Synthesis and structural characterization of novel palladium complexes chelated by bulky cobalt-containing phosphine ligands: Unusual palladium-cobalt bond formation

Article abstract of DOI:10.1039/b306228g

The reaction of a bulky phosphine, [Co₂(CO)₅{μ-P,P-(μ-PPh₂C≡ CPPh₂)}][Co₂(CO)₄{μ-P-(μ-PPh₂ C≡CPPh₂)}] 1 with P(OMe)₃ gave a phosphite substituted tetracobalt-complex, [Co₂(CO)₄ {P(OMe)₃}{μ-P,P-(μ-PPh₂C≡CPPh₂)}]- [Co₂(CO)₄{μ-P-(μ-PPh₂C≡ CPPh₂)}] 5. Further reaction of 5 with (COD)PdCl₂ yielded a 5-coordinated palladium complex, [Co₂(CO)₄ {P(OMe)₃}{μ-P,P-(μ-PPh₂C≡CPPh₂)}] [Co₂(CO)₃(μ-CO)(μ-CO){μ-P-(μ-PPh₂ C≡CPPh₂)}]PdCl₂ 7. Similar results were obtained for the reaction of 1 with (COD)PdCl₂, which yielded [Co₂(CO)₅ {μ-P,P-(μ-PPh₂C≡CPPh₂)}] [Co₂(CO)₃(μ-CO){μ-P-(μ-PPh₂C≡CPP h₂)}]PdCl₂ 6. Likewise, reaction of another bulky phosphine [(μ-Ph₂PCH₂PPh₂)Co₂ (CO)₄(μ-PPh₂C≡CP(=O)Ph₂)] 3 with (COD)PdCl₂ yielded [{μ-P,P-PPh₂CH₂PPh₂}Co₂ (CO)₃-(μ-CO) {μ-PPh₂C≡CP(=O)Ph₂}]PdCl₂ 8. The X-ray structural studies of 6, 7 and 8 reveal that unusual palladium-cobalt bonds were formed. A Suzuki type reaction employing complexes 6, 7 and 8, as catalysts in the reaction of 2-bromothiophene with boronic acid did not show encouraging signs.

Full text of DOI:10.1039/b306228g

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Synthesis and structural characterization of novel palladium
complexes chelated by bulky cobalt-containing phosphine ligands:
unusual palladium–cobalt bond formation
Fung-E Hong,* Chin-Pei Chang and Yu-Chang Chang
Department of Chemistry, National Chung-Hsing University, Taichung 40227, Taiwan.
E-mail: fehong@dragon.nchu.edu.tw
Received 2nd June 2003, Accepted 22nd August 2003
First published as an Advance Article on the web 5th September 2003
᎐
᎐
᎐
᎐
The reaction of a bulky phosphine, [Co (CO) {µ-P,P-(µ-PPh C᎐CPPh )}][Co (CO) {µ-P-(µ-PPh C᎐CPPh )}] 1 with
᎐
2
5
2
2
2
4
2
2
᎐
P(OMe) gave a phosphite substituted tetracobalt-complex, [Co (CO) {P(OMe) }{µ-P,P-(µ-PPh C᎐CPPh )}]-
3
2
4
3
2
2
᎐
[Co (CO) {µ-P-(µ-PPh C᎐CPPh )}] 5. Further reaction of 5 with (COD)PdCl yielded a 5 -coordinated palladium
᎐
2
4
2
2
2
᎐
᎐
complex, [Co (CO) {P(OMe) }}{µ-P,P-(µ-PPh C᎐CPPh )}][Co (CO) (µ-CO){µ-P-(µ-PPh C᎐CPPh )}]PdCl 7.
