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Bis(diisopropylamino)carbene.

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(quantitativc yield. eluent. CH,CI,,EtOH IOOjl to 1OO/S v p ) . [tCu]+BF:
(C,,,,H,,,N,O,,CuBF)- dark brown-red solid. FAB-MS : m / z : 1793.5 (calc. for
[ICu]': 1793 54). XY7.3 (calc. for [ l C u ] + H t : 897.2): ' H N M R (CD,CI,.
4
400 MHI): 6 = 9.97 (a. 2H,j. 8.26 (d. 2H,. J 2 8 . 3 Hz). 8.19 (d. 2Hk. J ~ 8 . Hz),
8.06(d.2H-. J:8.3 Hz),8.01 ( d , 2 H 5 , J z 8 . 7Hz),7.90(d.4H,,5=8.8 Hz),7.82(d,
2H,, JrX 7 H L ) . 7 74 (d, 2H;. 5-8.4Hz). 7.72 (AB, 4H;,,. J - 8 . 8 Hz), 7.56 (d.
2H,. ,128.2 H I ) . 7.13 (d, 2H,, 528.3 Hz), 6.96 (d, 4H,. 5-8.7 Hz). 6 91 (t, ZH,,
5-7.6 HL). 6.77 (d. ZH,,. 5-7.7 Hzj. 6.71 (d. 2Hh. 5-7.7 Hzj. 6.69 (d. 2HH.
5-8.4 HL). 6.11 (d. 2H,. 5 - 8 3 Hz). 5.77 (d, 4H:. 5-8.8 Hz), 5.52 (d. 4H,,
5-8.5 H L ~4.15
.
2.41 (m, 48H. OCH,CH,O)
Complete demetalation of [lCu]' : [ICuI'BF; (37 mg. 0.02 mmol) dissolved In
CH,CN (30 m L ) wxb treated with aqueous KCN (1.00 g, 15.3 mmol in 20 mL H,O)
at 80 C lor 24 h. The dark brown coloration of the initial solution faded progressibcly to hc p;ile yellow at the end. After evaporation of the solvents, the crude
product \+'is taken tip in CH,CI,:H,O and decanted. After elimination of excess
KCN (waahing ortheorgmic layer three times with H,O). a filtration through silica
(eluent c'H,CI2 McOH 100:5j afforded [IHH]'+(BF;), (33 mg, ca. 0.02 mmol.
quantitative yield). which can be converted to 1 by treatment with aqueous K,CO,.
1: c',08Hv,,NxO~4.
P ; l l ~yellow glass. ES-MS : I P I / Z : 1731.14, 1731.94, 865.85 ( c d k
for [IH] ' and I I H H ] ' . respectively- 1731.00. 1732.01. and 866.00, respectively):
' H NMR (c'D2c'12.200 MH/j. = 8.77 (dd. 4H,. 527.7. I 4 Hz), 8.71 (s. 2HJ.
, Xz jH. 8,. .0 9
X.37id.4H3..I : X ~ H ~ ~ . X . ? ~ ( ~ . ~ H , . J = ~ . ~ H Z ) . X . 5I 2~ 8( .~6 H
id. 4H,. J:8.3 H / ) . 7.90 (d, 4H,. 5 2 8 5 Hz). 7.68 (I,2Hc. 5 2 7 . 7 Hzj, 7.55 (AB,
XH, (,. J:X.X HL). 0 YX (d. XH,. 5-83 Hz). 4 25 (t. 8H,. J s 5 . 5 Hz). 3 82-3.60
(in. 40H. Oc'H,CHIOt
[lCuAgl"(BF;j,:
To a solution of [ICul'BF; (46mg. 0.024mmol. in lOmL
CH2C12jwas added ii large excess of AgBF, dissolved in C,H, (10 mL. 30 mg,
0.153mmol) at rooin temperature. After the mixture had been stirred at room
teinperalurc overnight ;I dark green precipitate was formed (oxidation of Cu' to Cu"
hy exceaa d v e r d t ) . Upon addition of water (10 mL) the latter copper(i1j complex
wiis easil) reduced and [ICuAg]' '(BF,),
was isolated pure after decantation,
washing the organic layer with H,O, drying over MgSO,. and recrystallization from
C,,H, C'H,C'I, (qu.intitativc yield. 50 mg 0.024 mmol) [ I C L I A ~ ] ~ + ( B F ; ) , .
