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DielsЦAlder Reactions at Carbene Ligands A Route to Olefin-Carbene Complexes.

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2.017(3)A places 3 in the class of complexes with short
Cr-Cc;lrbrnc
Diels-Alder Reactions at Carbene Ligands:
A Route to Olefin-Carbene Complexes**
By Karl Heinz DOtz,* Werner Kuhn, Gerhard Muller,
Brigitte Huher, and Helniut G. Alt
Carbene complexes containing unsaturated carbene ligands have proved to be versatile synthetic building
blocks.'*] In view of the isolobal r e l a t i ~ n s h i p between
~~]
a
pentacarbonylmetal fragment ( M = Cr, Mo, W) and an oxygen atom, alkenyl(a1koxy)carbene complexes may be regarded as analogues of acrylic esters and thus as potential
dienophiles in [4 + 21 c y c l ~ a d d i t i o n s . ~ ' ~ ~ ~
Pentacarbonyl[isopropen yl( methoxy)carbene]chromium
1 reacts with cyclopentadiene at room temperature to give
the endo/exo cycloadduct 2a,b. In the process, the endo
compound 2b already undergoes partial decarbonylation
to form the olefin-carbene complex 3.
38
Fig. 1. Molecular structure ot' 3 in the cryatal (ORTEP, thermal ellipsoids
with 50% probability, H atoms with arbitrary radius). Selected bond distances
and bond angles ["I: Cr-CI 2.017(3), Cr-C34 2.366(3), Cr-C35
2.286(3), Cr-CI I 1.887(3), Cr-C12 1.902(3), Cr-C13 1.896(3), Cr-C14 1.842(3),
CI-021 1.312(4), CILC31 1.523(4); C34-Cr-C1 86.l(l), C35-Cr-CI 79.2(1),
C1 I-Cr-CI 9l.4(1), CI2-Cr-CI 168.8(1), C13-Cr-CI 85.4(1), C14-Cr-CI
102.8(1), Cr-CI-C3l l18.0(2), Cr-CI-021 134.0(2), C31-CI-021 108.0(3).
[A]
Experimental Procedure
2a
2b
3
The stereocontrol exerted by the (C0)5Cr fragment is revealed in the endo/exo ratio of (2b + 3)/2a =60/40. A
similar ratio is observed for the isolobal methyl methacrylate in AICl,-catalyzed reactions;['] however, the uncatalyzed reaction is known to satisfy poorly the Alder endo
rule161and results therefore in a reversal of the product distribution."]
The olefin-carbene complex 3 belongs to a class of compounds that is important for the discussion of the mechanism of the olefin metathesis reaction.[*]To date only a few
compounds containing other metals have been isolated;191
3 is the first example of a chromium compound. Complex
3 is preferentially formed in good yield by heating the
mixture of isomers 2a,b and can be separated from the
unchanged ex0 isomer 2a by column chromatography.
The structure of 31"'1confirms the alkene coordination
of the olefin-carbene ligand to the Cr(CO), fragment,
which is possible owing to the endo position of the carbene
carbon atom C1 on the norbornene skeleton (Fig. 1). The
alkene function is thereby bonded unsymmetrically to the
metal ; the Cr-Calkene
distances (2.286(3) and 2.366(3) A'' 'I)
are relatively longLiZ1
Both findings are a consequence of
the rigidity of the norbornene skeleton and the short separation of the chromium-coordinated carbene and alkene
functions by only two carbon atoms (C31, C36). The deviation from ideal octahedral symmetry at the central metal
atom is due to the chelate structure. The Cr-C1 distance of
[*I
[**I
8 12
Priv.-Doz. Dr. K. H. Dotz, Dr. W. Kuhn, Dr. G. Muller, B. Huber
Anorganisch-chemisches lnstitut der Technischen Universitat Miinchen
Lichtenbergstrasse 4, D-8046 Garching (FRG)
Priv.-Doz. Dr. H. G. Alt
Laboratorium fur Anorganische Chemie der Universitat
Universitatsstrasse 30, D-8580 Bayreuth (FRG)
Reactions of Complex Ligands, Part 26. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. Part 25: [I].
