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Cyclotrimerization of Ethyne on the Complex Fragment [(1-tBu2PCH2PtBu2)Ni0] with Formation of an 6-Benzene-Nickel(0) Complex.

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Consequently, we conclude that nitroxides 5 and 6 form conglomerates consisting of a mixture of two enantiomeric crystals.
In the chiral molecule 5 (Fig. 1) the mean plane of the fused
rings forms an angle of 76" with the 3,5-dinitrobenzoyl group so
as to avoid steric repulsion; the dihedral angle between the mean
plane of the nitroxide portion (C-NO-C) and the 3,Sdinitrobenzoyl group is 51". More interesting is the crystal structure of 5
with two threefold screw axes along the c axis in the trigonal unit
cell (Fig. 2). The molecules are arranged around one axis be-
[I] G . I. Likhtenstem, Pure Appl. Chem. 1990, 62, 281; D . Marsh. rbid. 1990. 62.
265; C. Degrand, B. Limoges, R. L. Blankespoon, J. U r g . Chem. 1993. 5X.
2573.
[2] H. G. Aurich in Nifrones, Nifronates and Nitrriaides (Eds.: S . Patai, Z. Rappoport). Wiley, New York, 1989, pp. 313, 371.
[3] H. Iwamura. Adv. Phys. U r g . Chem. 1990,26,179;A. Rassat, Pure Appi. Chon.
1990. 62, 223: R. Chlarelli. M. A. Novak, A. Rassat, J. L. Tholence. Nature
1993, 363, 147: M. Tamura, Y. Nakarawa, D. Shiomi, K Nozawa. Y. Hosokoshi, M. Ishikawa, M. Tdkahashi, M. Kinoshita, Cheni. Phq..,. Lrrf. 1991,
186, 401.
[4] M. Yamaguchi, T. Miyazawa, T. Tdkata. T. Endo. Pure Appl. Ch6.m. 1990, 62,
217.
[S] E. G . Rozantsev, V. D. Sholle. Synthesis 1971. 190, 401; H. G. Aurich. W.
Weiss, Top. Curr. Chem. 1975, 59, 65: see also ref. [2].
[6] R. Tdmurd, K. Yamawaki. N. Azuma, J. Urg. Chem. 1991,56. 5743; R. Tamura. M. Kohno, S. Utsunomiya, K. Yamawaki, N. Azuma. A Matsumoto. Y
Ishii, ihid. 1993. 58. 3953.
[7] Y. Brunel, H. Lemaire, A. Rassat, Bull. Soc. Chim. Fr. 1964. 1895.
[8] J. S. Roberts, C . Thomson, J. Chem. Soc. Perkin Trans. 2 1972. 2129.
[9] J. L. Namy. P. Girard. H. B. Kagan, Nouv. J. Chem. 1981, 5. 479.
[lo] The ESR spectrum of 3 (g = 2.0059, aN= 14.4 G ) in the reaction mixture was
detected even at 25 'C in the presence of atmospheric oxygen, and no noticeable
decrease of the spectral intensity was noted after 1 h at 25 'C.
[ l l ] The use of powdered 4 and THF/Et,O was essential to avotd the undeslred
one-electron transfer from 3 to 4.
[12] A mixture (conglomerate) of two enantiomeric single crystals of 5 or 6 was
obtained by very slow evaporation of the saturated ether solution of 5 o r 6 at
25 "C. Crystal data for 5 : C,,H,,N,O,, trigonal. P3, or P.7,. rr = 17.274 (6).
L' = 6.166 (2) A, Y =1593 A', Z = 3,
= 1.308 gcm-3, p(Mo,,) =
0.94 cm-', 910 observed reflections ( I > 3.00 u(I), T = 298 K) were used for
the solution and refinement of the structure. R = 0.045, R, = 0.041 ;
R =(I:l'F,I - ~ ~ ~ ~ / I R: ,~=F[ I,: ~w () ~, F ~ /F,J)z/CwF~]'.'2
Further details
of the crystal structure investigation are avalbdble on request from the Director
of the Cambridge Crystallographic Data Centre. 12 Union Road. GB-Cambridge CB2 IEZ(UK). on quoting the full journal citation.
[I31 N. Azuma, T. Ozama. K. Yamawaki, R. Tamura. Bull. Chem. Soc. Jpn. 1992.
65. 2860.
[I41 The MOcalculations were performed with a 3-21G basis set (J. S. Binkley. J. A.
Pople, W. J. Hehre, J. Am. Chem. Soc. 1980. 102, 939) and the Gaussian 90
program.
[15] S . Kende. J. S. Mendoza, Tetrahedron Lett. 1991, 14. 1699.
