Unprecedented rhodium-mediated trimerization of alkynes HC≡CR (R = Ph, p-tolyl) leading to (η4-cyclobutadiene)rhodium complexes

Article abstract of DOI:10.1021/om960318t

The α-amino acidate complex [(η⁵-C₅Me₅)Rh(L-alaninate)Cl] (1) reacts with HC≡CR (R = Ph, p-tolyl), in methanol, in the presence of NEt₃, to form the new cyclobutadiene compounds [(η⁵-C₅Me₅)Rh(η⁴-C ₄HR₂C≡CR)] (R = Ph (2a), p-tolyl (2b)) as the major products. The X-ray molecular structure determination of complex 2a has been carried out. The complex exhibits a sandwichlike structure with the rhodium metal located between a η⁴-phenylethynyl cyclobutadiene ligand and a η⁵-pentamethylcyclopentadienyl group. A possible pathway for the formation of 2 from 1 is proposed.

Full text of DOI:10.1021/om960318t

4852
Organometallics 1996, 15, 4852-4856
Un p r eced en ted Rh od iu m -Med ia ted Tr im er iza tion of
Alk yn es HCtCR (R ) P h , p-Tolyl) Lea d in g to
(η4-Cyclobu ta d ien e)r h od iu m Com p lexes
Mar´ıa Pilar Lamata and Emilio San J ose´
Departamento de Quı´mica Inorga´nica, Escuela Universitaria de Ingenierı´a Te´cnica e
Industrial, Instituto de Ciencia de Materiales de Arago´n, Universidad de Zaragoza,
Corona de Arago´n 35, 50009 Zaragoza, Spain
Daniel Carmona,* Fernando J . Lahoz, Reinaldo Atencio, and Luis A. Oro
Departamento de Qu´ımica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-Consejo Superior de Investigaciones Cient´ıficas,
50009 Zaragoza, Spain
Received April 26, 1996X
The R-amino acidate complex [(η5-C5Me5)Rh(L-alaninate)Cl] (1) reacts with HCtCR (R )
Ph, p-tolyl), in methanol, in the presence of NEt3, to form the new cyclobutadiene compounds
[(η5-C5Me5)Rh(η4-C4HR2CtCR)] (R ) Ph (2a ), p-tolyl (2b)) as the major products. The X-ray
molecular structure determination of complex 2a has been carried out. The complex exhibits
a sandwichlike structure with the rhodium metal located between a η4-phenylethynyl
cyclobutadiene ligand and a η5-pentamethylcyclopentadienyl group. A possible pathway for
the formation of 2 from 1 is proposed.
In tr od u ction
never been the result of an alkyne trimerization process.
The most common trimerization process that alkynes
undergo is the cycloaddition reaction of three alkyne
molecules to render arenes,7 and very recently, it was
reported that the transition-metal-induced stepwise
trimerization of the terminal alkynes HCtCPh8 and
HCtCCO2Me9 does not lead to the expected benzene
derivatives but to the linear hexadienynes PhCtCC-
(Ph)dCHCHdCHPh and MeO2CCtCC(dCHCO2Me)-
CHdCHCO2Me, respectively.
In the course of our studies on transition-metal
complexes with chiral metal centers,10 we have at-
tempted the preparation of metal-acetylide com-
pounds, and in fact, we have recently reported the
synthesis, separation, characterization, and epimeriza-
tion studies of the RIr,SN,SC and SIr,SN,SC diastereo-
mers of the iridium acetylide [(η5-C5Me5)Ir(L-prolinate)-
(CtCCMe3)].10b These compounds have been prepared
by treating in methanol the chloride precursor [(η5-C5-
Me5)Ir(L-prolinate)Cl] with HCtCCMe3 and NEt3 in a
1/1/1 molar ratio. Following a similar synthetic strat-
Transition-metal-mediated oligomerization reactions
of alkynes have been known for many years1 and have
proved to be a source of a large variety of complexes
containing ligands formed from alkynes.2 Among them,
one interesting type is the cyclobutadiene complexes.