1'(11 l i ~ ~ i i i ~ s g e . ~ e l l . smbH.
c h a ~ i0-6940 Weinheim. 1986
813-816 Adueriisement
2a,b: A solution of I (0.68 g, 2.46 mmol) [I41 in 10 mL of cyclopentadiene
was allowed to warm slowly from -60°C to room temperature. After 4.5 h,
the solvent was removed and the residue was chromatographed at -30°C on
silica gel. The faster running orange-yellow band contained the mixture of
isomers 2a,b (0.57 g, 68%)). the following fraction afforded 3 (0.13 g,
17"/o).-Za,b: IR (hexane): G(C=O)=2061 m, 1983 w, 1960 s (sh), 1953 vs,
1938 s ; MS: m / z 342 ( M ' ) -2a: 'H-NMR (CDKOCD,): 6=6.2I (m, 2 H ,
=CHj. 5.03 (s, 3 H , OCH,), 3.50 (m. I H, CH), 2.82 (m, 3 H , CH, C H I ) , 1.42
(m, 2 H , CH,), 1.11 (s, 3 H , C H , ) ; "C-NMR (CDKOCD,): 6=371.7
(C,,,,,),
224.2 (Irons-CO), 217.6 (cis-CO), 140.9 (=CH). 135.1 (=CH), 73.1
(Cqu,,r,j,70.0 (OCH?), 51.7 (CHj, 50.3 (CH:), 43.2 (CH), 42.4 (CH?). 26.7
(CH,).-2b:
'H-NMR (CD,COCD?): 6=6.02 (m. 2H, =CH), 4.96 (s, 3H,
OCH,), 2.97 (m, 4H, C H , CH,), 1.44 (m, 2H, C H 2 ) , 1.37 (s, 3 H, C H , ) , "CNMR (CDKOCD,): 6=373.5 (C,,,,,),
224.3 (trans-CO), 217.3 (cis-CO),
137.2 (=CH), 136.8 (=CH), 74.3 (Cqu.,,,),69.3 (OCHZ),53.3 (CH),47.2 (CHI),
43.9 (CH), 43 2 (CH?), 28.6 (CH,).
3 : A stream of N 2 was bubbled for 64 h through a solution of 2a,b (0.48 g,
1.40 mmol) in 20 m L of tert-butyl methyl ether at 55°C.After removal of the
solvent, the residue was chromatographed at -30°C with hexane on silica
gel. Unchanged 2a (0.22 g) was eluted initially, followed by a fraction that
afforded orange-red crystals of 3 (0.21 g, 88%).-1R
(hexane):
G(C=0)=2018 s, 1955 s, 1940 vs, 1905 s; MS: m / z 314 ( M + ) ; ' H - N M R
(CDKOCD,): 6=6.27 (m, 1 H, =CH), 5.58 (m, I H, =CH), 4.61 (s, 3H,
OCHI),2.87(m,1H,CH),2.55(m,2H,CH,),2.17(m,1H,CH),1.41(m,2H,
C H 2 ) ,0.93 (s, 3 H, CH,); "C-NMR (CD,COCD,): S=363.6 (C,.,,,),
238.0
and 226.9 (trans-CO), 226.2 and 224.4 (cir-CO), 102.4 (=CH), 95.2 (=CH),
69.5 (C,,,,,,),
69.1 (OCH.3), 60.4 (CH2), 53.6 (CH), 48.5 (CH,), 42.2 (CH), 21.6
(CH,).
Received: May 2, 1986 [Z 1755 IE]
German version: Angew. Chem. 98 (1986) 826
CAS Registry numbers:
1, 87965-61-5: 2a, 103883-74-5; Zb, 103958-04-9; 3, 103904-00-3; cyclopentadiene, 542-92-7.
