Heterobimetallic indenyl complexes. Synthesis and carbonylation reaction of anti-[Cr(CO)3-μ,η:η-indenyl-Ir(COD)]

Article abstract of DOI:10.1021/om9706065

The reaction of the anti-[Cr(CO)₃-μ,η:η-indenyl-Ir(COD)] (I) complex with an excess of CO in CH₂Cl₂ at 203 K produces quantitatively the η¹-[η⁶-Cr(CO) ₃-indenyl]-Ir(COD)(CO)₂ intermediate which above 273 K converts into the fully carbonylated complex η¹-[η⁶-Cr-(CO)₃-indenyl]Ir(CO) ₄; this in turn is stable up to 313 K. Carbonylation of the anti-[Cr-(CO)₃-μ,η:η-indenyl-Ir(COE)₂] analogue (II) gives the η¹-[η⁶-Cr(CO)₃-indenyl]-Ir(CO) ₄ (VII) species in a single fast step. In contrast to the behavior of the corresponding rhodium complexes, for which η¹ intermediates have never been observed and the aromatized substitution product is the stable product, the rearomatization of the cyclopentadienyl ring in iridium complexes to give the normal substitution product, viz., anti-[Cr(CO)₃-μ,η:η-indenyl-Ir-(CO)₂] (III) is a difficult process which takes place only on bubbling argon through the solution. The final product III is barely stable in solution. If the carbonylation is carried out using a blanket of CO over the solution of complexes I and II, viz., failing CO, the scarcely soluble iridium dimer [η⁶-Cr(CO)₃-indenyl-η³-Ir(CO) ₃]₂ (IX) stable in the solid state is obtained, probably by dimerization of the unstable intermediate anti-[η⁶-Cr(CO)₃-indenyl-η³-Ir(CO) ₃] (X).

Full text of DOI:10.1021/om9706065

752
Organometallics 1998, 17, 752-762
Heter obim eta llic In d en yl Com p lexes. Syn th esis a n d
Ca r bon yla tion Rea ction of
a n ti-[Cr (CO)3-µ,η:η-in d en yl-Ir (COD)]
Pierluigi Cecchetto, Alberto Ceccon,* Alessandro Gambaro, and Saverio Santi
Dipartimento di Chimica Fisica, Universita` di Padova, Via Loredan 2, 35131 Padova, Italy
Paolo Ganis
Dipartimento di Chimica, Universita` di Napoli, Via Mezzocannone 4, 80134 Napoli, Italy
Roberto Gobetto
Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universita` di
Torino, Via Giuria 7, 10125 Torino, Italy
Giovanni Valle
CNR, Centro di Studio sui Biopolimeri, Via Marzolo 3, 35131 Padova, Italy
Alfonso Venzo
CNR, Centro di Studio sugli Stati Molecolari Radicalici ed Eccitati, Via Loredan 2,
35131 Padova, Italy
Received J uly 17, 1997
The reaction of the anti-[Cr(CO)3-µ,η:η-indenyl-Ir(COD)] (I) complex with an excess of CO
in CH2Cl2 at 203 K produces quantitatively the η1-[η6-Cr(CO)3-indenyl]-Ir(COD)(CO)2
intermediate which above 273 K converts into the fully carbonylated complex η1-[η6-Cr-
(CO)3-indenyl]Ir(CO)4; this in turn is stable up to 313 K. Carbonylation of the anti-[Cr-
(CO)3-µ,η:η-indenyl-Ir(COE)2] analogue (II) gives the η1-[η6-Cr(CO)3-indenyl]-Ir(CO)4 (VII)
species in a single fast step. In contrast to the behavior of the corresponding rhodium com-
plexes, for which η1 intermediates have never been observed and the aromatized substitution
product is the stable product, the rearomatization of the cyclopentadienyl ring in iridium
complexes to give the “normal” substitution product, viz., anti-[Cr(CO)3-µ,η:η-indenyl-Ir-
(CO)2] (III) is a difficult process which takes place only on bubbling argon through the
solution. The final product III is barely stable in solution. If the carbonylation is carried
out using a blanket of CO over the solution of complexes I and II, viz., failing CO, the scarcely
soluble iridium dimer [η6-Cr(CO)3-indenyl-η3-Ir(CO)3]2 (IX) stable in the solid state is
obtained, probably by dimerization of the unstable intermediate anti-[η6-Cr(CO)3-indenyl-
η3-Ir(CO)3] (X).
In tr od u ction
hapticity η3 or η1 intermediates, which are energetically
favored in the case of indenyl complexes because of
concomitant aromatization of the fused benzene ring.
As a matter of fact, direct evidence for the formation of
an η3 intermediate along the substitution path in both
Rh and Ir complexes is still elusive, even though its
postulation is sometimes necessary to explain the
kinetic data and the reaction products.2 In contrast,
there is direct experimental evidence for the presence
of an η1 species as an intermediate in the associative
substitution reaction of COD with carbon monoxide in
η5-indenyl-Ir(COD).3 Below 243 K, the reagent is
transformed into the stable η1-indenyl-Ir(COD)(CO)2
η5-Indenyl-ML2 (M ) Co, Rh, Ir, etc.) complexes are
far more reactive than the corresponding cyclopentadi-
enyl analogues in substitution reactions of the ancillary
ligands with nucleophiles.1 For example, easy substitu-
tion of two CO’s for COD takes place at room temper-
ature in η-indenyl-M(COD), whereas forced conditions,
viz., high temperature and high CO pressure, are
required in the case of the corresponding cyclopentadi-
enyl complexes. This enhanced reactivity was at-
tributed to an easier metal slippage to form lower
(1) (a) Rerek, M. E.; Basolo, F. Organometallics 1983, 2, 372. (b)
Moreno, C.; Macazaga, M. J .; Delgado, S. Organometallics 1991, 10,
1124. (c) Cheong, M.; Basolo, F. Organometallics 1988, 7, 2041. (d)
Rerek, M. E.; Basolo, F. J . Am. Chem. Soc. 1984, 106, 5908. (e) Kakkar,
A. K.; Taylor, N. J .; Marder, T. B.; Shen, J . K.; Hallinan, N.; Basolo,
F. Inorg. Chim. Acta 1992, 198-200, 219.
(2) (a) Rerek, M. E.; J i, L. N.; Basolo, F. J . Chem. Soc., Chem.
Commun. 1983, 1208. (b) Wescott, S. A.; Kakkar, A. K.; Stringer, S.;
Taylor, N. J .; Marder, T. B. J . Organomet. Chem. 1990, 394, 777.
(3) Bellomo, S.; Ceccon, A.; Gambaro, A.; Santi, S.; Venzo, A. J .
Organomet. Chem. 1993, 453, C4-C6.
S0276-7333(97)00606-7 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/22/1998

Heterobimetallic Indenyl Complexes
Organometallics, Vol. 17, No. 4, 1998 753
species which, on raising the temperature, is quantita-
tively converted into η5-indenyl-Ir(CO)2. This η1 f η5
rearrangement, involving the loss of the two π bonds
between the metal and COD and the restoration of the
aromaticity of the fused Cp ring, exhibits a relatively
high enthalpy of activation (∆Hq ) 79 kJ mol-1). In the
carbonylation reaction of the analogous η5-indenyl-Rh-
(COD) complex no η1 species was observed even at very
low temperature (-80 °C), indicating that if the poten-
tial η1-indenyl-Rh(COD)(CO)2 intermediate is formed,
it probably loses COD and restores the η5 coordination
mode much faster than the iridium complex.4
In order to avoid the η6 f η5 haptotropic migration of
the Cr(CO)3 group, η6-indene-Cr(CO)3 was metalated in
THF with KH at -40 °C.7 Quenching of the solution
with the appropriate iridium dimer afforded the bime-
tallic anti-[Cr(CO)3-µ,η:η-indenyl-Ir(COD)] (I) or anti-
[Cr(CO)3-µ,η:η-indenyl-Ir(COE)2] (II) complexes. We
attributed the anti stereochemistry to both products
1
because of the close similarity of their H and 13C NMR
spectral parameters with those of the corresponding
chromium-rhodium complexes. For I, the anti location
of the two inorganic units was also confirmed by X-ray
analysis (see below).
