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New Porphycene Ligands Octaethyl- and Etioporphycene (OEPc and EtioPc)ЧTetra- and Pentacoordinated Zinc Complexes of OEPc.

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In striking contrast to the octaethyltetraoxaporphyrin dication 1 b, the rneso-alkylated tetraoxaporphyrin dications
9c-e are not stable in dichloromethane or other inert organic solvents (stability in acids, however, is retained). Relatively rapid decomposition occurs (half-lifetimes in the range
0.5-2 h). which starts, according to 'H N M R experiments,
by deprotonation in the side chain. Precedents for such a
deprotonation exist in the case of meso-alkylated diprotonated porphyrins.["I The greater stability of 1 b relative to
9c-e, which makes 1 b a more suitable model compound for
the tetraoxaporphyrin dication.["] can be ascribed to the
different substitution pattern and also to the higher degree of
Expw iniental Pr ocedurr
6. To a aolution of p-toluenesulfonic acid (4.42g, 25 minol) in boiling nitromethaiie (160 mL) was added 3.4-diethyl-2-hydroxymethylfuran
( 5 , 3.85 g.
25 mmol) in nitromethane (20 mL). and the mixture heated under reflux for
15 min. After neutralization with saturated sodium bicarbonate solution the
reaction mixture was extracted three times with 200 m L ether. The combined
organic extracts were washed with water, dried over Na,SO,, and the solvent
was then removed under vacuum. Chromatography of the resulting product on
silica gel (3 x 70 cm column) with toluene,'hexane (1 :1)gnve 6 as a pale yellow
solid. which crystallized from ethanol as colorless rhomhic crystals; m.p. 1.18140 C, yield 545mg (16%).
1 b : Porphyrinogen 6 (268mg. 0.5 mmol) was dissolved in absolute acetonitrile
(40mL) and stirred with cerium(iv) ammonium nitrate (1.5g. 4 mmol) at room
temperature. After 45 min 0.5 mL of a 70% solution of perchloric acid was
added to the reaction mixture. and the solvent removed under vacuum. The
remaining amorphous residue was washed first with a little water m d then with
ether. and crystallized from formic acid containing 1 "lo of a 70% perchloric
acid solution. The dication I b was obtained as red needles, which decompose
above 300 C; yield 242 mg (65%).
Received: April 30. 1993 [26053IE]
German version Angevi.. Cheni. 1993, 105. 1667
[1]a) E.Vogcl. W. Haas. B. Knipp, J. Lex, H. Schmickler, Angeil-. C/iern. 1988,
100. 445: Angiw. CIIPIIIInr. €(I. Engl. 1988.27.406;b) W. Haas. B. Knipp,
M . Sicken. J. Lex. E. Vogel, ;bid. 1988, 100. 448 or 1988,27. 409;c) E.
Vogel. P. Rohrig. M Sicken, B. Knipp, A. Herrmann. M. Pohl, H
Schmickler. J. Lex. ihid. 1989,101, 1683 or 1989.28. 1651
[2]a) R. Bachmann. F. Gerson. G . Gescheidt. E. Vogel. J. Anr. Clwii. So<.
1992.114. 10855; b) E. Vogel. Pitw Alp'. C/?eiii.1993.65.143;c) E.Vogel.
B. Knipp. J. Lex, C. Putz. P. Rohrig. H . Schmickler. unpublished.
[3] M. Sicken. Dissertation. Univei-sitit Koln, 1991.
[4] J. L. Sessler. A. Mozaffari. M. R. Johnson. 0 1 ~ SuirA.
1992,70. 68.and
references therein.
[ 5 ] J. S. Lindsey, H. C. Hsu. I. C. Schreiman, 7rtruhadrori Lair. 1986.27,4969;
R . W. Wagner. D. S. Lawrence. J. S. Lindsey. ihrrl. 1987. 28. 3069. J. S.
Lindsey. I. C. Schreiman, H. C. Hsu. P. C Kearney. A. M. Marguerettaz.
J Org. Cheni. 1987.52, X27.
161 H.Fischer, W. Glenn, Liebig., Ann. Client. 1936,521, 157; S. Krol, J Org.
Chrnr. 1959. -74, 2065: F. R. Longo, E. J. Thorne, A. D. Adler. S. Dym.
J H c w r o c ~ ~ rCliern.
1975. 12. 1305.
[7]The method of preparation described in the literature for 4 (J. Froborg. G.
Magnusson, S. Thoren. J. O q . CIicni. 1975. 40. 122) suffers from the
disadvantage that the product contains small amounts of the structural
isomer 4-methyl-3-propylfuran, which is difficult to separate.
[ 8 ] H. Kiinig. F. Graf. V Weherndorfer. Lichig.\ Ann. Chiwi. 1981,668;M. S
Ho, H. N. C Wong, J. Chrni. Sor. C l i m . Coniniun. 1989. 1238.
[9] B. Franck. Angeii..C/icni. 1982.94, 327;Angew. Cheri?.In/.€d. €/rg/. 1982,
71. 343:G. Bringmann. B. Franck. Lit,hrg.s Ann. C/iern.1982. 1272. L. F.
Tietze, H . Geissler, A n ~ ~ c iChtw.
