Ligand dependence of π-complex character in disilene-palladium complexes

Article abstract of DOI:10.1039/b512414j

The synthesis and structures of new 16-electron disilene palladium complexes with 2,6-dimethylphenyl isocyanide and phenyldimethylphosphine ligands [L¹L²Pd((t-BuMe₂Si)₂SiSi(SiMe ₂Bu-t)₂), where L¹ = L² = PhMe ₂P; L¹ = (cyclohexyl)₃P, L² = 2,6-dimethylphenyl isocyanide; L¹ = L² = 2,6-dimethylphenyl isocyanide] are described. Comparison of the X-ray structural parameters around the disilene moiety among these complexes and related bis(trimethylphosphine)(disilene)palladium and 14-electron (tricyclohexylphosphine)(disilene)palladium revealed that the π-complex character is sensitive to the residual ligands and increases with decreasing the strength of σ-donation from the ligands. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b512414j

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PAPER
www.rsc.org/dalton | Dalton Transactions
Ligand dependence of p-complex character in disilene–palladium complexes†
Takeaki Iwamoto, Yumiko Sekiguchi, Naoki Yoshida, Chizuko Kabuto and Mitsuo Kira*
Received 1st September 2005, Accepted 1st November 2005
First published as an Advance Article on the web 15th November 2005
DOI: 10.1039/b512414j
The synthesis and structures of new 16-electron disilene palladium complexes with 2,6-dimethylphenyl
1
2
=
isocyanide and phenyldimethylphosphine ligands [L L Pd{(t-BuMe2Si)2Si Si(SiMe2Bu-t)2},
where L1 = L2 = PhMe2P; L1 = (cyclohexyl)3P, L2 = 2,6-dimethylphenyl isocyanide; L1 = L2 =
2,6-dimethylphenyl isocyanide] are described. Comparison of the X-ray structural parameters around
the disilene moiety among these complexes and related bis(trimethylphosphine)(disilene)palladium and
14-electron (tricyclohexylphosphine)(disilene)palladium revealed that the p-complex character is
sensitive to the residual ligands and increases with decreasing the strength of r-donation from the
ligands.
some of them have been investigated by X-ray crystallography.
Introduction
We have recently synthesized 16-electron platinum and palladium
2
complexes with a silyl-substituted g -disilene ligand 1–35a,b and 14-
The bonding of an alkene to a transition metal center in alkene
transition metal complexes1 is usually understood in terms of
alkene-to-metal r-donation and metal-to-alkene p-back donation,
according to the Dewar–Chatt–Duncanson model.2 The structure
of an alkene complex is significantly influenced by the relative
importance between the r-donation and the p-back donation, and
hence, they are classified into either a p-complex having major
contribution of r-donation or a metallacycle having dominant
p-back donation. The geometry around the alkene ligand in
the p-complex is not very much different from that of the free
alkene, while that in the metallacycle is significantly distorted and
characterized by an elongated C1–C2 bond length (d) and a large
bent angle (h) defined by the angle between the R1–C1–R2 (or
R3–C2–R4) plane and the C1–C2 bond (Chart 1).3
electron disilene complex 45c using the reactions of the correspond-
ing bis(phosphine)dichlorometals with 1,2-dilithiotetrakis(tert-
butyldimethylsilyl)disilane 5,9 which was prepared by the reaction
of stable disilene 610 with lithium in THF (eqn (1)–(3)).
(1)
(2)
(3)
Chart
1
Qualitative bonding description of alkene and disilene
complexes.
In contrast to alkene complexes, most of the disilene com-
plexes whose X-ray structures are known4–7 are characterized
as metallacycles, by applying the Dewar–Chatt–Duncunson type
bonding scheme to the disilene complexes. However, the character
may depend on the central metal, ligands, and substituents
on disilene. Actually, we have found that 16-electron disilene
palladium complex 2 has slightly larger p-complex character than
the corresponding platinum complex 1.5b The first 14-electron
disilene palladium complex 4 has stronger p-complex character
than the related 16-electron complexes 2 and 3.5c
Much attention has been focused recently on the structure of
2
transition metal complexes with g -silicon–silicon doubly bonded
species as ligands (disilene complexes).4–8 A variety of isolable
2
g -disilene complexes of platinum,4,5a palladium,5b,c tungsten,6
molybdenum,6 iron,7 and zirconium8 have been synthesized and
Department of Chemistry, Graduate School of Science, Tohoku University,
Aoba-ku, Sendai, Japan. E-mail: mkira@si.chem.tohoku.ac.jp; Fax: +81-
22-795-6589; Tel: +81-22-795-6585
† Electronic supplementary information (ESI) available: Data for DFT
calculations for model disilene complexes 8ꢀ, 8ꢀꢀ, 9ꢀ and 9ꢀꢀ. See DOI:
10.1039/b512414j
We wish herein to report the synthesis and structures of new
16-electron disilene palladium complexes with 2,6-dimethylphenyl
isocyanide (7) and phenyldimethylphosphine as the residual
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ligands. Comparison of the structural parameters around the
disilene moiety revealed that the p-complex character depends
remarkably on the residual ligands.
