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Charge and Potential Arenes as Oxidants.

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ether phase decanted. The precipitate was washed several times with ether and
finally dried to give the deprotected product as a white powder (13 mg. 91 %).
The reductive amination was carried out using a modification of a published procedure [13]. In a typical experiment, the protected peptide la (10 pmol) was dissolved
in 2 mL of a 10: 1 mixture of 0.1M phosphate buffer (pH 6.0)and CH3CN.To this
peptide solution were added the carbohydrate (200pmol) dissolved in 2 mL of the
Same buffer and sodium cyanoborohydride (200pmol) as a solid. The mixture was
stirred at room temperature and progress of the coupling reaction monltored by
analytical HPLC. The glycopeptides were purified by semipreparative HPLC and
characterized by ESI-MS.
Received: December 22, 1995 [286841E]
German version: A n g c w Chenl. 1996,108. 1325- 1328
Keywords: glycopeptides
- lipopeptides - oximes
[l]I. J. Goldstein. R. C. Hugues, M. Monsigny. T. Osawa. N. Sharon, Nature
1980,285, 66;N. Sharon, H.Lis, The Proreins. Vol. 5, Academic Press, New
York, 1982,pp. 1-123.
[2]J. F. Fisher. A. W. Harrison. G. L. Bundy. K . F. Wilkinson. B. D. Rush, M. J.
Ruwart, J. Med. Chem. 1991,34,3140-3143.
[3]H . Kunz, Angew. Chem. 1987,99,297;Angew. Chem. Int. E d EngI. 1987,26.
294-308,U.Sprengard, G. Kretzschmar. E. Bartnick. C. Huls. H. Kunz. ihid
1995. 107, 1104 and 1995.34. 990-993; 0.Frey, M. Hoffmann. H. Kessler,
ihrd. 1995,107,2194-2195 and 1995,34, 2026-2028.
[4]M. Schnolzer. S.B. H. Kent, Screnc~1992.256.221 -225;P. E. Dawson, T. W.
Muir. I. Clark-Lewis, S . B. H. Kent, ihid. 1994.266,776-779:G. Tuchscherer,
Tetraheilron Lerr. 1993. 34,8419-8422.
[5] P. E. Dawson, S. B. H. Kent, J. Arn. Cheni.So<.1993,115, 7263-7266.
[6]J. Shao. J. P. Tam, J. An?. Chern. Soc. 1995,117, 3893-3899.
[7]1. Fisch. G Kunzi. K. Rose. R. E. Offord, Biotonjugute Chern. 1992,3,147153.
181 K. Rose, J. An?. C h m . SOC.1994,116. 30-33.
[9]B. A. Schwartz. G . R. Gray. Arch. Biochem. Biophys. 1977,181. 542-549.
[lo]P. Finch. 2. Merchant. J. Chent. Soc Perkin Tran.~./,1975,16821686.Preliminary ‘ H and ”C N M R investigations on amino-oxy acetic acid u-glucose
oxime demonstrate the presence in solution of a mixture of three interconvertible isomers the B-cyclic form and the acyclic Ayn ( E )and unti ( 2 )forms.
[ll]P. Dumy, I. M. Eggleston, S. Cervigni, U. Sila, X. Sun, M. Mutter, Terrohedron
Lrtr. 1995. 36. 1255-1258.
[12]The use of different peptides did not particularly affect the course of the
[13]R. Albert, P. Marbach. W. Bauer. U. Briner, G. Fricker, C. Bruns, J. Pless. Life
Sci. 1993, 53. 517-525.
was prepared following the procedure
[14] Glucosone 2 (u-arabino-hexos-2-ulose)
of D. J. Walton, T. Hvidt, W. A. Szarek. Curbolijdrate Res. 1987,167. 123
[15] M. Mutter, R. Hersperger, Angew. Chem. 1990.102,115; Angew. Chem. Znr.
Ed. Engl. 1990,29, 185-187.