C,,,,H,,.N,O,,Cu.~~.?BF,): dark red needles. FAB-MS: in/;: 1986.4 (calc. for
[ICuAg]"BF;19X5.X). 1791.5 (calc. for [ICu]': 1791.9) and 949.7 (calc. for
[ICuAg]' . 950.0).' H NMR (CD,CI,, 400 MHz): 6 = 9.77 (s,2H,,), 8.45 (d. 2H;.
Js8 3 H I ) . 8.40 (d. ?H-. 5-8.3 Hz), 8 29 (d. 2Hk. 5 - 8 3 Hz). 8 15 (d. 2H;,
5 ~ 8 . HI).
8 7.99(d. 7H<,,5-8.8 Hz). 7.93 ( ~ . 4 H , , ~ j . 7 . 7 2 ( d . 2 H
5-8.2
~ , Hz). 7.67
(d.2H,.J:X.3H1).7~12(d.2H,.Jr8.3H~j.7.30(t.2H,.J=77Hz),7.16(d.4H~~,
5-8.6 H r ) . 7 07 (d. 4H,,. 5 2 8 . 8 Hz). 7.02 -7.05 (m. 2H, +ZHL). 6.76 (d. 2H;.
J z X . 3 HI). 6.32 (d. 2H,. 5-8.4 Hz). 5.84 (d, 4H,,, J: 8.6 Hz), 5 68 (d. 4H,.
J-X.5 H r ) . 4 2 0 . 2 80 (m. 48H. OCH,CH,O).
'
[ICuZn]"(BF;),. %n(NO,),.6H,0(20mg. 0.067mmol) and [lCu]+BF; (16mg.
0.008 mrnol) were mixed and dissolved in CHzCIz (10 mL) at room temperature:
[ICuZn].' ' . which was poorly soluble in CH,CI, as NO; salt, precipitated readily
as a brown solid. Alter subsequent anion exchange by addition of a large excess of
NdBF, 10 the suspension. thecomplex [ICuZn]"(BF:),
was obtained in CH,CI,.
(quantitative
A pure sninple wiis obtained by recrystallizlition from C,H,!CH,CI,
yield. 18 mg: 0.00X mmol).
[ICuZn], ' (BF; j J . C,,,,H,,N,O,,CuZn,3BF,.
brown-orange needles. FAB-MS:
2030 4 (calc.for [ICuZnj3+(BF; jz: 2029.8), 971 2 (calc.for [lCuZn]'+(BF;):
971 5) xnd 17Y1.4 (calc. for [ICu]': 1791.9); ' H N M R (CD,CI,. 400MHz): b
= 9.06 (a. ?Ha). 8 84 (d, 2Hq. J 2 8 . 4 Hz), 8.48 (d. 2H,, 5-8 4 Hz). 8.35 (d. 2H,,
[6] Characterization of the compounds: see Experimental Proccdure
[7] E.C. Constable. J. Walker, J Chem Suc. f h m r . Comm. 1992. 884; E. C. Constable, A. J. Edwards. P. R. Raithby. J. Walker. Angrit.. Chern. 1993, 105. 1486,
Angels. ChPm. Int. Ed. EngI. 1993. 32, 1465.
[8] C. Piguet, G. Hopfgartner, B. Bocquet, 0 . Schaad. A. Williams. J. Am. Chem.
Soc. 1994, 116,9092.
[9] C. 0. Dietrich-Buchecker. J.-P. Sauvage. J.-M. Kern, J. hi.Chern So(,. 1989.
111. 7791.
[lo] A. K. I. Gushurst, D. R. McMillin. C. 0. Dietrich-Buchecker. J.-P. Sauvage,
Inorg. Chem. 1989, 28. 4070; R. M. Everly, D. R. McMillin. J. P/ILY.Chwn.
1991, YS. 9071, and references therein.
[ l l ] E. M. Kober. J. V. Caspar. R. S . Lumpkin. T. J. Meyer, J. Phi \ Cheni. 1986.9(/,
3722.