In recent years we have been developing the chem-
istry of bimetallic indenylrhodium complexes in which
the benzene ring is π-bonded to the Cr(CO)3 group in a
syn or anti stereochemistry.5 We have found that the
rate of substitution of the ancillary ligands at rhodium
increases to a great extent if the benzene ring is
coordinated to Cr(CO)3 in a transoid arrangement. In
particular, we have been studying the kinetics of the
carbonyl substitution at rhodium with COD and NBD
in anti-[Cr(CO)3-µ,η:η-indenyl-Rh(CO)2] and have sug-
gested an η1-indenylrhodium species as the most prob-
able intermediate along the reaction pathway.4 Con-
versely, the syn coordination with Cr(CO)3 did not
induce significant changes in the substitution rate of
CO’s.
Since the third transition series elements generally
stabilize low-hapticity species to a greater extent than
the corresponding metals of the second series, we
undertook a study concerning the synthesis and the
reactivity of some bimetallic Cr(CO)3-µ,η:η-indenyl-IrL2
complexes with the aim of observing the corresponding
η1-iridium intermediates. We were particularly inter-
ested in the chemical behavior of anti-[Cr(CO)3-µ,η:η-
indenyl-Ir(COD)] in the presence of carbon monoxide.
Addition or loss of CO to or from a metal center
represents a crucial step in many transition metal-
catalyzed processes, and a comparison between the
iridium and rhodium species in this kind of reaction
under particularly mild conditions seemed promising.
In analogy with substitution rates of the ancillary
ligands in the corresponding rhodium complexes, we
expected that substitution of COD or COE by CO in the
bimetallic complexes I and II would take place faster
than in the monometallic η5-indenyl-IrL2. As a matter
of fact, carbonylation of I and II proceeds differently
from that of the monometallic complexes, and a detailed
description of the process will be reported below. Since
preparation and isolation of pure anti-[Cr(CO)3-µ,η:η-
indenyl-Ir(CO)2] (III) was not feasible by direct reaction
of I or II with CO, we explored the complexation of
monometallic η5-indenyl-Ir(CO)2 with Cr(CO)3 as an
alternative synthetic procedure. The reaction of this
complex with (CH3CN)3Cr(CO)3 in THF for 5 h at 25
°C afforded an orange-red compound the elemental
analysis of which corresponds to that of the expected
product. The IR spectrum shows two bands at 2046 and
1984 cm-1 due to the stretching modes of the CO groups
bonded to iridium and two bands at 1944 and 1895 cm-1
1
due to the tricarbonylchromium tripod. The H NMR
spectrum (submitted as Supporting Information) and
the 13C NMR parameters (see Experimental Section) of
this compound show that the chemical shift values of
the indenyl frame resemble more closely those of syn-
[Cr(CO)3-µ,η:η-indenyl-RhL2] complexes5b,c rather than
those of anti-[Cr(CO)3-µ,η:η-indenyl-RhL2] complexes.8
X-ray analysis (see below) showed that the two metals
are situated in the syn configuration giving rise to syn-
[Cr(CO)3-µ,η:η-indenyl-Ir(CO)2] (IV). The expected anti
isomer, III, was not detected. Complex III was obtained
only in solution as an unstable species by a different
route and its formation and spectroscopic characteriza-
tion will be presented below. It must be mentioned that
complexation of the benzene ring of the monometallic
η5-indenyl-Ir(CO)2 complex with Cr(CO)3 takes place
under milder conditions than in the case of most
aromatic hydrocarbons usually requiring much higher
temperatures for complexation (T > 100 °C). This
behavior is likely due to a significant decrease in
aromatic character of the six-membered ring whose π
electrons are in part engaged in the coordination with
iridium. As a consequence, electronic structures where
the six-membered ring exhibits a pronounced diene
character become important (cf. the X-ray analysis), and
therefore, complexation with Cr(CO)3 would take place
easily via the formation of an η4 intermediate. This
species appears to be particularly stable in the case of
bimetallic systems as suggested by recent results con-
Resu lts a n d Discu ssion
Metalation of indene, carried out at room temperature
by treatment with KH of its THF solution, produced the
indenyl anion potassium salt. Successive quenching of
the anionic solution with [Ir(L)2(µ-Cl)]2 or [Ir(L2)(µ-Cl)]2
(L ) cyclooctene (COE), L2 ) 1,5-cyclooctadiene (COD))
afforded the corresponding η5-indenyl-Ir(COE)2 and η5-
indenyl-Ir(COD) complexes in agreement with published
procedures.6 Both complexes react easily with CO (1
bar) at room temperature to give η5-indenyl-Ir(CO)2 in
quite good yield. The results of a study dealing with
the mechanism of this olefin substitution reaction have
been reported.3
Heterobimetallic chromium-iridium indenyl com-
plexes were prepared by using an analogous procedure.
(4) Bonifaci, C.; Carta, G.; Ceccon, A.; Gambaro, A.; Santi, S.; Venzo,
A. Organometallics 1996, 15, 1630.
(5) (a) Ceccon, A.; Gambaro, A.; Santi, S.; Valle, G.; Venzo, A. J .
Chem. Soc., Chem. Commun. 1989, 51. (b) Bonifaci, C.; Ceccon, A.;
Gambaro, A.; Ganis, P.; Santi, S.; Valle, G.; Venzo, A. Organometallics
1993, 12, 4211. (c) Bonifaci, C.; Ceccon, A.; Gambaro, A.; Ganis, P.;
Santi, S.; Valle, G.; Venzo, A. J . Organomet. Chem. 1995, 492, 35.
(6) Merola, J . S.; Kackmarcik, R. T. Organometallics 1989, 8, 778.
(7) Ceccon, A.; Gambaro, A.; Gottardi, F.; Santi, S.; Venzo, A. J .
Organomet. Chem. 1991, 412, 85.
(8) (a) Ceccon, A.; Gambaro, A.; Santi, S.; Venzo, A. J . Mol. Catal.
1991, 69, L1-L6. (b) Ceccon, A.; Elsevier, C. J .; Ernsting, J . M.;
Gambaro, A.; Santi, S.; Venzo, A. Inorg. Chim. Acta 1993, 204, 15.

754 Organometallics, Vol. 17, No. 4, 1998
Cecchetto et al.