~
Fig. 2. Crystal structure of 5. *: Points corresponding to the threefold screw axes;
0 : 0 atoms of the NO groups.
cause of the electrostatic intermolecular interaction between the
nitroxide oxygen atom and the nitrogen atom of one of two
nitro groups on the benzene ring (2.87 A), whereby a head-totail arrangement results. The other axis is surrounded by the
other nitro group owing to another electrostatic intermolecular
interaction between the nitro groups (3.02 A), giving a tail-totail arrangement. Thus, the unique molecular asymmetry and
arrangement seems to be responsible for the helical crystal structure and hence leads to the formation of conglomerates of the
stable free radical.
Solutions of 5 and 6 in T H F display an intense 1 : 1 : 1 triplet
in their ESR spectra at 25 "C (Table I ) , and the powdered materials exhibit exchange-narrowed spectra (5: AH = 12 G,
g = 2.007; 6 : A H = 16 C, y = 2.007) at 25 "C. The radical purity of 5 and 6 was determined to be approximately 100% by
magnetic susceptibility measurements by means of a Faraday
balance (55 K I
T I 250 K); in other words, the temperature
dependence of the static magnetic susceptibility of 5 and 6 follow the Curie- Weiss law; the Curie constants are approximately 0.38 0.01 Kemumol-' (theoretical value, 0.377).
The methods described here have provided conglomerates of
stable radicals with a unique crystal structure that leads to spontaneous optical resolution. The scope, limitations, and the reaction mechanism of this synthetic method along with the precise
magnetic properties of the newly prepared nitroxides are under
investigation
*
Received: October 19. 1993
Revised: December 1, 1993 [Z 6432 IE]
German version: Angew. Chrm. 1994, 106, 914
A n y r u . Chrm. l n t . Ed. Engi. 1994. 33. No. 8
Cyclotrimerization of Ethyne on the
Complex Fragment [ ( ~ , I ~ - ~ B ~ , P C H , P ~ B U , ) N ~ ~
with Formation of an $-Benzene- Nickel(o)
Complex**
Thomas Nickel, Richard Goddard, Carl Kruger,
and Klaus-Richard Porschke*
For a number of years we have directed our efforts to modifying the properties of nickel(0) centers with mono- and bidentate ligands, for example, with the phosphanes PR, (R = Me,
Et, Ph, iPr) ,[11 Me,PCH,PMe, ,['I and tBu,PC,H,PtBu, .13]
Ethene and ethyne are especially interesting coligands. For the
ligand combination tBu,PCH,PtBu, ( d t b ~ r n ) [ ~and
I stilbene
or diphenylacetylene, activated by electron-withdrawing substituents, Hofmann et al. first obtained nickel(0) complexes with
dtbpm as a chelating ligand.[51We report here on novel nickel(o)
complexes in which only one phosphorus atom of the bidentate
dtbpm ligand is coordinated to the nickel(o) center.
[*I
[**I
Priv.-Doz. Dr. K.-R. PBrschke, DipLChem. T. Nickel, DJ. R. Goddard.
Prof. Dr. C. Kruger
Max-Planck-lnstitut fur Kohlenforschung
D-45466 Mulheim an der Ruhr (FRG)
Telefax: Int. code + (208)306-2984
Part of the planned dissertation of T. Nickel. This work was supported by the
Fonds der Chemischen Industrie and by the Volkswagen-Stiftung.
V C H Veriagsgesellschaft m b H . 0-69451 Weinhernz,1994
0570-0833194/0ROX-OX793 10.00 i.25"0
879
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When a solution of equimolar amounts of [Ni(C,H4)3][61and
rBu,PCH,PtBu, in ether is cooled from - 10 "C to temperatures
between - 30 and - 78 "C. large yellow cubes of 1 form in 65 O h
yield [Eq.(a)]. When heated rapidly, 1 decomposes at 70'C; the
coinpound can be stored for longer periods only below 0 'C.
Complex 1 is stabilized in solution by addition of ethene.
