The rhodium-catalyzed cyclotetramerization of butadiene: Isolation and structural characterization of an intermediate

Article abstract of DOI:10.1002/1521-3773(20000703)39:13<2304::AID-ANIE2304>3.0.CO;2-V

The bis(butadiene)rhodium(I) complexes [Rh(s-cis-η⁴- C₄H₆)₂(PR₃)]A readily convert into the isomeric octadienediyl derivatives [Rh(η³:η³-C₈H₁₂)(PR₃)]A, which are apparently intermediates in the rhodium-catalyzed cyclotetramerization reaction of butadiene. R=iPr, Cy; A=OSO₂CF₃, B[3,5- (F₃C)₂C₆H₃](4); the structure of the complex with iPr and OSO₂CF₃ is shown.

Full text of DOI:10.1002/1521-3773(20000703)39:13<2304::AID-ANIE2304>3.0.CO;2-V

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[11] T. Bach, H. Bergmann, K. Harms, J. Am. Chem. Soc. 1999, 121,
10650 ± 10651.
[12] C. Kaneko, T. Suzuki, M. Sato, T. Naito, Chem. Pharm. Bull. 1987, 35,
112 ± 123.
[13] J. G. Stack, D. P. Curran, S. V. Geib, J. Rebek, Jr., P. Ballester, J. Am.
Chem. Soc. 1992, 114, 7007 ± 7018.
[14] M. Kajino, Y. Shibouta, K. Nishikawa, K. Meguro, Chem. Pharm. Bull.
1991, 39, 2896 ± 2905.
[15] The absolute configuration of the tetrahydronaphthalenoxazole
derivative (‡)-5 was concluded from comparison of its optical
rotation ([a]2D0 ˆ ‡7.4; c ˆ 1 in CHCl3) with the analogous benzox-
azole derivative[13] {[a]D20 ˆ ‡7.4; c ˆ 2 in CHCl3) and by the absolute
configuration of the irradiation product 2.
remarkable side product of this process was found to be
1,5,9,13-cyclohexadecatetraene. Although in the initial studies
the overall yield of this cyclotetramer was rather low (<5%),
we became interested to find out whether there could be a
relationship between this reaction and the well known,
ªnaked-nickelº-catalyzed, cyclotrimerization of butadiene
discovered by Wilke et al.[3, 4] Since a key step in the reaction
leading to all-trans-1,5,9-cyclododecatriene is the oxidative
coupling of two butadiene ligands in the coordination sphere
of nickel(0) to give the labile octadienediylnickel(ii) derivative
[Ni(h3:h3-C8H12)],[4] we focused our efforts on detecting or, if
possible, even isolating a related rhodium complex containing
a C8H12 ligand.
In a first attempt to elucidate the mechanism of the
rhodium-catalyzed cyclotetramerization of butadiene, we
treated the triflate [Rh{m-O2S(O)CF3}(C8H14)2]2 (2) with
C4H6 and isolated the neutral bis(butadiene)rhodium(i) com-
plex [Rh{h1-OS(O)2CF3}(s-cis-h4-C4H6)2] (3) in almost quan-
titative yield.[5] Since it was known that the addition of one
equivalent of tricyclohexylphosphane to the nickel(0) com-
pound [Ni(s-cis-h4-C6H10)2] induces the coupling of the two
coordinated 2,3-dimethylbutadiene ligands to generate the
substituted octadienediylnickel(ii) complex [Ni(h1:h3-
C12H20)(PCy3)],[6] we also treated compound 3 with PCy3.
However, under the conditions used (acetone, 5 min, 258C),
[16] The reactions were conducted at the indicated temperature with
toluene as the solvent (0.15m solution of 1). Further details regarding
the irradiation procedure can be found in: T. Bach, J. Schröder, J. Org.
Chem. 1999, 64, 1265 ± 1273. The ee values (ee ˆ [(À)-2 À (‡)-
2)] [(À)-2‡(‡)-2]) were determined by HPLC analysis (column:
/
Chiracel OD; eluent: hexane/2-propanol, 92/8) of the crude product
mixture. The separation of host and product is possible by flash
chromatography (pentane/tert-butylmethylether, 1/2). Both enan-
tiomers of the host 5 were employed. Naturally, the direction of the
face discrimination changes if (‡)-5 is replaced by (À)-5.