Ta ble 1. Selected Bon d Len gth s, Bon d An gles, a n d
Geom etr ica l P a r a m eter s for th e Com p lexes
a n ti-[Cr (CO)3-in d en yl-Ir (COD)] (I),
syn -[Cr (CO)3-in d en yl-Ir (CO)2] (IV), a n d
in d en yl-Ir (COD) (V)
I
IV
V
Bond Lengths/Å
Ir-C(1)
2.26(1)
2.26(2)
2.24(2)
2.36(2)
2.34(2)
2.33(2)
2.21(2)
2.20(2)
2.19(2)
2.24(3)
2.41(2)
2.25(2)
2.26(2)
2.23(2)
2.59(2)
2.56(2)
2.34(2)
2.25(2)
2.17(2)
2.19(2)
2.23(2)
2.42(2)
3.068(3)
1.45(2)
1.45(2)
1.43(2)
1.50(2)
1.45(2)
1.40(2)
1.42(2)
1.37(3)
1.53(3)
1.38(3)
2.211(9)
2.23(1)
2.23(1)
2.372(9)
2.38(1)
Ir-C(2)
Ir-C(3)
Ir-C(3a)
Ir-C(7a)
Cr-C(3a)
Cr-C(4)
Cr-C(5)
Cr-C(6)
Cr-C(7)
Cr-C(7a)
Ir-Cr
F igu r e 1. ORTEP view of syn-[Cr(CO)3-µ,η:η-indenyl-Ir-
(CO)2] (IV).
C(1)-C(2)
C(2)-C(3)
C(1)-C(7a)
C(3)-C(3a)
C(3a)-C(7a)
C(3a)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(7a)
1.44(3)
1.44(3)
1.40(3)
1.43(2)
1.50(3)
1.48(3)
1.32(2)
1.41(3)
1.43(3)
1.40(3)
1.45(2)
1.45(2)
1.41(2)
1.41(1)
1.46(1)
1.40(1)
1.37(2)
1.38(2)
1.39(2)
1.44(2)
ring indicate a slightly distorted η5 coordination of the
metal similar to that found for several others monome-
tallic indenyl complexes.2b,10 The distortion arises from
the puckering of the [C1,C2,C3] plane with respect to the
remainder of the indenyl skeleton (HA ) 8.6°), and the
distances of the metal from the C3a,C7a ring junction
carbons are only little longer than those from C1, C2,
and C3 (i.e., ∆(M-C) ) 0.15 Å). This situation is not
significantly modified by coordination of the six-
membered ring with Cr(CO)3 in the anti arrangement.
In fact, in the anti complex I, both the puckering of the
cyclopentadienyl ring (HA ) 5.8°) and the slippage of
iridium toward the external C1, C2, and C3 carbon atoms
(∆(M-C) ) 0.10 Å) are only slightly lower with respect
to the monometallic complex V. Moreover, the chro-
mium-carbon bond distances indicate a small slippage
of chromium from the ideal η6 hapticity toward an η4
one. As already observed in the analogous rhodium
complexes, anti coordination of the benzene ring with
Cr(CO)3 does not modify significantly the geometrical
parameters of the ortho-condensed CpML2 subunit; this
similarity in structure, however, does not translate into
similarity in reactivity in those reactions where rhodium
is directly involved, the bimetallic complexes being
much more reactive than the monometallic ones. We
expected to record a similar trend in iridium compounds.
As shown in Figure 1, the two metals in IV are located
on the same side of the indenyl plane. The parameters
that describe the coordination mode of iridium to the
Cp ring differ significantly from those of the other two
complexes, I and V; the geometric distortions observed
for the syn isomer are noticeably higher than those for
the anti isomer, the value of HA changing from 5.8 to
17°, and that of ∆(M-C) from 0.10 to 0.32 Å. These
data suggest a remarkable shift of iridium toward an
η3 hapticity. At the same time, the position of chromium
does not differ significantly between the anti and syn
complexes, as shown by the similar values of chromium-
carbon distances found in both cases, suggesting that
the slippage of iridium toward the external carbon
atoms of the five-membered ring is likely induced by
electronic rather than steric reasons.
Bond Angles/deg
Cr-C(8)-O(8)
Cr-C(9)-O(9)
Cr-C(10)-O(10)
C(8)-Cr-C(9)
C(8)-Cr-C(10)
C(9)-Cr-C(10)
Ir-C(11)-O(11)
Ir-C912)-O(12)
174(1)
178(2)
178(1)
89(1)
88(1)
89(1)
171(1)
179(2)
177(1)
85.7(8)
95.5(8)
84.6(8)
176(2)
176(1)
Parameters
0.10
5.8
∆(M-C)/Å
HA/deg
0.33
17
0.15
8.6
cerning the exchange of the Cr(CO)3 unit with cyclo-
heptatriene in bimetallic chromium-rhodium indenyl
complexes.4 At present we cannot explain the exclusive
formation of the syn isomer in any other way than by
comparison with the analogous indenyl complexes of
rhodium. For this class of compounds, at least with
norbornadiene as the ancillary ligand, the syn isomer
is thermodynamically more stable than the anti isomer,
even though its structure requires severe molecular
constraints.5b,9
X-r a y Mea su r em en ts. Crystals useful for diffrac-
tometric analysis were obtained by slow evaporation of
concentrated solutions of η5-indenyl-Ir(COD) (V), I, and
IV. Selected bond distances and the values of the
parameters conventionally adopted in order to describe
the metal coordination modes to arene ligands, i.e., ring
slip distortion (∆(M-C)) and hinge angle (HA),10 are
reported in Table 1. A perspective view of the structures
of IV is shown in the Figure 1 (those of I and V are
given as Supporting Information). In the monometallic
complex V, taken as a reference species, the distances
from iridium to the carbon atoms of the five-membered
(9) Bonifaci, C.; Ceccon, A.; Gambaro, A.; Ganis, P.; Santi, S.; Valle,
G.; Venzo, A. Organometallics 1995, 14, 2430.
The NMR results show that the difference between
the structural features of I and IV persists also in
solution. Taking the monometallic η5-indenyl-Ir(CO)2
as reference, the minor coordinative engagement of C3a
(10) (a) Merola, J . S.; Kackmarcik, R. T.; Van Engen, D. J . Am.
Chem. Soc. 1986, 108, 329. (b) Marder, T. B.; Calabrese, J . C.; Roe, D.
C. Organometallics 1987, 6, 2012. (c) Kakkar, A. K.; J ones, S. F.;
Taylor, N. J .; Collins, S.; Marder, T. B. J . Chem. Soc., Chem. Commun.
1989, 1454.

