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Metal Complexes of N-Heterocyclic CarbenesЧA New Structural Principle for Catalysts in Homogeneous Catalysis.

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171 There is little known ;ihout the I-aza-3-phosphaallyi anion. cf.: a ) K. Issleih.
H Schmidt. H. Meyer. J, Orgfiriorlw/. Chcrw 1978. 161). 47-57. b)
[PhPC(Ph)NSiMe,Li(dme)]. a monomeric lithium complex of an l-aza-3pho5ph;iallyl riiiioii, has also been prepared: G . Becker, Stuttgart. personal
communication. G . Bccker. G. Ditten. K Hubler. K . Merr. M. Niemeyer. N.
Seidler. M Westerinanii in O r g o ~ ~ o d ~ Cc' o/ i m~i i , v / r J , I 1 (Eds.: N. Auner. J.
Weis\). VCH. Weinheim. in presy.
structurc iiniilysis of 2 [7]: yellow [colorless] crystals, crystal dimensions
x 0. I 3 < U.20 mm [0.08 x 0.23 x 0.58 mm]: M , = 602.6 [255.3]:monoclinic
noclinic]. space group C2.'( (no. 15) [f'?,,~ (no. 14)]. ( I = 23.835(4)
=18.786(2) A
[14077Ii)]. /I = 8.818(2) [9.937(1)].
/f =l10.07(1) [10X.36(1)'], l ' = 3547(1)A3 [1411.9(2)A3], Z = 4 141.
p ( ( ' u h a )=1.3X[1.56]nim-'. T = 200[208]K.F(000) =1296[544].185112787]
iiitcnsitieh t i p t o 70n,,x= 100 [140'] were measured on on with Cu,, radiation. of which I778 (26711 were independent and Mere used for ;illcalculations. The structure was solved with direct
incthods and refined on F* anisotropically. the H atoms were refined with a
riding iniodel (prograin. SHELXL-93 [9]). The final quality coefficient IVR?
I F 2 ) u i i h 0.105 [0.145] hitli ii conventional R I F ) = 0.056 [0.049] for 223 11731
i n d 139 [?I restraints. The THF ligands in 2 are disordered. For 7
iiii extinetioil correction and a n empirical absorption correction was carried
out on the b x i h of"? s a n s . Further detailsofthecrystal structure investigation
ma) he obtained from the Fachinformationszentrum Karlsruhe. D-76344 Egpcnstcin-Lcop~,ldsh;rl'rn (Germ;iny) on quoting the depository number CSD59114.
(91 (i. M Sheldi-ick. SHELXL-93. Universitiit Gottingen. 1993.
[lo] W. N S e t x i - . P. voii I<. Schleyer. Adr. Oryorror?irf. Chcvii. 1985. 24. 354-450.
[ I 11 Q u a n t u m c1ieiiiic;il calculations on the configuration isomers of the parent
ccniip~iuiid[ H I T (H)NH]- show the wid+w/o form to be energetically fiivorcd. Relatice energies of the different configuration isomers of [HPC(H)NH]( i d i t i \ c to c v r d o . c f i r / i form) [kcal mol-'1: e\-o(PH),.eii~/[~(NH):
+ 0.6: c v do(PH),c.\dNH): + 4.4; e\-o(PH).'P\-o(NH):+ 5.1. We thank Prof. Dr. W. W,
Schoeller. Bielefeld. for providing us with the results.
I121 This \ % a h conlirmed by a inolecuiar weight determination.
Metal Complexes of N-Heterocyclic CarbenesA New Structural Principle for Catalysts
in Homogeneous Catalysis**
The carbene-palladium complexes 1 and 2 o f the imidazole
series were prepared from [Pd(OAc)J and 1.3-dimethylimidazolium iodide or 3.3'-dimethyl-l,1 '-methylenediimidazolium diiodide in more than 70 and 40% yield. respectively [Eq. (a)
and (h)]. They are extraordinarily stable to heat. oxygen. and
moisture. Catalyst 1 melts at temperatures as high as 299:C
with partial decomposition and resists several days treatment
with 0, in boiling THF. The complex 2 melts at 280'C, but
decomposes noticably in solution (N,N-dimethylacetamide) at
temperatures above 70 "C.