Results and discussion
(5)
Synthesis of new 16-electron disilene palladium complexes
To elucidate the electronic effects of phosphine ligands on the
p-complex character of the 16-electron complex 2, complex 13 was
synthesized by the conventional method5,11 (eqn (6)).
Very few reactions of disilene transition metal complexes have been
reported to date. Disilene–platinum complexes synthesized by
Pham and West react with small molecules like oxygen, hydrogen,
and methanol to afford the corresponding Si–Si or Si–Pt bond
cleavage products.4 Berry et al. have revealed that the Si–Si
and Si–metal bonds of molybdenum and tungsten complexes of
tetramethyldisilene show high reactivity toward methanol, carbon
dioxide and triphenylphosphine sulfide.6 However, there have been
no ligand exchange reactions of disilene complexes reported. We
have found the reactions of disilene palladium complexes 2 and 4
with isocyanide 7 to afford the corresponding disilene complexes
with isocyanide ligands; the disilene ligand remains intact during
the reactions.
(6)
Molecular structures of 16-electron disilene complexes
Molecular structures of disilene palladium complexes 8, 9 and
13 determined by X-ray crystallography are shown in Fig. 1–3.
The structural parameters are listed in Table 1 together with those
for disilene complexes 2, 3 and 4.12 Because mono(isocyanide)
complex 8 showed two crystallographically independent molecules
in an asymmetric unit, two sets of parameters are shown in the
table.
The reactions of 14-electron complex 4 with 1 and 2 equiv-
alents of isocyanide 7 gave mono(isocyanide) complex 8 and
bis(isocyanide) complex 9, respectively (Scheme 1).
The Si(1)–Si(2) bond distances (d) of all the disilene palla-
˚
dium complexes (2.273–2.3180 A) lie below the shortest limit
˚
of the reported Si–Si single bond (2.335–2.697 A) but depend
significantly on the ligands.13 The central palladium atom of the
disilene complexes 8, 9 and 13 adopts highly distorted square
planar geometry with the angle between Si1–Pd–Si2 and L1–
Pd–L2 planes (u in Table 1) of 36.4 (31.1), 20.0 and 31.0◦,
respectively; the angle u for 2 and 3 is 31.8 and 28.5◦, respectively,5b
while the geometry around palladium in the 14-electron disilene
complex 4 is almost planar.5d Steric repulsion between bulky
trialkylsilyl substituents and other ligands could be responsible
for the distorted geometry. The extent of the steric repulsion for
9 with less bulky isocyanide ligands is much smaller than that
for other 16-electron disilene complexes. The Si–Pd distances (d1
Scheme 1 Synthesis of disilene complexes with isocyanide ligands.
Interestingly, the reactions of 16-electron complex 2 with 1 and
2 equivalents of isocyanide 7 also gave new mono(isocyanide)
complex 11 in 83% isolation yield and 9 in quantitative yield,
respectively. The result suggests that 16-electron complex 2 exists
in equilibrium with 14-electron complex 10 and dissociated
trimethylphosphine (eqn. (4) and (5)); the subsequent dissociation
of trimethylphosphine from 11 followed by the addition of the
isocyanide will give bis(isocyanide) complex 9. Because no 14-
electron complexes 10 and 12 were detected in solution by NMR
spectroscopy, the concentration of 10 and 12 in the equilibrium
will be very low.
˚
and d2, 2.360–2.460 A) are a little longer than those of reported
14
˚
bis(phosphine)(disilyl)palladium complexes (2.34–2.38 A).