Heterobimetallic Indenyl Complexes
Organometallics, Vol. 17, No. 4, 1998 755
and C7a in IV with respect to I is suggested by the effect
of complexation with Cr(CO)3 on their chemical shift (∆δ
) δcomplex - δfree ) -5.65 ppm), which is close to that
found for the analogous syn rhodium complexes (∆δ )
-8.29 ppm).5b On the other hand, the Cr(CO)3 com-
plexation effects on quaternary carbon atoms are sub-
stantially larger in the case of anti-[Cr(CO)3-µ,η:η-
indenyl-Ir(CO)2] (∆δ ) -25.23 ppm; see below), as well
as in a wide series of anti-(Cr,Rh)-indenyl complexes
(mean value is ∆δ = -26.6 ppm)8b and, in general, in
substituted arenes (mean value is ∆δ = -28 ppm).11
Moreover, the tetrahedralization of the C4 and C7 carbon
atoms is evidenced by the much more pronounced
upfield shift of the resonances of the nuclei located in
these pivot positions with respect to those of the nuclei
in positions 5 and 6, as shown by comparing the NMR
data for η5-indenyl-Ir(CO)2 and IV [∆δ(C4,C7) ) -46.86
ppm, ∆δ(C5,C6) ) -36.42 ppm; ∆δ(H4,H7) ) -3.1 ppm,
∆δ(H5,H6) ) -1.9 ppm]. The increase of the hinge angle
from 8.6° in η5-indenyl-Ir(CO)2 to 17° in IV is also in
agreement with the observed large negative value of ∆δ-
(C1,C3) (-19.5 ppm). Conversely, the complexation
effects of an anti Cr(CO)3 group on the 1H and 13C NMR
parameters are markedly lower, and their values are
very close to those observed for the analogous anti-[Cr-
(CO)3-µ,η:η-indenyl-RhL2] complexes.5,8,9
Rea ction of I a n d II w ith Ca r bon Mon oxid e. (a )
η1-[η6-Cr (CO)3-in d en yl]-Ir L4 Com p lexes. On bub-
bling CO through a CH2Cl2 solution of I at 203 K (so
attaining a very large excess CO) the color changes
suddenly from orange to dark yellow. The solution
shows two IR bands at 2036.2 and 1989.8 cm-1, due to
the stretching modes of the CO ligands bonded to
iridium, and two strong absorptions at 1950.5 and
1870.1 cm-1, typical of the Cr(CO)3 group (see Figure
2a). The 1H NMR spectrum recorded at the same
temperature shows the absence of signals due to com-
plex I, and a new ABCDMNX pattern, characteristic of
an indene residue, appears (see Figure 3, trace A). The
COD ligand appears still coordinated to iridium as
indicated by the signals of its vinyl hydrogens at ∼3.9
and 4.1 δ, that is ∼1.5 ppm upfield with respect to the
resonance range of the free olefin. Thus, in analogy to
the behavior of the monometallic η5-indenyl-Ir(COD)
complex,3 we attribute the η1-[η6-Cr(CO)3-indenyl]-Ir-
(COD)(CO)2 structure VI to this species; the signals of
the olefinic COD protons appear as two distinct mul-
tiplets due to the chiral nature of the η1-indene ligand.
VI is stable until 273 K; above this temperature, the
intensity of the IR bands at 2036 and 1990 cm-1
diminishes until their disappearance and three new
absorptions grow at 2118.3, 2051.4, and 2024.1 cm-1 (cf.
Figure 2b). Moreover, the bands characteristic of the
Cr(CO)3 tripod are only slightly shifted to 1955.4 and
F igu r e 2. IR spectra (solvent, CH2Cl2) of η1-[η6-Cr(CO)3-
indenyl]-Ir(CO)2(COD) (VI) at 203 K (trace a), ax-η1-[η6-
Cr(CO)3-indenyl]-Ir(CO)4 (VII-ax) at 273 K (trace b), eq-
η1-[η6-Cr(CO)3-indenyl]-Ir(CO)4 (VII-eq) at 298 K (trace c),
[η6-Cr(CO)3-indenyl-η3-Ir(CO)3]2 (IX) at 213 K (trace d), [Cr-
(CO)3-indenyl-µ,η:η-Ir(CO)2]2 (XI) at 213 K (trace e), and
anti-[Cr(CO)3-µ,η:η-indenyl-Ir(CO)2] (III) at 298 K (trace
f). For other experimental conditions, see the text.
nated to iridium. We believe that the reaction of VI
with excess CO present in solution affords complex VII
where the Ir(CO)4 moiety is still η1-bonded to the indene
residue.
1
1876.4 cm-1. The H NMR spectrum (recorded at 203
K) of the final solution (Figure 3, trace B) shows again
the pattern characteristic for an indene residue; how-
ever, in this case, the resonance of COD olefinic protons
at 5.57 δ indicates that the olefin is no longer coordi-
The strong downfield shift exhibited by the signal of
H1 on going from VI to VII (∆δ ) 1.48 ppm) is in
agreement with a higher number of carbonyls bonded
to iridium. In the range of temperatures between 233
1
and 298 K, both IR and H NMR spectra of the CD2Cl2
(11) (a) Ceccon, A.; Gambaro, A.; Manoli, F.; Venzo, A.; Kuck, D.;
Bitterwolf, T. E.; Ganis, P.; Valle, G. J . Chem. Soc., Perkin Trans 2
1991, 233. (b) Ceccon, A.; Gambaro, A.; Manoli, F.; Venzo, A.; Kuck,
D.; Ganis, P.; Valle, G. J . Chem. Soc., Perkin Trans. 2 1992, 1111. (c)
Ceccon, A.; Gambaro, A.; Manoli, F.; Venzo, A.; Ganis, P.; Valle, G.;
Kuck, D. Chem. Ber. 1993, 126, 2053.
solution of VII change because of the occurrence of two
intramolecular rearrangements described below.
It must be mentioned that on reacting II with CO
under the same experimental conditions used with

756 Organometallics, Vol. 17, No. 4, 1998
Cecchetto et al.
F igu r e 3. 1H NMR spectra of η1-[η6-Cr(CO)3-indenyl]-Ir(CO)2(COD) (VI) (trace A), and η1-[η6-Cr(CO)3-indenyl]-Ir(CO)4
(VII) (trace B). L indicates the resonance of the olefinic protons of the free COD. For experimental conditions, see the text.
The signal at δ 5.32 is due to the undeuterated part of the solvent. The signals due to the methylene protons of COD in
VI are not reported.
1
those of the syn isomer IV (The H NMR spectra of I
and IV are given as Supporting Information).
(b) Dim er ic Ir idiu m Car bon yl Com plexes. Dimer-
ic iridium carbonyl complexes were obtained in different
carbonylation conditions. Instead of bubbling CO
through the solutions of complexes I and II as in the
previous experiment, the same solutions were kept
under a blanket of CO for a few minutes at room
temperature so realizing a lower CO concentration. The
color changed suddenly from orange to dark brown, and
a yellow solid, IX, precipitated in 50% yield. The solid
is stable under argon and its IR spectrum, recorded as
a Nujol dispersion (Figure 4, trace A), exhibits three
strong bands which have been assigned to the terminal
CO’s bonded to iridium (2090, 2070, and 2040 cm-1) two
complex I, one observes only the formation of VII. From
these results, it is evident that in this case CO addition
bands (1746 (sh) and 1740 cm-1) in the region of
bridging Ir-CO’s and five bands (1950 (sh), 1940, 1885,
1865 and 1840 cm-1) due to the CO’s bonded to
chromium. The syn structure of IX fully justifies the
number of active CO stretchings if we consider the Ir2-
(CO)6 and the Cr(CO)3‚‚‚Cr(CO)3 systems each one
belonging to the same vibrating system. Both have a
C2v local symmetry that provides three and two active
ν(CtO) modes for the terminal and bridged carbonyls
of iridium and five for the chromium CO’s. On the
contrary, an anti conformation should impose a C2h local
symmetry providing in the above given order two, one,
and three active ν(CtO) modes which are less than
those experimentally observed.12 The assignment of
bands to the different types of carbonyls was confirmed
by the IR spectrum of the product obtained using 13C-
labeled CO as reagent (see Figure 4, trace B). The
bands attributed to the carbonyls coordinated to iridium
are shifted ∼40 cm-1 to lower frequencies because of
the isotope effect whereas those of tricarbonylchromium
do not change. This demonstrates that both terminal
and bridging CO’s bonded to iridium arise from the
and COE elimination are indistinguishable processes
even at 203 K.
