Synthesis of rhodium complexes with bulky substituted cyclopentadienyl ligands. H/D exchange reactions and silane activation

Article abstract of DOI:10.1021/om100412q

Rh(I) complexes of the type (η⁵-C₅Me ₄R)Rh(olefin)₂ have been successfully synthesized through a novel procedure that makes use of zincocenes, Zn(C₅Me ₄R)₂, as mild cyclopentadienyl transfer reagents. This method proves to be also practical for the preparation of (η⁵- C₅Me₄SiR₃)Rh(olefin)₂ derivatives with no degradation of the C-Si bond of the cyclopentadienyl ligand. Complexes (η⁵-C₅Me₄R)Rh(CH₂=CHSiMe ₃)₂ have been tested in hydrogen/deuterium scrambling reactions with deuterated benzene. As expected, complexes (η⁵- C₅Me₄R)Rh(CH₂=CHSiMe₃)₂ (R = Bu^t, 3,5-Bu^t₂C₆H₃) incorporate deuterium into the α and β sites of the vinyl silane ligand at faster rates than derivative (η⁵-C₅Me ₅)Rh(CH₂=CHSiMe₃)₂, but silyl-substituted cyclopentadienyl species (η⁵-C ₅Me₄SiMe₂R′)Rh(CH₂=CHSiMe ₃)₂ (R′ = Me, Bu^t) exchange hydrogen at β sites of the vinyl silane at slower rates, as a consequence of the steric effects exerted by the SiMe₂R groups. Reaction of diolefin compounds (η⁵-C₅Me₄R)Rh(C₂H ₄)₂ with triethyl silane led to formation of Rh(V) complexes (η⁵-C₅Me₄R)Rh(H) ₂(SiEt₃)₂ along with carbosilane HEt ₂SiCH(Me)SiEt₃.

Full text of DOI:10.1021/om100412q

Organometallics 2010, 29, 5481–5489 5481
DOI: 10.1021/om100412q
Synthesis of Rhodium Complexes with Bulky Substituted Cyclopentadienyl
Ligands. H/D Exchange Reactions and Silane Activation†
Ana Cristina Esqueda, Salvador Conejero, Celia Maya, and Ernesto Carmona*
´
´
ꢀ
Instituto de Investigaciones Quımicas, Departamento de Quımica Inorganica,
ꢀ
CSIC and Universidad de Sevilla, Avenida Americo Vespucio 49, 41092 Sevilla, Spain
Received May 3, 2010
Rh(I) complexes of the type (η5-C5Me4R)Rh(olefin)2 have been successfully synthesized through a
novel procedure that makes use of zincocenes, Zn(C5Me4R)2, as mild cyclopentadienyl transfer reagents.
This method proves to be also practical for the preparation of (η5-C5Me4SiR3)Rh(olefin)2 derivatives
with no degradation of the C-Si bond of the cyclopentadienyl ligand. Complexes (η5-C5Me4R)Rh-
(CH2dCHSiMe3)2 have been tested in hydrogen/deuterium scrambling reactions with deuterated
benzene. As expected, complexes (η5-C5Me4R)Rh(CH2dCHSiMe3)2 (R = But, 3,5-But2C6H3) incor-
porate deuterium into the R and β sites of the vinyl silane ligand at faster rates than derivative
(η5-C5Me5)Rh(CH2dCHSiMe3)2, but silyl-substituted cyclopentadienyl species (η5-C5Me4SiMe2R0)Rh-
(CH2dCHSiMe3)2 (R0 = Me, But) exchange hydrogen at β sites of the vinyl silane at slower rates, as a
consequence of the steric effects exerted by the SiMe2R groups. Reaction of diolefin compounds
(η5-C5Me4R)Rh(C2H4)2 with triethyl silane led to formation of Rh(V) complexes (η5-C5Me4R)Rh(H)2-
(SiEt3)2 along with carbosilane HEt2SiCH(Me)SiEt3.
Introduction
bulky substituents at the cyclopentadienyl ring has been
studied to a lesser extent in comparison with C5H5 (Cp)
and C5Me5 (Cp*). Bulky cyclopentadienyls have been used
as ligands in compounds of the alkaline earth metals (Ca, Sr,
Ba),2 the lanthanides,3 and the actinides,4 giving rise to novel
structures and unusual coordination modes, in contrast with
cyclopentadienyls substituted with smaller groups. Late
transition metal complexes have also benefited from the
special properties of cyclopentadienyl ligands bearing large
substituents.5
Synthesis of complexes containing Cp0 ligands (Cp0 stands
for any substituted cyclopentadienyl) usually requires the
preparation of corresponding alkaline derivatives, which are
employed as Cp0 transfer reagents despite their low or
moderate solubility in common organic solvents. On some
occasions, formation of the desired MCp0 compounds can be
attained by direct reaction of the conjugated acid of the Cp0
ligand (i.e., Cp0H) with an appropriate metal precursor in the
presence of a base.
Cyclopentadienyl ligands occupy a prominent position in
organometallic chemistry. Compounds of these robust, ver-
satile ancillary groups have been found to promote different
transformations, including among others C-H, C-C, C-O,
and C-S bond-breaking and -forming reactions.1 Use of
† Part of the Dietmar Seyferth Festschrift.
*To whom correspondence should be addressed. E-mail: guzman@
us.es.
(1) (a) Deck, P. A. Coord. Chem. Rev. 2006, 250, 1032, and references
therein. (b) Scheirs, J.; Kaminsky, W. Metallocene-Based Polyolefins;
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Hayashi, T. Ferrocenes; Verlach Chemie: Weinheim, 1995.
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Maschmeyer, T.; Masters, A. F.; Wang, J.; Field, L. D. Organometallics
2008, 27, 4772. (b) Orzechowski, L.; Piesik, D. F.-J.; Ruspic, C.; Harder, S.
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2744. (b) Ruspic, C.; Moss, J. R.; Sch€urmann, R.; Harder, S. Angew. Chem.,
Int. Ed. 2008, 47, 2121. (c) Nief, F.; Tayart de Borms, B.; Ricard, L.;
Carmichael, D. Eur. J. Inorg. Chem. 2005, 637. (d) Giesbrecht, G. R.; Clark,
D. L.; Gordon, J. C.; Scott, B. L. Appl. Organomet. Chem. 2003, 17, 473. (e)
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Rhodium complexes containing Cp0 ligands have been ex-
tensively studied, particularly those of formula (η5-Cp0)Rh-
(olefin)2,6 which participate in numerous transformations
spanning from hydrosilylation7 to C-H bond activation and
(4) Sharma, M.; Eisen, M. S. Struct. Bonding (Berlin) 2008, 127, 1.
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Vollhardt, K. P. C.; Whitener, G. D. Angew. Chem., Int.Ed. 2006, 45, 1794. (e)
Daugulis, O.; Brookhart, M. Organometallics 2004, 23, 527. (f) Eichhorn, C.;
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Duckett, S. B.; Perutz, R. N. Organometallics 1992, 11, 90. (c) Duckett,
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748. (e) Duckett, S. B.; Haddleton, D. M.; Jackson, S. A.; Perutz, R. N.;
Poliakoff, M.; Upmacis, R. K. Organometallics 1988, 7, 1526. (f) Fernandez,
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r
2010 American Chemical Society
Published on Web 07/19/2010
pubs.acs.org/Organometallics

5482 Organometallics, Vol. 29, No. 21, 2010
Esqueda et al.
functionalization of hydrocarbons.8 In most cases, the cyclo-
pentadienyl ligand acts as a spectator ligand, stabilizing metal
intermediates involved in the reaction. The synthesis of these
Scheme 1
useful (η5-Cp0)Rh(olefin)2 derivatives begins with RhCl3 H2O
3
and Cp0H, to give [(η5-Cp0)RhCl2]2 dimers.9 Subsequently
these are reduced in the presence of an olefin, to produce the
desired Rh(I) (η5-Cp0)Rh(olefin)2 species.10,5e The main draw-
back of this methodology lies on the production of HCl in the
first step, which prevents the use of functional groups with no
tolerance to this byproduct, as it is the case of silyl-substituted
Cp0 ligands (C5H4SiMe3, C5Me4SiMe3, etc.). Thus, it would be
desirable to develop new routes for the preparation of (η5-
Cp0)Rh(olefin)2 derivatives under mild conditions and with
higher functional group tolerance. It is well known that ZnR2
organometallic compounds are mild hydrocarbyl transfer
reagents.11 Hence, we have conceived that zincocenes ZnCp02
might be used as Cp0 transfer reagents for the synthesis of
Cp0Rh derivatives, with the advantage of their high solubility in
common nonpolar solvents. ZnCp02 derivatives can be easily
prepared from ZnCl2 and the corresponding KCp0 compound
with, in principle, no limitations concerning the nature of
the cyclopentadienyl substituents.12 Herein, we report the
synthesis of a variety of (η5-Cp0)Rh(olefin)2 complexes from
[RhCl(olefin)2]2 and ZnCp02 starting materials. The reactivity
of some of these derivatives in H/D exchange processes along
with the activation of the Si-H bond of triethyl silane are also
described. Some of these results have been preliminarily
communicated.13
that requires harnessing conditions. At the same time, it
allows the presence of substituent groups on the Cp ligand
that are sensitive to the aforementioned reaction conditions.