These complexes open the possibility of studying the
reactivity of the carbocyclic ring with interesting im-
plications from both mechanistic and synthetic points
of view.3
Although there are many synthetic routes now avail-
able to transition-metal cyclobutadiene complexes,3
rhodium derivatives of this type are quite rare. In some
instances, their synthesis have been achieved by cy-
clodimerization of two disubstituted acetylenes4 or by
cyclization of one diacetylene5 precursor. It has been
also reported that the reaction of [{(η5-C5Me5)RhCl}2-
(µ-Cl)2] with phenylacetylene yields two rhodium com-
pounds containing a tetramer or a pentamer of the
starting terminal acetylene η4-coordinated through cy-
clobutadiene-moieties,6 but as far as we know, transi-
tion-metal cyclobutadiene containing complexes have
(6) Moreto, J .; Maruya, K.-I.; Bailey, P. M.; Maitlis, P. M. J . Chem.
Soc., Dalton Trans. 1982, 1341.
(7) (a) Winter, M. J . In The Chemistry of the Metal-Carbon Bond;
Hartley, F. R., Patai, S., Eds.; Wiley: Chichester, England, 1985; Vol.
3, p 259. (b) Schore, N. E. Chem. Rev. 1988, 88, 1081.
(8) Klein, H.-F.; Mager, M.; Isringhausen-Bley, S.; Flo¨rke, U.; Haupt,
H.-J . Organometallics 1992, 11, 3174.
(9) Werner, H.; Scha¨fer, M.; Wolf, J .; Peters, K.; von Schnering, H.
G. Angew. Chem., Int. Ed. Engl. 1995, 34, 191.
(10) (a) Carmona, D.; Mendoza, A.; Lahoz, F. J .; Oro, L. A.; Lamata,
M. P.; San J ose´, E. J . Organomet. Chem. 1990, 396, C17. (b) Carmona,
D.; Lahoz, F. J .; Atencio, R.; Oro, L. A.; Lamata, M. P.; San J ose´, E.
Tetrahedron: Asymmetry 1993, 4, 1425. (c) J imeno, M. L.; Elguero,
J .; Carmona, D.; Lamata, M. P.; San J ose´, E. Magn. Reson. Chem. 1996,
34, 42. (d) Carmona, D.; Cativiela, C.; Garc´ıa-Correas, R.; Lahoz, F.
J .; Lamata, M. P.; Lo´pez, J . A.; Lo´pez-Ram de V´ıu, M. P.; Oro, L. A.;
San J ose´, E.; Viguri, F. J . Chem. Soc., Chem. Commun. 1996, 1247.
(e) Carmona, D.; Lahoz, F. J .; Oro, L. A.; Lamata, M. P.; Viguri, F.;
San J ose´, E. Organometallics 1996, 15, 2961. (f) Carmona, D.; Lamata,
M. P.; Viguri, F.; Vega, C.; San J ose´, E.; Oro, L. A., unpublished results.
X Abstract published in Advance ACS Abstracts, September 15, 1996.
(1) Reppe, W.; Schlichting, O.; Klager, K.; Toepel, T. J ustus Liebigs
Ann. Chem. 1948, 560, 1.
(2) Grotjahn, D. B. In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Hegedus, L. S., Eds.;
Pergamon: Oxford, England, 1995; Vol. 12, Chapter 7.3, p 741, and
references therein.
(3) Efraty, A. Chem. Rev. 1977, 77, 691.
(4) (a) Cash, G. G.; Helling, J . F.; Mathew, M.; Palenik, G. J . J .
Organomet. Chem. 1973, 50, 277. (b) Nixon, J . F.; Kooti, M. J .
Organomet. Chem. 1976, 104, 231.
(5) (a) King, R. B.; Ackermann, M. N. J . Organomet. Chem. 1974,
67, 431. (b) Mu¨ller, E. Synthesis 1974, 761. (c) Winter, W. Angew.
Chem., Int. Ed. Engl. 1975, 14, 170. (d) Rausch, M. D.; Gardner, S. A.;
Tokas, E. F.; Bernal, I.; Reisner, G. M.; Clearfield, A. J . Chem. Soc.,
Chem. Commun. 1978, 187. (e) Reisner, G. M.; Bernal, I.; Rausch, M.
