Novel diphosphetene derivatives by reactions of di(isopropyl)aminophosphaethyne with chalcogens or halogens

Article abstract of DOI:10.1016/S0040-4020(99)00769-3

The 1λ³σ²,3λ⁵σ⁴-diphosphetene derivatives 6a, 6b are formed in quantitative yields by reactions of di(isopropyl)aminophosphaethyne 1a with sulphur and selenium, respectively, at 25°C. 6a is also produced slowly from 1a and CS₂. The tert-butylphosphaalkyne P?C-tBu (1b), however, does not react with sulphur or selenium, but undergoes a slow reaction with CS₂ to give the five-membered heterocycle 3,5-di-tert-butyl- 1-thia-2,4-diphosphole as one of the main products. Halogenation of 1a using SO₂Cl₂, Br₂ or I₂ as reagents leads to the 1λ³σ²,3λ³σ³-diphosphetenium salts 9a-9c. X- ray diffraction studies of 6a and 6b prove that the easy formation of the four-membered diphospha-heterocycles is obviously governed by electronically delocalized phosphaallyl units within the unsaturated rings.

Full text of DOI:10.1016/S0040-4020(99)00769-3

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 27–33
Novel Diphosphetene Derivatives by Reactions of
Di(isopropyl)aminophosphaethyne with Chalcogens or Halogens†
*
Joseph Grobe, Duc Le Van, Torsten Pohlmeyer, Franz Immel, Heike Pucknat,
¨
Bernt Krebs, Joachim Kuchinke and Mechtild Lage
¨
¨
¨
¨
Anorganisch-Chemisches Institut der Westfalischen Wilhelms-Universitat Munster, Wilhelm-Klemm-Strasse 8, D-48149 Munster, Germany
Received 15 March 1999; accepted 10 May 1999
Abstract—The 1l3s2,3l5s4-diphosphetene derivatives 6a, 6b are formed in quantitative yields by reactions of di(isopropyl)aminophos-
phaethyne 1a with sulphur and selenium, respectively, at 25ЊC. 6a is also produced slowly from 1a and CS2. The tert-butylphosphaalkyne
PxC–tBu (1b), however, does not react with sulphur or selenium, but undergoes a slow reaction with CS2 to give the five-membered
heterocycle 3,5-di-tert-butyl-1-thia-2,4-diphosphole as one of the main products. Halogenation of 1a using SO2Cl2, Br2 or I2 as reagents leads
to the 1l3s2,3l3s3-diphosphetenium salts 9a–9c. X-ray diffraction studies of 6a and 6b prove that the easy formation of the four-membered
diphospha-heterocycles is obviously governed by electronically delocalized phosphaallyl units within the unsaturated rings. ᭧ 1999 Elsevier
Science Ltd. All rights reserved.
Introduction
3. Oxidation of 1a by air in the presence of catalytic
amounts of CuCl unexpectedly yields the 1l3,3l5-
diphosphetene derivative 3.9 Structural investigations
of the resulting phospha-heterocycle have shown, that
3 like 2 contains a conjugated phosphaallyl system in
the four-membered ring.10 In addition, 3 can be
described as a compound isolobally related to the
rare binuclear complexes 4.11 Again, this surprising
reaction of 1a with oxygen was not observed for the
phosphaalkynes PxC–R. On the other hand, a remark-
able analogy to the formation of 3 was found by
Becker and coworkers12 for the p-donor substituted
diphosphetenes 5a, 5b produced from the l3-phos-
phaalkyne PxC–OLi(dme)2 with sulphur and selenium,
respectively.
