Synthesis and reactivity of rhodium complexes bearing [E(o -C 6H4PPh2)3]-type tetradentate ligands (E = Si, Ge, and Sn)

Article abstract of DOI:10.1021/om2011276

Rhodium complexes {(Ph₂P)C₆H₄} ₃ERh(CO) (1: E = Si; 2: E = Ge; 3: E = Sn) bearing EP3-type tetradentate ligands were synthesized by the reaction of the corresponding ligand precursors HE(o-C₆H₄PPh₂)₃ with tris(triphenylphosphine) carbonyl rhodium hydride RhH(CO)(PPh ₃)_3. In these complexes, the group 14 elements E exhibited a high σ-electron donor ability and elongated the Rh-CO bond trans to E in the order (H ?) Sn ≈ Ge < Si. The Rh-E strength has influence on the CO/P(OMe)₃ substitution reactions. The substitution of 1 is remarkably slower than those of 2 and 3, and the relative ratios of the pseudo-first-order rate constants k_obs for 1, 2, and 3 are 1:7.7:8.5. The kinetic study indicated that heavy group 14 elements E could induce the dissociation of a phosphine ligand cis to E, which eventually leads to CO/L substitution.

Full text of DOI:10.1021/om2011276

Article
pubs.acs.org/Organometallics
Synthesis and Reactivity of Rhodium Complexes Bearing [E(o-
C6H4PPh2)3]-Type Tetradentate Ligands (E = Si, Ge, and Sn)
Hajime Kameo, Sho Ishii, and Hiroshi Nakazawa*
Department of Chemistry, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka, 558-8585,
Japan
S
* Supporting Information
ABSTRACT: Rhodium complexes {(Ph2P)C6H4}3ERh(CO) (1: E = Si; 2: E = Ge; 3: E
= Sn) bearing EP3-type tetradentate ligands were synthesized by the reaction of the
corresponding ligand precursors HE(o-C6H4PPh2)3 with tris(triphenylphosphine)
carbonyl rhodium hydride RhH(CO)(PPh3)3. In these complexes, the group 14 elements
E exhibited a high σ-electron donor ability and elongated the Rh−CO bond trans to E in
the order (H ≪) Sn ≈ Ge < Si. The Rh−E strength has influence on the CO/P(OMe)3
substitution reactions. The substitution of 1 is remarkably slower than those of 2 and 3,
and the relative ratios of the pseudo-first-order rate constants kobs for 1, 2, and 3 are 1:7.7:8.5. The kinetic study indicated that
heavy group 14 elements E could induce the dissociation of a phosphine ligand cis to E, which eventually leads to CO/L
substitution.
similar to the well-known tris(triphenylphosphine) carbonyl
rhodium hydride RhH(CO)(PPh3)3 (4) and correspond to
complexes where the hydride in 4 is replaced by a group 14
element E. A comparison among them would provide
important information on the σ-electron-donating and trans-
labilizing abilities of group 14 elements.
INTRODUCTION
■
Transition metal complexes with multidentate ligands contain-
ing a carbon atom featuring a σ-electron donor as part of the
chelate architecture have attracted much attention owing to
their notable reactivities.1 The strong electron-donating and
trans-labilizing properties of a carbon donor play a crucial role
in the reactivity. The replacement of a carbon atom ligand by a
silicon atom ligand is of great interest, because it sometimes
leads to a remarkable stoichiometric and catalytic reactivity.2−7
Stobart and co-workers8 have reported the synthesis of a five-
coordinate rhodium carbonyl complex, Rh(tripsi)(CO) [tripsi
= (PPh2CH2CH2)3Si−], having a Rh−Si bond. This is an
example of the pioneering work on the incorporation of a silyl
group into a polydentate framework. The rhodium has a
trigonal-bipyramidal (TBP) geometry in which the apical
positions are occupied by the carbonyl and silyl ligands, and the
silyl ligand is demonstrated to exhibit high trans-labilizing
ability via the long rhodium−carbonyl distance (1.92 Å). Peters
and co-workers have extended a similar ligand system, where
the ethylene groups in Stobart’s tripsi ligand were displaced by
o-phenylene groups. They have prepared several coordination
complexes containing {(R2P)C6H4}3SiM− frameworks for
several transition metals (M = Fe, Ru, Os, Ir, Ni, Co; R = Ph
RESULTS AND DISCUSSION
■
New ligand precursors {(Ph2P)C6H4}3EH (6: E = Ge; 7: E =
Sn) were prepared (Scheme 1). Compound 6 was obtained by
treating the o-lithiated-phenyldiphenylphosphine with 1/3
equiv of Ge(OMe)4 in the presence of TMEDA (TMEDA =
tetramethylethylenediamine) and then with excess LiAlH4. The
last alkoxy-hydride exchange process imparted high stability to
the compound and allowed the isolation of 6 in 70% yield. The
related stannane compound 7 was prepared in a manner similar
to that of 6. Treatment of the o-lithiated-phenyldiphenylphos-
phine with 1/3 equiv of SnCl4 afforded {(Ph2P)C6H4}3SnCl
with some contaminations. Therefore, adequate elemental
analysis data for {(Ph2P)C6H4}3SnCl were not obtained.
