Rhodium(I) complexes with hemilabile N-heterocyclic carbenes: Efficient alkyne hydrosilylation catalysts

Article abstract of DOI:10.1021/om700728a

A series of alkylammonium-imidazolium chloride salts [RImH(CH ₂)_nNMe₂]Cl ·HCl (R = Me, t-Bu, Mes; n = 2, 3) have been prepared by alkylation of 1-substituted imidazole compounds with the corresponding chloro-alkyl-dimethylamine hydrochloride. These salts are precursors for the synthesis of a library of rhodium(I) complexes containing amino-alkyl functionalized N-heterocyclic carbene (NHC) ligands with hemilabile character by varying the substituent on the heterocyclic ring and the length of the linker with the dimethylamino moiety. The monodeprotonation of alkylammonium-imidazolium salts with NaH in the presence of [{Rh(μ-Cl)(cod)} ₂] gave the amino-imidazolium salts [RImH(CH₂)_n NMe₂][RhCl₂(cod)]. Further deprotonation with NaH under non anhydrous conditions gave the neutral complexes [RhCl(cod)(RIm(CH ₂)_nNMe₂)] in good yields. The abstraction of the chloro ligand by silver salts rendered the cationic complexes [Rh(cod)(k²C,N-RIm(CH₂)₃NMe₂)] [BF₄] (R = Me, Mes) by coordination of the NMe₂ fragment of the sidearm of the functionalized NHC ligands. The catalytic activity of the rhodium complexes in the hydrosilylation of terminal alkynes using HSiMe ₂Ph has been investigated with Ph-C≡CH, t-Bu-C≡CH, n-Bu-C≡CH, and Et₃Si-C≡CH as substrates. Higher activities were achieved using neutral complexes having small substituents at the heterocyclic ring (R = Me). Excellent selectivities in the β-(Z)-vinylsilane isomer were found in the hydrosilylation of 1-hexyne and predominandy the β-(E) and α-bis(silyl)alkene isomers were obtained in the hydrosilylation of triethylsilylacetylene.

Full text of DOI:10.1021/om700728a

224
Organometallics 2008, 27, 224–234
Rhodium(I) Complexes with Hemilabile N-Heterocyclic Carbenes:
Efficient Alkyne Hydrosilylation Catalysts
M. Victoria Jiménez,* Jesús J. Pérez-Torrente, M. Isabel Bartolomé, Verena Gierz,
Fernando J. Lahoz, and Luis A. Oro*
Departamento de Química Inorgánica, Instituto UniVersitario de Catálisis Homogénea, Instituto de
Ciencia de Materiales de Aragón, UniVersidad de Zaragoza-C.S.I.C., 50009-Zaragoza, Spain
ReceiVed July 20, 2007
A series of alkylammonium-imidazolium chloride salts [RImH(CH2)nNMe2]Cl · HCl (R ) Me, t-Bu,
Mes; n ) 2, 3) have been prepared by alkylation of 1-substituted imidazole compounds with the
corresponding chloro-alkyl-dimethylamine hydrochloride. These salts are precursors for the synthesis of
a library of rhodium(I) complexes containing amino-alkyl functionalized N-heterocyclic carbene (NHC)
ligands with hemilabile character by varying the substituent on the heterocyclic ring and the length of
the linker with the dimethylamino moiety. The monodeprotonation of alkylammonium-imidazolium salts
with NaH in the presence of [{Rh(µ-Cl)(cod)}2] gave the amino-imidazolium salts [RImH(CH2)n
NMe2][RhCl2(cod)]. Further deprotonation with NaH under non anhydrous conditions gave the neutral
complexes [RhCl(cod)(RIm(CH2)nNMe2)] in good yields. The abstraction of the chloro ligand by silver
salts rendered the cationic complexes [Rh(cod)(κ2C,N-RIm(CH2)3NMe2)][BF4] (R ) Me, Mes) by
coordination of the NMe2 fragment of the sidearm of the functionalized NHC ligands. The catalytic
activity of the rhodium complexes in the hydrosilylation of terminal alkynes using HSiMe2Ph has been
investigated with Ph-Ct CH, t-Bu-Ct CH, n-Bu-Ct CH, and Et3Si-Ct CH as substrates. Higher activities
were achieved using neutral complexes having small substituents at the heterocyclic ring (R ) Me).
Excellent selectivities in the ꢀ-(Z)-vinylsilane isomer were found in the hydrosilylation of 1-hexyne and
predominantly the ꢀ-(E) and R-bis(silyl)alkene isomers were obtained in the hydrosilylation of
triethylsilylacetylene.
sites and to protect the active catalytic site, a number of hybrid
hemilabile ligands, which can potentially provide a dynamic
“on and off” chelating effect for the metal complex during
catalysis, have been designed.4 Hybrid P,O-5 and P,N-based
ligands6 have been the most intensively studied since P usually
binds strongly to the metal center, whereas the other donor atom
(O or N) is generally only weakly bonded.
On the other hand, there is an increasing interest in the
chemistry of functionalized NHC carbenes7 in which a donating
group is attached to a strongly bonded imidazolyl ring. In this
context, a variety of heteroatom-functionalized carbene ligands
containing phosphine,8 pyridine,1a,9 amido,10 ester, keto or
ether11 and oxazoline12 donor functions have been synthesized
and, in some cases, used as catalysts for a number of catalytic
Introduction
N-Heterocyclic carbenes (NHCs) have attracted considerable
attention as a new class of ligands over the past few years.1
Their bonding characteristics are comparable to the well studied
tertiary phosphines, which are ubiquitous in their role as ligands
in transition metal catalyzed processes. Nevertheless, it has
become apparent that there are substantial differences between
the two families of ligands: NHCs are more electron-donating
and sterically more demanding than the most basic/bulky
phosphane ligands.2 NHC ligands have found widespread
application in homogeneous catalysis for processes as diverse
as C-C coupling, olefin metathesis, hydrosilylation, or carbon
monoxide/ethylene copolymerization.3
Ligand lability is a feature of many efficient catalysts;
however, this lability can also provide a route for the catalyst
decomposition. In order to have easily accessible coordination
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* To whom correspondence should be addressed. E-mail: oro@unizar.es;
vjimenez@unizar.es.
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2000, 600, 12–22. (c) Herrmann, W. A.; Köcher, C. Angew. Chem., Int.
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10.1021/om700728a CCC: $40.75
2008 American Chemical Society
Publication on Web 12/29/2007

Rhodium(I) Complexes as Efficient Alkyne Hydrosilylation Catalysts
Organometallics, Vol. 27, No. 2, 2008 225
transformations.13 The combination of a strongly bonded carbene
moiety with the appropiate donor function should allow for
potential hemilability. In fact, the hemilabile character of several
alkenyl-,14 thioether-,15 alkoxide,16 and pyrazolylmethyl17 func-
tionalized-imidazolylidene ligands and of the terdentate 1,3-
bis(2-pyridyl)imidazol-2-ylidene ligand18 have been demonstrated.
Scheme 1
Hydrosilylation of carbon-carbon multiple bonds has been
one of the most important laboratory and industrial methods of
forming silicon-carbon bonds and to functionalize organic
molecules.19 The hydrosilylation of alkynes represents the most
straightforward and atom-economical access to vinylsilanes,
which are useful intermediates for cross-linked silicones as well
as reagents in organic synthesis and nucleophilic partners in
Pd-catalyzed cross-coupling reactions.20 The hydrosilylation of
alkynes can be promoted by a variety of catalysts including
radical initiators, chloroplatinic acid, and Wilkinson-type rhod-
ium complexes.19,21 More recently some nickel,22 ruthenium,23
platinum,24 rhodium, and iridium25 complexes containing NHC
carbenes have been used as hydrosilylation catalysts. Most of
the recent efforts in the study of catalytic hydrosilylation concern
the design of efficient catalysts that enable the stereodivergent
preparation of both (Z)- and (E)-alkenylsilanes independently.
weak donor functions, as the -NMe2 group, and a flexible
backbone should allow for the potential of a dynamic interaction
with the metal center and/or stabilization of polar intermediates
in catalytic applications exerting some directing effect. In this
work we describe the synthesis and characterization of a series
of new rhodium(I) complexes with alkylamino-functionalized
NHC ligands of the type 1-dimethylaminoalkyl-3-R-imidazol-
2-ylidene that are efficient catalysts for the hydrosilylation of
1-alkynes.
Results and Discussion
Our interest is focused in the synthesis of transition metal
complexes containing heteroditopic ligands of hemilabile char-
acter that incorporate strong electron donors, such as tertiary
phosphines and carbenes. The design of ligands that combine
Synthesis of Precursors for Hemilabile NHC Ligands. The
imidazolium salts used as precursors for the new hemilabile
N-heterocyclic carbene ligands were prepared by direct alkyla-
tion of several 1-substituted imidazole compounds. The reaction
of chloro-alkyl-dimethylamine hydrochloride derivatives,
Cl(CH2)nNMe2 · HCl (n ) 2, 3), with stoichiometric amounts
of several 1-substituted imidazole compounds, RImH (R ) Me,
t-Bu, Mes), in refluxing acetonitrile for several days afforded
the corresponding alkylammonium imidazolium chloride salts
[RImH(CH2)nNMe2]Cl · HCl (1–5) (Scheme 1). The salts were
isolated as white hygroscopic solids in good yields and
characterized by elemental analysis, mass spectrometry (ES-
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1
1
MS), and H and 13C{1H} NMR spectroscopy. The H NMR
spectra of 1–5 in CDCl3 or CD3OD showed a highly downfield
shifted resonance in the range δ 12.0-9.0 ppm that is
characteristic of the NCHN imidazolium proton. The methyl
groups of the dimethylalkyl ammonium fragment were observed
as a single resonance between δ 3.5–2.8 ppm and around 43
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1997, 547, 357–366.
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1
ppm in the H and 13C{1H} NMR spectra, respectively. The
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2004, 33, 619–636. (b) Albrecht, M.; van Koten, G. Angew. Chem., Int.
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NH was observed as a broad resonance only in compounds 1
(δ 4.02 ppm) and 2 (δ 3.55 ppm), although the methylenic
groups of the side arms, triplet (N-CH2-) or multiplet (-CH2-),
have been clearly identified in the 1H NMR spectra of all
alkylammonium imidazolium salts. The remaining resonances
of the imidazolium fragment were observed at chemical shifts
typical for imidazolium salts.26
Synthesis of Rhodium(I) Salts Containing Dimeth-
ylalkylamino Imidazolium as Cations. The ammonium-
imidazolium salts may be sequentially deprotonated to give
different rhodium(I) compounds. The reaction of 1–5 with 1
molar equiv of sodium hydride in tetrahydrofurane followed
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226 Organometallics, Vol. 27, No. 2, 2008
Jiménez et al.
Scheme 2
Figure 1. Molecular structure of compound [(MeImH(CH2)2
NMe2)][RhCl2(cod)] (6). (Most hydrogen atoms have been omitted
for clarity).
are very similar to those reported in other ion-pair compounds
including this specific anionic metal complex.28
by 0.5 equiv of [{Rh(µ-Cl)(cod)}2] afforded cyclooctadiene-
dichlororhodate(I) salts [RImH(CH2)nNMe2][RhCl2(cod)] that
contain the amine-imidazolium cation (R ) Me, n ) 2, 6, n )
3, 7; R ) t-Bu, n ) 2, 8, n ) 3, 9; R ) Mes, n ) 3, 10)
(Scheme 2). The salts containing the 3-methyl imidazolium, 6
and 7, have been isolated in the solid state and fully character-
ized by analytical and spectroscopic means. In addition, the
molecular structure of 6 has been determined by X-ray diffrac-
tion methods. The salts 8–10 have been characterized in solution
as they are actually generated in situ and used as intermediates
in the synthesis of rhodium(I) containing N-heterocyclic carbene
ligands (see below).
