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Structure and Formation of Triorganylphosphoniocyclopropenylium Ions.

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Structure and Formation of Triorganylphosphoniocyclopropenylium Ions'"'
By Robert Weiss, CIaus Priesner, and Hilmar Wolf[']
Hetero[3]radialenes (I), in which X, Y , and/or Z are hetero atom functions, constitute a hitherto unexplored class of
substances which could be of interest particularly in connection with ring fragmentation[']. We have now synthesized
systems of type (2) for the first time.
4
Y
Z
Do
Do
M.p. ["C] 1R
la1
(KBr) [cm
(50)
163-165
uv
'1
1592 (m), 1485
(m), 1445 (s), 1328
b,,(log&)
'H-NMR
Tvalues [b]
310 (4.28)
2.3 (s, IOH), 2 62 (s,
15H)
(S)
-
~~
~
(Sb)
151-153
1834 (m), 1481
(m), 1438 (s), 1367
(m)
269 (3.83)
2 4 (mc, 15H), 8 88 (s.
18H)
(9a)
200
1915 (s). I650 (vs). 270 (4.51),
1440 (m). 1410 (m), 230 (4.62)
2.03 (mc, 15H), 6.48 (s,
6H), 7.17 (s, 6H)
@Do
(2a)
(1)
Table 1. Data of new compounds.
1220 ( W )
(26)
A triorganylphosphonio group served as acceptor A and
the donor group Do was vaned.
Reaction of the covalent dichlorides (3)[']with triphenylphosphane gives quantitative yields of the cyclopropenylphosphonium salts (4) which can be precipitated as stable
salts (5) from CH,Cl, with ethereal HBF,. The position of
the double bond follows from spectroscopic data (Table 1).
Compounds (4) and (5) are transformed by the strong Lewis
acid SbCI, into the bis(hexach1oroantimonates) (6).
(9b)
273
1865
(s), 1590
1440 (m).
1380 (w). 1365
(W)
277 (4.62),
235 (4.65)
2.0 (mc, 15H), 5.59
(mc, 2H). 6.57 (mc,
2H), 8.43/8.53 (d,
12H; J = 6 Hz), 9.10/
9.20 (d, 12H, J = 6
Hz)
1870 (\). I S X I ) (vs), 266 (4.30),
1470 (m). 1360(m). 210 (4.33)
1300 (m)
5.77 (mc, 4H). 7.03/
7.23 (d, 18H: J = 1 2
Hz), 8.46/8.59 (d,
24H: J = 7 . 8 Hz)
(vs),
(lo)
290
[a] All compounds decompose on melting.
[b] (Sa),(Sb) in CDCI,; (9aJ, (Yb). (10) in CD,CN.
Under the same reaction conditions, the salt-like dichlorides (7)[31react immediately with triphenylphosphane to
give the bis(dialky1amino)triphenylphosphoniocyclopropenylium dichlorides (8) which can be isolated in high yield as
stable bis(perch1orates) (9) after addition of HC10, (Table
1).
R2N
h8F'h3
R,N
t
(71
(8)
( a ) , R = CH,;
(b). R = i-C3H7
strong shielding of the phosphorus in the dications (9) relative to that in the system (6b) suggests extensive participation
of the [3]radialene resonance structure in (9) according to the
general form (26). This possibility of stabilization is reserved
for systems having strong + M substituents on the threemembered ring and occurs only to a limited extent, if at all,
in the salts (6).
The radialene character of (9) is also manifested in a high
rotational barrier about the C-N bond. The AG+ value of
(9a) was found to be >24 kcal/molisl, whereas that for
bis(dialky1amino)cyclopropenylium systems without acceptor substituent lies between 17 and 20 kcal/mol[61. The increase in positive charge of the nitrogen functions is manifested in a downfield shift of the alkyl signals by ca. 0.15
relative to reference systems without acceptor substituents
such as (7a)13].
The mode of formation of the dications (6) could be classified as an addition/elimination reaction. This would also
provide a formal explanation of the formation of the dications (9). However, the strong formation tendency of (9) is
surprising in view of the high ground state stabilization of
the cation (7) and the high-energy 1,2-bis(dialkyIamino)cyclopropene intermediates postulated. In fact, the formation
of the dications (10) and (11) strongly suggests that the systems (9) are actually produced by an elimination/addition
reaction of a kind hitherto undescribed for the C; system.