However, the structure was confirmed by X-ray diffraction
analysis.11 Reduction of crude {(Ph2P)C6H4}3SnCl with excess
LiAlH4 and a subsequent purification produced analytically
pure 7 as a white powder in 52% yield.
i
or Pr) and reported the dinitrogen silylation and N−N
coupling of aryl azides using a trigonal-bipyramidal {(R2P)-
C6H4}3SiFe− scaffold (R = Ph, Pr).
By allowing 59c to react with RhHCO(PPh3)3 (4) at 80 °C,
the desired rhodium complex 1 was obtained in 92% yield.
9
i
When the reaction in benzene-d6 was monitored by 1H and 31
P
Other heavier group 14 elements, such as Ge and Sn, are also
expected to serve as strong electron-donating and trans-
labilizing ligands. However, to the best of our knowledge,
multidentate ligands containing Ge or Sn in the chelate
architecture have been extremely limited.10 Hence, we focus on
the three complexes {(Ph2P)C6H4}3ERh(CO) (1: E = Si; 2: E
= Ge; 3: E = Sn), having a tetradentate ligand containing a
heavier group 14 element. These complexes have frameworks
NMR spectroscopy, the respective formation of free
triphenylphosphine and dihydrogen was confirmed (PPh3: δ
= −6.1 ppm in the 31P NMR spectrum; H2: δ = 4.47 ppm in the
1H NMR spectrum). Complex 1 exhibits a single doublet in 31
P
Received: November 15, 2011
Published: March 14, 2012
© 2012 American Chemical Society
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a
Scheme 1. Synthetic Pathways for the Rhodium Complexes [{(Ph2P)C6H4}3E]Rh(CO)
a
1: E = Si; 2: E = Ge; 3: E = Sn.
Figure 1. ORTEP drawings of 1 (left), 2 (center), and 3 (right) with 40% probability ellipsoids. Hydrogen atoms and phenyl groups (except for
ipso-carbon) are omitted for clarity.
NMR spectroscopy (δ = 60.0 ppm, JRh−P = 150.7 Hz), which is
consistent with the C3v symmetrical structure observed for a
solid state (see below). The related germanium and tin
analogues 2 and 3 were prepared according to a synthetic
procedure similar to that used to produce 1. Upon reactions of
6 and 7 with RhHCO(PPh3)3 at 80 °C, the desired complexes
2 and 3 were isolated in 87% and 85% yields, respectively. A
single doublet in each 31P NMR spectrum was observed at δ
63.8 (JRh−P = 147.1 Hz) and 62.3 ppm (JRh−P = 146.9 Hz),
respectively, indicating the symmetric coordination of the three
phosphorus atoms. The relatively small coupling constants of 2
and 3, compared to that of 1, might be attributable to the
weaker coordination of the phosphorus ligands.
The IR spectra of 1, 2, and 3 showed strong absorption
bands at 1958, 1948, and 1946 cm−1, respectively, and these
carbonyl stretching frequencies were significantly higher than
that of 4 (1918 cm−1). These ν(CO) values show that the CO
ligand in 1−3 coordinates more weakly to Rh than that in 4.
This trend can also be observed in the X-ray analysis data.
The structures of 1−3 were confirmed by X-ray diffraction
analyses using single crystals obtained from the slow diffusion
of n-hexane into the concentrated methylene dichloride
solutions (Figure 1). Each structure had a TBP geometry,
and the carbonyl and the group 14 element E (E = Si, Ge, and
Sn) were located at the apical positions. The average E−Rh−P
angles (1: 81.99°, 2: 80.21°; 3: 82.00°) were smaller than the
average H−Rh−P angle (4: 84.60°),12 and the TBP geometries
around the Rh centers were considerably distorted because of
the constrained tetradentate frameworks. The Rh−P distances
in 1−3 ranged from 2.3006 to 2.3367 Å. One of three P−Rh−P
angles in 1 (109.97°) is considerably smaller than the other two
(121.67° and 122.56°). In comparison, the deviations of three
P−Rh−P angles are smaller in 2 and 3 than in 1. The Rh−E
distances as well as the sum of the three C−E−C angles
increased down a group. It should be noted that the Rh−CO
distances in 1−3 (1: 1.921 Å; 2: 1.888 Å; 3: 1.888 Å) are
considerably longer than that in 4 (4: 1.829 Å).12 It is known
that an electron-donating ligand such as an alkyl or a hydride
ligand makes a central metal atom electron rich, resulting in a
strong M−CO bond owing to π back-donation from M to CO.
