0 2), 201 (16.3, M+ - C4H4N),
154 (9.7), 145 (47.3, MW - Ph - N0 2). Exact Mass calcd.
for CISHl3N302: 267.10078; found: 267.10080. Anal. calcd.
for C IS H l3 NP2: C 67.41, H 4.9, N 15.72; found: C 67.23, H
4.98, N 15.62.
5-Phenyl-4,6-dipyrrin (2)
meso-Pheny1dipyrromethane (15) (500 mg, 2.25 mmo1) was
dissolved with the help of a heat gun in benzene (25 mL). A
solution of 2,3-dich10ro-5,6-dicyano-1 ,4-benzoquinone (537
mg, 2.35 mmo1) dissolved in benzene (5 mL) was added and
the mixture stirred until no starting material could be detected
by tlc (1 h). The black precipitate was filtered off and air-dried
to provide 440 mg (85 %) of crude 2, which was used for metal
complex formation. An analytical sample was purified by column chromatography (silica gel, 25 g, 1% MeOH in CHCi 3).
The bright yellow main fraction was collected and evaporated
to dryness. The yellow film was dissolved in acetone (20 mL)
and precipitated by diffusion of cyclohexane into this solution
to yield a yellow-brown precipitate (55.0 % based on crude
material); mp 184°C; IR (neat): 1555, 1450, 1435, 1340, 1055
cm- I; UV-VIS (CH 2Ci2 - 0.5% MeOH - trace NH 40H) Amax
(log E): 310 (3.75), 434 (4.10) nm; (CH 2Ci2 - 0.5% MeOHtrace HC1) Amax (log E): 354 (4.02),466 (4.65) IH NMR (200
MHz, acetone-d6) 0: 6.39 (m, 2H), 6.47 (d, J = 3.5 Hz, 2H),
6.39-6.47 (m, 5H), 7.78 (s, 2H), ~ 12.5 (s, very broad, lH);
l3C NMR (50 MHz, acetone-d6 ) 0: 118.3, 128.5, 129.2, 129.7,
131.3,135.0, 138.0, 144.6; nm; LR-MS (EI, 180°C) mle: 220
(77, M+), 219 (100, M+ - H). Exact Mass calcd. for C IS H 12N2:
220.10005; found: 220.10012. A consistent elemental analysis
(deviation 3.0% from the calculated values) could not be
achieved, possibly due to varying amounts of solvation and
(or) salt formation.
5-(4-Nitrophenyl)-4,6-pyrrin (20)
This compound was prepared from 16 by a method analogous
to that used for the preparation of compound 2. Yield after
chromatography: 59%; mp 189-191°C; IR (neat): 1555,1520,
1515,1510,1450,1340, 1050cm- l ; UV-VIS (CH2Ci2 -0.5%
MeOH - trace NH 40H) Amax (log E): 264 (3.99), 300 (4.08),
434 (4.38) nm; (CH2Ci2 - 0.5% MeOH - trace HCl) Amax (log
E): 258 (4.16), 336 (4.17),470 (4.74) nm;IH NMR (200 MHz,
acetone-d6) 0: 6.21 (m, 2H), 6.40 (m, 2H), 7.36 (d, J = 8 Hz,
2H), 7.55 (s, 2H), 7.96 (d, J = 8 Hz, 2H), ~ 12.0 (very broad,
lH); l3C NMR (50 MHz, acetone-d6 ) 0: 119.0, 123.7, 128.8,
128.9, 132.4, 139.5, 140.9, 144.6, 145.6; LR-MS (EI, 150°C)
mle: 265 (100, M+), 234 (18.8, MW - 20),228 (68.2), 218
(96.5, M+ - HN0 2). Exact Mass ca1cd. for CIsHu02N3:
265.0851; found: 265.08501.