It seems appropriate to compare the thermal stability
and chemical behavior of the monometallic η1-indenyl-
Ir(COD)(CO)2 intermediate, VIII, with that of VI. In
fact, VIII already loses COD at 253 K to be quantita-
tively converted into η5-indenyl-Ir(CO)2,3 whereas the
bimetallic complex VI is thermally more stable and it
is preferably converted into VII, which in turn is stable
up to ∼313 K. Thus, in bimetallic VI the substitution
of COD with CO is an easier process than loss of COD
to form the η5-indenyl complex. As already reported,4
the complexation of the indenyl ligand with Cr(CO)3
stabilizes those species in which the second metal
(rhodium or iridium) is coordinated to the five-mem-
bered ring with the lowest hapticity mode.
In spite of this, we have obtained the rearomatized
product III by bubbling argon at room temperature
through a CD2Cl2 solution of VII. Complex III is not
very stable in solution, and attempts to isolate it in solid
state failed. Its characterization was accomplished by
analysis of the IR (Figure 2f) and NMR spectra of the
argon-purged solution. The anti configuration of III was
established on the basis of the close similarity of its
spectral parameters (see Experimental Section) with
those of the analogous anti-[Cr(CO)3-µ,η:η-indenyl-Rh-
(CO)2] complex,8 and of the marked difference from
(12) One of the reviewers suggested that, given the likely inequiva-
lence in the solid state arising from the crystal packing, the molecular
symmetry in IX could be broken so either a syn or anti structure could
be consistent with the reported number of the chromium and iridium
carbonyl bands. The identical number of CO bands observed in the IR
spectrum of IX either in solution (Figure 2d) or in solid (as a Nujol
dispersion, Figure 4A) seems not to be in accord with his interpretation.

Heterobimetallic Indenyl Complexes
Organometallics, Vol. 17, No. 4, 1998 757
F igu r e 4. IR spectra (Nujol dispersion) of IX obtained by
carbonylation of I or II with a blanket of CO (trace A) and
of 13CO (trace B). For experimental conditions, see the text.
F igu r e 6. 13C CPMAS NMR spectrum of complex I (trace
A) and of product of its reaction with natural-abundance
[13C]CO (trace B). For the experimental details, see Ex-
perimental Section.
value. The computed values (∆σ ) 132 ppm for the
signal at δ ) 217.9 ppm and ∆σ ) 365 ppm for the two
peaks at δ 166.3 and δ ) 164.0 ppm) are in the usual
range found for csa of bridging and terminal carbonyls,
respectively.14
In order to assess the hapticity mode of the indenyl
group we performed a 13C CPMAS spectrum of IX
obtained by using natural-abundance [13C]CO to avoid
the intense spinning side-band manifold of the carbonyls
(Figure 6, trace B), and we compared it with the 13C
solid-state spectrum of complex I (Figure 6, trace A).
The reagent I shows 10 peaks at 99.3 (1 C), 93.7 (1 C),
92.6 (1 C), 85.4 (3 C’s), 80.6 (1 C), 70.4 (2 C’s), 56.0 (2
C’s), 53.9 (2 C’s), 37.1 (2 C’s), and 30.7 (2 C’s) ppm,
respectively. Bearing in mind that inequivalences in
the solid state can arise from the crystal packing, we
assign on the basis of the solution spectrum (see
Experimental Section) the four higher field resonances
to the COD ligand and, among the other signals, the
two peaks at 99.3 and 70.4 ppm to the C2 and C1,3 of
the indenyl group. In the 13C solid-state spectrum of
the product obtained by reacting I with CO (lower trace),
we observed the disappearence of the higher field
resonances of the COD ligand, the formation of a broad
hump centered at 80.2 ppm, and the presence of a
sharper peak at 112.5 ppm. We tentatively assign this
low-field peak to the C2 atom of the indenyl group
whereas the broad envelope of resonances centered at
80.2 ppm corresponds to a dispersion of the chemical
F igu r e 5. 13C CPMAS NMR spectrum of species obtained
by reacting complex II with 13C-enriched CO. The inset
shows the region of δ 230-160 ppm. For the experimental
details, see Experimental Section.
added CO and that no exchange with those belonging
to Cr(CO)3 takes place. The presence of both terminal
and bridged carbonyls bonded to iridium was confirmed
by 13C solid-state NMR measurements.
The high-resolution {1H}13C solid-state spectrum of
the product obtained using 13CO as reagent is reported
in Figure 5, and the inset shows the presence of three
resonances at 217.9, 166.3, and 164.0 ppm in the
relative ratio of 2:3:1, respectively. The low-field reso-
nance falls in the typical range of bridging carbonyls
bonded to iridium atoms whereas the two high-field
resonances can readily be assigned to terminal carbo-
nyls. Further support to this assignment arises from
the spinning side-band analysis13 that allows one to
obtain the principal components for each resonance and
then to evaluate their chemical shift anisotropy (csa)
(13) Hawkes, G. E.; Sales, K. D.; Aime, S.; Gobetto, R.; Lian, L. Y.
Inorg. Chem. 1991, 30, 1489. Hawkes, G. E.; Sales, K. D.; Gobetto, R.;
Lian, L. Y. Proc. R. Soc. London, A 1989, 424, 93.
(14) Herzfeld, J .; Berger, A. E. J . Chem. Phys. 1980, 73, 6021.

758 Organometallics, Vol. 17, No. 4, 1998
Cecchetto et al.
shifts of the other aromatic carbons (On the basis of the
available data we cannot exclude that the broadening
feature has some contribution from slow motion of the
ligand around its equilibrium position.).
On the basis of the IR and 13C solid-state NMR data,
we suggest the syn dimeric structure IX for this
F igu r e 7. 1H NMR spectra (solvent, CD2Cl2; T 283 K) of
the process XI (trace A) f III (trace C): (A) t ) 0; (B) t
∼20 min; (C) t ) ∞.
precipitate, where the two indenyl moieties are located
on the same side of the plane defined by the iridium
atoms and the bridged carbonyls.
The η3 hapticity mode of the iridium atoms to the
indenyl ligand is justified on the basis of electron
counting. The large downfield shift of the C2 resonance
(∆δ ) 13.2 ppm) found by comparing the NMR data for
IX and I is in agreement with a change of the iridium
recorded. It exhibits two bands (2063 and 2030 cm-1
)
due to Ir-bonded terminal carbonyls, two strong bands
for the Cr(CO)3 tripods at 1954 and 1881 cm-1, and a
weaker band at 1762 cm-1 due to bridging carbonyls,
showing that a new complex, XI, is formed. This
spectrum differs markedly from that of III (see Figure
8b
hapticity from η5 to η3.
Iridium complexes where the metal is η3-bonded to
the cyclopentadienyl ring are not frequent; the only η3-
indenyl-IrL3 species isolated and structurally character-
ized is that reported by Merola et al.,10a in which L )
PPhMe2, i.e., a strong σ-donor phosphine. Dimer IX is
likely formed by rapid dimerization of the monomer
intermediate X, an η3 species likely very labile because
2f). In particular, the difference between the frequen-
cies of the two stretching bands attributed to the
terminal CO’s is 33 cm-1 for XI and 66 cm-1 for III.
The 1H NMR spectrum of XI (Figure 7, trace A) is
characteristic of an indenyl frame consisting of an
AA′BB′ pattern at δ ) 5.77 and 5.11 ppm (H4,7 and H5,6
,
of the presence of strong π-acceptor ligands, viz., the
CO’s.
respectively) and a doublet at δ ) 5.46 ppm and a triplet
at δ 5.86 ppm (H1,3 and H2, respectively) and is different
from that of III (Figure 7, trace C). However, on raising
the temperature to 273 K, both the IR and 1H NMR
spectra indicate that XI changes into III.