D.; Gardner, S. A.; Clearfield, A. J . Organomet. Chem. 1980, 184, 237.
S0276-7333(96)00318-4 CCC: $12.00 © 1996 American Chemical Society

(η4-Cyclobutadiene)rhodium Complexes
Organometallics, Vol. 15, No. 22, 1996 4853
Ch a r t 1
F igu r e 1. ORTEP view of [(η5-C5Me5)Rh(η4-C4HPh2Ct
CPh)] (2a ) showing the atom-labeling scheme.
mental Section. Besides the resonances for the protons
of the C5Me5 and the arene resonances, the 1H NMR
spectra showed a doublet at 4.73 ppm, J ) 1.9 Hz (2a )
or 4.65 ppm, J ) 1.7 Hz (2b) arising from coupling to
103Rh. The chemical shifts fall in the region of the
resonances due to the ring protons in a variety of
unsubstituted or partially substituted cyclobutadien-
emetal complexes (3.50-5.50 ppm),3 and the coupling
constants present values similar to those previously
reported for related cyclobutadienerhodium com-
pounds.6,11 As the most representative data, the carbon
NMR spectra showed three doublets from 50 to 80 ppm
(1J RhC ) 10.5-11.3 Hz) corresponding to the four
carbons of the cyclobutadiene ring. Again, the spectro-
scopic data are in good agreement with those reported
for cyclobutadienerhodium compounds.6,12 Additionally,
we attributed two resonances in the 85-92 ppm region
to the R- and â-carbons of the alkynyl group.
In order to provide conclusive evidence for the un-
usual structure of these products, single crystals of
complex 2a were grown by slow diffusion of hexane into
a chloroform solution and its structure was determined
by a X-ray diffraction study. Figure 1 displays the
molecular structure of the complex, and the most
relevant bond lengths and angles are given in Table 1.
The rhodium, η5-bonded on one side to the C5Me5 ligand,
is η4-linked on the other to a trisubstituted cyclobuta-
diene. Two of the substituents are phenyls, in an
opposite disposition, while the third is a phenylethynyl
group. The Rh-C (C5Me5 ring) distances (mean 2.207-
(2) Å) are comparable to those found in the related
complex [(η5-C5Me5)Rh(η4-C4Ph2HCPhdC5Ph2H2)] (mean
2.211(14) Å) and in the tetraphenylbenzocyclobutadiene
compound [(η5-C5Me5)Rh(η4-C4Ph2C4Ph2H2)] (means
2.231(14) and 2.233(5) Å).6 The rhodium atom is almost
equidistant from both carbocyclic rings. It lies 1.842-
(2) and 1.849(2) Å apart from the plane through the five-
and four-membered rings, respectively. The methyl
substituents are bent away from the rhodium atom;
displacements for C(6), C(7), C(8), C(9), and C(10) from
the mean plane throught the C5 ring are 0.034(3), 0.021-
egy, we have succeeded in preparing homologous iri-
dium, rhodium, or (η6-p-cymene)ruthenium acetylide
compounds with several R-amino acidates and terminal
acetylenes.10f However, the reaction of the R-alaninate
rhodium chloride [(η5-C5Me5)Rh(L-alaninate)Cl] (1) with
the monosubstituted alkynes HCtCR (R ) Ph, p-tolyl)
takes a completely different course. From the reaction
medium the alkynylcyclobutadiene complexes [(η5-
C5Me5)Rh(η4-C4HR2CtCR)] (R ) Ph (2a ), p-tolyl (2b))
can be isolated (Chart 1). Their formation implies a
novel type of rhodium-mediated trimerization reaction.
Here we report the preparation of complexes 2a and 2b
as well as their characterization, which includes the
determination of the molecular structure of 2a by
diffractometric means. The stepwise course of the
unique trimerization process that affords 2 is also
discussed.