The bent angles (h1 and h2), which are defined as an angle
between the Si1(2)–Si2(1)–R plane and the Si1–Si2 bond, are larger
than that of free disilene 6 (0.1◦)10 but the extent depends
remarkably on the ligands. The bond elongation estimated by
Dd/d0 values (Dd = d − d0, where d0 is the Si1–Si2 bond length of
free disilene 610), is not very sensitive to the ligands on palladium
but decreases in the order of 3 > 2 > 13 > 8 (av.) ∼ 9 > 4. On the
other hand, the averaged bent angles (hav. ) are significantly affected
by the ligands and decrease in almost the same order as the bond
elongation; 3 ∼ 2 > 13 > 8 (av.) > 9 > 4.15
If the Dewar–Chatt–Duncanson model is applicable to disilene
complexes, the Dd/d0 value and h value should decrease with
increasing the p-complex character of the disilene complexes. On
the basis of this criterion, the p-complex character is evaluated to
decrease in the following order: 4 > 9 > 8 (av.) > 13 > 2 ∼ 3. As
shown in a previous paper,5c the p-back donation in 14-electron
disilene complex 4 is the smallest because one basic ligand on
(4)
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Fig. 2 Molecular structure of complex 9. Thermal ellipsoids are drawn
at the 30% probability level. Hydrogen atoms are omitted for clar-
◦
˚
ity. Selected bond lengths (A) and angles ( ): Pd(1)–Si(1) 2.4340(11),
Pd(1)–Si(2) 2.4411(11), Si(1)–Si(2) 2.2891(14), Pd(1)–C(1) 2.014(4), Pd(1)–
C(2) 2.029(4); Si(1)–Pd(1)–Si(2) 56.01(4), Pd(1)–Si(1)–Si(2) 62.15(4),
Pd(1)–Si(2)–Si(1) 61.84(4), C(1)–Pd(1)–C(2) 97.59(15).
Fig. 3 Molecular structure of complex 13. Thermal ellipsoids are
Fig. 1 Molecular structure of complex 8. Two crystallographically
independent molecules were observed in an asymmetric unit: (a) molecule
1, (b) molecule 2. Thermal ellipsoids are shown in the 30% probability
drawn at the 30% probability level. Hydrogen atoms are omitted for
◦
˚
clarity. Selected bond lengths (A) and angles ( ): Pd(1)–Si(1) 2.6432(10),
Pd(1)–Si(2) 2.4287(10), Si(1)–Si(2) 2.2952(13), Pd(1)–P(1) 2.3574(10),
Pd(1)–P(2) 2.3566(10); Si(1)–Pd(1)–Si(2) 55.96(3), Pd(1)–Si(1)–Si(2)
61.26(3), Pd(1)–Si(2)–Si(1) 62.78(3), P(1)–Pd(1)–P(2) 101.14(4).
˚
level. Hydrogen atoms are omitted for clarity. Selected bond lengths (A)
and angles (◦): Pd(1)–Si(1) 2.4597(8), Pd(1)–Si(2) 2.4581(9), Si(1)–Si(2)
2.2861(11), Pd(1)–P(1) 2.4437(8), Pd(1)–C(43) 1.989(3); Si(1)–Pd(1)–
Si(2) 55.40(3), Pd(1)–Si(1)–Si(2) 62.26(3), Pd(1)–Si(2)–Si(1) 62.33(3),
P(1)–Pd(1)–C(43) 96.06(9), Pd(2)–Si(7) 2.4603(8), Pd(2)–Si(8) 2.4264(8),
Si(7)–Si(8) 2.2967(11), Pd(2)–P(2) 2.4352(8), Pd(2)–C(91) 2.001(3),
Si(7)–Pd(2)–Si(8) 56.06(3), Pd(2)–Si(7)–Si(8) 61.22(3), Pd(2)–Si(8)–Si(7)
62.72(3), P(2)–Pd(2)–C(91) 96.48(9).
the additivity of the extent of the r-donation to the metal. It is
expected that because of stronger trans influence of phosphine
than isocyanide, the bent angle around an unsaturated silicon
atom of complex 8 located at the trans position (h1) to tricyclo-
hexylphosphine should be much larger than that for the other
unsaturated silicon atom (h2). In reality, h1 and h2 in complex
8 are 5.2 (3.0) and 20.6 (36.5)◦, respectively; h1 is much smaller
than h2, in contrast to the above expectation. The incompatibility
between the expectation and the experimental results should not
be ascribed to the steric effects of bulky tricyclohexylphosphine,
because the geometrical characteristics for 8 was reproduced
qualitatively by the theoretical calculations for a model disilene
palladium complexes (vide infra).
palladium is missing. The r-donor ability of ligands is expected
to decrease in the order of Me3P > PhMe2P > RꢀNC on the basis
of the basicity of the ligands. Thus, the p-back donation from the
metal will increase in the order of 4 < 9 < 8 < 13 < 2 ∼ 3. As
expected, the order is in good accord with the observed order for
the p-complex character.