Phosphaalkynes of the type PxC–R (e.g. RˆtBu, Ad, Mes)
serve as valuable synthetic tools in organophosphorus
chemistry,1,2 in particular, with respect to the preparation
of saturated or unsaturated compounds with ring or cage
structures.3,4 Replacement of the alkyl or aryl substituent
R at the sp-hybridized carbon atom by an amino group
NR2 with a strong ϩM effect leads to considerable changes
in reactivity and opens additional synthetic possibilities.5 In
quite a number of reactions carried out under similar condi-
tions and with analogous partners aminophosphaalkynes
give rise to other products than PxC–R precursors. Some
typical experimental results are presented here as examples:
1. The reactions of PxC–R and PxC–N(iPr)2 (1a),
respectively, with 2,4,6-tri-tert-butyl-1,3,5-triphospha-
benzene, in general, yield 1,3,5,7-tetraphosphabarrelene
derivatives for RˆtBu or iPen, whereas with 1a the
1,3,4,7-tetraphosphasemibullvalene valence isomer with
RˆN(iPr)2 is formed in quantitative yield.6
2. 1a reacts with methylating agents like CH3I or
CH3OSO2CF3 to give the 1l3,3l3-diphosphetenium
cation 2 with a stable phosphaallyl building unit.7
PxC–R compounds do not react in a similar manner.
Becker et al.,8 however, have shown that PxC–tBu
(1b) adds bromine to the triple bond followed by
cleavage of the resulting PC single bond giving PBr3 as
one of main products.
Keywords: phosphaalkynes; 1,3-diphosphetenes; 1-thia-2,4-diphosphole.
* Corresponding author. Tel.: ϩ49-251-83-36098; fax: ϩ49-251-83-
36012.
†
Reactive EyC-(p–p)p Systems. 49. Part 48: Ref. 6.
0040–4020/00/$ - see front matter ᭧ 1999 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(99)00769-3

28
J. Grobe et al. / Tetrahedron 56 (2000) 27–33
Scheme 1.
The deviating reactivity of aminophosphaalkynes from the
broadly studied behaviour of the alkyl and aryl analogues
led us to investigate the reactions of PxC–N(iPr)2 (1a) with
chalcogens and halogens in some detail. Here we report on
the interesting results.
l5s4 P-atoms at dˆ86.8 (6a) and dˆ53.6 (6b). The corre-
2
sponding J(P,P) coupling constants amount to 18.2 (6a)
and 22.4Hz (6b), respectively, and thus are in accord with
the data of 2,7 3,9 and 4.11 The high-field resonance of 6b is
accompanied by characteristic 77Se satellites with
1J(P,Se)ˆ688.0Hz. This value was confirmed in the 77Se
NMR spectrum at dSeˆ185.3. The crystal structure analyses
of 6a and 6b are in excellent agreement with the NMR data
and verify the conclusion that both chalcogen atoms are
bound to only one of the phosphorus atoms in the four-
membered ring (Fig. 1).
Reaction of PxC–N(iPr)2 (1a) with Chalcogens
1a reacts at room temperature in CS2 solution with one
equivalent of sulphur or selenium to give the diphosphetene
derivatives 6a, 6b within 2–3h in quantitative yields. They
can be isolated in the form of yellow orange crystals
(Scheme 1). The analogous reaction with tellurium in CS2,
however, was unsuccessful, but after several days at 25ЊC
formed the sulphur containing diphosphetene 6a as the only
product indicated by the characteristic 31P and 13C reso-
nances showing up in the mixture besides the signals of
unreacted 1a. Obviously a slow reaction takes place
between 1a and CS2 as the source for sulphur. A separate
experiment with 1a in CS2 confirmed this result with the
additional information that—as expected—the reaction
with the dissolved sulphur is much quicker.
In both structures the 1l3,3l5-diphosphetene skeleton is
nearly coplanar with the NC2 fragments of the amino sub-
stituents. The units PS2 and PSe2, respectively, are arranged
perpendicularly to the skeleton plane. The angles SPS and
SePSe amount to 121.16(3) and 121.39(7)Њ, respectively.