To test this idea, we reacted Zn(C5Me5)212d with [RhCl(C2-
H4)2]215 in THF at 0 °C (Scheme 1) and observed a smooth
6c
reaction that yielded complex (η5-C5Me5)Rh(C2H4)2 (1a)
in high yield (85%), after simple extraction with pentane of
the crude reaction product. This procedure can be used with
12a,b
other bulky Cp0 ligands. Thus, zincocenes Zn(C5Me4But)2
and Zn(C5Me4Ar0)2 (see Experimental Section) (Ar0 = 3,5-
But2C6H3) react with [RhCl(C2H4)2]2 under conditions iden-
tical to those employed for the synthesis of 1a to form the
expected derivatives (η5-C5Me4R)Rh(C2H4)2 (R = But, 1b;
R = 3,5-ButC6H3, 1c), once again in high isolated yields. Note-
worthy, rhodium complexes (η5-C5Me4R)Rh(C2H4)2 (R =
SiMe3; 1d; SiMe2But, 1e) can be also prepared by this method
without degradation of the C-Si bond of the C5Me4SiR3 ligand.
As already mentioned, the synthesis of these species from
RhCl3 3H2O and C5Me4SiR3H is not possible since the HCl
3
Results and Discussion
released in the course of the reaction cleaves the C-Si bond of
the Cp0 ligand.16 Complexes 1a-e have been analytically and
Synthesis of Rh(I) Complexes Containing Substituted Cp0
Ligands. Although organozinc compounds are known to
transpose their alkyl or aryl fragments to other molecules,11
transmetalation of Cp0 units from zincocenes ZnCp02 to
transition metals is uncommon and to our knowledge has
not been applied to the synthesis of Cp0Rh(I) complexes.14
The high solubility of zincocenes in common nonpolar
solvents makes them especially valuable in this regard and
avoids the classical synthesis of (η5-Cp0)Rh(olefin)2 species
1
spectroscopically characterized. The H and 13C{1H} NMR
spectra for all five complexes are similar. Broad signals are
1
recorded in the H NMR spectra between 1.50 and 1.62 and
1.95-2.13 ppm for the C2H4 molecules, while the methyl groups
of the Cp0 ligands have chemical shift values ranging from 1.35 to
1.51 ppm (R-Me) and 1.67 to 1.74 ppm (β-Me). In the 13C{1H}
spectra the ethylene carbon nuclei resonate at ca. 45 ppm and
couple to 103Rh (J≈14 Hz). The crystallographic structure for 1c
has been ascertained by an X-ray diffraction study (see Figure 1).
As can be seen in Figure 1, the aryl group of the Cp0 ligand
is symmetrically oriented between the two olefin ligands and
forms an angle with the plane defined by the Cp0 ligand close
to 69°, minimizing steric repulsions between the methyl
groups on the Cp0 ligand and the aryl moiety. Rh-C bond
distances to the C2H4 ligands of ca. 2.12 A are comparable to
those previously reported.5e,17 The CdC bond lengths of
ethylene ligands in 1c (1.394(3) and 1.403(3) A) are also in
the range reported for known cyclopentadienyl rhodium
ethylene complexes (1.36-1.43 A).5e
(8) (a) Hartwig, J. F. In Activation and Functionalization of C-H
Bonds; Goldberg, K. I.; Goldman, A. S., Eds.; ACS Symposium Series 885.
(b) Jones, W. D. Inorg. Chem. 2005, 44, 4475. (c) Hartwig, J. F.; Cook, K. S.;
Hapke, M.; Incarvito, C. D; Fan, Y.; Webster, C. E.; Hall, M. B. J. Am. Chem.
Soc. 2005, 127, 2538. (d) Chen, H.; Schlecht, S.; Semple, T. C.; Hartwig, J. F.
Science 2000, 287, 1995. (e) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.;
Peterson, T. H. Acc. Chem. Res. 1995, 28, 154. (f) Periana, R. A.; Bergman,
R. G. J. Am. Chem. Soc. 1986, 108, 7332. (g) Periana, R. A.; Bergman, R. G.
J. Am. Chem. Soc. 1986, 108, 7336. (h) Jones, W. D.; Feher, F. J. J. Am.
Chem. Soc. 1984, 106, 1650.
(9) White, C.; Yates, A.; Maitlis, P. M.; Heinekey, D. M. Inorg.
Synth. 1992, 29, 228.
The synthetic procedure described herein is general and
has been utilized for the preparation of a variety of Cp0Rh-
(diene) and Cp0Rh(CH2dCHSiMe3)2 compounds. Reaction
of in situ generated [RhCl(η4-CH2dCMeC(R0)dCH2)]
(R0 = H, Me) with Zn(C5Me4R)2 zincocenes (R = But, 3,5-
But2C6H3, SiMe3, SiMe2But) results in clean formation of the
(10) (a) Lenges, C. P.; White, P. S.; Brookhart, M. J. Am. Chem. Soc.
1999, 121, 4385. (b) Lenges, C. P.; Brookhart, M. Angew. Chem., Int. Ed.
1999, 38, 3533.
(11) Elschenbroich, C. Organometallics, 3rd. ed.; Wiley-VCH:
Weinheim, 2006.
ꢀ
(12) (a) Fernandez, R.; Grirrane, A.; Resa, I.; Rodrıguez, A.; Carmona,
´
E.; Alvarez, E.; Gutierrez-Puebla, E.; Monge, A.; Lopez del Amo, J. M.;
ꢀ
ꢀ
ꢀ
ꢀ
Limbach, H.-H.; Lledos, A.; Masseras, F.; del Rıo, D. Chem.;Eur. J.
´
ꢀ
2009, 15, 924. (b) Fernandez, R.; Resa, I.; del Río, D.; Carmona, E. Organo-
metallics 2003, 22, 381. (c) Burkey, D. J.; Hanusa, T. P. J. Organomet. Chem.
1996, 512, 165. (d) Blom, R.; Boersma, J.; Budzelaar, P. H. M; Fischer, B.;
Haalan, A.; Volden, H. V.; Weidlein, J. Acta Chem. Scand. 1986, A40, 113.
(13) Esqueda, A. C.; Conejero, S.; Maya, C.; Carmona, E. Organo-
metallics 2009, 28, 45.
(15) Cramer, R. Inorg. Synth. 1974, 15, 14.
(16) Attempts to prepare derivative [(η5-C5Me4SiMe3)RhCl2]2 from
RhCl3 3H2O and C5Me4SiMe3H failed, giving instead complex [(η5-
C5Me4H)RhCl2]2 even in the presence of a base.
3
ꢀ
(17) (a) Nicasio, M. C.; Paneque, M.; Perez, P. J.; Pizzano, A.;
(14) It has been reported that zirconocene complex ZrCp2(NBut)(thf)
transfers the cyclopentadienyl ligand to iridium: Holland, P. L.;
Andersen, R. A.; Bergman, R. G. Organometallics 1998, 17, 433.
Poveda, M. L.; Rey, L.; Sirol, S.; Taboada, S.; Trujillo, M.; Monge,
A.; Ruiz, C.; Carmona, E. Inorg. Chem. 2000, 39, 180. (b) Day, V. M.;
Stults, B. R.; Reimer, K. J.; Shaver, A. J. Am. Chem. Soc. 1974, 96, 1227.

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Organometallics, Vol. 29, No. 21, 2010 5483
Figure 1. ORTEP representation of complex 1c. Selected bond distances (A): Rh-C1, 2.2248(11); Rh-C2, 2.2629(11); Rh-C3,
2.2744(11); Rh-C4, 2.2101(12); Rh-C5, 2.2413(10); Rh-C24, 2.1321(15); Rh-C25, 2.1251(15); Rh-C26, 2.1125(15); Rh-C27,
2.1140(14).
Scheme 2
corresponding (η5-C5Me4R)Rh(η4-CH2dCMeC(R0)dCH2)
species (R = But, R0 = H, 2; R = But, R0 = Me, 3a; R = 3,
5-But2C6H3, R0 = Me, 3b; R = SiMe3, R0 = Me, 3c; R =
SiMe2But, R0 = Me, 3d) (Scheme 2).
Scheme 3
If [RhCl(CH2dCHSiMe3)2]2 is used instead of [RhCl-
(η4-CH2dCMeC(R0)=CH2)], the expected derivatives (η5-
C5Me4R)Rh(CH2dCHSiMe3)2 (R = But, 4a; R = 3,5-But2-
C6H3, 4b; R = SiMe3, 4c; R = SiMe2But, 4d) are formed in
high yields (Scheme 3).
Spectroscopic characterization of compounds 2 and 3 is
straightforward and requires no additional discussion (see
Experimental Section). The structure of derivative 3d has
been established by X-ray diffraction studies (Figure 2). An
evident, albeit expected structural feature is the disposition
of the SiMe2But substituent with respect to the diene and the
metal center, oriented in a way such that its bulky But tilts
away from the rhodium atom and covers a region of space
opposite that occupied by the η4-diene methyl substituents.