Bis(diisopropy1amino)carbene
Roger W. Alder,* Paul R. Allen, Martin Murray, and
A. Guy Orpen
The isolation of stable crystalline imidazol-2-ylidenes by Arduengo and co-workers"] has aroused great interest. They have
shown that derivatives as simple as 1,3,4,5-tetramethylimidazol2-ylidene (1) are stable crystalline solids that
show no tendency to dimerize.[*] We are interested in developing these derivatives of di/N-Me
aminocarbene as bases and nucleophilic cata- Me-N,
c
lysts, and have recently shown that 1,3-diiso1
propyl-4,5-dimethylimidazol-2-ylidene
(2) has
a pK, value of 24 in [DJDMSO, making it one of the strongest
As an extension of these studies, we
known neutral ba~es.1~'
started to explore as wide a range of stable diaminocarbene
structures as possible. Both imidazol-2-ylidenes and their precursors, imidazolium ions, are aromatic, so aromaticity should
not have a first-order effect on the deprotonation. Indeed calculation of the proton affinity (PA) of a range of imidazol-2ylidenes, dihydroimidazol-2-ylidenes,and acyclic bis(dia1kylamino)carbenes, by using the AM1 semiempirical method,I41
showed that PA varied by less than 10 kJmol- among similarly
substituted examples of these systems (the calculated PAS
for 2,3, and 4 are 1066, 1055, and 1063 kJmol- respectively).
MeHM
'
111'::
825(d.2H,.J~8.4Hz),8.10(AB.4H,,..5=8.8Hz).
7.94 (d, 7H,. J - 8 . 4 Hz), 7.69 (d. 2H,, 5 - 8 . 3 Hz), 7.55 (1. 2H,, 5-7.7 Hz), 7.34:6.0(br
7.31 im,Zll, + ? H h i . 6 7 5 ( d . 2 H , . 5-8.4Hz),6.74(d,2H;.J28.4Hz).
4H,j, 5.74 (br d. 4H,). 4.08-3.26 (m, 48H. OCH,CH,Oj.
Received: November 24, 1995 [Z8589IE]
German version: Angeii-. Chen?. 1996, (OX. 1190-1 193
Keywords: complexes with nitrogen ligands * molecular knots
photophysics
-
[ I ] "Topology in Molecular Chemistry", N e w . 5. Chem. 1995, 17. 617 (special
issue)
[2] S A Wasserman. N. R. Cozzarelli. Srrenw 1986. 232. 951 and references
therein.
131 C. Liang. K. Mislow, J A m . Chem Soc. 1994, 116. 11189; ;bid. 1995. 117,
4201
[4] a) c'. 0 . Dietrich-Buchecker. JLP. Sauvage, Angeir. Chrm. 1989, 101. 192:
An,qm. Clwm l i i i . Ed. Engi. 1989, 28. 189: h) C. 0. Dietrich-Buchecker, J.
Guilhem, C. P'iscard, JLP. Sauvage. hid. 1990. 102. 1202 and 1990, 29. 1154:
c) C. 0 . Dietrich-Buchecker. J.-F. Nierengarten. J.-P. Sauvage. N. Arrnaroli. V.
Balzani, L. De Cola, 5. Am. Chem. Soc. 1993, 115. 11237.
[S] C. 0 Dietrich-Buchecker, J:P. Sauvage, A. De Cian, J. Fischer. J Clrem. Soc.,
(%ciii. Conm 1994. 2231.
A I I ~ ~ IChwn
I.
In! Ed Engi. 1996. 35. No. 10
This encouraged us to try to generate a diaminocarbene by
deprotonation of a suitable amidinium ion, even though it was
reported many years ago that N,N,N',N'-tetramethylformamidinium salts are difficult to C-deprotonate."] Extensive earlier
work by Wanzlick and othersl61 showed that 4,5-dihydroimidazol-2-ylidenes were readily generated by a variety of reactions,
but apparently always dimerized to give tetraaminoethene
derivatives."] While our work was in progress however, Arduengo et aI.[*l reported the isolation and X-ray crystal structure analysis of the first stable 4,5-dihydroimidazol-2-ylidene
3
by deprotonation of an N,N'-dimesityl-4,5-dihydroimidazolium
ion.