1993. 1115. 1087;Angeii. C/imr. Irit. Ed.
Eng/. 1993.37. 1038.
[lo] C,,H,,CI,O,,.
crystals from formic acid; triclinic. space group PT. Z = 1 ;
u =7.491(1),h = 9.129(1). i'=14.236(3)
A, 1 =75.25(2). =72.86(2),
7 =78.82(2)
=1.377 gem-'; intensity measureriientsweremadeon
a four-circle Enraf-Nonius CAD-4 diffractometcr (room temperature.
i,, = 0.71069A, H,,, = 27 ); refinement (C. CI, 0 atoms anisotropic, H
atoms ibotropic) taking account of 2126 reflections with b>> 40(&,);
R = 0.072.R, = 0.079.Further details of the crystal structure investigation may he obtained from the Fachinformationszentrum Karlsruhe.
Cesellschaft fur wissenschaftlich-teclinische Inforination mbH, D-76344
Eggenstein-Leopoldshafen (FRG) on quoting the depository number
CSD-57312,the names of the authors. and the journal citation.
[ll]J. W. Lauher. J. A. Ihers, J An?. CIiivn So(,. 1973. 95. 5148.
VCH V~r/ugs~esrllrc/iulr
m h H , 0.69451 Weinheinf.19Y3
[I21 The polarographic and cyclic voltammetric experiments in D M F were
carried out with a dropping mercury electrode (flow rate 0.61 mgs-I) at a
scan rate of 5-100 V s - ' . Purification of D M F and the supporting electrolyte TEAP was as previously described: H. J. Callot. A. Giraudeau. M.
Gross, J Chain. So(.. P d i h i Triiris. 2 1975,1321.
[13]Dichloromethane was both dried and stored over molecular sieves (4 A)
under argon. TBAPF, (FIuka. electrochemical grade) was used without
further purification as supporting electrolyte. The cyclic voltammetric
nieasurements in dichloromethane were carried out at a Pt electrode with
21 scan rate of 10 mVsC' -20 Vs-'. The potentials were measured against
'I saturated calomel electrode as reference; under the prevailing experimenla1 conditions.ferrocene (internal standard) was oxidired in dichloromethane and 0.1 M TBAPF, at 0.4V vs. SCE.
1141 A scan rate of 10 m V s - l to 10 Vs-' was used for peak analysis: For the
first two reductions I,, = / ( i t ')passes through the zero point and is linear:
third redox process AE, increases with increasing scan rate from 80 (at
10 mVs- I ) to 200 mV (at 10 Vs-I). whereas l p= f ( 2 ') is linear and passes through the origin.
[15]Y. Kobuke. K. Hanji. K. Horiguchi. M. Asada. Y. Nakayama. J. Fuiukawa. .I. Ajn. Clic~m.Soc. 1976.98. 7414;A G. S.Hogherg. M. Weber.
r l c l o C h n i . S(~anr/.Ser. B 1983.37. 55.
[16]R. B. Woodward. W. A. Ayer, J. M. Beaton, F. Bickelhaupt, R. Bonnett. P.
Buchschacher. G. L. Closs. H. Dutler. J. Hannah. F. P. Hauck, S. Ito, A.
Langemann. E. LeGoff. W. Leimgruber. W. Lwowski. J. Sauer. Z. Valenta.
H. Volz. fi,rruli(&rni 1990.46. 7599.
[17] An investigation into thestahilityof I bindrydichloromethaneand DMF.
undertaken in the light of the findings for 9c-e. showed that the compound can be kept i n these solvents for a few hours. Thereafter, decomposition becomes noticeable.
[18] P. Walgenbach. Dissertation. Universitit Koln, 1992.
New Porphycene Ligands: Octaethyl- and
Etioporphycene (OEPc and EtioPcFTetra- and
Pentacoordinated Zinc Complexes of OEPc
By Emanuel Vogel,* Peter Koch, Xue-Long Hou,
Johunn Lex, Michael Lausmann, Michael Kisters,
Mohamed Ally Aukauloo, Philippe Richard, and
Roger Guilurd*
The 2,7,12,17-tetrapropylporphycene ligand (TPrPc),
conceived as the counterpart of octaethylporphyrin (OEP) in
the porphycene series, has proved its value in metalloporphycene research on numerous occasions!" Although the
cavity of the N, coordination center in porphycenes is
smaller than that in porphyrins, and the lone electron pairs
on the pyrrolenine nitrogen atoms as well as the N-H bonds
are not strictly oriented towards the center of the molecule,
TPrPc readily forms stable complexes with the common
metal ions Ni", Cu", Co", Co"', Fe"', Mn"', Al"', and Sn'"
(each have small to medium crystal ionic radiirz1).In contrast
to previous experience, TPrPc can even form complexes with
the comparatively large osmium(r1) ion, as recently reported
by the groups of C.-M. Che and C . K. Chang.['jl
In the light of these findings, it seemed remarkable that
TPrPc shows only a relatively low tendency to coordinate to
a zinc ion to form porphycenatozinc. Given the importance
of zinc complexes in porphyrin chemistry, whether as photo[*]Prof. Dr.E. Vogel. Dr.P. Koch. Dr. X.-L. Hou, Dr. 1. Lex,
Dr. M. Lausmann, DipLChem. M. Kisters
lnstitut fur Organische Chemie der Universitit
Greinstrnsse 4. D-50939Koln (FRG)
Prof. Dr.R Guilard. M. A. Aukauloo. Dr. P. Richard
Universite de Bourgogne
Laboratoire de Synthese et d'Electrosynthese Organometallique Associe a u
C. N. R. S. (UA 33)
E'aculte des Sciences "Gabriel"
6. Boulevard Gabriel, F-21 100 Dijon (France)
0570-0833;Y3:1111-1600 S fO.O(J+ 25'0
Angeiv. Cliani. Ini. Ed. €ng/. 1993. 32, No. 11
sensitizer^!^] as model compounds for the study of photosynthesis,[41or as components in enzyme models,[51there is
considerable interest in porphycene ligands that are more
able than TPrPc to bind zinc(ir) and larger ions.