However, our system showed that all heavier group 14 element
ligands, such as silyl, germyl, and stannyl groups, which are
considered to be strong electron-donating ligands, weaken the
Rh−CO bond.13
To rationalize our findings, we performed density functional
theory (DFT) calculations for 1−3.14 The natural bond orbital
(NBO) analysis data15 together with their spectroscopic data
are listed in Table 1. The NBO analyses show that the Rh−E
bond is highly polarized as Rh(δ−)−E(δ+) irrespective of the
kind of E for 1−3 and that the NBO atomic charge values qRh
are almost equal for 1−3, whereas qE changes considerably
depending on the kind of E. As mentioned above, π back-
donation is stronger for 2 and 3 relative to 1. The question
raised here is why qRh values are the same for 1−3 whether the
extent of Rh−CO π back-donation differs. Two explanations
are conceivable: (i) the electron-donating ability of Si to Rh in
1 is weaker than that of Ge in 2 and that of Sn in 3, and (ii)
although the electron-donating ability of Si to Rh in 1 is almost
equal to that of Ge in 2 and that of Sn in 3, there is greater
electron flow from Rh to P for 1 via π back-donation than for 2
or 3. The value of qE is larger in 1 than in 2 (qSi = 1.64, qGe
=
1.49), and it is unlikely that its Si σ-donor ability is lower than
that of Ge. Therefore, we consider (ii) to be the more probable
explanation. In other words, the electron density resulting from
Si σ donation would strengthen the Rh−P bond, whereas the
electron density resulting from Ge and Sn σ donation would
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Table 1. Spatial, Spectroscopic, and NBO Analysis Data
1 (E = Si) 2 (E = Ge) 3 (E = Sn)
4
Rh−C distance (Å)
Rh−P1 distance (Å)
Rh−P2 distance (Å)
Rh−P3 distance (Å)
E−Rh−P angle (deg)
P1−Rh−P2 angle (deg) 121.67
P1−Rh−P3 angle (deg) 122.56
P2−Rh−P3 angle (deg) 109.97
1.921 (3)
2.3006
2.3150
2.3189
81.99
1.888(4)
2.3118
2.3172
2.3012
80.21
1.888(5)
2.3244
2.3161
2.3367
82.00
1.82911
2.33611
2.31611
2.31511
84.6011
115.811
120.511
116.711
115.03
115.88
120.58
2.3967
333.7
119.01
120.76
114.51
2.5419
338.7
Rh−E distance (Å)
Σ (C-E-C) (deg)
ν(CO)
2.3308
324.0
1958
60.0
1948
1946
191811
31P NMR (ppm)
63.8
62.3
JRh−P (Hz)
150.7
−1.74
1.64
147.1
146.9
a
NBO analysis (qRh
)
−1.71
1.49
−1.77
1.77
−1.54
0.10
a
NBO analysis (qE)
a
B3PW91 (SDD/Rh, Sn; 6-31G(d)/C, H, O, P, Si, Ge).
strengthen the Rh−CO bond. This hypothesis would be
supported by molecular orbital analysis of Frontier orbitals. The
highest occupied molecular orbital (HOMO) of 1 apparently
involves the π interaction between Rh and two phosphorus
atoms (Figure 2; frontier orbitals of 2 and 3 are given in the
Figure 3. Molecular structure of one of the two independent
molecules of 9 (40% probability). Hydrogen atoms and phenyl groups
(except for ipso-carbon) are omitted for clarity. Selected bond lengths
(Å) and angles (deg): Rh1−Ge1, 2.3767(5); Rh1−P1, 2.3189(11),
Rh1−P2, 2.3175(11); Rh1−P3, 2.3194(11); Rh1−P4, 2.2463(11);
Ge1−Rh1−P1, 82.19(3); Ge1−Rh1−P2, 81.96(3); Ge1−Rh1−P3,
81.46(3).
reactions were demonstrated to be first-order in the
corresponding carbonyl complexes. The rate constant of the
reaction at 110 °C with 1 is remarkably smaller than those with
2 and 3 by factors of 1/7.7 and 1/8.5, respectively [kobs in the
reactions with 2 equiv of P(OMe)3; 7.38 × 10−6 s−1 (for 1);
5.70 × 10−5 s−1 (for 2); 6.26 × 10−5 s−1 (for 3)]. Therefore, the
observation that there is a longer Rh−CO bond in 1 than in 2
and 3 seems to be inconsistent with the reactivity of the CO/
P(OMe)3 substitution.
In order to gain a better understanding of the mechanism of
the substitution reactions of carbonyl ligands, kinetic studies
were carried out by monitoring the reaction of 2 with
trimethylphosphite. The reaction of 2 depends strongly on
the concentration of the phosphite ligand, and the high
negative value of entropy (ΔS‡ = −16.4 eu) suggests that the
CO/P(OMe)3 substitution reaction does not proceed via the
mechanism initialized by a CO dissociation.
Figure 2. Highest occupied molecular orbital (HOMO) of 1 (−4.50
eV).
A plausible pathway for the substitution of carbonyl ligands is
the dissociation of one arm of the triphos ligand (Scheme 2).
