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Diphosphonio Isophosphindoles Phospholes with a Planar Phosphorus.

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rate law with rate constant kobs(equations (a)-(d)). For route
@ where k, 2 k,, equation (a) applies.
kobs= k,[aIkene]
For route @ with d[Z]/dt = 0, the observed rate constant is
described by equation (b),
kobs= (k,k, [alkene])/(k_,
+ k,[alkene]),
which reduces to equation (c) or (d).
kobs= k , , when k,[alkene]
kobs= (k,k,/k-
[alkene], when k, [alkene] < k _
We followed the decrease in concentration of 1a in benzene
in the presence of excess NPM by analytical HPLC.[14.''I
The dependence of the kobsvalues obtained from the function
In [l] = In [I],- kobst (correlation coefficient r 2 0.999) on
[NPM] at T = 303 K is plotted in Figure 1. Already at rela-
Chem. 47 (1982) 1837; d) R. W. Saalfrank, E. Ackermann, M. Fischer, B.
WeiD, R. Carrie, D. Danion, K. Peters, H. G. von Schnering, Bull. Sot.
Chim. Belg. 94 (1985) 475; further references cited in [I c, 21.
[4] Calculations at the MP2/6-31G* level yield AH* % 6.9 kcal mol- for the
reaction H,C=C=N, -t H,C=C M. A. Murcko, S. K. Pollack, P. M.
Lahti, J. Am. Chem. SOC.110 (1988) 364.
[5] P. M. Lahti, J. A. Berson, J. Am. Chem. Sor. 103 (1981) 7011.
161 W. Ando, T. Furuhata, T. Takata, Tetrahedron Left. 26 (1985) 4499.
[7] Formation of diazoalkenes during HID exchange on primary ethene diazonium salts: K. Bott, Chem. Ber. 120 (1987) 1867.
[8] Diazomethylene phosphoranes, (iPr,N),HalP = C = N,, have been isolated; they also undergo [3 21 cycloadditions: J.-M. Sotiropoulos, A.
Baceiredo. G. Bertrand, J. Am. Chem. SOC.109 (1987) 471 1.
[9] The structures o f 6 and 7 (R = rBu), @ = SiPh,tBu) were determined by
X-ray crystallography, which will be reported elsewhere.
(101 a) A. G. Brook, A. R. Bassindale in P. de Mayo (Hrsg.): Rearrangements
in Ground and E-rrited States, Vol. 2. Academic, New York 1980. S. 149;
b) 1. Matsuda, S. Sato, M. Hattori, Y. Izumi, Terrahedron Letr. 26 (1985)
[l I] The contrasting ease of the 1,3-(C + 0) silyl shift (1 2) is probably due
to the contribution of a (2)-configured diazonium enolate resonance formula to the bonding in 1.
[I21 a) U. Schollkopf, D. Hoppe, N. Rieber, V. Jacobi, Liebigs Ann. Chem. 730
(1969) 1; b) T. Allspach, H. Giimbel, M. Regitz, J. Organornet. Chem. 290
(1985) 33.
[13] a ) R. Huisgen, H. Seidl, Tetrahedron Lett. 46 (1964) 3381; b) R. Huisgen,
E Mietzsch, Angew. Chem. 76 (1964) 36; Angew. Chem. Int. Ed. Engl. 3
(1964) 83. c)R. Huisgen, ibid. 82 (1970) 783 and 9 (1970) 751; d) F.-G.
Klirner. D. Schroer, Chem. Ber. 122 (1989) 179.
[14] Merck/Hitachi LiChrograph, LiChrospher RP-18 (125 x 4 mm), eluant
= 254 nm, 1.4-diiodobenzene
acetonitrile (1.25 mL min-'); detection at i.
as internal standard; no further absorptions between 1. = 254 and 300 nm.
[15] The k,,, values were determined for the decrease in the concentration of
l a , because the calculation of the concentration of 6 a involves larger
errors (partial overlapping of peaks, lability of 6 a under HPLC conditions). For comparison one example run under optimal conditions for the
detection of 6 a (acetonitrile/water. 95/5 (v/v); 1.25 mL min-', 2 =
290 nm) at 290 K yielded for the decrease in [ l a ] k,,, =
(2.692 _+ 0.005) x
min-' (correlation coefficient r = 0.99998), and
for the increase in [6a], k,, = (2.77 f 0.13) x
min-' (r = 0.9906).