The electronic structure of the PX2 fragments (XˆS, Se)
provides for a fairly uniform charge distribution and leads
to only small differences of the PS (6a) and PSe (6b)
distances, which correspond very well to literature data13
˚
for thio- or seleno-phosphoranes R3PyX [XˆS: (1.954A);
ء
14
˚
˚
Se: (2.093A)], and also for Mes P(yS)2 (1.90A) or the
diselenophosphorane derivative Ph3PyC(Ph)–P(ySe)2
15
˚
[2.079(2) and 2.081(2)A] (see Table 1).
Composition and constitution of the novel compounds 6a
and 6b have been determined by NMR [1H, 13C, 31P, 77Se
(6b)] and mass spectra, and finally proved by X-ray diffrac-
5
4
˚
Whereas the l s PC distances of 1.804–1.841A are in the
range of PC single bonds, the l3s2 PC bond lengths of
1.769–1.783A indicate a bond order Ͼ1 and so considerable
1
tion analyses of 6a and 6b. For both derivatives the H and
13C NMR spectra reveal the non-equivalence of the N-iso-
propyl groups due to hindered rotation of the N(iPr)2 substi-
tuents around the (P)C–N bond. The 31P{1H} NMR spectra
show two doublets of a typical AX spin system expected for
1l3,3l5-diphosphetenes. The resonances of the l3s2 phos-
phorus atoms are detected at low field (6a: dˆ96.9; 6b:
dˆ92.1) and do not differ strongly from the values of the
˚
double bond character. The mesomeric contribution of the
lone pair of electrons on the N(iPr)2 substituents shows up
both in the planar structure of the NC3 units (sum of bond
angles: 359.92 and 360.01Њ) and in the drastic shortening of
˚
the C1–N1 and C2–N2 distance (1.287–1.303A) reaching
˚
almost the typical double bond length of 1.27A. The
Figure 1. Molecular structure of 6a.

J. Grobe et al. / Tetrahedron 56 (2000) 27–33
Table 1. Selected bond lengths (A) and angles (degrees) for 6a (EˆS) and 6b (EˆSe)
29
˚
Bond lengths
6a
6b
Angles
6a
6b
79.2(3)
111.4(2)
113.1(2)
113.3(2)
110.9(2)
121.4(7)
82.4(3)
P(1)–C(1)
P(1)–C(2)
P(2)–C(1)
P(2)–C(2)
P(1)–E(1)
P(1)–E(2)
N(1)–C(1)
N(1)–C(3)
N(1)–C(6)
N(2)–C(2)
N(2)–C(9)
N(2)–C(12)
1.839(2)
1.839(2)
1.783(2)
1.777(2)
1.9557(6)
1.9536(6)
1.299(2)
1.497(2)
1.496(2)
1.303(2)
1.493(2)
1.497(2)
1.829(6)
1.841(5)
1.782(6)
1.769(5)
2.109(2)
2.109(2)
1.302(7)
1.497(6)
1.496(6)
1.300(6)
1.491(7)
1.512(7)
C(1)–P(1)–C(2)
C(1)–P(1)–E(1)
C(1)–P(1)–E(2)
C(2)–P(1)–E(1)
C(2)–P(1)–E(2)
E(1)–P(1)–E(2)
C(1)–P(2)–C(2)
P(1)–C(1)–P(2)
P(1)–C(1)–N(1)
P(2)–C(1)–N(1)
P(1)–C(2)–P(2)
P(1)–C(2)–N(2)
P(2)–C(2)–N(2)
79.62(7)
111.28(5)
113.27(5)
113.12(5)
111.02(5)
121.16(3)
82.82(7)
98.66(7)
99.2(3)
127.67(11)
133.64(11)
98.90(8)
127.56(12)
133.54(12)
127.6(4)
133.2(4)
99.2(3)
126.8(4)
134.1(4)
bonding situation in 6a, b obviously corresponds to that in
derivatives 2–4, i.e. it is determined by the electronically
stabilized structural unit NCPCN and can be rationalized
by the mesomeric forms A to C (Scheme 2). A very
similar description applies to the 1l3,3l5-diphosphetenes
5a, b.12
over yellow to red. Complete reaction of 1b was observed
within 3days yielding a mixture of products. The main
component (25%, relative to 1b) was characterized by 31P
and 13C NMR spectra to be the known 3,5-di-tert-butyl-1-
thia-2,4-diphosphole 8.16 The NMR control experiments
have also shown that at the beginning of the reaction 8 is
the only detectable product and that the composition of the
reaction mixture does not change if sulphur or selenium is
added to the CS2 solution.
