Synthesis of (vinylallene)rhodium(III) complex of planar structure: Perfect π → σ conversion of 1,3-diene system

Full text of DOI:10.1021/ja962486i

11672
J. Am. Chem. Soc. 1996, 118, 11672-11673
on the substitution patterns, probably due to steric reasons.9
Herein, we report the synthesis of a σ2-bonded (vinylallene)-
rhodium complex (5) having an essentially planar structure
which is determined by X-ray crystallography.
Synthesis of (Vinylallene)rhodium(III) Complex of
Planar Structure: Perfect π f σ Conversion of
1,3-Diene System
Vinylallene (4) lacking substituents at the vinylic terminus
was treated with RhCl(PPh3)3 in benzene at room temperature.
The vinylallene 4 displaced one molecule of PPh3 on the
rhodium to afford a metallacycle (5) as a solid in 92% isolated
yield, for which satisfactory analytical data were obtained.10
Recrystallization from CH2Cl2/methanol gave air-stable orange
crystals as a methanol solvate.
Masahiro Murakami,* Kenichiro Itami, and Yoshihiko Ito*
Department of Synthetic Chemistry and Biological Chemistry
Kyoto UniVersity, Yoshida, Kyoto 606-01, Japan
ReceiVed July 18, 1996
The structures of conjugated diene-transition metal com-
plexes have attracted considerable attention owing to the great
diversity of the binding modes. For example, most middle and
late transition metal-diene complexes assume the conventional
π2-bonded structures 1.1 On the other hand, early transition
metals prefer the bent σ2,π-bonded metallacyclo-3-pentene form
2.2 The s-trans binding has been also reported.3 Stereochemical
fluxionality of s-cis complexes has been often observed and
explained by a ring-flipping mechanism.4 Although implicated
as a transitory species in the ring flipping, examples of
thermodynamically stable planar σ2-bonded complexes (3)
remain few in number5-7 and are mostly limited to perfluoro-
1,3-butadiene6 and vinyl ketene complexes.7 Vinylallene is
The solid state structure of 5 was determined by a single-
crystal X-ray diffraction study.11 An ORTEP diagram of the
molecule is shown in Figure 1. The most notable feature of
the structure is that the five-membered rhodacyclo-3-pentene
ring constitutes an almost perfect plane. The maximum
deviation from the mean plane is only 0.018 Å. There is no
interaction between the C6-C7 double bond and rhodium. The
arrangement of the pentacoordinated rhodium atom can be
considered as a flat square pyramid or a distorted octahedral
geometry with one vacant site over which the C10 methyl group
at the allenic terminus hangs. The chlorine atom sits trans to
the sp2 carbon atom (C8) [Cl2-Rh1-C8 ) 163.1(2)°], and the
two PPh3 ligands are also trans. The C5-C6 and C7-C8
linkages [1.510(5) and 1.452(6) Å, respectively] are longer than
that of C6-C7 [1.332(6) Å], reflecting the bond order. The
dihedral angle C6-C7-C8-C9 is 179.2°, which infers effective
conjugation between the endocyclic (C6-C7) and exocyclic
(C8-C9) double bonds.12 In fact, the C7-C8 distance is
significantly shorter than the C5-C6 distance, probably due to
the conjugation. This is consistent with the lengthening of the
exocyclic C8-C9 double bond [1.362(6) Å] as compared with
the corresponding double bond distances in the η4-bound
(vinylallene)rhodium complexes [1.326(6) and 1.321(5) Å]
previously reported.9 The sp2 carbon-metal distance (C8-Rh1
regarded as a conjugated diene with an additional cumulated
double bond. However, very little is known about the bonding
character of vinylallenes.8 While studying (vinylallene)rhodium
complexes, we found that the binding modes greatly depended
(1) (a) Elschenbroich, Ch.; Salzer, A. Organometallics 2nd ed.; VCH:
Weinheim, 1992; pp 262-265. (b) Pruchnik, F. P. Organometallic
Chemistry of the Transition Elements; Plenum: New York, 1990; Chapter
8. (c) Mignos, D. M. P. In ComprehensiVe Organometallic Chemistry;
Wilkinson, G. W., Stone, F. G. A., Abel, K. W., Eds.; Pergamon: Oxford,
1982; Vol. 3, Chapter 19. (d) Collman, J. P.; Hegedus, L. S.; Norton, J.
R.; Finke, R. G. Principles and Applications of Organotransition Metal
Chemistry; University Science Books: Mill Nalley, CA, 1989; Chapter 17.