The p-complex character of unsymmetrically substituted 16-
electron disilene complex 8 is between those of 2 and 9, suggesting
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Table 1 Comparison of structural parameters of various disilene palladium complexes (R = t-BuMe2Si)
◦
h1/◦
h2/◦
hav
/
d1/A
d2/A
uc/◦
d(29Si)
a
b
L1
L2
d/A
Dd/A (%Dd/d0)
˚
˚
˚
˚
Compound
2
PMe3
Me2PCH2CH2PMe2
PhMe2P
RꢀNCd
RꢀNCd
RꢀNCd
Cy3P
PMe3
2.3027(8)
2.3180(8)
0.101(5.2)
0.118(4.6)
0.093(4.2)
0.085(3.9)
0.094(4.3)
0.087(4.0)
0.072(3.3)
27.2
27.3
14.4
5.2
3.0
9.5
27.2
27.3
26.8
20.6
36.5
8.9
27.2
27.3
20.6
12.9
19.8
9.2
2.4369(5)
2.4184(4)
2.4632(10)
2.4597(8)
2.4603(8)
2.4340(11)
2.3610(9)
2.4369(5)
2.4184(4)
2.4287(10)
2.4581(9)
2.4264(8)
2.4411(11)
2.4168(8)
31.8
28.5
31.0
36.4
31.1
20.0
—
−46.5
−51.9
−44.8
−39.4, −60.4
—
3
13
PhMe2P 2.2952(13)
8 (mol. 1)
Cy3P
Cy3P
RꢀNCd
—
2.2861(11)
2.2967(11)
2.289(2)
8 (mol. 2)
9
4
−41.2
2.273(1)
4.4
9.7
7.0
+65.3
a d0 is the Si Si distance in free (t-BuMe2Si)2Si Si(SiMe2Bu-t)2 (2.202 (1) A). Dd = d − d0 = d − 2.202. Standard deviations of %Dd/d0 and h
10
˚
=
=
are estimated to be at most 0.13 and 0.05◦, respectively. hav = (h1 + h2)/2. c Dihedral angle between plane (L1–Pd–L2) and plane (Si–Pd–Si). d Rꢀ =
b
2,6-dimethylphenyl.
Interestingly, even symmetrically substituted disilene complexes
9 and 13 showed two different bent angles and Pd–Si distances.
The results may be attributed to the fact that the steric and
electronic environments around two unsaturated silicon atoms
in these complexes are different to each other in the solid state
because the two residual ligands in complex 9 or 13 adopt the
different rotational conformations.
To evaluate the steric effects on the bent angles h1 and h2,
theoretical calculations were performed for model 16-electron
disilene–palladium complexes 8ꢀ and 9ꢀ at the B3LYP/6-31G* level
(Chart 2).16,17 The h values for 2ꢀ5c 8ꢀ and 9ꢀ are 27.9, 25.3 (av.) and
22.4, and %Dd/d0 values for 2ꢀ, 8ꢀ and 9ꢀ are 4.3, 4.4 and 4.1,
respectively. Despite the geometry around palladium of all these
model complexes is planar (torsion angles u are less than 5◦), the
orders of h and %Dd/d0 values are well in accord with those for
a set of 2, 8 and 9. The bent angle hav and the bond elongation
Dd/d0 may serve as good indices for the p-complex character of
disilene complexes, even though disilene complexes are distorted
significantly from the ideal square planar geometry.
As shown in Table 1, h1 is unexpectedly much smaller than
h2 for unsymmetrically substituted disilene complex 8. The un-
symmetrical distortion is not ascribed to the steric hindrance
between ligands, because the tendency was reproduced in less
hindered model complex 8ꢀ with h1 and h2 of 19.6 and 31.0◦,
respectively. Because h1 is larger than h2 in 14-electron disilene
complex 4 whose fourth ligand is missing, sole smaller r donor
ability of aryl isocyanide than trialkylphosphine cannot explain
the unsymmetrical distortion in 8 and 8ꢀ. Further work is required
to elucidate the origin of the unsymmetric bent angles in 8.
We have recently shown 14-electron disilene complexes 4 show
the 29Si resonance at very low field of +65.3 ppm compared to those
of 16-electron disilene complexes 2 (−46.5 ppm) and 3 (−51.9
ppm) and the very low field resonance was taken to be an indication
of the strong p-complex character.5c Although the 29Si resonance of
the unsaturated silicon nuclei for 9 (−41.2 ppm) appears at a little
lower field than those for 2 and 3, the extent of the down-field shift
for 9 is much smaller than that observed for 4. The remarkable low-
field shift of the 29Si resonance of 4 is characteristic of 14-electron,
three-coordinate complexes.