We believe that, under a blanket of CO, the reagent
I is first quickly converted into the η1-indenyl species
VI; in the successive slow step, failing CO, the unstable
X is formed, which quickly dimerizes to the scarcely
soluble IX. Conversely, in presence of a large excess of
CO the η1-Ir(CO)4 species, VII is formed.
The dimer IX, however, is stable only in the solid
state. In fact, when it is dissolved in CH2Cl2 at 213 K,
the initially observed IR spectrum (see Figure 2d) is very
similar to that recorded in Nujol (Figure 4a); however,
within a few minutes a new IR spectrum (Figure 2e) is
1
The changes of the H NMR spectra due to the XI f
III process are shown in Figure 7 for 283 K. The
chemical shift values indicate that the indenyl protons
of XI resonate at higher field with respect to the protons
of complex III, the most significant upfield shift being
shown by H2. Therefore, the value of the parameter ∆δ
) δ(H1,3) - δ(H2), which was previously taken as a
measure of the distortion from an η5 hapticity toward

Heterobimetallic Indenyl Complexes
Organometallics, Vol. 17, No. 4, 1998 759
8b
η3,
decreases from 0.68 ppm for III to 0.40 ppm for
XI, indicating a less distorted η5 coordination in XI than
in III. Thus, the IR and NMR data agree with the
persistence of a dimeric structure in XI where the
restoration of the η5 hapticity is due to loss of two
terminal CO’s.
1
In tr a m olecu la r Rea r r a n gem en ts of VII. The H
NMR spectrum of η1-[η6-Cr(CO)3-indenyl]-Ir(CO)4 (VII)
in methylene chloride solution manifests a marked
temperature dependence (see Figure 8) suggesting the
occurrence of intramolecular rearrangement processes.
Stepwise increase in temperature from 233 to 273 K
shows complete collapse of resonances relative to H1 and
H3 along with change of the shape of the H2 signal from
a doublet of doublets to a triplet. This spectral behavior
as well as the changes shown by the signals of the
benzene ring protons can be explained by the occurrence
of a [1,3]-shift of the Ir(CO)4 group (a similar process
involving the [Ir(CO)2(COD)] group was shown for the
analogous monometallic intermediate):3
F igu r e 8. Temperature dependence of the 1H NMR
spectrum of VII in CD2Cl2. The signal at δ 5.32 is due to
the undeuterated part of the solvent.
symmetry of the Ir(CO)4 fragment, i.e., the intercon-
version of two stereoisomers, both having a bipyramidal
trigonal structure, where the indene residue occupies
either an axial or an equatorial coordinative position
(Berry pseudorotation mechanism):
In addition, raising the temperature above 273 K
induces further line broadening and, at 283 K, the
complete collapse of all the resonances of the spectrum.
At 293 K two broad signals at about δ 6.0 and 5.3 appear
which at higher temperature change into a well-resolved
AA′BB′ system due to H4,7 and H5,6 (at δ 5.98 and 5.25,
respectively) corresponding to III. Also the resonances
corresponding to H2 and H1,3, at δ 6.43 and 5.75,
respectively, appear above 283 K, and the whole spec-
trum is identical to that recorded for complex III.
Additional information on intramolecular geometric
changes of VII was obtained from the analysis of the
IR spectra of the same solution recorded in the same
temperature range. By raising the temperature above
203 K, the intensity of the bands corresponding to the
iridium carbonyls of VII gradually decreases until
complete disappearance at 298 K when they are re-
placed by four new bands at 2112, 2078, 2049, and 2034
cm-1 (see Figure 2c). In the same temperature range,
no significant changes in the Cr(CO)3 absorptions are
observed. This behavior suggests the existence, above
273 K, of a dynamic process which changes the local
In fact, the isomer stable at low temperature (VII-
ax) exhibits three stretching bands relative to the
carbonyls coordinated to iridium as required by the local
symmetry C3v of the Ir(CO)4 group. Conversely, the four
bands present in the spectrum of the isomer stable at
higher temperature are consistent with the C2v local
symmetry of the Ir(CO)4 group of the isomer VII-eq. In
the spectrum recorded at room temperature (see Figure
2c), the additional strong single band observed at 2068
cm-1 is still unassigned.
Scheme 1 depicts the formation and the behavior of
the species involved in the carbonylation reaction of the
bimetallic complexes I and II. All the reported species
except X have been spectroscopically detected and
identified.
Con clu sion s
The carbonylation reaction of two heterobimetallic
anti-[Cr(CO)3-µ,η:η-indenyl-IrL2] complexes (L2 ) COD;

760 Organometallics, Vol. 17, No. 4, 1998
Cecchetto et al.
Sch em e 1. P r op osed Mech a n ism for th e Rea ction of a n ti-[Cr (CO)3-µ,η:η-in d en yl-Ir (COD)] (I) a n d
a n ti-[Cr (CO)3-µ,η:η-in d en yl-Ir (COE)2] (II) w ith CO
200 spectrometers operating at 67.8 and 50.5 MHz, respec-
tively. In a typical experiment the CP contact time was 5 ms,
the recycle time was 20 s, and the spinning speed was in the
L ) COE) has been studied under different experimen-
tal conditions. In the presence of a large excess of CO,
the stepwise formation of stable η1-[η6-Cr(CO)3-indenyl]-
range from 3.5 to 6.0 kHz. For all samples, the magic angle
Ir(COD)(CO)2 and η1-[η6-Cr(CO)3-indenyl]-Ir(CO)4 in-
was carefully adjusted from the 79Br MAS spectrum of KBR
termediates has been observed by NMR and IR spec-
by minimizing the line width of the spinning side-band satellite
troscopy. The rearomatization of the cyclopentadienyl
transitions.
ring is made difficult by the presence of the Cr(CO)3
IR spectra were run as CH2Cl2 solutions (optical length 0.2
moiety and occurs only under forced conditions giving
rise to the scarcely stable anti-[Cr(CO)3-µ,η:η-indenyl-
Ir(CO)2] species. This behavior differs from that of the
corresponding rhodium complexes, for which low-hap-
ticity intermediates have been never detected, and
where the carbonylation ends up with the formation of
the stable “normal” substitution product, anti-[Cr(CO)3-
µ,η:η-indenyl-Rh(CO)2].
On the other hand, at low CO concentrations, a poorly
soluble iridium dimer, stable in the solid state, is
obtained probably through the intermediacy of an
unstable anti-[η6-Cr(CO)3-indenyl-η3-Ir(CO)3] species.
mm, CaF2 windows) on a Perkin Elmer 580B spectrophotom-
eter equipped with a Perkin Elmer 3600 data acquisition
system. The 70-eV EI mass spectra were recorded on a VG
MicroMass-16 spectrometer.
All reactions were carried out in oxygen-free solution.
Solvents were purified according to standard procedures,16
distilled, and purged with argon before use. Commercial-grade
COD and COE were twice distilled and deoxygenated before
use.
η5-In d en yl-Ir (COD) (V) a n d η5-in d en yl-Ir (CO)2 were
prepared as described in ref 6, and their IR and NMR data
(in CD2Cl2 at 298 K) have been reported in ref 3.
a n ti-[Cr (CO)3-µ,η:η-in d en yl-Ir (COD)] (I). Indene-Cr-
(CO)3 (1.39 × 10-3 mol) in 15 mL of THF was metalated by
treatment with an excess of KH at -40 °C under argon
atmosphere.7 The anion solution was added at -40 °C to an
equivalent amount of [Ir(µ-Cl)(COD)]2 in 25 mL of THF. After
stirring for 1 h, the solvent was pumped off and the residue
was extracted with diethyl ether and crystallized from diethyl
ether-hexane to give deep red crystals. Yield, 60%. Mp, 155-
160 °C dec. Anal. Calcd for C20H19CrIrO3: C, 43.59; H, 3.52.