[17] Crystal data of host (À)-4 (C22H37NO3 ´ CH2Cl2, Mr ˆ 448.45): crystal
size 0.3  0.3  0.15 mm3, orthorhombic, space group P212121, a ˆ
852.0(1), b ˆ 1212.3(1), c ˆ 2410.5(1) pm, Vˆ 2489.9(4) Š3, 1calcd
ˆ
1.196 gcmÀ3
,
Z ˆ 4, F(000) ˆ 968, m ˆ 2.516 mmÀ1
, Enraf-Nonius-
CAD4 diffractometer, l ˆ 1.54178 Š, w-scans, 4875 measured reflec-
tions (Àh, ‡k, Æl), Vmax ˆ 658, 4245 independent and 3575 observed
reflections [F ꢀ 4s(F)], 272 refined parameters, R ˆ 0.0608, wR2 ˆ
0.2080, max. residual electron density 0.22 eŠÀ3, direct methods,
À
instead of a C C coupling a substitution of the coordinated
À
carbon-bound hydrogen atoms calculated, N H atom refined. Crys-
triflate occurred and the ionic product [Rh(s-cis-h4-
C4H6)2(PCy3)]OTf (4b) was formed (Scheme 1, OS(O)2CF3 ˆ
OTF). The triisopropylphosphane analogue 4a, which like 4b
is a white, moderately air-stable solid, is accessible in a similar
way.[5] Salt metathesis of 4a and 4b with NaB(Arf)4 (Arf ˆ 3,5-
bis(trifluoromethyl)phenyl) affords the corresponding com-
pounds 5a and 5b in 83 and 86% yield, respectively.
tallographic data (excluding structure factors) for the structure
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-142268. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax:
(‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
[18] T. Bach, H. Bergmann, K. Harms, unpublished results.
Although both 4a and 4b are stable in solution at room
temperature and thus can be characterized by 1H, 13C{1H},
The Rhodium-Catalyzed Cyclotetramerization
of Butadiene: Isolation and Structural
Characterization of an Intermediate**
Marco Bosch, Maurice S. Brookhart, Kerstin Ilg, and
Helmut Werner*
We have recently shown that the square-planar sulfonato-
rhodium(i) complex cis-[Rh{h2-O2S(O)CF3}(PiPr3)2][1] (1) is an
active catalyst for the polymerization of butadiene.[2]
A
[*] Prof. Dr. H. Werner, Dipl.-Chem. M. Bosch, Dipl.-Chem. K. Ilg
Institut für Anorganische Chemie der Universität
Am Hubland,97074 Würzburg (Germany)
Fax : (‡49)931-8884605
E-mail: helmut.werner@mail.uni-wuerzburg.de
Prof. Dr. M. S. Brookhart
Department of Chemistry, Venable and Kenan Laboratories
University of North Carolina
Chapel Hill, North Carolina 27599-3290 (USA)
[**] This work was supported by the Deutsche Forschungsgemeinschaft
(SFB 347). K.I. thanks the Fonds der Chemischen Industrie for a Ph.D.
scholarship.
Supporting information for this article is available on the WWW under
http://www.wiley-vch.de/home/angewandte/ or from the author.
Scheme 1. a: R ˆ iPr; b: R ˆ Cy.
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and 31P{1H} NMR spectroscopy, they react in CH2Cl2 under
reflux (12 h for 4a and 6 h for 4b) to give, after recrystalliza-
tion from CH2Cl2/pentane, the isomeric octadienediyl com-
plexes 6a and 6b (Scheme 2). The red crystalline solids
are soluble in polar organic solvents and can be stored with-
out decomposition under argon at room temperature for
days.
