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Stoichiometric and Catalytic Metathesis of Carbodiimides and Pentacarbonylcarbenetungsten Complexes.

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Stoichiometric and Catalytic Metathesis of
Carbodiimides and Pentacarbonylcarbenetungsten
Complexes**
By Karin Weiss* and Petra Kindl
The carbene complexes pentacarbonyl(dipheny1carbene)tungsten la['] and pentacarbonyl[methoxy(phenyl)carbene]tungsten 1b"I exhibit low activity as metathesis catalysts and so are especially suitable for the investigation of stoichiometric model reactions such as, e.g., metathesis with alkenes o r vinyl ether^'^.^'. Stoichiometric or catalytic metathesis reactions have so far been achieved with
cyclic or acyclic alkenes, which only in exceptional cases
contained substituents bearing heteroatoms. Metathesis
reactions of heteroaljenes with carbene complexes were hitherto unknown. Isocyanates react as heteroallenes with
carbonyl compounds as catalysts to give carbodiimides
and C0,[41, a metathesis which has so far not been recognized as such. On reaction of the model catalysts 1 with
the heteroallenes dicyclohexylcarbodiimide 2a and diisopropylcarbodiimide 2b, we obtained the metathesis products pentacarbonyl(cyclohexy1isocyanide)tungsten 3 a or
pentacarbonyl(isopropy1isocyanide)tungsten 3b, as well as
the Schiff bases N-(diphenylmethylene)cyclohexylamine
4a, N-(diphenylmethy1ene)isopropylamine 4 b and N-(amethoxybenzy1idene)isopropylamine 4c. The reactions (in
pentane at 20°C) were monitored spectroscopically (IR: vN=C=N-). Reaction of complex la was complete after 3
h, whereas 1b was completely converted only after 24
h15'.
1
2
C6H5
N,
I
'
R2
-C
I
B
R R2
thesis reactions of alkenes@].Two different orientations of
the carbodiimides with respect to the W=C(carbene) bond
are conceivable (A and B). From the reaction products it
follows that there is a clear selectivity for orientation A; a
pentacarbonyl(imido)tungsten should be formed from B
(cf. "I).
In metathesis reactions with cdrbene complexes of the
Fischer-type, cyclopropanes are often also formed in a
competing reaction by formal [2 I]-cycloaddition of the
olefins with the carbene ligands'"]. However, in the reaction of the carbodiimides 2 with the carbene complexes 1
cycloadducts were not observed, only the products resulting from metathesis.
At 20°C, the carbene complexes 1 are not active as catalysts for the metathesis of symmetrical carbodiimides, e.g.
2a and 2b.
+
C,H,,N=C=NC,H,,
+ (CH,)zCHN=C=NCH(CH3)z +
2a
2b
Rather, the isocyanide complexes 3 and the Schiff bases 4
are formed stoichiometrically. The carbene complexes 1
and 2 catalyze the metathesis of 2a and 2b at temperatures greater than or 140°C to give "mixed" carbodiimides 5 . That is, the isocyanide complexes 3, formed in the
course of the reaction from I and 2, are thought to be the
actual catalysts for the carbodiimide metathesis (2nd generation catalysts). Indeed, under these conditions (i.e. at
140°C) 3a and 3b show the same catalytic activity as the
carbene complexes 1.
Since 1 and 3 catalyze both the forward as well as the
reverse reaction, the conversion proceeds only until equilibrium is established, as in the case of the metathesis of
acyclic olefin~[*.~].
R'
(C01,jW-
C-C6H5
I
,
1
ICOI~WIC-NR~
+
R~N:C,
ICO),
,R'
w- c
I
CHICHJIZ
I
C6H5
3
Reaction
+
+
l a 2a-3a
4a
l a + Zb-3b
4b
l b t 2 b - 3 b + 4~
+
R'
(from 1 )
RZ
(from 2)
3
Yield.[%]
4
Ph
Ph
OMe
c-Hex
iPr
iPr
98
88
7Y
95
93
90
(CO)gW=C:N C6H11
+ (CH~)~CHN=C-NCH(CH,)
2b
-c
I
The course of the metathesis can be easily explained in
terms of an azatungstacyclobutane intermediate. Similar
metallacyclobutane intermediates are postulated for meta[*] Dr. K. Weiss, P. Kindl
C6H 1, N -C - N C H ( CH3)
+
5
ll
3a
(C01,W
[**I
C6H 1 1
C6H11N
4
//NC6H11
1
tl
Laboratorium fiir Anorganische Chemie der Universitat
Postfdch 3008, D-8580 Bayreuth (FRG)
Investigations of Polymerization and Metathesis Reactions Part 2.Part I : K. Weiss, K. Hoffmann, J . M o k Catal., in press.
Angew. Chem. Int. Ed. Engl. 23 (1984) N o . 8
0 Verlag Chemie GmhH, U-6940 Weinheim, /9#4
0570-0833/#4/0~OX-o62Y $ 02 50/0
629
The course of the reaction can be readily explained in
terms of an (not detected) azatungstacyclobutane intermediate. With the exception of the formation and decomposition of the intermediates, the partial reactions can also be
monitored stepwise. If, e.g., 3b is allowed to react at 140°C
with excess dicyclohexylcarbodiimide 2a, then 3a as well
as 3b can be detected in the reaction mixture by mass
spectrometry. Correspondingly, 3a reacts with excess diisopropylcarbodiimide 2b to give 3b. These findings support the postulated reaction course as proceeding via isocyanide complexes, which are newly formed in each reaction step. The metathesis of two symmetrical carbodiimides to give "mixed carbodiimides" such as 5 with pentacarbonyl(isocyanide)tungsten complexes 3 as catalysts
provides a facile route to these compounds, which can be
used for numerous organic syntheses['01.