31PNMR control measurements during the preparation of
6a, b only in case of the reaction of 1a with selenium
pointed to an intermediate which was quickly transformed
to 6b. Immediately after the start of the reaction two AX
Consequently, the sulphur necessary for the formation of 8
has to be supplied by the solvent CS2. A possible, but
not established pathway is presented in Scheme 3. The
frequently postulated, but so far not detectable thiocarbonyl
phosphinidene [:P–C(yS)tBu] could well be one of the
highly reactive intermediates.17
2
doublets at dPˆ129.8 and 124.6 with J(P,P)ˆ33.4Hz were
detected in the 31PNMR spectrum in addition to the reso-
nances of 1a and 6b. A plausible explanation for this result
is the formation of the monoseleno diphosphetene 7.
Because of the fast following reaction leading to 6b this
intermediate could not be isolated even in a further reaction
of 1a with only 0.5 equivalents of selenium. 7 can be
considered as product of a formal [2ϩ2] cycloaddition of
1a with the first step intermediate [SeyPxC–N(iPr)2]. A
similar sequence of steps can be assumed for the analogous
formation of the sulphur compound 6a.
The difference in reactivity of 1a and 1b with CS2 (1a!6a;
1b!8) can be attributed to the distinct polarity of the PxC
bond. While the charge distribution in PxC–tBu is mainly
determined by the electronegativity values of carbon (2.5)
and phosphorus (2.1), the aminophosphaalkyne 1a exhibits
a polarity strongly influenced by the delocalization of the
lone pair of electrons on nitrogen into the p-system
resulting in a large contribution of the zwitterionic form
B (Scheme 4) to the electronic ground-state of the
molecule.5a Therefore, an inverse attack of one of the
sulphur atoms of CS2 on the PxC fragment in 1a or 1b
seems plausible.
To elucidate the influence of the p-donor substituent NR2 on
the reactivity of aminophospha-ethynes with chalcogens the
related reactions of tert-butylphosphaethyne 1b are of par-
ticular interest. In order to avoid problems which could be
caused by the reactivity of CS2, benzene was used as solvent
for the experiments with sulphur or selenium. Neither at
25ЊC nor by heating the reaction mixture at 70ЊC for several
hours an attack of the phosphaalkyne 1b by the chalcogens
could be detected. Even the addition of triethylamine to
activate the degradation of the S8 molecules was unsuccess-
ful. On the other hand, 1b reacts with CS2 already at room
temperature indicated by a colour change from colourless
Reaction of PxC–N(iPr)2 (1a) with Halogens
The addition of SO2Cl2, Br2 or I2 to 1a, in general, produces
the corresponding diphosphetenium cations 9a–9c in good
Scheme 2.

30
J. Grobe et al. / Tetrahedron 56 (2000) 27–33
Scheme 3.
Scheme 4.
considerably smaller than those of the related 2,4-bis(tri-
phenylphosphoranediyl)-1,3-diphosphetenium salts18 (ca.
120Hz).
