New acyclic (π-Allyl)-closo-rhodacarboranes with an agostic CH 3...Rh bonding interaction that operate as unmodified rhodium-based catalysts for alkene hydroformylation

Article abstract of DOI:10.1021/om300432j

A series of new agostic (CH₃...Rh) (π-allyl)-closo- rhodacarboranes (π-allyl = 1,1-dimethylallyl, 1,2-dimethylallyl, 1,1,2-trimethylallyl, 1,2,3-trimethylallyl), stable in the solid state, have been synthesized via one-pot reactions between the K⁺ salts of the [7-R-8-R′-7,8-nido-C₂B₉H₁₀]^- monoanions (1a, R = R′ = Me; 1b, R,R′ = μ-(o-xylylene); 1c, R,R′ = μ-(CH₂)₃) and the di-μ-chloro cyclooctene rhodium dimer [(η²-C₈H₁₄) ₄Rh₂(μ-Cl)₂] (2) in the presence of a 3-fold excess of the conjugated 1,3-dienes 2-methylbuta-1,3-diene (isoprene, 3), 2,3-dimethylbuta-1,3-diene (4), and 3-methylpenta-1,3-diene (5). The agostic structures of [3-{(1-3-η³)-1,1-dimethylallyl}-1,2-(CH ₃)₂-3,1,2-closo-RhC₂B₉H ₉] (7a) and [3-{(1-3-η³)-1,1,2-trimethylallyl}-1,2- (CH₃)₂-3,1,2-closo-RhC₂B₉H ₉] (8a) have been unambiguously confirmed by single-crystal X-ray diffraction studies. Two of these π-allyl complexes prepared were evaluated for their efficacy in hydroformylation of the model alkenes under syngas (CO/H₂) using supercritical carbon dioxide (scCO₂) as the solvent, and both display excellent conversion and high regioselectivity in the formation of aldehyde products.

Full text of DOI:10.1021/om300432j

Article
pubs.acs.org/Organometallics
New Acyclic (π-Allyl)-closo-rhodacarboranes with an Agostic CH3···Rh
Bonding Interaction That Operate as Unmodified Rhodium-Based
Catalysts for Alkene Hydroformylation
Konstantin I. Galkin, Sergey E. Lubimov, Ivan A. Godovikov, Fedor M. Dolgushin,
Alexander F. Smol’yakov, Elena A. Sergeeva, Vadim A. Davankov, and Igor T. Chizhevsky*
A. N. Nesmeyanov Institute of Organoelement Compounds, 28 Vavilov Street, 119991, Russian Federation
S
* Supporting Information
ABSTRACT: A series of new agostic (CH3···Rh) (π-allyl)-closo-rhodacarboranes
(π-allyl = 1,1-dimethylallyl, 1,2-dimethylallyl, 1,1,2-trimethylallyl, 1,2,3-trimethy-
lallyl), stable in the solid state, have been synthesized via one-pot reactions
between the K+ salts of the [7-R-8-R′-7,8-nido-C2B9H10]− monoanions (1a, R =
R′ = Me; 1b, R,R′ = μ-(o-xylylene); 1c, R,R′ = μ-(CH2)3) and the di-μ-chloro
cyclooctene rhodium dimer [(η2-C8H14)4Rh2(μ-Cl)2] (2) in the presence of a 3-
fold excess of the conjugated 1,3-dienes 2-methylbuta-1,3-diene (isoprene, 3), 2,3-
dimethylbuta-1,3-diene (4), and 3-methylpenta-1,3-diene (5). The agostic structures of [3-{(1−3-η3)-1,1-dimethylallyl}-1,2-
(CH3)2-3,1,2-closo-RhC2B9H9] (7a) and [3-{(1−3-η3)-1,1,2-trimethylallyl}-1,2-(CH3)2-3,1,2-closo-RhC2B9H9] (8a) have been
unambiguously confirmed by single-crystal X-ray diffraction studies. Two of these π-allyl complexes prepared were evaluated for
their efficacy in hydroformylation of the model alkenes under syngas (CO/H2) using supercritical carbon dioxide (scCO2) as the
solvent, and both display excellent conversion and high regioselectivity in the formation of aldehyde products.