Besides the expected square-planar core geometry. ii crystal
structure analysis of 1 (Fig. 1)[51 shows that the two carbene
Wolfgang A. Herrmann,* Martina Elison, Jakob
Fischer, Christian Kocher, and Georg R. J. Artus
A basic functional principle in homogeneous complex catalysis is based o n the fact that phosphane and phosphite ligands not
only protect low-valent metal centers from aggregation (stabilization effect), but also create coordination sites in dissociation
equilibria at which the catalytic elementary steps proceed (activation effect)."' Examples of industrial importance are hydrocyanation (Nio]P(OR),) and hydroformylation (Co'/PR,, Rh'/
PR,). Generally, as a result of the notorious phosphane
degradation by P-C bond cleavage,r21an excess of the ligandoften 100 times more than the metal-is required to control the
equilibrium i n the activation and propagation steps in homogeneous catalysis. This excess increases the running costs of technical plants.[31 Phosphane and phosphite complexes are also
often water- and air-sensitive. Using the Heck coupling as exwe now describe a new catalyst principle that does
not have these disadvantages. I t relies on the special ligand
properties of N-heterocyclic carbenes and stands out because of
its simplicity and efficiency.
h i . Di. W A. Herrmann. M. Elison. J. Fischer. C. Kocher. G. R. J. Artus
..Znorgani~ch-chemischeslnstitut der Technischen Universitiit Munchen
Liclitenbergctrasse 4. D-85747 Garching (Germany)
+ (XY)3?09-3473
Telclhu- I n t code
oordiniilioii Chemistry nnd Mechanisms of Metal-Catalyzed CC Coupling
Reaction,. Part 9. Part 8: W. A. Hcrrmann. C. P. Reisinger. K. Ofele. C. Bross-
inrr. M Hellcr. H. Fiacher, J. Moi. Ccxal., in press.
Fig. 1. PLATON representation of the crystal structure of the "carbene" complex
1. The ellipsoids represent 50% probability; H atoms are omitted for clarity. Selected distances [A] and angles [']: Pdl-I1 2.6479(3). Pdl-I2 2.6572(3). Pdl-Cl 1.990(3),
Pdl-C6 1.997(3). NI-Cl 1.347(4). NZ-C1 1.363(4). N3-C6 1.357(4). N4-C6
1.336(4); 12-Pdl-I1 93.590(9). Cl-Pdl-I1 87.32(8). Cl-Pdl-I? 178.08(8). C6-Pdl-I1
175.52(9),C6-Pdl-12 88.97(8), C6-Pdl-CI 90.2(1).
ligands are in a cis arrangement and twisted relative to the PdI,
plane (70.5 and 69.4"). The [(PR,),PdX,J (X = halogen) complexes with monodentate phosphane ligands that were known
previously and characterized by crystal structure analyses have
tr~znsconfigurations. which reflects the greater steric demand of
the phosphane ligand. In contrast to the planar carbene ligands,
the phosphane ligands cannot relieve the steric congestion by
rotation about themetal-ligand bond (Pd-P instead ofPd-C).
The Pd-C bond lengths (1.990(3)/1.997(3) A) lie in the range of
those of known carbene complexes (1.95-2.07 A)[']- true
Pd-C single bonds (Pd-C(alkyl), Pd-C(benzy1)) are. however,
hardly longer: 1.99-2.05 A,['] In accord with results from vibrational spectroscopy,[s1it is therefore certainly valid that heterocyclic carbenes of the imidazole type have pronounced donor
properties similar to the electron-rich phosphanes and that Ebackbonding is insignificant. The formal depiction of this class
of compounds as A (o-donor) and B (n-donor) probably most
closely represents the bonding; on the contrary. the conventional, formal notation C i s certainly inaccurate in that it does not
reflect the apparent analogy between these "carbenes" and
other donor ligands.
Table 1 . Heck olefination of chloro- and bromoarenes with carhene-pulladium
catalysts [;I]
of catalyst
[mol YO]
> 99
> 99
1 [bl
1 Ibl
4-BrC ,H,CHO
4-BrC,H4C( =O)CH
4-BrC,H4C( =O)CH
4-BrC ,,H,OCH,
2 x 10-3
4 x lo-*
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
[a] For reaction conditions. see Experimental Procedure. The catalyst 3 is the car-
bene complex [PdOLJ formed in situ from [Pd(dba)z]and free carbene L (see lext).