Conclusion
We have shown that the p-complex character of disilene transition
metal complexes is significantly modified by the residual ligands.
The p-complex character in L2Pd(disilene)-type 16-electron com-
plexes remarkably increases by changing L from trialkylphosphine
to aromatic isocyanide with poorer r-donating ability, while the
p-complex character is smaller than that of the previously re-
ported 14-electron disilene complex having one trialkylphosphine
ligand.
Experimental
1H, 13C, 29Si and 31P NMR spectra were recorded on a Bruker
AC300P FT-NMR spectrometer at 300, 75.4, 59.6 and 121 MHz,
respectively, and a Bruker Avance 400P FT-NMR spectrometer
at 400, 100, 79 and 161 MHz, respectively. Mass spectra and
high resolution mass spectra were recorded on a HX-110 mass
spectrometer (FAB, nitrobenzyl alcohol matrix). Air-sensitive
compounds were manipulated in a VAC Nexus 100027 glove
box. cis-Bis(phenyl isocyanide)dichloropalladium,18 tetrakis(tert-
butyldimethylsilyl)disilene (6)10 and 1,2-dilithiotetrakis(tert-
butyldimethylsilyl)disilane (5)9 were prepared according to the
procedure in the literature.
Chart 2
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[g2-Tetrakis(tert-butyldimethylsilyl)disilene](2,6-dimethylphenyl
isocyanide)(tricyclohexylphosphine)palladium 8
Stepwise ligand exchange of disilene complex 2 with isocyanide 7
followed by NMR spectroscopy
To a mixture of disilene complex 4 (0.070 g, 0.077 mmol) and
isocyanide 7 (0.010 g, 0.076 mmol) in a degassed Schlenk flask
(50 cm3) was introduced dry THF (5 cm3) through a vacuum line at
−50 ◦C. Increasing the temperature from −50 ◦C to rt during 4.5 h
resulted a clear yellow solution. Evaporation of THF and then re-
crystallization from toluene at −20 ◦C afforded mono(isocyanide)
complex 8 (0.080 g, 0.025 mmol) in 32% yield. 8: Found: C, 59.07;
H, 9.88. C51H102PNPdSi6 requires C, 59.17; H, 9.93%; mp 145 ◦C
(decomp.); dH (400 MHz, C6D6) 0.47 (s, 6 H), 0.51 (s, 6 H), 0.56 (s, 6
H), 0.63 (s, 6 H), 1.23–2.16 (m, 33 H), 1.29 (s, 18 H), 1.33 (s, 18 H),
2.43 (s, 6 H), 6.63 (d, J = 7.6 Hz, 2 H), 6.73 (dd, J = 7.6 Hz, 1 H);
When disilene complex 2 (10 mg, 1.5 × 10−5 mol) and isocyanide
7 (2.0 mg, 1.5 × 10−5 mol) were dissolved in benzene-d6 in
1
an NMR tube, H NMR spectrum of the mixture showed the
existence of 2 and mono(isocyanide) complex 11 in 1 : 4 ratio.
Addition of isocyanide 7 (2.0 mg, 1.5 × 10−5 mol) to the resulting
solution afforded bis(isocyanide) complex 9 almost quantitatively
as observed by 1H NMR spectroscopy.
cis-Bis(dimethylphenylphosphine)dichloropalladium 14
To a benzene (10 cm3) solution of cis-bis(phenyl isocyanide)-
dichloropalladium17 (0.472 g, 1.23 mmol) in a Schlenk flask
(50 cm3) was added dimethylphenylphosphine (0.4 cm3, 2.8 mmol).
The red solution was stirred for 40 min and then the solvent was
distilled off. Recrystallization of the resulted sticky solid from
benzene afforded 14 as orange needles in the yield of 0.540 g
(1.19 mmol, 97%).
dC (100 MHz, THF-d8) 1.1, 1.4, 1.6, 1.7 (SiCH3), 17.7 (CArCH3),
2
18.5, 18.7 (C(CH3)3), 25.4 (PCHCH2CH2CH2), 26.7 (d, JP–C
=
10 Hz, PCHCH2), 28.2, 28.3 (C(CH3)3), 30.0 (PCHCH2CH2), 33.0
(d, 1JP–C = 6 Hz, PCH), 126.8 (Cipso), 127.2 (CAr(m)), 127.3 (CAr(p)),
132.6 (CAr(o)), 164.1 (C≡N); dSi (79 MHz, C6D6) −60.4 (d, 2JP(cis)–Si
=
2
15 Hz), −39.4 (d, JP(trans)–Si = 48 Hz), +4.97, +4.99, 5.8, 5.9; dP
(161 MHz, C6D6) +30.9.