[16]The pure products 18 and 19 were characterized by electrospray ionization
mass spectroscopy (ESI-MS). Found: 2135.6 (calcd: 2135.2).
considered whether the electrostatic activation of the electron
affinity of aromatic systems could be raised to such an extent
that their “antiaromatic” (LUMO-filled) reduction products
would be capable of existing as thermodynamically stable compounds such that their chemical properties could be investigated. This would open up new perspectives in the chemistry even
of conventional aromatic compounds.
The protocol for transforming arenes into powerful oxidants
by electrostatic activation is based on the fundamental conditions of Coulomb’s Law:
1 ) introduction of the maximum number of onio substituents
structurally possible at the organic x-electron system (per(onio) substitution);
2) the use of onium centers of the highest possible electropositivity so as to generate high pole strengths;
3 ) choice of the shortest possible distances of the positive poles
from the organic system.
For a given structural type there is no freedom of choice with
criterion 1). However, for criteria 2) and 3) it must be considered
carefully whether the use of an element from the first period as
an onium center produces a more efficient electrostatic effect
than an isoelectronic element from a higher period, because the
development of the positive charge of the onium center and its
distance from the central system in this comparison are inversely
related. Semiempirical calculations show that phosphonio substitutents are far more efficient for our purpose than triorganoammonio substituents.[’] This is consistent with the
comparatively higher stability of phosphonium relative to ammonium ylides.
The attempt to achieve per(onio) substitution on hexafluorobenzene (1) by the reaction with PR,/Me,SiOTf (Tf = trifluoromethanesulfonyl) under a variety of conditions led only to
the formation of the 1,4-bis-phosphonio-substitutedsystem
4a,b (Scheme
I +
+ 2 Me,SiOTf 3
chlorobenrere. A
- 2 MeaSiF
4a, L = PEtpPh
4b, L = PEtPhp
Scheme 1. Synthesis of 1.4-bis-phosphonio-substituted benzene derivatives
Charge and Potential: Arenes as Oxidants**
Robert Weiss,* Robert May, and Bernd Pomrehn
We have shown that the transition from neutral to cationic
sets of substituents achieved for both inorganic and organic
systems by using the trimethylsilyltriflate-assisted poly(onio)
substitution method developed by us leads to a marked increase
in their electrophilicities and electron affinities.“
This is attributed primarily to the electrostatic field effects of the cationic
substituents. Recently we reported on the first per(onio) substitution of hexafluorobenzene with 4-dimethylaminopyridine
(DMAP) as a preliminary highlight of this
[*] Prof. D r R. Weiss, Dr. R May, Dr. B. Pomrehn
Institut fur Organische Chemie der Universitlt Erlangen-Nurnberg
Henkestrasse 42,D-91054 Erkangen (Germany)
Fax: Int code +(9131)859132
This work was supported by the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie.
$.? VCH Verlag.~~es~~llsc/iufi
m h H , D-69451 Weinherrn, 1996
Cyclic voltammetric investigations of the salts 4a,b reveal two
quasi-reversible redox steps at remarkably positive potentials
(Table I).[’] In spite of the relatively high electron affinity of
4a,b these salts are not activated towards further nucleophilic
substitution. This in sharp contrast to the analogous substitution of hexafluorobenzene with DMAP, which under autoactivation leads to per(onio)-substituted products.[6] In this case, in
Table 1 Half-wave potentials of the poly(onio)-substituted arenes [a].
Compound [9]
1st Reduction [V]
2nd Reduction [V]
- 0.83(q)
- 0.76 (q)
- 1.46 (q)
- 1.36(4)
- 0.09 (I)
- 0.19 (r)
- 0.06(r)
- 0.04(r)
[a] r
0.04 (q)
0.03 (r)
0.14 (r)
reversible, q
quasi-reversible. i
$ 15.00+ ,2510
Angeiv. Chem. Inr. Ed. Engl. 1996.35, No. 1 1
addition to steric effects. electronic effects are probably responsible for the resulting products. According to PM3 calculations
the LUMO of 4a,b is predominantly localized on C atoms positioned cx to the phosphonio substitutents. so that the electronic
prerequisites for further onio substitution are unfavorable.