The 1H NMR spectra of the vinyl silane complexes 4a-d
indicate the existence of several isomers, of which the pre-
dominant one is responsible for ca. 95% of the observed
spectra. For this major species the two CH2dC(H)SiMe3
groups are equivalent, and therefore only three complex
multiplets are recorded for their dCH protons. However,
the four methyl groups of the C5Me4R rings are inequivalent
and give rise to singlet 1H resonances (for instance at δ 1.98,
1.72, 1.59, and 1.57 ppm for 4a). These data are not con-
sistent with symmetric structures such as A in Figure 3. In the
13C{1H} NMR spectra the two olefinic 13C nuclei give well-
defined doublet signals as the result of their coupling to the
103Rh nucleus (for complex 4a at δ 47.8 and 46.6 ppm, with
identical one-bond 13C-103Rh couplings of ca. 13.6 Hz).

5484 Organometallics, Vol. 29, No. 21, 2010
Esqueda et al.
Figure 4. ORTEP view of complex 4c. Selected bond dis-
tances (A): Rh-C1, 2.2559(13); Rh-C2, 2.2168(14); Rh-C3,
2.2835(13); Rh-C4, 2.2729(13); Rh-C5, 2.2150(12); Rh-C13,
2.1093(14); Rh-C14, 2.1575(14); Rh-C18, 2.1181(13); Rh-
C19, 2.1584(13).
Figure 2. ORTEP representation of complex 3d. Selected bond
distances (A): Rh-C1, 2.198(2); Rh-C2, 2.187(2); Rh-C3,
2.257(3); Rh-C4, 2.252(2); Rh-C5, 2.183(2); Rh-C16, 2.136(3);
Rh-C17, 2.098(2); Rh-C18, 2.106(2); Rh-C19, 2.136(3);
C16-C17, 1.438(4); C17-C18, 1.437(4); C18-C19, 1.433(4).
Scheme 4
arrangement, facing away from the Cp0 ligand (structure B in
Figure 3) to relieve steric repulsions with the methyl groups
of the cyclopentadienyl ligand. Such an arrangement has
been previously found in somewhat related species.10a The
C13-Rh-C18 angle (93.09o) is significantly smaller than
C14-Rh-C19 (114.22o). This difference may serve as an
indication of the steric repulsion between the two olefins. The
SiMe3 group that is part of the Cp0 ligand is slightly tilted up
(5.3°) with respect to the plane defined by the ring carbon atoms.
As expected, the Rh-C bond distances to the vinylsilane are
slightly shorter for the unsubstituted C atoms, in comparison
with the silyl-substituted carbon atoms (ca. 2.12 vs 2.16 A).
Reactions of Complexes 1b-e with Carbon Monoxide.
Compounds 1b-e contain olefin ligands that can be dis-
placed by carbon monoxide, although rather forcing condi-
tions are needed. Thus, pressurizing CO (2 atm) into hexane
solutions of complexes 1b-e, at 115 °C for 2 days, results in
quantitative formation of carbonyl derivatives 5a-d, which
are isolated as orange crystalline compounds (Scheme 4).
NMR experiments evidence the lack of signals for the olefin
ligands. Instead, 13C{1H} NMR spectra show resonances at
ca. 195 ppm attributable to the CO moieties (JRh-C = 82-84
Hz), which are also responsible for IR absorptions with wave
numbers in the range 2025-2030 and 1960-1965 cm-1. The
νCO stretching frequencies of metal carbonyls are often
used as an indication of the electron donor properties of
the co-ligands around the metal center. As expected, the
Figure 3. Schematic drawing of the three possible isomers ob-
served by NMR for complexes 4a-d.
Accordingly a dynamic process implying olefin dissociation
and formation of a 16-electron intermediate [(η5-C5Me4R)-
Rh(CH2dCHSiMe3)] can be ruled out. The aforesaid NMR
data and those included in the Experimental Section would
be consistent with structures B and C. However the assump-
tion must be made that despite the presence of the R
substituent in the C5Me4R ring, fast rotation of this group
creates an effective C2 axis, which makes the two vinylsilanes
equivalent by NMR spectroscopy. Although isomers B and
C can interconvert by internal rotation around the Rh-
olefin bond, the latter would probably exist as a minor
component due to the steric repulsions between the SiMe3
groups of the vinylsilane and the substituents of the Cp0
ligand. Therefore structure B would probably account for
the major isomer observed by NMR spectroscopy.
These experimental observations were further borne out
by an X-ray diffraction study of complex 4c, which is shown
in Figure 4 as an ORTEP plot. The representation shows the
expected coordination of the rhodium atom, surrounded
by a C5Me4SiMe3 ligand and two molecules of the vinylsi-
lane. The two SiMe3 groups of the alkene are in an anti

Article
Organometallics, Vol. 29, No. 21, 2010 5485
Scheme 5
mechanism involved in C-H activation and functionalization
reactions.8b,22 Almost three decades ago Seiwell reported that
the olefinic C-H bonds of the rhodium complex (η5-C5H5)Rh-
(C2H4)2 undergo isotopic hydrogen exchange with deuterium
when heated at high temperatures in deuterated benzene.23
More recently, Brookhart and co-workers observed an increase
in the rate of H/D scrambling when the C5H5 and the ethylene
ligands were replaced by C5Me5 and the vinyl silane CH2d
CHSiMe3, respectively.10a The main reason for this reactivity
difference arises from the greater lability of vinylsilane com-
pared to ethylene in the respective complexes, making easier the
formation of the coordinatively unsaturated 16-electron inter-
mediates [(η5-C5Me5)Rh(olefin)] needed for the C6D6-assisted
H/D scrambling. Accordingly, when complex (η5-C5Me5)Rh-
(CH2dCHSiMe3)2 is heated at 50 °C for 115 min in C6D6, the
intensity of the 1H NMR signal of the R olefinic protons of the
CH2dCHSiMe3 fragment decreases to 50% of its initial value,
while β protons need 250 min at the same temperature to reach
an identical intensity reduction. Thus, we have tested four
related rhodium compounds containing coordinated vinyl
silane and differing only in the nature of the R group of the
C5Me4R cyclopentadienyl ligand (R = But, 3,5-But2C6H3,
SiMe3, and SiMe2But) to study the effect of the substituents
on the rate and selectivity of deuterium incorporation into the
CH2dCHSiMe3 groups. The electronic properties of C5Me5,
Figure 5. ORTEP view of complex 5b. Selected bond lengths
(A) and angles (deg): Rh-C1, 2.2678(12); Rh-C2, 2.2724(14);
Rh-C3, 2.2929(2); Rh-C4, 2.2157(14); Rh-C5, 2.2984(13);
Rh-C24, 1.8580(16); Rh-C25, 1.8579(16); C24-O1, 1.147(2);
C25-O2, 1.141(2); Rh-C24-O1, 178.26(17); Rh-C25-O2,
176.94(18); C24-Rh-C25, 90.96(7).
values of νCO for (η5-C5Me4But)Rh(CO)2 are approximately
5 cm-1 lower in energy than those of homologues 5b-d.18
Crystals of 5b suitable for an X-ray diffraction study were
grown from concentrated solutions of the complex in pen-
tane at -23 °C (Figure 5). At variance with the observed
orientation of the bulky cyclopentadienyl substituent in
complexes 1c, 3d, and 4c, the aryl group in 5b is directed
toward one of the carbonyl ligands. Close inspection of bond
distances within this molecule reveals that one of the ortho-
hydrogen atoms of the bulky aryl group is close to the oxygen
Ar0
C5Me4But, C5Me4SiMe2R, and Cp ligands are not very
different taking into account the ν(CO) average values of
compounds 5a-d and data reported by Bercaw, Parkin, et al.
in complexes (CpR)2Zr(CO)2.18 Therefore they cannot be taken
into consideration to explain differences in the observed rates of
deuteration. However, the steric requirements of C5Me4R,
measured from values of solid angles,24 appear to be signifi-
cantly different from those of the C5Me5 ligand: 187° for R =
Me, versus 197° (But) and 194° (SiMe3). Thus bulkier substi-
tuents should increase the rate of deuteration at the vinylic sites,
given that dissociation of one of the CH2dCHSiMe3 groups to
form the required rhodium 16-electron intermediate should be
easier. In accord with expectations, at 50 °C, 50% of deuterium
incorporation at the R sites is achieved for derivatives 4a-d in
ca. 15 min, which means that the exchange is about 1 order
of magnitude faster than reported for the C5Me5 analogue
(115 min) (Scheme 5).
atom of the carbonyl moiety (d(O H) = 3.0 A).19 This
3 3 3
observation might be indicative of a very weak O
H
3 3 3
interaction. The Rh-C bond distances to the carbonyl
groups are similar to those found for related compounds.20
Hydrogen/Deuterium Exchange Reactions of Complexes
(η5-C5Me4R)Rh(CH2dCHSiMe3)2 (R = But, 4a; 3,5-But2-
C6H3, 4b; SiMe3, 4c; SiMe2But, 4d). Deuterium incorporation
into organic molecules by means of H/D exchange reactions
catalyzed by organometallic complexes is of importance for the
preparation of isotopically labeled compounds. The search for
efficient and selective catalysts is in fact an active research
area.21 Moreover, hydrogen/deuterium exchange processes at
C-H bonds provide valuable information with regard to the
Interestingly, important differences are observed for deu-
terium scrambling at β sites. Thus, compound 4a requires
only 50 min to exchange 50% of hydrogen atoms for
deuterium, once again faster than for complex (η5-C5Me5)-
Rh(CH2dCHSiMe3)2, which needs 250 min. But in sharp
contrast, deuterium incorporation at these sites in the silyl-
substituted complexes 4c,d is slower (550 min for 50% of
(18) Zachmanoglou, C. E.; Docrat, A.; Bridgewater, B. M; Parkin,
G.; Brandow, C. G.; Bercaw, J. E.; Jardine, C. N.; Lyall, M.; Green,
J. C.; Keister, J. B. J. Am. Chem. Soc. 2002, 124, 9525.
(19) (a) Gu, Y.; Kar, T.; Scheiner, S. J. Am. Chem. Soc. 1999, 121,
9411. (b) Desiraju, G. R. Dalton 2000, 3745.