[Ni(C2H4)J
+ tBu,PCH,PtBu,
f
[(r~l-tBu,PCH,PtBu,)Ni(C,H,),l
+ C,H,
(a)
In the 300MHz ' H N M R spectrum ([D,]THF) of 1 at
- 8 0 T two signals are observed at 6 = 2.60 and 2.51, which are
assigned to the "inner" and "outer" protons, respectively, of
two equivalent ethene ligands in a trigonal-planar L-Ni(C,H,),
complex.[" The phosphane ligand gives rise to two equally intense methyl signals; the broad signal (6 = 1.35) is attributed to
a coordinated PrBu, group, the sharp one (6 = 1 .I 8) to a noncoordinated PtBu, group. Corresponding signals are found in the
13C N M R spectrum (75.5 MHz, -SoPC). In the 31P N M R
spectrum ( - 80 -C) the coordinated and the noncoordinated
phosphorus atoms of the dtbpm ligand give rise to an AX system [6 = 63.5, 23.8; *J(PP) = 17 Hz]. In the ' H and I3C N M R
spectra at -30 *C the ethene signals are coalesced, and both
PrBu, signals are sharp. Apparently, for solutions of 1 the rotation of the ethene ligands about the bond axis to the nickel atom
is restricted at low temperatures, and in addition the mobility of
the terr-butyl groups of the coordinated phosphorus atom is
reduced ; when the temperature is increased the ethene ligands
and the rert-butyl groups undergo facile rotation. A (fast) exchange of the phosphorus atoms is not observed at - 30 "C.
The results of the crystal str,ucture analysis of 1 Iaal are summarized in Figure 1. The Ni atom is coordinated in a trigonal-
nc 2
It\,C\l
C4 n
c 3 A c20
center is unsaturated (16e). is explained by the high conformational strain connected with this coordination mode.[']
When a yellow solution of 1 in pentane with an excess of
ethyne is warmed from - 78 to - 55 " C, it becomes dark and a
few flakes of red-colored polyacetylene precipitate. At - 78 'C
and in the course of several days, orange rosette-shaped crystals of the benzene-nickel(o) complex 2 form in 50% yield.[""'
According to these results, the ethene hgdnds of l l l O bare
l
displaced. and ethyne is cyclotrimerized on the 12e [(qltBu2PCH,PtBu,)Ni] complex fragment to give a benzene hgdnd
[Eq.(b)]. [ l O c . d l
I
+ 3 HC=CH
~-+
[ ( ~ ~ ' - ~ B U ~ P C H , P / B U , ) N ~+( ~Z ~C2H4
- C ~ H ~ )(b)
~
Crystalline 2 melts at 83 "C with decomposition. In the EI
mass spectrum (80 "C) the molecular ion (440) undergoes cleavage of benzene to give the complex fragment [(dtbpm)Ni]+
(362); benzene cation gives rise to the base peak. Complex 2
decomposes in solution (THF) above - 30 "C, presumably by
release of the benzene ligand.["] In the 400MHz ' H and
75.5 MHz I3C NMR spectra at -80 "C very sharp singlets
at 6(H) = 5.95 and 6(C) = 92.0 are observed for the benzene
ligand; the chemical shifts and the coupling constant
J(CH) = 168 Hz are comparable to those of [(C,H,)Cr(CO),]
[6(H) = 5.67; 6(C) = 95.5; J(CH) = 175 Hz].['~]Thus for 2 in
solution the benzene ligand is $-coordinated to the nickel atom.
Since the 'H and I3C N M R signals of the tert-butyl groups
occur in pairs, only one phosphorus atom of the bidentate
dtbpm ligand in 2 is bound to the nickel(0) center [31PN M R
( - 8O-,C):6 = 53.4, 19.1 ; 'J(PP) = 37 Hz]. Within the temperature range at which the complex is stable the phosphorus Iigand was not observed to change hapticity (accompanied by
plausible y4-coordination of the benzene ligand), nor could an
exchange of the benzene ligand with free benzene be proved by
N M R spectroscopy.
The crystal structure of 218b1
is shown in Figure 2. The benzene ligand is planar [maximum deviation (C2): 0.005 %.I and
symmetrically coordinated to the Ni atom [average Ni-C bond
length: 2.138(6) A]; the center D of the C, ring is 1.606(5) A
away from the Ni atom.['31The C-C bonds within the six-membered ring 11.41(1) A] are all the same length within the margin
of error. In addition the PI atom of the dtbpm ligand is coordi-
c10
c2
c5
,212
C17
C15
Fig. 1. Crystal structure of 1. Selected bond lengths [A], angles [ 1. and torsion
angles [ I (Ca.b: midpoint between atoms Ca and Cb): Ni-P1 2.238(1). Ni-C1
2.013(2), Ni-C2 2.000(2), Ni-C3 2.016(2), Ni-C4 1.999(2). PLC5 1.872(2), P2-C5
1.877(2), Ni-C1.2 1.883(4). NibC3.4 1.886(4), C1.2...C3.4 3.319(6), N i . . . P 2
4.696(1), Ni-PI -CS 1 16.5(1), Pl-CS-P2 125.9(1 ) , C5-P2-C14 98.2(1), C5-P2-C18
104.7(1). PI-NI-Cl.2 120.3(1). PI-NiCC3.4 116.O(I), C1.2-Nl-C3,4 123.5(1). Ni-P1C5-P2 89.7(2), C3.4-Ni-PLC5 29.5(2).
planar fashion by two ethene molecules and one P atom of the
diphosphane ligand [Ni-PI 2.238(1) A]. The second P atom of
the phosphane ligand is far enough from the Ni center [Ni . . P2
4.696(1) A] that both intramolecular and intermolecular
Ni . . . P2 interactions in the crystal lattice can be discounted.