Bis[5-(4-nitrophenyl)-4,6-pyrrinato]Zn(II) (23)
To a solution of dipyrrin 20 (100 mg, 3.77 x 10-4 mol) in
MeOH (10 mL) was added zinc acetate dihydrate (420 mg, 5
equiv.) in MeOH (10 mL) and the mixture was heated on a
water bath for 4 h. The mixture was evaporated to dryness on
2191
the rotary evaporator and the remaining solids were tritrurated
with CHCI 3. The resulting bright orange-yellow solution was
filtered though a short plug of silica gel and allowed to slowly
evaporate. Compound 23 was obtained as dark orange lumps
with a bright green metallic lustre, which were, after drying
(0.1 Torr/50°C), analytically pure (180 mg, 81 %); mp >
300°C; IR (neat): 1590, 1541, 1515, 1405, 1372, 1335, 1243,
1190, 1025, 995 cm- I; UV-VIS (CH2Ci2) Amax (log E): 486
(4.97),352 (4.08), 308 (4.30), 272 (4.42) nm; (pyridine) Amax
(reI. intensity): 440 (0.2), 316 (1.0); IH NMR (200 MHz,
CDC13) 0: 6.45 (dd, J = 0.8, 4.2, lH), 6.59 (dd, J = 0.8, 4.2,
lH), 7.59 (s, lH), 7.75 (d, 9.2 Hz, lH), 8.35 (d, 9.2 Hz, lH);
LR-MS (EI) mle: 592 (40.3, M+), 295 (88.8), 280 (48.7), 265
(100, ligand+). Anal. ca1cd. for C30H20N604Zn: C 60.63, H
3.39, N 14.1; found: C 60.71, H 3.3, N 14.00.
Bis[5-(4-nitrophenyl)-4,6-pyrrinato ]Ni(II) (21)
Compound 20 was prepared using the procedure for the preparation of 23. Slow evaporation of a CHC1 3 - 1% MeOH solution of 21 yielded a dark brown-orange microcrystalline
material, which was, after drying (0.1 Torr/50°C) analytically
pure; mp, 230°C; IR (neat): 1595, 1555, 1520, 1335, 1370,
1240, 1040, 1020,995 cm- I; UV-VIS (CH 2C2) Amax (log 274
(4.58),318 (4.47), 484 (4.63) nm; (MeOH) Amax (reI. intensity):
272 (0.47), 292, sh (0.45), 466, sh (0.96), 482 (1.0) nm; (pyridine) Amax (reI. intensity): 316 (1.0),456, br (0.43), 486 (0.48);
IH NMR (200 MHz) 0: 6.66 (d, J =4.1 Hz, lH), 7.52 (d, J =8.6
Hz, lH), 8.26 (2 overlapping d, 2H), 10.83 (s, lH); LR-MS (EI,
180°C) mle: 586 (48.3, M+), 539 (15.6, M+ - HN0 2), 464
(15.3, M+ - Ph - N0 2). Exact mass ca1cd. forC30H2oN6Ni04:
586.08997; found: 586.08992. Anal. ca1cd. for C30H2oN6Ni04:
C 61.36, H 3.43, N 14.31; found: C 6.57, H 3.36, N 14.20.
Bis[5-(4-nitrophenyl)-4,6-pyrrinato ]Cu(II) (24)
Dipyrrin (20) (100 mg, 3.77 mmol) was dissolved in minimal
warm MeOH (~5 mL) and, with stirring, a solution of copper
acetate monohydrate (380 mg, 5 equiv) in MeOH (5 mL) and
concentrated ammonia (0.5 mL) was added. The metal complex precipitated from the dark orange solution almost instantaneously. The precipitate was filtered off after stirring for 12
h at room -temperature, then dried and chromatographed on a
short (10 x 2.5 cm, 1% MeOH - CHCI 3) column of silica gel.
The first intensely orange band was collected and slow evaporation of the solvent furnished 160 mg (72%) of the metal
complex 24 as black needles with a green metallic lustre.