'?bPPh3
2
R,ON
clop
(9)
While alkyl- and aryltriphenylphosphonium salts show
3'P-NMR signals in the range 6= - 20 to - 35l41, (6b) gave a
signal at 6= - 53.6 and (9a) and (96) signals at 6= -6.66
and - 8.44, respectively (CD3CN; H,PO, internal). The
R2N
( l o ) , 11%
Dor. Dr. R. Weiss [ '1, Dr. C. Priesner, Dip1.-Chem. H. Wolf
Institut fur Organische Chemie der Universititt Erlangen-Numberg
Henkestrasse 42, D-8520 Erlangen (Germany)
[' ] To
I\
hom correspondence should be addressed.
[**I
F-unctiimal cydo-C, Derivatives, Pari 7. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen 1ndustrie.Part 6: R. Weiss, C. Priesner, Angew. Chem. 90. 491 (1978); Angew. Chem. Int.
Ed. Engl. 17, 457 (1978).
472
0 Verlag Chemie, GmhH, 6940 Wrinheim. 1979
clop
ill), 60%
R = i-C,H,
['I
2
Thus, reaction of (7b) with tris(dimethy1amino)phosphane, which is more nucleophilic than PPh,, under otherwise identical conditions no longer affords the dication
(10)Isb' [corresponding to (9b)Jas major product but instead
the known triafulvalene dication (11). These observations indicate the reaction course shown in Scheme 1.
05 70-0833/79/M06-0472 $02.50/0
Angeiu.
Chrm. lnr. Ed. Engl. 18 (1979) No. 6
r
1
substituent'']. We have now exploited this property of (1) in
order to synthesize novel polycationic cyclopropenylium systems.
Scheme I . R=i-CIH,
A crucial step is the nucleophilic attack of PL, at the u*
orbital or the C --CI bond in (7b) with liberation of the nucleophilic carbene (12) and formation of the chlorophosphonium ion (13). The electrophilic character of (13) which
can be varied by way of L probably determines the further
course of the reaction. The reaction observed with L = Ph is
strongly reminiscent of that between CCI, and P(Ph),[*I.
With L=N(CH,), this course only plays a minor role because of the greatly reduced electrophilic character of (13),
for (76) can then successfully compete for (12) to give the
triafulvalene dication in a coupling reaction of known
kind[7h1.This reaction is also of preparative interest.
Received: February 8, 1979 [ Z 224a IE]
German version: Angew. Chem. 91, 505 (1979)
CAS Registry numbers:
( 3 4 , 2570-00-5; (36), 66633-01-0: (4a). 70287-90-0: (46), 70287-91-1; (So),7028793-3. 156). 70287-95-5: (6a). 70304-34-6: 166). 70304-32-4; (7a).70287-96-6: (76).
66466-64-6: (8a), 70287-97-7; (Xb), 70287-98-8: (Pa). 70288-00-5; (96). 70288-027; (10). 70304-30-2; 11 1). 61695-57-6; triphenylphosphane, 603-35-0 tris(dimethy1amino)phosphane. 1608-26.0
[ l ] R. West, D. C. Zecher, S. K. Kosrer, D. Eggerding, J. Org. Chem. 40, 2295
(1975).
[2] (36) was obtained by analogy with (3a) from the pertinent cyclopropenone
and SOCI, pa].
131 a) C Priesner. Dissertation, Universitat Miinchen 1978; b) M . Herrel,
Diplomarbeit, Universitat Erlangen-Nurnherg 1978.
[4] G. M . Kusolapoff; L. Maier: Organic Phosphorus Compounds. Wiley-Interscience. New York 1972, Vol. 27, pp. 217ff.
[S] a) Exact determination of the rotation barrier was not possible since the coalescence temperature for the methyl signals could not be reached
( T ,> 150 'C); b) H. Wolf; Diplomarbeit, Universitat Erlangen-Niirnberg
1978.