Resu lts a n d Discu ssion
Addition of HCtCR (R ) Ph, p-tolyl) and NEt3 to a
methanolic solution of complex [(η5-C5Me5)Rh(L-alani-
nate)Cl] (1)10a (molar ratio 1/1/1) caused the intensifi-
cation of the initial orange color of the solution and
the subsequent precipitation of the complexes [(η5-
C5Me5)Rh(η4-C4HR2CtCR)] (R ) Ph (2a ), p-tolyl (2b))
as orange-yellow solids in moderate isolated yield
(∼22%). This yield did not change significantly by
adding stoichiometric amounts of alkyne, but in this
case, spectroscopic analysis of the filtrate showed that
the formation yield of 2a was at least 75%, although
we have not been able to separate further fractions of
analytically pure product.
Complexes 2 were shown by mass spectrometry to
contain, along with the Rh(C5Me5) unit, a trimer of the
corresponding alkyne less two hydrogens. The isotopic
distributions of the molecular ions matched those
expected for the mentioned stoichiometry. The presence
of an alkynyl group was inferred from a weak ν(CtC)
1
absorption at 2180 (2a ) or 2185 cm-1 (2b). The H and
(11) Gardner, S. A.; Rausch, M. D. J . Organomet. Chem. 1973, 56,
365.
(12) Hughes, R. P.; Kowalski, A. S.; Donovan, B. T. J . Organomet.
Chem. 1994, 472, C18.
13C{1H} NMR data of these complexes agree with the
proposed formulation and are collected in the Experi-

4854 Organometallics, Vol. 15, No. 22, 1996
Lamata et al.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
Sch em e 1
(d eg) for [η5-C5Me5)Rh (η4-C4HP h 2CtCP h ] (2a )
Rh-C(1)
Rh-C(2)
Rh-C(3)
Rh-C(4)
Rh-C(5)
Rh-G(1)a
Rh-C(11)
Rh-C(12)
Rh-C(13)
Rh-C(14)
Rh-G(2)a
C(1)-C(2)
C(2)-C(3)
2.203(3)
2.203(2)
2.205(2)
2.213(2)
2.211(2)
1.842(2)
2.118(3)
2.117(2)
2.125(2)
2.114(2)
1.849(2)
1.424(4)
1.433(3)
C(3)-C(4)
1.419(4)
1.430(3)
1.437(3)
1.458(3)
1.452(4)
1.472(3)
1.470(4)
1.458(3)
1.454(3)
1.420(4)
1.199(4)
1.443(4)
C(4)-C(5)
C(1)-C(5)
C(11)-C(12)
C(12)-C(13)
C(13)-C(14)
C(11)-C(14)
C(11)-C(29)
C(13)-C(23)
C(14)-C(15)
C(15)-C(16)
C(16)-C(17)
3 or 4 in the preparation of the cyclobutadiene com-
pound 2a .
G(1)a-Rh-G(2)a
C(12)-C(11)-C(14)
C(12)-C(11)-C(29) 136.2(2) C(11)-C(14)-C(15) 133.8(2)
C(14)-C(11)-C(29) 134.0(2) C(13)-C(14)-C(15) 136.2(2)
C(11)-C(12)-C(13)
C(12)-C(13)-C(14)
C(12)-C(13)-C(23) 136.1(2)
177.7(1) C(14)-C(13)-C(23) 133.9(2)
89.7(2) C(11)-C(14)-C(13) 89.6(2)
When, in the absence of NEt3, 1 was allowed to react
with 3 equiv of HCtCPh, in methanol, the precipitation
1
of a mixture, identified by H NMR spectroscopy as 2a
90.9(2) C(14)-C(15)-C(16) 177.4(3)
89.9(2) C(15)-C(16)-C(17) 177.9(3)
and R-alanine, was observed. This result could be
accounted for by assuming the formal abstraction of the
phenylacetylene proton by the R-alaninato ligand.