(2) (a) Yasuda, H.; Nakamura, A. Angew. Chem., Int. Ed. Engl. 1987,
26, 723. (b) Erker, G.; Kru¨ger, C.; Mu¨ller, G. AdV. Organomet. Chem.
1985, 24, 1.
(3) (a) Erker, G.; Wicher, J.; Engel, K.; Rosenfeldt, F.; Dietrich, W.;
Kru¨ger, C. J. Am. Chem. Soc. 1980, 102, 6344. (b) Kai, Y.; Kanehisa, N.;
Miki, K.; Kasai, N.; Mashima, K.; Nagasuna, K.; Yasuda, H.; Nakamura,
A. J. Chem. Soc., Chem. Commun. 1982, 191. (c) Okamoto, T.; Yasuda,
H.; Nakamura, A.; Kai, Y.; Kanehisa, N. J. Am. Chem. Soc. 1988, 110,
5008. (d) Hunter, A. D.; Legzdins, P.; Nurse, C. R.; Einstein, F. W. B.;
Willis, A. C. J. Am. Chem. Soc. 1985, 107, 1791. (e) Benyunes, S. A.;
Green, M.; Grimshire, M. J. Organometallics 1989, 8, 2268.
(4) (a) Faller, J. W.; Rosan, A. M. J. Am. Chem. Soc. 1977, 99, 4858.
(b) Kru¨ger, C.; Mu¨ller, G.; Erker, G.; Dolf, U.; Engel, K. Organometallics
1985, 4, 215. (c) Eaton, B.; King, J. A., Jr.; Vollhardt, K. P. C. J. Am.
Chem. Soc. 1986, 108, 1359. (d) Smith, G. M.; Suzuki, H.; Sonnenberger,
D. C.; Day, V. W.; Marks, T. J. Organometallics 1986, 5, 549. (e) Bu¨rgi,
H.-B.; Doubler-Steudle, K. C. J. Am. Chem. Soc. 1988, 110, 4953.
(5) (a) 2,3-Dimethyl-1,3-butadiene: Barker, G. K.; Green, M.; Howard,
J. A. K.; Spencer, J. L.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1978,
1839. (b) Bis(ketenimine): Wakatsuki, Y.; Aoki, K.; Yamazaki, H. J. Chem.
Soc., Dalton Trans. 1986, 1193.
(6) (a) Hitchcock, P. B.; Mason, R. J. Chem. Soc., Chem. Commun. 1967,
242. (b) Hunt, R. L.; Roundhill, D. M.; Wilkinson, G. J. Chem. Soc. A
1967, 982. (c) Roundhill, D. M.; Lawson, D. N.; Wilkinson, G. J. Chem.
Soc. A 1968, 845. (d) Hughes, R. P.; Rose, P. R.; Rheingold, A. L.
Organometallics 1993, 12, 3109.
(9) Murakami, M.; Itami, K.; Ito, Y. Angew. Chem., Int. Ed. Engl. 1995,
34, 2691.
(10) Anal. Calcd for C49H44ClP2Rh: C, 70.64; H, 5.32. Found: C,
70.91; H, 5.48. As frequently observed with pentacoordinate complexes,14
5 became stereochemically nonrigid in solution to present complicated NMR
spectra. The data for the predominant isomer, which are consistent with
the planar crystal structure, are given below: 1H NMR (C6D6, 400 MHz)
δ 1.41 (s, 3 H), 1.66 (s, 3 H), 4.25-4.33 (br, 2 H), 5.35 (s, 1 H), 6.80-
8.10 (m, 35 H); 13C{1H} NMR (C6D6, 100 MHz) δ 19.6, 25.7, 31.1 (d,
JRh-C ) 32.8 Hz), 120-145 (m); 31P{1H} NMR (C6D6, 121.5 MHz) δ 26.5
(d, JRh-P ) 126.2 Hz).
(11) Crystal data: C50H48ClOP2Rh (5 + MeOH), MW ) 865.2,
orthorhombic, space group P212121; a ) 19.33(1), b ) 21.74(1), and c )
10.13(1) Å; U ) 4259.9(4) Å3, Z ) 4, Dc ) 1.349 g/cm3, µ ) 48.90 cm-1
.