Synthesis of Neutral and Cationic Rhodium(I) Com-
plexes Containing Hemilabile NHC Ligands. We envisaged
that the double deprotonation of the ammonium-imidazolium
salts [RImH(CH2)nNMe2]Cl · HCl with a strong base should
produce the free carbene ligands that could be trapped by
[{Rh(µ-Cl)(cod)}2] to give rhodium(I) complexes containing the
hemilabile NHC ligands. However, the reaction of the am-
monium-imidazolium salts with 2.2 molar equiv of NaH in THF,
followed of addition of 0.5 molar equiv of [{Rh(µ-Cl)(cod)}2],
unexpectedly afforded the amino-imidazolium salts [RImH
(CH2)nNMe2][RhCl2(cod)] (6–10). Interestingly, we have dis-
covered that the reaction of these salts with NaH under
nonstrictly anhydrous conditions resulted in the formation of
the expected complexes. Thus, when water was deliberately
added to yellow suspensions of compounds 6–10 and NaH in
THF, darker suspensions were immediately formed, and the
neutral mononuclear complexes [RhCl(cod)(RIm(CH2)nNMe2)]
(11–15) were isolated as yellow microcrystalline solids in
60–70% yield after the convenient workup. It is evident that
the NaOH formed in the reaction of NaH and water was
responsible for the acid–base reaction resulting in the effective
deprotonation of the imidazolium fragment. In agreement with
this proposal, complexes 11–15 can be prepared directly from
the ammonium-imidazolium salts in THF using a KOH aqueous
solution (2 molar equiv) as base; most probably, side-reactions
account for the lower yields obtained following this synthetic
path. The more efficient one-pot synthesis of complexes 11–15
from the ammonium-imidazolium salts [RImH(CH2)nNMe2]-
Cl · HCl requires the in situ generation of the intermediate
amino-imidazolium salts [RImH(CH2)nNMe2][RhCl2(cod)] and
their deprotonation using NaH/H2O.
The 1H NMR spectra of compounds 6–10 showed a resonance
around δ 10.5 ppm, diagnostic of the presence of a NCHN
imidazolium proton, and the absence of any resonance attribut-
able to NH in agreement with the deprotonation of the
ammonium fragment. The amino-imidazolium cations were
observed in the ES-MS+ of compounds 6 and 7 at m/z 154.1
[MeImH(CH2)2NMe2]+ and 168.3 [MeImH(CH2)3NMe2]+, re-
spectively. Furthermore, the anion [RhCl2(cod)]- was identified
1
in the H NMR spectra of the compounds as three resonances
in a 1:1:1 ratio (4 protons each) corresponding to the dCH,
and >CH2 protons (exo and endo protons) of the 1,5-cyclooc-
tadiene ligand. According to the C2V symmetry of the anion, the
13C{1H} NMR displayed two resonances at δ 77.70 (d, JC-Rh
11.1 Hz) and 31.09 ppm.
)
The molecular structure of compound [(MeImH(CH2)2
NMe2)][RhCl2(cod)] (6) is shown in Figure 1, and selected bond
lengths and angles are listed in Table 1. The crystal structure
shows the presence of both ions: the amino-imidazolium cation
and the dichlorocyclooctadienerhodate(I) anion. The unique
connection between both entities involves a clear hydrogen bond
between the H(1) proton of the imidazolium cation and one of
the chloro ligands of the metal complex (Cl(1) · · · C(1) 3.468(3),
Cl(1) · · · H(1) 2.56(3) Å and C(1)-H(1) · · · Cl(1) 168(2)°). The
internal bond distances and angles in the imidazolium ring lie
within the range observed for other imidazolium salts.27 In
particular, the C-N distances at the C(1) atom are 1.374(3)
and 1.378(3) Å, and the N-C-N angle is 108.3(2)o. On the
other hand, the structural parameters of the [RhCl2(cod)]- anion
The mononuclear neutral complexes containing the 1-(dim-
ethylaminoalkyl)-3-R-imidazol-2-ylidene ligands [RhCl(cod)-
(RIm(CH2)nNMe2)] (11–15, Scheme 2) have been fully char-
acterized by elemental analysis, mass spectrometry, and
multinuclear NMR spectroscopy. In particular, the full assign-
1
ment of the resonances is based on the H-1H COSY NMR
spectra of the complexes. Although the MALDI-TOF mass
spectra showed peaks at m/z corresponding to the cations
[Rh(cod)(RIm(CH2)nNMe2)]+, the complexes are neutral as was
(27) (a) CSD Structural Data Base for metrical parameters. See, for
example: Arduengo, A. J., III; Goerlich, J. R.; Marshall, W. J. J. Am. Chem.
Soc. 1995, 117, 11027–11028. (b) Arduengo, A. J., III; Gamper, S. F.;
Tamm, M.; Calabrese, J. C.; Davidson, F.; Craig, H. A. J. Am. Chem. Soc.
1995, 117, 572–573.
(28) (a) See, for example: Stylianides, N.; Danopoulos, A. A.; Tsoureas,
N. J. Organomet. Chem. 2005, 690, 5948–5958. (b) Martínez, A. P.; García,
M. P.; Lahoz, F. J.; Oro, L. A. Inorg. Chim. Acta 2003, 347, 86–98.

Rhodium(I) Complexes as Efficient Alkyne Hydrosilylation Catalysts
Organometallics, Vol. 27, No. 2, 2008 227
Table 1. Selected Bond Distances (Å) and Angles (deg) for Compounds 6 and 11a
11
2.3868(4)
6
6
11
Rh-Cl(1)
2.3766(5)
Rh-M(1)a
Rh-M(2)a
Rh-C(12)
Rh-C(13)
N(2)-C(1)
N(2)-C(3)
N(2)-C(5)
C(2)-C(3)
C(5)-C(6)
1.981(3)
1.994(2)
2.109(2)
2.115(5)
1.326(3)
1.378(3)
1.470(3)
1.344(4)
1.516(4)
1.9843(19)
2.0927(17)
2.1985(17)
2.2078(17)
1.355(2)
1.387(2)
1.466(2)
1.341(3)
1.517(2)
Rh-Cl(2)/C(1)
Rh-C(9)
2.3878(5)
2.102(2)
2.095(2)
1.328(3)
1.375(3)
1.467(3)
1.448(4)
1.457(4)
1.451(4)
89.752(19)
177.87(7)
90.16(7)
91.80(8)
178.69(8)
88.32(10)
108.94(19)
125.1(2)
126.0(2)
108.73(19)
125.0(2)
2.0292(17)
2.1101(17)
2.1016(18)
1.356(2)
1.389(2)
1.460(2)
1.458(2)
1.457(3)
1.462(2)
88.15(5)
179.44(5)
92.01(5)
92.25(7)
177.61(7)
87.60(7)
111.18(16)
124.21(15)
124.61(16)
110.91(15)
124.66(15)
Rh-C(16)
N(1)-C(1)
N(1)-C(2)
N(1)-C(4)
N(3)-C(6)
N(3)-C(7)
N(3)-C(8)
Cl(1)-Rh-Cl(2)/C(1)
Cl(1)-Rh-M(1)a
Cl(1)-Rh-M(2)a
Cl(2)/C(1)-Rh-M(1)a
Cl(2)/C(1)-Rh-M(2)a
M(1)-Rh-M(2)a
C(1)-N(1)-C(2)
C(1)-N(1)-C(4)
C(2)-N(1)-C(4)
C(1)-N(2)-C(3)
C(1)-N(2)-C(5)
C(3)-N(2)- C(5)
C(6)-N(3)-C(7)
C(6)-N(3)-C(8)
C(7)-N(3)-C(8)
Rh-C(1)-N(1)
Rh-C(1)-N(2)
N(1)-C(1)-N(2)
N(1)-C(2)-C(3)
N(2)-C(3)-C(2)
N(2)-C(5)-C(6)
N(3)-C(6)-C(5)
126.1(2)
109.4(3)
112.5(3)
110.3(3)
123.71(15)
112.54(15)
109.63(15)
110.34(17)
124.88(13)
130.72(13)
104.37(15)
106.44(16)
107.09(16)
112.24(14)
113.05(15)
108.2(2)
106.9(2)
107.2(2)
111.4(2)
113.0(2)
a M(1) and M(2) represent the midpoints of the olefinic double bonds C(9)-C(16) and C(12)-C(13), respectively.
evidenced by the conductivity measurements in acetone. The
mononuclear complexes are moderately stable in the solid state
or in solution under an inert atmosphere. However, solutions
of compounds 11 and 13 in chlorinated solvents (CH2Cl2 or
CHCl3) slowly decompose at room temperature to unidentified
products as observed in related compounds.29,30
3-methyl-imidazol-2-ylidene group, and the chloro ligand. The
sum of the four cis intraligand angles at the metal environment
is equal to 360 ° within experimental uncertainty, but the
individual angles are distorted from ideal values as a result of
the steric influence of the bulky 1,5-cyclooctadiene ligand. Thus,
the largest bond angles, 92.25(7)° and 92.01(5)°, are M(1)-Rh-
C(1) and M(2)-Rh-Cl (M(1) and M(2) represent the midpoints
of the coordinated olefinic bonds). In contrast, the smallest angle,
88.15(5)°, is observed between the chloro (Cl(1)) and carbene
(C(1)) ligands. A remarkable feature of molecular structure is
the location of the NMe2 fragment of the functionalized 1-N
substituent (2-dimethylaminoethyl) oriented clearly away from
the metal center.
The rhodium-carbene bond distance, 2.0292(17) Å, is within
the range reported for Rh(I)-carbene complexes (mean 2.026
Å, CSD search on complexes of the type [RhCl(cod)(imidazol-
2-ylidene)]). This carbene ligand exerts a high trans influence,
producing a significant elongation of the Rh-C bonds situated
in relative trans position (mean Rh-C 2.2031(12)Å) if com-
pared to those trans to the chloride ligand (mean Rh-C
2.1058(13)Å). The imidazol-2-ylidene ring is placed almost
perpendicular to the coordination plane of the rhodium center
(dihedral angle 84.62(5)°). A comparison of the molecular
structures of the functionalized imidazolium cation 6 and the
imidazol-2-ylidene complex 11 shows the typical increase in
the C-N bond distances (1.328(3) and 1.326(3) Å in 6, 1.356(2)
and 1.355(2) Å in 11) and the decrease in NCN angle (108.2(2)
in 6 and 104.37(15)° in 11) upon deprotonation and coordination
to the rhodium center, reflecting the enhanced s character of
the in-plane carbene lone pair σ-bonded to metal in the metal
NHC complexes.32
The 1H NMR spectra of compounds 11–15 showed no
resonances attributable to the NCHN proton, which confirms
the deprotonation of the imidazolium fragment. In addition, the
coordination of the carbene to the rhodium center becomes
evident as a doublet resonance in the range δ 182–180 ppm
(JC-Rh ≈ 50 Hz) is observed in the 13C{1H} NMR spectra. These
chemical shifts and coupling constant values lie in the usual
range for related Rh(I)-NHC complexes.25 The olefinic carbons
of the 1,5-cyclooctadiene ligand feature four resonances (JC-Rh
≈ 8 and 15 Hz) in the 13C{1H} NMR spectra of the complexes.