᎐
᎐
2
4
3
2
2
2
3
2
2
2
᎐
᎐
2
Similar results were obtained for the reaction of 1 with (COD)PdCl , which yielded [Co (CO) {µ-P,P-(µ-PPh C᎐
CPPh )}][Co (CO) (µ-CO){µ-P-(µ-PPh C᎐CPPh )}]PdCl 6. Likewise, reaction of another bulky phosphine
[(µ-Ph PCH PPh )Co (CO) (µ-PPh C᎐CP(᎐O)Ph )] 3 with (COD)PdCl yielded [{µ-P,P-PPh CH PPh }Co (CO) -
(µ-CO){µ-PPh C᎐CP(᎐O)Ph }]PdCl 8. The X-ray structural studies of 6, 7 and 8 reveal that unusual palladium–
2
2
5
᎐
᎐
2
2
3
2
2
2
᎐
᎐
᎐
2
2
2
2
4
2
2
2
2
2
2
2
3
᎐
᎐
᎐
2
2
2
cobalt bonds were formed. A Suzuki type reaction employing complexes 6, 7 and 8, as catalysts in the reaction of 2-
bromothiophene with boronic acid did not show encouraging signs.
result. This course of aggregation might be avoided by
1
Introduction
replacing one of the three carbonyls by a better electron-
donating and bulky ligand such as a phosphite, e.g. P(OMe)3.
Our previous work also described a new type of metal-
Phosphine ligands have played an indispensable role in metal
complexes catalyzed organic syntheses.1 As known, most of the
metal complexes catalyze reactions involving both oxidative
addition and reductive elimination processes.2 A phosphine
with both electron-rich and bulky nature is believed to be able
to facilitate both steps and is regarded as a promising candidate
for an effective catalytic performance.3 Early efforts were
mainly focused on preparing phosphine ligands derived from
pure organic compounds, which have proved to be competent in
most of the designated cases.4 Recent studies, although reports
are few, have involved searching for effective transition-metal-
containing phosphine ligands with both electron-rich and bulky
characteristics.5
containing bidentate phosphine ligand, [(µ-Ph2PCH2PPh2)-
᎐
Co (CO) (µ-PPh C᎐CPPh )] 2, which was prepared from the
᎐
2
4
2
2
reaction of DPPA with one equivalent of a bis(diphenyl-
phosphino)methylene (DPPM) bridged dicobalt complex,
Co2(CO)6(µ-Ph2PCH2PPh2).8 Two oxidized complexes, [{µ-P,P-
᎐
PPh CH PPh }Co (CO) {µ-PPh C᎐CP(᎐O)Ph }] 3 and [{µ-
᎐
᎐
2
2
2
2
4
2
2
᎐
P,P-PPh CH PPh }Co (CO) {µ-P(᎐O)Ph C᎐CP(᎐O)Ph }] 4,
᎐
᎐
᎐
2
2
2
2
4
2
2
were obtained along with 2 during the chromatographic separ-
ation process (Chart 2).
Our previous work had demonstrated the preparation of a
particularly bulky, monodentate, phosphine ligand, which is
an alkyne-bridged, diphosphine-chelated tetracobalt-complex
᎐
[Co (CO) {µ-P,P-(µ-PPh C᎐CPPh )}][Co (CO) {µ-P-(µ-PPh -
᎐
2
5
2
2
2
4
2
᎐
᎐
C᎐CPPh )}] 1, from the reaction of PPh C᎐CPPh (DPPA)
᎐
᎐
2
2
2
with Co2(CO)8.6 (Chart 1). Compound 1 can be regarded as a
dimerized product of the bis(diphenylphosphino)acetylene
᎐
(DPPA) bridged dicobalt complex, [Co (CO) (µ-PPh C᎐
᎐
2
6
2
CPPh2)].
Chart 2 Bulky phosphine ligands 2, 3 and 4.
In this paper, the synthesis and structural characterization of
some novel palladium complexes coordinated by the above
mentioned bulky cobalt-containing phosphine ligands are
reported.
Chart 1 A bulky, monodentate, phosphine ligand 1.