[ I ] K. H. Dotz, W. Kuhn, J Organomet. Chem. 286 (1985) C23.
121 Recent reviews: K. H. Dotz, Angew. Chem. 96 (1984) 573; Angew. Chem.
Int. Ed. Engl. 23 (1984) 5 8 7 ; H. U. Reissig, Nachr. Chem. Rech. Lab. 34
(1986) 22.
[3] Cf. F. G. A. Stone, Angew. Chem. 96 (1984) 8 5 ; Angew. Chem. Int. E d
Engl. 23 (1984) 89.
[4] W. D. Wulff, D. C . Yang, J . Am. Chem. SOC.105 (1983) 6726; 106 (1984)
7565; W. D. Wulff, P.-C. Tang, K.-S. Chan, J. S . McCallum, D. C. Yang,
S . R. Gilbertson, Tetrahedron 41 (1985) 5813.
[5] T. Inukai, T. Kojima, J Org. Chem. 31 (1966) 2032.
[6J Review: H. Wollweber: Diels-A[der-Reaktion,Thieme, Stuttgan 1972.
[7] J . A. Berson, Z. Hamlet, W. A. Mueller, J . Am. Chem. SOC.84 (1962)
297.
0570-0833/86/0909-08/z $ 02.5010
Angew. Chem. Int. Ed. En@ 25 (1986) No. 9
t
[8] Recent review: K. J. lvin: Olefin Metuthesrs, Academic Press, London
1983.
[9] M. J. McGeary, T. L. Tonker, J. L. Templeton, Orgunometalks 4 (1985)
2 102, and references cited therein.
[lo] 3 is triclinic, space group Pi, u=6.848(1), b=8.412(1), c = 13.353(2)
a=9?.74(1), /i=
100.14(1), y = lll.21(l)o, Y=700.7
p r , l , c ~ 1.489
=
g
cm ' for 2 = 2 at -4O"C, F(000)=324,~~(Mo,,)=S.I c m - ' . 2468 independent reflections, 2232 "observed" with 12 2.00(1), Lorentz and empirical absorption correction (0 scan, Am= 1.4'. + h , +k, i l , (sin,9/
,i),,,,,,=0.595, Mo,,,, A=0.71069
Patterson methods, Rz0.042,
R , =0.056, w=[u'(F,,)+0.00013F2]-' for 181 refined parameters (anisotropic. H constant, A&,.= +0.99/-0.28 e/A', SHELX 76). Further details of the crystal structure investigation may be obtained from the Fachinforrnationszentrum Energie, Physik, Mathematik GmbH, D-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number
CSD 51 952, the names of the authors, and the journal citation.
[ I I] Cf. Cr-C 2.168(8) and 2.185(6)
in (q'maleic acid)(q"-mesitylene).
Cr(C0):: Yu. T. Struchkov, V. G. Andrianov, V. N. Setkina, N. K. Baranetskaya. V. I. Losilkina, D. N. Kursanov, J . Orgunomer. Cfiem. 182
(1979) 213. Also the Cr-C distances to the conjugated double bonds in
$-bonded arenes are generally shorter: cf. B. Rees, P. Coppens, Acfa
Crvstalfogr. 8 2 9 (1973) 2515.
[I21 Only a few examples of monoalkene complexes of chromium have been
reported earlier. I n most of the examples known that have been characterized structurally, the coordinated double bond is part of a chelate ligand as in 3; cf. R. Davis, L. A. P. Kane-Maguire in G. Wilkinson, F. G.
A. Stone, E. W. Abel (Eds.): Comprehensive Organometallic Chemistry.
Vol. 1. Pergamon Press, Oxford 1982, p. 953.
[I31 U. Schubert in K. H. Dotz, H. Fischer, P. Hofmann, F. R. Kreissl, U.
Schubert, K. Weiss: Transition Metal Carbene Complexes, Verlag Chemie, Weinheim 1983, p. 73ff; U. Schubert, Coord. Chem. Rev. 55 (1984)
261.