This observation is indicative of the lack of an effective
symmetry plane in the molecules probably as a result of the
hindered rotation31 about the carbene-rhodium bond due to the
presence of the sidearm in the hemilabile NHC ligands. As a
consequence, the methylenic protons of the 2-dimethylamino-
ethyl and 3-dimethylaminopropyl sidearms are diastereotopic.
Although no direct evidence of the coordination of the
dimethylamino fragment to the rhodium center was obtained
1
from the observed NMR chemical shifts, the H NMR spectra
showed sharp resonances at room temperature, excluding a
potential penta-coordinated structure. This fact has been further
corroborated by the single-crystal X-ray diffraction analysis
carried out on complex [RhCl(cod)(MeIm(CH2)2NMe2)] (11).
The molecular structure of compound 11 is shown in Figure 2,
and the more significant bond distances and angles are collected
in Table 1. The coordination geometry at the rhodium center is
slightly distorted square-planar formed by coordination to the
metal of the two olefinic bonds of a 1,5-cyclooctadiene
molecule, the carbene atom of the 1-(2-dimethylaminoethyl)-
The coordination of the dimethylamino fragment of the
hemilabile NHCs in complexes 11–15 could be induced by
abstraction of the chloro ligand. Thus, the reaction of complexes
12 and 15 with 1 molar equiv of silver tetrafluoroborate in
CH3CN/acetone at 0 °C resulted in the precipitation of AgCl
and the formation of yellow solutions from which the cationic
complexes [Rh(cod)(RIm(CH2)3NMe2)][BF4] (R ) Me, 16;
Mes, 17) were isolated as microcrystalline yellow solids in good
(29) Zeng, J. Y.; Hsieh, M. H.; Lee, H. M. J. Organomet. Chem. 2005,
690, 5662–5671.
(30) (a) Allen, D. P.; Crudden, C. M.; Calhoun, L. A.; Wang, R. Y.;
Decken, A. J. Organomet. Chem. 2005, 690, 5736–5746. (b) Allen, D. P.;
Crudden, C. M.; Calhoun, L. A.; Wang, R. Y. J. Organomet. Chem. 2004,
689, 3203–3209.
(32) (a) Baba, E.; Cundari, T. R.; Firkin, I. Inorg. Chim. Acta 2005,
358, 2867–2875. (b) Arduengo, A. J., III. Acc. Chem. Res. 1999, 32, 913–
921.
(31) Enders, D.; Gielen, H. J. Organomet. Chem. 2001, 617–618, 70–
80.

228 Organometallics, Vol. 27, No. 2, 2008
Jiménez et al.
complexes with a six-membered metallacycle ring having a
rather small dihedral angle have been structurally character-
ized.33
For comparative purposes, the cationic bis-carbene rhodi-
um(I) complex [Rh(cod)(MeIm(CH2)3ImMe)][BF4] (18) was
34
prepared from the bis-imidazolium [MeImH(CH2)3ImHMe]Br2
salt following a procedure similar to that used by Crabtree33 in
thesynthesisoftherelatedcompound[Rh(cod)(n-BuIm(CH2)3Imn-
Bu)][PF6]. As expected, the spectroscopic properties of com-
pound 18 matches with those reported for the related PF6- salt
described independently by Peris35 and Raubenheimer.36
Hydrosilylation of 1-Alkynes. The neutral [RhCl(cod)-
(RIm(CH2)nNMe2)] (11–15) and cationic [Rh(cod)(RIm(CH2)n
NMe2)][BF4] (16–18) complexes were found to be active
catalyst precursors for the hydrosilylation of terminal alkynes.
The catalytic reactions were carried out in CDCl3 at 60 °C using
Figure 2. Molecular diagram of complex [RhCl(cod)(MeIm
(CH2)2NMe2)] (11).
1
HSiMe2Ph and were routinely monitored by H NMR spec-
Scheme 3
troscopy. The influence of the 1-alkyne has been studied using
phenylacetylene, 3,3-dimethyl-but-1-yne, 1-hexyne, and trieth-
ylethynylsilane as substracts, and the results are summarized
in Table 2.
Transition metal catalyzed hydrosilylation of 1-alkynes often
gives a mixture of the three possible isomeric vinylsilane
derivatives: (Z)- or (E)-1-silyl-1-alkenes, products from the anti-
Markovnikov addition (ꢀ-(Z) and ꢀ-(E) isomers, respectively),
and 2-silyl-1-alkene from the Markovnikov addition (R
isomer).19a,21,37 In addition, the formation of dehydrogenative
silylation products, alkynylsilane and the corresponding
alkene, have been sometimes observed in the case of sterically
demanding substituents on the alkyne and/or the hydrosilane
(Scheme 4).37,38
yield. The MALDI-TOF mass spectra gave peaks at m/z 378.1
(16) and 482.2 (17) that correspond to the cations [Rh
(cod)(RIm(CH2)3NMe2)]+. The IR spectra of the complexes
showed the presence a broad band at 1071 cm-1 corresponding
–
to uncoordinated BF4 anions. In addition, the conductivity
measurements in acetone solutions were in agreement with a
formulation of the complexes as 1:1 electrolytes. Further support
of the coordination of the dimethylamino group to the rhodium
center comes from the 1H NMR, as no coordinated solvent was
detected when the reaction was conducted in the presence of
diverse coordinating solvents as acetone or acetonitrile. The 1H
and 13C{1H} NMR spectra of both compounds are consistent
with a chelating coordination mode (κ2C,N) of the NHC ligands
that results in the formation of a seven-membered metallacycle
(Scheme 3). The most relevant features of the NMR spectra
are the significant reduction in the magnitude of the JC-Rh of
the carbenic atom, only observed for compound 16 at δ 179.63
ppm (JC-Rh ≈ 28 Hz), and the downfield shifting of ca. 1 ppm
of the methylenic -CH2-NMe2 resonance relative to the related
neutral complex, which is observed as a broad triplet and could
be a diagnostic for the coordination of the -NMe2 fragment.
When the hydrosilylation of phenylacetylene was preformed
in the presence of the catalyst precursors 11, 13–14, and 16
(entries 1, 3, 4, 6), the massive formation of polyphenylacetylene
was observed even at room temperature.39,21 However, the
polymerization was considerably reduced for the cationic
complexes 17 (entry 7) and 18 (entry 8) and was marginally
(33) (a) Leung, C. H.; Incarvito, C. D.; Crabtree, R. H. Organometallics
2006, 25, 6099–6107. (b) Mata, J. A.; Chianese, A. R.; Miecznikowski,
J. R.; Poyatos, M.; Peris, E.; Faller, J. W.; Crabtree, R. H. Organometallics
2004, 23, 1253–1263. (c) Burling, S.; Field, L. D.; Li, H. L.; Messerle,
B. A.; Turner, P. Eur. J. Inorg. Chem. 2003, 3179, 3184.
(34) (a) Fu, S. K.; Liu, S. T. Synth. Commun. 2006, 36, 2059–2067. (b)
Anderson, J. L.; Ding, R.; Ellem, A.; Amstrong, D. W. J. Am. Chem. Soc.
2005, 127, 593–604.
(35) (a) Viciano, M.; Poyatos, M.; Sanaú, M.; Peris, E.; Rossin, A.;
Ujaque, G.; Lledós, A. Organometallics 2006, 25, 1120–1134. (b) Mas-
Marzá, E.; Peris, E.; Castro-Rodriguez, I.; Meyer, K. Organometallics 2005,
24, 3158–3162.
(36) Neveling, A.; Julius, G. R.; Cronje, S.; Esterhuysen, C.; Rauben-
heimer, H. G. Dalton Trans. 2005, 181, 192.
Unfortunately, the chloro abstraction by silver salts in the
neutral complexes containing the ligands 1-(2-dimethylamino-
ethyl)-3-R-imidazol-2-ylidene (R ) Me, 11; t-Bu, 13) resulted
in decomposition products even when the reaction was per-
formed in coordinating solvents (acetone or acetonitrile) and/
or in the presence of coordinating anions (triflate). Although
the chelating coordination mode (κ2C,N) of the 2-dimethylamino-
ethyl sidearm with a perpendicular disposition of the imidazol-
2-ylidene fragment relative to the rhodium coordination plane
produces a constrained six-membered metallacycle, the twist
of the NHC diazole ring plane could relieve the strain and should
allow the coordination of labile -NMe2 fragment. In this context,
it has been demonstrated that the dihedral angle between both
planes in N-heterocyclic (CH2)n-linked bis-NHC complexes is
strongly dependent on the length of the linker.33b Thus, several
methylene-linked (n ) 1) bis-NHC square planar rhodium(I)
(37) The vinylsilane derivatives were unambiguously characterized on
the basis of the coupling constants of 1H NMR spectra and GC-MS. (a)
Derivates from n-BuCt CH. Jun, C. H.; Crabtree, R. H. J. Organomet.
Chem. 1993, 447, 177–187. (b) Derivates from PhCt CH. Katayama, H.;
Taniguchi, K.; Kobayashi, M.; Sagawa, T.; Minami, T.; Ozawa, F. J.
Organomet. Chem. 2002, 645, 192–200. (c) Derivates from t-BuCt CH.
Andavan, G. T. S.; Bauer, E. B.; Letko, C. S.; Hollis, T. K.; Tham, F. S.
J. Organomet. Chem. 2005, 690, 5938–5947, references therein. (d)
Derivatives from Et3SiCt CH: See experimental section. Similar alkene-
disilanes: Inoue, A.; Kondo, J.; Shinokudo, H.; Oshima, K. Chem.-Eur. J.
2002, 8, 1730–1740. (e) Sudo, T.; Asao, N.; Gevorgyan, V.; Yamamoto, Y
J. Org. Chem. 1999, 64, 2494–2499.
(38) The dehydrogenative silylation product, t-BuCt CSiMe2Ph, has
beendetectedbyGC-MSinthecatalyticsolutions.See,forexample:Shimizu,
R.; Fuchikami, T. Tetrahedron Lett. 2000, 41, 907–910.
(39) Rhodium(I) complexes can promote undesirable polymerization
of aryl-substituted alkynes such as phenylacetylene. See, for example: Mori,
A.; Takahisa, E.; Yamamura, Y.; Kato, T.; Mudalige, A. P.; Kajiro, H.;
Hirabayashi, K.; Nishihara, Y.; Hiyama, T. Organometallics 2004, 23, 1755–
1765.