cyclic (π-allyl)-closo-metallacarborane clusters are, at
present, well documented among 12-vertex icosahedral
18-electron (π-allyl)-closo-metallacarboranes involve the direct
reactions of the dicarbollide [nido-7,n-R,R′-C2B9H9]2− (n = 8,
9) dianions with appropriately constructed π-allyl transition
metal halide complexes.2,3 We found that the room-temper-
ature reactions of the K+ salts of the [7-R-8-R′-7,8-nido-
C2B9H10]− monoanions (1a, R = R′ = Me; 1b, R,R′ = μ-(o-
xylylene); 1c, R,R′ = μ-(CH2)3) with the di-μ-chloro
cyclooctene rhodium complex [(η2-C8H14)4Rh2(μ-Cl)2] (2)
in the presence of a 3-fold molar excess of the conjugated 1,3-
dienes 2-methylbuta-1,3-diene (isoprene, 3), 2,3-dimethylbuta-
1,3-diene (4), and 3-methylpenta-1,3-diene (5) proceed
smoothly in benzene, yielding together a short series of seven
new (π-allyl)-closo-rhodacarboranes: [3-{(1−3-η3)-C5H9}-1,2-
(CH3)2-3,1,2-closo-RhC2B9H9] (6a and 7a, two isomers) and
[3-{(1−3-η3)-C5H9}-1,2-μ-(o-xylylene)-3,1,2-closo-RhC2B9H9]
(6b and 7b, two isomers), [3-{(1−3-η3)-1,1,2-trimethylallyl}-1-
R-2-R′-3,1,2-closo-RhC2B9H9] (8a−c), and [3-{(1−3-η3)-1,2,3-
trimethylallyl}-R-2-R′-3,1,2-closo-RhC2B9H9] (9a,b), respec-
tively (Scheme 1).
In contrast to the last two series of compounds 8a−c and
9a,b, complexes 6 and 7 exist in solution as a mixture of
isomers with 1,2-dimethylallyl (6a,b) and 1,1-dimethylallyl
(7a,b) ligands at the rhodium vertex, which are, moreover, in
equilibrium. Thus, lowering of the temperature of the 1H NMR
spectra of 6 or 7 from +22 to −80 °C leads to a change in the
relative ratio of isomers from ca. 1:1.5 to 1:2.25 for 6a and 7a
and from ca. 1:1 to 1:1.5 for 6b and 7b, respectively. Note that
A
metallacarboranes;1−3 some other (π-allyl)-metallacarborane
complexes with different vertices were also reported.4 Many of
them are very versatile starting materials with great potential in
the carborane-containing cluster chemistry of the d-block
metals and play a significant role in the development of novel
chemistry in this area.1a,2d,4c,d On the other hand, none of these
(π-allyl)metallacarboranes found in the literature can be
regarded as the agostic (C−H···M or CH3···M) species that
could be potentially valuable in homogeneous catalysis by
metallacarboranes.5 In this connection, the development of a
simple and efficient synthesis of π-allyl-containing metal-
lacarborane systems stabilized via an agostic bonding
interaction and assessment of their role in catalysis are of
considerable interest.
Herein, we report our preliminary results on facile one-pot
reactions leading to isolation of acyclic (π-allyl)-closo-
rhodacarboranes of the general formula [3-{π-(R″-allyl)}-1-R-
2-R′-3,1,2-closo-RhC2B9H9] (where R″ is an aliphatic sub-
stituent) that exhibit an agostic CH3···Rh bonding interaction.
Two of these phosphorus-free π-allyl complexes have been
tested as catalyst precursors for the regioselective hydro-
formylation of model alkenes under syngas (CO/H2) using
supercritical carbon dioxide (scCO2) as the solvent. Both
species, even in the absence of the typical cocatalysts such as
phosphines and phosphites, exhibit excellent conversion and
high regioselectivity in the formation of the desired saturated
formyl derivatives.