The formation of 9a–9c occurs so quickly that intermedi-
ates on the way to the final products could not be detected by
NMR spectroscopy. Two possible pathways are considered
in Scheme 6. In the first step the addition of X2 to the
aminophosphaethyne leads either to a cis/trans mixture of
the corresponding 1,2-dihalogenophosphaalkenes 10 (as
reported for 1b) or by heterolytic cleavage of X2 at the
positive ammonium center of form B (Scheme 4) to an
electrophilic attack of Xϩ at the negatively charged P-
atom to give intermediates of type 11. For the next step a
formal [2ϩ2] cycloaddition of 10 or 11 with 1a is
suggested, furnishing either the heterocyclic systems 12 or
the final products 9. In the case of 12 dissociation of XϪ is
necessary, but conceivable under the p-donor effect of the
(iPr)2N group. Pathways according to Scheme 6 gain
support from the fact that phosphaalkenes are known to be
reactive partners in [2ϩ2] cycloaddition reactions of
phophaalkynes forming 1,2-dihydro-1,3-diphosphetes.5c,19
Since 1a spontaneously reacts with methylating agents
like CH3I or CH3OSO2CF3, affording the diphosphetenium
salts 2,7 we favour the shorter route 1a!11!9 as the more
likely sequence.
yields. The complete degradation with formation of PX3,
which is observed for PxC–tBu (1b), is of some importance
only in case of the chlorination of 1a (Scheme 5).
In contrast to the chlorinated derivative 9a, compounds 9b
and 9c are stable at room temperature even in chloroform or
dichlormethane solutions and have been characterized by
multinuclear NMR and mass spectroscopic investigations.
Very probably, 9a decomposes by following reactions with
SO2Cl2 yielding a complex mixture of products and, there-
fore, could not be isolated. One of the decomposition
products is PCl3.
Similar to the diphosphetenium derivatives 2 the salt-like
compounds 9a–9c generally show two doublets of the AX
spin system in the 31P{1H} NMR spectra. The signals of the
l3s2 phosphorus atom of the iodine compound 9c
(dPˆ192.2) are shifted to low field as compared to the chlor-
ine or bromine systems 9a (dPˆ123.4) or 9b (dPˆ123.2).
On the other hand, the dP-values of the l3s3 P-atoms vary
only in a small range as a function of X (dPˆ62.3–90.4).
In conclusion, the work presented in this paper is a valuable
contribution both to the chemistry of unsaturated four-
membered diphospha heterocycles, especially to the rare
2
The J(P,P) coupling constants amount to 23.1–54.0Hz and
thus are larger than in the derivatives of type 2, but
Scheme 5.

J. Grobe et al. / Tetrahedron 56 (2000) 27–33
31
Scheme 6.
representatives of 1l3,3l5-diphosphetenes, and to the class
of cyclic phosphaallyl cations. It clearly demonstrates the
differences in reactivity between alkyl- and amino-substi-
tuted phosphaalkynes induced by the R2N p-donor.
[d, 3J(P,C)ˆ14.4Hz, CH], 209.1 [dd, 1J(P,C)ˆ60.0 and
44.0Hz, PyC]. 31P{1H} NMR (C6D6, 25ЊC): dˆ86.8 [d,
EI-MS (70eV, selected), m/z (%): 350 (54) [Mϩ], 318 (4)
[MϩϪS], 307 (5) [MϩϪCH(CH3)2], 286 (100) [MϩϪ2S].
C14H28N2P2S2 (350.44): calcd. C 47.98, H 8.05, N 7.99;
found C 48.06, H 8.13, N 7.73.
2
2J(P,P)ˆ18.2Hz, l5 P], 96.9 [d, J(P,P)ˆ18.2Hz, l3 P].
Experimental
General
1,1-Diselenoxo-2,4-bis(diisopropylamino)-1,3-diphos-
phetene (6b). 1H NMR (C6D6, 25ЊC): dˆ1.21
3
3
[d, J(H,H)ˆ7.1Hz, 12H, CH3], 1.34 [d, J(H,H)ˆ7.1Hz,
All experiments were carried out under argon (or by using a
standard vacuum line) in anhydrous solvents. Reaction
vessels were either Schlenk flasks or ampoules with several
break seals and an NMR tube. Solvents and deuterated
compounds for NMR measurements were carefully dried
and degassed. NMR: Bruker AC 200 (200.13MHz, 1H, stan-
dard: TMS; 50.32MHz; 13C, standard: TMS; 81.02MHz;
31P, standard: 85% H3PO4), Bruker AM 360 (68.68MHz;
77Se, standard: (CH3)2Se). MS: Model CH 5 MAT Finnigan.