The hitherto unknown per(onio) substitution on naphthalene
should. because of the larger number of cationic substituents
and the inherently higher electron affinity of naphthalene, lead
to a further increase of the electron affinity relative to that of the
analogous benzene derivatives. By using DMAP/Me,SiOTf and
octafluoronaphthalene (5)we achieved per(onio) substitution in
the naphthalene system for the first time. The octacationic salt
6 could be isolated as a stable, water-soluble, pale yellow compound in almost quantitative yield (Scheme 2 ) . The replacement
+ 8 MenSiOTf 3
- 8 MeaSiF
8 OTf-
6, L = DMAP
4 OTf -
3 OTf -
9a, L = PEt3
9b, L = PPh3
10, L = PPh3
Scheme 3 Onio substitution of tetrachloropyrimido[5.4-c~pyrim1dine.
agents used in organic synthesis.["] As a consequence of the
increasing positive charge on the phosphorus center when alkyl
is replaced by ary118b1
the intially formed salt 9b, obtained when
PPh, is used analogously as a nucleophile, already has such a
high electron affinity that it is quantitatively reduced by excess
phosphane to the new tricationic radical salt 10. The latter is a
deep green isolable salt that has been fully characterized, including by a high-resolution ESR spectrum. With a strong oxidizing
agent such as NO' 10 may be reconverted to 9b. The measured
half-wave potential for this conversion of 0.80 V (vs. Ag/AgCl)
establishes this compound as the most powerful "aromatic oxidant" known to date. Calculations show that the charge distributions in the antiaromatic red-forms of the polyphosphonio
salts 4, 7, 9 are characterized by a maximum charge pairing in
terms of the bis-ylidic mesomeric structures A and B/C (Fig. 1 ) .
4 OTfblwobenzene. A
- 4 MenSiF
7a, L = PEt2Ph
7b, L = PEtPh2
Scheme 2. Octakic- and tetrakis(onio) substitution of octafluoronaphthalene
of DMAP with tertiary phosphanes led under otherwise identical conditions exclusively to the formation of good yields of the
tetrasubstituted products 7a,b, i n which the fluoro and triorganophosphonio substituents alternated along the periphery
of the naphthalene core. Investigations into the regiochemistry
of the S,Ar reaction at octafluoronaphthalene indicate that substitutions at C-2/C-6 precede those at C-4/C-8.['01The interplay
of steric and electronic factors evidently hinders per(onio) substitution by phosphonio substituents as for the benzene system.
Electrochemical measurements on salts 6 and 7a,b confirm an
unprecedented high electron affinity for benzenoid aromatic
compounds (cf Table 1). Remarkably, four triorganophosphonio substituents are as effective in raising the redox potentials as
eight pyridinio substituents-an expected trend (see above) in
view of the higher capability of phosphonio substituents to stabilize carbanions. The tetraphosphonio-substituted salts 7a,b
represent the ox-forms of a new, completely reversible two-step
redox system whose oxidizing power is similar to that of chloranil.[' '1
According to PM3 model calculations, replacement of the C F
groups by N in salts of the type 7a,b should lead to an even
larger increase in the electron affinity.['] This could be confirmed experimentally. The reaction of tetrachloropyrimido[5,5-Lijpyrimidine[1zl(8) with four molar equivalents of PEtJ
Me,SiOTf led smoothly to the formation of the corresponding
tetrakis(oni0)-substituted salt 9 a (Scheme 3).[l3I
The "aromatic" compound 9 a is the ox-form of a completely
reversible two-step redox system (Table 1) and, with a half-wave
potential of 0.60 V (vs. Ag/AgCl) for the transition oxjsem, has
at least the oxidizing power of 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) one of the most powerful organic oxidizing
Fig. I. Bis-yl~dicmesomeric structures of the red-forms. X
= CF.
The position of the pertinent redox potentials and the reversibility of the corresponding reduction steps (cf Table 1)
opens up the prospect of generating such systems in a straightforward manner by chemical methods. With the synthesis of the
sem-form 10 the first step in this direction has already been
taken. Owing to the clear structural analogy with the corresponding quinones we designate the red-forms A-C as "quinobis-ylide~".['~IThe controlled reductive generation of suitable
representatives of this class of substances is the subject of current investigations.