(20) Lichtenberger, D. L.; Blevins, C. H.; Ortega, R. B. Organome-
tallics 1984, 3, 1614.
(21) (a) Campos, J.; Esqueda, A. C.; Carmona, E. Chem.;Eur. J.
2010, 16, 419. (b) Hanson, S. K.; Heinekey, D. M.; Goldberg, K. I.
Organometallics 2008, 27, 1454. (c) Atzrdot, J.; Derdan, V.; Fey, T.;
ꢀ
Zimmermann, J. Angew. Chem., Int. Ed. 2007, 46, 7744. (d) Corberan,
(22) (a) Parkin, G. Acc. Chem. Res. 2007, 42, 315. (b) Lersch, M.; Tilset,
M. Chem. Rev. 2005, 105, 2471. (c) Klei, S. R.; Tan, K. L.; Golden, J. T.;
Yung, C. M.; Thalji, R. T.; Ahrendt, K. A.; Ellman, J. A.; Tilley, T. D.;
Bergman, R. G. In Activation and Functionalization of C-H Bonds;
Goldberg, K. I.; Goldman, A. S., Eds.; ACS Symposium Series 885.
(23) Seiwell, L. P. J. Am. Chem. Soc. 1974, 96, 7134.
R.; Sanaꢀu, M.; Peris, E. J. Am. Chem. Soc. 2006, 128, 3974. (e) Tenn, W. J.,
III; Young, K. J. H.; Bhalla, G.; Oxgaard, J.; Goddard, W. A., III; Periana,
R. A. J. Am. Chem. Soc. 2005, 127, 14172. (f) Feng, Y.; Lail, M.; Barakat,
K. A.; Cundari, T. R.; Gunnoe, T. B.; Petersen, J. L. J. Am. Chem. Soc. 2005,
127, 14174. (g) Yung, C. M.; Skaddan, M. B.; Bergman, R. G. J. Am. Chem.
Soc. 2004, 126, 13033. (h) Santos, L. L.; Mereiter, K.; Paneque, M.; Slugovc,
C.; Carmona, E. New J. Chem. 2003, 27, 107.
(24) (a) White, D.; Coville, N. J. Adv. Organomet. Chem. 1994, 36, 95.
(b) White, D.; Carlton, L.; Coville, N. J. J. Organomet. Chem. 1992, 440, 15.

5486 Organometallics, Vol. 29, No. 21, 2010
Esqueda et al.
Figure 6
deuteration), while for 4b (R = 3,5-But2C6H3), although still
faster than for the C5Me5 analogue, it is slightly slower than
for complex 4a (see Experimental Section). An inspection of
the intermediates involved in the H/D scrambling process
helps to understand this unexpected behavior. Figure 6
depicts the two intermediates responsible for H/D exchange
at R (A) and β (B) positions in complexes 4c,d. The slower
deuterium incorporation in the β position in comparison
with 4a,b might be ascribed to a more congested intermediate
B than that involved in the analogous exchange when
C5Me4But and C5Me4Ar0 ligands are employed. This could
be due to differences in the Cring-CMe3 and Cring-SiMe2R
bond lengths, which become apparent when values of cova-
lent radii25 for Csp2 (0.73 A), Csp3 (0.77 A), and Si (1.11 A) are
analyzed. Thus the Cring-SiMe2R bond is approximately
0.34 A longer than Cring-CMe3, a fact that probably forces
the two silyl substituents in B to span over the same region of
space. In other words, even if C5Me4But, C5Me4SiMe3, and
C5Me4SiMe2But probably feature rather similar solid angles,
their steric requirements at longer distances from the metal
center may be different as a result of longer Cring-SiMe2R
bonds in comparison with Cring-CMe3.
Scheme 6
derivatives (η5-C5R5)Rh(H)2(SiEt3)2.7f,e Given the related
nature of complexes 1a-d, their reactivity toward triethyl-
silane has been studied.
When a solution of complexes 1b-e is heated in neat Et3SiH,
at 70 °C, for 3 days, Rh(V) complexes 6a-d are formed
together with carbosilane 7 in a ca. 1:1 ratio (Scheme 6). The
rhodium complexes can be purified by column chromato-
1
graphy and isolated as white solids in good yields. H NMR
spectra for compounds 6a-d show distinctive hydride signals
as doublets (JHRh ≈ 35 Hz) at ca. -14 ppm, in addition to
signals for the Et3Si moieties at ca. 0.9 (Si-CH2CH3) and 1.1
ppm (Si-CH2CH3). The methyl groups of the cyclopenta-
dienyl ligands give rise in all cases to two sets of signals (see
Experimental Section) indicative of the high symmetry of
these molecules. IR spectra for 6a-d show medium bands at
2020-2035 cm-1 for the Rh-H stretching.
Although the metal oxidation state in rhodium complexes
of this type has been a matter of debate,30 our data support a
Rh(V) formulation. Theoretical calculations suggest these
compounds should be described as (η5-C5R5)Rh(H)(SiEt3)-
(η2-HSiEt3) Rh(III) species,30 but a neutron diffraction
study on complex (η5-C5R5)Rh(H)2(SiEt3)2 reported by
Koetzle, Maitlis, and co-workers7f demonstrates Si-H bond
distances on the order of 2.27 A (av), which are 0.27 A longer
than expected for a Si-H bonding interaction.31 NMR
29Si-1H coupling constants have been used to discern between
these two possibilities. In general, JHSi values in the range
40-80 Hz are indicative of η2-SiH coordination.7e,32 However,
complexes 6a-d have JHSi values of ca. 8 Hz, similar to those
reported for complex (η5-C5Me5)Rh(H)2(SiEt3)2.
Previous reports indicate an irregular variation of the
ligand solid angle with distance, whose quantification has
been achieved by different methods.24a,26
Activation of Si-H Bonds by Complexes 1a-d. Cleavage of
Si-H bonds by transition metal complexes is of fundamental
importance in catalytic reactions such as hydrosilylation
(hydrosilylation) of double and triple bonds or hydrocarbons,
carbonyls, imines, etc., or dehydrogenation of silanes.27 These
methods have been successfully employed for the prepara-
tion of alkylsilanes, vinylsilanes, alcohols, and amines, among
others. With regard to hydrosilylation of alkenes, several
Rh(I) and Rh(III) complexes have been reported to be
active catalysts,27 possibly through Chalk-Harrod7b,27,28
and Chalk-Harrod-modified7b,27,29 mechanisms. Silyl-hy-
dride rhodium intermediates, formed by oxidative addition
of Si-H bonds, are postulated as relevant in these mecha-
nisms, and particularly (η5-C5R5)Rh(C2H4)2 complexes (R =
H, Me) react with triethyl silane, Et3SiH, thermally or photo-
chemically giving rise to the formation of silyl-hydride Rh(V)
The structure of complex 6d has been ascertained by X-ray
diffraction studies (Figure 7).
The rhodium atom is η5 bonded to the cyclopentadienyl
ligand, with two hydrides and two SiEt3 groups completing
the coordination sphere. As found for complex 3d, the tert-
butyl group of the SiMe2But fragment is facing away from the
metal center. The two triethylsilyl ligands are mutually trans, in
accord with the symmetry deduced from NMR data. The Rh-Si
and Rh-H bond distances (the latter located in the Fourier
map) of ca. 2.38 and 1.55 A are almost identical to those reported
(25) Cordero, B.; Gomez, V.; Platero-Plats, A. E.; Reves, M.; Eche-
verria, J.; Cremades, E.; Barragan, F.; Alvarez, S. Dalton Trans. 2008,
2832.
(26) Smith, J. M.; Pelly, S. C.; Coville, N. J. J. Organomet. Chem.
1996, 525, 159.
(27) (a) Hartwig, J. F. Organotransition Metal Chemistry: From
Bonding to Catalysis; University Science Books: Sausalito, CA, 2009.
(b) Roy, A. K. Adv. Organomet. Chem. 2008, 55, 1. (c) Ball, Z. T. In
Comprehensive Organometallic Chemitry III; Crabtree, R. H.; Mingos, M.,
Eds.; Elsevier: Oxford, U.K., 2007; Vol. 10, p 789. (d) Ball, Z. T. In
Comprehensive Organometallic Chemitry III; Crabtree, R. H.; Mingos, M.,
Eds.; Elsevier: Oxford, U.K., 2007; Vol. 10, p 815. (e) Marciniec, M. Coord.