The fact that the dtbpm ligand in 1 does not act as a chelating
ligand with formation of a NiPCP ring, even though the Ni
880
,(''
VCH Verlu,~sge.srllschu/tmhH. 0-69451 Weinhrinl, 1994
c
1
9 C18
~ L
c
1
7
Fig. 2. Crystal structure of 2 Selected bond lengths [A]. angles ['I. and torsion
angles ['I (D. center of the six-membered ring (Cl-C6): Ni-PI 2.111(1), Ni-Cl
2.140(4). Ni-C2 2.128(5). Ni-C3 2.136(5). Ni-C4 2.143(5). Ni-C5 2.142(5), Ni-C6
2.136(5). Ni-D 1.606(5). N L . P? 4.507(1). P1-C7 1 S67(4). P2-C7 1.867(4); D-NiPI 174.2(2), Ni-PI-C7 122.2(1). P1-C7-P2 123.6(2). Ni-Pl-C7-P2 74.6(7).
OS7a-OR33i9410ROR-08XI) S lO.OO+ .2S,'O
Angew. Chrm. Int. Ed. €ng/. 1994, 33, No. 8
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A
nated to the Ni center. The Ni-PI bond of 2.111(1) is relatively short, and the D-Ni-P1 angle is 174.2(2)". The coordination geometry of the nickel atom can be considered pseudolineal-. The torsion angle Ni-P1 -C7-P2 [74.6(7)"] is smaller than
the related angle in 1 [89.7(2)"]; this can be explained by the
reduced spatial requirement of the ($-C,H,)Ni unit in comparison to that of the (C2H&Ni unit. The P-C-P angles in 1
[125.9(1)']and 2 [123.6(2)"]are similar andmarkedly larger than
the P-C-P angles in transition metal complexes with a
rBu2PCH2PrBu,chelating ligand [95.5(2)-99.2(2)"] .[5, 14] Force
field calculations[' 51 on the uncomplexed tBu,PCH,PtBu, molecule indicate a P-C-P angle of 122.3" [P-C 1.89
P'.'P
3.30 A]. The calculated molecule has a twofold rotational
axis that bisects the P-C-P angle. In the related diphosphane
(c-C,H, I)2PCH,P(c-C6H,l), this angle is determined to be
1 2 0 31 ) ' [ l h l (calcd: 120.6")."51
Nickel(o) complexes with benzene or other arene ligands have
been relatively uncommon. Jonas prepared the first complexes
of the type [{R,P(CH,),PR,}Ni(arene)]
by reducing
[{R,P(CH,),PR,}NiCl] (R = c-C,H, I ; n = 2,3) with lithium in
the presence of benzene (or other arenes)!"]
The bidentate
phosphane ligand is presumably bound to the nickel(o) center in
a chelating fashion and the arene ligand like an alkene (1' or q4)
(NMR data are not available). This coordination mode was
proven for the analogous naphthalene"'] and anthracene complexes['"] by NMR spectra and crystal structures. In contrast,
the benzene ligand in 2 serves as a six-electron ligand for the
nickel atom. which attains an 18e configuration including the
electron pair of the coordinating phosphorus atom. Complex 2
completes the series of complexes of the type [L,M($-C,H,)],
n = 2 -4, with the parent structure, n = 1. The reaction providing 2 [Eq.(b)] at temperatures below - 50 "C (!) may serve as a
for a reaction step in Reppe's nickel(o)-catalyzed cyclotrimerization of ethyne to benzene.[201
A,
E~qwin zmi a lProcedure
1: A solution of [Ni(C,H,),][6] in ether (30mL), prepared from [Ni(trun>.
Iruiis.Iruii.s-I .5.9-cyclododecatriene)] (1.165 g. 5.0 mmol) and ethene. was combined
with il solution of dtbpm (1.522 g. 5.Ommol) in ether (20mL) at -1O'C. The
solution was filtered through a cooled D4 frit to remove insoluble impurities: large
yellow cubes formed at -3O'C The crystallization was completed at -78°C; the
mother liquor was removed from the crystals with a capillary, and the crystals were
washed twice with cold pentane and dried at -30'C under vacuum (oil pump)
Yield 1.36 g (65%). -Correct elemental analyses; m.p. 70-C (decomp): ' H N M R
(300 MHz. - X O C). 6 = 2.60, 2.51 (4H each. H,C=CH;); 2.05 (2H, PCH,P').