Interestingly, the formation of the cyclobutadiene
compounds 2 was only observed for the rhodium alani-
nate derivative 1 and for the terminal alkynes phenyl-
and p-tolylacetylene. Thus, for example, the iridium
analogue of 1, [(η5-C5Me5)Ir(L-alaninate)Cl],10a or the
rhodium prolinate [(η5-C5Me5)Rh(L-prolinate)Cl]10a re-
acted with HCtCPh in the presence of NEt3, rendering
the corresponding alkynyl compounds [(η5-C5Me5)M(L-
amino acidate)(CtCPh)]10f (Chart 1). On the other
hand, under the same conditions, complex 1 did not
react with the terminal alkyne HCtCCMe3, and from
the reaction of 1 with HCtCCO2Me, only organic
compounds derived from the alkyne could be recovered.10f
a
G(1) and G(2) represent the centroids of the cyclopentadienyl
and cyclobutadiene ligands, respectively.
(3), 0.003(3), 0.042(3), and 0.107(3) Å, respectively. The
Rh-C (C4 ring) distances (mean 2.118(2) Å) are in the
range of those found in related cyclobutadiene rhodium
complexes (2.102(2)-2.152(14) Å).4a,5e,6 The cyclobuta-
diene ring is strictly planar and almost parallel to the
pentamethylcyclopentadineyl ligand, the angle between
them being 2.6(1)°. The cyclobutadiene ring is slightly
distorted from a square geometry, with the two C-C
bond distances involving the CH moiety (C(12) labeled,
1.458(3) and 1.452(4) Å) being shorter by ∼0.02 Å than
the other two cyclic C-C bonds (1.472(3) and 1.470(4)
Å). The mean C-C distance (1.464(4) Å) is comparable
to the corresponding distances reported for cyclobuta-
dienerhodium complexes4a,5e,6 (means 1.470(9)-1.482-
(19) Å). The phenyls and the ethynyl group are subtly
bent away from the metal atom by small amounts
(0.074(2) Å for C(29), 0.069(2) Å for C(23), and 0.107(2)
Å for C(15) from the mean plane through the C4 ring).
The phenyl substituents attached to C(11) and C(13) are
almost coplanar with the cyclobutadiene ring (1.7(1) and
3.0(1)°, respectively), but the phenyl ethynyl group is
twisted away from coplanarity with the coordinate
cyclobutadiene by 78.9(1)°. The C(15)-C(16) bond
distance of 1.199(4) Å is a normal carbon-carbon triple
bond distance.
1
We have also monitored, by H NMR spectroscopy,
the reaction of 1 with HCtCPh and NEt3 (1/3/2 molar
ratio) in CDCl3. The reaction mixture remained homo-
geneous and after 27 h a 52% of conversion to 2a was
measured showing that, in a solvent with lower coor-
dination tendency, such as chloroform, complex 2a is
also formed.
On the basis of these observations it is not possible
to unequivocally establish the mechanistic steps for the
formation of compounds 2, and no intermediates have
been detected to elucidate this problem. Nevertheless,
the structure of the organic ligand indicates that the
formation of these complexes must involve both oligo-
merization and cyclization steps, and in accord with
previously reported alkyne oligomerization processes,
the pathway shown in Scheme 2 could be suggested. The
reaction could start with the protonation of the R-alani-
nate ligand by one alkyne molecule, the resulting
R-alanine remaining η1-coordinate to the metal. Sup-
port for this proposal stems from the formation of 2a
and R-alanine in the reaction of 1 with HCtCPh in the
absence of NEt3 (see above) and, indirectly, from the
observations that 1 reacts with LiCtCPh but does not
afford 2a and that the reaction of the alkynylrhodium
compound [(η5-C5Me5)Rh(L-prolinate)(CtCCMe3)]10f with
HCtCPh and NEt3 proceeds with substitution of the
coordinated alkynyl ligand rendering [(η5-C5Me5)Rh(L-
prolinate)(CtCPh)]. Subsequently, one second alkyne
molecule could methatetically substitute the chloride
anion that will be eliminated as HNEt3Cl. In this way,
the neutral species i, related to the Maitlis intermediate
[(η5-C5Me5)Rh(C2Ph)2(NCMe)], could be formed. At this
In order to gain some insight into the mechanism of
formation of complexes 2, we carried out the reaction
of the solvate complex13 [(η5-C5Me5)Rh(MeOH)3]2+ with
phenylacetylene in the presence of NEt3. A mixture of
unidentified products was obtained, but it is interesting
to point out that, according to spectroscopic measure-
ments, complex 2a was not present in the mixture. In
a related reaction (Scheme 1), Maitlis et al. reported the
preparation of complexes 3 and 4, which contain cyclo-
butadiene derivatives, formed by oligomerization of
phenylacetylene, as ligands. The authors proposed that
the reaction proceeds via intermediates such as [(η5-C5-
Me5)Rh(C2Ph)2(NCMe)] and [(η5-C5Me5)Rh(C2Ph)2(HC2-
Ph)].6 We have not detected either by NMR spectros-
copy or by mass spectrometry the formation of either
(13) White, C.; Thompson, S. J .; Maitlis, P. M. J . Chem. Soc., Dalton
Trans. 1977, 1654.