[*I
Dr. R. W. Alder, Dr. P. R. Allen, Dr. M. Murray, Prof. A. G Orpen
School of Chemistry, University of Bristol
Cantock's Close, Bristol, BS8 ITS (UK)
Fax: Int. code +(117)929-8611
e-mail: Rog. Alder@ bristol.ac.uk
6; VCH Verlugsgeselischuji m b H , 0-69451 Weinheirn, 1996
0570-0833196/3510-1121 15.00+ .25,0
1121
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We now report on the isolation
of bis(diisopropy1amino)LDA
4
carbene (N,N,N',N'-tetraisopropylformamidinylidene) 4 as
H,C CH, H H3CCH,
a stable solid by deprotonation
5
of N ,N,N', N'-tetraisopropylformamidinium chloride 5 with lithium diisopropylamide
(LDA) in THE['] The formamidinium salt 5 was prepared by
reaction of N,N-diisopropylformamide with phosphorus oxychloride in ether, followed by treatment with diisopropylamine.'"I Reaction of 5 with LDA in T H F led to the formation
of 4 in 5 5 % yield. Diaminocarbene 4 sublimes readily and is
stable under rigorously dry nitrogen, but appears to be significantly more sensitive to oxygen and moisture than other species
of this type that we have handled. The X-ray crystal structure of
4 was determined from a crystal grown by sublimation.[' ' I The
structure (Fig. 1) shows that the molecule has approximate C,
the observed process, the rotational process must have a higher
barrier, and it is therefore clear that there is as much double
bond character to the C - N bonds in 4 as those in amidinium ion
5.Thus, while it is convenient to call 4 a diaminocarbene rather
than a formamidinylidene, it would be just as realistic to describe an amidinium ion as a diaminocarbenium ion!
In solutions containing both 4 and 5, separate N M R signals
are seen for these two species, although there is some indication
of exchange broadening at higher temperatures. This indicates
that proton transfer between 4 and 5 is slow on the N M R time
scale. We previously found that proton transfer between 2 and
the corresponding imidazolium ion was close to the fast exchange limit at ambient t e m p e r a t ~ r e .The
~ ~ ] slower exchange for
4 is in keeping with the greater steric hindrance in this species.
The co-existence in solution o f 4 and 5 is interesting from another point of view, since attack of the carbene on the electrophilic
carbon atom of the amidimium ion is proposed to be the major
route to tetraaminoethenes."1
In summary. we have isolated the first acyclic diaminocarbene, and shown that its C - N bonds have substantial double
bond character. It will be interesting to discover what minimal
steric hindrance is required in these species before dimerization
of the carbene sets in, but the preparation of 4 suggests that a
wide range of these interesting species can be isolated.
Esperinien t al Procedure
5: Solvents were stored over 3 A molecular sieves prior to use, and all manipulations
Fig. 1 . Molecular structure of 4. Important bond lengths [A] bond angles ] and
torsion angles [ ] C(1)-N(1) 1363(6), C(I)-N(2) 1.381(6). N-CHMe, (av) 1.492:
N(l)-C(l)-N(Z) 121.0(5), C(l)-N(l)-C(2) 135.1(4). C(I)-N(l)-C(S) 11 1.2(4) C(2)N(l)-C(S) 113.4(4) C(l)-N(?)-C(8) 133.5(4). C(l)-N(Z)-C(ll) 110.7(4). C(X)-N(2)C(11) 115.5(4), C(?)-N(l)-C(l)-N(2) - 13.7(9), N(l)-C(l)-N(Z)-C(X) - 10.6(9).
symmetry; the N-C-N angle (121.0") is much larger than that in
any previously studied diaminocarbene derivative (this angle is
104.7" for 3). The nitrogen atoms are planar, but the C-N-C
angles are strongly distorted by the repulsive interactions
between the isopropyl groups. The 13C N M R chemical shift
of the carbene center at 6 = 255.5 is 30-40 ppm downfield of
the carbene carbon chemical shifts for imidazol-2-ylidenes,
and 10 ppm downfield of that reported for 3.18]The further
downfield shift for 4 may be related to the increased N-C-N
angle.