1161 Norbornadiene yields cycloadducts (endo and exo isomers) with I a, which
are analogous in structure to 7 a . In contrast to norbornene, norbornadiene is a liquid at room temperature and thus suitable for kinetic studies
Fig. 1. k,,, = - d[laj/dt as a function of [NPM]; see text. Conditions:
T = 303 K, solvent benzene, [ l a ] = 0.035 mol L-*, 2.5- to 39.9-fold excess of
tively low excess of NPM a plateau is reached, that is the
condition, k,[alkene] k- of Eq. (c) is satisfied. Thus
route 0,
via the diazoalkene intermediate 2a, is confirmed
by the kinetic study. From the temperature dependence of
the limiting rate constant k , for T = 293-303 K,the following activation parameters were calculated: E, = 21.6
0.4kcal mol-I, AH' = 21.0 0.4 kcal mol-',
AS* =
- 3.4 1.2 cal K-' mol-'. In an analogous study with
norbornadiene as trapping agent,['61 a plot of the dependence of rate on concentration of norbornadiene yields a line
through the origin. This relationship is described by equations (a) and (d) and no distinction between routes @ and 0
can be made.
Diphosphonio Isophosphindoles, Phospholes with
a Planar Phosphorus **
By Alfed Schmidpeter,' and Martin Thiele
Dedicated to Professor Rolf Appel on the occasion
of his 70th birthday
CAS Registry numbers:
l a , 106435-62-5; l b , 132298-34-1; Za, 132298-35-2; Zb, 132298-36-3; 3a,
132298-43-2; 3b, 132298-44-3; 4 a , 106435-70-5; 4b, 132298-45-4; Sb, 13229846-5; 6a, 132298-37-4; 6b, 132298-38-5; 7a, 132298-39-6; 7b. 132298-40-9; 8 a ,
132298-41-0; 8b. 132298-42-1; NPM, 941 '69-5; norbornene, 498-66-8.
Phosphole is an exception among the quartet of heterocycles, pyrrole, phosphole, furan, and thiophene, because it
lacks aromaticity:l" 1' The expected energy gain from cyclic
delocalization is too small to meet the energy demand for a
planar coordination for the phosphorus atom (inversion barrier for phospholane: 36 kcal mol-'r31). Thus in all the Psubstituted phospholes as yet studied, phosphorus is pyraniidal; the known phospholes unsubstituted at phosphorus are
unstable at room temperature."] Their phosphorus atom is
also pyramidal, but in one phosphole the inversion barrier is
at least reduced to 16 kcal m01-'.['~~]A planar environment
for phosphorus in the ground state is conceivable when electron-withdrawing substituents occupy 2,5 positions. In fact,
this was achieved in the 1,3-bis(triphenylphosphonio)isophosphindoles 6 and 7.
[I] a) G. Maas, R. Briickmann, J. Org. Chem. 50 (1985) 2801; b) R.
Briickmann, G. Maas, J. Chem. SOC.Chem. Commun. 1986, 1782; c) R.
Briickmann, G. Maas. Chem. Ber. 120 (1987) 635.
[2] J. C. Brahms, W. P. Dailey, J. Am. Chem. SOC.112 (1990) 4046.
[3] a) P. J. Stang, Chem. Rev. 78 (1978) 385: b) K. Bott in S. Patai, Z. Rappoport (Eds.): The Chemistry of Functional Groups, Supplement C, Wiley,
Chichester 1983, Chap. 16; c) J. C . Gilbert, U. Weerasooriya. 1 Org.
[*] Prof. Dr. A. Schmidpeter, DipLChem. M. Thiele
lnstitut fur Anorgdnische Chemie der Universitat
MeiserstraDe 1, W-8000 Miinchen 2
[**I Four- and five-membered phosphorus heterocycles, Part 76. This work
was supported by the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie. part 75: K.-H. Zirzow, A. Schmidpeter, Z .
Naturforsrh. B43 (1988) 1475.
Received: October 12, 1990 [Z 4239 IE]
German version: Angew. Chem. 103 (1991) 312
VerlagsgesellschafrmbH. W-6940 Weinheim, 1991
0570-0833/9110303-0308 $3.50+.25/0
Angew. Chem. h i . Ed. Engl. 30 (1991) No. 3
The o-xylylenebis(triphenylphosphonium) ion (l),["]
which is easily prepared from ap-dibromo-o-xylene and
triphenylphosphane, undergoes cyclocondensation with
phosphorus trichl~ride[~I
and triethylamine to form the 1,3bis(tripheny1phosphonio)isophosphindole cation (3). As intermediate only the PC1,-substituted ylide cation 2[61can be
detected spectroscopically and also isolated. Cation 3 is obtained as the bromide; the counterion can be exchanged for
BPh,', SbCI,', or HgI,e by precipitating the respective
salts from a methanol solution.