Elemental analyses: Perkin Elmer CHN-Analysator 240.
The phosphaalkynes PxC–N(iPr)2 (1a),20 PxC–tBu (1b)21
were prepared according to the literature.
3
4
12H, CH3], 3.70 [dsept, J(H,H)ˆ7.1, J(P,H)ˆ2.7Hz, 2H,
3
4
CH], 5.35 [dsept, J(H,H)ˆ7.1, J(P,H)ˆ2.5Hz, 2H, CH].
13C{1H} NMR (C6D6, 25ЊC): dˆ18.8 (s, CH3), 19.5
[d, 4J(P,C)ˆ8.1Hz, CH3], 51.3 [d, 3J(P,C)ˆ7.1Hz, CH],
59.0 [d, 3J(P,C)ˆ15.4Hz, CH], 199.1 [dd, 1J(P,C)ˆ61.8
and 29.4Hz, PyC]. 31P{1H} NMR (C6D6, 25ЊC): dˆ53.6
[ddSe, 2J(P,P)ˆ22.4, 1J(P,Se)ˆ688.0Hz, l5 P], 92.1
[d, 2J(P,P)ˆ22.4Hz, l3 P]. 77Se NMR: 185.3
1
[d, J(P,Se)ˆ687.0Hz]. EI-MS (70eV, selected, based on
80Se), m/z (%): 446 (26) [Mϩ], 366 (12) [MϩϪSe], 286
(100) [MϩϪ2Se], 223 (11) [(Pr2NCPSeϩ]. C14H28N2P2Se2
(444.24): calcd. C 37.85, H 6.35, N 6.31; found C 37.99, H
6.31, N 6.29.
General procedure for the preparation of the 1l3,3l5-
diphosphetene derivatives 6a, b
General procedure for the preparation of the 1l3, 3l5-
diphosphetenium salts 9a–9b
36.5mg (1.14mmol) sulphur or 90.0mg (1.14mmol)
selenium were placed in an ampoule with break seals and
an NMR tube together with 5mL CS2. 160mg (1.12mmol) of
di(isopropyl)amino-phosphaethyne 1a were then introduced
by vacuum condensation at Ϫ196ЊC. On warming up to
room temperature the mixture was continuously stirred
and afterwards transfused into the NMR tube. NMR
measurements at 25ЊC indicated a complete reaction of 1a
and the quantitative formation of the 1l3, 3l5-diphosphe-
tene derivatives 6a or 6b after 2–3h. After evaporation of
the solvent in vacuo, 6a or 6b was obtained as an orange red
powder (6a: 372mg, 1.06mmol, 95% yield; 6b: 462mg,
1.04mmol, 93% yield). Crystals of 6a or 6b were obtained
on cooling the pentane solution at Ϫ30ЊC. Their quality was
sufficient for a single crystal X-ray structure analysis.
