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Biomimetic Synthesis of an Inverted Porphyrinoid with Peripheral N Atoms.

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singlet grows in intensity relative to the other singlet until,
finally, it is the only signal observed. The implications of
these cryoscopic and spectroscopic results are that there are
(at least) two species present: presumably the hexamer (especially at lower concentrations; [b ('Li) z -1.61 and an aggregate with n > 6 [6 ('Li) z -0.51.
Experimental Procedure
1: nBuLi (6.25 ml o f a 1.60 M solution in hexane, L
O mmol) was added under N,
to a chilled solution of hexamethyleneimine H , C ( C m N H (0.99 g, 10 mmol)
in hexane/toluene (6 m1/4 ml). At room temperature, a white solid precipitated;
this dissolved on warming to give a pale yellow solution. Cooling gave large
colorless cube-shaped crystals which were filtered and characterized as 1,
[0.90g.86%,m.p. 112-115"C;foundC68.4%,H11.3%,Li6.8%,N13.4%.
CalculatedforC,H,,LiN =C68.6%,H11.4%,Li6.7%,N13.3%.'HNMR
(C,D,, 80 MHz, 20°C) 6 = 1.71 (br s, 8H), 3.02 (br m, 4H)]. Single crystals
suitable for X-ray crystallography were sealed under NZin Lindemann capillary
tubes prior to data collection.
Received: April 12, 1989 [Z 3282 IE]
German version: Angew. Chem. 1Of (1989) 1279
[I] a) For uses in the syntheses of metal amides, see M. F, Lappert, P. P.
Power, A. R. Sanger, R. C. Srivastava: Metal and Metalloid Amides, Wiley, Chichester 1980; b) For uses in organic syntheses, see M. Fieser:
Fieser 'sReagentsfor Organic Synthesis, Vol. 12, Wiley-Interscience, New
York 1986 and earlier volumes.
[2] The advantages ofisolating lithium amides as crystalline materials prior to
subsequent reaction were first pointed out in: M. F. Lappert, M. J. Slade,
A. Singh, J. L. Atwood, R. D. Rogers, R. Shakir, J. Am. Chem. SOC.105
(1983) 302; see also Ref. [9].
[3] For a review of organolithium X-ray structures up to 1984 (and including
N-Li species) see W. N. Setzer, P. von R. Schleyer, Adv. Organornet. Chem.
24 (1985) 353; for related reviews covering work published 1985- 1987, see
R. Snaith, Prog. Chem. Annu. Rep. A82 (1986) 3; ibid. A 8 3 (1987) 3; &id.
A84 (1988) 3.
[4] a) D. Reed, D. Barr, R. E. Mulvey, R. Snaith, J. Chem. SOC.Dalton Trans.
1986, 557; b) A. S. Galinano-Roth, E. M. Michaelides, D. 8 . Collum. J
Am. Chem. SOC.110 (1988) 2658; c) J. S. DePue, D. B. Collum, ibid. 110
(1988) 5518, and references therein.
[5] a) D. R. Armstrong, D. Barr, W. Clegg, R. E. Mulvey, D. Reed, R. Snaith,
K. Wade, J. Chem. SOC.Chem. Commun. 1986,869; b) D. Barr, W Clegg,
R. E. Mulvey, R. Snaith, D. S. Wright, ibid. 1987,716;see also Ref. [9] and
references cited therein.
161 Uncomplexed lithium amides (RRNLi), with (NLi). ring structures are a)
R = R = Me& n = 2 (gas phase, by electron diffraction), T. Fjeldberg,
P. B. Hitchcock, M. F. Lappert, A. J. Thorne, J. Chem. SOC.Chem. Commun. 1984, 822; b) R = R = Me& n = 3 (crystal structure), R. D.
Rogers. J. L. Atwood, R. Griining, J Organomet. Chem. 157 (1978) 229; c)
R = R = PhCH,, n = 3 (crystal structure), D. R. Armstrong, R. E. MulJ. Chem. Soc.
vey. G. T. Walker, D. Barr, R. Snaith, W.Clegg&Reed,
Dalton Trans. 1988,617; d) R R N = Me,k(CH,),CMe,N, n = 4 (crystal
structure), Ref. [2].