C2 C3 together with the bond angle C1-C2-C3 are in good
agreement with those in related h3-allylrhodium[5, 8] and
octadienediylruthenium complexes.[9] In contrast to the C1-
C2-C3 unit, the C6-C7-C8 fragment is slightly distorted which
À
À
results in a lengthening of the two C C bonds by approx-
imately 0.05 Š and of the Rh C bonds by approximately
0.1 Š. An even more characteristic feature is that the Rh1 O1
À
À
bond length (2.473(3) Š) is significantly longer than in the
precursor molecule 3 (2.289(1) Š),[5] which explains why, as
indicated by the IR spectrum of 6a in CH2Cl2, a dissociation
of the neutral compound into the triflate anion and the cation
‡
[Rh(h3:h3-C8H12)(PiPr3)] occurs (see Scheme 2). To the best
of our knowledge, compounds 6a and 6b are the first
octadienediyl complexes of the Group 9 elements (Co, Rh,
Ir) described in the literature.[10]
Similarly to 4a and 4b, also the B(Arf)4 complexes 5a and
À
5b, upon heating in dichloromethane, undergo a C C
coupling process to give the corresponding ionic octadiene-
diylrhodium(iii) derivatives 7a, b in approximately 70% yield
(Scheme 2). From a high-level density functional theory
‡
(DFT) study using [Rh(s-cis-h4-C4H6)2(PH3)]
and
[Rh(h3:h3-C8H12)(PH3)] as model compounds, a difference
in energy of DG ˆ À4.1 kcalmolÀ1 between the two isomers
‡
was calculated.[11] This indicates that the C C coupling
À
reaction is thermodynamically favored. The conversion of
the bis(diene) compounds 4a, b and 5a, b to their octadiene-
diyl derivatives 6a, b and 7a, b, respectively, follows a first-
order rate law. In nitromethane, the reactions of 4b and 5b are
somewhat faster than those of the PiPr3 analogues 4a and 5a.
The free energy of activation DG= has been determined as
23.7(1) kcalmolÀ1 (for 4a and 5a) and 23.3(1) kcalmolÀ1 (for
4b and 5b).
Scheme 2. a: R ˆ iPr, b: R ˆ Cy.
The observation that 1 reacts under mild conditions with
C4H6 to give 4a in nearly quantitative yield (Scheme 1)
supports the assumption that the bis(diene) complex 4a plays
an important role as an intermediate in the poly- and
oligomerization of butadiene catalyzed by triflate 1. In order
to prove this, we treated 4a as well as 4b at elevated
temperatures with an excess of C4H6 and found that a mixture
of (cyclo)oligomers and polymers of butadiene in a ratio of
43:57( 4a) and 34:66 (4b) is formed (see Table 1, entry 1 and
2). GC/MS analysis of the mixture of products revealed that
the oligomeric fraction predominantely (ca. 90%) consists of
a mixture of C12 and C16 hydrocarbons. Among the tetrameric
fraction, a high selectivity, 83% with 4a and 79% with 4b as
catalyst, for the cis,cis,trans,trans isomer of 1,5,9,13-cyclo-
hexadecatetraene (8) is observed (Scheme 3). This results in
an overall selectivity for 8 in the oligomeric fraction of 34 and
41%, respectively. When the catalyst is prepared in situ from 2
and two equivalents of PiPr3 (Table 1, entry 3), both the
activity and selectivity compare well with that for 4a. Raising
the temperature to 958C (Table 1, entry 4) leads to a higher
selectivity for the tetrameric products in the oligomeric
fraction (60%) but also to a significant increase of the
relative amount of polymeric material.
The result of the X-ray crystal structure analysis of 6a is
shown in Figure 1.[7] The coordination geometry around the
rhodium(iii) center is distorted octahedral with atoms P1, C1,
C6, and C8 occupying the equatorial and C3 and O1 the axial
À
À
À
positions. The bond lengths Rh1 C1, Rh1 C3, C1 C2, and
The 13C NMR spectrum of 8, which can be isolated as a
colorless oil, shows four signals of equal intensity at around
d ˆ 129 for the CH carbon atoms, from which the config-
uration was derived as c,c,t,t (and not c,t,c,t).
Figure 1. Molecular structure of 6a in the crystal. Selected bond lengths
[Š] and angles [8]: C1-C2 1.398(10), C2-C3 1.412(10), C3-C4 1.501(12), C4-
C5 1.528(12), C5-C6 1.508(10), C6-C7 1.461(17), C7-C8 1.453(17), Rh1-C1
2.158(17), Rh1-C3 2.179(6), Rh1-C6 2.262(5), Rh1-C8 2.286(14), Rh1-P1
2.478(1), Rh1-O1 2.473(3); C1-C2-C3 116(1), C6-C7-C8 112(2).
Angew. Chem. Int. Ed. 2000, 39, No. 13
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Table 1. Metal-catalyzed poly- and oligomerization reactions of butadiene. Standard conditions for entries 1 ± 4: CH3NO2 (10 mL), C4H6 (3 mL), 5 h, 758C.