This type of reaction has been observed in several organo-
metallic and catalytic reactions.17 First, a vacant coordination
site for an incoming substrate is created by the dissociation of
one of the phosphine arms to give IA, featuring square-planar
geometry (step A). Trimethylphosphite can access the rhodium
atom from the opposite face of the dissociating phosphine arm
with respect to the plane around the rhodium atom (step B);
therefore, the CO ligand is pushed to the equatorial position to
give IC (step C). Alternatively, a trimethylphosphite approach-
ing the rhodium from the same face of the pendant phosphine
ligand might be expected to form ID, followed by the site
exchange between CO and P(OMe)3 to give IC. Finally, the
dissociation of the carbonyl ligand in IC and the recoordination
Supporting Information), and this interaction is most probably
strengthened by the small P2−Rh−P3 angle in 1 due to the
2
2
relatively large overlap between the dx −y orbital and the π*
orbital of phosphorus atoms.
The Rh−E bond strength is expected to influence the
reactivities of 1−3. We examined the reactions of 1−3 with
P(OMe)3 and found the formation of the corresponding CO/
P(OMe)3 exchange products (eq 1).16 The reactions were
monitored by 1H and 31P NMR spectroscopy, and it was found
that no intermediate was detected. Compounds 8−10 were
characterized by 1H and 31P NMR spectroscopy, and the
structure of 9 was confirmed by X-ray diffraction analysis
(Figure 3). The disappearance of the carbonyl complexes 1−3
was monitored by 31P NMR spectroscopy, and the substitution
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Scheme 2. Possible Mechanism for Substitution Reactions
of the phosphine arm generate the final complex (step D). DFT
calculation using model compounds [{o-(H2P)C6H4}3E]Rh-
(CO) (1A: E = Si; 2A: E = Ge; 3A: E = Sn) indicates that the
dissociation of one arm of the triphos ligand proceeds smoothly
in the order 1A(Si) < 2A(Ge) < 3A(Sn).18 The result supports
somewhat the mechanism of the dissociation of one arm of the
triphos ligand. However, the high negative value of entropy
(ΔS‡ = −16.4 eu) observed in the kinetic study appears to be
inconsistent with the hypothesis that the dissociation of one
arm of the triphos ligand is the rate-determining step. These
results might support the concerted mechanism involving the
dissociation of one phosphine arm and the incorporation of a
phosphite ligand.
Neutral monocarbonyl complexes of rhodium(I) rarely show
the CO replacement reaction because of strong back-donation
from the metal center. For example, Baird and his co-worker
reported that in the presence of a large excess of PMe3,
RhMe(CO)[η3-MeC(CH2PPh2)3] produced a perceptible
amount of RhMe(CO)(PMe3)[η2-MeC(CH2PPh2)3] by a
process involving the dissociation of one arm of the triphos
ligand; however they did not observe the dissociation of CO.19
Therefore, the CO dissociation in 1−3 is perhaps induced by
the presence of group 14 elements.
EXPERIMENTAL SECTION
■
General Procedures. The compounds described below were
handled under a dinitrogen atmosphere, and air and water were
removed completely using the Schlenk techniques. 2-(PPh2)C6H4Br,20
RhH(CO)(PPh3)3 (4),21 and {(Ph2P)C6H4}3SiH (5)9c were prepared
according to literature procedures. Benzene-d6, tetrahydrofuran-d8,
diethyl ether, and benzene were dried over sodium benzophenone
ketyl and distilled under the dinitrogen atmosphere. Tetrahydrofuran,
hexane, and toluene were purified using a two-column solid-state
purification system. Chloroform-d, dichloromethane-d2, and dichloro-
methane were dried over P2O5 and stored over 4 Å molecular sieves.
The other reagents used in this study were purchased from commercial
sources and used without further purification. The H, 13C, and 31P
1
1
NMR spectra were recorded on a JNM-AL-400 spectrometer. H and
13C NMR data were referred to the residual peaks of the solvent, and
31P NMR data were referred to the external standard. IR spectra were
recorded on a Perkin-Elmer FTIR spectrometer. Mass spectra were
obtained with a Jeol AX-500 or Jeol JMS-700T spectrometer. The
elemental analyses were recorded on a Perkin-Elmer 2400 II elemental
analyzer.
Preparation of {(Ph2P)C6H4}3GeH (6). A 600 mg portion of o-
PPh2(C6H4)Br (1.76 mmol) was dissolved in 10 mL of dimethyl ether,
and the solution was cooled to −78 °C. To the cold solution was
slowly added 1.17 mL of n-BuLi (1.65 M in hexane, 1.93 mmol), and
then the mixture was gradually warmed to room temperature.
Additionally, the solution was stirred at room temperature for 1 h,
and then the volatile materials were removed under vacuum. The
white residue was washed with 1.5 mL of Et2O to afford 0.557 g of {o-
PPh2(C6H4)}Li·Et2O (1.63 mmol) as a white solid in 93% yield. After
{o-PPh2(C6H4)}Li·Et2O (0.56 g, 1.63 mmol) was dissolved in THF
(10 mL), TMEDA (0.27 mL, 1.79 mmol) was added to the solution.