Chem. Rev. 2005, 249, 2374.
by Maitlis.7f The closest Si H separation of 2.166 A is above
3 3 3
the 2 A value reported for bonding interactions.
(30) Vyboishchikov, S. F.; Nikonov, G. I. Organometallics 2007, 26,
4160.
(28) Chalk, A. J.; Harrod, J. F. J. Am. Chem. Soc. 1965, 87, 16.
(29) Schroeder, M. A.; Wrighton, M. S. J. Organomet. Chem. 1977,
128, 345.
(31) Schubert, U. Adv. Organomet. Chem. 1990, 30, 151.
(32) Taw, L. F.; Bergman, R. G.; Brookhart, M. Organometallics
2004, 23, 886.

Article
Organometallics, Vol. 29, No. 21, 2010 5487
at the cyclopentadienyl ligand. Alkyl (But) and aryl (3,5-But2-
C6H3) groups accelerate the process (in comparison to (η5-
C5Me5)Rh(CH2dCHSiMe3)2), but SiR3 substituents slow it
appreciably. These differences seem to be due to steric interac-
tions between the remote silyl substituent of the rhodium-alkyl
intermediate and the SiR3 group of the Cp0 ring. Finally, as
expected, complexes (η5-C5Me4R)Rh(C2H4)2 react with triethyl-
silane to yield Rh(V) bis(silyl) bis(hydride) derivatives, (η5-
C5Me4R)Rh(H)2(SiEt3)2.
Experimental Section
General Considerations. All syntheses were performed under
an argon atmosphere using standard Schlenk techniques, em-
ploying dry solvents and glassware. Spectra were referenced to
external SiMe4 (δ 0 ppm) using the residual protio solvent peaks
as internal standards (1H NMR experiments) or the character-
istic resonances of the solvent nuclei (13C NMR experiments).
Spectral assignments were made by routine one- and two-
dimensional NMR experiments where appropriate. X-ray crystal
structures were determined in a Bruker-AXSX8Kappa diffract-
ometer. Zincocene complexes Zn(η5-C5Me4R)2 (R = But, SiMe3,
SiMe2But),12a,b [RhCl(C2H4)2]2,15 and [RhCl(C2H3SiMe3)2]2
34
were prepared as previously described.
Synthesis of Zincocene Zn(C5Me4Ar0)2 (Ar0 = 3,5-But2C6H3).
C5Me4(3,5-But2C6H3)H (prepared from 1-bromo-3,5-di-tert-
butylbenzene, nBuLi, and 2,3,4,5-tetramethylcyclopenta-2-
enone)35 (3.1 g, 10.1 mmol) is slowly added to a suspension of
KH (378 mg, 9.8 mmol) in 50 mL of THF, and the resulting
mixture is stirred at room temperature for 16 h. The solvent is
then removed under vacuum, and the resulting brown solid
is washed with pentane (2 ꢀ 40 mL) and dried in vacuo to yield
6.6 g of K[C5Me4(3,5-But2C6H3)], which is used without any
further purification. Then ZnCl2 (434 mg, 3.19 mmol) and
K[C5Me4(3,5-But2C6H3)] (2.2 g, 3.19 mmol) are stirred for 6 h
at 20 °C in 60 mL of THF. The solvent is then removed under
vacuum and the residue extracted with pentane (2 ꢀ 50 mL).
Colorless crystals of Zn(C5Me4Ar0)2 can be obtained from
Figure 7. ORTEP view of complex 6d. Selected bond lengths (A)
and angles (deg): Rh-C1, 2.3075(15); Rh-C2, 2.3042(15); Rh-
C3, 2.2756(16); Rh-C4, 2.2837(15); Rh-C5, 2.3038(15); Rh-
Si2, 2.3853(5); Rh-Si3, 2.3952(5); Rh-H1, 1.51(3); Rh-H2,
1.60(3); Si2-Rh-Si3, 107.486(17); H1-Rh-H2, 95.1(2).
1
concentrated pentane solutions at -23 °C (1.95 g, 75%). H
NMR (C6D6) δ: 7.40 (t, 1 H, 4JHH = 1.8 Hz, p-CHAr), 7.20 (d,
2 H, 4JHH = 1.8 Hz, o-CHAr), 2.14 (s, 12 H, 2 MeR), 2.02 (s, 12 H,
The formation of carbosilane compound 7 is well prece-
dented. Berry et al. reported that this compound is the major
reaction product in the reaction of triethylsilane and tert-
butylethylene, as hydrogen acceptor, catalyzed by rhodium
complex (η5-C5Me5)Rh(H)2(SiEt3)2.33 This compound is
formed through a formally dehydrogenative coupling of
two molecules of triethylsilane. This intriguing reaction
product can be considered a rare case of a selective C-H
bond functionalization reaction of a CH2 fragment of
triethylsilane.
t
2 Meβ), 1.31 (s, 36 H, Bu). 13C{1H} NMR (C6D6) δ: 150.5
(m-CqAr), 136.8 (CqAr), 125.4 (o-CHAr), 119.7 (p-CHAr), 119.6
(CqC5Me4), 116.0 (CqMeR), 110.0 (4 C, CqMeβ), 35.0 (CMe3),
31.6 (tBu), 12.5 (Meβ), 11.3 (MeR). Anal. Calcd for C46H66Zn: C,
80.7; H, 9.7. Found: C, 80.7; H, 9.8.
General Procedure for the Synthesis of Complexes 1a-e. A
solution of Zn(C5Me4R)2 (0.77 mmol) in 1 mL of THF is added,
at 0 °C, to a solution of [RhCl(C2H4)2]2 (355 mg, 0.85 mmol) in
2 mL of THF. The reaction mixture is stirred for 12 h, after
which the solvent is removed under vacuum. The products are
extracted with pentane to yield analytically pure 1a-e as yellow
solids after removal of the solvent.
Conclusions
A new procedure for the mild synthesis of (η5-C5Me4R)-
Rh(olefin)2 compounds has been established with the use of
zincocenes ZnCp02 as cyclopentadienyl transfer reagents.
This preparative method proves useful even when cyclopen-
tadienyl ligands substituted with SiR3 functional groups are
employed. Compounds (η5-C5Me4R)Rh(CH2dCHSiMe3)2
(4a-d) undergo H/D exchange at the olefinic sites when
heated in deuterated benzene. As expected, the rates for H/D
scrambling at R sites are faster than previously found for
complex (η5-C5Me5)Rh(CH2dCHSiMe3)2, but rate exchanges
at β positions depend on the nature of the bulky R substituent
(η5-C5Me4But)Rh(C2H4)2 (1b). Yield: 80%. 1H NMR (C6D6)
δ: 1.98 (m, 4 H, dCH2), 1.67 (s, 6 H, Meβ), 1.52 (m, 4 H, dCH2),
1.46 (s, 6 H, MeR), 1.38 (s, 9 H, But). 13C{1H} NMR (C6D6):
110.2 (d, Cp-Cq-But, J = 4.8 Hz), 99.3 (d, CqMe, J = 4.4 Hz),
93.8 (d, CqMeβ, J = 4.3 Hz), 44.3 (d, dCH2, J = 13.7 Hz), 33.7
(CBut), 33.3 (But), 11.0 (MeR), 9.9 (Meβ). Anal. Calcd for
C17H29Rh: C, 60.71; H, 8.69. Found: C, 60.5; H, 8.3.
(η5-C5Me4Ar0)Rh(C2H4)2 (1c). Yield: 80%. 1H NMR (C6D6)
δ: 7.59 (d, 2 H, 4JHH = 1.7 Hz, o-CHAr), 7.48 (t, 1 H, 4JHH = 1.7
Hz, p-CHAr), 2.13, 1.62 (m, 8 H, 2 C2H4), 1.74 (s, 6 H, 2 Meβ),
1.51 (s, 6 H, 2 MeR), 0.35 (s, 18 H, But). 13C{1H} NMR (C6D6)
(34) Blazejewska-Chadyniac, P.; Kubicki, M.; Maciejewski, H.;
Marciniec, B. Inorg. Chim. Acta 2003, 350, 603.
(35) Bjorgvinsson, M.; Halldorsson, S.; Arnason, I.; Magull, J.;
(33) (a) Ezbiansky, K.; Djurovich, P. I.; LaForest, M.; Sinning, D. J.;
Zayes, R.; Berry, D. H. Organometallics 1998, 17, 1455. (b) Djurovich,
P. I.; Dolich, A. R.; Berry, D. H. J. Chem. Soc., Chem Commun. 1992, 1897.
€
Fenske, D. J. Organomet. Chem. 1997, 544, 207.

5488 Organometallics, Vol. 29, No. 21, 2010
Esqueda et al.
1
δ: 149.3 (m-CqAr), 133.9 (CqAr), 126.8 (o-CHAr), 120.1 (p-CHAr),
108.2 (d, 1JCRh = 3 Hz, CqC5Me4), 98.1, 95.8 (d, 1JCRh = 4 Hz,
1JCRh = 7 Hz), 81.8 (d, JCRh = 6 Hz, CqSiMe3), 41.5 (d,
1JCRh = 17 Hz, dCCH2), 18.3 (dCMe), 13.9 (MeR), 9.2 (Meβ),
3.7 (SiMe3). HRMS (EI): calcd for C18H31RhSi (Mþ) requires
378.1250, found 378.1251.