It is a common observation that a cobalt center with more
than three carbonyl ligands is susceptible to the replacement by
a strong electron-donating ligand such as a phosphine.7 There-
fore, it was speculated that the only available phosphine site of 1
might attack another molecule of 1 at the designated cobalt
center, with three carbonyl ligands, and replace one of them
at elevated temperature. Consequently, products with high
molecular weights might be formed and insolubility might
2
Results and discussion
2.1 Reaction of 1 with trimethoxylphosphine
Direct treatment of 1 with 1.2 molar equivalent of P(OMe)3
and trimethylamine oxide (TMNO) in mixed solvent (CH2Cl2–
D a l t o n T r a n s . , 2 0 0 3 , 3 8 9 2 – 3 8 9 7
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
3892

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Scheme 1
THF) at 25 ЊC for 3 h gave the phosphite coordinated bulky
᎐
᎐
2
tetracobalt complex, [Co (CO) {P(OMe) }{µ-P,P-(µ-PPh C᎐
2
4
3
᎐
CPPh )}][Co (CO) {µ-P-(µ-PPh C᎐CPPh )}] 5. Compound 5
᎐
2
2
4
2
2
was characterized by spectroscopic means, as well as by X-ray
diffraction studies. The X-ray study reveals that the structure of
5 is almost the same as its unsubstituted precursor, 1, with the
exception of the replacement of one of the carbonyls by a
phosphite ligand (Fig. 1). Interestingly, the phosphite ligand
adopts an equatorial position at the cobalt center, which is in
contrast to the common observation where the phosphine lig-
and adopts an axial position (Chart 3). A search for phosphine
substituted alkyne-bridged dicobalt complexes from the Cam-
bridge Crystallographic Database shows that all the 26 reported
crystal structures have the substituted phosphine ligands
located at the axial position.9 Out of these 26 compounds, a
total of 34 P–Co(2)–Co(1) bond angles, ranged from 147.50 to
159.85Њ, were measured. In the case of 5, the bond angle of
P–Co(2)–Co(1) is 96.95(8)Њ, which is much sharper than all the
reported instances. To the best of our knowledge, this is the first
case in which the P(OMe)3 is located at the equatorial position
of the alkyne-bridged dicobalt complex. It is believed that the
Chart 3 A generalized structure of a phosphine substituted alkyne-
bridged dicobalt complex.
location of the phosphite ligand in the molecule results from
the compromise of the steric hindrance between the phosphite
ligand and the bulky alkyne substituent phenyl groups. The
existence of the substituted P(OMe)3 in 5 is also evidenced from
1
the H, 13C, 31P NMR spectra of this dark-brown compound
which show doublet, singlet and singlet signals at δ 3.57, 52.05,
and 159.1 ppm, respectively. Judging from its structure, 5 is a
promising, bulky, monodentate phosphine ligand.
2.2 Reactions of 1 and 5 with (COD)PdCl2
The reaction of 1 with one molar equivalent of (COD)PdCl2
was carried out in CH2Cl2 at 25 ЊC for 1 h and gave a yellow–
᎐
brown colored product, [Co (CO) {µ-P,P-(µ-PPh C᎐CPPh )}]-
᎐
2
5
2
2
᎐
[Co (CO) (µ-CO){µ-P-(µ-PPh C᎐CPPh )}]PdCl 6 (Scheme 1).