[g2-Tetrakis(tert-butyldimethylsilyl)disilene]bis-
(dimethylphenylphosphine)palladium 13
[g2-Tetrakis(tert-butyldimethylsilyl)disilene]bis(2,6-
To a mixture of palladium dichloride 14 (0.102 g, 0.293 mmol)
and 1,2-dilithiodisilane 5 (0.157 g, 0.296 mmol) in a degassed
Schlenk flask (50 cm3) was introduced THF (5 ml) dried over K
mirror through a vacuum line. The mixture was stirred for 2 h at
rt and then THF was distilled off. Addition of toluene (40 cm3) to
the yellow–brown residue and then the resulting precipitate was
filtered off. Removal of toluene in vacuo and then recrystallization
from toluene at −20 ◦C gave 13 (0.035 g, 0.04 mmol) in 20% yield.
13: mp 148 ◦C (decomp.); dH (400 MHz, C6D6) 0.49 (s, 12 H), 0.54
dimethylphenyl isocyanide)palladium 9
To a mixture of disilene complex 4 (7.0 mg, 7.7 × 10−3 mmol)
and isocyanide 7 (2.0 mg, 1.5 × 10−2 mmol) in a degassed NMR
tube (5 mm φ) was introduced dry benzene-d6 (0.4 cm3) through a
vacuum line at −50 ◦C. Quantitative formation of bis(isocyanide)
complex 9 was confirmed by 1H, 29Si and 31P NMR spectroscopies.
Evaporation of benzene-d6 and recrystallization from toluene at
−20 ◦C gave 9 as orange plates. 9: mp 136 ◦C (decomp.); dH
(400 MHz, C6D6) 0.56 (s, 12 H), 0.59 (s, 12 H), 1.30 (s, 36 H),
2.28 (s, 12 H), 6.65 (d, J = 7.6 Hz, 4 H), 6.77 (dd, J = 7.6 Hz,
2 H); dC (100 MHz, THF-d8) 1.4, 1.6 (SiCH3), 17.5 (CArCH3),
18.1 (C(CH3)3), 28.3 (C(CH3)3), 126.3 (Cipso), 127.1 (CAr(m)), 127.7
(CAr(p)), 133.3 (CAr(o)), 161.6 (C≡N); dSi (79 MHz, C6D6) −41.2,
+6.6.
2
(s, 12 H), 1.25 (s, 36 H), 1.38 (d, JP–H 4.8 Hz, 12 H), 7.00 (dd, 4
H), 7.07 (d, 2 H), 7.47 (dd, 4 H); dC (100 MHz, THF-d8) 3.1, 3.3
1
(SiCH3), 20.1 (SiC(CH3)3), 20.8 (dd, JP–C 11 Hz, P(CH3)3), 30.2
3
5
(C(CH3)3), 128.9 (dd, JP–C = 4 Hz, JP–C = 2 Hz, CAr(m)), 129.4
2
4
(CAr(p)), 131.5 (dd, JP–C = 6 Hz, JP–C = 4 Hz, CAr(o)), 141.9 (dd,
1JP–C = 12 Hz, 2JP–C = 5 Hz, Cipso); dSi (79 MHz, C6D6) −44.8 (dd,
2
2JP(cis)–Si = 21 Hz, JP(trans)–Si = 80 Hz), +4.8; dP (161 MHz, C6D6)
−19.0.