To the cold (−78 °C) THF solution of Ge(OMe)4 (80.5 μL, 0.542
mmol) was added the prepared reaction solution, and the mixture was
allowed to warm to room temperature. Additionally, the reaction
mixture was stirred at room temperature for 15 h. After removing the
volatile materials under vacuum, the residue was extracted with
benzene (15 mL). After removal of the volatile materials under
vacuum, the residue was dissolved in THF (10 mL). The THF
solution was cooled to −78 °C, and a suspension of LiAlH4 (26.4 mg,
0.70 mmol) in THF (5 mL) was added. After the mixture was allowed
to warm to room temperature, the reaction mixture was stirred at
room temperature for 12 h. To quench an excess amount of LiAlH4,
0.25 mL of H2O was added to the mixture at −78 °C. After the
mixture was allowed to warm to room temperature, the reaction
mixture was stirred at room temperature for 2 h. The resulting solution
was filtered through a Celite pad, and the volatile materials were
SUMMARY
■
We report the synthesis of the first rhodium complexes
featuring polydentate ligands containing σ-electron donating
germyl and stannyl groups as a part of the chelate architecture.
To the best of our knowledge, there is no preceding systematic
study on the σ-electron donor abilities of group 14 elements E
(E = Si, Ge, and Sn) in the TBP system. Group 14 elements E
were found to exhibit a high σ-electron donor ability and to
elongate the M−CO bond trans to E in the order (H ≪) Sn ≈
Ge < Si. Furthermore, the reactivity study indicates that heavy
group 14 elements E can induce the dissociation of a phosphine
ligand cis to E, which eventually leads to CO/L substitution.
We are currently investigating a new catalytic process that takes
full advantage of high σ-electron donor and strong trans-
influencing abilities of group 14 elements.
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removed in vacuo. The white residue was washed with Et2O (2 mL ×
3) and dried under vacuum to afford 6 (0.325 g, 0.378 mmol) in 70%
yield as a white powder. 1H NMR (400 MHz, C6D6): δ 6.94−7.05 (m,
25H), 7.19−7.40 (m, 15H), 7.61−7.62 (m, 3H). 31P{1H} NMR (163
MHz, C6D6): δ −10.3 (s). Anal. Calcd for C55H43P3Ge: C, 75.64; H,
5.05. Found: C, 75.33; H, 5.24. HRMS (FAB+): [M − H]+ calcd for
C54H42P3Ge 857.1711, found 857.1714.
H, 4.24. HRMS (m/z): [M]+ calcd for C55H42OP3RhGe 988.0715,
found 988.0717.
Preparation of {(Ph2P)C6H4}3SnRh(CO) (3). A Schlenk tube was
charged with 243 mg of 7 (0.269 mmol), 247 mg of 4 (0.269 mmol),
and 15 mL of toluene, and then the reaction mixture was stirred at 60
°C. After 12 h, the mixture was cooled to room temperature, and the
volatile materials were removed under reduced pressure. The residue
was washed with Et2O (2 mL × 3) and dried under vacuum to afford
236 mg of 3 (0.228 mmol) as a yellow powder in 85% yield. 1H NMR
(400 MHz, C6D6): δ 6.70−6.73 (m, 9H), 6.80−6.84 (m, 6H), 6.92−
6.96 (m, 3H), 7.04−7.49 (m, 18H), 7.73−7.78 (m, 3H), 8.22−8.24
(m, 3H). 13C{1H} NMR (100 MHz, C6D6): δ 128.4, 128.6, 128.9,
129.3, 132.0, 132.2, 135.4, 141.4, 148.4, 154.6, 209.3. 31P{1H} NMR
(163 MHz, C6D6): δ 62.3 (d, JP−Rh = 146.9 Hz, JP‑119Sn = 165.2 Hz). IR
(KBr, cm−1) ν(CO): 1946. Anal. Calcd for C55H42OP3RhSn: C, 63.92;
H, 4.42. Found: C, 63.51; H, 4.42. HRMS (FAB+): [M]+ calcd for
C55H42OP3RhSn 1034.0526, found 1034.0522.
Preparation of {(Ph2P)C6H4}3SnH (7). A 1.00 g portion of o-
PPh2(C6H4)Br (2.93 mmol) was dissolved in 15 mL of diethyl ether,
and the solution was cooled to −78 °C. To the cold solution was
slowly added 1.95 mL of n-BuLi (1.65 M in hexane, 3.22 mmol), and
then the mixture was gradually warmed to room temperature.