Experimental Procedure
All reactions were carried out under N, and in dried solvents. Correct C. H. N
analyses were obtained for all compounds prepared.
4a,b. Compound 3 (2 mmol) and PEt,Ph or PEtPh, (2 mmol) were added to a
solution of 1 ( I mmol) in chlorobenzene (20 mL) and the solution was stirred under
reflux. After 24 h (4a: or 72 h for 4b) the white precipitate was filtered off. washed
with Et,O ( 5 x 5 m L ) and dried for 12 h under high vacuum.
4 a : Yield: 99%: ' H NMR (400.05 MHz, CD,NO,!CF,COOD.
21 C. TMS):
6 =7.95 (m. 6H: H-2jH-4:H-6, phenyl). 7.80 (m. 4 H ; H-3;H-5. phenyl), 3.20 (m.
XH: CH,). 1.38 (dt. ,J(H.P) = 22.21 Hz. 3.1(H.H) = 7 56 HI. 12H: CH,);
"C NMR (100.5 MHz. CD,NO,iCF,COOD, 21 C. TMS). d = 150.27 (dm.
'J1C.F) = - 255.5 Hz. C2 C3/CS!C6. benzene). 137 54 (s: C4. phenyl). 133.61 (d.
'J(C.P) = 9.2 Hz: C2;C6. phenyl). 132.03 (d. 'J(C,P) =12.8 HI. Ci.;C5. phenyl).
121.67 (4. 'J(C.F) = - 319.8 Hz, CF,). 116.40(d. 'J(C,P) = 84.5 Hz: C1. phenyl).
109.43 (dm. '4C.P) = 84.5 Hz; CIIC4, benzene), 15.65 (d. './(C.P) = 49 7 H7.
CH,). 6.09 (d. 'J(C.P) = 3.7 Hz, CH,); "P NMR (I61 7 M H r , CD,NO,
CF,COOD. 21 C. ext. H,PO,): d = 35.53 (s).
4 b : Yield- 50%: ' H NMR (400.05 MHz. CD,NO,/CF,COOD. 23 C, TMS):
6 =7.99 (m. 12H. H-2:H-4.'H-6. phenyl). 7.85 (m. 8 H : H-3iH-5. phenyl). 3.54(m.
411. ( ' H 2 ) . 1 4 1 ((It. .'./(H.P) = 72.10 H7. './(H.H) =7.33 Hz: 6 H : CH,).
"C NMR (100.5 MHI. C'D,NO, CW,COOD. 23 C. TMS). d =15O.I4 (dm.
'./(C'.F) = -- 265.7 HL. C?:C3,CS C6. benzene). 137.83 (d. 'J(C,P) = 3.6 Hz: C4.
phenyl). 134.82 (d. 'J(C.P) = 11.1 H / : C3,C6. phenyl). 132.14 (d. ,J(C.P) =
11.9 H<: C3 C5. phcnyl). 121.71 (q. ' J ( C . F ) = - 318.0 Hr: CF,). I15.XO (d.
'J(C.P) = 88.3 H7: C l . phenyl). I10 65 (dm. './(C,P) = 88 3 Hz: C1 C4. benrenc).
19.36 (d. 'J(C.P) = 49.7 H r , CH,). 6.94 (d. 'J(C.P) = 5.5 Hz. CH,): "P NMR
(161.7 MHz. CD,NOZ CF,COOD, 23 C. ext H,PO,): 0 = 26.71 (s).
6: Compound 3 (0.80 inL. 4.43 mmol) and 6 (0.605 g. 4.95 inmol) were added to a
solution o f 5 (0.149 g. 0 55 mmol) i n chlorobenzene (20 mL) and the solution was
stirred under reflux. After 12 h the yellow precipitate \+as filtered off. washed with
CH,CI, ( 4 x 5 mL) and dried for 13 h under high vacuum. Yield: 1.34g (98%):
' H NMR (400.05 MHr. CD,CN. 24 C . TMS): 0 = 8.05 (d. 'J(H.H) =7.57 HL.