᎐
2
3
2
2
2
A reaction was also carried out for 5 with (COD)PdCl2 under
the same conditions and yielded a yellow–brown colored
᎐
product,
[Co (CO) {P(OMe) }{µ-P,P-(µ-PPh C᎐CPPh )}]-
᎐
2
4
3
᎐
2
2
[Co (CO) (µ-CO){µ-P-(µ-PPh C᎐CPPh )}]PdCl 7. Both
6
᎐
2
3
2
2
2
and 7 were characterized by spectroscopic means, as well as by
X-ray diffraction studies. The 31P NMR spectrum of 6 shows
singlet, singlet and triplet signals at δ 23.65, 49.70, and 65.69
ppm, respectively, for the phosphorus atoms. The most upfield
signal corresponds to the palladium-coordinated phosphorus
atom. Similarly, there are signals at δ 24.31, 50.53, and 59.08
ppm, respectively, for the three phosphorus atoms in 7. Again,
the most upfield one corresponds the palladium-coordinated
phosphorus atom. For 7, there is one more highly downfielded
signal at δ 158.76 ppm, which corresponds to the substituted
P(OMe)3 ligand. The X-ray structural studies of both 6 and 7
reveal that the palladium fragment, PdCl2, is coordinated by
bulky phosphine ligands 1 and 5, respectively (Figs. 2 and
3). Interestingly, an unusual palladium–cobalt bonding was
formed accompanied with a semi-bridging carbonyl in both
compounds. The axial carbonyls, C(7)–O(7), for both 6 and 7
are slightly bent. The bond angles, Co(4)–C(7)–O(7), for 6 and
7 are 166.51 and 168.59Њ, respectively, indicating a weak semi-
bridging interaction with Pd. The formal oxidation states for
the two metal centers are assigned as Pd() and Co(0) for both
compounds. To the best of our knowledge, this is the first
example of forming a direct Pd–Co bond through the reaction
Fig. 1 ORTEP drawing with the numbering scheme of 5. Some carbon
and hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (Њ): P(4)–C(12) 1.797(6), Co(4)–C(7) 1.788(8), Co(4)–C(12)
1.970(6), Co(4)–C(11) 1.959(6), Co(3)–C(12) 1.960(6), Co(3)–C(11)
1.979(6), Co(3)–Co(4) 2.5052(13), C(11)–C(12) 1.368(9), P(3)–C(11)
1.781(6); C(7)–Co(4)–C(12) 101.1(3), C(7)–Co(4)–C(8) 94.9(4), C(7)–
Co(4)–Co(3) 151.1(2), C(12)–Co(4)–Co(3) 50.22(19), C(8)–Co(4)–
Co(3) 92.4(3), C(11)–Co(4)–Co(3) 50.85(18), C(12)–Co(3)–C(11)
40.7(3), C(11)–Co(3)–Co(4) 50.13(17), C(11)–C(12)–Co(4) 69.2(3),
P(4)–C(12)–Co(3) 143.0(4).
D a l t o n T r a n s . , 2 0 0 3 , 3 8 9 2 – 3 8 9 7
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Scheme 2
ized by spectroscopic means, as well as by X-ray diffraction
studies. The 31P NMR spectrum of 8 shows three singlet signals
in the ratio of 1 : 1 : 2 at δ 24.76, 28.70, and 33.92 ppm, respect-
ively, for all phosphorus atoms. Again, the most upfield signal
corresponds to the palladium-coordinated phosphorus atom.
The crystal structure of 8 reveals that the bulky phosphine
ligand, 3, coordinates to the palladium fragment, PdCl2,
with both phosphorus and cobalt sites (Fig. 4). An unusual
palladium–cobalt bonding was formed accompanied with two
semi-bridging carbonyls. The structure also reveals that the
distance between the oxide (P᎐O) and the adjacent methylene
᎐
proton, 2.238 Å, is well within the range of an intramolecular
hydrogen bonding.10 This is also evidenced by the fact that a
highly downfield shift of the adjacent methylene proton (6.79
ppm), compared with the remote methylene proton (3.83 ppm),
was observed. As known, the 16-electron rule is obeyed for
most of second and third row transition metal complexes with
d8 configuration.11 This rule is observed for 8 (and for 6, 7) if
the Pd–Co bonding is regarded as a Co to Pd dative bond. Once
more, the formal oxidation states for the two metal centers are
assigned as Pd() and Co(0) for 8. Interestingly, strikingly simi-
lar bonding modes, surrounding the Pd center, were established
for 6, 7 and 8. As a result, it is safe to state that the formation
of a direct Pd–Co bond through this reaction route is not
serendipitous, but rather, a general process.