1
CqMeR, CqMeβ), 45.0 (d, JCRh = 13 Hz, C2H4), 34.7 (CqBut),
31.4 (But), 9.5 (Meβ), 8.8 (MeR). Anal. Calcd for C27H41Rh: C,
69.2; H, 8.8. Found: C, 68.8; H, 8.8.
(η5-C5Me4SiMe2But)Rh(η4-CH2dCMeCMedCH2) (3d). Yield:
85%, yellow solid. 1H NMR (C6D6) δ: 1.95 (s, 6 H, 2 MeR), 1.70
(s, 6 H, 2 dCMe), 1.64, 0.63 (br, 2 H each, dCH2), 1.51 (s, 6 H, 2
Meβ), 1.10 (s, 9 H, But), 0.57 (s, 6 H, SiMe2). 13C{1H} NMR
(η5-C5Me4SiMe3)Rh(C2H4)2 (1d). Yield: 83%. 1H NMR
(C6D6) δ: 1.98, 1.50 (m, 8 H, 2 C2H4), 1.67 (s, 6 H, 2 Meβ),
1.35 (s, 6 H, 2 MeR), 0.37 (s, 9 H, SiMe3). 13C{1H} NMR (C6D6)
δ: 103.8, 100.5 (d, 1JCRh = 3 Hz, CqMeR, CqMeβ), 86.8 (d, 1JCRh
= 4 Hz, CqSiMe3), 44.7 (d, 1JCRh = 14 Hz, C2H4), 10.3 (Meβ),
9.7 (MeR), 9.5 (SiMe3). Anal. Calcd for C16H29RhSi: C, 54.5; H,
8.3. Found: C, 54.7; H 8.1.
1
1
(C6D6) δ: 101.9, 99.6 (d, JCRh = 6, JCRh = 4 Hz, CqMeR,
CqMeβ), 88.0 (d, 1JCRh = 7 Hz, dCMe), 79.9 (d, 1JCRh = 6 Hz,
CqSi), 40.6 (d, 1JCRh = 17 Hz, CdCH2), 42.2 (d, 1JCRh = 17 Hz,
dCCH2), 27.5 (But), 19.7 (CqBut), 18.30 (dCMe), 14.2 (MeR),
9.4 (Meβ), -0.2 (SiMe2). Anal. Calcd for C21H37RhSi: C, 60.0; H,
8.9. Found: C, 59.8; H, 8.7. HRMS (EI): calcd for C21H37RhSi
(Mþ) requires 420.1720, found 420.1710.
1
(η5-C5Me4SiMe2Ar0)Rh(C2H4)2 (1e). Yield: 75%. H NMR
(C6D6) δ: 1.95, 1.54 (m, 8 H, 2 C2H4), 1.69 (s, 6 H, 2 Meβ), 1.38 (s,
6 H, 2 MeR), 0.97 (s, 9 H, But), 0.43 (s, 6 H, SiMe2). 13C{1H}
1
1
NMR (C6D6) δ: 104.4, 100.9 (d, JCRh = 4, JCRh = 5 Hz,
General Procedure for the Synthesis of Complexes 4a-d.
Complex [RhCl(CH2CHSiMe3)2]2 (150 mg, 0.22 mmol) and
Zn(C5Me4R)2 (0.25 mmol) are dissolved in 2 mL of THF. The
resulting mixture is stirred for 12 h at 60 °C, and then the solvent
is removed under vacuum. Complex 4 was extracted with
pentane (10 mL), and the solvent is evaporated to yield yellow
oils or solids. The oils were dissolved in the minimum amount of
acetone and stored at -78 °C to obtain yellow solids.
CqMeR, CqMeβ), 84.7 (d, 1JCRh = 3 Hz, CqSi), 45.2 (d, 1JCRh
=
14 Hz, 2 C2H4), 26.8 (But), 19.3 (CqBut), 10.6 (Meβ), 9.8 (MeR),
-1.2 (SiMe2). Anal. Calcd for C19H35RhSi: C, 57.6; H, 8.9.
Found: C, 57.6; H, 8.6.
General Procedure for the Synthesis of Complexes 2 and 3a-d.
Complex [RhCl(C2H4)2]2 (300 mg, 0.77 mmol) is dissolved in
10 mL of THF, and 0.75 mL of 2,3-dimethylbutadiene is added
at 0 °C. The reaction mixture is stirred for 15 min at 0 °C and for
1.5 h at room temperature. Thereafter, a solution of the corres-
ponding zincocene Zn(C5Me4R)2 (0.77 mmol) in 2 mL of THF is
added, and the resulting solution is stirred for 12 h. After
removal of the solvent under vacuum the products are extracted
with pentane to yield analytically pure compounds 2 and 3a-d
as yellow oils or solids, after removal of the solvent.
(η5-C5Me4But)Rh(CH2dCHSiMe3)2 (4a). Yield: 63%. 1H
NMR (THF-d8) δ: 2.34 (m, 1 H, dCHβ), 1.98, 1.59 (s, 3 H each,
Meβ), 1.72, 1.57 (s, 3 H each, MeR), 1.36 (s, 9 H, But), 1.19 (m,
2 H, dCHR and dCHβ), 0.08 (s, 18 H, SiMe3). 13C{1H} NMR
(THF-d8) δ: 112.1 (d, J = 5.0 Hz, Cp-Cq-But), 101.5, 98.9, 97.4,
96.0 (d, J = 4.3 Hz, CqMeR, CqMeβ), 47.8 (d, J = 13.6 Hz,
dCH2), 46.6 (d, J = 13.7 Hz, dCH), 35.1 (CBut), 33.4 (But),
13.1, 11.7 (MeR), 11.8, 9.1 (Meβ), 2.6 (SiMe3). HRMS (EI): calcd
for C23H45RhSi2 (Mþ) requires 480.2127, found 480.2115.
(η5-C5Me4Ar0)Rh(CH2dCHSiMe3)2 (4b). Yield: 62%. 1H
(η5-C5Me4But)Rh(η4-CH2dCMeCHdCH2) (2). Yield: 95%,
1
3
yellow oil. H NMR (C6D6) δ: 4.42 (t, 1 H, JHH= 7.1 Hz,
0
CHdCH2), 2.03, 1.94 (s, 3 H each, MeR, MeR ) 1.89, 0.57 (d, 1 H
4
each, 3JHH = 6.2 Hz, CHdCH2), 1.77 (s, 9 H, But), 1.75, 1.70 (s,
NMR (C6D6) δ: 7.32 (t, 1 H, JHH = 1.9 Hz, p-CHAr), 7.14
(d, 2 H, 4JHH = 1.9 Hz, o-CHAr), 2.42 (br d, 2 H, 2JHH = 10.3
0
3 H each, Meβ, Meβ ) 1.73, 0.62 (br, 2 H each, MeCdCH2), 1.44
(s, 6 H, dCMe). 13C{1H} NMR (C6D6) δ: 108.7 (d, 1JCRh = 7
0
Hz, dCHβ,), 2.05, 1.50 (s, 3 H each, Meβ, Meβ ), 1.94, 1.72 (s, 3 H
t
each, MeR, MeR ), 1.34 (s, 18 H, Bu ), 1.30 (m, 4 H, dCHR and
Hz, Cp-Cq-But), 96.0, 95.1 94.1, 93.8 (d, 1JCRh = 6 Hz, CqMeR,
0
dCHβ), 0.08 (s, 18 H, SiMe3). 13C{1H} NMR (C6D6) δ: 150.9
(m-CqAr), 133.9 (CqAr), 128.9 (o-CHAr), 121.1 (p-CHAr), 107.7
1
CqMeR , CqMeβ, CqMeβ ), 89.5 (d, JCRh = 7 Hz, MeCdCH2),
0
0
1
78.7 (d, JCRh = 7 Hz, CHdCH2), 38.5 (d, JCRh = 17 Hz,
1
(d, 1JCRh = 4 Hz, CqC5Me4), 99.7, 99.0, 98.3, 97.3 (d, 1JCRh
=
4 Hz, CqMeR, CqMeR , CqMeβ, CqMeβ ), 49.3 (d, JCRh = 14 Hz,
MeCdCH2), 37.7 (d, 1JCRh = 17 Hz, CHdCH2), 38.7 (CqBut),
1
t
0
0
0
0
33.6 (Bu ), 21.3, 10.7 (Meβ, Meβ ), 14.7, 14.2 (MeR, MeR ), 10.9
(dCMe). HRMS (EI): calcd for C18H31Rh (Mþ) requires
348.1324, found 348.1320.
dCH2), 47.1 (d, JCRh = 14 Hz, dCH), 35.1 (CqBut), 32.1
1
t
0
0
(Bu ), 12.1, 8.0 (MeR, MeR ), 11.4, 11.0 (Meβ, Meβ ), 2.5 (SiMe3).
Anal. Calcd for C33H57RhSi2: C, 64.7; H, 9.3. Found: C, 64.9;
H, 8.9.