To a solution of 0.5mmol SO2Cl2 or the halogens (Br2, I2) in
dichloromethane (2mL), prepared in an ampoule with break
seals and an NMR tube, 145mg (1.0mmol) di(isopropyl)-
aminophosphaethyne 1a were added by vacuum condensa-
tion at Ϫ196ЊC. The mixture was stirred during a warming-
up period of ca. 1h to reach room temperature. NMR control
measurements indicated a complete consumption of 1a and
the formation of the corresponding 1,3-diphosphetenium
salts 9a–9c. In case of 9a some side products (e.g. PCl3)
were detected by 31P NMR measurements. After evapora-
tion of the solvent in vacuo and recrystallization (from
acetonitrile or toluene), 9b and 9c were obtained as pale
yellow powders (9b: 124.8mg, 0.28mmol, 56% yield; 9c:
167.3mg, 0.31mmol, 62% yield). Due to the air and mois-
ture sensitivity of 9b and 9c reliable analytic data could not
be obtained. However, their identity was proved by the
NMR and MS data including the simulation of isotopic
patterns. This is exemplified for 9b by comparison of
measured and calculated intensities for the overlapping
1,1-Dithioxo-2,4-bis(diisopropylamino)-1,3-diphosphe-
1
tene (6a). H NMR (C6D6, 25ЊC): dˆ1.0–1.5 (m, 24H,
CH3), 3.7 (m, 2H, CH), 5.2 [dsept, 3J(H,H)ˆ7.0,
4J(P,H)ˆ2.0Hz, 2H, CH]. 13C{1H} NMR (C6D6, 25ЊC):
dˆ20.1 (m, CH3), 51.0 [d, 3J(P,C)ˆ7.9Hz, CH], 60.5

32
J. Grobe et al. / Tetrahedron 56 (2000) 27–33
EI-MS (70eV, selected), m/z (%): 413 (10) [MϩϪI], 286
(13) [MϩϪ2I], 243 (2) [MϩϪ2I-C3H7], 143 (4) [iPr2NCPϩ],
128 (100) [iPr2NCPϩϪCH3].
Table 2. Crystallographic data and parameters of the crystal structure
determinations
Compound
6a
6b
Empirical formula
Fw
C14H28N2P2S2
350.44
C14H28N2P2Se2
444.24
X-Ray structural analyses of 6a, 6b
Crystal size (mm)
Crystal system
Space group
0.23×0.20×0.26
Monoclinic
P21/n
10.635(2)
13.081(2)
14.919(3)
108.53
1967.9(6)
4
1.183
0.427
752
173(2)
10–17
0ՅhՅ13
0ՅkՅ16
Ϫ19ՅlՅ18
4528
0.20×0.22×0.25
Monoclinic
P21/n
10.635(2)
13.081(2)
14.919(3)
108.53
1967.9(6)
4
1.499
3.914
896
153(2)
10–17
0ՅhՅ12
0ՅkՅ15
Ϫ17ՅlՅ16
3388
Single crystals of good quality were obtained by crystal-
lization from pentane solution. X-ray data of 6a and 6b
were collected with a Syntex P21 diffractometer (Mo Ka
radiation); structure solution by direct methods (shelxs-
8622) and structure refinement by shelxl-93.23 Crystallo-
graphic data are given in Table 2. Data for the structures
reported in this paper have been deposited with the
Cambridge Crystallographic Centre as supplementary
publication no. CCDC-136868 (6a) and -136869 (6b)
and can be obtained free of charge on application to
The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: int.codeϩ(1233)336-033; e-mail:
teched@chemcrys.cam.ac.uk).
˚
a (A)
˚
b (A)
˚
c (A)
b (Њ)
V (A )
3
˚
Z
rcalcd (g cmϪ3
)
m (mmϪ1
F(000)
)
Temperature (K)
u (degrees)
Index ranges
No. of reflns measd
No. of indep rflns with IϾ2s(I) 3448
1829
No. of parameters
R1 (obs. data)
wR2 (obs. data)
R1 (all data)
293
0.0319
0.0841
0.0410
0.0866
1.024
ϩ0.353/Ϫ0.337
181
0.0407
0.0749
0.0831
0.807
0.807
ϩ0.763/Ϫ0.379
Acknowledgements
The authors are grateful to the Deutsche Forschungs-
gemeinschaft and the Fonds der Chemischen Industrie for
financial support.
wR2 (all data)
GooF on F2
Ϫ3
˚
Resid. electron density (eA
)
peaks [Mϩ]/[MϩϪH] as well as for the basis peak
[MϩϪBr].
References
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2
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¨
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3
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¨
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¨
¨
¨
¨