XH. H-2,H-6). 7.83 (d. 'J(H.H) =7.51 Hz. XH; H-2,H-6). 6.87 (d. .'J(H,H) =
CH,). 3.20 ( s . 24H: CH,); "C NMR (100.5MHz. CD'CN. 24 C. TMS):
h =157.30 ( s : C4. DMAP). 156.81 (s: C4. DMAP). 142.29 (s: C2;C6. DMAP).
14042 (s: C2C6. DMAP). 140.37 (s. C1 C4.C5 CX, naphthalene). 138.49 (5. C2:
C3 C6.C7. naphthalene). 131.34 (s: C9:CIO. naphthalene). 121.88 (q. 'J(C.F) =
- 319.9 HziCF,). I I ~ . ~ ~ ( S : C ~ , C S , D M1 A
1 0P. 7) 0. ( ~ ; C 3C5.DMAP).41.80(s,
C H , ) . 4 1 . 6 0 ( ~ CH,):
I9F NMR (470.4 MHz. CD,CN. 20 C.C,F,): d = -77.9 ( s .
7a,b- Compound 3 ( 2 mmol) and PEt,Ph or PEtPh, ( 2 mmol) were added to :I
solution of 5 (0.5 mmol) i n chlorobenzene (20 m L ) and the solution was stirred
under reflux. After 48 h the suspension was cooled to - 20 C. the precipitation was
coinpleted by the addition of Et,O (20 mL). and the precipitate was filtered off.
washed with E t 2 0 ( 5 x 5 mL). and dricd for 1 2 h under high vacuum.
[I] R. Weiss. N. J. Salomon, G E. Miess. R. Roth. AiiLqrw.Chmi. 1986, YH. 925,
Angrn. C h i f . In2 E d €fig(. 1986, 25, 9 17.
121 R . Weiss, R. Roth, J. Chciii Soc. C h i i . Con?fiiwi.1987, 317.
[3] R. Weiss. R. Roth. .Tnithc\t.\ 1987. 870.
[4] R. Weiss. J. Seuhert. Atlgiw. Cbcm 1994. 106. 900: A n p i t . . Cbcfi?.In/.E d Engl.
1994. 33, 891.
[5] R. Weiss, J. Seubert, F. Hainpel, Angeii'. Cliriii. 1994, 106. 2038: Aiigew. C/icwi.
lm. Ed. Eiig1. 1994, 33. 1952.
[h] R. Weiss. B. Pomrehn. E Hampel. W. Bauer. A!~goic C ~ E I1995.
~ I . 107, 1446;
c/iPt7I. / f i r . Ed. Etlg/ 1995. 34, 1319.
[7] B. Pomrehn. Dissertation, Universitit Erlangen-Nurnberg. 1996.
[XI The corresponding salts of the benzene parent structure have already been
reported- a ) L Homer, G. Mummenthey. H. Moser, P. Beck. CIi~ni.BPI.1966.
YY. 2782: b) H Bock. U. L. Knoblauch. P. Hamel. ibid 1986, 119, 3749
191 The electrochemical invcstigationa were carried out at room temperature under
N 2 with ferrocenc as the internal standard in a 0.1 k NEt,BF,.'CH,CN elecrrolyte solution against a saturated Ag;AgCl electrode iinincrsed in a 0.1 ~i
NEt,CI'CH,CN solution. Auxiliary and working electrodes were made of platinum.
[lo] C L. Cheong. B. J. Wakefield. J, Cliivii. So<..PerXiii Truns. 1 1988. 3301.
[ l I ] M. E. Peovcr. J. C/iwii. Sol,. 1962. 4540.
[12] F. G. Fischer. J. Roch. W. P. Neumann. Liebig.5 A m . C h i ? . 1960. 631, 147.
[I31 R. May. Dissertation. Universitilt Erlangen-Niirnberg, 1993.
[I41 Because of the inverse polarity of the functional groups the red-forms may also
be designated as "antiquinones".
7a. pale yellow powder: yield. 9 5 % : ' H NMR (400.05 MHz, CD,CN, 24 C.
TMS) h=7.85(m.XH;H-2 H-6.phenyl).7.73(rn.4H.H-4.phenyI).7.67(m,SH.
