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Evidence for Equilibria between -Alkyne and Alkylidyne Complexes of Tungsten Alkoxides [W2(OR)6(-C2R2)] 2[(RO)3W CR].

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genation of higher-molecular-weight samples in organic
solvents afforded insoluble products.['61
This polymer synthesis can be considerably varied by
the choice of the bridges and the reducible 7c-system.L'21
brium constant K is dependent upon the nature of R and
R', bulky combinations favoring the alkylidyne species.
Received: November 21, 1985;
revised: February 24, 1986 [Z 1548 IE]
German version: Angew. Chem. 98 (1986) 446
[ I ] J. Fiedler, W. Huber, K. Mullen, Angew. Chem. 98 (1986) 444; Angew.
Chem. Inr. Ed. Engl. 25 (1986)443.
[2] W. Huber, H. Unterberg, K. Mullen, Angew. Cbem. 95 (1983) 239; Angew. Chem. I n t . Ed. Engl. 22 (1983) 242; Angew. Chem. Suppl. 1983.
288.
131 J. H. Golden, J . Cbem. SOC.1961. 3741.
[4] K. Miillen, W. Huber, G. Neumann, C . Schnieders, H. Unterberg, J. Am.
Cbern. SOC.107 (1985) 801.
151 M. Daney, G. F. R. Lapouyade, H. Bouas-Laurent, Fr. Pat. Appl.
2314165 (1977).
161 E. Hobolth, H. Lund, Acra Chem. Scand. 8 3 1 (1977) 395.
[7] D. Lipkin, G. J. Divis, R. W. Jordan, Am. Chem. Soc. Diu. Pet. Chem.
Prepr. 13 (1968) D60.
181 F. J. Burgess, A. V. Cunliffe, D. H. Richards, Eur. Polym. J. I0 (1974)
665.
[9] F. Vogtle, P. K. T. Mew, Angew. Cbem. 90 (1978) 58;Angew. Chem. In!.
Ed. Engl. 17 (1978) 60.
[lo] R. G. Harvey, L. Nazareno, H. Cho, J . Am. Cbem. Soc. 95 (1973) 2376.
[ I I] Column combination: p-ultrastyragel 10' A, p-styragel 500 A and 100
mobile phase: chloroform. We thank Prof. Dr. R . C. Scbulz and Dipl:
Chem. K . Miihlbach for experimental assistance.
[I21 Chemical and physical properties of 6 and 7 : D. Bender, K. Mullen, M.
Przybylski, unpublished results.
[I31 Typical "C-NMR chemical shifts of 6 ( n = 3 ) (CDCI,, 100 MHz): 6, for
nonterminal fragments: 46.2 (-CH), 42.2 (a-CH,), 27.0 (B-CH2).
[I41 The elemental analyses gave correct values and showed at the same time
that type 6a (with two dihydroanthracene moieties) predominates.
[IS] F. J. Burgess, A. V. Cunliffe, D. H. Richards, Eur. Polym. J . I0 (1974)
657.
[I61 The dehydrogenation was also achieved with chlorantl as well as with
nBuLi/tetramethylethylenediamine and iodine; however, the reaction
mixtures were difficult to purify. The structural assignment of the insoluble samples of 7 was achieved by comparison of the IR spectra with
those of model compounds (see 1-3 in [I]). For the partially dehydrogenated samples, the formation of anthracene n-systems could be fol\owed by 'H- a n d "C-NMR spectroscopy.
A;
Evidence for Equilibria between p-Alkyne and
Alkylidyne Complexes of Tungsten Alkoxides:
[WZ(OR)&-C,R;)I $ 2 [ ( R 0 ) 3 W ~CR'I**
By Malcolm H . Chisholm,* Brian K . Conroy.