Additionally, the solution was stirred at room temperature for 1 h,
and then the volatile materials were removed under vacuum. The
white residue was washed with 3.0 mL of Et2O to afford 0.948 g of {o-
PPh2(C6H4)}Li·Et2O (2.77 mmol) as a white solid in 94% yield. The
toluene solution (5 mL) of {o-PPh2(C6H4)}Li·Et2O (0.948 g, 2.77
mmol) was added dropwise to the cold (−78 °C) toluene solution of
SnCl4 (1 M in toluene, 0.92 mL, 0.923 mmol), and the mixture was
allowed to warm to room temperature. Additionally, the reaction
mixture was stirred at room temperature for 15 h. After the resulting
solution was filtered through a glass filter, the volatile materials were
removed under vacuum to afford crude ClSn(o-C6H4PPh2)3 as a white
Preparation of Rh(P(OMe)3)(Si(o-C6H4PPh2)3) (8). A Schlenk
tube was filled with 1 (78.7 mg, 0.0835 mmol) and xylene (4 mL),
trimethylphosphite (197 μL, 1.67 mmol) was added, and the reaction
mixture was stirred at 140 °C. After 20 h, removal of the solvent under
reduced pressure gave a pale yellow solid. The residue was washed
with hexane (2 mL × 3) and dried under vacuum to afford 78.2 mg of
1
1
solid. [The formation of ClSn(o-C6H4PPh2)3 was confirmed by H
8 (0.0753 mmol) as a yellow powder in 90% yield. H NMR (400
and 31P NMR spectroscopy. 1H NMR (400 MHz, C6D6): δ 6.86−7.13
(m, 30H), 7.36−7.43 (m, 9H), 8.21−8.24 (m, 3H). 31P{1H} NMR
(163 MHz, C6D6): δ −1.4 (s, JP‑119Sn = 40.4 Hz).] After the white
residue was dissolved in THF (10 mL), the solution was cooled to
−78 °C. A suspension of LiAlH4 (52.6 mg, 1.39 mmol) in THF (5
mL) was added dropwise to the cold solution. After the mixture was
allowed to warm to room temperature, the reaction mixture was stirred
at room temperature for 12 h. To quench an excess amount of LiAlH4,
a 0.25 mL portion of H2O was added to the mixture at −78 °C. After
the mixture was allowed to warm to room temperature, the solution
was stirred at room temperature for 2 h. The resulting solution was
filtered through a Celite pad, and the volatile materials were removed
in vacuo. The white residue was washed with hexane (2 mL) and Et2O
(2 mL × 3) and dried under vacuum to afford 7 (0.458 g, 0.507 mmol)
in 55% yield as a white powder. 1H NMR (400 MHz, C6D6): δ 7.00−
7.05 (m, 25H), 7.19−7.41 (m, 15H), 7.77−7.79 (m, 3H). 31P{1H}
NMR (163 MHz, C6D6): δ −4.1 (s, JP‑119Sn = 84.4 Hz). HRMS (FAB
+): [M − H]+ calcd for C54H42P3Sn 903.1521, found 903.1525.
Preparation of {(Ph2P)C6H4}3SiRh(CO) (1). A Schlenk tube was
charged with 164.5 mg of 5 (0.202 mmol), 186.0 mg of 4 (0.202
mmol), and 15 mL of toluene, and then the reaction mixture was
stirred at 80 °C. After 12 h, the mixture was cooled to room
temperature and filtered through a glass filter. After removal of the
volatile materials under reduced pressure, the residue was washed with
hexane (2 mL × 3) and dried under vacuum to afford 175.2 mg of 1
MHz, C6D6): δ 2.85 (d, JH−P = 10.3 Hz, 9H, OMe), 6.75−7.04 (m,
18H, Ph), 7.16−7.36 (m, 21H, Ph), 8.27−8.29 (m, 3H, Ph). 31P{1H}
NMR (163 MHz, C6D6): δ 51.7 (dd, JP−Rh = 157.9 Hz, JP−P = 51.4 Hz,
Ph2P), 147.9 (qd, JP−Rh = 176.2 Hz, JP−P = 51.4 Hz, P(OMe)3). Anal.
Calcd for C57H51O3P4RhSi: C, 65.90; H, 4.95. Found: C, 66.03; H,
5.22. HRMS (FAB+): [M]+ calcd for C57H51O3P4RhSi 1038.1613,
found 1038.1619.
Preparation of Rh(P(OMe)3)(Ge(o-C6H4PPh2)3) (9). A Schlenk
tube was filled with 2 (65.8 mg, 0.0666 mmol), and toluene (4 mL).
Trimethylphosphite (157 μL, 1.33 mmol) was added, and the reaction
mixture was stirred at 110 °C. After 24 h, removal of the solvent under
reduced pressure gave a pale yellow solid. The residue was washed
with hexane (2 mL × 3) and dried under vacuum to afford 66.4 mg of
1
9 (0.0613 mmol) as a yellow powder in 92% yield. H NMR (400
MHz, C6D6): δ 2.86 (d, JH−P = 10.3 Hz, 9H, OMe), 6.72−6.96 (m,
18H, Ph), 7.20−7.33 (m, 21H, Ph), 8.33−8.35 (m, 3H, Ph). 31P{1H}
NMR (163 MHz, C6D6): δ 56.7 (dd, JP−Rh = 154.2 Hz, JP−P = 47.7 Hz,
Ph2P), 149.0 (qd, JP−Rh = 194.6 Hz, JP−P = 47.7 Hz, P(OMe)3). Anal.