[7] The so-called "ring-stacking principle" is applicable to organolithium ring
compounds whose R , R groups are relatively coplanar with the (ELI),
rings (n = 2 or 3) e.g., in imidolithium compounds ( R R C = NLi),,
E = N. in alkoxy- and enolatolithium compounds (ROLi),, and
[R(H,C=)COLi], respectively, E = 0, and in alkynyllithiums, ( R C r
CLi)., E = C. Such relatively flat systems can thus associate vertically,
giving clusters (e.g.. two dimeric rings, to give a pseudocubane tetramer;
two trimeric ones to give a hexamer). See a) D. Barr, W. Clegg, R. E.
Mulvey, R. Snaith, K. Wade, J. Chem. SOC.Chem. Commun. 1986,295; b)
D. R. Armstrong, D. Barr, R. Snaith, W. Clegg, R. E. Mulvey, K. Wade,
D. Reed. J. Chem. Soc., Dalton Trans. 1987, 1071; c) D. Barr. R. Snaith,
W. Clegg, R. E. Mulvey, K. Wade, J. Chem. Soc. Dalton Trans. 1987,2141,
and references cited therein.
181 The term "fences" was first used in H. Kato, K. Hirao, K. Akagi, Inorg.
Chem. 20 (1981) 3659, to describe lateral associations of (LiH), rings
within a theoretical MO study of structural options for lithium hydride.
[91 D. R. Armstrong, D. Barr, W. Clegg, S. M. Hodgson, R. E. Mulvey, D.
Reed, R. Snaith, D. S. Wright, J. Am. Chem. Soc., in press. See also
Ref. 5 a].
[lo] 1: C,,H,,Li,N,,
M, = 630.7, triclinic, space group Pi, a = 9.966(4),
b = 10.539(4), c = 11.692(5)A, a = 116.01(2), p = 96.76(2), y =
108.90(2)". V = 914.2 A3, Z = 1, D , = 1.053 g cm-', F(OO0) = 348, Cu,.
radiation, I = 1.54184 A, p = 0.41 mm- '. The structure was determined
by direct methods and refined from 1522 unique observed reflections measured at room temperature with a Stoe-Siemens diffractometer (20,..
110). with anisotropic thermal parameters, and with isotropic H atoms in
Angeu. C'hem. Int. Ed. Engl. 28 (1989) Nr. 9
0 VCH
calculated positions; R = 0.098, R, = 0.098, S = 1.06 for 218 parameters.
Further details of the crystal structure investigation can be obtained from
the Director of the Cambridge Crystallographic Data Centre, University
Chemical Laboratory, Lensfield Road, Cambridge, CB2 1EW (UK). Any
request should be accompanied by the full literature citation for this communication.
[ l l ] These calculations (K. Raghavachari, A.-M. Sapse, D. C. Jain, inorg.
Chem. 26 (1987) 2585 showed, for (LiNH,), as two stacked trimeric rings,
two "short" Li-N bonds (1.99 A) and one ''long'' bond (2.06 A) for each
triply-bridging N atom. The fact that three sets of bond lengths are found
for experimental imidolithium hexamers'I21was attributed to crystal packing effects. This attribution, and the validity of comparing theoretical
amidolithium structures with experimental imidolithium ones, was challenged (W. Clegg, R. Snaith, K. Wade, ibid. 27 (1988) 38611, drawing a
response from the original authors (K. Raghavachari, A,-M. Sapse, D. C.
Jain. ibid. 27 (1988) 3862).
1121 The hexameric imidolithiums, (RRC=NLi),, R = R = fBuMe,N,
R = Ph, R = tBuMe,N, display average lengths of 1.98,2.01, and 2.05 8,
for their N-Li bonds. See Refs. [7a] and [7b].
[13] Cryoscopy was carried out on benzene solution of 1. Relative molecular
mass values found (molarity of solution, M , expressed in terms of the
empirical formula of 1, n = 1). and hence association states (n) were:
564 f 23 n ( 0 . 0 5 5 ~ )= 5.37 f 0.22; 895 f 33 n(0.113 M) = 8.52 f 0.32;
1061 f 53 n(0.139 M ) = 10.11 f 0.51.