The 'Hand 13C N M R signals of the iPr groups of 4 are broad
at room temperature, and split to reveal two types of iPr groups
at - 30 "C. The C H signals coalesce at - 10 " C , leading to a
calculated AG * of 53 kJ mol
Similar behavior was observed
for the formamidinium ion precursor 5,where the coalescence of
the C H absorptions occurred at + 8 ' C , AG * 55 kJ mol - '. A
barrier of 64 kJ mol- ' has been reported for the tetramethylformamidinium ion.['21The fact that the barrier is lower for 5 is
understandable in terms of steric destabilization of the ground
state relative to the transition state for rotation about a C - N
bond. Coalescence of the signals for the iPr groups in 5 must
involve rotation about a C-NiPr, bond, accompanied by rotations about N-iPr, bonds. In the diaminocarbene 4 interconversion might occur by an inversion mechanism with a linear
N-C-N transition state, although AM1 calculations suggest a
rotation process will be preferred. However, even if inversion is
were performed under dry nitrogen. Diisopropylformamide ( 5 mL, 34.5 mmol) in
Et,O (10 mL) was added at 0 C to a stirred solution of POCI, (3.2 mL, 34.5 mmol)
in EtiO (25 mL). After the mixture had been stirred for 0.5 h a t room temperature,
the white precipitate was allowed to settle and the supernatant was removed. The
solid was washed with Et,O (2 x 30 mL), dissolved in dichloromethane (30 mL),
and diisopropylamine (4.5 mL, 34.5 mmol) in dichloromethane (10 mL) added
dropwise at 0 C. The solution was stirred at room temperature for 0 5 h. Et,O
(30 mL) added, and the precipitate collected by filtration. The solid, a mixture of the
required formamidinium salt and diisopropylammonium chloride (4.4 g), was treated with acetone (30 mL) m which only the formamidinium salt is soluble After
removal of the diisopropylammonium chloride by filtration, Et,O (30 mL) was
added to precipitate the product a s a white crystalline solid (2.14 g) which was dried
in vacuo over P,O, before use. m. p. 214-220 C with decomposition. ' H N M R :
(300 MHz, CDCI,). 6 =1.49 (d, 24H). 4.25 (br. s. 4 H ) , 7.60 (s. 1 H); "C N M R
(75.45 MHz, CDCI,): 6 = 22.72 (br.). 52.0 (br.), 151.05
4: N,N,N',N'-tetrdisopropy~formamidinium
chloride (0.3 g. 1.21 mmol) was added
~
to a solution of LDA (formed by the addition of n-butyllithium (0.5 mL, 2 . 4 in
hexdnes) to diisopropylamine (0.21 mL, 1.5 mmol) in tetrahydrofuran at -78 c)
The reaction mixture was allowed to stir at room temperature for 0.5 h by which
time complete dissolution had occurred. The solvent was removed under vacuum to
give an off-white solid. which was treated with hexane. The supernatant was removed and evaporated under vacuum to give a white solid. which was sublimed at
40 C'0.2 mm Hg to yield white crystals (0.142 g. 5 5 % ) . m. p. 51 - 5 5 C. Elemental
analysis calculated for C,,H,,N; C 73 5. H 13.3, N 13.2%: found- C 73.8, H 13.5.
N 13.2: 'HNMR(SOOMHz.[D,]benzene) 6 =1.28(br.,24H);3.70(br..4H). "C
N M R (125.7 M H L [DJbenzene): 6 = 24.2 (br.). 49.6 (br.), 255.5.
Received: December 8, 1995
Revised version February 10. 1996 [ZX6261E]
German version: Airpea. Cliem. 1996. 108. 1211-1213
Keywords: amidinium ions
- carbenes - structure elucidation
[I] A. J Arduengo 111. R. L. Harlow, M. Kline. M . J A m . C'lienr. Soc 1991, ff3.
361
[ I ] A J Arduengo 111. H V R Dias, R. L. Harlow. M. Kline, J A m . Cfrrtn. Sot
1992, f14.5530: A J Arduengo 111. H. V. R . Dias. D. A. Dixon. R. L Harlow.
W. T. Klooster, T. F Koetzle, ibrd 1994, 116, 6812. report calculations that
suggest that dimerization of 1 is endothermic
[ 3 ] R. W Alder. P. R. Allen, S. J. Williams. J. Clieni. Soc. Clirm. Cornmrm. 1995,
1267.
[4] Calculation of the proton affinities of a wide range of compounds by this
method has been reported: M. J. S. Dewar. K M. Dieter. J. Am. C'lreni. Soc.
1986. ION, 8075.
[5] N. Wiberg, J W. Buchler. Z. Nrr/rrr/or.sch. B 1964, 19. 953-955.