Rhodium(I) Complexes as Efficient Alkyne Hydrosilylation Catalysts
Organometallics, Vol. 27, No. 2, 2008 229
Table 2. Hydrosilylation of Terminal Alkynes with
Aminoalkyl-Functionalized NHC Carbene Rhodium(I) Complexesa,b
conv, % ꢀ- % ꢀ-
%
%
entry
alkyne
catalyst time, h
%
(E) (Z) % R alkene polym
1c PhCt CH
11
12
13
14
15
16
17
18
11
12
13
14
15
16
17
18
11
12
13
14
15
16
17
18
2.00 97
2.00 99
0.50 97
0.50 99
12.00 98
0.25 97
12.00 98
4.00 95
12.00 99
12.00 97
12.00 95
12.00 99
24.00 87
7.00 90
24.00 72
5.35 93
1.50 96
1.25 97
1.00 95
8.00 87
5.00 82
2.00 98
4.50 92
4.25 94
5.00 93
12.00 98
1.00 98
9.00 94
24.00 81
1.75 98
24.00 78
5.35 90
20 13
58 16 19
0
0
6
0
0
4
0
0
3
3
10
4
7
14
10
9
10
0
0
0
0
3
67
1
49
75
8
62
18
18
2
PhCt CH
3c PhCt CH
41
0
10
1
8
6
15
4c PhCt CH
14 10
67 13
5
PhCt CH
6c PhCt CH
32
67
0
0
7
8
9
PhCt CH
PhCt CH
t-BuCt CH
47 17 15
79
76
77
74
9
6
9
9
9
8
10
11
10 t-BuCt CH
11 t-BuCt CH
12 t-BuCt CH
13 t-BuCt CH
14 t-BuCt CH
15 t-BuCt CH
16 t-BuCt CH
17 n-BuCt CH
18 n-BuCt CH
19 n-BuCt CH
20 n-BuCt CH
21 n-BuCt CH
22 n-BuCt CH
23 n-BuCt CH
24 n-BuCt CH
25 Et3SiCt CH 11
26 Et3SiCt CH 12
27 Et3SiCt CH 13
28 Et3SiCt CH 14
29 Et3SiCt CH 15
30 Et3SiCt CH 16
31 Et3SiCt CH 17
32 Et3SiCt CH 18
58 13 15
65 12 13
Figure 3. Reaction profile of conversion vs time for the hydrosi-
lylation of n-BuCt CH with different precursors.
73
57
2
5
5
6
5
11
28
0
0
0
4
3
6
2
unselective because although the ꢀ-(E) vinylsilane is the major
product (50–75%), variable amounts of the ꢀ-(Z) (5–12%) and
R (8–35%) isomers were also formed. In addition, the dehy-
drogenative silylation process is operative as significant percent-
ages of 3,3-dimethyl-but-1-ene (5–20%) were observed and
t-Bu-Ct C-SiMe2Ph was detected by GC-MS. Interestingly,
the less active catalyst precursors were 15 and 17, which have
the bulky mesityl substituent in imidazol-2-ylidene ligand,
probably as a consequence of the steric interference with the
bulky substrate. As expected, complexes containing the less
sterically demanding methyl-substituted NHC ligands (12, 16,
and 18) were the most active in the series, although the regio-
and stereoselectivities attained with the bis-carbene complex
18 were lower.
98
95
95
88
85
7
9
14 79
10 88
22 64
0
0
6
2
0
0
0
0
8
56
74
45
51
67
38
55
81
0
4
0
0
0
1
1
2
42
21
55
49
33
61
43
17
0
0
0
a Reactions were monitored by 1H NMR. b Experiments were carried
Higher regio- and stereoselectivities were obtained in the
hydrosilylation of 1-hexyne (entries 17–24, Table 2). In general,
an opposite stereoselectivity toward the ꢀ-(Z) vinylsilane was
observed in all cases, in clear contrast to the catalytic processes
involving the precedent substrates. The activities and selectivities
are comparable or slightly higher than the previously reported
for other rhodium-catalyzed 1-hexyne hydrosilylation reac-
tions.19a,25h Outstandingly, the catalyst precursor [RhCl(cod)-
(MeIm(CH2)2N(CH3)2)] (11) gave a 96% of conversion in 1.5 h
with complete selectivity in ꢀ vinylsilanes, a Z/E ratio of 49,
and a TOF of 64 turnover/h (entry 17, Table 2). The reaction
profile, conversion versus time, for the hydrosilylation of
1-hexyne catalyzed by complexes 11–18 is shown in Figure 3.
The neutral complexes [RhCl(cod)(RIm(CH2)nN(CH3)2)]
(11–13) are, in general, far more active and selective than the
cationic counterparts or complexes containing the bulky mesityl-
substituted NHC ligand. Interestingly, the hydrosilylation reac-
tion can be carried out on a preparative scale as has been
demonstrated for the synthesis of ꢀ-hexen-1-enyl-methyl-
diphenyl-silane using compound 12 as catalyst precursor (see
Experimental Section).
Compound [Rh(cod)(MeIm(CH2)3N(CH3)2)][BF4] (16) is the
most active and selective in the cationic series (16–18).
Interestingly, complexes 16 and 17 are more selective than the
biscarbene catalyst 18 (entries 22–24). The effect of the length
of the linker becomes important in complexes [RhCl
(cod)(RIm(CH2)nN(CH3)2)] (R ) t-Bu, 13, 14) compound 13
(n ) 2) being considerably more active and selective than
compound 14 (n ) 3). However, this effect is not so significant
in complexes 11 and 12 (R ) Me) (entries 17 and 18). The
influence of the size of the R substituent on the heterocyclic
ring became evident along the series [RhCl(cod)(RIm(CH2)3
N(CH3)2)] (R ) Me, 12; t-Bu, 14; Mes, 15). Thus, the excellent
activity observed for complex 12 contrasts with that of the
out using a HSiMe2Ph/RCt CH/catalyst ratio of 110/100/1, [catalyst]0
)
1.54 × 10-3 M in CDCl3, temperature 60 °C. c Room temperature.
Scheme 4
observed for the neutral catalysts precursors 12 (entry 2) and
15 (entry 5). The major isomer formed was the ꢀ-(E) vinylsilane,
particularly for 12, 15, and 17. In general, the dehydrogenative
silylation product, styrene, was not detected, or it is negligible
when the polymerization process is operative. In these cases,
considerable amounts of the R and ꢀ-(Z) vinylsilanes were also
formed except for 17, which gave only the ꢀ-(E) and R isomers.
The lack of selectivity in hydrosilylation of phenylacetylene has
also been observed with cationic rhodium(I) precursors contain-
ing diphosphine as ancillary ligands.40
The hydrosilylation of tert-butylacetylene at room temperature
is quite slow, and even at 60 °C long reaction times are generally
required. Under these experimental conditions the reactions are
(40) Cervantes, J.; González-Alatorre, G.; Rohack, D.; Pannell, K. H,
Appl. Organomet. Chem. 2000, 14, 146–151.

230 Organometallics, Vol. 27, No. 2, 2008
Jiménez et al.
Scheme 5
Figure 4. ꢀ-(E)/ꢀ-(Z) ratio for the hydrosilylation of n-BuCt CH
catalyzed by [RhCl(cod)(t-BuIm(CH2)2N(CH3)2)] (13) at 60 °C.
Total consumption of 1-hexyne at t ) 120 min.
Table 3. Distribution of Products after Prolonged Heating at 60 °C
for the Hydrosilylation of n-BuCt CH in CDCl3
entry catalyst time, h conv, % ꢀ-(E)/ꢀ-(Z) % R % allyl % alkene
1
2
3
4
5
6
7
8
11
12
13
14
15
16
17
1.50
10.00
1.25
12.00
1.00
12.00
5.00
15.00
3.50
10.00
2.00
9.00
4.50
12.00
96
100
97
100
95
100
57
100
70
100
98
100
92
0.02
0.13
0.05
0.27
0.05
1.29
0.32
4.09
0.10
0.24
0.18
0.64
0.11
0.35
0
5
0
7
0
3
6
3
3
7
6
0
2
0
0
0
0
0
18
0
41
0
0
0
0
0
0
5
0
0
0
0
2
4
0
0
0
0
catalyze the hydrosilylation of 1-octyne to allylsilanes by precise
adjustment of the reaction conditions.41
The hydrosilylation of alkynylsilanes has been scarcely
studied.42 In order to evaluate the electronic effects introduced
by the silyl group on the selectivity, the hydrosylilation of
Et3SiCt CH has also been investigated (Table 2). Surprisingly,
in almost all cases the reaction gave exclusively the ꢀ-(Z) and
R bis(silyl)alkenes but not ꢀ-(E)-vinylsilane. Again the less
active catalyst precursors were 15 and 17, which have the bulky
mesityl substituent on the imidazol-2-ylidene ligand. Interest-
ingly, the cationic compounds 16 and the neutral compounds
11 are the more selective catalyst precursors in R-vinylsilane,
with R/ꢀ ratios of 1.60 and 1.15, respectively. Nevertheless, it
is difficult to establish a clear correlation with either the length
of the linker or the steric effect of the substituents.
It has been reported that cationic rhodium(I) complexes
catalyze the hydrosilylation of 1-alkynes to give preferentially
the ꢀ-(E)-vinylsilane isomer, whereas neutral analogs show the
opposite stereoselectivity, as they are highly selective for the
ꢀ-(Z)-vinylsilane.37b,39,43 In contrast, the above-described results
indicate that this trend should not be considered a general rule
as it is not applicable to NHC carbene containing complexes,25b,44
since in these cases the selectivity is essentially determined by
the alkyne substitution.
Mechanistic Considerations. The strong influence of the
1-alkyne structure on the selectivity can be rationalized in the
frame of the widely accepted mechanism for the metal-catalyzed
hydrosilylation, that is, the modified Chalk-Harrod mechanism
that accounts for the unusual ꢀ-(Z)-vinylsilane isomer resulting
from a formal trans addition. The mechanism starts with Si-H
oxidative addition to the metal and invokes the insertion of a
coordinated alkyne into the Rh-Si bond to form the alkenyl-
Rh intermediate (A), instead of the insertion into the Rh-H
bond. Direct reductive elimination from A would give the ꢀ-(E)-
vinylsilane isomer. Alternatively, this intermediate could un-
dergo a metal-assisted isomerization to alkenyl-Rh (B) via a
zwitterionic carbene-like intermediate (i)19a or a η2-vinyl
complex (ii)19b (Scheme 5). The driving force for this isomer-
9
10
11
12
13
14
23
0
0
100
12
catalyst precursors 14 and 15 (Figure 3). As far as the
selectivitity is concerned, the regioselectivity remains constant,
but bulky substituents reduce the stereoselectivity as was
evidenced by a significant reduction of the Z/E ratio (19, R )
Me; 12.6, R ) t-Bu and 9.4, R ) Mes) (entries 18, 20, and 21)
that is more pronounced in the Mes complex.
We have checked the E/Z ratio dependence versus time in
the hydrosilylation of 1-hexyne using the catalyst precursor
[RhCl(cod)(t-BuIm(CH2)3N(CH3)2)] (13). As can be seen in
Figure 4, the E/Z ratio remained approximately constant (0.05)
during the catalytic process; however, after the complete
consumption of 1-hexyne (t ) 120 min), the E/Z ratio increases
owing to the isomerization of the ꢀ-(Z)-vinylsilane into the
thermodynamically favored ꢀ-(E)-vinylsilane isomer. Thus, the
stability of the E/Z ratio during the catalysis suggests the kinetic
control of the product distribution. The isomerization activity
has been observed in all of the catalytic systems under
investigation (Table 3) and is particularly important for com-
pounds [RhCl(cod)(t-BuIm(CH2)nN(CH3)2)] (13, 14) (entries 6
and 8, Table 3). Taken into account that the catalytic reactions
were conducted with 10% excess of hydrosilane in order to
avoid the polymerization process, the responsible species for
the isomerization should be generated by mediation of hydrosi-
lane. In fact, the isomerization of (Z)-alkenylsilanes to (E)-
alkenylsilanes catalyzed by rhodium(I) complexes in the pres-
ence of hydrosilanes has already been observed.37a Also in some
systems the heating of the catalytic solutions resulted in the
formation of minor amounts of n-hexenes. More important, in
the catalytic systems based on precursors 13, 14, and 16
significant amounts of hex-2-enyl-dimethyl-phenyl-silane were
formed (entries 6, 8, and 12, Table 3). The slow rearrangement
of vinylsilanes to allylsilane has been reported by Crabtree et
al. in the hydrosilylation of 1-hexyne with HSiMePh2 catalyzed
by [RhCl(PPh3)3].37a Interestingly, Doyle et al. have also found
that dinuclear rhodium(II) perfluorobutyrate-bridged complexes
(41) Doyle, M. P.; High, K. G.; Nesloney, C. L.; Clayton, T. W.; Lin,
J. Organometallics 1991, 10, 1225–1226.
(42) Molander, G. A.; Antoinette, J.; Romero, C.; Corrette, C. P. J.