[b] With ;rddition of [N(n-C,H,),]Br (SO mmol).
The Pd complexes 1 and 2 catalyze the Heck coupling of aryl
halides [Eq. (c)].[~"'The higher turnovers are obtained with 1
C(=O)H C(=O)CH,
because of its pronounced thermal stability in solution (see
Table 1). As shown by kinetic measurements (see Fig. 2), the
activity at the beginning of the reaction of bromoarenes (for
example 4-bromobenzaldehyde) is lower than that of the partic-
t [min]
Fig, Concentrationi'timediag'am (amount of substance y[X,l.
[mini) for
the Heck oletination of 4-brornobenzaldehyde (m) with n-butyl acrylate to form
n-butyl (Ej-4-formylcinnamate (oj; for reaction conditions see Experimental Procedure and Tdble 1. 0.5 m o l % I . The loss of the stntrting material (approximately
1O0/b)immediately after the start ofthe reaction is attributed to the formation ofthe
Heck coupling product and appears to be correlated to the activation ofthe catalyst.
for example by reduction through the aldehyde.
ularly active p a l l a d a ~ y c l e sybl
, ~ but
~ ~ ~the advantages of the new
catalyst 1 lie in the formation of stable active species and in the
length of time it remains stable even a/ high /enzpera/ures. a
property that is still essential for the activation of chloroarenes.
The sigmoidal turnover characteristics (concentration/time
diagram; Fig. 2) result in an initially sluggish product forma-
tion. As the reaction proceeds the turnover per time increases
markedly. An activating conversion step must thus be assumed
for the catalytic activity of 1. N o inductive phase is observed for
1 after treatment with reducing agents: whereas 4-bromoacetophenone i s converted only very slowly with 1 under mild conditions and no other additives (Fig. 3), the concentration of the
starting material decreases suddenly and exponentially after addition of hydrazine (after 67 min). Sodium formate is a particularly advantageous reducing agent in this context (no metal
complexation. nontoxic).
t [minlFig. 3. Concentrati0n;time diagram (amount of substance .r["/]. time / [inin]) for
thc Heck olefination of 4-hromoacetophenone (m) with n-butyl acrylate t o form
fr-butyl (E)-4-acetylcinnalnate( 0 ) : for reaction conditions see Experimental Procedure and Table 1. 0.5 m o l % 1. addition of 8 5 p L hydrazine hydrate after 67 min.
The conversions of 4-chlorobenzaldehyde and 4-chloronitrobenzene with n-butyl acrylate [Eq. (c)] proceed quantitatively
at 130°C with 1 ( 1 and 0.1 mol%. respectively) on addition of
[N(n-C,H,),]Br (Fig. 4, Table 1 ) . Here too, the usual induction
period is absent. We conclude that the formyl group of the
chloroarene or [N(n-C,H,),]Br acts as reducing agent.
The results raise the expectation that a carbene complex
[Pd(carbene),] (3) with a zerovalent palladium center prepared
in situ should be immediately active without induction period.
[Pd(dba),] (dba = dibenzylidene acetone) was therefore treated
t [hlFig. 4 Concentriitioii'tiniediagram (amount of substance .Y[%]. time r [h]) for the
Heck olefination of 4-chlorobenzdldehyde (m) with f7-butyl acrylate to form n-butyl
(€)-4-forinylcinniimate(a): for reaction conditions see Experimental Procedure and
Tahle I . I inol:c~ 1. 50 mmol [K(/f-CJHgjA]Br.