With some exceptions,1 the most frequently employed
synthetic routes to the reported anionic or neutral/zwitterionic
Received: May 18, 2012
© XXXX American Chemical Society
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Scheme 1
Figure 1. ORTEP representation of the molecular structures of 7a (left) and 8a (right) with the numbering scheme for these complexes. Ellipsoids
are drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg) for complexes 7a and 8a, respectively, are as follows: Rh(3)−
C(1) = 2.180(2), 2.180(2), Rh(3)−C(2) = 2.146(2), 2.140(2), Rh(3)−B(4) = 2.188(3), 2.190(2), Rh(3)−B(7) = 2.199(3), 2.202(2), Rh(3)−B(8)
= 2.135(3), 2.138(2), Rh(3)−C(1′) = 2.168(3), 2.168(2), Rh(3)−C(2′) = 2.164(2), 2.187(2), Rh(3)−C(3′) = 2.172(3), 2.153(2), Rh(3)···C(4′) =
2.515(3), 2.484(2), Rh(3)···H(4′A) = 2.09(4), 2.03(3), C(1)−C(2) = 1.790(4), 1.839(3), C(1′)−C(2′) = 1.403(4), 1.415(3), C(2′)−C(3′) =
1.429(4), 1.423(3); C(1′)−C(2′)−C(3′) = 119.8(3), 116.71(17), C(4′)−H(4′A)−Rh(3) = 53(3), 52.9(14).
the most likely intermediates through which these isomeric
complexes 6a,b and 7a,b undergo interconversion appeared to
be the classical diene hydride species6 with the terminal hydride
at the rhodium vertex, [3-(η4-diene)-3-H-1-R-2-R′-3,1,2-closo-
RhC2B9H9]. These intermediate species, however, could not be
observed at the lowest temperature limit that was achieved
experimentally (−80 °C for both 6 and 7 series).
Since all of the above π-allyl complexes proved to be quite
stable both in the solid state and in solution, these compounds
would be expected to contain a two-electron, three-center
bonding arrangement, either C−H···Rh or CH3···Rh. Indeed,
an analysis of the 1H and 13C{1H} NMR spectra of each pair of
isomeric complexes 6a/7a and 6b/7b as well as of other π-allyl
complexes 8a−c and 9a−c show the presence of the one
unique π-allyl methyl resonance with very high shielding values
compared to the others (6a, δ, ppm (−80 °C) −0.21 (CH3-
agost) and 12.7 (CH3-agost); 7a, δ, ppm (−80 °C) −0.17 (s,
CH3-agost) and 18.1 (CH3-agost); 8b, δ, ppm (22 °C) −0.9 (s,
CH3-agost) and 16.7 (CH3-agost); 9a, δ, ppm, (22 °C) +0.29
(s, CH3-agost) and +12.8 (CH3-agost)); the room- and low-
temperature H NMR spectra for 6b/7b are given in the
1
Supporting Information. Such methyl resonances observed in
the highest field of the NMR spectra of the above species
which, in addition, displayed no visible J(103Rh,Hag.) coupling in
the 1H NMR spectra are typical of π-allyl organometallic
complexes in which the CH3 group is involved in the agostic
CH3···M interaction.7
A low-temperature X-ray diffraction study of 7a and 8a8
provided firm confirmation of their agostic structure (Figure 1).