This first catalytic metathesis of carbodiimides shows
that not only alkenes and alkynes undergo metathesis reactions, but that heteroallenes are also capable of doing so in
the presence of suitable catalysts.
Received: March 26, 1984;
revised: May 29, 1984 [Z 7791780 IE]
German version: Angew. Chem. 96 (1984) 616
[l] C. P. Casey, T. J. Burkhardt, J. Am. Chem. Soc. 96 (1974) 7808.
121 E. 0. Fischer, A. Maasbol, Cheni. Ber. 100 (1967) 2445.
[3] K. Weiss, K. Hoffmann, J. Organomet. Chem. 255 (1983) C24.
141 H. Ulrich, B. Tucker, A. A. R. Sayigh, Tetrahedrun Lett. 1967, 1731.
[5] Procedure for stoichiometric metathesis: A solution of 1 (1 mmol) in
pentane (20 mL) is treated at 20°C with 1 mmol of 2. After 3 h ( l a ) and
24 h ( l b ) , respectively, the reaction mixture is separated by column
chromatography (2.5 x 10 cm, silica gel, calcined at,80O0C).The isocyanide complexes 3 are first eluted with pentane, and then the Schiff bases
4 with ether. 3 and 4 were identified by their IR, "C-NMR, 'H-NMR,
and mass spectra.
(61 K. Weiss in K. H. Dotz: Transition Metal Carbene Complexes, Verlag
Chemie, Weinheim 1983.
[7] S. F. Pedersen, R. R. Schrock, J. Am. Chem. Soc. 104 (1982) 7483; D. C.
Bradley, M. B. Hursthouse, K. M. Malk, J. A. Nielson, R. L. Short, J.
Chem. Sor. Dalton Trans. 12 (1983) 2651.
[S] K. J. Ivin: Olefin Metathesis. Academic Press, London 1983.
[Y] Procedure for catalytic metathesis: A mixture of 2a (2 g, 10 mmol) and
2b (1.3 g, 10 mmol) is treated with 30 mg (0.08 mmol) 3b and then
heated in a n oil bath at 140°C. In a control experiment a mixture of the
same amounts of 2a and 2b without catalyst is heated to 140°C. The
course of the reaction is monitored by gas-chromatography (capillary
column: OV 101, T=6O-27O0C, 3"C/min). The reaction mixture with
added catalyst contained 47% N-cyclohexyl-N'-isopropylcarbodiimide
5
after 14 h (at 140"C), that without catalyst only 0.12% 5 . The reaction
products were identified by GC/MS.
[lo] A. Williams, I. T. Ibrahim, Chem. Reu. 81 (1981) 589.
have now synthesized Ir(CO)C12(PEt3)2(P'F4),whose 19Fand 3'P-NMR spectra unequivocally show the presence of
the Ir-P'F4 group.
Ir(CO)C1z(PEt,)zF'Fz+ XeF,
By E. A . V. Ebsworth*, John H . Holloway,
NicholasJ. Pilkington, and David W. H. Rankin
Compounds containing metal atoms bound to pentaWe re~ently'~]
coordinated P, As, or Sb atoms are
described the complex Ir(CO)C12(PEt3)2(P'C14)and characterized it by NMR spectroscopy and elemental analysis;
however, the characterization of P' as pentacoordinated
was based on the failure of solutions to conduct. By treating 1 with XeF,, a valuable, mild, fluorinating agent[41,we
0 Verlug Chrmir GmhH, 0-6940 Weinheim, 1984
+
I ,co
C1-Ir.-P'F4
Cl'
I
The reaction is very slow at 220 K but rapid at or above
280 K. The product, which appears to be stable at room
temperature in the absence of air or moisture, has been isolated as a white solid and characterized by partial elemental analysis and by NMR spectroscopy. The 31P('H]-NMR
spectrum in CDzClzat 300 K consists of a broad quintet of
triplets due to the P' nucleus (see Fig. la) and a narrow
.
a)
500Hz
-50
-6 0
-70
-80
-90 -6
(3'p)
bl
-10 --F(3'pj
Fig. 1. Part of the 80. I MHz "P{'lIJ-NMR spectrum of 2 at 300 K i n CD,CI,:
a) is assigned to the P' nucleus and b) to the P nuclei.
doublet of quintets due to the P nuclei (see Fig. lb); the
I9F-NMR spectrum at 220 K in the same solvent is a broad
doublet of triplets. The "P( I9F}-NMRspectrum is sharp at
220 K, but becomes very broad at 190 K, showing that the
molecule is fluxional and that there must be at least two
different F sites in the static structure.
Received: March 26, 1984;
revised: May 3, 1984 [Z 776 IE]
German version: Angew. Chem. 96 (1984) 608
Department of Chemistry, University of Edinburgh
West Mains Road, Edinburgh EHY 353 (Scotland)
630
Xe
L
[*] Prof. Dr. E. A. V. Ebsworth, N. J. Pilkington, Dr. D. W. H. Rankin
Dr. J. H. Holloway
Department of Chemistry, University of Leicester
University Road, Leicesler LEI 7RH (England)
CHzClz
280 K
1
-9
An Iridium(m) Complex Containing
a PF,-Group Bound to the Metal
-
[I] W. Malisch, H. A. Kaul, E. (iross, U. Thewald, Anyew. Chem. 92 (1984)
554; Angew. Chem. Inr. Ed. Enql. 21 (1982) 549; Angew. Chem. Suppl.
IY82, 1281.
0570-0833/84/080~-0630$ 02.5(1/0
Angew. Chem. inl. Ed. Enql. 23 (1984) No. 8
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carbodiimide, metathesis, pentacarbonylcarbenetungsten, stoichiometry, catalytic, complexes
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