Entry
Catalyst
Cat.-
Yield
[%]
TON[b]
Polymer:
Product distribution
loading[a]
[mol %]
Oligomer[c]
of oligomeric fraction [%]
[d]
C8
C12
49
C16
C20
C24
4
1
2
3
4[e]
5
4a
4b
0.33
0.30
0.56
0.45
0.26
23
2788
39
47104 2:28
58
69
66:34
70
57:43
±
55:45
28
±
41 (34)
6
6
3572 (41)
±
60 (39)
74
2 ‡ 2PiPr3
2 ‡ 2PiPr3
[Ni(C3H5)2]/
[NiCl(C3H5)]2
46
41
44 (31)
8 ( ± )
4
7
±
6
6
224
56:44
9
22
20
[f]
[a] Based on the amount of butadiene employed. [b] TON ˆ turnover numberˆ {amount of C H [mmol]} [amount of catalyst [mmol]}. [c] The polymeric
/
4
6
product consists of oligobutadienes (C4H6)n with n ꢀ 8. [d] Percentage of cis,cis,trans,trans-1,5,9,13-cyclohexadecatetraene (8) in parenthesis. [e] C4H6 (5 mL),
958C. [f] In toluene, 85 h, room temperature.
5.3 Hz; C2), 91.1 (dd, 1J(Rh,C) ˆ 8.4 Hz, 2J(P,C) ˆ 6.4 Hz; C3), 69.9 (dd,
1J(Rh,C) ˆ 6.1 Hz, 2J(P,C) ˆ 3.8 Hz; C1), 29.2 (s; C4), 27.1 (d, 1J(P,C) ˆ
18.3 Hz; PCHCH3), 19.8, 19.7(both s; PCH CH3); 19F{1H} NMR
(376.4 MHz, CD2Cl2): d ˆ À78.8 (s); 31P{1H} NMR (162.0 MHz, CD2Cl2):
d ˆ 40.2 (d, 1J(Rh,P) ˆ 170.4 Hz). For assignment of protons and carbon
atoms of the C8H12 ligand see Scheme 2.
8: The cyclotetramer was obtained after fractional distillation of the
combined oligomeric fractions obtained with 4a, 4b and 2/PiPr3 as catalysts
Scheme 3. [Rh]-cat. ˆ 4a, 4b or 2 ‡ 2PiPr3.
(Table 1, entries 1 ± 4) in a Kugelrohr apparatus; colorless oil; b.p. 100 ±
‡
1108C (1 mbar); MS (70 eV): m/z: 216 [M ]; 1H NMR (200 MHz, CDCl3):
d ˆ 5.41 (br s, 8H, CH), 2.08 (br s, 16H, CH2); 13C{1H} NMR (50.3 MHz,
In summary, it is rather surprising that, despite the
numerous studies about the poly- and oligomerization reac-
tions of butadiene, the transition metal catalyzed cyclotetra-
CDCl3): d ˆ 129.9, 129.7, 129.6, 129.4 (all s, CH), 32.6, 28.0, 27.7 (all s, CH).
2
The catalytic reactions were carried out as follows: In a typical experiment,
a 50-mL glass autoclave was loaded with a solution of 4a (58 mg,
0.11 mmol), 4b (65 mg, 0.10 mmol), or a mixture of 2 (89 mg, 0.09 mmol)
and PiPr3 (37mL, 0.18 mmol), in freshly distilled nitromethane (10 mL)
merization of C4H6 has received little attention in the
literature.[4a] There are two reports by Dzhemilev et al.[12]
and Miyake et al.[13] who generated a catalytic system in situ,
and butadiene (3 mL, 33.8 mmol). The mixture was heated for 5 h at 758C
and then cooled to room temperature. The solvent and excess butadiene
either from TiCl4/Et2AlCl and 2-vinylfuran or from p-
were removed, the oily residue was extracted with pentane (2 Â 35 mL),
and the extract was flash-chromatographed on Al2O3 (neutral, activity
grade V). Evaporation of the solvent afforded in each case a waxy colorless
product which was analyzed by GC/MS; yield 413 mg (4a), 488 mg (4b),
708 mg (2, entry 3) and 1488 mg (2, entry 4, Table 1). The relative amount
of polymer in the isolated product was calculated from the difference
between the yield of product and the yield of oligomers determined by the
sum of the integrated signals in the GC spectrum for the C8 ± C24
hydrocarbons.