1.35 (d. 18 H, PtBu, complexed). 1.18 (d, 18H. PIBu, free); ( - 3 0 ' C ) : 2.58 (XH,
C,H,). 2.07 ( 2 H , PCH,P). 1.37 (d, 18H. PtBu, complexed), 1.17 (d, 18H, PtBu,
free): " C NMR (75.5 MHz, - 8 0 T ) : 6 = 54.3. 50.5 (2C each, H,C=CH,); 38.1
(2C. sharp. PCMe,). 34.0 (2C. br. PCMe,). 30.2 (12C. br, CH, and CH;). 18.0
( 1 C. 'J(PC) = 50. 2 Hz. PCH,P'); ( - 30 C): 6 = 52.7 (4C, C,H,); 38.1, 34.0 (2C
each. sharp. PCMe, and P C M e , ) , 30.7. 30.5 ( 6 C each. CH, and CH;). 18.2 (1 C ,
PCH,P'j: "P N M R (121.5 MHz, -8OO.C): 6 = 63.5, 23.8 ("(PP) =17 Hz).
2 : A yellow solution of I (419 mg. 1.0 mmol) in pentane (25 mL), which was prepared at 0 ' C . was exposed to ethyne (100 mL. 4 minol) at -78°C. The reaction
mixture wxs stirred and warmed to - 5 S C Any 1 that had precipitated then
redissolved. The solution became dark, and a red precipitate of polyacetylene
formed. At - 78°C orange. rosette-shaped crystals form over the course of several
days, which were washed twice with ether at -78-C and dried under vacuum (oil
pump) at -30 C. Yield 220 mg (50 ''A). - Correct elemental analyses, m.p. 83 T ;
EI-MS (80 Cj. m:: = 440 ([MI', 2). 362 ([(dtbpm)Ni]+. 4). 78 ([C,H,]+, 100); IR
(KBr): 3060 (\,(=C-H)). 1748, 1585 cm-' (v(C=C); C,H,); ' H N M R (400 MHz,
-80 C ) , 6 = 5.95 (s. 6 H , C,H,). 1.58 ( 2 H , PCH,P), 1.24, 1.18 (each 18H,
C(CH,), and C(CH,);); "C N M R (75.5 MHz. -80°C): S = 92.0 (6C, 'J(CH) =
16X Hr. C,H,). 35.9 ( 2 C . PCMe,), 33.1 ( 2 C . P'C'Me,). 34.0, 32.2. 30.7 (2C each,
C ( C H , ) d . 30.8 (6C. C(CH,);), 15.6 ( I C . PCH,P); ' ' P N M R (121.5MHz.
- X O c ) .6 = 53.4. 19.1 (*J(PP) = 37 HZ).
Received: November 9, 1993 [Z 6487 IE]
German version: Angru.. Chern. 1994, 106, 908
Anxeii ~ ' h w 7 1171.
.
Ed. EngI.
1994. 33. N o . 8
(1:) b T H
[I] a) K.-R. Porschke, Y-H. Tsay. C. Kruger, Angew'. Chem. 1985, Y7.334; A n g r ~
Chcm. I n f . Ed. Engl. 1985,24,323; b) K.-R. Porschke. J. Am. Chem. SO<.1989.
111. 5691.
[2] a ) K.-R. Porschke, Y.-H. Tsdy, C. Kruger. Inorg. Chani. 1986. 25. 2097: b) K:
R. Porschke, R. Mynott. Z. Nuiurforsch. B 1987. 42, 421
[3] K.-R. Porschke, C. Pluta, B. Proft, F. Lutz, C. Kruger, 2. Nururforrrh. B 1993,
48, 608.
[4] H. H. Karsch, Z. Nuturforsch. B 1983, 38. 1027.
[5] a) P. Hofmann, L. A. Perez-Moya, M. E. Krause, 0. Kumberger. G. Muller,
Z. Nuturfbrsch. B 1990.45. 897; b) P. Hofmann, L. A. Perez-Moya, 0 Steigelmann. J. Riede, Or~unonirrullics1992, 11. 11 67.
[6] K . Fischer. K. Jonas. G. Wilke. Angew. Chem. 1973,85,620: Anjiew. Chern. /nt.
Ed. EngI. 1973. 12. 565.
[7] For comparison (Me,P)Ni(C,H,),: K.-R. Porschke. G. Wilke. R. Mynott.