[14] Variable-temperature (25°C. -90 "C) and variable-concentration (0.19 M,
0.25 M , 0.61 M solutions) 'Li NMR spectra (139.96 MHz) were recorded
for solutions of 1 in C,D,CD,. At 25 "C each solution afforded a singlet:
these were sharp (6 = -1.13, -1.24) in the relatively dilute solutions.
much broader (6 = -0.80) in the concentrated one. At -90 "C, the 0.19 M
and 0.25 M solutions each displayed two signals, though of differing relative integrals [b = -0.50, -1.63 (ca. 1 : l ) and -0.49, -1.61 (ca. 2:1),
respectively]; the 0.61 M solution spectrum consisted of just one. very
broad resonance, at 6 = -0.48.
Biornirnetic Synthesis of an Inverted Porphyrinoid
with Peripheral N Atoms**
By Karl-Heinz Schumacher and Burchard Franck *
Dedicated to Dr. Giinther OhloJJ on the occasion of his 65th
birthday
A key step in the biosynthesis of all porphyrin natural
products is the cyclocondensation of monopyrrole porphobilinogen 1 to give a colorless, nonconjugated porphyrinogen 2.'**31 We have mimicked this biosynthetic reaction to
2
1
condense derivatives of 1 in vitro under acid catalysis to give
novel, structurally modified p ~ r p h y r i n o g e n s . ~ ~These
.~'
biomimetictS1porphyrin syntheses excel other procedures in
the low number of steps and the good overall yields.
Of particular interest is the question whether it is possible
to prepare an inverted porphyrinogen 4 a by biomimetic condensation of a porphobilinogen isomer such as 3. Here we
[*] Prof. Dr. B. Franck, Dr. K.-H. Schumacher
['I
["I
['I
Organisch-chemisches Institut der Universitat
Orleansring 23, D-4400 Miinster (FRG)
Present address:
BASF AG, D-6700 Ludwigshafen
Novel Porphyrinoids, Part 7. This work was supported by the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen Industrie. Part 6:
[11.
Verlagsgesellschaft mbH. 0-6940 Weinheim, 1989
0570-0833/89/0909-1243$02.S0/0
1243
Me
Ho2)
B?
Me
Bf'
Me
C,O,H
d
CHO
Et0,C
Me
Me
7, R
68, R
6
3
= C0,Et
= CO,H
- 5 -
e
Me
9
4a,n=l
4b,n=2
report the first biomimetic synthesis of a compound with the
ring system of 4 b.
Inverted porphyrinogens, the nitrogen atoms of which are
on the periphery of the molecule instead of in the interior,
give rise to several questions which are important for understanding porphyrin systems:
Can inverted porphyrinogens be dehydrogenated to give
the corresponding, possibly aromatic porphyrins?
Are cyclic tetrapyrroles preferentially formed in the
biomimetic synthesis of inverted porphyrinogens as they
are for natural porphyrinogens?
Does the comparison of inverted porphyrinogens with
normal porphyrinogens offer evidence of transannular
interactions between the N atoms of the latter?
The porphobilinogen isomer 3 and the structurally similar
monopyrroles, which were initially considered as starting
pyrroles for the biomimetic synthesis of an inverted porphyrinogen, proved unsuitable because of their tendency to
undergo polymerization. Therefore, the better protected Nbenzylpyrrole 5 was chosen for subsequent investigations.
<'"
.
Me
&OH
5
Me
Although this pyrrole was expected to undergo some cyclocondensation to give products in which the C-methyl groups
are directed toward the center of the ring, earlier experience[4a1indicated that this reaction would not interfere with
the cyclization.
The synthesis of monopyrrole 5 (Scheme 1) started from
the knownL6]pyrrole aldehyde 6, accessible in two steps from
acetylacetone and diethylhydroxyiminomalonate by Kleinspehn condensation^'] and formylation. N-Benzylation to
give 7,ester saponification to give 8, and thermal decarboxylation afforded aldehyde 9 (m.p. 64 "C), which crystallizes as
needles and serves as a stable synthetic precursor.