We report here on 2,3,6,7,12,13,16,17-octaethylporphycene and 2,7,12,17-tetraethyl-3,6,13,16-tetramethylporphycene (OEPc 1 and EtioPc 4, respectively), and on the
readily obtained four- and five-coordinate zinc complexes of
(Table I ) .
should-as concluded from structural results with the nickel
complex of TPrPc['"]-Iargely if not completely cancel in the
conversion of such porphycenes to metal complexes.
Table 1 Selected physical and spectroscopic data for the new compounds.
' H N M R : 300 MHz: ',C N M R : 75.5 MHz, CDCI,; MS: EL 70eV: IR: Csl;
I : M.p 181 -183 C (methanolichloroform); 'H NMR (CDCI,): 6 = 9.48 (s.
4 H : H- 4.02 (4, 8 H ; H-3a.6a.l3a,16a), 3.87 (4, 8 H ; H2a.7a.12n.17a). 1.65 (t. 12H: H-2b.7b.l2b,17b), 1.58 (t. 1 2 H ; H3b.6b.lib.16b). 0.65 (br. s. 2H: NH): " C N M R : d =143.27, 142.02, 137.23,
136.72. 109.82. 21.39, 19.94, 18.08(2Catoms): MS:m/;(%): 534(100)[Mt],
267 (14) [M"]; I R : ? = 2964. 2930, 2869, 1518, 1471. 1060, 989. 946, 929,
8 5 6 c m - ' ; UV'VIS:2,,,,,x(t:)= 385(144000). 576(35200).625(19700)~665nm
(30 700).
2 : M.p.263-265 C(hexane/chloroform); ' H NMR(CDCI,):d =9.80(s,4H;
H-,,4.15 (4, 8 H ; H-3a.6a.13a,16a),4.04 (4. 8 H ; H-2d.7a.I2d,17%),
1.84 (t. 12H: H-2b.7b.12b.17b). 1.78 (t. 12H; H-3b.6b.13b.16b); I3C N M R :
H = 146.91. 142.69. 140.78. 137.44. 109.78. 21.06, 20.31, 18.74. 18.69; MS: mi;
596 (100) [ M i ] .298 (19) [ M " ] ; IR. i = 2963. 2930. 2869. 1488, 1314,
F ) = 375 (77500) sh. 393
1301. 1132. 1013. 994. 948cm-'; UVjVIS: i.,,
(161 000). 590 (21 900). 638 nm (94600).
3: M.p. 743 -245 C (pyridineidioxdne); ' H N M R (CDCI,): d = 9.61 (s, 4 H ;
H- 6.49 [m, 1 H; H-;. (pyridine)]. 5.74 [m. 2 H : H-p (pyridine)], 4.06
(4, 8 H ; H-3a.6a.l3a,16a), 3.96 (4, 8 H ; H-Za.7a.12a.17a). 3.59 [m, 2 H ; H-a
(pyridint')]. 1.76 (1. 1 2 H ; H-2b.7b.12b.17b). 1.69 (t. 1 2 H ; H-3b.6b.13b.16b);
" C N M R : 8 =145.87. 144.64, 142.68, 141.60, 136.51, 135.65, 122.27, 109.19.
21.04. 20.29. 18.81. 18.71; MS: m/: (%): 596 (100) [ M t - C,H,N], 298 (24)
[ M z t - C,H,N]: IR: i. = 2963,2930,2868. 1484.1277,1225.1134,1009,995.
9 4 8 c m - ' : UV VIS. i,,, ( i : ) = 371 (81000) sh. 395 (146400). 598 (22400).
644 nm (91 900)
4: M.p. 268-270'C (hexanelchloroform); ' H N M R (CDCI,): 6 = 9.52(s,4H;
H-9.10,19.20).3.85(q,4H;H-2a,7a,12a.17d),3.57(s,12H;H-3a,6a, 13a, 16a).
1.70 (t, 12H: H-Zb,7b.l2b,l7b), 0.86 (br. s, 2 H ; NH); 13C N M R : b =143.88.