161 The rotation barrier for bis(diisopropylamino)cyclopropenylium perchlorate
is 17.8 kcal/mol ( Z . Yoshidu, H . Kunishi. Y. Kumitori, H. Ogushi, Chem. Lett.
1977. 1341) and that for bis(dimethylamino)cyclopropenyliumperchlorate
20.2 kcal/mol (R. Weiss, H. WOK unpublished).
171 a) Z. Yushida, H. Kunishi, S. Suwadu, H. Ogoshi, J . Chem. Soc. Chem. Commun IY77, 850, b) R. Weiss, C. Priesner, H. Wolf; Angew. Chem. 90, 486
(197X); Angew. Chem. Int. Ed. Engl. 17, 446 (1978); c) R. Gompper. E. Bartmann. ibid. 90, 490 (1978) and 17%456 (1978).
[8] R. Appel, Angew. Chem. 87,863 (1975); Angew. Chem. Int. Ed. Engl. 14.801
(1975).
Synthesis of a Donor-Substituted
Tris(cyclopropenylio)cyclopropenylium Saltf**]
Reactions of trichlorocyclopropenylium salts with arenes
to form triaryl-substituted cyclopropenylium salts have been
known for some time[21.We wish to report a novel variant of
this structural type in which the aromatic donor ligands are
themselves cyclopropenylium systems of type (1). For this
purpose the carbenoid (2)[,"',which has meanwhile become
readily accessible, was treated with trimethylsilyl trifluorogiving an 82% yield of the first
methylsulfonate (Scheme I),
silyl-substituted cyclopropenylium system (3) as thermally
stable salt showing considerable resistance to water [m. p.
131°C; IR (KBr): 1845 (m), 1587 (m), 1535 (s), 1453 (w),
1373/1348 (m) cm-I; 'H-NMR (CDCI,): ~ = 5 . 9 5(mc, 4H),
8.64/8.74 (d, 24H; J = 6 Hz), 9.58 (s, 9H)I.
Compound (3) is a potential precursor of the nucleophilic
cyclopropenylidene (4) (cf. ref. ['I) which has so far defied attempts at generation in the free state13'l. The method of
choice is F- -induced desilylation which has already proved
of value in the case of the trimethylsilyltropyliurn
(3) is rapidly and quantitatively desilylated to (5) at room
temperature in water on addition of one equivalent of
F - PI,
These results suggest the occurrence of the free nucleophilic carbene (4) (Scheme 1). Only one of the possible trapping reactions will be mentioned. While (3) fails to react with
tetrachlorocyclopropene (C,Cl,) in tetrahydrofuran, in the
presence of F - ion under otherwise identical conditions the
highly symmetrical stable tetracationic salt (6) is formed in
ca. 40% yield within 24 h. This system can also be obtained
in ca. 80% yield directly from (2) and C&I, in CH,Cl,; however, the product thus obtained is contaminated by highly
persistent dark-colored by-products.
KF,THFI2O"C
- KC104
Hz0
1 . C,Cb
20 "c
(CHzC12/- 78°C
2. HClOa
By Robert Weiss, Marion Hertel, and Hilmar Wolf'']
J
As a result of cyanine resonance, the bis(dia1kylamino)cyclopropenylium group (1) can assume the character of a + M
elHz0
1. C,CI,
2. HC104
[*] Doz. Dr. R. Weiss [ '1. Dipl.-Chem. M. Hertel. DipLChem. H. Wolf
lnstitut fur Organische Chemie der Universitat Erlangen-Nurnberg
Henkestrasse 42. D-8520 Erlangen (Germany)
1 To whom correspondence should be addressed.
[**IFunctional cyclo-C, Derivatives, Part 8.-This work was supported by the
[
+
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen 1ndustrie.Part 7: ref. [I].
Anyrw. c'iiwi. Inr. Ed. Etigl. 18 (1979) N o . 6
Scheme 1. R = i-C3H7. L'*'= [(CC,H,),N],C'~
0 Verluy Chemie, GmbH, 6940 Weinheim,1979
0570-0X33/79/0~06-0473 ,$ 02..50/0
473
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structure, triorganylphosphoniocyclopropenylium, formation, ions
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