Found: C, 43.55; H, 3.47. m/z 552 (M+, based on 193Ir).
Spectroscopic data: IR νmax (CH2Cl2): 1955 vs and 1872 vs
cm-1 (CtO). 1H NMR (CD2Cl2): δ 6.17 (t, 3J (H1,H2) )
3J (H2,H3) ) ∼2.8 Hz, 1H, H2), 5.24 (d, 2H, 3J (H1,H2) )
3J (H2,H3) ) ∼2.8 Hz, H1,3), 6.08 and 5.23 (two multiplets, 2H
each, AA′BB′ spin system, H4,7 and H5,6), 4.25 (m, 4H, dCH
COD protons), and 1.78 (m, 8H, CH2 COD protons). 13C NMR
(CD2Cl2) δ ) 233.19 (CtO), 94.72 (C2), 69.713 (C1,3), 84.91
Exp er im en ta l Section
Solution NMR spectra were measured on a Bruker AM400
spectrometer operating in the FT mode at 400.133 and 100.614
MHz for 1H and 13C, respectively. Chemical shifts are given
in ppm from Me4Si as internal standard. The 3J (H,H) coupling
constants, obtained from a first-order analysis, are given in
hertz. The 13C NMR peak assignment was based on selective
proton decoupling experiments and partially relaxed spectra.
The proton assignments were accomplished by 1H-{1H} NOE
measurements: the usual procedure for gated experiments
was modified,15 and the selected multiplet was saturated by a
10-s cyclic perturbation of all lines with a 42-dB attenuation
of a nominal 0.2-W decoupling power.
Solid-state 13C NMR. High-resolution 13C CPMAS NMR
spectra were measured with J eol GSE-270 and Bruker MSL-
(16) Perrin, D. D.; Armageo, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: Oxford, England, 1988.
(15) Kinns, M.; Sanders, J . K. M. J . Magn. Reson. 1984, 56, 518.

Heterobimetallic Indenyl Complexes
Organometallics, Vol. 17, No. 4, 1998 761
Ta ble 2. Su m m a r y of th e Cr ysta l Da ta a n d In ten sity Collection for In d en yl-Ir (COD) (V),
a n ti-[Cr (CO)3-in d en yl-Ir (COD)] (I), a n d syn -[Cr (CO)3-in d en yl-Ir (CO)2] (IV)
V
I
IV
formula
M
space group
C
17H19Ir
C20H19CrIrO3
551.55
P21/c
C14H7CrIrO5
499.42
P212121
415.54
C2/c
a/Å
b/Å
c/Å
15.704(2)
6.421(2)
26.754(3)
90
100.6(2)
90
2561.7(9)
8
8.401(2)
14.180(2)
16.327(2)
90
95.9(2)
90
12.388(2)
16.535(2)
6.612(1)
90
90
90
1354(7)
4
R/deg
â/deg
γ/deg
V/Å3
1934.7(9)
4
Z
cryst dimens/mm
Dc, g cm-3
µ/cm-1
0.20 × 0.40 × 0.40
0.30 × 0.30 × 0.60
0.10 × 0.16 × 0.50
2.08
96.7
297
2.02
2.45
105.0
298
74.8
298
T, K
radiation (λ/Å)
take-off angle/deg
scan speed/deg min-1
2θ range/deg
graphite-monochromated Mo-KR (λ ) 0.7107)
3
3
3
2.0 in the 2θ mode
3.0 e 2q e 45
3323
2
no. of unique reflctns [Fo ) 2σ(Fo2)]
2888
1749
0.063
827.8
0.830
R (on Fo)
F(000)
GOF
0.058
1583.6
0.940
0.061
1123.8
0.930
(C3a,7a), 84.43 (C4,7), 90.20 (C5,6), 54.12 (dCH COD carbon
atoms), 33.00 (CH2 COD carbon atoms).
an unstable yellow powder. IR νmax (CH2Cl2): 2036.2 s and
1989.8 s cm-1 (Ir-CtO), 1950.5 vs and 1870.1 vs cm-1 (Cr-
CtO). 1H NMR (CD2Cl2, T 203 K): δ 6.80 (d, 1H, 3J (H1,H2) )
a n ti-[Cr (CO)3-µ,η:η-in d en yl-Ir (COE)2] (II). A solution of
indene-Cr(CO)3 (1.19 × 10-3 mol in 12 mL of THF) was
converted into the corresponding anion by treatment with an
excess of KH at -40 °C under argon atmosphere.7 The anion
solution was added at -40 °C to an equivalent amount of [Ir-
(µ-Cl)(COE)2]2 dimer in 22 mL of THF. After stirring for 1 h,
the solvent was pumped off and the residue was extracted with
diethyl ether and crystallized from diethyl ether-hexane to
give a deep red powder. Yield, 42%. Mp, 110-115 °C dec.
Anal. Calcd for C28H35CrIrO3: C, 50.60; H, 5.31. Found: C,
50.64; H, 5.20. m/z 664 (M+, based on 193Ir). IR νmax (CH2-
Cl2): 1954 vs and 1880 vs cm-1 (CtO). 1H NMR (CD2Cl2): δ
6.26 (t, 1H, 3J (H1,H2) ) 3J (H2,H3) ) ∼2.5 Hz, H2), 5.02 (d, 2H,
3J (H1,H2) ) 3J (H2,H3) ) ∼2.5 Hz, H1,3), 6.03 and 5.28 (two
multiplets, 2H each, AA′BB′ spin system, H4,7 and H5,6), 2.09
(m, 4H, dCH COD protons), and 1.2-1.8 (m, 24H, (CH2)6 COD
protons). 13C NMR (CD2Cl2): δ 234.19 (CtO), 97.66 (C2), 76.59
(C1,3), 86.85 (C3a,7a), 85.532 (C4,7), 90.83 (C5,6), 56.97 (dCH COD
carbon atoms), 26.7, 32.8, 33.5 (CH2 COD carbon atoms).
syn -[Cr (CO)3-µ,η:η-in d en yl-Ir (CO)2] (IV). A suspension
of freshly sublimated 3.5 × 10-3 mol of Cr(CO)6 in 25 mL of
CH3CN was refluxed for 22 h under argon. After cooling to
room temperature, the solvent was pumped off and the yellow
Cr(CO)3(CH3CN)3 obtained as a powder was dissolved at 25
°C in 8 mL of a THF solution of indenyl-Ir(CO)2 (2.75 × 10-4
mol). After 5 h stirring, the precipitate formed was filtered,
washed with THF, and then extracted with diethyl ether. After
filtration on a silica column, the solvent was evaporated and
the product obtained as a yellow powder. Yellow crystals were
obtained by recrystallization from diethyl ether-hexane solu-
tion. Yield, 57%. Mp, 220-225 °C dec. Anal. Calcd for
3
∼3.2 Hz, H2), 6.10 (d, 1H, J (H1,H2) ) ∼3.2 Hz, H3), 6.09 (d,
3
3
1H, J (H6,H7) ) ∼7 Hz, H7), 5.95 (d, 1H, J (H4,H5) ) ∼7 Hz,
3
3
H4), 5.38 (t, 1H, J (H4,H5) ) J (H5,H6) ) ∼7 Hz, H5), 5.27 (t,
1H, 3J (H5,H6) ) J (H6,H7) ) ∼7 Hz, H6), 4.11 and 3.99 (two
3
multiplets, 2H each, olefinic COD signals), 3.30 (s, 1H, H1),
2.65 and 2.35 (two m, 8H overall, methylene COD protons).