142.13. 137.32, 130.46. 109.84, 19.96, 17.23. 16.19; MS: mi; (%): 478 (100)
[ M ' ] . 239 (19) [ M " ] ; IR: G = 2960, 2928, 2867. 1466, 1196, 1083, 1057,982,
( E ) = 382 (144200). 570 (34200). 617
938. 864. 8 0 6 c m - ' ; UViVIS: imdx
(18400). 657 nm (30000).
6a: M.p. 103-105 C (ethanol); ' H N M R (CDCI,): 6 = 9.10, 4.34, 2.75. 1.96,
1.33. 1 08. 6 b : M.p. 97-99-C (ethanol); ' H NMR (CDCI,): 6 = 8.87, 4.30,
2.74, 2.37, 1.33. 1.12. 1.06. 7 a : Subl. > 170°C (hexane/dlchloromethane);
' H NMR (CDCI,): S = 8.68,4.33,2.77, 2.04, 1.34, 1.14. 7b: M.p. 161-163°C
(hexaneldichloromethane); 'H NMR (CDCI,): 6 = 8.78,4.28, 2.76,2.44, 1.33,
1.17. 1.05. 8 a : decomp. >218"C; ' H N M R ([DJDMSO): S =10.96, 2.69,
2.49. 1.05.8 b : decomp. >260"C; ' H N M R ((DJDMSO): 6 =11.94, 11.11.
2.69. 2.30. 1.09, 0.88 9 a : M.p. 76-78°C (sublimation); 'H N M R (CDCI,):
6 =7.68. 6.55. 2.49, 2.02, 1.22. 9 b : M.p. 90-92°C (sublimation); ' H NMR
(CDCI,): 0 =, 1.24. 1.06. 10a: decomp. >245"C (hexme/
dichloromethane); ' H NMR (CDCI,): S = 9.85, 9.65, 2.75, 2.10, 1.23. l o b :
decomp. > 227 C (hexane/dichloromethane); 'H N M R (CDCI,): 6 = 9.64.
9.47, 2.76. 2.50. 1.26. 1.05.
Consideration of models['] which predict that the introduction ofalkyl groups to the 3,6- and 13,16-positions ofthe
porphycene structure would cause an increase in the
N1 ...N4
and N 2 . . - N 3 distances as a result of van der
Wads repulsion, was decisive for the choice of 1 and 4 as
ligands. Thus with these ligands, in addition to a weakening
of the N-H . . . N hydrogen bonds, the pronounced rectangular N,coordination center in the parent compound[*]and
in TPrPc['"I would now adopt an almost square arrangement. An improved tendency toward complex formation
should result in both cases. The assumed deviations from
planarity of the ring framework in 3,6,13,16-alkyl-substituted porphycenes, caused by steric interaction^,[^] which had
originally prevented us from considering 1 as a model ligand,
A n g m . Ch1w1. I n ! . Ed. EngI. 1993, 32. N o I 1
3 M = Zn(C,H,N)
The synthesis of octaethylporphycene 1 was achieved according to the general method of preparation for porphycenes,1'a.71 by subjecting 3,3',4,4-tetraethyl-5,5'-diformyl-2,2'-bipyrrole (lob), made as described in Scheme 1,
to reductive carbonyl coupling with low valent titanium.
After standard workup and recrystallization of the product
from methanol/chloroform ( 5 : I), 1 was obtained as violet
needles (blue, nonfluorescent solutions), which melt without
decomposition at 181-183 "C (yield 15 %, see Experimental
a: R = C H 3
b: R = CzHs
Scheme 1. 5 a / 5 b - 6 a / 6 b : 12/HI03, CClJdiIute acetic acid, reflux. 45 min
(85-90%); 6a/6b+7a/7b: Cu, dimethylformamide (DMF), 110°C. 3 h (4550% for 7a, 35-40% for 7b); 7 a / 7 b + S a / 8 b : NaOH in C,H,OH/H,O, reflux, 2 h (90-95%); 8a/8b-.9a/9b: sublimation at 195"C/0.01 Torr (8590%); 9a/9b+lOa/lOb: POCIJDMF; CH,COONa, H,O (90-95%). For
physical and spectroscopic data, see Table 1.
The 'H NMR spectrum (300 MHz, CDCI,) shows that 1
is an aromatic porphycene. Comparison with the signals of
the corresponding protons in TPrPc reveals that the signal of
H9,10,19,20 occurs at almost the same field (singlet at
6 = 9.48versus 9.62 in TPrPc), whereas that of the N-protons (6 = 0.65 versus 3.04) experiences a marked shift to
higher field (A6 = 2.39), which could be foreseen in view of
the increase in the N 1 . I . N 4and N 2 . . . N 3 distance (weakening of the N-H ... N hydrogen bonds). The IR spectrum
of 1 shows, analogous to that of TPrPc, no stretching vibration in the range 3300-3600 cm-', which indicates that the
hydrogen bonds are weakened only gradually.
1 exists
According to an X-ray crystallographic analy~is,~']
in the crystal as a molecule with C, symmetry (Fig. 1). The
crystal exhibits a statistical distribution of the two N-hydrogen atoms with half occupancy of the four possible positions.