allylnickel(ii) compounds. With the titanium system, a mixture
of cyclic all-trans tri- and tetramers in a ratio of 7:3 was
formed, whereas with the nickel(ii) compound a variety of
poly- and (cyclo)oligomers of butadiene was obtained (Ta-
ble 1, entry 5). In contrast, the phosphanerhodium(i) com-
plexes 4a, 4b, and 2, if used as catalysts, have the advantage of
a narrow product distribution and a high selectivity for 8 in the
oligomeric fraction. With regard to the role that the isolated
octadienediyl complex 6a plays in the rhodium-catalyzed
cyclooligomerization of C4H6, the results of preliminary NMR
experiments indicate that in the initial stage of the reaction
the formation of 6a is the rate-determining step and the
bis(diene) compound 4a is the catalyst resting state.
Received: February 18, 2000 [Z14732]
[1] H. Werner, M. Bosch, C. Hahn, F. Kukla, M. Laubender, M. Manger,
M. E. Schneider, B. Weberndörfer, B. Windmüller, J. Chem. Soc.
Dalton Trans. 1998, 3549 ± 3558.
[2] a) M. E. Schneider, H. Werner, 10th International Symposium on
Homogeneous Catalysis, Princeton, 1996; b) M. E. Schneider, PhD
thesis, Universität Würzburg, 1997.
Experimental Section
[3] a) G. Wilke, Angew. Chem. 1988, 100, 189 ± 211; Angew. Chem. Int. Ed.
Engl. 1988, 27, 185 ± 206; b) G. Wilke, B. Bogdanovic, P. Hardt, P.
Heimbach, W. Keim, M. Kröner, W. Oberkirch, K. Tanaka, E.
Steinrücke, D. Walter, H. Zimmermann, Angew. Chem. 1966, 78, 157±
172; Angew. Chem. Int. Ed. Engl. 1966, 5, 151 ± 164; c) G. Wilke,
Angew. Chem. 1963, 75, 10 ± 20; Angew. Chem. Int. Ed. Engl. 1963, 2,
105 ± 115.
[4] a) G. Wilke, A. Eckerle in Applied Homogeneous Catalysis with
Organometallic Compounds, Vol. 1 (Eds.: B. Cornils, W. A. Herr-
mann), VCH, Weinheim, 1996, Chap. 2.3.6; b) P. W. Jolly, G. Wilke,
The Organic Chemistry of Nickel, Vol. 2, Academic Press, New York,
1975, Chap. 3.
6a: A solution of of 4a (175 mg, 0.34 mmol) in dichloromethane (20 mL)
was heated under reflux for 12 h. A gradual change of color from light red
to dark red occurred. After the reaction mixture was cooled to room
temperature, the solvent was removed in vacuo. The oily residue was
washed with pentane (3 Â 5 mL) and the resulting red solid recrystallized
from dichloromethane/pentane (1:5); yield 131 mg (74%); m.p. 1048C
(decomp); IR (CH2Cl2): nÄ ˆ 1270 ± 1260 (OSOasymm.), 1239 (CFsymm.), 1162
(CFasymm.), 1031 cmÀ1 (OSOsymm.); 1H NMR (400 MHz, CD2Cl2):[14] d ˆ 5.23
(ddd, 2H, 3J(H,H) ˆ 11.6 Hz, 3J(H,H) ˆ 10.6 Hz, 3J(H,H) ˆ 7.0 Hz; H ),
c
4.88 (dd, 2H, 3J(H,H) ˆ 7.0 Hz, 4J(H,H) ˆ 1.8 Hz; Ha), 4.21 (br ddd, 2H,
3
4
3J(H,H) ˆ 10.6 Hz, J(H,H) ˆ 3.5 Hz, J(H,H) ˆ 1.8 Hz; Hd), 3.07(dd, 2H,
3J(H,H) ˆ 11.6 Hz, 3J(P,H) ˆ 6.3 Hz; Hb), 2.63 (m, 3H; PCHCH3), 2.28 (m,
2H; He), 1.53 (m, 2H; Hf), 1.28 (dd, 9H, 3J(P,H) ˆ 14.3 Hz, 3J(H,H) ˆ
7.0 Hz; PCHCH3), 1.15 (dd, 9H, 3J(P,H) ˆ 13.8 Hz, 3J(H,H) ˆ 7.3 Hz;
PCHCH3); 13C{1H} NMR (100.6 MHz, CD2Cl2): d ˆ 97.0 (d, 1J(Rh,C) ˆ
[5] M. Bosch, M. Laubender, B. Weberndörfer, H. Werner, Chem. Eur. J.