Fig. 2 ORTEP drawing with the numbering scheme of 6. Some carbon
and hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (Њ): Pd–Cl(2) 2.350(4), Pd–Cl(1) 2.382(4), Pd–P(4) 2.202(4),
P(4)–C(12) 1.728(16), Co(4)–C(7) 1.780(14), Co(4)–C(11) 2.011(14),
Co(4)–C(12) 2.038(15), Co(3)–C(12) 1.941(15), Co(3)–C(11) 1.990(13),
Co(3)–Co(4) 2.555(2), C(11)–C(12) 1.372(19), P(3)–C(11) 1.784(16),
Pd–C(7) 2.290(14), Pd–Co(4) 2.677(2); C(7)–Co(4)–C(8) 107.8(6),
C(7)–Co(4)–C(12) 105.6(6), C(7)–Co(4)–Pd 57.7(4), C(8)–Co(4)–Pd
73.9(5), Co(3)–Co(4)–Pd 109.04(8), Cl(1)–Pd–Co(4) 99.61(12), C(7)–
Pd–Cl(1) 84.2(4), P(4)–Pd–Cl(2) 91.18(16), P(4)–Pd–Co(4) 75.31(11),
C(7)–Pd–Co(4) 41.1(3).
Fig. 3 ORTEP drawing with the numbering scheme of 7. Some carbon
and hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (Њ): Pd–Cl(2) 2.3270(18), Pd–Cl(1) 2.3857(17), P(4)–C(12)
1.757(5), Co(4)–C(7) 1.806(6), Co(4)–C(12) 2.057(5), Co(4)–C(11)
1.995(5), Co(3)–C(12) 1.918(5), Co(3)–C(11) 1.987(5), Co(3)–Co(4)
2.5468(9), C(11)–C(12) 1.341(7), P(3)–C(11) 1.796(5), Pd–P(4)
2.1966(15), Pd–Co(4) 2.6861(8), Pd–C(7) 2.409(6); C(7)–Co(4)–C(8)
105.4(3), C(7)–Co(4)–C(12) 107.7(2), C(7)–Co(4)–Pd 61.20(18), C(8)–
Co(4)–Pd 73.36(19), Co(3)–Co(4)–Pd 107.42(3), Cl(1)–Pd–C(7)
85.20(13), Cl(1)–Pd–Co(4) 101.52(5), P(4)–Pd–Co(4) 76.35(4), P(4)–
Pd–Cl(2) 89.10(7), C(7)–Pd–Co(4) 41.08(14).
Fig. 4 ORTEP drawing with the numbering scheme of 8. Some carbon
and hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (Њ): Pd–Cl(2) 2.3282(9), Pd–Cl(1) 2.3997(9), P(2)–C(2)
1.766(3), Co(2)–C(30) 1.807(4), Co(2)–C(29) 1.819(4), Co(2)–C(1)
1.991(3), Co(2)–C(2) 2.049(3), Co(1)–Co(2) 2.4999(6), C(1)–C(2)
1.348(4), Pd–P(2) 2.2050(9), Pd–Co(2) 2.6171(5), Pd–C(30) 2.434(3),
Pd–C(29) 2.556(3); C(30)–Co(2)–C(29) 114.12(15), C(30)–Co(2)–Pd
63.70(11), C(29)–Co(2)–Pd 67.62(10), P(2)–Pd–Cl(2) 92.04(3), P(2)–
Pd–Cl(1) 171.98(3), Cl(2)–Pd–Cl(1) 94.58(4), Cl(1)–Pd–C(30) 83.69(8),
P(2)–Pd–C(29) 93.99(8), Cl(2)–Pd–C(29) 140.80(9), Cl(1)–Pd–C(29)
78.02(8), C(30)–Pd–C(29) 75.12(11), P(2)–Pd–Co(2) 75.90(2), Cl(1)–
Pd–Co(2) 97.33(3), C(30)–Pd–Co(2) 41.73(8), C(29)–Pd–Co(2)
41.15(8).
of a cobalt-containing phosphine ligand with a palladium
compound.