John C. Huffman, and Nancy S . Marchant
The cleavage of alkynes to form two alkylidyne moieties
has been observed at dinuclear,"." t r i n ~ c l e a r , ' ~ -and
~ ] tetranuclearr8]metal centers. The reverse reaction, the coupling of two alkylidyne ligands, is also k n o ~ n . [In
~ .cer~~
tain instances a reversible process can be induced by C O
elimination o r ~ p t a k e . [ ~Recently,
.~I
we suggested that a dynamic equilibrium between the p-alkyne ditungsten complex l a and the alkylidynetungsten complex 2a, involving
the elimination or uptake of pyridine, exists in solution at
room temperature [Eq. (a)].['] Here, we present evidence for
a general equilibrium of this type for which the equili-
[*] Prof. M. H. Chisholm, B. K. Conroy, Dr. J. C. Huffman,
N. S. Marchant
Department of Chemistry and Molecular Structure Center,
Indiana University
Bloomington IN 47405 (USA)
I**] This work was supported by the Department of Energy, Office of Basic
Sciences, Chemical Division, and by the Wrubel Computing Center.
446
0 VCH Verlagsgesellschafi mbH. 0-6940 Weinheim, 1986
1.2
[
n
a
b
C
d
e
tEu
H
I
fBuCHa
H
2
tBuCHz
Me
2
fBuCHz
Et
I
IBUCHz
Ph
1
The addition of sterically bulky alkynes to [W,(OtBu),]
results in the formation of alkylidyne species in high yields
(i. e., alkyne cleavage).[11By reducing the steric demands of
the alkoxide ligands, we were able to prepare the stable
p-alkyne complexes lb-e [Eq.(a)].I2]
In principal the equilibrium (a) should be observable by
UV/VIS spectroscopy since the alkyne adducts are blue or
green whereas the alkylidyne species are yellow and d o not
show an absorption maximum in the visible region of the
spectrum. The alkyne adducts lc-e d o not obey the BeerLambert Law for their absorptions in the visible region.
Hydrolysis by traces of water or oxidation by adventitious
0, under the high-dilution conditions employed, which are
necessary to drive the equilibrium to the right, may be responsible for such behavior. This precludes determination
of the equilibrium constant K . Consequently, we have used
trapping reagents to obtain chemical evidence for the existence of the equilibrium (a).
The alkyne adducts lc-e can be used as alkylidyne
sources for the preparation of alkylidyne clusters 3 according to Equation (b).
Addition of the alkyne to [w,(oCH,tB~),(py)~](molar
ratio 1 :3) results in the direct formation of the alkylidynecapped tritungsten compounds 3. 'H-NMR studies
showed that the complexes 1 were formed initially [Eq.
(b)]. The rate of formation of 3 follows the order
Et = Ph > Me, which probably reflects the magnitude of K
in Equation (a). Interestingly, no p3-CH cluster could be
prepared by this route. Furthermore, in a double labeling
experiment involving [Wz(OCH2tBu)6(py),(p-*C2H2)]and
[W2(OCH2tBu)6(py)2(p-C2D2)],
we found no evidence for
formation of [W,(oCHtBU),(py)z(~-L-H*CCD)J (*C represents 92.5 mol-% "C).
The new compounds 3 are analogous ('H-, I3C-NMR)
to [W3(p3-CMe)(OiPr)9],which was previously prepared by
the comproportionation of [(tBuO),W=CMe] 419] and
[W,(OiPr),] in the presence of iPrOH."']
Further evidence for equilibrium (a) is provided by the
reaction of 4 with CO. Addition of C O ( 1 atm) to a hexane
solution of 4 results in a color change (pale yellow to blue)
and the quantitative formation of complex 5 (Eq. (c)].[l'l
2[(tBuO),W=CMe]
+ CO
4
0570-0833/86/0505-0446 $ 02.50/0
-
[W2(OtBu),(CO)(~-C2Me2)] (c)
5
Angew. Cbem. In!. Ed. Engl. 25 (1986) No. 5
Reaction (c) is complete after 24 h ('H-NMR). Under
analogous conditions, the complexes [(tBuO),W=CR'],
R=Et, Ph, d o not react, suggesting that, for these complexes, the equilibrium (a) lies far to the right.