The porphycene skeleton of 1, in contrast to that of TPrPc,
is no longer planar, but experiences a slight twist because of
the van der Waals repulsions of the ethyl groups in the 3,6-
Q V C H Verlugsgesellscliu~mbH, 0-69451 Weinheirn, 1993
and 13,16-positions (maximum distance of the C and N
atoms from the central plane of the porphycene ring structure: k0.27 A). Deviation of the structure from the planar
arrangement is accompanied by angle deformations, in particular by contraction of the bond angles in the NCCN segments ( I 18.5" versus 121.8" in TPrPc). Consequently, in accordance with the prediction, the N, coordination center
adopts an approximately square arrangement. Remarkably,
the N ... N distance of the hydrogen bonds in 1 is now slightly larger than that between the nitrogen atoms within the
bipyrrole units.
system is shown to be planar (maximum distance of the
heavy atoms from the central plane: +0.05A). From the
structural parameters of 2 it follows that the metalation of I
with zinc profits if the bond angles in the NCCN segrnentin the interests of a better alignment of the nitrogen electron
pairs and bonds towards the center of the molecule-undergo further contraction (relative to TPrPc and 1). The formation of a rectangular N, center must be tolerated here. The
average Zn-N distance in 2 is 2.007 A and is thus somewhat
shorter than that found in tetracoordinated zinc porphyrinates (Zn-N: 2.024-2.06 8 , ) . [ l6 ] As the metalation of 1 is
associated with a considerable reduction in the nonbonding
substituent interactions, the unusual situation arises that a
nonplanar porphyrinoid ligand experiences a flattening effect on the incorporation of metal
Fig. 1 Structure of 1 in the crystal (top- viewed from above; bottom: side
view). Vihrationai ellipsoids represent 40% probability. Also shown are selected bond lengths [A] and angles [ ] (standard deviations about 0.002 A or
0.2 respectively); inner hydrogen atoms in 1 disordered. The ethyl groups are
not shown in the side view. N1 ... N2 2.799, N l ... N1' 2.732 A.
The expectation that 1 is more suitable than TPrPc as a
complexing agent for the zinc(1r) ion is borne out by experiment. The new ligand can be converted quantitatively into
complex 2 within 15 niin by treatment with methanolic zinc
acetate solution in refluxing chloroform, whereas in the case
of TPrPc even extensive heating in D M F at 150 "C does not
lead to complete reaction.'"l Simple workup gave 2 in the
form of violet needles (from hexane/chloroform, m.p. 263265 "C; yield 87 O h ) . [ '
Compared to that of 1, the 'H N M R spectrum (300 MHz,
CDCI,) of 2 exhibits a slight downfield shift for the signal
of H 9,10,19, 20 (A6 = 0.32) as well as for the signals of the
ethyl protons. The main reason for this may be ascribed to
the fact that metalation of 1 enhances the ring current effect
due to the increase in symmetry of the molecular framework.['21Apart from that, an electron transfer from the porphycene TI system to the metal ion, operative in the same
direction, is likely to be involved.1131The UVjVIS spectrum
shows a Soret band that is almost congruent with that of the
free ligand in addition to two absorption bands in the visible
range. The band positions are solvent dependent, which is
linked to the ability of the zinc ion to enter into axial pentac ~ o r d i n a t i o n ; [ ' ~donor
solvents such as pyridine cause
bathochromic shifts.
According to an X-ray structural analysis," 1' complex 2 is
centrosymmetric (Fig. 2); moreover, the porphycene ring
d'l VCH V F r l u ~ . ~ ~ e s e l l . ~n?hH,
~ / i U f0.69451
Weinhrmi, I993
Fig. 2. Structure of the zinc complexes 2 and 3 in the crystal (top: 2 viewed
from above; center: side view of 2, bottom: side view of 3). Vibrational
ellipsoids represent 40% probability. Selected bond lengths [A] and angles [ ]
are also given (standard deviations ca. 0.003 A o r 0.2 -,respectively). The ethyl
3.066, N1 . - . N 2 2.588 A
groups are not shown in the side views. N1 ..-N2'
in 2.
By analogy with the corresponding zinc porphyrinates, 2
also shows a tendency to increase the coordination number
of zinc by adding an axial donor Iigand. A typical example
is the formation of pyridine(octaethylporphycenato)zinc(rr)
(3) by crystallization of 2 from pyridine/dioxane (1 :1). On
the strength of an X-ray crystal structure analysis['*] (Fig. 2
bottom), the new complex shows great similarity with 2 in
terms of bond lengths and angles, but the zinc atom resides
0.39 8, above the N, plane as a result of the axial ligand
(corresponding distance in quinquidentate zinc porphyrin-
$ 10.00+ .2510
Angew. Chem. I n t . Ed EngI. 1993. 32. N o . 11
ates: 0.22-0.39
The other distances involving the zinc
atom lie within normal range.