Calcd for C57H51O3P4RhGe: C, 63.19; H, 4.74. Found: C, 62.85; H,
5.01. HRMS (FAB+): [M]+ calcd for C57H51O3P4RhGe 1084.1055,
found 1084.1045.
Preparation of Rh(P(OMe)3)(Sn(o-C6H4PPh2)3) (10). A Schlenk
tube was filled with 3 (53.0 mg, 0.0513 mmol) and touene (2.5 mL).
Trimethylphosphite (12.1 μL, 0.103 mmol) was added, and the
reaction was stirred at 110 °C. After 48 h, removal of the solvent under
reduced pressure gave a pale yellow solid. The residue was washed
with hexane (2 mL × 3) and dried under vacuum to afford 37.6 mg of
1
(0.186 mmol) as a yellow powder in 92% yield. H NMR (400 MHz,
C6D6): δ 6.73−6.77 (m, 9H), 6.83−6.87 (m, 6H), 6.94−6.98 (m, 3H),
7.02−7.05 (m, 6H), 7.13−7.24 (m, 9H), 7.36−7.39 (m, 6H), 8.31−
8.33 (m, 3H). 13C{1H} NMR (100 MHz, C6D6): δ 128.3, 128.7, 129.0,
129.4, 132.4, 132.9, 134.3, 141.4, 148.2, 154.1, 207.3. 31P{1H} NMR
(163 MHz, C6D6): δ 60.0 (d, JP−Rh = 150.7 Hz). IR (KBr, cm−1)
ν(CO): 1958. Anal. Calcd for C55H42OP3RhSi: C, 70.00; H, 4.49.
Found: C, 70.10; H, 4.73.
1
10 (0.0333 mmol) as a yellow powder in 65% yield. H NMR (400
MHz, C6D6): δ 2.82 (d, JH−P = 10.7 Hz, 9H, OMe), 6.69−6.95 (m,
18H, Ph), 7.19−7.36 (m, 21H, Ph), 8.21−8.22 (m, 3H, Ph). 31P{1H}
NMR (163 MHz, C6D6): δ 55.7 (dd, JP−Rh = 150.5 Hz, JP−P = 47.7 Hz,
JP‑119Sn = 179.9 Hz, Ph2P), 153.3 (qd, JP−Rh = 223.9 Hz, JP−P = 47.7 Hz,
JP‑119Sn = 51.4 Hz, P(OMe)3). Anal. Calcd for C57H51O3P4RhSn: C,
60.61; H, 4.55. Found: C, 60.31; H, 4.47. HRMS (FAB+): [M]+ calcd
for C57H51O3P4RhSn 1130.0866, found 1130.0868.
Reactions of 8−10 with CO. A 50 mL Schlenk tube was filled
with 8 (13.4 mg, 0.0142 mmol) and toluene (2 mL). After the solution
was evacuated at −196 °C using a high-vacuum line, 1 atm of CO
(about 2.0 mmol) was transferred into the tube. The reaction mixture
was stirred at 60 °C. After 10 h, the mixture was cooled to room
temperature, and the solvent was removed under reduced pressure.
Washing the residual solid with hexane (2 mL × 1) afforded 1 as a pale
yellow solid (13.7 mg, 0.0132, 93%). The P(OMe)3/CO substitution
reactions of 9 and 10 with CO were similarly carried out by using 9
and 10 instead of 8, and the almost quantitative formation of 2 and 3
was confirmed.
Preparation of {(Ph2P)C6H4}3GeRh(CO) (2). A Schlenk tube was
charged with 106.0 mg of 6 (0.124 mmol), 113.6 mg of 4 (0.127
mmol), and 10 mL of toluene, and then the reaction mixture was
stirred at 100 °C. After 12 h, the mixture was cooled to room
temperature, and the volatile materials were removed under reduced
pressure. The residue was washed with Et2O (2 mL × 3) and dried
under vacuum to afford 106.2 mg of 2 (0.108 mmol) as a yellow
1
powder in 87% yield. H NMR (400 MHz, C6D6): δ 6.71−6.75 (m,
9H), 6.82−6.86 (m, 6H), 6.96−7.40 (m, 24H), 8.32−8.34 (m, 3H).
13C{1H} NMR (100 MHz, C6D6): δ 128.7, 128.9, 129.1, 129.6, 132.4,
133.1, 134.2, 141.4, 145.7, 156.2, 207.7. 31P{1H} NMR (163 MHz,
C6D6): δ 63.8 (d, JP−Rh = 147.1 Hz). IR (KBr, cm−1) ν(CO): 1948.