Alternatively, repeated recrystallization from CHClrMeOH
yields dark green, dichroic microcrystals with a metallic lustre. After drying (0.1 Torr/50°C) an analytically pure sample
was obtained; mp> 300°C; UV-VIS (CHCI 3) Amax (log E):
274 (4.52), 314 (4.21), 368 (4.26),474 (4.72) nm; (MeOH)
Amax (reI. intensity): 268 (0.72), 308 (0.47), 374 (0.39), 468
(1.0), 502, sh (0.53); LR-MS (EI) mle: 591 (6.6, M+), 295
(100), 280 (68.6),264 (44.3), 248 (26.5), 234 (49.0). Exact
Mass ca1cd. for C30H2004N66SCu: 593.08240; found:
593.08305. Anal. ca1cd. for C30H20CuN604: C 60.63, H 3.39,
N 14.15; found: C 60.70, H 3.54, N 14.03.
Bis[5-phenyl-4,6-pyrrinato]Ni(II) (22)
Prepared in 76% yield in an analogous fashion as described for
23. Slow evaporation of an acetone solution gave 22 as dichroic crystals; mp (dec.) 240°C; IR (neat): 1575, 1535, 1505,
Can. J. Chem. Vol. 74, 1996
2192
1410, 1380, 1345, 1245, 1035, 1030, 1000 cm- I ; UV-VIS
(CHC1 3 ) Amax (log E): 324 (4.33), 472 (462) nm; (MeOH) Amax
(reI. intensity): 264 (0.18), 314 (0.23), 458 (0.83), 478 (1.0);
IH NMR (300 MHz, CDC1 3 ) 0: 6.73 (d, J = 4.6 Hz, 4H), 7.387.46 (m, lOH), 7.60 (d, J = 4.5 Hz, 4H), 9.63 (s, 4H); l3C NMR
(50 MHz, CDCI 3) 0: 127.4,129.1,130.7,134.5,136.8,139.4,
143.7,147.7,173.0; LR-MS (EI, 200°C) mle: 496 (100, M+),
430 (18.8), 419 (18.2), 219 (74.8). Exact Mass calcd. for
C30H22N4Ni: 496.11978; found: 496.12071. Anal. ca1cd. for
C30H22N4Ni: C 72.47, H 4.46, N 11.27; found: C 72.33, H
4.70, N 11.3.
X-ray crystallographic analysis of bis[S-phenyl-4,6pyrrinato)Ni(II) (22)
Crystallographic data appear in Table 4. The final unit-cell
parameters were obtained by least squares on the setting
angles for 25 reflections with 29 = 23.3°-33.6°. The intensities
of three standard reflections, measured every 200 reflections
throughout the data collection, decayed linearly by 2.3%. The
data were processed, corrected for Lorentz and polarization
effects, decay, and absorption (empirical, based on azimuthal
scans for three reflections). The structure was solved by direct
methods, the coordinates of the non-hydrogen atoms being
determined from an E-map or from subsequent difference
Fourier syntheses (52). The molecule has exact D2 (crystallographic 222) symmetry. Non-hydrogen atoms were refined
with anisotropic thermal parameters and hydrogen atoms were
fixed in calculated positions with C-H = 0.98 A and BH = 1.2
Bbonded atom' No correction for secondary extinction was necessary. Neutral atom scattering factors for all atoms and anomalous dispersion corrections for the non-hydrogen atoms were
taken from the International Tables for X-Ray Crystallography (53). Hydrogen atom parameters, anisotropic thermal
parameters, torsion angles, intermolecular contacts, scheme of
the unit cell, symmetry operators, and least-squares planes are
included as supplementary material. 2
Acknowledgements
We thank the Natural Sciences and Engineering Council of
Canada for financial support.
Note added in proof:
Since the submission of the manuscript, another report
describing meso-phenyl-4,6-dipyrrin and its BF2 complex has
appeared in the literature: R.W. Wagner and J.S. Lindsey. Pure
Appl. Chern. 68, 1373 (1996).
2
Supplementary material metioned in the text may be purchased
from: The Depository of Unpublished Data, Document Delivery,
CISTI, National Research Council of Canada, Ottawa, Canada,
KIA OS2. Tables of hydrogen atom coordinates and bond lengths
and angles involving hydrogen atoms have also been deposited
with the Cambridge Crystallographic Data Centre and can be
obtained on request from The Director, Cambridge
Crystallographic Data Centre, University Chemical Laboratory,
12 Union Road, Cambridge CB2 lEZ, U.K.
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