To perform the biomimetic condensation, 9 was reduced
to the reactive hydroxymethylpyrrole 5 by treatment with
NaBH,. Compound 5 was then treated in situ at -50°C
under oxygen-free conditions with p-toluenesulfonic acid/
glacial acetic acid. Subsequent warming to 20 "C afforded a
71 % yield of an oxygen-sensitive solid, which was pure according to thin layer chromatography. Elemental analysis
and mass spectrometry ( M @ ,m/z 985,40%) gave the empirical formula C,,H,,N, for the condensation product; structure 10 was derived from the fragment peaks in the EI mass
spectrum and from the 'H NMR data."']
Compound 10 is the first inverted porphyrinoid. It is especially interesting that, in this biomimetic condensation, the
1 244
Q VCH VerlqygeseNschu/r mhH. 0.6940 Weinheim, 1989
E
Bzl
Bzl
10
11
Scheme 1. Synthesis of the inverted porphyrinoid 10 via N-henzyl-3-formyl2,4-dimethylpyrrole 9. Reaction conditions: a) BzlBr, NaH/DMF, 20 "C,
30min; 96% 7 (m.p. 48'C). b) 25% NaOH, 100°C. 2 h; 86% 8 (m.p. 157158°C). c) Kugelrohr distillation 180"C/0.2 mbar; 8 0 % 9 (m.p. 64°C). d)
NaBH,/MeOH. 20 "C, 15 min. e) p-TosOHIAcOH, -80 "C, 1 h; 71 % 10 [lo].
inversion of the pyrrole rings leads with high selectivity to a
cyclic pentapyrrole instead of a tetrapyrrole. This has never
been observed before in similar condensations with porphobilinogen 1.IZl We propose the name inverto-pentaphyrinogen
for the basic framework of
Further noteworthy are the chemical reactivity and oxidation sensitivity of 10. Whereas non-inverted porphyrinogens,
like our new vinylogously enlarged porphyrinogens,r'.4d-f1
are smoothly dehydrogenated by bromine and other oxidation agents to give stable, aromatic porphyrins, we failed,
despite extensive attempts, to transform 10 under these conditions into a conjugated, possibly aromatic inverto-pentaphyrin such as 11 ; instead, only decomposition products
were obtained. A possible explanation might be that, although 11, the hypothetical dehydrogenation product of 10,
can form an aromatic 22 n-electron perimeter, this results in
a destabilizing accumulation of charge."
Received: April 12, 1989 [Z 3283 IE]
German version: Angew Chem. 10f (1989) 1292
CAS Registry numbers:
5, 122069-36-7; 6,2199-64-6; 7, 122069-33-4; 8, 122069-34-8; 9, 122069-35-6;
10, 122069-37-8.
[l] G. Kniihel, B. Franck, Angew. Chem. 100 (1988) 1203-1204; Angew.
Chem. Inr. Ed. Engt. 27 (1988) 1170-1172.
[2] L. Bogorad in D. Dolphin (Ed.): The Porphyrins, Vo/.6, Academic Press,
New York 1979, pp. 128-178.
[3] B. Franck, Angew. Chem. 94(1982) 327-337; Angew. Chem. In!. Ed. Engf.
21 (1982) 343 -353.
[4] a) B. Franck, C. Wegner, Angew. Chem. 87(1978)419-420; Angew. Chem.
Int. Ed. Engl. 14 (1975) 424; b) B. Franck, G. Bringmann, C. Wegner. U.
Spiegel, Liebigs Ann. Chem. 1980,263-274; c ) G. Bringmann, B. Franck,
ihid. 1982, 1272-1279; d) M. Gosmann, B. Franck, Angew. Chem. 98
(1986) 1107-1108; Angew. Chem. Inf. Ed. Engf. 25 (1986) 1100-1101; e)
B. Franck, M . Gosmann, G. Kniibel, DOS 3 635 820 (1988), BASF "Vinyloge Porphyrine"; Chem. Ahsfr. 109 (1988) 9 4 7 4 8 ~0
; R. Timmermann, R.
Mattes, B. Franck, Angew. Chem. 9911987) 74-77; Angew. Chrm. Int. Ed.