Organomet. Chem. 2002, 647, 225–235.
(43) (a) Sato, A.; Kinoshita, H.; Shinokubo, H.; Oshima, K. Org. Lett.
2004, 6, 2217–2220. (b) Faller, J. W.; Alliesi, D. G. Organometallics 2002,
21, 1743–1746.
(44) Mas-Marzá, E.; Poyatos, M.; Sanaú, M.; Peris, E. Inorg. Chem.
2004, 43, 2213–2219.

Rhodium(I) Complexes as Efficient Alkyne Hydrosilylation Catalysts
Organometallics, Vol. 27, No. 2, 2008 231
ization, which leads to the thermodynamically less stable ꢀ-(Z)-
vinylsilane, is the relief of steric strain between the metal and
the adjacent silane. However, the direct trans addition, without
cis–trans isomerization, resulting in the formation of the
Markovnikov product has been observed in cationic ruthenium
complexes45and sustained by DFT calculations.46 In the same
way, we have proposed that the involvement of dinuclear
ruthenium complexes could also explain the formal trans
addition.47 Additionally, an alternative reaction mechanism that
accounts for the observed trans addition in the intramolecular
alkyne hydrosilylation catalyzed by ruthenium complexes have
been also described.48,49
based on the stabilization of the silylalkenyl catalytic intermedi-
ate A and the destabilization of the probable intermediates i or
ii, could give full account of the experimental observations.
It is worth mentioning that some methods for the regiose-
lective production of 1,1-disubstituted vinyl-silanes (R isomer)
by direct trans addition have been recently described.45,46
Interestingly, 1,1-bis(silyl)alkenes have been obtained by cis
addition of hydrosilanes to alkyl-silyl acetylenes.42
Conclusions
We have described the synthesis of several ammonium-
imidazolium chloride salts that are precursor for the synthesis
of a range of rhodium(I) complexes containing amino-alkyl
functionalized NHC ligands with hemilabile character of the
type 1-dimethyl-amino-alkyl-3-R-imidazol-2-ylidene. The se-
quential deprotonation of the ammonium-imidazolium salts
allowed the preparation of amine-imidazolium cyclooctadiene-
dichlororhodate(I) salts and neutral mononuclear complexes
[RhCl(cod)(RIm(CH2)nNMe2)]. When the length of the linker
is appropriate (n ) 3), chloride abstraction by silver salts
resulted in the formation of cationic mononuclear complexes
by coordination of the dimethylamino fragment to the rhodium
center.
The rhodium complexes are efficient catalyst precursors
for the hydrosilylation of terminal alkynes. It has been found
that the stero- and regioselectivity of the reactions is determined
mainly by the substitution of the 1-alkyne, whereas the charge
of the complexes, the length of the sidearm, and the 3-R
substituents on the heterocyclic ring strongly influence the
activity and, in some extent, the selectivity. Neutral complexes
having amino-functionalized NHC ligands with a small sub-
stituent at the heterocycle are generally the most active and
selective catalysts. Good selectivities in the ꢀ-(Z)-vinylsilane
isomer were found in the hydrosilylation of 1-hexyne. However,
moderate selectivities in the opposite ꢀ-(E)-vinylsilane stereo-
isomer were obtained in the hydrosilylation of tert-butyl-
acetylene. Unexpectedly, only the ꢀ-(E) and R bis(silyl)alkenes
isomers where observed in the hydrosilylation of triethylsilyl-
acetylene.
When the R group in R-Ct C-H is not sterically demanding,
as is the case of 1-hexyne (R ) n-C4H9), the ꢀ-(Z)-vinylsilane
isomer is selectively formed because the position of the
equilibrium is shifted toward B. However, when the R group is
very bulky, as is the case of tert-butylacetylene (R ) t-C4H9),
the reactions are unselective.37 Probably the introduction of
additional steric congestion results in a equilibration between
A and B that is expected to be translated to a mixture of ꢀ-(E)-
vinylsilane and ꢀ-(Z)-vinylsilane isomers after reductive
elimination.19b Besides, the bulkiness of R produces an ad-
ditional steric repulsion with the metal center that makes the
alkenyl-Rh intermediate C less sterically demanding, resulting
in the formation of the R-vinylsilane isomer.50 However, an
alternative pathway for the formation of the R regioisomer could
be the 1,2-silyl shift in the η2-vinyl intermediate (ii).49,51,52 In
addition, the dehydrogenative silylation products, which also
are frequently formed in catalytic systems using alkynes and/
or hydrosilane with sterically demanding substituents, can be
formed by ꢀ-reductive elimination from B.37
In the particular case of Et3SiCt CH, no formation of the
ꢀ-(Z)-vinylsilane isomer strongly suggests that the isomerization
of the alkenylrhodium intermediate A does not take place and,
in consequence, only the ꢀ-(E) and the R-vinylsilane isomers
are formed from A and C. Although the steric influence of the
-SiEt3 moiety could completely inhibit the AaB equilibrium,
probably the electronic effects are even more important.
Although the silyl group at the ꢀ carbon stabilizes the adjacent
carbanion through a pπ-dπ interaction in the zwitterionic
intermediate i,19a the silyl group at the R carbon should
destabilizes the carbenic fragment in both intermediates (i and
ii). In addition, the (Z)-silylalkenyl catalytic intermediate A
should be stabilized by the hyperconjugative interaction between
low-lying silicon-substitutent-based unoccupied molecular orbit-
als and occupied π-type orbitals.53 This effect is further
reinforced by the presence of two silyl groups in trans position
in A. Thus, the interplay between steric and electronic effects,
Experimental Section
Scientific Equipment. Elemental analyses were carried out in a
Perkin-Elmer 2400 CHNS/O analyzer. Infrared spectra were
recorded on a FT-Perkin-Elmer Spectrum One spectrophotometer
using Nujol mulls between polyethylene sheets. NMR spectra were
recorded on Bruker Avance 300 MHz and Bruker Avance 400 MHz
spectrometers. 1H (300.1276 MHz, 400.1625 MHz) and 13C
(75.4792 MHz, 100.6127 MHz) NMR chemical shifts are reported
in ppm relative to tetramethylsilane and referenced to partially
deuterated solvent resonances. Coupling constants (J) are given in
hertz. Spectral assignments were achieved by combination of
(45) (a) Trost, B. M.; Ball, Z. T. J. Am. Chem. Soc. 2001, 123, 12726–
12727. (b) Trost, B. M.; Ball, Z. J. Am. Chem. Soc. 2005, 127, 17644–
17655.
1
1H-1H COSY, NOESY, 13C DEPT and H-13C HMQC experi-
(46) Chung, L. W.; Wu, Y. D.; Trost, B. M.; Ball, Z. T. J. Am. Chem.
Soc. 2003, 125, 11578–11582.
ments. MALDI-TOF mass spectra were obtained on a Bruker
MICROFLEX spectrometer using DCTB (trans-2-[3-(4-tert-bu-
tylphenyl)-2-methyl-2-propenylidene]malononitrile) as matrix.54
Electrospray mass spectra (ESI-MS) were recorded on a Bruker
MicroTof-Q using sodium formiate as reference. Conductivities
were measured in ca. 5 × 10-4 M acetone solutions of the
complexes using a Philips PW 9501/01 conductimeter.
(47) Martín, M.; Sola, E.; Lahoz, F. J.; Oro, L. A. Organometallics 2002,
21, 4027–4029.
(48) Trost, B. M.; Ball, Z. T. J. Am. Chem. Soc. 2003, 125, 30–31.
(49) Crabtree, R. H. New J. Chem. 2003, 27, 771–772.
(50) Kawanami, Y.; Sonoda, Y.; Mori, T.; Yamamoto, K. Org. Lett.
2002, 4, 2825–2827.
(51) (a) See, for example: Jiménez, M. V.; Sola, E.; Lahoz, F. J.; Oro,
L. A. Organometallics 2005, 24, 2722–2729. (b) Braunstein, P.; Knorr,
M.; Reinhard, G.; Schubert, U.; Stährfeldt, T. Chem. Eur. J. 2000, 6, 4265–
4278. (c) Huang, D.; Folting, K.; Caulton, K. G. J. Am. Chem. Soc. 1999,
121, 10318–10322.
Synthesis. All experiments were carried out under an atmosphere
of argon using Schlenk techniques, and the solvents were distilled
(52) Patel, P. P.; Zhu, Y.; Zhang, L.; Herndon, J. W. J. Organomet.
Chem. 2004, 689, 3379–3387.
(54) Ulmer, L.; Mattay, J.; Torres-García, H. G.; Luftmann, H. Eur. J.
Mass Spectrom. 2000, 6, 49–52.
(53) Giordan, J. C. J. Am. Chem. Soc. 1983, 105, 6544–6546.

232 Organometallics, Vol. 27, No. 2, 2008
Jiménez et al.
immediately prior to use from the appropriate drying agents.
Oxygen-free solvents were employed throughout. CDCl3 was dried
using activated molecular sieves, and methanol-d4 (<0.02% D2O)
was purchased from Euriso-top and used as received. The com-
pounds t-BuImH,55 MesImH,56 and MeImH(CH2)3ImHMe33 were
prepared by the reported methods. MeImH was obtained from
Sigma-Aldrich and distilled prior to use. The alkynes, HSiMe2Ph,
and chloro-alkyl-dimethylamine hydrochloride compounds were
obtained from common commercial sources and, unless otherwise
stated, were used as received. [{Rh(µ-Cl)(cod)}2] was prepared
following a published method.57
General Procedure for Preparation of [RImH(CH2)n
NMe2]Cl · HCl (1–5). The alkylammonium imidazolium chloride
salts were synthesized through the following procedure. A mixture
of 2-chloro-N,N-dimethylalkylamine hydrochloride, Cl(CH2)n
NMe2 · HCl, and imidazole, RImH, in deoxygenated CH3CN (10
mL) was refluxed for several days until reaction was completed.
The white solid formed was filtered, washed with a CH3CN/diethyl
ether mixture, and vaccuum-dried.
Yield: 78%. Anal. Calcd for C17H27Cl2N3: C, 59.30; H, 7.90; N,
12.20. Found: C, 59.28; H, 7.41; N, 12.63. 1H NMR (298 K,
CDCl3): δ 11.84 (br s, 1H, NH), 10.31 (s, 1H, CHNCHN), 8.57 (s,
1H, CH), 7.15 (s, 1H, CH), 7.89 (s, 2H, CH Mes), 4.98 (t, JH-H
)
10.0, 2H, NCH2), 3.45 (t, JH-H ) 10.0, 2H, NCH2), 2.93 (s, 6H,
NMe2), 2.83 (m, 2H, CH2), 2.32 (s, 3H, CH3 Mes), 2.05 (s, 6H,
CH3 Mes). 13C{1H}NMR (298 K, CDCl3): δ 141.37 (s, CN CHN),
134.08, 130.67 (Mes), 129.87 (CH Mes), 124.26, 123.04 (CH Im),
54.10, 47.17 (NCH2), 43.07 (NMe2), 25.92 (CH2), 21.03, 17.57
(CH3 Mes). ESI-MS (CH3OH) m/z ) 272.1 [M - 2Cl - H]+.