(η4-Cyclobutadiene)rhodium Complexes
Organometallics, Vol. 15, No. 22, 1996 4855
Sch em e 2
point, the reductive tail-to-tail coupling of the two
alkynyl ligands at rhodium could take place rendering
intermediate ii. This reductive coupling is a key step
since it has been proposed that, in the absence of the
amino acid ligand, [(η5-C5Me5)Rh(C2Ph)2(NCMe)] inserts
acetylenes into the rhodium acetylide bond in a series
of stepwise cis insertions which ultimately yields 3 and
4.6,14 Linear dimerization is rare for alkynes2 but it is
interesting to point out that an essencial step in the
linear dimerization of terminal alkynes by copper salts
is the formation of M(CtCR)2 moieties usually facili-
tated by the addition of bases.15,16 The substitution of
the R-amino acid by an alkyne molecule in ii followed
by the oxidative coupling of the two alkyne ligands in
iii may occur to give the coordinatively unsaturated
metallacyclopentadiene iv, in which the metal has
adopted the formal oxidation state +3. The coupling
would proceed to preferentially give the isomer of iv in
which the bulkier substituents CtCR and R are apart
from the metal atom. The transformation of two
coordinated acetylenes into metallacyclopentadienes has
been previously reported,2,3,5b,7,17,18 and in particular, a
series of rhodacyclopentadienes have been isolated.5b,18
Probably, coordination of the amino acid on iv avoids
the formation of an alkyne-metallacyclopentadiene
complex and precludes the formation of benzene deriva-
tives. Finally, compound iv could, through a reductive
elimination, give the cyclobutadiene complexes 2, as has
been previously proposed for the preparation of related
η4-cyclobutadienerhodium compounds.3,6
In summary, the reaction of [(η5-C5Me5)Rh(L-alani-
nate)Cl] (1) with HCtCR (R ) Ph, p-tolyl), in basic
media, affords the transition-metal trisubstituted cy-
clobutadiene complexes 2a and 2b. The process in-
volves an unique type of alkyne trimerization that only
in the case of complex 1 and the aforementioned alkynes
has been observed. The iridium analogue or related
pentamethylcyclopentadienyl rhodium or iridium amino
acidates do not promote this type of oligomerization.
Although the mechanistic route leading to these com-
pounds has not been elucidated, a possible path with
the reductive coupling key step i f ii is discussed.
Exp er im en ta l Section
(14) A referee suggested an alternative mechanism based on alkyne
insertion steps mediated by Rh intermediates. According to this
suggestion, the alanine ligand could be substituted in i by a third
alkyne molecule rendering A. Two alkyne insertion steps will afford
iv from A through the intermediate B.
Gen er a l Com m en ts. Solvents were dried over appropriate
drying agents, distilled under N2, and degassed prior to use.
The reactions were carried out under nitrogen. Infrared
spectra were recorded on a Perkin-Elmer 1330 spectropho-
tometer. The C and H analyses were carried out with a
Perkin-Elmer 240B microanalyzer. NMR data were recorded
on a Varian Unity 300 spectrometer. Chemical shifts (1H and
13C{1H} NMR spectra) are expressed in ppm upfield from
SiMe4. Coupling constants J are given in hertz. Mass spectra
were measured on a VG Autospec spectrometer. The starting
complex [(η5-C5Me5)Rh(L-alaninate)Cl] was prepared by a
published method.10a
P r ep a r a tion of [(η5-C5Me5)Rh (η4-C4HP h 2CtCP h )] (2a ).