[g2-Tetrakis(tert-butyldimethylsilyl)disilene](2,6-dimethylphenyl
isocyanide)(trimethylphosphine)palladium 11
Crystallography
To a mixture of 16-electron disilene complex 2 (0.100 g, 0.129
mmol) and isocyanide 7 (0.017 g, 0.130 mmol) in a degassed
Schlenk flask (50 cm3) was introduced dry toluene (5 cm3) through
a vacuum line. Stirring the resulting light orange solution for 16 h
at rt, distilling off the solvent, and recrystallization from hexane
at −20 ◦C gave 11 (0.089 g, 0.107 mmol) as orange prisms in 83%
yield. 11: dH (400 MHz, C6D6) 0.46 (s, 6 H), 0.47 (s, 6 H), 0.51
Single crystals of complexes 8, 9 and 13 were obtained by recrystal-
lization from toluene, mounted in Apiezon grease and transferred
to the cold gas stream of the diffractometer. X-Ray data were
collected on a Rigaku/MSC Mercury CCD diffractometer with
˚
graphite-monochromated Mo-Ka radiation (k = 0.71073 A). The
data were corrected for Lorentz and polarization effects. The
structures were solved by direct methods and refined by full-matrix
least squares against F2 using all data (SHELXL-97).19
2
(s, 6 H), 0.56 (s, 6 H), 1.23 (d, JP–H = 6 Hz, 9 H), 1.25 (s, 18
H), 1.27 (s, 18 H), 2.27 (s, 6 H), 6.67 (d, J = 7.0 Hz, 2 H), 6.76
(dd, J = 7.0 Hz, 1 H); dC (100 MHz, THF-d8) 1.2 (br), 1.3, 1.4
(SiCH3), 17.6 (CArCH3), 18.3 (d, 1JP–C = 3 Hz, PCH3), 18.4, 18.5
(C(CH3)3), 28.2, 28.3 (C(CH3)3), 126.7 (Cipso), 127.2 (CAr(m)), 127.4
(CAr(p)), 132.9 (CAr(o)), 163.1 (C≡N); dSi (79 MHz, C6D6) −48.0 (d,
2JP(cis)–Si = 17 Hz), −44.7 (d, 2JP(trans)–Si = 60 Hz), 5.8, 5.9, 6.0, 6.1;
dP (161 MHz, C6D6) −31.4 (m).
In the single crystal of complex 8, two crystallographically
independent molecules (molecule 1 and molecule 2) exists in an
asymmetric unit. In molecule 1, one t-BuMe2Si group on Si(2)
is disordered over two sites with occupancies 0.862(3) [central
silicon atom: Si(6)] and 0.138(3) [central silicon atom: Si(13)]. All
tert-butyl and methyl carbon atoms on minor Si(13) were refined
with isotropic displacement parameters.
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The Royal Society of Chemistry 2006
Dalton Trans., 2006, 177–182 | 1 8 1
©

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Crystal data for complex 8. C51H102NPPdSi6, M = 1035.25,
monoclinic, space group P21/c (no. 14), a = 25.4468(8), b =
3 Bent angle h (degrees) defined here is similar to the pyramidalization
angle defined for alkene complexes by Morokuma and Borden: (a) K.
Morokuma and W. T. Borden, J. Am. Chem. Soc., 1991, 113, 1912; The
bent angle is related to bent-back angle (b) defined by Ibers and Stalick
as h = 90 − b; (b) J. K. Stalick and J. A. Ibers, J. Am. Chem. Soc., 1970,
92, 5333; (c) S. D. Ittel and J. A. Ibers, Adv. Organomet. Chem., 1976,
14, 33.
4 (a) E. K. Pham and R. West, J. Am. Chem. Soc., 1989, 111, 7667;
(b) E. K. Pham and R. West, Organometallics, 1990, 9, 1517; (c) E. K.
Pham and R. West, J. Am. Chem. Soc., 1996, 118, 7871.
5 (a) H. Hashimoto, Y. Sekiguchi, T. Iwamoto, C. Kabuto and M. Kira,
Organometallics, 2002, 21, 454; (b) H. Hashimoto, Yu. Sekiguchi, Yo.
Sekiguchi, T. Iwamoto, C. Kabuto and M. Kira, Can. J. Chem., 2003,
81, 1241; (c) M. Kira, T. Iwamoto, Y. Sekiguchi and C. Kabuto, J. Am.
Chem. Soc., 2004, 126, 12778.
6 (a) D. H. Berry, J. H. Chey, H. S. Zipin and P. J. Carroll, J. Am. Chem.
Soc., 1990, 112, 452; (b) P. Hong, N. H. Damrauer, P. J. Carroll and
D. H. Berry, Organometallics, 1993, 12, 3698; D. H. Berry, J. H. Chey,
H. S. Zipin and P. J. Carroll, Polyhedron, 1991, 10, 1189.
7 H. Hashimoto, K. Suzuki, W. Setaka, C. Kabuto and M. Kira, J. Am.
Chem. Soc., 2004, 126, 13628.
◦
3
˚
˚
20.6003(5), c = 23.6113(7) A, b = 108.2453(4) , V = 11755.1(6) A ,
T = 173 K, Z = 8, l(Mo-Ka) = 0.497 mm−1, 122930 reflections
measured, 26666 unique (Rint = 0.0354) which were used in all
calculations. Final R1 and wR2 were 0.0631 (I > 2r(I)) and 0.1178
(all data), respectively.