General Procedure for Preparation of Dichlorocyclooctadi-
enerhodate(I) Salts [RImH(CH2)nNMe2][RhCl2(cod)] (6–10).
[RImH(CH2)nNMe2]Cl · HCl (2.21 mmol) (1–5) and NaH (55.7 mg,
2.32 mmol) were reacted in THF (10 mL) for 30 min. Then [{Rh(µ-
Cl)(cod)}2] (1.11 mmol) was added, and the suspension was stirred
overnight at room temperature. The pale yellow solids formed were
separated by filtration, washed with diethyl ether, and dried in
vacuo.
[MeImH(CH2)2NMe2][RhCl2(cod)] (6). Yield: 84%. Anal.
Calcd for C16H28Cl2N3Rh: C, 44.05; H, 6.47; N, 9.63. Found:
[MeImH(CH2)2NMe2]Cl · HCl (1). Cl(CH2)2NMe2 · HCl (3.16
g, 21.93 mol) and MeImH (1.75 mL, 21.93 mmol), reflux for 5
days. Yield: 82%. Anal. Calcd for C8H17Cl2N3: C, 42.49; H, 7.58;
1
C, 44.09; H, 6.34; N, 9.60. H NMR (298 K, CDCl3): δ 10.41
(s, 1H, CHNCHN), 7.38 (s, 1H, CH), 7.13 (s, 1H, CH), 4.45 (t,
JH-H ) 5.4, 2H, NCH2), 4.21 (m, 4H, CH cod), 4.05 (s, 3H,
NMe), 2.73 (t, JH-H ) 5.4, 2H, NCH2), 2.39 (m, 4H, CH2 cod),
2.26 (s, 6H, NMe2), 1.65 (m, 4H, CH2 cod). 13C{1H} NMR (298
K, CDCl3): δ 122.27, 121.78 (CH), 77.70 (d, JC-Rh ) 11.1, CH
cod), 58.60, 47.29 (NCH2), 45.27 (NMe), 36.62 (NMe2), 31.09
1
N, 18.58. Found: C, 42.72; H, 7.45; N, 18.68. H NMR (298 K,
CDCl3): δ 9.15 (s, CHNCHN), 7.8 (s, 1H, CH), 7.65 (s, 1H, CH),
4.75 (t, JH-H ) 6.5 Hz, 2H, NCH2), 4.02 (br s, 1H, NH), 3.97 (s,
3H, NMe), 3.76 (t, JH-H ) 6.5, 2H, NCH2), 2.99 (s, 6H, NMe2).
13C{1H} NMR (298 K, CD3OD): δ 124.25, 122.35 (CH), 55.62,
55.30 (NCH2), 42.91 (NMe), 35.43 (s, NMe2). ESI-MS (CH3OH)
m/z ) 154.1 [M - 2Cl - H]+.
(CH2
cod).
ESI-MS
(CH3CN)
m/z
)
154.1
[MeImH(CH2)2NMe2]+, 211.0 [Rh(cod)]+.
[MeImH(CH2)3NMe2]Cl · HCl (2). Cl(CH2)3NMe2 · HCl (0.79
g, 5.01 mol) and MeImH (0.40 mL, 5.01 mol), reflux for 5 days.
Yield: 75%. Anal. Calcd for C9H19Cl2N3: C, 45.01; H, 7.97; N,
17.49. Found: C, 44.92; H, 7.54; N, 16.99. 1H NMR (298 K,
CD3OD): δ 9.03 (s, 1H, CHNCHN), 7.70 (s, 1H, CH), 7.61 (s, 1H,
CH), 3.76 (t, JH-H ) 7.2, 2H, NCH2), 3.94 (s, 3H, NMe), 3.55 (br
s, 1H, NH), 3.19 (m, 2H, NCH2), 2.89 (s, 6H, NMe2), 2.34 (m,
2H, CH2). 13C{1H} NMR (298 K, CD3OD): δ 125.43, 123.86 (CH),
55.57, 47.81 (NCH2), 43.77 (NMe), 36.82 (NMe2), 26.52 (CH2).
ESI-MS (CH3OH) m/z ) 168.1 [M - 2Cl - H]+.
[t-BuImH(CH2)2NMe2]Cl · HCl (3). Cl(CH2)2NMe2 · HCl (1.48
g, 10.28 mol) and t-BuImH (1.28 g, 10.28 mol), reflux for 4 days.
Yield: 82%. Anal. Calcd for C11H23Cl2N3: C, 49.26; H, 8.64; N,
15.66. Found: C, 49.20; H, 8.40; N, 15.90. 1H NMR (298 K,
CD3OD): δ 9.35 (s, 1H, CHNCHN), 7.95 (s, 1H, CH), 7.81 (s, 1H,
CH), 4.73 (t, JH-H ) 6.3, 2H, NCH2), 3.78 (t, JH-H ) 6.6, 2H, NCH2),
3.42 (s, 6H, NMe2), 1.71 (s, 9H, t-Bu). 13C{1H} NMR (298 K,
CD3OD): δ 141.35 (CN CHN), 124.15, 122.37 (CH), 57.18 (C, t-Bu),
56.87, 45.39 (NCH2), 44.18 (NMe2), 29.87 (CH3, t-Bu). ESI-MS
(CH3OH) m/z ) 196.6 [M - 2Cl - H]+.
[t-BuImH(CH2)3NMe2]Cl · HCl (4). Cl(CH2)3NMe2 · HCl (1.28
g, 8.08 mol) and t-BuImH (1.00 g, 8.08 mol), reflux for 4 days.
Yield: 73%. Anal. Calcd for C12H25Cl2N3: C, 51.06; H, 8.93; N,
14.81. Found: C, 51.22; H, 8.33; N, 14.72. 1H NMR (298 K,
CD3OD): δ 10.47 (s, 1H, CHNCHN), 8.04 (s, 1H, CH), 7.40 (s, 1H,
CH), 4.69 (t, JH-H ) 12.3, 2H, NCH2), 3.32 (t, JH-H ) 6.9, 2H,
NCH2), 2.87 (s, 6H, NMe2), 2.67 (m, 2H, CH2), 1.66 (s, 9H, CH3,
t-Bu). 13C{1H} NMR (298 K, CDCl3): δ 123.56, 119.03 (CH),
60.45 (C, t-Bu), 54.12, 46.83 (NCH2), 43.07 (NMe2), 30.06 (CH3,
t-Bu), 25.63 (CH2). ESI-MS (CH3OH) m/z ) 210.2 [M - 2Cl -
H]+.
[MeImH(CH2)3NMe2][RhCl2(cod)] (7). Yield: 84%. Anal.
Calcd for C17H30Cl2N3Rh: C, 45.35; H, 6.71; N, 9.33. Found: C,
44.84; H, 6.34; N, 9.60. 1H NMR (298 K, CDCl3): δ 10.64 (s, 1H,
CHNCHN), 7.24 (s, 1H, CH), 7.10 (s, 1H, CH), 4.47 (t, JH-H ) 6.8,
2H, NCH2), 4.26 (m, 4H, CH cod), 4.13 (s, 3H, NMe), 2.47 (m,
4H, CH2 cod), 2.35 (t, JH-H ) 6.5, 2H, NCH2), 2.25 (s, 6H, NMe2),
2.15 (m, 2H, CH2), 1.71 (m, 4H, CH2 cod). 13C{1H} NMR (298
K, CDCl3): δ 122.14, 121.96, 120.99 (CH), 77.70 (d, JC-Rh ) 11.1,
CH cod), 54.97, 47.57 (NCH2), 44.92 (NMe), 36.78 (NMe2), 31.09
(CH2 cod), 27.61 (CH2). ESI-MS (CH3CN) m/z ) 168.3
[MeImH(CH2)3NMe2]+, 211.0 [Rh(cod)]+.
[t-BuImH(CH2)2NMe2][RhCl2(cod)] (8). NMR data. 1H NMR
(298 K, CDCl3): δ 10.20 (s, 1H, CHNCHN), 7.97 (s, 1H, CH), 7.23
(s, 1H, CH), 5.16 (t, JHH ) 7.5, 2H, NCH2), 4.22 (m, 4H, CH cod),
4.10 (t, JHH ) 7.5, 2H, NCH2), 3.06 (s, 6H, NMe2), 2.42 (m, 4H,
CH2 cod), 1.80 (s, 9H, CH3, t-Bu), 1.68 (m, 4H, CH2 cod).
[t-BuImH(CH2)3NMe2][RhCl2(cod)] (9). NMR data. 1H NMR
(298 K, CDCl3): δ 10.38 (s, 1H, CHNCHN), 7.63 (s, 1H, CH), 7.27
(s, 1H, CH), 4.68 (t, JHH ) 7.8, 2H, NCH2), 4.22 (m, 4H, CH cod),
2.99 (t, JHH ) 7.5, 2H, NCH2), 2.66 (s, 6H, NMe2), 2.52 (m, 2H,
CH2), 2.40 (m, 4H, CH2 cod), 1.77 (s, 9H, CH3, t-Bu), 1.68 (m,
4H, CH2 cod).
[MesImH(CH2)3NMe2][RhCl2(cod)] (10). NMR data. 1H NMR
(298 K, CDCl3): δ 10.20 (s, 1H, CHNCHN), 7.80 (s, 1H, CH), 7.20
(s, CH Mes), 7.03 (s, 1H, CH), 6.96 (s, 2H, CH Mes), 4.79 (t,
JH-H) 7.1, 2H, NCH2), 4.09 (m, 4H, CH cod), 3.68 (m, 2H, NCH2),
2.85 (m, 2H, CH2 cod), 2.51 (s, 3H, CH3 Mes), 2.45 (m, 2H, CH2
cod), 2.29 (s, 6H, NMe2), 2.04 (s, 6H, CH3 Mes), 1.78 (m, 2H,
CH2), 1.58 (m, 4H, CH2 cod).
General Procedure for Preparation of Complexes [RhCl
(cod)(RIm(CH2)nNMe2)] (11–15). Method A. A suspension of the
compounds [RImH(CH2)nNMe2][RhCl2(cod)] (6–10) (1 mmol) in
THF (10 mL) was treated with NaH (27.85 mg, 1.16 mmol) and
H2O (0.3 mL) to give an orange suspension. The solid was removed
by filtration, and the resulting orange solution was evaporated to
dryness. Recrystallization from diethyl ether/pentane rendered the
products as yellow solids, which were filtered, washed with pen-
tane, and dried in vacuo. Method B. The corresponding [RImH
[MesImH(CH2)3NMe2]Cl · HCl (5). Cl(CH2)3NMe2 · HCl (0.85
g, 5.37 mol) and MesImH (1.00 g, 5.37 mmol), reflux for 7 days.
(55) Bedford, C. D.; Harris, R. H., III; Howd, R. A.; Goff, D. A.; Koolpe,
G. A.; Petesch, M.; Koplovitz, I.; Sultan, W. E.; Musallam, H. A. J. Med.
Chem. 1989, 32, 504–516.
(56) Gardiner, M. G.; Herrmann, W. A.; Reisinger, C. P.; Schwarz, J.;
Spiegler, M. J. Organomet. Chem. 1999, 572, 239–247.
(57) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1979, 19, 218–219.