Chenr. Ber. 1985. 118. 298.
[XI a) Crystal structure analysis of 1: C,,H,,NiP,. M , = 419.3 gmo1-l. crystal
dimensions 0.28x0.42 xO.53 mm. (I =13.471(1). h = 8.342(1). < ' =
21.504(2) A. /i =103.48(1)". V = 2350.0A3, pcdlcd
=1.18 gem-,.
=
9.65 cm-'. F(000) = 920 e. Z = 4, crystal system monoclinic, space group
P 2 , % (No. 14), Enraf- Nonius CAD-4 diffractometer. 1. = 0.71069 method
of measurement w - 28, 5882 measured reflections ( + h . + k .
I ) . [(sinfk
4,.,, = 0.65 k ' ,5360 independent and 4747 observed rellections ( / > 2 0 / ) .
217 relined parameters; heavy atom method. H atom positions calculated and
included in the least-squaresrefinement. R = 0.030. R, = 0 0 4 0 [ ~= l;u'(F,d].
maximum residual electron density 0.38 eA - 3 . b) Crystal structure analysis of
2: C,,H,,NiP,.
M , = 441.3 gmol-'. crystal dimensions 0.39 x 0.46 x
0.28mm. u=11.113(2). h=15.355(2), c = 1 4 . 1 5 4 ( 3 ) , /(= 93.84(2)",
V = 2409.9
pcalcd
= 1.22 gcrn-,,
= 24.35 c n - ' , 4 0 0 0 ) = 960 e. Z = 4.
crystal system monoclinic, space group, P 2 J n (No. 14). Enraf-Nonius CAD4 diffractometer, >. = 1.54178 A,method of measurement f,i - 20, 5508 mea] ~0.63
~ ~ k ' .4953 independent
sured reflections ( k h . + k . + I). [ ( ~ i n @ / J . =
and 4680 observed reflections ( I > 2uI), 259 refined parameters: heavy atom
method, positions of H1 -H6 were found and refined isotropically. the positions of the other H atoms were calculated and not included in the least-squares
refinement, R = 0.066, R, = 0.125 [ M = l/02(Fo)],maximum residual electron
density 1.04 e k 3 . Further details of the crystal structure investigation may be
obtained from the Fachinformationszentrum Karlsruhe. D-76344 EggensteinLeopoldshafen (FRG) on quoting the depository number CSD-57884. the
names of the authors, and the journal citation.
[9] The monoethene complex [(dtbpm)Ni(C,H,)] with dtbpm as a chelating ligand
can be prepared from 1 by a laborious procedure. This complex converts back
to 1 immediately upon treatment with ethene. This implies that bidentate coordination of dtbpni on the nickel(o) center with ethene as a coligand is possible
but high in energy. In contrast. activated alkenes acting as strong acceptors
Stabilize thechelatingcoordinationofdtbpm o n nickel(o)[S]. since they take up
the excess charge pushed onto the nickel(o) center by the two phosphorus
atoms.
[ 101 a) Uncomplexed benzene in the reaction mixture was evident in the ' H and ' ' C
NMR spectra. b) The mixed etheneiethyne complex [(q'-rBu,PCH,PtBu,)Ni(CH,=CH,)(HC=CH)] was isolated in crude form as an intermediate in the
displacement reaction at -78 "C and charactenzed by ' H a n d "P N M R spectroscopy. c) It was shown qualitatively ('H, "P N M R ) that the benzene complex 2 catalyzes the cyclotrimeriration of ethyne at - 50°C to give benzene. d)
For comparison [(fBu,MeP)Ni(C,H,),)] was prepared as a model compound
for 1 and treated with ethyne under the same conditions. The formation of
benzene was also observed, but a benzene complex analogous to 2 was not
found. Benzene is also formed as a side product in the synthesis o f the
bisfethyne) complexes [(R,P)Ni(HC=CH),] (R = Me, Et, etc.)[l b].
[ l l ] Upon warming to -30°C the red solutions of 2 turn yellow. According to the
"P N M R spectrum a number of compounds are formed, which have not yet
been identified.
[12] The 'H and " C N M R signals of [(C,H,)Cr(CO),] are shifted upfield from
those of uncompkxed benzene [d(H) =7.35: 6(C) = 129.0: J(CH) = 159 Hz];
this is explained by the increased charge density on the C atoms ;is a result of
backbonding. This is apparently accompanied by an increase in the s character
of the C - H bonds, which leads to a stronger coupling J(CH). R . Aydin. H.
Giinther, J. Runsink, H. Schmickler, H. Seel, Org. Mugn. Reson. 1980, 13,210.