with two equivalents of free 1.3-dimethyldihydroimidazole-2ylidene ( L ) in toluene at room temperature. The coordination of
the metal center by the carbene can be monitored by the color
change from violet to red, as well as by 'H and I3C NMR
spectroscopy (hCtcarbenel
= 180.2, [D,]toluene). The Pdo-carbene
catalyst 3 does indeed have an extremely large initial activity
with long-term stability in the Heck olefination (Table 1): with
only 4 x lo-' mol % (!) catalyst, 50 mmol 4-bromoacetophenone can be completely converted in 43 h without palladium
deposition. Because of the absence of an induction period and
of the high activity. turnover numbers (TON) of more than
250000 can be achieved with 3 for activated bromoarenes,
whereas with [Pd(dba),] without the stabilizing carbene ligands
turnovers are only low in the same time. In the catalytic conversion of 4-bromoanisol with [Pd(dba),], inactive palladium separates quantitatively at room temperature already. Even with
these deactivated bromoarenes the stabilizing influence of the
carbene ligands is obvious: here the turnover numbers per hour
(TOF = I SOOO) reach higher values than with all classical phosphane complexes.
The "carbenes" derived from imidazole appear to stabilize
Pd" and Pd" complexes because of their pronounced donor
properties. This picture also encompasses the existence of the
recently described complexes [BeCI.L,]+Cl-, [TiCI;L,], and
[MoO,CI. L,] +CI-, in which the carbene ligand L replaces conventional solvent ligands like acetonitrile, tetrahydrofuran, and
NN-dimethylformamide by formation of a stable dative bond,
or breaks dimeric and polymeric
In contrast to
the common Pd:phosphane catalysts, in the new Pdkarbene
systems the ligunds d o not undergo deactivating degradation
reactions." ' I N o deposition of (catalytically inactive) palladium
can be detected.
The new catalyst type described here has a series of advantageous properties and potential for development: a) high thermal
and hydrolytic durability resulting from exceptionally stable
M -C bonds (long shelf-life. stability to oxidation); b) easy accessibility. and c) no need for an excess of the ligand. The
prospects for derivatization to water-soluble catalysts (twophase catalysis). immobilization. and chiral modification seem
promising because of the constitution of the ligands.
Espcritiietirtrl Procetiiire
I : A soltition of[Pd(OAc),](2.00 g, X 9 mmol) and 1,3-dimethylimidazoliuiniodide
(4.10 g. 18.7 niiiiol) i n T H F ( 1 50 mL)w a s heated for 30 min under reflux. during
which lime the initially b r o s n solution bleached to yellow. After evaporation to
drynesb undcr v:icutiin. the residue was washed with diethyl ether (three 50 mL
portions). taken up in CH,CI, (100 mL). and the solution layred with n-pentane
(200 mL). At 25 C 1 crystallized as a yellow solid that was ver) soluble in CHCI,.
and slightly soluble in T H F and toluene. Yield: 3.70 g (75%). '1-1 NMR (400 MHz.
CDCI,.?O C):d =7.24(~.4H.NCH).3.92(~.12H.CH,);'~CNMR(100.1
CDCI,, 20 C): d = I 6 8 2 (carbene-C). 122.3 (NCHj. 38.2 (CH,): correct C.H.N
2: [Pd(OAcj,] (200 mg. 0.89 mmol) was treated at 170 C with 3.3'-dtmethyl-l . I , methylenediimidazolium diiodide (400 mg. 0.89 mmol). After heating for 5 min
under vacuum the residue was extracted %ith T H F and filtered over a frit covered
with a layer of silica gel. The solvent was removed under bacuum. the residue
washed with absolute diethyl ether (three 20 mL portions). taken up in CH,CI,
( I 0 mL). and t h e solution carefully layered with i7-pentane (30 m L ) . The yellow
crystals of 2 were dried under vacuum. The! dissolve well in CHCI,. CH,CI,. THF.
and toluene. to give a yellow solution. Yield: 190 mg (40'10). ' H NMR (400 MHz.
CDCI,. 20 C) 6 = 3.92 (s, 6H. NCH,). 6.61 (s. ZH.CH,). 7.41. 7.43 (s. 4 H ,
NCH): "C NMR (100.1 MHz. CDCI,. 20-C): 6 = 36.31 (NCH,). 53.60 (CH,).
121.87. 124.35 (NCH). 185.50 (carbene-C): correct C.H.N aniilysis.
General procedure for Heck olefination of chloro- and bromo'irenes: In a l0OmL
three-necked flask fitted with a septum. thermometer. and reflux condensor (with
mercury overpressure valve) were placed the haloarene (50 mmol). anhydrous sodium acetate (4.51 g. 55 inmolj and diethyleneglycol di-n-butyl ether ( G C standard.