Rhodium(I) Complexes as Efficient Alkyne Hydrosilylation Catalysts
Organometallics, Vol. 27, No. 2, 2008 233
(CH2)nNMe2]Cl · HCl (1 mmol), NaH (1.16 mmol), and [{Rh(µ-
Cl)(cod)}2] (0.5 mmol) were reacted in THF (10 mL) for 16 h to
give suspensions of the compounds [RImH(CH2)nNMe2][RhCl2
(cod)] (6–10). Further reaction with NaH (27.85 mg, 1.16 mmol)
and H2O (0.3 mL) afforded orange suspensions from which the
compounds were isolated following the procedure described above.
[RhCl(cod)(MeIm(CH2)2NMe2)] (11). Yield: 55% (Method A).
Anal. Calcd for C16H27ClN3Rh: C, 48.07; H, 6.81; N, 10.51. Found:
1H, CH Mes), 7.00 (d, JH4-H5 ) 1.8, 1H, CH), 6.85 (s, 1H, CH
Mes), 6.67 (d, JH4-H5 ) 1.8, 1H, CH), 5.11 (m, 1H, NCH2), 4.79
(m, 1H, CH cod), 4.71 (m, 1H, CH cod), 4.36 (m, 1H, NCH2),
3.35 (m, 1H, CH cod), 2.92 (m, 1H, CH cod), 2.37 (s, 3H, CH3
Mes), 2.35 (m, 1H, CH2), 2.32 (s, 3H, CH3 Mes), 2.31 (m, 1H,
CH2), 2.22 (s, 7H, CH2 and NMe2), 2.13 (m, 1H, CH2), 2.09 (m,
2H, CH2 cod), 1.91 (m, 2H, CH2 cod), 1.65 (m, 2H, CH2 cod),
1.76 (s, 3H, CH3 Mes), 1.42 (m, 2H, CH2 cod). 13C{1H} NMR
(298 K, CDCl3): δ 181.88 (d, JC-Rh ) 51.1, CN CN), 138.59, 137.22,
136.27, 134.31 (Mes), 129.56, 128.02 (CH), 126.48 (CH Mes),
96.80, 96.75 (m, CH cod), 68.03 (d, JC-Rh ) 14.3, CH cod), 67.40
(d, JC-Rh) 14.3, CH cod), 56.46, 49.38 (NCH2), 45.09 (NMe2),
33.75, 31.41 (CH2 cod), 28.80 (s, CH2 and CH2 cod), 27.86 (CH2
cod), 20.83, 19.50, 17.45 (CH3). MS (MALDI-TOF, DCTB matrix,
CH2Cl2) m/z ) 482.3 [M - Cl] +, 272.2 [MesImH(CH2)3NMe2]+.
1
C, 46.95; H, 6.59; N, 9.47. H NMR (298 K, CDCl3): δ 6.99 (d,
JH4-H5 ) 1.8, 1H, CH), 6.78 (d, JH4-H5 ) 1.8, 1H, CH), 5.02 (m,
2H, CH cod), 4.73 (m, 1H, NCH2), 4.50 (m, 1H, NCH2), 4.07 (s,
3H, NCH3), 3.34 (m, 1H, CH cod), 3.26 (m, 1H, CH cod), 2.84
(m, 1H, NCH2), 2.74 (m, 1H, NCH2), 2.40 (m, 4H, CH2 cod), 2.35
(s, 6H, NMe2), 1.99 (m, 4H, CH2 cod). 13C{1H} NMR (298 K,
CDCl3): δ 182.37 (d, JC-Rh ) 50.9, CNCN), 121.72, 121.16 (CH),
98.46 (m, CH cod), 68.13 (d, JC-Rh ) 14.4, CH cod), 67.39 (d,
JC-Rh ) 15.1, CH cod), 59.89 (NCH2), 48.39 (s, NCH2), 45.64
(NCH3), 37.65 (NMe2), 33.32, 32.59, 29.22, 28.52 (CH2 cod). MS
(MALDI-TOF, DCTB matrix, CH2Cl2) m/z ) 364.2 [M - Cl]+,
ΛM (acetone) ) 0.82 Ω-1 cm2 mol-1
.
Preparation of [Rh(cod)(MeIm(CH2)3NMe2)][BF4] (16).
AgBF4 (47 mg, 0.24 mmol) was added to a solution of complex
12 (100 mg, 0.24 mmol) in CH3CN/acetone. After 6 h of stirring
a 0 °C the solid formed was separated by filtration. The resulting
yellow solution was concentrated to ca. 1 mL and treated with
diethyl ether to give a yellow solid. The solid was separated by
decantation, washed with diethyl ether, and dried in vacuo. Yield:
62%. Anal. Calcd for C17H29BF4N3Rh: C, 43.90; H, 6.28; N, 9.03.
154.1 [MeImH(CH2)2NMe2]+. ΛM (acetone) ) 1.42 Ω-1cm2mol-1
.
[RhCl(cod)(MeIm(CH2)3NMe2)] (12). Yield: 63% (Method A).
Anal. Calcd for C17H29ClN3Rh: C, 49.34; H, 7.06; N, 10.15. Found:
1
C, 49.06; H, 6.69; N, 9.75. H NMR (298 K, CDCl3): δ 6.86 (d,
JH4-H5 ) 1.8 Hz, 1H, CH), 6.80 (d, JH4-H5) 1.8 Hz, 1H, CH), 5.02
(m, 2H, CH cod), 4.66 (m, 1H, NCH2), 4.39 (m, 1H, NCH2), 4.09
(s, 3H, NMe), 3.36 (m, 1H, CH cod), 3.26 (m, 1H, CH cod), 2.41
(m, 6H, CH2 cod and NCH2), 2.30 (s, 6H, NMe2), 1.95 (m, 6H,
CH2 cod and CH2). 13C{1H} NMR (298 K, CDCl3): δ 121.79,
120.75 (CH), 98.39 (d, JC-Rh ) 7.1, CH cod), 98.24 (d, JC-Rh) 6.8,
CH cod), 68.23 (d, JC-Rh ) 14.7, CH cod), 67.41 (d, JC-Rh ) 14.6,
CH cod), 56.46, 48.71 (NCH2), 45.45 (NMe), 37.75 (NMe2), 33.36,
32.55, 29.23 (CH2 cod), 29.11 (CH2), 28.53 (CH2 cod). ESI-MS
(CH3CN) m/z ) 378.1 [M - Cl]+. ΛM (acetone) ) 3.60 Ω-1 cm2
1
Found: C, 44.10; H, 6.17; N, 9.09. H NMR (298 K, CDCl3): δ
7.06 (d, JH4-H5 ) 2.0, 1H, CH), 7.01 (d, JH4-H5 ) 2.0, 1H, CH),
5.65 (m, 1H, NCH2), 4.63 (m, 2H, CH cod), 4.32 (m, 1H, NCH2),
3.96 (s, 3H, NMe), 3.66 (m, 2H, CH cod), 2.68 (m, 3H, CH2 and
CH2 cod), 2.54 (m, 2H, CH2 cod), 2.41 (m, 6H, NMe2), 2.24 (m,
3H, CH2 and CH2 cod), 2.17 (m, 1H, CH2), 1.89 (s, 3H, CH2 and
CH2 cod). 13C{1H} NMR (298 K, CDCl3): δ 179.63 (d, JC-Rh
)
28.8, CN CN), 125.86, 123.99 (CH), 100.40 (d, JC-Rh ) 8.4, CH cod),
100.21 (d, JC-Rh ) 7.8, CH cod), 77.33 (d, JC-Rh ) 13.5, CH cod),
72.45 (m, CH cod), 65.13 (NCH2), 51.51 (NMe), 49.35 (NCH2),
39.21 (NMe2), 35.79 (CH2), 32.14, 31.60, 29.67, 27.86 (CH2 cod).
MS (MALDI-TOF, DCTB matrix, CH2Cl2) m/z ) 378.1 [M]+. ΛM
mol-1
.
[RhCl(cod)(t-BuIm(CH2)2NMe2)] (13). Yield: 63% (Method B).
Anal. Calcd for C19H33ClN3Rh: C, 51.65; H, 7.53; N, 9.59. Found:
1
(acetone) ) 74 Ω-1 cm2 mol-1
.
C, 51.15; H, 7.44; N, 9.57. H NMR (298 K, CDCl3): δ 7.09 (d,
JH4-H5 ) 1.8, 1H, CH), 7.00 (d, JH5-H4 ) 1.8, 1H, CH), 5.43 (m,
1H, NCH2), 4.96 (m, 2H, CH cod), 4.67 (m, 1H, NCH2), 3.27 (m,
2H, CH cod), 2.93 (m, 1H, NCH2), 2.78 (m, 1H, NCH2), 2.45 (m,
4H, CH2 cod), 2.39 (s, 6H, NMe2), 1.96 (s, 9H, t-Bu), 1.80 (m,
4H, CH2 cod). 13C{1H} NMR (298 K, CDCl3): δ 180.15 (d, JC-Rh
) 49.8, CNCN), 120.55, 119.55 (CH), 96.27 (d, JC-Rh ) 7.5, CH
cod), 94.01 (d, JC-Rh ) 7.5, CH cod), 69.84 (d, JC-Rh ) 15.1, CH
cod), 66.95 (d, JC-Rh ) 14.3, CH cod), 59.72 (NCH2), 58.22 (t-
Bu), 50.22 (NCH2), 45.66 (NMe), 33.25 (CH2 cod), 32.27 (CH3,
t-Bu), 31.85, 29.15, 28.50 (CH2 cod). MS (MALDI-TOF, DCTB
matrix, CH2Cl2) m/z ) 406.2 [M - Cl]+, 196.1 [t-BuImH
[Rh(cod)(MesIm(CH2)3NMe2)][BF4] (17). AgBF4 (37.6 mg,
0.19 mmol) and 15 (100 mg, 0.19 mmol) were reacted in CH3CN/
acetone at 0 °C for 6 h. Workup as described above gave the
compound as a yellow solid. Yield: 71%. Anal. Calcd for
C25H37BF4N3Rh: C, 52.74; H, 6.55; N, 7.38. Found: C, 52.79; H,
1
6.31; N, 7.39. H NMR (298 K, CDCl3): δ 7.45 (d, JH4-H5 ) 1.7,
1H, CH), 7.09 (s, 1H, CH Mes), 6.93 (s, 1H, CH Mes), 6.79 (d,
JH4-H5 ) 1.7, 1H, CH), 5.90 (m, 1H, NCH2), 4.79 (m, 1H, CH cod),
4.61 (m, 1H, NCH2), 4.06 (m, 1H, CH cod), 3.50 (m, 1H, CH cod),
3.13 (m, 1H, CH cod), 2.39 (m, 2H, CH2 cod), 2.29 (s, 9H, NMe2
and CH3 Mes), 2.22 (m, 3H, CH2 and CH2 cod), 2.18 (s, 3H, CH3
Mes), 1.85 (m, 3H, CH2 and CH2 cod), 1.73 (s, 3H, CH Mes),
1.65 (m, 3H, CH2 and CH2 cod), 1.55 (m, 1H, CH2). 13C{1H} NMR
(298 K, CDCl3): δ 139.47 (CN Mes), 135.33, 134.85, 134.24 (Mes),
129.32 (CH Mes), 125.32, 122.24 (CH), 98.97 (d, JCRh ) 8.7, CH
cod), 94.97 (m, CH cod), 72.64 (d, JCRh ) 11.8, CH cod), 71.38
(m, CH cod), 62.58, 47.14 (s, NCH2), 32.99, 30.84, 28.79, 28.30,
25.25 (s, CH2 cod and CH2), 20.99, 18.99, 17.78 (s, CH3). MS
(MALDI-TOF, DCTB matrix, CH2Cl2) m/z ) 482.2 [M]+. ΛM
(CH2)2NMe2]+. ΛM (acetone) ) 1.14 Ω-1 cm2 mol-1
.