Intensity data were measured on a Mac Science MXC3 diffractometer using
ω - 2θ scan technique with graphite monochromated Cu KR radiation (λ
) 1.54178 Å), and 3918 unique reflections within 3 e 2θ e 130° were
collected. No decay correction was applied. The data were corrected for
Lorentz and polarization effects. The structure was solved by a direct
method and refined by the full-matrix least-squares to R ) 0.063 (Rw )
0.067) for 3616 reflections [I > 3.0σ(I)] using a Crystan GM package
program. The crystal contains one molecule of 5 and one molecule of
MeOH in an asymmetric unit. The non-hydrogen atoms, except those of
MeOH, were refined anisotropically. Hydrogen atoms were included in
the refinement at the calculated distances (0.96 Å) with isotropic temperature
factors calculated from those of the bonded atoms. Specific interaction is
absent between rhodium and MeOH, although there are a few of relatively
(7) (a) Mitsudo, T.; Watanabe, H.; Sasaki, T.; Takegami, Y.; Watanabe,
Y.; Kafuku, K.; Nakatsu, K. Organometallics 1989, 8, 368. (b) Bleeke, J.
R.; Haile, T.; Chiang, M. Y. Organometallics 1991, 10, 19. (c) Huffman,
M. A.; Liebeskind, L. S. Organometallics 1992, 11, 255.
(8) (a) Trifonov, L. S.; Orahovats, A. S.; Trewo, R.; Heimgartner, H.
HelV. Chim. Acta 1988, 71, 551. (b) Saberi, S. P.; Thomas, S. E. J. Chem.
Soc., Perkin Trans. 1 1992, 259. (c) Areces, P.; Jeganathan, S.; Okamura,
W. H. An. Quim. 1993, 89, 101.
short intermolecular contacts observed (C(MeOH)-C11 ) 3.99 Å, O(MeOH)
-
C11 ) 3.91 Å).
(12) The dihedral angles in the previous η4-bound (vinylallene)rhodium
complexes which correspond to the C6-C7-C8-C9 angle of 5 are 140.6°
and 127.8°.9
S0002-7863(96)02486-9 CCC: $12.00 © 1996 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 118, No. 46, 1996 11673
at room temperature for 4 h. Hydrogenation proceeded to give
diene 6 (91%) with retention of the stereochemistry of the double
bond. Hydrosilation took place on treatment of 5 with Et3SiH
to afford dienylsilane (7) in 61% isolated yield together with
the diene 6 (30%). In the formation of 7, the triethylsilyl group
was regioselectively introduced on the sp3 carbon (C5) of 5
with the double-bond geometry retained. Like η4-bound
(vinylallene)rhodium complexes, carbonylative [4 + 1] cy-
cloaddition was effected by simply stirring a solution of 5 in
CH2Cl2 under 1 atm of CO atmosphere. A conjugated cyclo-
pentenone (9) was produced in 96% yield, presumably by
isomerization of cyclopentenone (8) formed initially.
Figure 1. Molecular structure of 5 with the hydrogen atoms and the
solvated methanol omitted for clarity (40% probability thermal el-
lipsoids).
) 2.025(4) Å) is identical with the sp3 carbon-metal distance
(C5-Rh1 ) 2.024(4) Å), suggesting little contribution of metal
to olefin π* back-bonding.13
The most effective delocalization of the π-electrons of the
endo- and exocyclic double bonds can be relevant to the
observed preference for the planar structure with the vinylallene
ligand 4. We have found that a vinylallene having a trimeth-
ylsilyl group at the vinylic terminus reacts with RhCl(PPh3)3 to
displace two molecules of triphenylphosphine, affording a (η4-
vinylallene)RhCl(PPh3) complex.9 In this case, it might be that
the steric bulk of the trimethylsilyl group disfavors the
coordination of two molecules of bulky triphenylphosphine,
instead resulting in participation of the whole conjugated diene
system in the bonding to furnish the 16-electron η4-complex as
the most stable form.
In summary, a planar (vinylallene)rhodium complex is
directly synthesized by simple ligand displacement of RhCl-
(PPh3)3 with vinylallene, wherein the conjugated diene system
binds to rhodium in a purely σ2-manner. The present study
lends direct evidence to the ring flipping of a η4-complex via a
planar metallacyclopentene complex.
Supporting Information Available: Synthetic details, crystal
structure determination data, tables of atomic coordinates, anisotropic
thermal parameters, and bond lengths and angles for 5 (8 pages). See
any current masthead page for ordering and Internet access instructions.
Several stoichiometric reactions of 5 were examined. A
solution of 5 in CH2Cl2 under 1 atm of dihydrogen was stirred
(13) Tanke, R. S.; Crabtree, R. H. Inorg. Chem. 1989, 28, 3444.
(14) Muetterties, E. L. Acc. Chem. Res. 1970, 3, 266.
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