[13] The corresponding distances in the Ni" complexes [ (C,F,),Ni(qb-toluene)]
[l3a] and [(C,F,),Ni(qb-mesitylene)][13b]
are considerably longer (1.693 and
respectively); moreover, the q6-bound six-membered rings are not
1.691
planar. a) L. J. Radonovich, K. J. Klabunde, C. B. Behrens, D P. McCollor,
B. B. Anderson. Inorg. C h m . 1980. 19, 1221; b) L. J. Radonovich, F. J. Koch,
T. A. Albright, ibid. 1980, f9. 3373.
[I41 a ) P . Hofmann, C. Meier. U. Englert. M. U . Schmidt. Chein. Ber. 1992, 125,
3 5 3 : b) P. Hofmann, H. Heiss, G. Muller, Z. Nuturforsch. B 1987.42, 395; c) P.
Hofmann, H. Heiss, P. Neiteler, G. Muller, J. Lachmann, Angcw. Chem. 1990,
102. 935; Angew. Chcn7. Int. Ed. Engl. 1990, 29. 880.
[15] SYBYL 6.0, Tripos Associates, Inc., St. Louis, MO. USA. C,H: Tripos
force field; P: F. Lutz, Dissertation. Universitat Wuppertal, 1993.
Minimization algorithm: BFGS. Convergence criterion' rms gradient
+
A.
A',
A.
Verlu~sgesellschaf!mhH. 0-69451 Weinhcrm, 1994
0570-0833/94i0808-0881 $ 10.00
+ .25:11
881
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<0.01 kcdlrnoi-’ k ‘ .
Nonbonded cutoff: 8 A. steric demands of the phosphorus lone pair were taken into account.
1161 Crystal dard (EDD investigation): C,,H,,P,, M , = 408.6 gmol-I, crystal dimensions 0.06 x 0.35 x 0.33 mm. u = 9.718(2). b = 10.423(2). c = 12.775(1) A,
z = 98.21(1).
[j = 96.84(1),
7 =105.23(1)’-,
V=1218.8 A’,
pE,I,td=
1.11 gcm-3, j t = I 2 1 cm-’. F(000) = 4 5 2 e , 2 = 2 , crystal system triclinic,
space group Pi (No. 2), Enraf-Nonius CAD-4 diffractometer, i= 0.71069 A.
method of measurement (1) - 2 8 , 68524 measured reflections ( & h . & k . t O .
[(sinO).:l.],,, =1.0 k ‘ .18953 independent (Ras= 0.05) and 8822 observed
reflections (f > 2 ~ 1 )428
. refined parameters; direct methods, H atom posttions found and included in the least-squares refinement, R = 0.060,
R, = 0.051 [bt =l/uz(Fo)]. maximum residual electron density 1.09 e k ’ .
[I71 K. Jonas, J Orgunomer. Chern. 1974, 78. 273.
[l8] a) R . Benn. R. Mynott. I. Topalovic. F. Scott. Orgunornefullics 1989. 8, 2299;
b) F. Scott. C. Kruger. P. Betz, J. Orgunomet. Chem. 1990, 387, 113.
1191 a) D. J. Brauer, C. Kriiger Inorg. Ci7rm. 1977. 16, 884; b) A. Stanger, Orgunometullits 1991, 10, 2979; c) A. Stanger. R. Boese, J Orgunomet. Chem. 1992.
430. 235; d ) R. Boese, A. Stanger, P. Stellberg. A. Shazdr. Angeir. Chem. 1993.
105, 1500: Angew. Chem. fnt. Ed. Engl. 1993, 32. 1475.
1201 See P. W. Jolly in Comprehensne Orgunomrtullic Chemivtrr, Vol. 8 (Eds.: G.
Wilkinson. F. G. A. Stone, E. W. Abel), Pergamon. Oxford, 1982, p. 649ff..
and references therein.