To a solution of 1 (167.0 mg, 0.461 mmol) in 20 mL of
methanol, phenylacetylene (50.6 µL, 0.461 mmol) and NEt3
(64.5 µL, 0.461 mmol) were added. After 5 min, the color of
the solution changed from orange to dark orange. The mixture
was stirred for 20 h, and the orange-yellow solid which
precipitated was filtered off, washed with methanol, and
(15) Sonogashira, K. In Comprehensive Organic Synthesis; Trost,
B. M., Fleming, I., Pattenden, G., Eds.; Pergamon: Oxford, England,
1991; Vol. 3, Chapter 2.5, p 551.
(16) The transient formation of PhCtCCtCPh as a result of the
oligomerization of two PhCtC groups has been recently suggested by
Koridze et al. in the formation of the dirhenium compound [Re2-
(CO)7(C2Ph)4]: Koridze, A. A.; Zdanovich, V. I.; Kizas, O. A.; Yanovsky,
A. I.; Struchkov, Y. T. J . Organomet. Chem. 1994, 464, 197.
(17) Vollhardt, K. P. C. Acc. Chem. Res. 1977, 10, 1.
(18) See, for example: Bianchini, C.; Caulton, K. G.; Chardon, C.;
Eisenstein, O.; Folting, K.; J ohnson, T. J .; Meli, A.; Peruzzini, M.;
Rauscher, D. J .; Streib, W. E.; Vizza F. J . Am. Chem. Soc. 1991, 113,
5127.
vacum-dried. Yield: 54 mg (22%). Anal. Calcd for C34H31
-
Rh: C, 75.27; H, 5.75. Found: C, 74.97; H, 5.92. 1H NMR
2
(CDCl3): δ 1.55 (s, 15H, C5Me5), 4.73 (d, 1H, J RhH ) 1.9, η4-

4856 Organometallics, Vol. 15, No. 22, 1996
Lamata et al.
Cr ysta l Str u ctu r e Deter m in a tion of [(η5-C5Me5)Rh (η4-
C4HP h 2CtCP h )] (2a ). A summary of crystal data and
refinement parameters are reported in Table 2. A yellow
crystalline needle of approximate dimensions 0.194 × 0.190
× 0.741 mm grown by slow diffusion of hexane into a
chloroform solution of 2a was used for the analysis. The
selected crystal was glued onto the tip of a glass fiber. A set
of randomly searched reflections was indexed to the corre-
sponding crystal symmetry, and accurate unit cell dimensions
were determined by least-squares refinement of 59 carefully
centered reflections (20 e 2θ e 50°). Data were collected on
a Stoe AED diffractometer, with graphite-monochromated Mo
KR radiation (λ ) 0.710 73 Å) by the ω/2θ scan method. Three
orientation and intensity standards were monitored through-
out data collection; no variation was observed. All data were
corrected for absorption using a semiempirical method (ψ
scan).19 The structure was solved by Patterson methods
(SHELXTL PLUS)20 and conventional Fourier techniques. All
non-hydrogen atoms were refined anisotropically and the
hydrogen atoms included in the last cycles of refinement in
observed positions and refined riding on their carbon atoms.