COMMUNICATIONS
[6] H.-W. Wanzlick. E Schikora. AngPn. C/7rm., 1960. 72. 494; H.-W. Wanzlick,
Ang<,ii'. <'hem. 1962, 74. 129; Angra. Chem. Inr. Ed. Engl 1962, 1. 75; H: J.
Schiinherr, H -W. Wanzlick. Chem. Bcv. 1970, 103, 1037--1046, and references
therein.
[ i ] For discussion of this dimerization see: D. M. Lemal, R. A. Lovald. K . I.
Kawano. J. A m . <'/7em.SOC.1964, 86, 2518; H. E. Winberg. J. E. Carnahan,
D. D. Coffmm. M Brown. ibid 1965. 87. 2055; N. Wiberg. J. W. Buchler,
Chrm Bcv. 1963. Y6. 3000.
[XI A. J Arduengo 111. J. R. Goerlich, W. J. Marshall, J. Am. Chern. Soc. 1995. 117.
11027.
19' 1 The ability of iPr groups to stabilize unusual structures at nitrogen is wellknown: H. Bock. H. Gobel. Z. Havlas. S. Liedle, H, Oberhammer, Angeiv.
< ' h i w i 1991. i03. 193; A n p i . (%em. Inr. Ed. Engl 1991, 30. 187.
[lo] H. Bredereck. R Gompper, K. Klemm. H. Rempfer, Chem. Ber. 1959.92,837.
[ l l ] Crystal data (or 4: C,,H,,N,, M , = 212.4, triclinic, space group PT (no. 2),
p=
a=7..5346(11). h = 8.844(2), ~=12.113(3).&. 1 =110.718(12).
104.868(123. ;' = 92.700(9) , V =721.2(2) A', 2 = 2. P,,,~= 0.978 gcm-',
L = 0 71073 A. p(MoK,) = 0.57 crn-', F(OO0) = 240, T = 1 7 3 K, crystal size
0.2 x 0.2 x 0.2 mm. All diffraction measurements were made on a Siemens
SMART areii detector diffractometer. using graphite monochromated Mo,,
X-radiation. Unit cell dimensions were determined from 89 reflections. Diffracted inlensities were measured in a hemisphere of reciprocal space for
3.0110<45.0 by 0.3 (0 scans, frames observed for 30 s. Crystal decay of
about 40% viia observed over a period of 13 h. Data collected after about 6 h
were discarded because of poor agreement with earlier data. A total of 1259
data were intcgrdted of which 977 had I z 2u(f). N o absorption correction was
applied. Loreiitr and polariation corrections were applied. The structure was
solved by direct methods. All non-hydrogen atoms were assigned anisotropic
displacement parameters. All hydrogen atoms were located in difference maps
and conatrained to idealized geometries. Full-matrix least-squares refinement
on I;> of this model using the SHELXL-93 program (SHELXTL version 5.03.
Siemens Analytical Xray, Madison WI, 1994) (144 parameters) converged to
final residual indices Rl = 0.084, irR2 = 0.198, S = 1.15. Final difference electron density maps showed no features outside the range t 0 . 2 6 to -0.22 e k '
(cf inethine hydrogen atom peaks 0.39-0.49 e k - ' ) . Crystallographic data
(excluding structure Factors) for the structure(s) reported in this paper have
been deposited with the Cambridge Crysta!lographic Data Centre as supplementary publication no. CCDC-179-26. Copies of the data can be obtained
free of charge on application to The Director. CCDC. 12 Union Road.
Cambridge C'B2 lEZ, UK (fax: int. code +(1223) 336-033, e-mail:
techedw chemcrys.cam.ac.uk)
1121 J. Schmetzer. J. Daub. P. Fischer. Angeir. Chem. 1975. 87, 489; AngeM-. Chern.
In/ Ell. E q l . 1975. 14. 487. I'or barriers for other amidinium ions see: R. C.
Neumann and V Jonas. J. f'/iy.\. C/7em. 1971, 75. 3532.