The high quality of monocrystals grown from both samples
allowed us to locate objectively and reliably refine all hydrogen
atoms, including those forming the agostic bond. As expected,
one of the methyl groups in complexes 7a and 8a, positioned
anti to the π-allyl ligands, is involved (through one of its H
atoms) in the agostic bonding interaction to the rhodium
center, thus forming the very short H(4′A)···Rh distances
2.09(4) and 2.03(3) Å in 7a and 8a, respectively. The latter
distances, although they are at the upper limit for known
B
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a
Table 1. Results of Hydroformylation Reactions of Selected Alkenes Catalyzed by (π-Allyl)-closo-rhodacarboranes 8c and 9a
8c
9a
b
b
b
b
substrate R in RCHCH2
conversn,
%
regioselectivity, branched/linear
conversn,
%
regioselectivity, branched/linear
Ph
100
92
88/12
66/34
89/11
89/11
92/8
100
30
88/12
66/34
86/14
97/3
c
Ph
4-Me-Ph
4-Br-Ph
4-iPr-Ph
tBu
93
91
100
45
100
95
88/12
0/100
0/100
98
0/100
0/100
100
76
(S)-limonene
83
a
All reactions were performed in a stainless steel high-pressure autoclave (10 mL capacity): the catalysts (0.01 mmol) and substrate (2 mmol) were
placed into a reactor which was pressurized with syngas (30 atm, CO/H2 = 1/1) and then filled with scCO2 via a syringe press. The mixture was
allowed to equilibrate to the reaction temperature (60 °C, ∼10 min) and stirred for 3−5 h. The reactor was cooled to 5 °C and slowly depressurized.
b
1
Conversion and regioselectivity were determined from the analysis of the H NMR spectra of the liquid reaction mixture (see the Supporting
c
Information). Reactions were carried out in toluene under reflux.
agostic C−H···M distances (1.77−2.2 Å),6c,9 may usefully be
compared with that found in [{(1−3-η3)-C6H11}Rh(η5-
C5Me5)] (CH2−H···Rh = 1.88 Å),10 the known Cp* analogue
of 8a. Interestingly, both complexes 7a and 8a are characterized
by rather long C(1)···C(2) cluster distances of 1.790(4) and
1.839(3) Å, respectively. These values seem to be typical of so-
called semipseudocloso type metallacarboranes, which are now
well recognized.11
The reactivity associated with these and related acyclic π-allyl
metal carborane complexes of rhodium and iridium as well as a
detailed study of the catalytic activity of (π-allyl)-closo-
rhodacarboranes of these series (other then 8c and 9a),
including comparisons with the related Cp* rhodium
derivatives with the aim of elucidating the role of carborane
ligands in the catalytic process, are currently in progress in our
group.
The one-pot method we currently explored for the synthesis
of the agostic complexes 6, 7, 8a−c, and 9a,b is conceptually
based on the ligand-exchange reactions. The first step of these
reactions would involve the displacement of cyclooctene
ligands from 2 for the acyclic diene 3, 4, or 5 to form one of
the two possible intermediate species, either [(η4-diene)2RhCl]
or [(η4-diene)RhCl]2, as might be expected by analogy with
EXPERIMENTAL SECTION
■
General Considerations. All reactions were carried out under an
atmosphere of dry argon using standard Schlenk techniques. Solvents,
including those used for column chromatography, were distilled from
appropriate drying agents under argon prior to use. Chromatography
columns (ca. 12−15 cm in length and 1.8 cm in diameter) were
packed with silica gel (Acros, 230−400 mesh). The starting rhodium
and nido-carborane reagents 2,14 1a,15 and 1c16 were prepared as
described in the literature; [1,2-μ-(o-xylylene)-1,2-closo-C2B10H10]17
was degraded to form 1b according to the literature methods.15 The
1H, 11B, and 13C NMR spectra were obtained on Bruker AMX-400 and
Avance-600 instruments (J values are given in Hz). IR spectra in KBr
were recorded on a Nicolet Magna-750 spectrometer. Proton and
boron chemical shifts were referenced to residual protons in CD2Cl2
(5.32 ppm vs Me4Si), with downfield shifts taken as positive.