[I41 Synthesized analogously to the procedure in K. H. Dotz, W. Kuhn, K.
Ackermann, 2. Nuturforsch. 8 3 8 (1983) 1351.
A',
+ 3 co
w
A,
-
oc
A).
A
co,
3
*
4
t
t
-$?--
w
+ 3 co
Re - 0,
/
'5
R6
-
t
+
3
t
co
7
*
Reductive Carbonylation of
High-Valent Oxorhenium CompIexesa New Route to Low-Valent Carbonylrhenium
Compounds**
By Wolfgang A . Herrmann,* Ulrich Kiisthardt,
Adolf Schafer, and Eberhardt Herdtweck
The Re"" complex trioxo($-pentamethylcyclopentadieny1)rhenium I has proved to be a versatile, key compound
in organorhenium chemistry, because its 0x0 ligands can
be both functionalized and exchanged."] If complexes having rhenium in intermediate oxidation states are specifically accessible by redox processes, these complexes would
be of interest with respect to olefin metathesis, the best catalysts of which are oxidic molybdenum, tungsten, and rhenium species.'21 With this goal in mind, we have investigated the stepwise reduction of 1 in the presence of ligands that are capable of stabilizing both higher and lower
oxidation states of the metal.
Suitable precursors are the metallacycles 3 and 5 , which
may be obtained in smooth two-step reactions from 1 and,
respectively, diphenylketene and phenyl isocyanate via the
binuclear complex Z.L3.4) The Re" complex 3 can be reduced under CO (50 bar) at room temperature in tetrahy-
8
= CH3; R = C,H,
drofuran (THF), with cleavage of the terminal 0x0 ligand,
to give quantitatively the chiral Re"' derivative 4.
The air- and heat-stable compound 4 (m.p. = 171"C),
like its precursor 3, contains a four-membered metallacycle (Fig. 1); the 1,Lethenediolato ligand, which was 0 , O -
c25
cr4
1
c-43
c33
["I
Prof. Dr. W. A. Herrmann, U. Kiisthardt, A. Schafer,
Dr. E. Herdtweck
Anorganisch-chemisches Institut der Technischen Universitat Miinchen
Lichtenbergstrasse 4, D-8046 Garching (FRG)
[**I Multiple Bonds between Main-Group Elements and Transition Metals,
Part 29. This work was supported by the Bundesministerium fur Forschung und Technologie, the Deutsche Forschungsgemeinschaft, the
Fonds der Chemischen Industrie, Hoechst AG, and the Hermann
Schlosser-Stiftung der Degussa AG (fellowship for U . K . ) . Part 28: [4].
Anger. Chem.
I n / . Ed.
Engl. 25 11986) No. 9
c34
Fig. I. Molecular structure of 4 in the crystal. Selected bond lengths Ipm]
and bond angles ["I: Re-CI 187.6(8), Re-C2 193.5(8), Re-C4 229.0(6), Re-04
207.5(4), 04-C3 129.8(8), C3-C4 152.5(9), C 3 - 0 3 I l9.1(7), Re-C(I 1 - . . 15)
219-244; C4-Re-04 62.4(2), Re-C4-C3 86.4(4), C4-C3-04 106.6(6), Re-04-C3
102.3(4), CI-Re-C4 80.9(3), C2-Re-04 87.6(3), CI-Re-C2 79.4(3).-Further
details of the crystal structure investigation may be obtained from the Fdchinformationszentrum Energie, Physik, Mathematik GmbH, D-75 14 Eggenstein-Leopoldshafen 2 (FRG), o n quoting the depository number CSD51 877, the names of the authors, and the journal citation.
0 VCH Verlagsge.vdkhuj2 mbH. 0-6940 Weinheim. 1986
0570-0833/86/0909-0~~/
7 S 0 2 5 0 '11
8 17
8 13-8 16 Aduerfisemen I
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