2.3 Reactions of 3 with (COD)PdCl2
The reaction of 3 with one molar equivalent of (COD)PdCl2
was carried out in CH2Cl2 at 25 ЊC for 1 h (Scheme 2). The
resulting red–brown colored product, [{µ-P,P-PPh2CH2PPh2}-
᎐
Co (CO) (µ-CO){µ-PPh C᎐CP(᎐O)Ph }]PdCl 8 was character-
᎐
᎐
2
3
2
2
2
D a l t o n T r a n s . , 2 0 0 3 , 3 8 9 2 – 3 8 9 7
3894

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Some selected structural data for 6, 7 and 8 are shown in
Chart 4 for comparison. Basically, the variations of the geo-
metrical parameters for all three compounds are small. The
four atoms, Co, Pd, P, C, are almost coplanar with the semi-
bridging carbonyl(s) off the plane. The measured Pd–P bond
lengths for all three compounds are within experimental error.
It was also found that the distances between the two metal
centers are close to the short side of all reported Pd–Co single
bonds.12 The Pd–Co bond lengths of 6 and 7 are similar and
slightly longer than that of 8.
phosphine ligands have proved to act as authentically mono-
dentate phosphine ligands in coordinating to palladium. In
addition, an unusual palladium–cobalt bonding was formed
with semi-bridging carbonyl(s) in the products.
3
Experimental
3.1 General
All operations were performed in a nitrogen-flushed glove-box
or in a vacuum system. Freshly distilled solvents were used. All
processes of separations of the products were performed by
Centrifugal Thin Layer Chromatography (CTLC, Chromato-
1
tron, Harrison model 8924). H NMR spectra were recorded
(Varian VXR-300S spectrometer) at 300.00 MHz; chemical
shifts are reported in ppm relative to internal CHCl3 or CH2Cl2.
31P and 13C NMR spectra were recorded at 121.44 and 75.46
MHz, respectively. Variable-temperature 1H NMR experiments
1
were recorded by the same instrument. Some other routine H
NMR spectra were recorded on a Gemini-200 spectrometer at
200.00 MHz or Varian-400 spectrometer at 400.00 MHz. IR
spectra of sample powders in KBr were recorded on a Hitachi
270–30 spectrometer. Mass spectra were recorded on a JOEL
JMS-SX/SX 102A GC/MS/MS spectrometer. Elemental analy-
ses were recorded on a Heraeus CHN–O–S-Rapid instrument.
3.2 Preparation of 5
Into a 100 cm3 round flask was placed 1 (0.780 g, 0.611 mmol)
in 10 cm3 of THF and 1.2 molar equivalents of P(OCH3)3
(0.090 ml, 0.763 mmol). A solution containing TMNO (0.055 g,
0.736 mmol) in 10 cm3 CH2Cl2 was transferred to the 100 cm3
round flask dropwise. Then, the solution was stirred at 25 ЊC
for 3 h. Subsequently, the mixture was concentrated in a
Chart 4 Selected structural parameters for 6, 7 and 8.
reduced pressure and was subjected to chromatography. Dark
᎐
As revealed from the crystal data, there are two semi-
bridging carbonyls between Pd and Co in 8 whilst only one for
either 6 or 7. As known, it is necessary for the metal center to
release the strain caused by the excess electron density accumu-
lation, donated from the ligand, a phosphine in this case. In a
structurally related compound (dppe)(CH3)Pd–Co(CO)4, with
a direct Pd–Co single bond and two semi-bridging CO groups, a
theoretical study has demonstrated that part of the electron
density flows from the occupied Pd d orbitals to the Co through
the π* orbitals of the bridging CO groups.13 While electron
density is donated to the Pd center, supplementary channels,
bridging CO(s) in these cases, are employed in conveying the
excess electron density away from Pd. Judging from the number
of the semi-bridging CO, it is believed that the coordinated
phosphine ligand of 8 donates more electron densities to Pd
than in the case of either 6 or 7. This is also evidenced by the
fact that the 31P NMR chemical shifts change is larger for 8
than that of 6 or 7 after coordination.14
brown [Co (CO) {P(OMe) }{µ-P,P-(µ-PPh C᎐CPPh )}][Co -
᎐
2
4
3
2
2
2
᎐
(CO) {µ-P-(µ-PPh C᎐CPPh )}] 5 (0.390 g, 0.284 mmol) was
᎐
4
2
2
eluted out with mixed solvent (CH2Cl2–hexane (1 : 1)); yield
46.5%.