The idea of increasing the complex-forming ability of porphycenes by alkyl substitution in the 3,6,13,16-positions was
followed not only in Cologne but also in Dijon. Considering
the fact that many porphyrins possess the alkyl substitution
pattern of etioporphyrin-II,1201the French coauthors chose
2,7,12.17-tetraethy1-3,6.13.16-tetramethylporphycene(etioporphycene) (4) rather than 1 as model compound. The synthesis of 4. using the same route as that employed for 1
(Scheme 1). is somewhat more advantageous because the
Ullmann coupling of the 3,4-dialkyi-2-ethoxycarbonyl-5iodopyrrole to afford the bipyrrole derivative gives a better
yield, on evident steric grounds. Analogous to 1, a solution
of 4 is intense blue and nonfluorescent. Compound 4 is obtained as violet crystals [needles from hexane/chloroform
( l : l ) , m.p. 268-270°C, yield l5%].
The spectra of 4 show only slight changes relative to those
of 1, so it could not be determined whether the exchange of
the 3.6.1 3,16-ethyl groups for methyl groups had a noticeable effect on the conformation of the ring skeleton. This is,
in fact. the case. According to an X-ray crystal structure
analysis,[”” the planarity of the ring framework in TPrPc is
almost restored in 4 (maximum distance of the heavy atoms
from the central plane of the porphycene macrocycle :
+0.15 A,Fig. 3). As far as the other geometric features are
concerned there is no major difference between 4 and 1.
Fig. 3. Structure of 4 in the crystal (top: viewed from above; bottom; side
view) Vibrational ellipsoids represent 4 0 % probability. Selected bond lengths
[A] and angles [ ] are also shown (standard deviations about 0.002 A or 0.1 <.
respectively); inner hydrogen atoms in 4 disordered. The ethyl and methyl
groups are not shown in the side view N1 .. ”2’ 2.791, N1 . . . N 2 2.737
The two new alkyl-substituted porphycenes 1 and 4 complement TPrPc (representing the porphycene parent compound) as ligands that, on the grounds of “optimized coordinating ability”, should encourage research into the
metalloporphycenes-especially as they invite comparison
with the corresponding metalloporphyrins.
Experiniental Procedure
lOa/lOb: The bipyrrole dialdehydes 10a[22]/10b were obtained a s shown in
Scheme 1.
1/4: Activated zinc (13.1 g. 200 mmol) and CuCl (2.0 g, 20 mmol) were placed
in tetrahydrofuran (800 mL). TiCI, (11.O mL. 100 mmol) added dropwise. and
the resulting mixture heated at reflux for 3 h. Within 4 min (for 1) o r 15 min (for
4) a solution of 10b (1.Sg. 5 mmol) o r IOa (1.4g. Smmol) in T H F (200mL)
was added dropwise. and the reaction mixture stirred at reflux for 3 min. FinalAfigc,ii.. Chrnf In/. Ed Engi. 1993. 32. N o . I 1
ly. the resulting product was hydrolyzed with 200 mL of 10% K,CO, solution
and worked up.
1: After chromatography on neutral aluminum oxide (activity 111. column
3 x 30 cm) with hexane/dichloromethane ( I : 1). 1 was obtained as thc first fraction. Crystallizatioii from methanol/chloroform (5: 1) gave octaethylporphycene (1) a s violet needles. m.p. 181 -183 C: yield 200 mg (15%).
4 : After chromatography on silica gel (column 4 x 15cm) with
dichloromethane. 4 was obtained as the first fraction. Crystallization from
hexanelchloroform (1 :1) gave etioporphycene (4) as violet needles. m.p. 268
270’C; yield 180mg(15%).
2: Compound I (106 mg. 0.2 mmol) in chloroform (60 mL) was heated at reflux
for 15 min with 2 mL of a saturated solution ofzinc acetate in methanol. The
solvent was then removed. the resulting zinc complex taken up in chloroform.
and the solution filtered. Crystallization from hexanelchloroform (4: 1 ) gave 2
as violet needles, m.p. 263-265°C; yield 104 mg (88%).
Received : April 30. 1993 [Z 6054 I E]
German version: Angeii,. C/7rf77.1993. 105. 1670
[I] a) E. Vogel, M. Balci, K. Pramod, P. Koch. J. Lex. 0. Ermer. Aqvii..
Chem. 1987, 99. 909; Angew. Chem. In[. Ed. Engi. 1987, 26. 928: b) M. W.
Renner, A. Forman, W. Wu, C. K. Chang, J. Fajer. J. An?. Chrm. Soc. 1989,
l I t , 8618. c) M. Toporowicz. H. O h . H. Levanon. E. Vogel, M. Kocher.
K. Pramod. R. W. Fessenden, Photoihwn. Phorohioi. 1989, 50, 37; d) E.
Vogel. Purr Appl. Chrm. 1990, 62. 557; e) L. R. Furenlid, M W. Renner.
K. M. Smith, J. Fajer. J. Am. Chem. Soc. 1990. 112. 1634; f ) J.
Schlupmann, M. Huber, M. Toporowicz, M . Plato, M. Kocher. E. Vogel,
H. Levanon, K. Mobius. ;bid. 1990, 112. 6463: g) J. P. Gisselbrecht. M.
Gross. M. Kocher. M. Lausmann, E. Vogel. ihid. 1990,112.8618;h) W. A.
Oertling, W. Wu. J. J. Lopez-Garriga, Y Kim. C. K Chang, ihrd 1991. 113,
127: 1) J. Waluk. M. Miiller. P. Swiderek. M. Kocher. E. Vogel, G . H o h neicher, J. Michl, ihid. 1991. 113, 551 1 ; j ) Z.-Y. Li. J.-S. Huang. C -M. Che.