Elemental analyses were performed by the Analytical Laboratory of
the Institute of Organoelement Compounds of the RAS.
reactions of the same dienes 3 and 4 with [(C2H4)2RhCl]2,12
a
closely related acyclic analogue of 2. Since the endo-hydrogen
atom in the nido-carboranes 1a,b displays acidic character, one
may consider that the second step of these three-component
reactions is, probably, protonation at the metal center of the
aforementioned intermediate complexes; then a metal hydride
could add to one of the double bonds of the η4-diene ligands,
giving rise to an unsymmetrical η3-allyllic unit. The ultimate
formation of (π-allyl)-closo-rhodacarboranes can be readily
explained through an open-face metalation of the nido-
carborane cage ligand formed as the dianionic {7-R-8-R′-nido-
C2B9}2− species after elimination of an endo-hydrogen atom
from starting monoanions 1a,b.
The preliminary screening of two arbitrarily selected π-allyl
complexes, 8c and 9a, as catalyst precursors for the hydro-
formylation of the model alkenes under syngas using either
scCO2 or toluene as solvent has been performed. Examination
revealed (Table 1) that both rhodacarborane compounds are
unique in their catalytic activity and display success in the
conversion of styrene, its 4-substituted derivatives, and some
other alkenes and terpenoids into their saturated aldehyde
products, where very good to excellent yields (in some cases
quantitative) as well as high regioselectivities have been
achieved. Remarkably, these procatalysts work very well even
without phosphine or phosphite as cocatalyst. Although the
catalytic hydroformylation of alkenes with a rare unmodified
rhodium-based system is known,13 the efficient use of such
phosphorus-free carborane-containing procatalysts, as far as we
are aware, is unprecedented for hydroformylation under the
conditions described above.
General Method for the Synthesis of closo-(π-Allylic)-
rhodacarborane Complexes 6, 7, 8a−c, and 9a,b. To a solution
of 2 (0.1 mmol) in 5 mL of degassed benzene was added dropwise the
1,3-diene 3, 4, or 5 (0.3 mmol). The resulting mixture was stirred for
0.5 h at ambient temperature, and then the corresponding potassium
salt of nido-carborane 1a, 1b, or 1c (0.24 mmol) was added in one
portion as a solid. After 1−3 h of vigorous stirring the reactions were
complete (TLC control, eluent CH2Cl2/n-hexane, 1/1), and the deep
red solution that formed was purified by column chromathography.
Eluting with CH2Cl2/n-hexane (1/2) gave a colored fraction, removal
of solvent from which followed by washing with n-hexane afforded 6,
7, 8a−c, or 9a,b as crystalline solids that could be successfully
recrystallized from a CH2Cl2/n-hexane mixture.
Preparation of Isomeric Complexes [3-{(1−3-η3)-C5H9}-1,2-
(CH3)2-3,1,2-closo-RhC2B9H9] (6a and 7a). The general method
described above was employed: 2 (50 mg, 0.07 mmol), 3 (21 μL, 0.21
mmol), 1a (35 mg, 0.175 mmol), degassed benzene (2 mL), reaction
time, 2 h. Yield of 6 (light red microcrystals): 37 mg (82%).
C
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1
1
Selected NMR characterization data are as follows. H NMR (600
MHz, CD2Cl2, −80 °C; J(H,H), Hz; ratio of isomers 6a:7a = 1:2.25):
6.00 [br s, 1H, H(1′), 6a], 4.75 [t-like, 1H, H(2′), 7a], 4.25 [m, 2H,
red crystals): 76 mg (76%). H NMR (400 MHz, CD2Cl2, 22 °C;
J(H,H), Hz): 4.39 [d, 1H, Jgem = 1.7, H(3′-syn)], 2.75 [m, 2H, H(3′-
anti), −CH2-carb], 2.66 (t, 2H, J = 7.7, −CH2-carb), 2.51 (m, 1H,
−CH2-carb), 2.40 (m, 1H, −CH2-carb), 2.34 [s, 3H, CH3(syn)], 2.11
(s, 1H, −CH2-carb), 1.68 [d, 3H, J = 2.3 Hz, CH3(2′)], +0.09 [s, 3H,
CH3(anti, agost)]. 13C{1H} NMR (101 MHz, CD2Cl2, 22 °C;
J(Rh,C), Hz): 112.9 [d, J = 6.2, C(2′)], 97.9 [d, J = 6.5, C(1′)], 89.5
(C-carb), 84.9 (C-carb), 58.5 [d, J = 11.1, C(3′)]; 39.9, 38.5, 33.1
(−CH2-carb), 21.3 [CH3(syn)], 19.5 [C(2′)-CH3], 19.1
[CH3(anti,agost)].