(η5-C5Me4But)Rh(η4-CH2dCMeCMedCH2) (3a). Yield: 93%,
yellow oil. 1H NMR (C6D6) δ: 2.00 (s, 6 H, 2 MeR), 1.77 (s, 2 H,
dCHH), 1.75 (s, 6 H, 2 dCMe), 1.57 (s, 6 H, 2 Meβ), 1.51 (s, 9H,
But), 0.58 (br, 2 H, dCHH). 13C{1H} NMR (C6D6) δ: 107.7
(d, 1JCRh = 8 Hz, Cp-Cq-But), 95.2, 93.6 (d, 1JCRh = 5, 1JCRh = 6
Hz, CqMeR, CqMeβ), 87.6 (d, 1JCRh =7Hz, dCMe), 40.6 (d, 1JCRh
= 17 Hz, CdCH2), 33.8 (CqBut), 33.7 (But), 18.3 (dCMe), 14.6
(MeR), 9.9 (Meβ). Anal. Calcd for C19H31Rh: C, 63.0; H, 8.6.
Found: C, 63.0; H, 8.6. HRMS (EI): calcd for C19H31Rh (Mþ)
requires 362.1481, found 362.1476.
(η5-C5Me4SiMe3)Rh(CH2dCHSiMe3)2 (4c). Yield: 65%. 1H
NMR (THF-d8) δ: 2.39 (dt, 2 H, J = 8.8 Hz, 2.5 Hz, dCHβ),
1.99, 1.62 (s, 3 H each, Meβ), 1.61, 1.46 (s, 3 H each, MeR), 1.20
(m, 4 H, dCHR and dCHβ), 0.28 (s, 9 H, Cp-SiMe3), 0.08 (s, 18
H, SiMe3). 13C{1H} NMR (THF-d8) δ: 105.7, 104.3 103.1, 102.5
0
0
(d, J ≈ 4.0 Hz, CqMeR, CqMeR , CqMeβ, CqMeβ ), 89.4 (d, J =
4.9 Hz, Cp-Cq-SiMe3,), 48.1 (d, J = 13.7 Hz, dCH2), 46.5 (d,
J = 13.7 Hz, dCH), 12.5, 10.7 (MeR), 11.6, 8.9 (Meβ), 2.6
(Cp-SiMe3), 2.5 (SiMe3). HRMS (EI): calcd for C22H45RhSi3
(Mþ) requires 496.1884, found 496.1894.
(η5-C5Me4Ar0)Rh(η4-CH2dCMeCMedCH2) (3b). Yield: 89%,
yellow solid. 1H NMR (C6D6) δ: 7.62 (d, 2 H, 4JHH = 2.0 Hz,
o-CHAr), 7.48 (t, 1 H, JHH = 2.0 Hz, p-CHAr), 2.00 (s, 6 H,
(η5-C5Me4SiMe2But)Rh(CH2dCHSiMe3)2 (4d). Yield: 57%.
4
2 MeR), 1.90 (s, 2 H, dCHH), 1.79 (s, 6 H, 2 dCMe), 1.74 (s, 6 H,
2 Meβ), 1.37 (s, 18 H, But), 0.70 (br, 2 H, dCHH). 13C{1H}
NMR (C6D6) δ: 150.2 (m-CqAr), 133.8 (CqAr), 127.2 (o-CHAr),
120.2 (p-CHAr), 104.6 (d, 1JCRh = 7 Hz, CqC5Me4), 94.9, 94.7 (d,
1H NMR (THF-d8) δ: 2.29 (br d, 2 H, 2JHH = 10.3 Hz, dCHβ),
0
1.99, 1.73 (s, 3 H each, Meβ, Meβ ), 1.50, 1.42 (s, 3 H each, MeR,
t
MeR ), 1.23 (m, 4 H, dCHR and dCHβ), 0.87 (s, 9 H, Bu ), 0.45,
0
0.32 (s, 3 H each, SiMe2), 0.09 (s, 18 H, SiMe3). 13C{1H} NMR
1JCRh = 4, JCRh = 5 Hz, CqMeR, CqMeβ), 88.3 (d, JCRh
=
(THF-d8) δ: 107.2, 104.1, 103.6, 102.8 (d, 1JCRh = 4 Hz, CqMeR,
1
1
1
CqMeR , CqMeβ, CqMeβ ), 87.4 (d, JCRh = 4 Hz, CqSiMe2), 48.7
7 Hz, CMe), 41.8 (d, 1JCRh = 17 Hz, CdCH2), 35.1 (CBut), 31.9
(But), 18.3 (dCMe), 11.9 (MeR), 10.0 (Meβ). Anal. Calcd for
C29H43Rh: C, 70.9; H, 8.2. Found: C, 70.5; H, 7.9. HRMS (EI):
calcd for C29H43Rh (Mþ) requires 494.2420, found 494.2405.
(η5-C5Me4SiMe3)Rh(η4-CH2dCMeCMedCH2) (3c). Yield:
90%, yellow oil. 1H NMR (C6D6) δ: 1.92 (s, 6 H, 2 MeR), 1.68,
0.62 (br, 2 H each, dCH2), 1.71 (s, 6 H, 2 dCMe), 1.51 (s,
6 H, 2 Meβ), 0.48 (s, 9 H, SiMe3). 13C{1H} NMR (C6D6) δ: 101.0,
99.2 (d, 1JCRh = 6, 1JCRh = 5 Hz, CqMeR, CqMeβ), 87.9 (d, dCMe,
0
0
(d, 1JCRh = 14 Hz, dCH2), 47.1 (d, 1JCRh = 14 Hz, dCH), 27.5
t
(Bu ), 20.65 (CqBu ), 12.1, 10.8 (MeR, MeR ), 11.7, 9.4 (Meβ,
t
0
0
Meβ ), 2.6 (SiMe3), -0.3, -0.9 (SiMe2). Anal. Calcd for C25H51-
RhSi3: C, 55.7; H, 9.5. Found: C, 55.6; H, 9.2.
General Procedure for the Synthesis of Complexes 5a-d.
Complexes (η5-C5Me4R)Rh(C2H4)2 (1b-e) are dissolved in
5 mL of hexane in a pressurizing vessel that is then charged
with 2 atm of CO. The mixture is heated at 115 °C for 48 h, after

Article
Organometallics, Vol. 29, No. 21, 2010 5489
which the volatiles are removed under vacuum to give orange
solids. Yields are quantitative in all cases.
(Meβ), 11.0 (CH2CH3), 9.3 (CH2CH3), 2.6 (SiMe3). 29Si NMR
(C6D6) δ: 35.7 (SiEt3), -6.8 (SiMe3). IR (Nujol): ν(Rh-H) 2035
cm-1. Anal. Calcd for C24H53RhSi3: C, 54.5; H, 10.1. Found:
C, 54.6; H, 9.8.
(η5-C5Me4But)Rh(CO)2 (5a). 1H NMR (C6D6) δ: 1.93 (s, 6 H,
2 MeR), 1.72 (s, 6 H, 2 Meβ), 1.51 (s, 9 H, But). 13C{1H} NMR
(C6D6) δ: 195.1 (d, 1JCRh = 82 Hz, CO), 115.4 (d, 1JCRh = 4 Hz,
CqBut), 101.9, 99.7 (d, 1JCRh = 4, 1JCRh = 3 Hz, CqMeR, CqMeβ),
33.0 (But), 32.8 (Cq But), 13.9 (MeR), 10.8 (Meβ). IR (Nujol):
ν(C-O) 2025, 1960 cm-1. Anal. Calcd for C15H21O2Rh: C, 53.6; H,
6.0. Found: C, 53.4; H, 6.1.
(η5-C5Me4SiMe2But)Rh(H)2(SiEt3)2 (6d). Yield: 60%. 1H
NMR (C6D6) δ: 1.96 (s, 6 H, 2 MeR), 1.71 (s, 6 H, 2 Meβ),
1.10 (t, 18 H, CH2CH3), 0.90 (q, 12 H, CH2CH3), 0.87 (s, 9 H,
1
But), 0.37 (s, 6 H, SiMe2), -13.92 (d, 2 H, JHRh = 35.8 Hz,
RhH). 13C{1H} NMR (C6D6) δ: 109.4, 105.9 (d, 1JCRh = 3 Hz,
CqMeR, CqMeβ), 91.6 (d, 1JCRh = 3 Hz, CqSi), 28.0 (But), 20.5
(CqBut), 14.4 (MeR), 11.2 (Meβ), 10.8 (CH2CH3), 9.2 (CH2CH3),
-0.9 (SiMe2). IR (Nujol): ν(Rh-H) 2030 cm-1. Anal. Calcd for
C27H59RhSi3: C, 56.8; H, 10.4. Found: C, 56.6; H, 10.0.
Hydrogen-Deuterium Exchange Reactions. In a glovebox,
a J-young NMR tube was charged with 0.02 mmol of complex
(η5-C5Me4R)Rh(CH2dCHSiMe3)2 (4a-d) and dissolved in
1 mL of freshly dried C6D6. The NMR tube was immediately
inserted in a NMR apparatus previously calibrated at 50 °C, and
1H NMR spectra were recorded at 1-10 min intervals. Decrease
of the intensity of the signals of vinylsilane was monitored with
respect to one of the methyl groups of the cyclopentadienyl
ligand. All experiments were run in quintuplicate with similar
results. The data given correspond to average values. Time
required for deuterium incorporation (50%) at R sites (in
minutes): 15 (4a), 20 (4b), 10 (4c), 15 (4d). Time required for
deuterium incorporation (50%) at β sites (in minutes): 50 (4a),
150 (4b), 550 (4c), 550 (4d).