1000 mg) in 50 mL Y,Y-dimeth~lacetdmide. After repeated degassing under oil
pump vacuum and flushing with argon. ri-butyl acrylate (10 rnL. 70 mmol) was
injected through the septum. The charge was heated to I00 C. whereupon the
freshly prepared catalyst mixture or the solution of the P d " - ~ i r b e n ecomplex was
added through the septum. and the mixture heated to the reaction temperature
(125 C with bromoarenes. 140 C with chloroarenesj. To monitor the reaction.
50011L samples were taken at regular intervals. wished with 5 niL dilute hydrochloric acid ( 5 % ) . and extracted with 3.5 m L CH,Cl2. The organic phases were analyzed by gas chromatograph) (GC,FID. GC-MS. GC-IR-MS). For quantitative
analysis and the recording of concentration:time diagrams ii gas chromatograph
G C 5980A with flame ionization detector (FID). automatic sainpler, and an HP-I
capillary column (12.5 m) from Hewjlett Packard H B S used.
Received: June 16. 1995 [Z8131 IE]
German version: Angeir. Clfein. 1995. 107. 2602-2605
Keywords: carbenes . catalysis . Heck reactions . palladium compounds
[ I ] a) J. P. Collman. L. S. Hegedus. J. R. Norton. R. G. Finke. Princfples r i n d
App/iculioii.s of Orgoiiolrun.\ilron Meld ClieniisrrJ-.University Science Books.
Mill Valley. CA. USA. 1987: b) G. W. Parshall. S. D. Ittel. Hoiiwpi7eoii.s CumlL,.w. 2nd ed., Wiley. New York. 1992: c) Appplieri ~oii71)fit,fi[,~)if.s
Cmuli,.sf,s h>,
(Eds.: B. Cornils. W. A. Herrmann). VCH. Weinheim. 1996, in press.
[2] P. E. Garrou. Chefif. RPY. 1985. 85, 171 --385.
[3] A well documented example of this problem is the hydroformylation (annual
uorld capacity 6-Xmillion metric tons): a) B. Cornils in Yrii. Svi//wsr.swit/?
Cmhon A4ofio.i.ide (Ed.: J. Falbe). Springer. Berlin. 1980. Chap. 1 : b) W. A.
Herrmann. C. W. Kohlpaintner. Angrw. C h m . 1993. l0i. 1588-1609; Angew.
Client. / i t / . Ed. EngI. 1993. 33. 1524- 1544.
[4] Review: a) V. V. Grushin. H. Alper. C/wm R E V 1994.
Y-I. 1047- 1062: b) A.
deMeijere. F. E. Meyer. A f f g e i r .Cliem. 1994, 106. 2473 1506: Angcii. C h ~ n i .
/ f i r . E d E q I . 1994. 33. 2379-241 1
[5] The complex 1 (C,,H,,I,N,Pd. 552.49 gmol-I, F(000) = 1024) crystallizes in
the form of yellow crystals of X-ray quality at 25 C after layering a CH,CI,
solution with ii-pentane. Space group P2,:n (no. 14). cell constants by leastsquares refinement of 25 reflections in the angle range 32.6 <2fl<41.5"
.;( = 0.70930 A. Mo,,,):
ii = X.875(3). h = 16.375(1). L' = 11.216(3) A,
[<= 94.87(2j . I; = 1624.0 A'. Z = 4. (irrlrd = 2.26 g o i 1 F . CAD4-EnrafNonius diffractometer, graphite monochromator (; = 0.71073 A. Mo,,),
T = 50 -f- 3 'C. measurement range: 1 .O < H < 25.0 . inode 1.1 scan. scan time
max. 60 s. scdn width (1.0 + O.2tanO) , every 3600 s three reflections used to
check the intensit). every 100 reflections three used to check orientation: 5923
measured reflections. 232 systematic absences. 447 with negative intensity (/;
n ( I )<0.01). 4583 reflections averaged. of 2758 independent reflections 2461
( 1 > 1 . 0 a ( / ) )used in the refinement. structure solution h? Patterson methods
(SHELXS-86). refinement with the program CRYSTALS All H positions
were calculated b t assuming ideal geometry. but not refined. %veightingscheme
according to Tukey and Prince with three parameters. 154 parameters refined.