C. K . Chang, Inorg. Chem. 1992, 31. 2670.
[2] CRC Hondh. Chrm. PI7j.s.. 70th ed.. 1989-1990. F-187.
131 K. Kalyanasundaram, M. Grdtzel. E. Pelizzetti, Coord. Chem. Rev. 1986,
69. 57; W. Schuhmann, H.-P. Josel, H. Parlar, Angeii. Chrm. 1987.99.264;
Angrw. Chem Inr. Ed. Engl. 1987. 26, 241.
[4] H. A. Staab. J. Weiser, E. Baumann. Chefn. Ber. 1992, 125. 2275; H. A.
Staab, J. Weiser. M. Futscher, G Volt. A. Ruckemann. C . Anders. ihid.
1992, f25.2285; J. L. Sessler, M. R. Johnson. S. E. Creager, J. C. Fettinger.
1. A. Ibers, J. Am. Cheni Sor. 1990, 112.9310.
A. Hamilton, J.-M. Lehn. J. L. Sessler, J. An7. Chrm. Sor. 1986. 108. 5158.
For photophysical investigations on 1 and 2 see: A. Berman. A Michaeli.
1. Feitelson. M. K. Bowman, J. R. Norris. H. Levanon. E. Vogel. P. Koch,
I Phys. Chem. 1992. 96. 3041
E. Vogel, M . Kocher, J. Lex, 0. Ermer, in.. J. Chem. 1989, 29. 257.
E. Vogel, M. Kocher, H. Schmickler. J. Lex, Angeic. Chem. 1986. 98.262;
Angew. Chrm. Int. Ed. Engl. 1986, 25. 257.
1: C,,H,,N,,
crystals from hexane/dichloromethane (1 :1): orthorhombic.
space group Fdd2, Z = 8; u = 14.046(3), h = 28.852(6). c = 15.043(4) A.
pCAlcd= 1.165
intensity measurements were made on a four-circle
Enraf-Nonius CAD4 diffractometer (room temperature, iM0
= 0.71069 A.
Om,, = 27’); refinement (C and N atoms anisotropic. H atoms isotropic)
taking account of 1582 reflections with I>2u(I), R = 0.031, R , = 0.039:
For the isolation of dimethylformamide(2,7,12.17-tetrapropylporphycenato)zinc(ii) see: M . Lausmann, Dissertation, Universirit Koln, 1993.
Stability class IV after Buchler; J. W. Buchler. Porphvrinv 1978-1979. I .
H. Scheer, J. J. Katz, Porphyrins Me~~lloporphjrms
1975. p. 399.
D. R. Benson, R. Valentekovich, C. B. Knobler, F. Diederich, 7erruhrdron
1991, 47, 2401.
C . H. Kirksey, P. Hambright, C. B. Storm, Inorg. Cl7em. 1969, A’. 2141.
2: C,,H,,N,Zn, crysials from benzene; triclinic, space group P i . Z = 1 ;
u = 5.202(1), h =12.265(3), c = 12.43613) A. LY =73.47(2). /I = 89.23(2),
7 = 86.55(2)’, plrlid = 1.308 gem-’; conditions of measurement as for 1:
refinement (C, N and Zn atoms anisotroplc. H atoms isotropic) taking
account of 3338 reflections with I > 2 u ( / ) . R = 0.050. R , = 0.060; [24].
For typical examples see: W. R. Scheidt, J. U. Mondal. C. W Eigenbrot. A.
Adler, L. J. Radonovich. J. L. Hoard, Inorg. Chem. 1986,25,795;A. Chiaroni, C. Riche, C. Bied-Charreton, J. C. Dubois. A r m Crysruilogr. Sect
C 1988,44,429; 1131.
Compare on the other hand the saddlelike deformation of porphyrin ligands and hydroporphyrinoid ligands in the formation of complexes with
Ni(i1) ions: 3. L. Hoard, Ann. N . Y. Acad. Sci. 1973, 206, 18; C. Kratky, R.
Waditschatka. C. Angst. J. E. Johansen, J. C. Plaquevent. J. Schreiber, A.
Eschenmoser, Helv. Chim. Acto 1985. 68, 1312
3: C,,H,,N,Zn. crystals from pyridine/dioxan (1 : 1); triclinic. space group
PT. Z = 2; u = 8.994(2), b = 14.079(3), c = 15.324(3) a =78.36(2). /I =
72.01(2), = 80.70(2)‘, p,,,,, = 1.258 gem-’; conditions of measurement
as for 1; refinement (C, N, and Zn atoms anisotropic, H atoms isotropic)
VCH Verlugsgr.sell.schafinthH, 0-69451 Wrinhrim, 1993
O57O-O833/93/f Ill-16O3 3 lO.OO+ ,2510
taking account of 5969 reflections with 1>20(1). R = 0.035. R, = 0.040;
For typical examples see: K. M. Barkigia, M. D. Berber, J. Fajer. C. J.