- 2 HCI
The resonance formulas 3a, 3b, and 3c can be written for
3. Formula 3a presents the cation as a phosphenium ion
stabilized by two methylenephosphorane groups (whose
ylide nature is not reflected in the formula), 3 b as a phosphonio-substituted phosphaalkene,['] and in 3c a phospholide
anion modified by two phosphonio substituents. In fact 3
proves to be more thoroughly "ambiphilic" than other compounds with two-coordinate phosphorus. The 31P NMR
shift in 3, however, (6 = 242) corresponds to a C-substituted
phosphenium ion (range: 6 = 168-266)['] rather than a
phospholide ion (6 = 40-103).['991 This suggests that forms
3a and 3b predominate.
The Lewis acidity of 3 is small in comparison with other
phosphenium ions.[sb1 Thus the cyclic chlorophosphane
which probably forms en route from 2 to 3 spontaneously
loses a chloride ion. Furthermore, cation 3 does not react
with water, although it adds the more strongly basic anions
MeOe and H o e to form 4 and 5, respectively.["]
Cation 3, on the other hand, is more basic than otherwise
found for phosphenium ions, which can be neither protonated nor alkylated. Cation 3 is protonated by strong acids like
HBF, and CF,SO,H. Formula 3b would suggest a protonation at the ylide carbon, 3c at the two-coordinate phosphorus atom. In fact, the symmetric dication 6 is formed and can
be isolated as, for example, the tetrafluoroborate salt. Its
formation corresponds to the protonation of phospholide
ions to 1H-phospholes at low temperature,['] which are, in
contrast to 6 , unstable at room temperature and isomerize to
2H-phospholes, which promptly dimerize. Thus 6 is the first
stable phosphole not substituted at phosphorus.
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 3
The decreasing negative charge on atoms Cl and C3 in the
series 4,3, and 6 is reflected in the 31PNMR spectrum by an
increase in the deshielding of the onium phosphorus. In particular the P-H coupling of 586 Hz for the isophosphindol6
is significant: it is extremely high for a three-coordinate phosphorus atom, and far larger than for any other phosphane,
in particular, for all known phospholes (217-234 Hz[']). As
the s character of the bond is reflected in the coupling constant, the phosphorus atom in 6 must be spz hybridized and
is thus in a planar environment. This bonding, best expressed
by formula 6 b, corresponds to that of the bismethylenephosphoranes" 'I, which have been shown to be planar by X-ray
crystallography. Till now for the only existing, but unstable,
hydrobismethylenephosphorane HP[ = C(SiMe,),], , lJpH
was found to be 406 Hz.["~]The distinctly higher value of
for 6 probably results from the CPC angle, which must
be much smaller in the five-membered ring of 6 than in
acyclic bismethylenephosphoranes (ca. 130"). With the exception of some azaphosphole transition metal complexes, 6
is the first phosphole or heterophosphole with phosphorus in
a planar environment.["]
Cation 3 can be alkylated by Me,OBF, to the methyl
derivative of 6, the dication 7,which also has a planar phosphorus atom in the ring. The coupling constant between
phosphorus and the methyl carbon atom is 14 Hz in
trimethyl phosphane, around 19 Hz in l-methylphosp h ~ l e s , [ ' but
~ ] 98 Hz in 7.Again this value is far greater than
the corresponding coupling in alkylbismethylene phosphoranes (33-44 H Z ~ ' ~ ~ ) .
Besides the phosphonio substituents, the condensed benzene ring probably also favors the planar structure of 6. The
planarity of phosphorus in a phosphindole ([2.3]-annelation)
demands about 8 kcal mol-' more energy"] than in a phosphole; it should demand less energy in an isophosphindole.
The resonance formula 6 b gains in importance through the
Earlier attempts to prepare isophosphindoles were unsuccessful and even their oxides proved to be too reactive for
The arsenic cations analogous to 3 and 6 can also be prepared and other heteroatoms may be stabilized in unusual
coordination environments in the same position.