26 (1987) 64-68; g) B. Franck, G. Fulling, M. Gosmann. G. Kniihel, H.
Mertes, D. Schroder, S P I E Proc. Ser. 5 . W .997 (Symp. Adv. Photochemotherapy, Boston 1988), p. 107-112.
[S] B. Franck, Angew. Chem. 91 (1979) 483-464; Angew. Chem. I n r . Ed. Engl.
lil(1979) 429-439.
0570-0833189/0909-1244B 02.5010
Angen. Chem. Int. Ed. Engl. 28 (1989) N r . 9
[6] E. J.-H. Chu, T. C. Chu, J. Org. Chem. 19 (1954) 266-269.
[7] G . C. Kleinspehn. J. Am. Chem. Soc. 77 (1955) 1546-1548.
[8] Thls nomenclature proposal corresponds to the term "pentaphyrin". introduced by Rerhausen and Gossauer [9], for porphyrin-like cyclic pentapyrroles. Accordingly, the porphyrinogen analogues of cyclic pentapyrroles are called "pentaphyrinogens". Since 10 differs from these in
the inversion of the five pyrrole rings, it is called an "inverto-pentaphyrinogen".
[9] H. Rexhausen, A. Gossauer, J. Chem. SOC.Chem. Commun. 1983. 275.
[lo] The new compounds 7-10 were completely characterized by elemental
analyses and spectroscopic data.
[ l l ] Structure I 1 may be regarded as the most likely tautomer of a dehydrogenation product of 10. A smaller conjugated perimeter, which would
enclose the inward directed methyl-substituted C atoms of all pyrrole
rings, would contain 20 a electrons and thus be antiaromatic. Likewise,
less charged structures, in which the outer C N double bonds not involved
in the a-electron perimeter are hydrogenated, may presumably beexcluded
for the dehydrogenation product of 10.
this disturbance on the electrical conductivity and other
physical properties in a fundamentally similar crystal lattice.
For the synthesis of the necessary single crystals of binary
alloys of the type [(2,5-W,X-DCNQI),(2S-Y,Z-DCNQ1),JzCu 3 we first resorted to the usual method of electroIn this way (method A), 3a-c, 3g, 3i and
cry~tallization.[~"~
3 k (Table 1) could be obtained. However, the much simpler
method of immersing a polished copper wire into a solution
of the DCNQIs in acetonitrile (method B)[' also led to well
crystallized alloys, as demonstrated by the examples 3d-f,
3h, 3j, 31, and 3m. The ratio of the two components in the
alloy frequently deviate thereby from that obtained by electrocrystallization, even though equimolar amounts of the
two DCNQIs were employed in all cases.
Binary Alloys of 2,5-Disubstituted DCNQI
Radical Anion Salts of Copper
and Their Electrical Conductivity **
By Peter Erk, Hans-Jiirg Gross, SiegfYied Hunig,*
Uwe Langohr, Hubert Meixner, Hans-Peter Werner,
Jost Ullrich von Schutz, and Hans Christoph Wolf
.
Dedicated to Professor Goltfried Mark1 on the occasion
of his 60th birthday
N,N-Dicyanoquinodiimines (DCNQIs),"] particularly in
the form of their 2,5-substituted benzoquinone derivatives,
have proven very useful as novel acceptors in charge transfer
(CT) compounds[". 'I and especially in radical anion salts of
the type [2,5-X,Y-DCNQI],M (M = monovalent metal
ion).13' Despite wide variation of the substituents X and Y
(see below) and of M (Li, N a , K, Rb, Cu, Ag,
NH, [3c.4a1 all these salts crystallize in the same structure
type:[3a.3c*41 by tetrahedral coordination of the metal ions
these are strung out like a pearl necklace and surrounded by
four stacks of DCNQI
3c,4a1 The retainment of the
same structure type despite large variation of the substituents and counterions is unknown in the case of other
conductive radical salts.