H-3.H-5. pheiiyl). 2.85 (m. 1 6 H ; CH,). 1.06 (dt. ,J(H.P) = 21.73 Hr, .'J(H.H) =
7.57 Hz. IZH;CH,), 1.01 (dL3J(H.P) = 22.22 Hr.'..I(H.H) =7.32 Hz.12H.CH,);
"C NMR (100 5 MHz. CD,CN. 24 C. TMS). d = 167.65 (dd. 'J(C.F) =
- 362.9 Hr. './(C.F) =10.1 Hz: C4 C8. naphthalene). 166.26 (din. 'J(C.F) =
- 270 3 Hr: C?,C6. naphthalene). 136.82 (d. 'J(C.P) = 3 7 Hr: C4, phenyl).
135.99 (s: C4, phenyl). 133.39 (d. 'J(C.P) =11.0 Hz: C2 C6. phenyl). 132.27 (d.
'J(C.P) = 9.2 H7; C 2 C6. phenyl). 131.63 (d. 'J(C.P) = 12.8 Hr: C3 C5. phenyl).
131.46 (d. 'J(C.P) = I 2 9 Hz: C3 C5. phenyl). 119.88 (in: C9 C10. naphthalene).
121.92 (q, 'J(C.F) = 319.9 Hz: CF,). 120.01 (d. 'J(C.P) = 86.4 Hz: CI. phenyl).
Jan Foerstner, Falk Olbrich, and Holger Butenschon*
116.31 (d. 'J(C.P) = 84.6 Hz: CI. phenyl). 106.46 (in: C 3 C7. naphthalene). 102.26
(dd. 'J(C.P) =75.3 Hz. 'J(C.F) =19.4 H r : CI C5. naphthalene). 17.78 (d.
Dedicated to Prqf>ssor Ertt,in Weis.,
'J(C.P) = 44.1 H7: CH,). 15.40 (d. 'J(C.P) = 47.8 HL: CH,). 6.64 (d. 'J(C,P) =
3.7 H r . CH,). 6.1 1 (d. './(C.P) = 5.5 Hz: CH,): "F NMR (470.4 MHz. CD,CN.
on the occcision of' his 70ih biriliday
20 C. C,)F,,): 6 = -78.0 (5. 12F: CF,). -14.8 (in. 2 F . F-4 F-8). -67.9 (in. 2 F:
F-2.F-6). "P NMR (161 7 MHz. CD,CN. 20 C. cxt. H,PO,): 6 = 42.98 (dd.
"Phosphaalkynes correspond to alkynes in all aspects, to ni'./(P.F) =18 4 HI: "J(P.F) = 8.7 HI: P-3 P-7). 35.71 (d. ',/(P.F) = 6 2 H7:
triles in nothing." This remark by Regitz"] is substantiated by
P-I P-5).
A New Mode of Reaction of tevt-Butylphosphaethyne: Trinuclear Cyclopentadienylcobalt Clusters with P, PS, and PO as
Complex Ligands**
7 b . pale orange powder: yield. 88%: 'H N M R (400.05 MHz. CD,CN. 21 C.
TMS): h =7.85 7.62 (m. 4 0 H ; phenyl). 3.33 (m. 8 H ; CH,), 1.11 (m, 12H: CH,).
" C NMR (100.5 MHz. CD,CN, 21 C. TMS): 6 =137.19 (s: C4. phenyl). 136 69
(s: C4. phenyl), 133.34 (d. 'J(C,P) = 1 I .0 Hz: C2:C6. phenyl). 132.55 (d. 'J(C.P) =
1 1 1 Hz: C2tC6. phenyl). 131.66 (d. 'J(C,P) = 14.7 Hz: C3 C5. phenyl). 130 70 (d.
.'J(C.P) =12.9 Hz; C3 C5. phenyl). 129.66 (m: CY'CIO. naphthalene). 121.92 (9.
' J ( C . F ) = - 3 1 9 . 9 H z : C F 3 ) , I 1 9 . l 0 ( d . ~ J ( C , P )86.4Hr:Cl.phenyl).