H(3′-syn)-6a, 7a], 2.66 [br s, 1H, H(3′-anti), 6a], 2.55 [br d, 1H, Jvic
=
9.8, H(3′-anti), 7a], 2.33 [s, 3H, CH3(syn), 7a], 2.21 and 2.13 (s, 3H +
3H, CH3-carb, 6a), 2.17 and 2.08 (s, 3H + 3H, CH3-carb, 7a), 1.65 [s,
3H, CH3(2′), 6a], −0.17 [s, 3H, CH3(anti, agost), 7a], −0.21 [s, 3H,
CH3(agost), 6a]. 13C{1H} NMR (100.61 MHz; CD2Cl2, 25 °C;
J(C,Rh), Hz): 119.7 [C(2′), 6a], 102.6 [C(1′), 7a], 102.1 [C(2′), 7a],
93.5, 91.4, 85.9−84.9 (C-carb, 6a, 7a), 84.2 [C(1′), 6a], 58.9 [C(3′),
6a], 55.7 [d, J = 7.9, C(3′), 7a], 31.1, 31.2, 29.0, 28.4 (CH3-carb, 6a,
7a), 24.7 [CH3(syn), 7a], 22.3 [C(2′)-CH3, 6a], 18.1 [CH3(anti,
agost), 7a], 12.7 [CH3(anti, agost), 6a].
Preparation of [3-{(1−3-η3)-C6H11}-1,2-(CH3)2-3,1,2-closo-
RhC2B9H9] (9a). The general method described above was employed:
2 (53 mg, 0.074 mmol), 5 (27 μL, 0.222 mmol), 1a (37 mg, 0.187
mmol), degassed benzene (4 mL), reaction time 0.3 h. Yield of 8a
(orange microcrystals): 33 mg, 65%.
Preparation of Isomeric Complexes [3-{(1−3-η3)-C5H9}-1,2-μ-
(o-xylylene)-3,1,2-closo-RhC2B9H9] (6b and 7b). The general
method described above was employed: 2 (72 mg, 0.1 mmol), 3 (30
μL, 0.3 mmol), 1b (69 mg, 0.25 mmol), degassed benzene (5 mL),
reaction time 1 h. Yield of 6b and 7b (deep red microcrystals): 53 mg
1
(62%). Selected NMR characterization data are as follows. H NMR
(600 MHz, CD2Cl2, −80 °C; J(H,H), Hz; ratio of isomers 6b:7b =
1:1.5): 7.21−6.91 (8H, H-aryl, 6b, 7b), 5.81 [q, 1H, Jq = 6.2, H(1′),
6b], 4.54 [dd, 1H, Jvic(1) = 7.4, Jvic(2) = 10.4, H(2′), 7b], 4.41 [br s, 1H,
H(3′-syn), 6b], 4.39 [br d, 1H, Jvic = 7.4, H(3′-syn), 7b], 4.01 [d, 1H,
JAB = 17.0, CHH-aryl, 6b], 3.85 (d, 1H, JAB = 17.0, CHH-aryl, 6b),
3.88 − 3.56 (3 m, 6H, CH2-aryl, 6b, 7b), 2.29 [br d, 1H, Jvic = 10.4,
H(3′-anti), 7b], 2.23 [s, 3H, CH3(syn), 7b], 2.05 [br s, 1H, H(3′-anti),
6b], 1.45 [s, 3H, CH3(2′), 6b], −0.38 [d, 3H, Jd = 6.2, CH3(agost),
6b], −1.03 [s, 3H, CH3(anti, agost), 7b]. 13C{1H} NMR (101 MHz;
CD2Cl2, 22 °C; J(C,Rh), Hz): 134.0, 132.5, 130.6, 130.5, 130.3, 129.9,
129.6, 129.0, 128.8 (C-aryl), 119.8 [C(2′), 6b], 102.2 [C(1′), 7b],
102.1 [C(2′), 7b], 80.2 [d, J = 7.4, (C(1′), 6b], 78.6, 74.9, 74.3, 72.1
(C-carb), 68.4 [d, J = 4.0, C(3′), 6a], 60.6 [d, J = 10.4, C(3′), 7a],
43.9, 43.4, 43.4, 43.0 (CH2-aryl), 25.4 [CH3(syn), 7b], 22.7 [C(2′)-
CH3, 6b], 16.6 [CH3(anti, agost), 7b], 12.3 [CH3(anti, agost), 6b].