16 reflections per parameter. shift err t0.0001. R = Z(llf,,l - l F c l l ) ~ X l & l =
0.027. R , = [Zii.(lFol-lF,I)zXirF3' ' = 0.026. Refined: Zii,(l& - I F J ) , .
Residual electron density: max. + 1 13 e k 3 ;it a distance of O.X? A from a Pd
atom. min -0.94 e k ' . Further details of the crystal sti-ucture investigation
may be obtained from the Fdchinformationszentrum Karlsruhe. D-76344 Eggenstein-Leopoldshafen (Germany) on quoting the depourorq number CSD-
Examples: a) R. D. Wilson. Y. Kamitori. H. Ogoshi. Z:I. Yoshida. J. A. Ibers.
J. 0rganoino.t. Chon. 1979. 173, 199-209: b) A. Modinos. P. Woodward. J.
C/rerit. Soc. Da/rofi Earr.\. 1974. 2065-2069; c) P. Domiano. A. Musatti. M.
Nardelli, G . Predieri, J. Chrrii. Soc. Dalrorr nuns. 1975. 2165-2168: d ) H. C.
Clark. C. R. C. Milne. N C. Payne. J. .4r77. Chiwr. So(..1978. 100. 1164-1 169:
e ) W. M. Butler. J. H. Enemark, Irrorg. C/riwf.1971. 10. 2416 2419: f j 0. P.
Anderson. A. B. Packard. rhrd. 1978. 17. 1333-1337.
Examples. a) P. K. Beyers. A. J. Canty. L. M. Engelhardt, A. H. White. J.
Chcnr. Soi,.Dullon Trcii7.s. 1986. 1731 -1734: b) W. A. Herrmann, C. BroDmer.
K. Ofele, C:P. Reisinger. T. Priermeier, M. Beller, H. Fischer. A f i g c w . Chew
1995. ifJ7. 1989-1992: A f g e i i . . C/ww Ir7.t.Ed. G i g / . 1995, 34. 1844-1848: c )
A. L. Rheingold, W. C. Fultr. Org[rfioirre~/ii/i~.\
1984. 3. 1414 1417: d) W. De
GtXdf, J. Boersnia. W. J. J. Smeets. A. L. Spek, G. van Koten, O,.Kafforrrerrr/lii,.s.
1 9 8 9 . 2907~
K. Ofele, W. A. Herrmann. D. Mihalioa. M. Eliion. E. Herdtweck. W Schei-er.
J. Mink, .
Orgufiofrrc,.t.Chcvrf. 1993. 459. Ill- 184.
a ) W. A. Herrmann, M. Elison. J. Fischer, C. Kiicher (HoechstAGj. DE4447068. 1994; b) W. A. Herrmann. C. Brossmer. M . Beller, H. Fischer
(Hoechst AG). DE-4421730. 1994 and DE-4421753, 1994
a ) W A. Herrmann. K. Ofele. M. Elison. F. E. Kuhn. P. W. Roesky. J.
0rgrinoine.t. Cheii?.1994.4NO. C7 C9: b j W. A. Herrmann. 0. Runte. G . Artus.
;hid. 1995. 501. CI -C4: c ) W. A. Herrmann. M . Elison. J. Fischer. C. Kocher.
G. R. J Artus. Chwn. Eur. J . I n press: d j W, A. Herrmann. G. M Lobmaier.
M. Elison. J. Orgar?oiire.t. Chrni.. in press
W, A. Herrmann. C. Bi-ossmer. K ofele. M. Beller. H. Fischer. J. Or,qrifioifie/
C/iiwi. 1995. 4Yi. C1 C4.
distribution consistent with ["'Ag([l 8]aneS6)J+.The ESR spectrum is featureless, showing that the dark blue color cannot be
due to the formation of a radical Ag" complex." Recrystallization of the initial blue product from MeCN and EtOH affords
lustrous red crystals of 1 and brown crystals of 2. respectively.