XeF, .C2l The chemistry of the fluoroxenon cations of XeF, has
been established with the ions XeF; and Xe,F;, . In solution
and in the melt XeF, exists as monomer and tetramer in equil i b r i ~ m , ' ~at' low temperatures in solution only the tetramer is
observed.[41 Tetrameric and (less often) hexameric units are
characteristic for the solid state.[51 Because of the amphoteric
character of XeF, fluoroxenon anions are expected to exist, and
XeF; and X e F i - have been described.['] However, only the
structure of X e F i - has been confirmed; it is square antisprimatic with no detectable steric activity of the nonbonding pair of
eIe~trons.'~1
Little is known about the structure of XeF;. It is formed from
CsF and XeF, as a yellow solid; however, it readily loses XeF,,
resulting in colorless Cs,XeF,. Likewise with N O F the final
product is XeF;-.I6] By using an excess of the weaker fluoride
donor NO,F crystalline, sublimable NO; XeF; is formed;
however, this is always multiply twinned therefore not allowing
a single-crystal X-ray structure analysis. XeF; presents an interesting structure, since it contains seven identical ligands and
a nonbonding electron pair. This is the only example of such a
combination known to date in main group chemistry.
CsXeF, freshly prepared from CsF and XeF, dissolves in
BrF, to give a lemon yellow colored solution, and crystallizes a t
4 "C to give yellow crystals. According to the results of a singlecrystal X-ray structure determination the anion has a capped
octahedral structure, which is strictly obeyed because of the
symmetry constraints of the cubic lattice system (Fig. 1).
Structures of XeF, and Xe,FT3**
Fig. 1. Structure of the XeF; ion in the crystal of Cs'XeF; (ORTEP plot, 50%
probability). Distances [pm]. Xe-F1 193.2(3), Xe- F2 210.0(6). X e e F 3 197.0(3).
, s - - F 3 310.3(3), 341.5(4); angles
Cs.-321.7(3), 344.2(4), C s - - . F 23 ~ 3 2 6 . 5 ( 2 ) C
[ 1: F2-Xe-F1 132.2(1), F2-Xe-F3 75.91(1).
Arkady Ellern, Ali-Reza Mahjoub, and
Konrad Seppelt*
XeF, is an amphoteric solvent; however, it has not been investigated very much, mainly because of its extreme fluorinating
power, the difficulties associated with its purification, and because of the extraordinary explosive power of its final hydrolysis
product, XeO,. The conductivity of XeF, is found to be
1.45 x lo-' R - I , which suggests a dissociation into fluoroxenon cations and fluoroxenon anions.[" Nevertheless, the first
preparation of Au' as Xe,F:,AuF;
was achieved in liquid
[*] Prof. Dr. K. Scppelt
lnstitut f i r Anorganische und Analytische Chemie der Freien Universitit
p b..
Lckstrassc 34 - 36, D-14195 Berlin (Germany)
[**I
Telefiix: Int. code +(30)838-2424
e-mail: seppeltvr blume.chemie.fu-berlin.de
Dr. A. Ellern
Chemistry Dcpartment. Ben-Gurion University of the Negev, Beer-Sheva
(Israel)
Dr A,-R Mahloub
Department of Chemistry, Tarbiat Modarres University. Teheran (Iran)
We thank thc Alexandervon Humboldt Stiftung forastipend for A. E..and the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie
for financial support.
Angrir. <'hem I n t Ed. Engl. 1996.
35. No. 10
In the last few years it has been shown that main group compounds with the coordination number 7 in absence of nonbonding electron pairs always adopt a pentagonal bipyramidal structure (IF7, TeF;, IOF;, ROTeF;, (RO),TeF:-), possibly
because this structure has one linear ligand-central atomligand arrangement (e.g. I-F-I)-in contrast to all other structural alternatives-to satisfy the high p character of the bonding."] Among the comparable transition metal compounds
(MoF; , WF;) the capped octahedron is observed;191however,
not always (ReF;, TeF:-).1'o-'21 The comparison of the
capped octahedra of XeF; in Cs'XeF; with those of MoF;
and WF; reveals an important difference. The Xe-F bond to
the capping fluorine atom in XeF; is remarkably long (210 pm).
Thus, one can assume that this direction in space might also
contain the remaining weak influence of the nonbonding electron pair. Whereas the fluorine atoms of the distorted octahedron interact with two cesium ions, the capping fluorine atom
interacts with three. This may also explain the length of the
bond between xenon and the capping fluorine atom.
VCH Verlu~sgesellsc-liatrmbH, 0-69451 Weinheim, 1996
0570-0833/96/3510-t123$ 15.011+ , 2 5 0
1123
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