Kattrin Moller, Cornelia Bretzke, Heinrich
Huhnerfuss,* Roland Kallenborn, Jochen N. Kinkel,
Jurgen Kopf, and Gerhard Rimkus
Because of its ubiquitous nature and its relative persistence,
a-1,2,3,4,5,6-hexachlorocyclohexane
(3-HCH) plays an important role in most studies of the “fate” of organic pollutants in
marine and terrestrial ecosystems. In Western Europe its direct
application mixed with the insecticide p-hexachlorocyclohexane
Qj-HCH, lindane) is no longer permitted, but in other parts of
Europe, especially in eastern Europe, it may still be entering the
environment by way of such formulations. In the marine environment y-HCH is also transformed to a-HCH by marine microorganisms. The amounts involved are very low, but they may
be significant over longer periods of time.[’]
In the last two years, a-HCH has received additional attention
in process studies, because it is the only one of the eight possible
H C H isomers which is chiral, and can therefore be studied by
chiral gas chromatography. The cyclodextrin separation phases
which have recently been developed”] have made it possible to
distinguish between enzymatic and nonenzymatic degradation
processes.[31This method has been used to study the pathways
of microbial degradation of a-HCH in North Sea water, and its
[*I Priv.-Doz D r H. Huhnerfuss, Dipl.-Chem. K. Moller. Dr. R. Kallenborn
Institut fur Organische Chemie der UniversitPt
Martin-Luther-King-Platz6. 0-20146 Hamburg ( F R G )
Telefax: I n t . code + (40)4123-2893
C. Bretzke. Priv.-Doz. Dr J. Kopf
Institut f i r Anorganische und Angewandte Chemie
der Universitgt Hamburg ( F R G )
Dr. J. N Kinkel
Abt. FO REAG CHROM. E. Merck ( F R G )
D r G. Rimkus
Lebensmittel- und Veteriniruntersuchungsamt
des Landes Schleswig-Holstein (FRG)
[**I Chromatographic Separation of Enantiomers of Chirdl Organic Pollutants.
Part 7. This work was supported by the Ministry of Research and Technology.
Part 6: 141.
0 VCH Verlugsgesellscha/t mbH 0-69451 WPmheim, 1994
+I
Fig. 1. Comparison of chromatograms for
n-hexane extracts of blubber (left) and brain
tissue (right) from the harbor seal (Phocu
virulina). For experimental conditions see
Experimental Procedure.
The Absolute Configuration of
( + )-~-1,2,3,4,5,6-Hexachlorocyclohexane,
and Its Permeation through the
Seal Blood-Brain Barrier**
882
enzymatic degradation in marine and terrestrial organisms from
various trophic level^.[^-^] In the liver of the common eider
duck, for example, preferential degradation of (-)-a-HCH was
demonstrated.[6]
During analysis of brain tissue from the harbor seal (Phoca
vitulina) we encountered a surprising phenomenon. In brain
samples from eight Icelandic seals we detected almost exclusively ( +)-a-HCH (the values for the enantiomer ratio (+)-a-HCH/
(-)-a-HCH were 55.6. 66.2, and six values of 1OO:O; Fig. 1). In
H
3o 4o
t [min]
3o
5o
contrast, blubber tissue from the same animals yielded enantiomer ratios of only 1.2 to 1.4. This finding is especially interesting because of the widespread hypothesis that the bloodbrain barrier is also partially effective towards certain
fat-soluble organic pollutants. The “blood- brain barrier” is
normally understood as mechanisms which greatly inhibit the
transport of non -lipid-soluble substances such as proteins from
blood vessels into the surrounding interstitial nervous system
tissue (glia) and the capillary endothelium. These mechanisms
thus ensure a constant environment for the neurons.[71The respiratory gases carbon dioxide and oxygen, however, can cross
the capillary walls with ease. The exact mechanisms involved,
especially for the selective inhibition of entry for certain lipidsoluble pollutants into the brain tissue, still require more detailed study. Whether the barrier effect is enhanced by enzymes
in the endothelial cells (enzyme barrier) also still appears controversial.
Concentrations of polychlorinated biphenyls (PCBs) in brain
tissue have been found to be a factor of ten lower than those
found in other organs of the same animals.[*]This well-known
effect is also often ascribed to the influence of the blood-brain
barrier. Other authors, however, have shown that a-HCH is
accumulated very efficiently in the brain tissue of mice and
rats[’] and of fur seals.[’’] The brain samples from ratscga1
and
two of the fur seal samples[’’] also revealed the first indications
of preferential accumulation of (+)-a-HCH. The systematic investigation of eight Icelandic seals carried out in the present
study shows that this phenomenon can obviously be generalized, at least for the less pollutant-exposed Icelandic animals. In
addition, our studies show that as for the PCBs, y-HCH is
present at much lower concentrations in the brain samples than
in other organs of the same animals. Such extreme concentration differences between p-HCH and a-HCH, when comparing
values from brain and other organs, have also been reported by
Mossner et al. for fur seals.“01 However, these results are difficult to reconcile with our previous experience with enzymatic
and nonenzymatic degradation processes for H C H isomers. We
therefore interpret the enantioselective enrichment of (+)-aHCH in seal brain tissue less as the result of enzymatic degrada-
0570-08331941080R-08R2$ I0 00+ 2510
Angen Chem Inr Ed Engl 1994. 33, N o R
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