1999, 5, 2203 ± 2211.
[6] R. Benn, B. Büssemeier, S. Holle, P. W. Jolly, R. Mynott, I.
Tkatchenko, G. Wilke, J. Organomet. Chem. 1985, 279, 63 ± 86.
2306
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[7] Data for the X-ray structure analysis of 6a: Crystals from dichloro-
methane/pentane, C18H33F3O3PRhS (Mr ˆ 520.46); crystal size 0.19 Â
0.18  0.16 mm; monoclinic, space group P21/c, Z ˆ 4, a ˆ 8.498(1),
Novel 1,2,4-Triphosphole and 1,2,3-Triphos-
phetene Derivatives from N,N'-Bis(2,2-di-
methylpropyl)benzimidazolin-2-ylidene and
Phosphaalkynes**
b ˆ 15.383(1), c ˆ 16.899(2) Š, b ˆ 94.18(2)8, Vˆ 2201.9(5) Š3, 1calcd
ˆ
1.570 gcmÀ3; Tˆ 173(2) K; 2q ˆ 50.048; 17827 reflections measured,
3884 were unique, (Rint ˆ 0.0569), and 2922 observed (I > 2s(I)); IPDS
(Stoe), MoKa radiation (l ˆ 0.71073 Š), graphite-monochromated; Lp
correction. The structure was solved by direct methods and refined
with the full-matrix, least-square method; R1 ˆ 0.0360, wR2 ˆ 0.0877
(for 2922 reflections with I > 2s(I)), R1 ˆ 0.0509, wR2 ˆ 0.0936 (for all
3884 data); data-to-parameter ratio 11.99; residual electron density
‡0.797/ À 0.636. All non-hydrogen atoms were refined anisotropi-
cally, and a riding model was employed in the refinement of the
hydrogen atom positions. The octadienediyl ligand in 6a is disordered
and found with an occupancy of 0.69:0.31, it was refined anisotropi-
cally with restrains.Crystallographic data (excluding structure factors)
for the structure reported in this paper has been deposited with the
Cambridge Crystallographic Data Centre as supplementary publica-
tion no. CCDC-139992. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge
CB21EZ, UK (fax: (‡44)1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk).
F. Ekkehardt Hahn,* Lars Wittenbecher, Duc Le Van,
Roland Fröhlich, and Birgit Wibbeling
Halocarbenes react with phosphaalkynes primarily to form
unstable 2H-phosphirenes, which undergo rearrangements
through [1,3] halogen shift to yield the isomeric 1H-phosphir-
enes.[1] Addition of the phosphanylsilylcarbene (Bertrand
carbene) to tert-butylphosphaacetylene affords the stable
1l5,2l3-diphosphetene (probably due to the ring expansion of
2-phosphino-2H-phosphirene, which is an intermediate pro-
duced through a [1‡2] cycloaddition).[2] The analogous
ꢁ
reactions of silylenes, germylenes, and stannylenes with P CR
produce three- or four-membered-ring systems containing a
phosphaalkene structural element.[3] However, to date noth-
ing has been reported about the reactivity of the intensively
studied N-heterocyclic carbenes[4] toward phosphaalkynes.
We now report the unexpected formation of functionalized
1,2,4-triphosphole[5] and 1,2,3-triphosphetene[6] derivatives by
reaction of the recently discovered stable N-heterocyclic
annelated carbene N,N'-bis(2,2-dimethylpropyl)benzimidazo-
[8] a) R. Wiedemann, R. Fleischer, D. Stalke, H. Werner, Organometal-
lics 1997, 16, 866 ± 870; b) H. Werner, M. Schäfer, O. Nürnberg, J. Wolf,
Chem. Ber. 1994, 127, 27± 38.
[9] a) S. Wache, W. A. Herrmann, G. Artus, O. Nuyken, D. Wolf, J.