Analytical and spectroscopic data are consistent with these formulations. In order to fully establish the structure of these products, single-crystal X-ray determinations were undertaken.
The single-crystal structure of 1
shows the
[Ag([18]aneS6)]+ ions embedded in a three-dimensional polymeric polyiodide matrix (Fig. 1). The structure of the (I;)"
polyiodide network in the crystal lattice can best be described as
Self-Assembly of Polyanions at a Metal Cation
Template: Syntheses and Structures of
w g ( ~ 1 ~ 1 a n e ~ , ) 1 1 ,and
1 , ~4g([18ianes,)11,**
Alexander J. Blake, Robert 0. Gould, Simon Parsons,
Christian Radek, and Martin Schroder*
The formation and stability of extended polyiodide species
has been found to be dependent on the size of the accompanying
cation."] We have been interested over the past few years in the
coordination chemistry of transition metal ions with homoleptic
macrocyclic S-donor ligands.[21In the context of this work we
were interested in ascertaining whether metal macrocyclic
cations could be used to template-synthesize extended polyiodide arrays. While numerous examples of small polyiodides
such as I;, Ti-, and I; have been r e p ~ r t e d , ' ~ only
. ~ ] a few large
and very large polyiodide species such as 1.; I;-, I,, I;;, I,:
I;;, and 1;: are k n ~ w n . [ ~ - We
' ~ ] report
herein the synthesis of a new polymeric (I;),,
polyiodide species assembled around a central macrocyclic cation, [Ag([18]aneS6)1+.
Reaction of [Ag([l 8]aneS6)]BF4 with I,
afforded, after evaporation of the solvent in
vacuo, a dark blue powder. No precipitation
of AgI was observed, confirming the effec[ 1 8]anS6
tive encapsulation of the Ag+ ions by
[18]aneS6. The elemental analysis data are
consistent with the stoichiometry [Ag([l8]aneS,,)]Is. while the
FAB mass spectrum shows a peak at rn/z 469 with an isotopic
Prof. Dr. M. Schroder. Dr. A. J. Blake
Department of Chemistry, The University of Nottingham
University Park. Nottingham NG7 2RD ( U K )
Telefax: Int. code (115)9513563
Dr. R . 0. Gould, Dr. S. Parsons. Dr. C. Radek
Department of Chemistry. The University of Edinburgh
West Mains Road. Edinburgh. EH9 3JJ ( U K )
This work was supported by the Engineering and Physical Sciences Research
Council, UK. [IX]aneS, = 3,16-hexathiacyclooctadecane.
Fig. 1. View of the polymeric matrix of I
a distorted cubic structure in which 1- ions occupy the lattice
points of a primitive rhombohedral lattice with one I, molecule
[ILI 2.7519(14) A] placed along each edge, bridging two I - ions,
I . I 3.3564(15) A. The 1-1 bond length in the I, molecule in
1 is longer than that in I, in the vapor [2.667(2) A][''] and in the
solid state [2.715(6)
This elongation is attributable to
donation of electron density from I - into the o*-antibonding
LUMO of the I, molecule. The structure is completed by an
[Ag([18]aneS6)]+ ion sitting inside each rhombohedral interstice
(Fig. 2).
I; polyiodide species have been reported previously although
none with the current cubic structure. The structures of
(Et,N)17L51and [(py),I]17r61(py = pyridine) show a three-dimensional network of symmetrical I; anions and I, molecules
and these are therefore better described as an adduct of
[(I;).(I,)J. The two compounds (Hpy),I,I,[71 and [(N-methylbenzothiazole-2(3 H)-thione),I]I,[*] feature I; ions which are
to a first approximation isolated species but linked through
long-range 1 . . I interactions of 3.545(13) and 3.502(1) A, respectively. to give one-dimensional infinite chain structures. The
I; ion in these two structures can be described as adducts of
[(I-).(T,)J. The structure of (PPh,)I,, however, does show discrete I; units.[']
The single-crystal structure determination of 2[12]shows discrete metal macrocyclic cations [Ag([l 8]aneS6)]+and symmetrical I; ions [I- I2.9137(3) A] in the crystal lattice. The packing
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structure, metali, catalysing, homogeneous, complexes, heterocyclic, carbenes, new, catalyst, principles
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