(η5-C5Me4Ar0)Rh(CO)2 (5b). 1H NMR (C6D6) δ: 7.50 (t,
4
4JHH = 1.7 Hz, 1 H, p-CHAr), 7.49 (d, JHH = 1.7 Hz, 2 H,
o-CHAr), 1.90 (s, 6 H, 2 Meβ), 1.82 (s, 6 H, 2 MeR), 1.34 (s, 18 H,
1
But). 13C{1H} NMR (C6D6) δ: 194.6 (d, JCRh = 83 Hz, CO),
150.4 (m-CqAr), 132.6 (CqAr), 126.7 (o-CHAr), 120.8 (p-HAr),
112.6 (d, 1JCRh = 3 Hz, CqC5Me4), 101.5, 100.6 (d, 1JCRh = 3,
1JCRh = 5 Hz, CqMeR, CqMeβ), 34.6 (CqMe3), 31.3 (But), 11.2
(MeR), 10.6 (Meβ). IR (Nujol): ν(C-O) 2025, 1965 cm-1. Anal.
Calcd for C25H33O2Rh: C, 64.1; H, 7.1. Found: C, 64.0; H, 7.0.
(η5-C5Me4SiMe3)Rh(CO)2 (5c). 1H NMR (C6D6) δ: 1.83 (s, 6
H, 2 MeR), 1.72 (s, 6 H, 2 Meβ), 0.31 (s, 9 H, SiMe3). 13C{1H}
1
NMR (C6D6) δ: 194.8 (d, JCRh = 84 Hz, CO), 107.6 (d,
=
1
1
1JCRh = 3, JCRh = 4 Hz, CqMeR, CqMeβ), 94.1 (d, JCRh
4 Hz, CqSiMe3), 13.6 (MeR), 10.8 (Meβ), 2.9 (SiMe3). IR (Nujol):
ν(C-O) 2030, 1965 cm-1. Anal. Calcd for C14H21RhO2Si: C,
47.7; H, 6.0. Found: C, 47.5; H, 6.1.
(η5-C5Me4SiMe2But)Rh(CO)2 (5d). 1H NMR (C6D6) δ: 1.89
(s, 6 H, 2 MeR), 1.74 (s, 6 H, 2 Meβ), 0.95 (s, 9 H, But), 0.38 (s,
6 H, SiMe2). 13C{1H} NMR (C6D6) δ: 194.7 (d, 1JCRh = 84 Hz,
X-ray Crystallography. Suitable crystals of the compounds 1c,
3d, 4c, 5b, and 6d were mounted in a glass fiber covered with
perfluoropolyether oil (FOMBLIN, Aldrich). Intensity data
were performed on a Bruker-AXSX8Kappa diffractometer
equipped with an Apex-II CCD area detector, using a graphite
monochromator Mo KR1 (λ = 0.71073 A) and a Bruker Cryo-
Flex low-temperature device. Data collection was carried out
with APEX-W2D-NT (Bruker, 2004), cell refinement with
SAINT-Plus (Bruker, 2004), and data reduction with SAINT-
Plus (Bruker, 2004).
In all cases the structures was solved by direct methods and
difference Fourier synthesis and refined by full-matrix least-
squares procedures, with anisotropic thermal parameters in the
last cycles of refinement for all non-hydrogen atoms.
All the hydrogen atoms were introduced into the geometri-
cally calculated positions and refined riding on the correspond-
ing parent atoms. Exceptions are H1 and H2 in structure 6d and
H24A, H24B, H25A, H25B, H26A, H26B, H27A, and H27B in
structure 1c. These hydrogen atoms were determined by differ-
ence Fourier synthesis and refined (together with their isotropic
thermal parameters) by least-squares procedures.
1
CO), 108.3, 106.0 (d, JCRh = 4 Hz, CqMeR, CqMeβ), 92.3 (d,
1JCRh = 4 Hz, CqSi), 27.2 (But), 19.2 (CqBut), 13.9 (MeR), 10.9
(Meβ), -0.4 (SiMe2). IR (Nujol): ν(C-O) 2030, 1965 cm-1
.
Anal. Calcd for C17H27O2RhSi: C, 51.77; H, 6.90. Found: C,
51.92; H, 7.09.
General Procedure for the Synthesis of Complexes 6a-d.
Complexes (η5-C5Me4R)Rh(CH2dCHSiMe3)2 are dissolved in
2 mL of triethylsilane in a thick-wall vessel. The reaction mixture
is heated at 90 °C for 72 h, and the volatiles are then removed
under vacuum. The crude reaction mixture is dissolved in
pentane and filtered through silica. The solvent is concentrated
to ca. 1 mL and the solution stored at -23 °C, to yield colorless
crystals of the title compounds.
(η5-C5Me4But)Rh(H)2(SiEt3)2 (6a). Yield: 73%. 1H NMR
(C6D6) δ: 1.95 (s, 6 H, 2 MeR), 1.68 (s, 6 H, 2 Meβ), 1.27 (s, 9
H, But), 1.10 (t, 18 H, CH2CH3), 0.89 (q, 12 H, CH2CH3),
1
2
-13.64 (d, 2 H, JHRh = 35.9, JHSi = 8 Hz, RhH). 13C{1H}
NMR (C6D6) δ: 114.7 (d, JCRh = 2 Hz, Cp-Cq-But), 102.9,
1
101.2 (d, JCRh = 3 Hz, CqMeR, CqMeβ), 32.6 (CqBut), 32.5
1
(But), 13.9 (MeR), 10.9 (Meβ), 10.2 (CH2CH3), 8.7 (CH2CH3).
29Si NMR (C6D6) δ: 34.6 (SiEt3). IR (Nujol): ν(Rh-H) 2020
cm-1. Anal. Calcd for C25H53RhSi2: C, 58.6; H, 10.4. Found: C,
58.5; H, 10.8.
Weighted R factors (wR) and all goodness-of-fit (S) are based
on F2; conventional R factors (R) are based on F. The
SHELXTL software package36 (based on SHELXS and
SHELXL) was used for structure solution and refinement.
(η5-C5Me4Ar0)Rh(H)2(SiEt3)2 (6b). Yield: 64%. 1H NMR
4
(C6D6) δ: 7.44 (t, JHH = 1.5 Hz, 1 H, p-CHAr), 7.34 (d,
4JHH = 1.5 Hz, 2 H, o-CHAr), 1.99 (s, 6 H, 2 MeR), 1.80 (s,
6 H, 2 Meβ), 1.35 (s, 18 H, But), 1.09 (t, 18 H, CH2CH3), 0.88 (q,
Acknowledgment. Financial support from the Spanish
ꢀ
Ministerio de Ciencia e Innovacion (MICINN) (project
CTQ2007-62814), Consolider-Ingenio 2010 (CSD2007-
1
12 H, CH2CH3), -13.70 (d, 2 H, JHRh = 35.9 Hz, RhH).
13C{1H} NMR (C6D6) δ: 150.4 (m-CqAr), 133.4 (CqAr), 127.0
(o-CHAr), 120.9 (p-CHAr), 110.2 (d, 1JCRh = 3 Hz, CqC5Me4),
00006) (FEDER support), and the Junta de Andalucıa
´
1
(projects FQM-3151 and FQM-672) is gratefully ac-
knowledged. C.E. thanks CONACYT for a research
grant (ref 229340).
102.8, 101.3 (d JCRh = 3 Hz, CqMeR, CqMeβ), 35.1 (CqBut),
31.8 (But), 11.8 (MeR), 11.1 (Meβ), 10.8 (CH2CH3), 9.5 (CH2-
CH3). IR (Nujol): ν(Rh-H) 2025 cm-1. Anal. Calcd for C35H65-
RhSi2: C, 65.2; H, 10.1. Found: C, 65.7; H, 9.9.
(η5-C5Me4SiMe3)Rh(H)2(SiEt3)2 (6c). Yield: 58%. 1H NMR
(C6D6) δ: 1.90 (s, 6 H, 2 MeR), 1.69 (s, 6 H, 2 Meβ), 1.09 (t, 18 H,
CH2CH3), 0.92 (q, 12 H, CH2CH3), 0.37 (s, 9 H, SiMe3), -14.03
Supporting Information Available: CIF files giving crystal-
lographic data for structural analysis of complexes 1c, 3d, 4c, 5b,
and 6d. This material is available free of charge via the Internet
at http://pubs.acs.org.
(d, 2 H, JHRh = 35.9, JHSi = 8 Hz, RhH). 13C{1H} NMR
1
2
1
1
(C6D6) δ: 109.5, 105.3 (d, JCRh = 4, JCRh = 3 Hz, CqMeR,
CqMeβ), 91.7 (d, JCRh = 2 Hz, CqSiMe3), 13.6 (MeR), 11.1
1
(36) SHELXTL; Bruker AXS Inc.: Madison, WI, 2000.