Fig. I . Crystal structure of 5. Selected bond distances [A] and angles ["I: W-W
2.633( I), W( 1)-C(4) 2.124(15), W( 1)-C(5) 2.169(16), W(2)-C(4) 2.173( 14),
W(2)-C(5) 2.098( 15). C(4)-C(5) 1.36(2), W-O(termina1) 1.90(2) (averaged),
W-O(bridging) 2.065( lo), W(2)-C(37) 1.988(15), C(4)-C(5)-C(6) 12611).
C(S)-C(4)-C(3) 130(I), W(2)-C(37)-0(38) 173(1). Further details of the crystal
structure investigation are available on request from the Fachinformationszentrum Energie, Physik, Mathematik GmbH, D-75 14 Eggenstein-Leopoldshafen 2(FRG),on quotingthe depositorynumberCSD 51748,the namesofthe
authors, and the full journal citation.
[6] a) J. R. Shapley, J. T. Park, M. R. Churchill, C. Bueno, H. J . Wasserman,
J . Am. Chem. SOC.103 (1981) 7385; b) M. R. Churchill, C. Bueno, H. J.
Wackerman, Inorg. Chem. 21 (1982) 640.
[7] a) L. Busetto, M. Green, J. A. K. Howard, B. Hessner, J. C. Jeffrey, R.
M. Mills, F. G. A. Stone, P. Woodward, J . Chem. Soc Chem. Commun.
1981. 1 I01 ; b) L. Buestto, J. C. Jeffery, R. M. Mills, F. G. A. Stone, M. J.
Went, P. Woodward, J. Chem. SOC. Dalton Trans. 1983, 101; c ) J . C.
Jeffery, J. C. V. Laurie, F. G. A. Stone, Polyhedron 4 (1985) 1135; d) M.
Green, S. J. Porter, F. G. A. Stone, J. Chem. SOC. Dalton Trans 1983,
513; e) M. Green, J. C. Jeffery, S. J. Porter, H. Razay, F. G. A. Stone, J.
Chem. SOC.Dalton Trans. 1982. 2475.
[8] J. T. Park, J. R. Shapley, M. R. Churchill. C. Bueno, J . Am. Chem. Soc.
105 (1983) 6182.
191 M. H. Chisholm, D. M. Hoffman, J. C. Huffman, Inorg. Chem. 22 (1983)
2903.
[lo] M. H. Chisholm, K. Folting, J. A. Heppert, D. M. Hoffman, J. C. Huffman, J. Am. Chem. SOC.107 (1985) 1234.
[ I I] Schrock and co-workers have studied reactions of other alkyhdynes with
CO: a) M. R. Churchill, H. J. Wasserman, S. J. Holmes, R. R. Schrock,
Organometallics I (1982) 766; b) J. H. Wengrovius, R. R. Schrock, M. R.
Churchill, H. J. Wasserman, J. Am. Chem. Soc. 104 (1982) 1739.
1121 C. N. Wilker, R. Hoffrnann, 0. Eisenstein, N o w . J . Chim. 7 (1983)
535.
Cphenyl-H.
. . O and Cphenyl-H.
. .N Interactions:
Crystal Structure of
(.Z)-4-Benzylidene-2-methyl-5(4H)-oxazolone,
an Intermediate for Dehydropeptide Synthesis
By Mohamed Souhassou, Andre Aubry, Guy Boussard,
and Michel Marraud*
Complex 5 can be isolated as dark blue crystals from
hexane. 'H- and I3C-NMR spectroscopic studies support
the existence of a static structure, having a mirror plane of
symmetry, on the N M R time scale. The molecular structure deduced from a single-crystal X-ray study i s shown in
Figure 1 . In the IR spectrum v ( C 0 ) occurs at 1917 cm-',
which is indicative of extensive W-to-CO back-bonding. It
is this n-acceptor property of C O that stabilizes the
p-C2MeZadduct relative to the alkylidyne species 4.