Anal. Calcd for C55H42OP3RhGe: C, 66.90; H, 4.29. Found: C, 66.53;
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Estimate of the Rate Constants Concerning the Reactions of
1−3 with 2 equiv of Trimethylphosphite. An NMR tube was
charged with 1 (6.2 mg, 6.6 μmol), toluene-d8 (0.4 mL),
trimethylphosphite (1.55 μL, 0.0132 mmol, 2 equiv), and
triphenylphosphine oxide (5.5 mg) as an internal standard. The
reactions were performed at 110 °C, and the reactions were monitored
by 31P NMR spectroscopy. The reactions were demonstrated to be
first-order at the initial step, and the rate constants were calculated on
the basis of the time conversion of [1]: k = 7.38 × 10−6 s−1. The rate
constants concerning the reactions of 2 and 3 with P(OMe)3 were
calculated by using 6.5 mg of 2 (6.6 μmol) and 6.8 mg of 3 (6.6 μmol)
instead of 1: k = 5.70 × 10−5 s−1 (for 2); 6.26 × 10−5 s−1 (for 3).
Kinetic Experiments of the Reaction of 2 with Trimethyl-
phosphite. A Schlenk tube was charged with 2 (26.0 mg, 0.0263
mmol), toluene-d8 (1.6 mL), and triphenylphosphine oxide (22.0 mg)
as an internal standard. The solution was divided evenly into four
NMR sample tubes. Different equivalents of trimethylphosphite (1.55
μL, 0.0132 mmol, 2 equiv; 6.20 μL, 0.0528 mmol, 8 equiv; 10.9 μL,
0.0924 mmol, 14 equiv; 15.5 μL, 0.132 mmol, 20 equiv) were
introduced into each tube, and the reactions were performed at 110
°C. The reactions were monitored by 31P NMR spectroscopy, and the
rate constants were calculated on the basis of the time conversion of
[2]: k = 5.70 × 10−5 s−1 (2 equiv); 6.73 × 10−5 s−1 (8 equiv); 1.00 ×
10−4 s−1 (14 equiv); 2.01 × 10−4 s−1 (20 equiv).
Eyring Plot for the Reaction of 2 with Trimethylphosphite. A
Schlenk tube was charged with 2 (26.0 mg, 0.0263 mmol), toluene-d8
(1.6 mL), and triphenylphosphine oxide (14.8 mg) as an internal
standard. The solution was divided up evenly into four NMR sample
tubes. Then 20 equiv of trimethylphosphite (14.5 μL, 0.132 mmol)
was introduced into each tube, and the reactions were performed at
appropriate temperature (80, 90, 100, and 110 °C). The reactions
were monitored by 31P NMR spectroscopy. The rate constants were
calculated on the basis of the time conversion of [2]: k = 1.46 × 10−5
s−1 (80 °C); 3.75 × 10−5 s−1 (90 °C); 9.09 × 10−5 s−1 (100 °C); 2.01
× 10−4 s−1 (110 °C). The temperature dependence of the rate
constants yielded the following activation parameters (Eyring plot was
shown in Figure S1): ΔH‡ = 22.8 0.3 kcal mol−1 and ΔS‡ = −16.4
0.7 cal mol−1 K−1.
Structure Determination by X-ray Diffraction. Suitable single
crystals of {(Ph2P)C6H4}3SnCl and 9 were obtained from slow
diffusion of n-hexane into the CH2Cl2 solution of {(Ph2P)C6H4}3SnCl
or the toluene solution of 9. Single crystals of 1, 2, and 3 were
obtained from the preparations described above. The prepared single
crystals were mounted on the CryoLoop with Palaton oil, and the X-
ray diffraction experiments were carried out using a Rigaku/MSC
Mercury CCD diffractometer with a graphite-monochromated Mo Kα
radiation source (λ = 0.71069 Å) at 200 K. Cell refinement and data
reduction were carried out using the CrystalClear program.22 The
intensity data were corrected for Lorentz−polarization effects and
empirical absorption. The structures were determined by the direct
method (SIR 97). All non-hydrogen atoms were found by a difference
Fourier synthesis and were refined anisotropically. The refinement
using the SHELXL-97 package23 was carried out by the least-squares
methods based on F2 with all measured reflection data. The crystal
data and results of the analyses are listed in Tables S2−S11.
Density Functional Theory Calculation. DFT calculations were
carried out at the B3PW91 level24 in conjunction with the Stuttgart/
Dresden ECP1925 and associated with triple-ξ basis sets for Rh and Sn.
For H, C, O, P, Si, and Ge, 6-31G(d) was employed. Calculations
utilizing the Gaussian09 program26 were performed on the actual
structures of 1−3 by using the atomic coordinates determined from X-
ray diffraction analysis.
available in CIF format. This material is available free of charge
via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: nakazawa@sci.osaka-cu.ac.jp.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The present research is supported by Challenging Exploratory
Research (No. 23655056) and a Grant-in-Aid for Young
Scientists (B) (No. 23750064) from Japan Society of the
Promotion of Science. H.K. acknowledges financial support
from the Sasakawa Scientific Research Grant from the Japan
Science Society.
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ASSOCIATED CONTENT
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■
S
* Supporting Information
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