Organomet. Chem. 1995, 491, 181 ± 188; b) J. W. Steed, D. A. Tocher,
Polyhedron 1994, 13, 167± 173; c) B. Kavanagh, J. W. Steed, D. A.
Tocher, J. Chem. Soc. Dalton Trans. 1993, 327± 335; d) D. N. Cox, R.
Roulet, J. Organomet. Chem. 1988, 342, 87± 95; e) D. N. Cox, R.
Roulet, Organometallics 1985, 4, 2001 ± 2005; f) A. Colombo, G.
Allegra, Acta Crystallogr. Sect. B 1971, 27, 1653.
lin-2-ylidene (1),[7] with the phosphaalkyne P CtBu (2a) or
ꢁ
ꢁ
P C-NiPr2 (2b).
[10] In the rhodium-catalyzed coupling reaction of butadiene and CO2 to
give 2-ethyl-2,4,9-undecatrien-4-olide, the formation of an octadiene-
diylrhodium complex has been postulated: A. Behr, R. He, K.-D.
Treatment of carbene 1 with the phosphaacetylene 2a at
room temperature in a molar ratio of 1:1 affords the
crystalline adduct 5 after 48 h in a near quantitative yield
(calculated from 2a) (Scheme 1). The 31P{1H} NMR spectrum
shows an AMX spin system. The positions of the signals and
corresponding couplings of the resonances, and in particular
Juszak, C. Krüger, Y.-H. Tsay, Chem. Ber. 1986, 119, 991 ± 1015.
‡
[11] The calculated structures of [Rh(s-cis-h4-C4H6)2(PH3)]
and
[Rh(h3:h3-C8H12)(PH3)] are very close to that found in the solid
state for the PiPr3 analogues 4a and 6a despite the lack of the
coordinated triflate anion in the latter (the PH3 ligand is positioned
symmetrically with respect to the octadienediyl moiety); L. Perrin, E.
Clot, O. Eisenstein, private communication.
‡
1
the characteristic size of the J(P1,P2) coupling of 528.1 Hz,
are similar to those reported for the 1,2,4-triphosphole
[12] a) U. M. Dzhemilev, L. Y. Gubaidullin, Zh. Org. Khim 1976, 12, 44 ±
46 [Chem. Abstr. 1976, 84, 121244]; b) G. A. Tolstikov, U. M.
Dzhemilev, L. Y. Gubaidullin, Ivz. Akad. Nauk SSSR Ser. Khim
1975, 2, 487[ Chem. Abstr. 1975, 82, 139467].
1
P3C2tBu2R (R ˆ CH(SiMe3)2)[5a]. The H and 13C NMR pa-
rameters also fit well with the literature data.[5a] Information
on the structure and bonding in the new 1,2,4-triphosphole
derivative 5 is provided by the X-ray crystal structure analysis
(Figure 1). The phosphorus heterocycle is almost planar
(maximum deviation from the best plane through the ring is
0.016 Š for P2. The sum of the angles at the tricoordinate
[13] A. Miyake, H. Kondo, M. Nishino, Angew. Chem. 1971, 83, 851 ± 852;
Angew. Chem. Int. Ed. Engl. 1971, 10, 802 ± 803.
1
[14] The H and 13C{1H} NMR data of the anionic ligand are omitted for
clarity.
3
À
phosphorus atom is 359.88). The s -P CRing bond (1.721(2) Š)
2
À
is noticeably shorter than the other s -P CRing bonds
(1.734(2) ± 1.738(2) Š). These structural parameters indicate
a
completely delocalized 1,2,4-triphosphacyclopentadiene
system, which is in agreement with the results recently
published by Niecke and Nixon et al.[5b] on aromatic 1-[bis-
(trimethylsilyl)methyl]-3,5-bis(trimethylsilyl)-1,2,4-triphos-
[*] Prof. Dr. F. E. Hahn, Dr. L. Wittenbecher, Dr. D. Le Van
Anorganisch-chemisches Institut der Universität
Wilhelm-Klemm-Strasse 8, 48149 Münster (Germany)
Fax : (‡49)251-833-3108
E-mail: fehahn@uni-muenster.de
Dr. R. Fröhlich, B. Wibbeling
Organisch-chemisches Institut der Universität
Corrensstrasse 40, 48149 Münster (Germany)
[**] This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
Angew. Chem. Int. Ed. 2000, 39, No. 13
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