'J(C.P) = 84.6 Hz: C1. phenyl). 103.72 (m. C3:C7. naphthalene), 101.18 ( m ; C1
C5. naphthalene). 18.53 (d. 'J(C.P) = 51.5 Hz; CH,). 17.44 (d. 'J(C.P) = 53 3 Hz:
CH,). 8.21 (d. 'J(C,P) = 5.5 H7: CH,). 7.09 (d. 'J(C.P) = 3.7 Hz: CH,):
"FNMR(470.4 MHz.CD,CN.20 C.C,F,)-h = -78.0(s. 12F:CF,). -69.0(m.
2F. F-4 F-X), -66.6(m. 2 F ; F-2 F-6): "P NMR(161.7 MHr,CD,CN,20 C.ext
H,PO,): d = 32.63 (d. 'J(P,F) = 18.2 Hz. P-3 P-7). 26.07 (d. ',/(P.F) = 4 I f l / :
P-I P-S)
9a: Compound 9 ( I inmol) *as suspended in CH,CI, (30 niL) and 3 (4 inniol) nab
added. Subsequently. PEt, (4 mmol) dissolved in CH,CI, (10 inL) was added to the
mixture. After the mixture had been stirred for 12 h a t room temperature. the pale
green precipitate was filtered off, washed with CH'CI, (3 x 5 m L ) and dried for 12 h
under high vacuum. Yield. 62"h: ' H NMR (399.65 MHz. CD,3CN. 20 C. TMS):
2 85 (m, 24H: CH,) 1.29 (in, 36H; CH,).
10. Compound 9 ( I minol) was suspended i n CH,C12 (20 inL) and 3 (4 inmol) was
added. Subsequently PPh, (6 mmol) dissolved in CH,CI, (20 InL) was added to the
mixture. After the mixture had been stirred for 12 h at room temperature Et,O
(100 mL) was added to precipitate a green solid. The solid h a s filtered off, washed
with Et,O (3 x 5 mL) and dried for 12 h under vacuum Yield: 6 9 % ; UV.Vis
(CH ,CN). i,,, (c) = 668 (4870). 614 ( 5 3 5 5 ) . "'072 (2920). 439 (6330). 382 (8520).
270 (370x5). 214 (91945).
Receiwd: Deceinbei- 15. 1995 [ Z 8655 IE]
Germail version: ,Aiigiw C h i l i . 1996. 108. 1319 1371
Keywords: arenes . heterocycles . nucleophilic aromatic substitutions phosphoniurn salts * polycations
the results of our investigations of the chemistry of [w-phosphanyl(ethylcyclopentadienyl)]cobalt complexes. Herein we report on reactions of such complexes with terr-butylphosphaethyne that in addition to diphosphete complexes result in
the formation of p,-phosphido clusters in good yields. The
"naked" phosphorus ligand in these clusters can be oxidized
with elemental sulfur or with oxygen in the air to give PS and PO
ligands, respectively.
The chemistry of phosphaethynes has been investigated intensely in the past few years.[2J In a few cases mononuclear
transition metal complexes with a monomeric phosphaethyne
ligand have been
Because we were able to coordinate alkynes with the [(o-di-/cv/-butylphosphanyl)ethylcycIopentadienyl]cobalt (Cp'Co) fragment without di- or trimerization.''.
we investigated reactions of Cp'Co complexes with
tcrt-butylphosphaethyne. The paramagnetic chloride 1 and the
[*I Prof. Dr H. ButenschBn. DiplLChem. J. Foerstner
lnstitut fur Orgdnische Chemie der Universitit
Schneiderberg 1 B. D-30167 Hannover (Germany)
Fax: Int. code +(511)762-4616
e-mail: holger.butenschoenin
Dr. F. Olbrich
Chemisches Institut der Universitat Magdeburg (Germany)
We thank the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen lndustrie for their financial support and BASF AG. Bayer AG.
Chemetall GinbH, and Hiils AG for donations ofchemicals. We are indebted
to ENRAF-NONIUS for their kind support in performing the X-ray crystal
structure analysis. We thank Dr G Remherg. GBttingen, and Dr. A. Kornick.
Hannover. for mass spectra and helpful discussions.
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potential, areneв, oxidant, charge
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