Experimental Procedure
3-Br: 40.2 g (51 mmol) l-Br, and 7.0 g (51 mmol) PCI, were heated under reflux
in 100 mL Et,N and 50 mL CH,CI, for 48 h. More CH,CI, was added and the
ammonium halides were separated by shaking with water. The organic phase
was concentrated and 3-Br separated on addition of TH E After drying. digestion in THF, and recrystallization from ethanol, the yield of pale yellow crystals
was 29.8g (80%). M.p. 302°C (decomp.); 31PNMR (AB, spin system):
b(A) = 241.8,6(B) = 16.8 (J(AB) = 91.4 Hz); '-'C('H}NMR (ABB'Xspinsystem): 6 = 109.0 (J(AX) = 56.0 Hz, J(BX) = 96.6 Hz, J(BX) = 14.0 Hz).
6-(BF4),: A solution of 1.48 g (2.0 mmol) 3-Br in 5 mL CH,CI, was mixed with
0.65 mL of a 6.15 M HBF, solution in Et,O and allowed to stand for 30 min.
On addition of 10 mL Et,O, the product precipitated. Recrystallization from
CH,CI, yielded 0.80 g (48 %) colorless, extremely moisture-sensitive crystals.
31P NMR (AB, spin system): S(A) = 41.7, 6(B) = 23.1 (J(AB) = 12.3 Hz,
Vrrlagsgesellschafr mbH. W-6940 Weinheim. 1991
+ ,2510
'J(PH) = 586.2 Hz); '3C{1H}NMR: 6 = 110.1 (dd, 'J(PC) = 52.7. 38.4 Hz.
7-(BF4),: 30 min after the preparation of a solution of 2.50 g (3.4 mmol) 3-Br
and 1.01 g (6.8 mmol)Me,OBF, in 10 mL CH,CI,, the volume was reduced to
half. A colorless, very moisture-sensitive powder (1.75 g, 61 %) precipitated on
addition of 10 mL Et,O and was recrystallized from CH,CI,/Et,O. 31PNMR
(AB, spin system): 6(A) = 69.3, d(B) = 22.4 (J(AB) = 11.O Hz, ,J(PH) =
12.8 Hz; "C('H)NMR: 6 = 116.9 (dd, 'J(PC) = 49.0. 36.4 Hz, Cl), 43.0 (d.
'J(PC) = 97.5 Hz, CH,).
Received: August 2. 1990 [Z 41 12 IE]
German version: Angew. Chem. 103 (1991) 333
monophosphacyclobutadiene complex, formed from 1,2bis(trimethylsily1)acetyleneand 1a has been described.[']
We now report the cooligomerizations of tert-butylphosphaacetylene (1 a) [31 and of N-isopropyl-N-trimethylsilyl-2aminophosphaacetylene (1 b)[41with tolane or acetylene in
the coordination sphere of rhodium(1) complexes. The starting point for the syntheses described here was provided by
the rhodium(1) complexes of tolane, 2 and 3, first synthesized
by H. Werner et al.J5] as well as of the vinylidene 6.L6I
[l] E Mathey, Chem. Rev. 88 (1988) 429.
M. H. Palmer, R. H. Findlay, J. Chem. SOC.Perkin Trans. 2 1975. 974.
W. Egan, R. Tang, G. Zon, K. Mislow. J. Am. Chem. SOC.93 (1971) 6205.
C. E. Griffin, K. R. Martin. B. E. Douglas, J. Org. Chem. 27 (1962) 1627.
For reactions of phosphonium ylides with chlorophosphances see: K.
Issleib, M. Lischewski, J. Prukr. Chem. 311 (1969) 857; ibid. 312 (1970)
135; H. Schmidbaur. W. Tronich, Chem. Ber. 101 (1968) 3545; G. Mirkl,
W. Bauer, Angew. Chem. 101 (1989) 1698; Angew. Chem. Int. Ed. Engl. 28
(1989) 1695; H. Grutzmacher, Z. Naturforsch. B 45 (1990) 170.
[6] 3'P NMR (ABC spin system): &A) = 170.6 (-PC12),6(B) = S(C) = 22.6
(-PPh3'), J(AB) = 219.0 Hz.
171 a) H. H. Karsch, H.-U. Reisacher, G. Muller. Angew. Chem. 98 (1986)
467; Angew. Chem. Int. Ed. Engl. 25 (1986) 454; b) H. Grutzmacher, H.
Pritzkow, ibid. 10f (1989) 768 and 28 (1989) 740.
[S] a)S. Lochschmidt. A. Schmidpeter, Phosphorus Sulfur 29 (1986) 73;
b) A. H. Cowley, R. A. Kemp. Chem. Rev. 85 (1985) 367.