No 13C spectra were obtained because of the low solubility of
this species.
η1-[η6-Cr (CO)3-in d en yl]-Ir (CO)4 (VII). The above men-
tioned solution of VI was warmed to 273 K. IR νmax (CH2Cl2):
2118.3 s, 2051.4 s, and 1976.4 s cm-1 (Ir-CtO), 1955.4 vs and
1876.4 vs cm-1 (Cr-CtO). 1H NMR (in CD2Cl2, recorded at
203 K to avoid the intramolecular dynamic processes described
in the text): δ 6.75 (d, 1H, 3J (H1,H2) ) ∼3 Hz, H2), 6.15 (d,
3
3
1H, J (H1,H2) ) ∼3 Hz, H3), 5.98 (d, 1H, J (H6,H7) ) ∼7 Hz,
H7), 5.90 (d, 1H, 3J (H4,H5) ) ∼7 Hz, H4), 5.40 (t, 1H, 3J (H4,H5)
3
3
3
) J (H5,H6) ) ∼7 Hz, H5), 5.25 (t, 1H, J (H5,H6) ) J (H6,H7)
) ∼7 Hz, H6), and 4.78 (br s, 1H, H1). The spectrum also
shows the signals of the uncoordinated COD at δ 5.57 (br s,
4H, olefinic protons) and δ 2.23 (s, 8H, methylene protons).
No 13C spectra were obtained because of the low solubility of
this species.
a n ti-[Cr (CO)3-µ,η:η-in d en yl-Ir (CO)2] (III). This species
was obtained (i) by bubbling argon for few minutes at room
temperature through the above mentioned methylene chloride
solution of VII or (ii) by warming the same solution at 313 K
(some decomposition occurred in the last case). IR νmax (CH2-
Cl2): 2051 s and 1987 s cm-1 (Ir-CtO), 1962 vs and 1882 vs
3
cm-1 (Cr-CtO). 1H NMR (CD2Cl2): δ 6.43 (t, 1H, J (H1,H2)
3
3
) ∼2.6 Hz, H2), 5.75 (d, 2H, J (H1,H2) ) J (H2,H3) ) 2.6 Hz,
C
14H7CrIrO5: C, 33.61; H, 1.41. Found: C, 33.67; H, 1.41. m/z
H1,3), 5.98 and 5.25 (two multiplets, 2H each, AA′BB′ spin
499 (M+, based on 193Ir). IR νmax (CH2Cl2): 2046 s and 1984 s
cm-1 (Ir-CtO), 1944 vs and 1895 vs cm-1 (Cr-CtO). 1H
system, H4,7 and H5,6). 13C NMR (CD2Cl2): δ 232.55 (Cr-
CtO), 169.00 (Ir-CO), 106.80 (C2), 69.71 (C1,3), 90.65 (C3a,7a),
84.03 (C4,7), 91.29 (C5,6).
NMR (CD2Cl2): δ 6.48 (t, 1H, 3J (H1,H2) ) J (H2,H3) ) ∼2.8
3
3
3
Hz, H2), 4.25 (d, 2H, J (H1,H2) ) J (H2,H3) ) ∼2.8 Hz, H1,3),
[η6-Cr (CO)3-in d en yl-η3-Ir (CO)3]2 (IX). I (or II) (4.35 ×
10-4 mol) dissolved in 8 mL of CH2Cl2 was stirred at room
temperature under a blanket of CO. After a few minutes, the
solution turned from orange to dark red and a yellow precipi-
tate appeared. The reaction mixture was cooled to -20 °C;
the solid product was recovered by filtration, washed with cold
CH2Cl2, and dried under a stream of argon. Yield, 50%. Mp,
120-125 °C dec. Anal. Calcd for C30H14Cr2Ir2O12: C, 34.16;
H, 1.34. Found: C, 31.50; H, 1.55. IR νmax (Nujol): 2090 w,
4.35 and 5.42 (two multiplets, 2H each, AA′BB′ spin system,
H
4,7 and H5,6). 13C NMR (CD2Cl2): δ 235.45 (Cr-CtO), 171.92
(Ir-CtO), 80.47 (C2), 52.67 (C1,3), 110.23 (C3a,7a), 73.70 (C4,7),
90.21 (C5,6).
η1-[η6-Cr (CO)3-in d en yl]-Ir (CO)2(COD) (VI). On bubbling
precooled CO into a 10-2 M solution of I in CH2Cl2 cooled to
203 K, the color of the solution changes from orange to dark
yellow in a few minutes. More concentrated solutions deposit

762 Organometallics, Vol. 17, No. 4, 1998
Cecchetto et al.
2070 vs, 2040 vs, 1746 sh, and 1740 s cm-1 (Ir-CtO), 1950
sh, 1940 vs, 1885 vs, 1865 vs, and 1840 vs cm-1 (Cr-CtO).
Cr ysta llogr a p h y. Crystals suitable for diffractometric
analysis were obtained by slow solvent evaporation from
concentrated solutions of V, I, and IV in methylene chloride.
Crystal data, intensity data collection, and processing details
are presented in Table 2. The data were obtained with a
Philips PW-100 four-circle automated diffractometer with a
graphite monochromator. Standard centering and autoindex-
ing procedures indicated a monoclinic lattice for V and I and
an orthorhombic one for IV. The orientation matrix and
accurate unit cell dimensions were determined from angular
settings of 25 high-angle reflections. Intensity data were
collected at 25 °C using the 2θ scan method. Two reference
reflections, monitored periodically, showed no significant
variation in intensity. Data were corrected for Lorentz and
polarization effects, and an empirical absorption correction was
applied to the intensities (Ψ scan). The positions of Cr and Ir
atoms were determined from the three-dimensional Patterson
function. All the remaining atoms, including hydrogens, were
located from successive Fourier maps using SHELX-76.17 The
crystal structure of I contains 0.5 mol of solvent (CH2Cl2) per
mole of the complex. Its two chlorine atoms are symmetrically
located around inversion centers at 1/2,0,1/2 determining a
statistical disorder of methylene groups spread out on a circle
centered at 1/2,0,1/2 and normal to the chlorine-clorine axis.
Anisotropic thermal parameters were used for all the non-
hydrogen atoms. Blocked-cascade least-squares refinements
converged to R 0.058, 0.061, and 0.063 for V, I, and IV,
respectively.
Ack n ow led gm en t. This work was supported in part
by the CNR, Roma, through its “Centro di Studio sugli
Stati Molecolari Radicalici ed Eccitati” and through its
Progetto Strategico “Tecnologie Chimiche Innovative”.
Su p p or tin g In for m a tion Ava ila ble: Tables giving the
positional parameters of the non-hydrogen atoms, the aniso-
tropic thermal parameters of the non-hydrogen atoms, the
positional parameters of the hydrogen atoms, and full lists of
1
bond lengths and angles for I, IV, and V, H NMR spectra of
III and IV, and ORTEP views of I and V (17 pages). Ordering
information is given on any current masthead page.
(17) Sheldrick, G, M. SHELX-76, Program for Crystal Structure
Determination, Cambridge University: Cambridge, England, 1976.
OM9706065