The structure was refined by full-matrix least squares. The
function minimized was ∑[w(Fo - Fc)2] with the weight defined
as ω-1 ) [σ2(Fo) + gFo2]. Atomic scattering factors, corrected
for anomalous dispersion for rhodium, were used as imple-
mented in the refinement program.20
Ta ble 2. Su m m a r y of Cr ysta llogr a p h ic Da ta for
[(η5-C5Me5)-Rh (η4-C4HP h 2CtCP h )] (2a )
formula
fw
C34H31Rh
542.52
symmetry
a, Å
b, Å
monoclinic, P21/c
11.0287(8)
16.5073(9)
14.5030(8)
99.507(6)
c, Å
â, deg
V, Å3
2604.1(3)
Z
4
radiation
µ, cm-1
method of collcn
scan range, deg
no. of indep rflns
Mo KR (λ ) 0.710 73 Å)
6.76
ω/2θ scan
3 e 2θ e 52
8971 (h, -13 to +13; k,
-20 to +10; l, 0-17)
5160 (Rmerg ) 0.0160)
4282 (Fo g 4.0σ(Fo))
0.0265
no. of unique rflns
no. of obsd rflns
R
Rw
0.0259
S, goodness of fit
data-to-param ratio
largest diff peak, e/Å3
1.37
13.5/1
0.39
C4H), 7.0-7.6 (m, 15H, Ph). 13C{1H} NMR (CDCl3): δ 8.93
1
1
(s, C5Me5), 54.03 (d, J RhC ) 11.3, C3CCtCPh), 57.33 (d, J RhC
) 11.0, η4-C3CH), 79.11 (d, J RhC ) 10.5, η4-C2C2Ph2), 85.92
1
2
1
(d, J RhC ) 1.4, CtCPh), 91.20 (s, CtCPh), 94.00 (d, J RhC
)
6.9, C5Me5), 123.00 (s) and 128.28 (s) (o-C and m-C of η4-C4Ph2),
124.79 (s, p-C of η4-C4Ph2), 127.45 (s, p-C of CtCPh), 128.39
(s) and 131.12 (s) (o-C and m-C of CtCPh). IR (Nujol, cm-1):
ν(CtC) 2180 (w), ν(CdC) 1595 (s) cm-1. MS (FAB+) m/ z 542
(M+, 100).
Ack n ow led gm en t. We thank the Direccio´n General
de Investigacion Cient´ıfica y Te´cnica for financial sup-
port (Grant PB92/19). E.S.J . thanks the Ministerio de
Educacio´n y Ciencia for a fellowship, and R.A. is grateful
to the CONICIT for a grant.
Complex 2b was similarly prepared. Yield: 22%. Anal.
Calcd for C37H37Rh: C, 76.02; H, 6.37. Found: C, 75.65; H,
6.02. 1H NMR (CDCl3): δ 1.57 (s, 15H, C5Me5), 2.27 (s, 6H,
η4-C4-p-C6H4Me), 2.38 (s, 3H, CtC-p-C6H4Me), 4.65 (d, 1H,
2J RhH ) 1.7, η4-C4H), 7.11, 7.05 (AB system, 8H, J AB ) 8.2,
η4-C4-p-C6H4Me), 7.43, 7.18 (AB system, 4H, J AB ) 8.1, CtC-
p-C6H4Me). 13C{1H} NMR (CDCl3): δ 9.01 (s, C5Me5), 21.32
Su p p or t in g In for m a t ion Ava ila b le: Refined atomic
coordinates, anisotropic displacement parameters, hydrogen
positional parameters, all crystallographic and experimental
data, and all bond distances and angles for 2a (Tables
S1-S5) (16 pages). Ordering information is given on any
current masthead page.
1
(s, η4-C4-p-C6H4Me), 21.53 (s, CtC-p-C6H4Me), 53.77 (d, J RhC
1
) 10.5, C-CtC-p-C6H4Me), 56.78 (d, J RhC ) 10.5, η4-C3CH),
1
79.24 (d, J RhC ) 10.1, η4-C2C2-(p-C6H4Me)2), 85.32 (s, CtC-
1
p-C6H4Me), 91.03 (s, CtC-p-C6H4Me), 93.74 (d, J RhC ) 6.9,
C5Me5), 121.88 (s) and 137.40 (s) (ipso-C or p-C of CtC-p-C6H4-
Me), 123.06 (s) and 128.93 (s) (o-C and m-C of η4-C4-p-C6H4-
Me), 129.10 (s) and 130.99 (s) (o-C and m-C of CtC-p-C6H4Me),
133.28 (s) and 134.20 (s) (ipso-C or p-C of η4-C4-p-C6H4Me)).
IR (Nujol, cm-1): ν(CtC) 2185 (m), ν(CdC) 1620 (s), cm-1. MS
(FAB+) m/ z 584 (M+, 100).
OM960318T
(19) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.
(20) Sheldrick, G. M. SHELXTL PLUS, Siemens Analytical X-ray
Instruments, Inc., Madison, WI, 1990.