Crystal data for complex 9. C42H78N2PdSi6, M = 886.00,
¯
triclinic, space group P1 (no. 2), a = 12.998(4), b = 13.561(4),
◦
˚
c = 16.667(5) A, a = 97.695(2), b = 104.615(2), c = 114.174(3) ,
3
−1
˚
V = 2496.3(12) A , T = 150 K, Z = 2, l(Mo-Ka) = 0.554 mm ,
18243 reflections measured, 10160 unique (Rint = 0.0313) which
were used in all calculations. Final R1 and wR2 were 0.0538 (I >
2r(I)) and 0.1112 (all data), respectively.
Crystal data for complex 13. C40H82P2PdSi6, M = 899.94,
¯
triclinic, space group P1 (no. 2), a = 11.326(3), b = 11.988(3),
8 R. Fischer, M. Zirngast, M. Flock, J. Baumgartner and C. Marschner,
J. Am. Chem. Soc., 2005, 127, 70.
9 M. Kira, T. Iwamoto, D. Yin, T. Maruyama and H. Sakurai, Chem.
Lett., 2001, 910.
10 M. Kira, T. Maruyama, C. Kabuto, K. Ebata and H. Sakurai, Angew.
Chem., Int. Ed. Engl., 1994, 33, 1489; M. Kira, T. Iwamoto, T.
Maruyama, T. Kuzuguchi, D. Yin, C. Kabuto and H. Sakurai, J. Chem.
Soc., Dalton Trans., 2002, 1539.
◦
˚
c = 19.426(5) A, a = 93.507(3), b = 94.393(3), c = 100.588(4) ,
3
−1
˚
V = 2577.5(11) A , T = 173 K, Z = 2, l(Mo-Ka) = 0.586 mm ,
19373 reflections measured, 10555 unique (Rint = 0.0329) which
were used in all calculations. Final R1 and wR2 were 0.0503 (I >
2r(I)) and 0.0882 (all data), respectively.
11 A digermene platinum complex was synthesized by a similar method:
A. Castel, P. Riviere, J. Satge, D. Desor, M. Ahbala and C. Abdenadher,
Inorg. Chim. Acta, 1993, 212, 51.
12 Unfortunately, no single crystals of 11 suitable for X-ray crystallogra-
phy were obtained.
CCDC reference numbers 282912–282914.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b512414j
13 M. Kaftory, M. Kapon and M. Botoshansky, in The Chemistry of
Organic Silicon Compounds, ed. Z. Rappoport and Y. Apeloig, John
Wiley & Sons, Chichester, 1998, vol. 2, ch, 5, p. 181.
14 Y. Pan, J. T. Mague and M. H. Fink, Organometallics, 1992, 11, 3495;
M. Murakami, T. Yoshida and Y. Ito, Organometallics, 1994, 13, 2900;
M. Suginome, H. Oike, S.-S. Park and Y. Ito, Bull. Chem. Soc. Jpn.,
1996, 69, 289.
15 We assume that the avaraged bent angles (hav. ) are taken as indices of
the mean strength of r-donor abilities of two residual ligands.
16 All calculations were carried out at the B3LYP level using a Gaussian
98 program, revision A.11.4; Gaussian, Inc.: Pittsburgh, PA, 2001. The
basis sets were 6-31G(d) for H, C, Si, P atoms and Lanl2dz for Pd atom.
17 Theoretical calculations for related disilene complexes with methyl
isocyanide ligands 8ꢀꢀ and 9ꢀꢀ showed no serious differences in the effects
between pheny isocyanide and methyl isocyanide as ligands. See the
ESI† for the details of the calculations.
Acknowledgements
This work was supported by the Ministry of Education, Culture,
Sports, Science, and Technology of Japan (Grants-in-Aid for
Scientific Research on Priority Areas (No. 14078203, “Reaction
Control of Dynamic Complexes”) and on Scientific Research (A)
(No. 16205007). We also thank Dow Corning Toray Co. Ltd for
their generous gift of several silicon chemicals.
References
1 G. Frenking and W. Fro¨hlich, Chem. Rev., 2000, 100, 717; F. R.
Hartley, in Comprehensive Organometallic Chemistry, ed. G. Wilkinson,
F. G. A. Stone and E. W. Abel, Pergamon Press, Oxford, 1982, vol. 6.
2 M. J. S. Dewar, Bull. Soc. Chim. Fr., 1951, 18, C71; J. Chatt and L. A.
Duncanson, J. Chem. Soc., 1953, 2939.
18 J. R. Doyle, P. E. Slade and H. B. Jonassen, Inorg. Synth., 1960, 6, 218.
19 G. M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Germany, 1997.
1 8 2 | Dalton Trans., 2006, 177–182
This journal is
The Royal Society of Chemistry 2006
©