Preparation of [3-{(1−3-η3)-C6H11}-1,2-(CH3)2-3,1,2-closo-
RhC2B9H9] (8a). The general method described above was employed:
2 (72 mg, 0.1 mmol), 4 (34 μL, 0.3 mmol), 1a (50 mg, 0.25 mmol),
degassed benzene (4 mL), reaction time 0.5 h. Yield of 8a (light red
microcrystals): 65 mg, 94%.
1H NMR (400 MHz, CD2Cl2, 22 °C): 5.81 [br m, 1H, H(1′-syn)],
3.71 [br m, 1H, H(3′-anti)], 2.36 (s, 3H, CH3-carb), 2.11 (s, 3H, CH3-
carb), 1.96 [br s, 3H, CH3(syn)], 1.69 [br s, 3H, CH3(2′)], 0.29 [br s,
3H, CH3(anti, agost)]. 13C{1H} NMR (101 MHz, CD2Cl2, 22 °C):
118.8 [C(2′)], 90.1, 84.0 (C-carb), 80.4 [C(1′)], 78.3 [C(3′)], 30.3
(CH3-carb), 28.7 (CH3-carb), 18.4 [C(2′)-CH3], 15.5 [CH3(syn)],
12.8 [s, CH3(anti, agost)].
Preparation of [3-{(1−3-η3)-C6H11}-1,2-μ-(o-xylylene)-3,1,2-
closo-RhC2B9H9] (9b). The general method described above was
employed: 2 (150 mg, 0.21 mmol), 5 (71 μL, 0.63 mmol), 1b (144
mg, 0.525 mmol), degassed benzene (6 mL), reaction time 3 h. Yield
1
of 9b (deep red microcrystals): 118 mg, 67%). H NMR (600 MHz,
CD2Cl2, −50 °C; J(H,H), Hz): 7.31 (m, 1H, H-aryl), 7.26 (d, 1H, Jd =
7.3, H-aryl), 7.15 (t-like, 1H, Jt = 7.1, H-aryl), 5.66 [q-like, 1H, Jq = 6.8,
H(1′-syn)], 4.10 [d, 1H, JAB = 16.3, CHH-aryl], 4.05 (d, 1H, JAB= 16.3,
CHH-aryl), 3.58 (d, 1H, JAB= 16.4, CHH-aryl), 3.37 (d, 1H, JAB= 16.4,
CHH-aryl), 2.21 [br s, 1H, H(3′-anti)], 1.78 [d, 3H, Jd = 5.5,
CH3(syn)], 1.28 [s, 3H, CH3(2′)], 0.56 [d, 3H, Jd = 6.8, CH3(anti)].
13C{1H} NMR (101 MHz, CD2Cl2, 20 °C, J(C,Rh), Hz): 134.6, 131.0,
129.5, 129.1, 128.7, 126.8 (C-aryl), 118.6 [d, J = 5.2, C(2′)], 89.9 [br s,
C(3′)], 77.0 (C-carb), 75.8 [d, J = 8.5, C(1′)], 66.3 (C-carb), 43.0
(CH2-aryl), 42.8 (CH2-aryl), 19.6 [C(2′)-CH3], 15.3 [CH3(anti,
agost)], 14.7 [CH3(syn)].