[RhCl(cod)(t-BuIm(CH2)3NMe2)] (14). Yield: 72% (Method B).
Anal. Calcd for C20H35ClN3Rh: C, 52.69; H, 7.74; N, 9.22. Found:
1
C, 52.48; H, 7.44; N, 9.35. H NMR (298 K, CDCl3): δ 7.03 (d,
JH4-H5 ) 2.0, 1H, CH), 6.94 (d, JH5-H4 ) 2.0, 1H, CH), 5.25 (m,
1H, NCH2), 4.95 (m, 3H, CH cod and NCH2), 4.61 (m, 1H, NCH2),
3.29 (m, 3H, CH cod and NCH2), 2.38 (m, 5H, CH2 cod and CH2),
2.31 (s, 6H, NMe2), 1.98 (s, 9H, t-Bu), 1.93 (m, 5H, CH2 cod,
CH2). 13C{1H} NMR (298 K, CDCl3): δ 180.35 (d, JC-Rh ) 51.4,
CN CN), 119.00, 119.60 (s, CH), 96.27 (d, JC-Rh ) 7.7, CH cod),
93.99 (d, JC-Rh ) 7.5, CH cod), 69.78 (d, JC-Rh ) 15.5, CH cod),
67.07 (d, JC-Rh ) 14.4, CH cod), 58.29 (t-Bu), 56.86, 50.80 (NCH2),
45.53 (NCH3), 33.15 (CH2 cod), 32.30 (CH3, t-Bu), 31.98 (CH2
cod), 29.12 (CH2 cod and CH2), 28.59 (CH2 cod). MS (MALDI-
TOF, DCTB matrix, CH2Cl2) m/z ) 420.1 [M - Cl]+, 210.1
(acetone) ) 77 Ω-1 cm2 mol-1
.
Preparation of [Rh(cod)(MeIm(CH2)3ImMe)][BF4] (18). A
mixture MeIm(CH2)3ImMe (0.138 g, 0.5 mmol) and Ag2O (0.462
g, 2.0 mmol) was stirred in water (10 mL) at 0 °C for 30 min. The
excess of Ag2O was removed by filtration, and a saturated solution
of NaBF4 (0.137 g, 1.25 mmol) in water was added to the resulting
solution. The white solid formed was filtered and dried under
vacuum. The solid was dissolved in CH2Cl2 at reflux temperature,
[{Rh(µ-Cl)(cod)}2] (0.25 mmol, 123.3 mg) was added, and the
mixture was heated for further 30 min. The AgCl formed was
removed by filtration, and the solvent was pumped off from the
[t-BuImH(CH2)3NMe2]+. ΛM (acetone) ) 0.38 Ω-1 cm2 mol-1
.
[RhCl(cod)(MesIm(CH2)3NMe2)] (15). Yield: 63% (Method B).
Anal. Calcd for C25H37ClN3Rh: C, 57.97; H, 7.20; N, 8.11. Found:
1
C, 56.94; H, 7.34; N, 7.97. H NMR (298 K, CDCl3): δ 7.03 (s,

234 Organometallics, Vol. 27, No. 2, 2008
Jiménez et al.
resulting yellow solution. The yellow residue was washed and
treated with pentane until a yellow solid was formed, which was
isolated by filtration, washed with pentane, and dried in vacuum.
The compound was recrystallized from THF/pentane. Yield: 63%.
Anal. Calcd for C19H28BF4N4Rh: C, 45.44; H, 5.62; N, 11.16.
Data were corrected for Lorentz and polarization effects, and
multiscan absorption corrections were applied with SADABS
program.58 The structures were solved by Patterson method and
completed by successive difference Fourier syntheses (SHELXS-
86).59 Refinement, by full-matrix least-squares on F2 with
SHELXL97,59 was similar for both structures, including isotropic
and subsequent anisotropic displacement parameters for all non-
hydrogen atoms. Most of the hydrogen atoms were included from
observed positions and refined as free isotropic atoms; details are
included below. All of the highest electronic residuals (smaller than
1.0 e/Å3) were observed in close proximity of the Rh metal and
have no chemical sense. Atomic scattering factors, corrected for
anomalous dispersion, were used as implemented in the refinement
program.59
Crystal Data for Compound 6. C16H28Cl2N3Rh, M ) 436.22;
yellow needle, 0.198 × 0.055 × 0.052 mm3; trigonal, R-3; a )
36.9644(10), c ) 7.2845(4) Å; Z ) 18; V ) 8619.8(6) Å3; Dc )
1.513 g/cm3; µ ) 1.171 mm-1, min and max transmission factors
0.801 and 0.942; 2θmax ) 56.70°; 30 250 reflections collected, 4698
unique [Rint ) 0.0396]; number of data/restrains/parameters 4698/
0/287; final GoF 1.020, R1 ) 0.0289 [4066 reflections, I > 2σ(I)],
wR2 ) 0.0684 for all data. Only hydrogens of three methylenic
-CH2- groups of the cod molecule required a restrained refinement
(calculated positions and positional and displacement riding refine-
ment); all the rest were refined as free isotropic atoms.
1
Found: C, 45.30; H, 5.60; N, 10.72. H NMR (298 K, CDCl3): δ
6.96 (d, JH4-H5 ) 1.8 Hz, 1H, CH), 6.88 (d, JH4-H5 ) 1.8 Hz, 1H,
CH), 4.93 (m, 2H, NCH2), 4.50 (m, 4H, CH cod), 4.35 (m, 2H,
NCH2), 3.96 (s, 6H, NMe), 2.47 (m, 4H, CH2 cod), 2.25 (m, 4H,
CH2 cod), 1.75 (m, 2H, CH2). 13C{1H} NMR (298 K, CDCl3): δ
181.8 (d, JC-Rh) 47.3, CN CN), 122.86, 122.64 (CH), 89.71 (d, JC-Rh
)
7.8, CH cod), 88.52 (d, JC-Rh) 7.7, CH cod), 78.86, 78.67 (s, CH
cod), 52.55 (NCH2), 37.81 (NMe), 32.76 (CH2), 30.83, 30.69, 30.49
(s, CH2 cod). ESI-MS (CH3CN) m/z ) 415.1 [M]+, 307.0 [M -
cod]+.
General Procedure for Hydrosilylation of 1-Alkynes with
HSiMe2Ph. A 5 mm NMR tube was charged with the catalyst
precursors (11–18) (7.7 × 10-4 mmol), CDCl3 (0.5 mL), the
corresponding alkyne (PhCt CH, t-Bu-Ct CH, 1-hexyne or
Et3Ct CH) (0.077 mmol), and a light excess of HSiMe2Ph (0.085
mmol). The solution was kept in a thermostatic bath at 60 °C, and
the progress of the reactions was monitored by 1H NMR spectros-
copy. The reaction products were identified by NMR by comparison
with literature reported data. The catalytic solutions obtained from
Et3Ct CH were filtered through a pad of Celite, and the volatiles
were removed under reduced pressure. The new compounds were
Crystal Data for Compound 11. C16H27ClN3Rh, M ) 399.77;
yellow irregular block, 0.167 × 0.125 × 0.079 mm3; monoclinic,
P21/c; a ) 10.3428(7), b ) 13.0938(9), c ) 12.7756(9) Å, ꢀ )
97.2510(10)°; Z ) 4; V ) 1716.3(2) Å3; Dc ) 1.547 g/cm3; µ )
1.148 mm-1, min and max transmission factors 0.831 and 0.915;
1
characterized by H NMR and GC-MS.
1-(Dimethylphenilsilyl)-1-(triethylsilyl)ethene. 1H NMR
(CDCl3): δ ) 7.35, 7.19 (m, 5H, Ph), AB system (δA ) 6.22, δB
) 6.21, JAB ) 5.2, 2H, CH), 0.64 (t, JHH ) 7.8, 6H, CH2), 0.32 (q,
JHH ) 7.8, 9H, CH3), 0.19 (s, 6H, CH3).
2θmax ) 56.60°; 20 970 reflections collected, 4181 unique [Rint
)
1
0.0310]; number of data/restrains/parameters 4181/0/298; final GoF
1.106, R1 ) 0.0233 [3921 reflections, I > 2σ(I)], wR2 ) 0.0522
for all data. All hydrogens were refined as free isotropic atoms.
(E)-2-(Dimethylphenylsilyl)-1-(triethylsilyl)ethene. H NMR
(CDCl3): δ ) 7.32, 7.15 (m, 5H, Ph), AB system (δA ) 6.55, δB
) 6.47, JAB ) 22.8, 2H, CH), 0.76 (t, JHH ) 8.0, 6H, CH2), 0.41
(q, JHH ) 8.0, 9H, CH3), 0.15 (s, 6H, CH3).
Acknowledgment. Financial support from Ministerio de
Educación y Ciencia (MEC/FEDER) is gratefully acknowl-
edged (Projects CTQ2006-03973/BQU and Factoría de
Cristalización, CONSOLIDER INGENIO-2010). M.I.B.
(project BQU2003-05412-C02-01) is grateful for a graduate
scholarship, and V.G. thanks the Socrates-Erasmus Program
for financial support and mobility.
Synthesis of ꢀ-Hexen-1-enyl-methyl-diphenyl-silane. A Schlenk
tube with a screw top was charged with the catalyst precursors 12
(38.5 × 10-3 mmol, 16 mg), CHCl3 (5 mL), 1-hexyne (3.85 mmol,
456 µL), and HSiMe2Ph (4.25 mmol, 675 µL). The solution was
stirred at 60 °C for 30 min and then transferred to a round-botton
flask under argon. Distillation in a Kugelrohr oven 160 °C (ca. 0.1
Torr) gave ꢀ-hexen-1-enyl-methyl-diphenyl-silane as a colorless
liquid (Z:E ) 94:6, 817 mg, 97%). The R isomer was observed
only in traces amounts.
X-ray Structural Determination of Compounds [MeImH
(CH2)2NMe2][RhCl2(cod)] (6) and [RhCl(cod)(MeIm(CH2)2
NMe2)] (11). Suitable yellow crystals for X-ray diffraction experi-
ments were obtained by slow diffusion of diethyl ether (6) or
pentane (11) into concentrated THF solutions of the complexes.
Intensity data were collected at low temperature (100(2) K) on a
Bruker SMART CCD area detector diffractometer equipped with
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) using
narrow frames (0.3° in ω). Cell parameters were refined from the
observed setting angles and detector positions of strong reflections
(9406 reflections, 2θ < 56.3°, 6; 9743 reflections, 2θ < 56.6°, 11).
Supporting Information Available: X-ray crystallographic
information files containing full details of the structural analysis
of complexes 6 and 11 in CIF format. This material is available
free of charge via Internet at http://pubs.acs.org.
OM700728A
(58) SAINT+ Software for CCD Diffractometers; Bruker AXS: Madison,
WI, 2000. Sheldrick, G. M. SADABS Program for Correction of Area
Detector Data; University of Göttingen: Göttingen, Germany, 1999.
(59) SHELXTL Package, v. 6.10; Bruker AXS: Madison, WI, 2000.
Sheldirck, G. M. SHELXS-86 and SHELXL-97; University of Göttingen;
Göttingen, Germany, 1997.