The copper salts [2,5-X,Y-DCNQIl2Cu play a special
61 and signifirole, for only they show a multidimen~ional[~.
cantly increased metallic conductivity. As in many
analogous
in the salts with X,Y = Me/Cl, Me/Br,
CljCl, Cl/Br, Br/Br a metal-semiconductor transformation
takes place on cooling as a result of a Peierls distortion, [ 3 c . 4 c , 51 Contrastingly, when X,Y = Me,Me,13"]
Me,I[3b1and MeO, MeOI4'I the conductivity steadily increases up to < 3 K , whereby values of u p to 5 x lo5 S cm-'
So far, however, neither the substituent-deare
pendence['I nor the unusual pressure-dependence" 1' of the
phase transitions are fully understood. It was therefore considered of interest to prepare alloys of the corresponding
copper salts in which two differently substituted DCNQIs
are incorporated in the stack, so as to study the influence of
[*I
Prof. Dr. S. Hunig, Dr. P. Erk, DipLChem. H. Meixner
Institut fur Organische Chemie der Universitiit
Am Hubland. D-8700 Wiirzburg (FRG)
Prof. Dr. H. C. Wolf, Dr. J. U. von Schiitz. DipLPhys. H.-J. Gross.
Dip].-Phys. U. Ldngohr, Dr. H . 2 . Werner
3. Physikalisches lnstitut der Universitiit
Pfaffenwaldring 57, D-7000 Stuttgart (FRG)
[**I This work was supported by the Volkswagen Stiftung, the Fonds der
Chemischen Industrie, and BASF AG, Ludwigshafen. - DCNQI = N , N dicydnoq uinodiimine.
Anyrii. (%em.Inr. Ed Enyl. 2X (1989) N r . 9
0 VCH
3
2
1
The ratios 1m/2nin the salts 3 were ascertained from the
elemental analyses and are therefore subject to the corresponding errors. All alloys crystallize isotypically to the individual components (space group Z4,,JC1'I Which factors determine the composition is still unknown. The difference AE
in the redox potentials of the components 1 and 2
(Table 1)[2c,3c1
can only play a subordinate role; e.g. for
Table 1. Binary alloys 3 of the DCNQI components 1 and 2 and copper(t1)
bromide in acetonitrile by electrocrystallization (method A) or immersion of a
copper wire (method B). Amounts of the components 1 (m)and 2 (n) and their
potential difference AE. Powder(P) conductivity or single-crystal(S) conductivity u of 3 at room temperature (highest measured values).
W
X
m
Me
Me
Me
Me
Me
Me
CI
CI
CI
CI
Br
I
I
0.5
0.5
0.6
1.0
0.8
1.0
0.8
1.0
1.0
1.5
1.2
0.8
1.3
~
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Y
Z
n
Me-AE
thod [V] [a]
3
a
[Scm-'1
Me
Me
Me
Me
Me
OMe
Me
Me
Me
Me
Me
Me
OMe
C1
Br
I
1.5
1.5
1.4
1.0
1.2
1.0
1.2
1.0
1.0
0.5
0.8
1.2
0.7
A
A
A
a
200 (S)
200 (S)
200 (S)
0.2 (P)
0.2 (P)
200 (S)
400 (S)
0.2 (P)
400 (S)
400 (S)
200 ( S )
250 (S)
200 (S)
~~
I
OMe
OMe
Br
Br
I
I
I
OMe
OMe
B
B
B
A
B
A
B
A
B
B
f0.22
+0.21
+0.21
+0.21
-0.01
-0.06
f0.01
+0.01
-0.01
-0.01
20.0
-0.22
-0.27
b
c
d
e
f
g
h
i
j
k
I
m
[a] E, (l)-E2 (2); cf. [2c, 3c].
A E = +0.21 V corresponding to an energy difference of
4.8 k calmol-', a ratio of easily reducible to difficulty reducible components of ca. 3000: 1 would be expected if thermodynamic factors alone were to be responsible. Thin (1030 pm), black, shiny crystalline needles of ca. 1 15 mm in
length are obtained by methods A and B. Their structureless
IR spectrum (KBr) in the region 4000-600 cm-' immediately points to high electrical conductivity." 31 This is confirmed
by powder conductivities['41 of ca. 0.1 -0.2 S cm- and sin-
~~rluys~escIlsr.huft
mhH, 0-6940 Weinherm, t989
-
0570-0833jSUj0909-1245 $02.5010
1245
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