Theoretical studies predicted"" that there would be virtually no energy barrier for the interconversion of L3M(pL ) ( F - C R ) ~ M Land
~
L6M2(p-L)(p-C2R2)complzxes where
the electron count on each metal was between d4 and d8
(the ligands L being counted as neutral rather than
charged).
The spatial distribution of atoms in the environment of
the phenylalanine aromatic rings in protein"] and peptide1*]crystal structures has revealed that the carbonyl oxygen atoms are preferentially situated in the plane of these
aromatic rings; a b initio calculations on benzene and
formamide have suggested the existence of a favorable enthalpic interaction."' Moreover, Taylor and Kennard have
presented crystallographic evidence, obtained by neutron
diffraction experiments, for hydrogen bonds involving
C-H bonds and 0 or N
A C - H . . ' 0 contact can
be described as a hydrogen bond when the H. . ' 0 distance
is shorter than 2.4 A (i.e., C . . .O < 3.5 A for a linear
arrangement of the three atoms) and the C-H. ..O angle is
greater than 90".
Received: December 11, 1985;
revised: January 27, 1986 [Z 1581 IE]
German version: Angew. Chem. 98 (1986) 448
CAS Registry numbers:
la, 87667-98-9; Ib, 101518-65-4; lc, 88608-51-9; Id, 101077-89-8; le,
101164-93-6; Za, 91389-20-7; Zb, 101518-69-8; Zc, 101077-93-4; Zd, 10107792-3; Ze, 101077-91-2; 3 (R'=Me), 101518-66-5; 3 (R'=Et), 101518-67-6; 3
(R'=Ph), 101518-68-7; 4, 82209-23-2; 5, 101077-90-1; [W2(0CH~tB~),(py)z],
88608-50-8.
[ I ] a) R. R. Schrock, M. L. Listemann, L. G. Sturgeoff, J. Am. Chem. SOC.
104 (1982) 4291: b) M. L. Listemann, R. R. Schrock, Organometallics 4
(1985) 74; c) J. H. Freudenberger, S. F. Pedersen, R. R. Schrock, Bull
SOC. Chim. Fr. 1985, 349; d ) F. A. Cotton, W. Schwotzer, E. S. Shamshoum, O r g a n o m e f a l h 3 (1984) 1770.
[2] a) M. H. Chisholm, K. Folting, D. M. Hoffman, J. C. Huffman, J. Am.
Chem. SOC. 106 (1984) 6794; b) M. H. Chisholm, D. M. Hoffman, J. C.
Huffman, Chem. SOC.Rev. 14 (1985) 69.
[3] a) A. D. Clauss, J. R. Shapley, C. N. Wilker, R. Hoffmann, Organometallic.~3 (1984) 619; b) Y. Chi, J . R. Shapley, ibid. 4 (1985) 1900.
[4] D. Nuel, F. Daham, R. Mathieu, Orgonometalks 4 (1985) 1436.
[5] N. T. Allison, J. R. Fritch, K. P. C. Vollhardt, E. C. Walborsky, J. Am.
Chem. Soc. I05 (1983) 1384.
Angew. Chern. Int. Ed. Engl. 25 11986) No. 5
1
We report here on the crystal structure of 1, which contains two short C-H. . .O and C - H . . . N contacts involving aromatic H atoms.
The existence of a$-dehydro amino acid residues in naturally occurring microbial peptides exhibiting antibiotic
activity has incited chemists to introduce these modified
[*] Dr. M. Marraud, Dr. G. Boussard
Laboratoire d e Chimie Physique MacromolCculaire
C.N.R.S.-UA-494, ENSIC-INPL
1 rue Grandville, F-54042 Nancy (France)
Dr. A. Aubry, M. Souhassou
Ldboratoire de Mineralogie et Cristallographie
C.N.R.S:UA-809
Universite de Nancy I, BP 239, F-54506 Vandcmvre (France)
0 VCH Verlagsgesellschafi mbH. 0-6940 Weinheim. 1986
0570-0833/86/0505-0447 $I 02.50/0
447
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alkynes, evidence, alkoxide, c2r2, complexes, tungsten, equilibrium, alkylidyne
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