Medforth. M. W. Renner, K. M. Smith, 1 Am. Chem. Sac. 1990. f 12,8851 ;
K . Hatano. K. Kawasaki, S. Munakata. Y. Iitaka, BUN. Chem. Soc. Jpn.
1981. 60. 1985; D. L. Cullen, E. F. Meyer, Jr., Actu Crystallogr. Serl. B
1916, 32, 2259.
K. M. Smith, Porpfijnns Meral1oporpli)rins 1975, 3.
4: C,,H,,N,. crystals from hexane/chloroform (1 : 1); monoclinic. space
group P2,/n. Z = 2; (1 = 6.884(2), h =14.183(3), c =13.684(3) A. /3 =
97.05(2)". pEIlcd= 1.199 g ~ m - conditions
~ ;
of measurement as for I : refinement (C and N atoms anisotropic. H atoms isotropic) taking account
of 2706 reflections with I > 2 0 ( 1 ) . R = 0.048, R, = 0.053; [24].
J. L. Sessler. M. J. Cyr. A. K. Burrell, Syn/e;n[elt1991, 127.
D. H. R. Barton. S. 2. Zard, 1 Chrm. Soc. Chon. Commun. 1985, 1098.
Further details of the crystal structure investigations may be obtained
from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH. D-76344 Eggenstein-Leopoldshafen (FRG) on quoting the depository number CSD-57 31 1, the names of
the authors, and the journal citation.
The Nature of the 7-Norbornyl Cation and its
Rearrangement into the 2-Norbornyl Cation**
By Stefan Sieber. P a d von RaguP Schleyer,* Hrvoj VanEik,
Milan MesiC, and Dionis E. Sunko
The structure of the 7-norbornyl cation has always been
an enigma.", 'I The exceptionally slow soivolysis rates of
7-norbornyl derivatives first suggested the absence of
anchimeric assistance and the intervention of a classical
cationic intermediate. However, a symmetrical C,, structure
(1, see Fig. 1) was later ruled out by the demonstration that
the substitution product retains its stereochemistry.["-el
While this is also consistent with a C, formulation (2), more
recent interpretations favor a nonclassical, bridged structure
(3) (Fig. I).['d] This is consistent with the formation of small,
but significant amounts of 2-bicyclo[3.2.0]heptyl rearrangement products, as well as extensive evidence from, for example, D and CH, labeling experiments.
Before the present study, attempts at direct observation of
the 7-norbornyl cation in superacid media all failed. In one
of the earliest papers on studies in superacids, Schleyer, OIah
et al. reported that ionization of 7-norbornyl derivatives led
only to the 2-norbornyl cation."a1 Subsequent attempts in
our laboratories led to similar results.
Earlier computational studies were not definitive.12]These
were carried out at lower levels of theory, known now to give
inadequate descriptions of such electron deficient species.[31
As part of a comprehensive examination of the C,H:, potential energy surface, we now report computations[4. on the
C,, (1) and C, (2) structures of the 7-norbornyl cation, the
bridged ion 3, as well as other stationary points related to the
conversion into the 2-norbornyl cation (4)[63 71 at the
MP4(sdq,fc)/6-31G*//MP2(fu11)/6-31G*+ ZPE(MP2(full)/
[*] Prof. Dr. P. von R. Schleyer, S. Sieber
Institut fur Organische Chemie der Universitit Erlangen-Niirnberg
Henkestrasse 42, D-91054 Erlangen (FRG)
Telefax: Int. code +(9131) 85-91 32
VCH Verlog.~~e.~ellsclta~l
mbH, 0-69481 Weinheim, 1993
Scheme 1. The "same-side bridge-flipping" process
This work was supported in Erlangen by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie, and in Zagreb by the
Ministry of Science of Croatia and the National Science Foundation
(USA, Grant No. 841).
6-31G*) level.[*] The vibrational frequencies, computed at
the correlated level given, assist in the unambiguous identification of the C,HT, ion that we have now been able to
observe experimentally.
Early ab initio calculations favored 1, but this was due to
the use of inadequate basis sets (STO-3G, 3-21G, 4-21G).
Adequate searches of the carbocation potential energy surface requirel3I the use at least of polarized double-< (DZ or
split valence) basis sets with electron correlation. Thus,
whereas at the HF/6-31G* level, 2 is favored over 1 by
0.4 kcalmol-' and over 3 by 0.7 kcalmol-I, the order
changes with correlation. The (central) bridge flipping barri)
to 2.3 kcal mol- * at our final theoer (2+ 1 ~ 2 ' increases
retical level. The relative stability of 2 and 3 reverses; the
Dr. H. VanEik. Dip].-Chem. M. MesiC, Prof. Dr. D. E. Sunko
Faculty of Natural Sciencies and Mathematics
Laboratory of Organic Chemistry, University of Zagreb
Strossmayerov trg 14. QKR-41000 Zagreb (Croatia)
Fig. 1. MPZ(fu11)/6-31G* optimized structures of the norbornyl cation isomers; see also [14].
[*I MP4 = Moller-Plesset fourth-order perturbation theory; sdq: singly, doubly. and quadruply excited configurations are taken into account; fc =
frozen core (that is, electrons of the inner orbitals are not considered in the
generation of the configurations); full: all configurations are taken into
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