[9] K. Karaghiosoff. A. Schmidpeter, Phosphorus Sulfur 36 (1988) 217.
[lo] "P NMR (AB, spin systems ): 4 (X = OMe) 6(A) = 83.2, 6(B) = 11.9
(J(AB) = 50.8 Hz); 5: 6(A) = 27.6, S(B) = 12.6 (J(AB) = 48.5 Hz.
'J(PH) = 504.9 Hz).
1111 a) R. Appel in M. Regitz, 0.J. Scherer (Eds.): Multiple Bonds and Low
Coordination in Phosphorus Chemistrj', Thieme, Stuttgart, 1990. p. 157;
b) A. R. Barron, A. H. Cowley, J. Chem. Soc. Chem. Commun. 1987,1092.
[12] A. Schmidpeter, K. Karaghiosoffin H. W. Roesky (Ed.): Rings, Clusters
and Polymers o j Main Group and Transirion Elements, Elsevier, Amsterdam 1989, p. 308.
[13] L. D. Qum, S. G. Borleske, R. C. Stocks, Org. Magn. Reson. 5(1973) 161;
G. A. Gray, J. H. Nelson, ibid. 14 (1980) 14.
(141 R. Appel, T. Gaitzsch, F. Knoch, G. Lenz, Chem. Ber. f19(1986) 1977; E.
Niecke, Bonn, personal communication.
[15] L. D. Quin, The Heteroryclic Chemisrry ojPhosphorus, Wiley. New York
1981, p. 90.
Cooligomerization of Phosphaalkynes and
Alkynes in the Coordination Sphere
of Rhodium Complexes **
By Paul Binger,* Josef Haas, Albert 7: Herrmann,
Franz Langhauser, and Carl Kruger
Dedicated to Professor Rolf Appel on the occasion
of his 70th birthday
Cyclizations of phosphaalkynes,['' especially of the kinetically stable, readily accessible terr-butylphosphaacetylene
(1 a), in the coordination sphere of transition-metal complexes have attracted increasing interest in recent years. For example, long-sought phosphorus heterocycles such as 1,3diphosphacyclobutadiene and 1,3,5-triphospha-Dewar-benzene are now accessible via this route.[ll Cooligomerizations
between phosphaalkynes and other unsaturated systems
(e.g., alkynes), however, are very rare. So far only one
[*] Prof. Dr. P. Binger, Dipl.-Chem. J. Haas, DipLChem. A. T. Herrmann,
DipLChem. F. Langhauser, Prof. Dr. C. Kruger
3 10
Max-Planck-Institut fur Kohlenforschung,
Kaiser-Wilhelm-Platz 1, D-4330 Mulheim a.d. Ruhr (FRG)
This work was supported by the Volkswagen-Stiftung.
Verlagsgesellschafl mbH. W-6940 Weinheim, 1991
1 a,b
90 %
a. R = tBu;
b, R
The rhodium tolane complex 2 reacts at - 20 "C with two
equivalents of 1 a to give the cotrimer 4 (yield 76 %), in which
a monophosphacyclobutenyl group, formed from one molecule of 1a and the tolane ligand, is bonded as q 3 ligand to
rhodium. The second molecule of 1 a is bonded to the P atom
of the phosphacyclobutenyl ligand and to the rhodium center in a (r fashion.[71On the other hand, the rhodium (q5-cyclopentadieny1)tolane complex 3 reacts with the two phosphaalkynes 1 a and 1 b in refluxing THF to give the two
rhodium q4-monophosphacyclobutadiene complexes 5a
and 5 b, respectively, in 90 YOyield; that is, complex 3 undergoes codimerization with only one molecule of the phosphaalkyne.
Complex 7, the first l-phospha-2-rhodacyclobutene,is
formed upon reaction of the rhodium vinylidene complex 6
with 1a in a [2+2] cycloaddition as yellow needles (79%).r71
The regiochemistry of this cycloaddition indicates that the
carbene carbon of 6 has electrophilic character.['' Replacement of the chloro ligand in 7 by a cyclopentadienyl ligand
results in smooth formation of the l-phospha-2-rhoda-3methylenecyclobutene 8.
The crystal structure analyses of the rhodium complexes 4
and 7 reveal several structural features.tg1The rhodium atom
in 4 is coordinated in a distorted tetrahedral fashion; the
corners of the tetrahedron are occupied by CI, P2, P3,and
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Angew. Chem. Int. Ed. Engl. 30 (1991) No. 3
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