1H NMR (600 MHz, CD2Cl2, −40 °C): 4.13 [br s, 1H, H(3′-syn)],
2.46 [br s, 1H, H(3′-anti)], 2.24 [s, 3H, CH3(syn)], 2.17(s, 3H, CH3-
carb), 2.11 (s, 3H, CH3-carb), 1.64 [s, 3H, CH3(2′)], −0.24 [s, 3H,
CH3(anti, agost)]. 13C{1H} NMR (151 MHz, CD2Cl2, −40 °C;
J(C,Rh), Hz): 111.5 [d, J = 6.1, C(2′)], 97.4 [d, J = 5.6, C(1′)], 88.8
(C-carb), 78.9 (C-carb), 55.8 [d, J = 10.2, C(3′)], 30.9 (CH3-carb),
27.3 (CH3-carb), 20.0 [CH3(syn)], 19.2 [C(2′)-CH3], 18.4 [CH3(anti,
agost)].
ASSOCIATED CONTENT
* Supporting Information
CIF files giving X-ray crystallographic data for complexes 7a
and 8a, selected figures giving H NMR spectra of hydro-
formylation products, room- and low-temperature H NMR
■
S
1
1
1
spectra of the isomeric mixture 6b/7b, low-temperature H
NMR and [1H−1H]-COSY spectra of 6a/7a as well as
[13C−1H]-HSQC NMR spectra of complexes 8a and 9b, and
text giving some additional characterization data (analytical, IR,
11B/11B{1H} NMR) of complexes 6, 7, 8a−c, and 9a,b. This
material is available free of charge via the Internet at http://
pubs.acs.org.
Preparation of [3-{(1−3-η3)-C6H11}-1,2-μ-(o-xylylene)-3,1,2-
closo-RhC2B9H9] (8b). The general method described above was
employed: 2 (50 mg, 0.07 mmol), 4 (21 μL, 0.21 mmol), 1b (48 mg,
0.175 mmol), degassed benzene (2 mL), reaction time 1 h. Yield of 8b
1
(deep red crystals): 35 mg (58%). H NMR (600 MHz, CD2Cl2, 24
°C; J(H,H), Hz): 7.18 (m, 2H, H-aryl), 7.03 (dd, 2H, J1 = 21.9, J2 =
6.8, H-aryl), 4.20 [br s, 1H, H(3′-syn)], 3.69−3.89 (m, 4H, CH2-aryl),
2.22 [m, 4H, CH3-syn, H(3′-anti)], 1.64 [s, 3H, CH3(2′)], −0.9 [s,
3H, CH3(anti, agost)]. 13C{1H} NMR (151 MHz, CD2Cl2, 24 °C;
J(C,Rh), Hz): 133.4, 132.2, 130.0, 129.9, 128.3, 128.2 (C-aryl), 112.9
[d, J = 6.0, C(2′)], 97.0 [d, J = 6.7, C(1′)], 75.3 (C-carb), 72.2 (C-
carb), 61.0 [d, J = 10.8, C(3′)], 43.8, 43.0 (CH2-aryl), 21.1
[CH3(syn)], 19.0 [C(2′)-CH3], 16.7 [CH3(anti, agost)].
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
Preparation of [3-{(1−3-η3)-C6H11}-1,2-μ-(CH2)3-3,1,2-closo-
RhC2B9H9] (8c). The general method described above was employed:
2 (100 mg, 0.142 mmol), 4 (50 μL, 0.43 mmol), 1c (74 mg, 0.35
mmol), degassed benzene (4 mL), reaction time 3 h. Yield of 8c (deep
■
This work has been supported by Grants 12-03-00102, 11-03-
12010-ofi-m-2011, and 10-03-00505 from the Russian
Foundation for Basic Research. We are also grateful to Dr. I.
D
dx.doi.org/10.1021/om300432j | Organometallics XXXX, XXX, XXX−XXX

Organometallics
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dx.doi.org/10.1021/om300432j | Organometallics XXXX, XXX, XXX−XXX