3.2.1 Characterization of 5. 1H NMR (CDCl3, δ/ppm): 3.57
(d, JP–H = 11.1 Hz, P(OCH3)3), 6.93–7.65 (m, 40H, arene); 13C
NMR (CDCl3, δ/ppm): 52.05(3C, d, JP–H = 19.5 Hz, –OCH3),
127.28–138.56 (48C, arene), 202.52 (CO), 205.15 (CO), 206.51
(CO); 31P NMR (CDCl3, δ/ppm): 13.0 (s, 1P, dppa), 50.0 (s, 2P
dppa), 58.8 (s, 1P, dppa), 159.1 (s, 1P, P(OCH3)3). Anal. Calc.
for 5: C, 55.12; H, 3.60. Found: C, 54.89; H, 3.52%.
3.3 Reaction of 1 with (COD)PdCl2
Into a 100 cm3 flask was placed 1 (0.536 g, 0.420 mmol) and
(COD)PdCl2 (0.120 g, 0.420 mmol) with 15 ml of CH2Cl2. The
solution was stirred at 25 ЊC for 1 h. Purification with centri-
fugal thin-layer chromatography (CTLC) was carried out. The
first band, yellow–brown in color, [Co2(CO)5{µ-P,P(µ-PPh2-
Many attentions have been focused on the Suzuki cross-
coupling reaction in recent years because of its convenience in
generating sp2–sp2 carbon–carbon bonds. The palladium-cata-
lyzed cross coupling of aryl halides with organoboron reagents
᎐
᎐
C᎐CPPh )}][Co (CO) {µ-P(µ-PPh C᎐CPPh )}]PdCl 6 (0.139
᎐
᎐
2
2
4
2
2
2
g, 0.096 mmol), was eluted with mixed solvent (ethyl acetate–
CH2Cl2 (1 : 1)); yield 22.6%.
has become one of the most widely utilized methods.15
A
Suzuki type coupling reaction employing the above mentioned
palladium complexes, 6, 7 and 8, as catalysts in the reaction of
2-bromothiophene with boronic acid, was studied.16 Unfortu-
nately, preliminary results did not show encouraging signs. The
yields were below 20% in several trial reaction conditions. A
strong bonding between the palladium and halide as well as the
bulkiness of the ligand might account for the retardation of
the coupling reaction. More systematic investigations of these
reactions are currently being undertaken.
3.3.1 Characterization of 6. 1H NMR (CD2Cl2, δ/ppm):
6.99–7.83 (m, 40H, arene); 13C NMR (CDCl3, δ/ppm): 127.90–
137.49 (m, 40C, arene), 199.48–205.45 (m, terminal CO); 31P
NMR (CD2Cl2, δ/ppm): 23.65 (s, 1P, dppa), 49.70 (d, JP–P = 37.4
Hz, 2P, dppa), 65.69 (t, JP–P = 42.3 Hz, 1P, dppa). Anal. Calc.
for 6: C, 48.82; H, 3.19. Found: C, 45.35; H, 3.34%; IR (KBr)/
cmϪ1: νCO 1980, 2007, 2068; MS: m/z 1416 (P Ϫ Cl)ϩ; mp 120 ЊC
(decomp.).
3.4 Reaction of 5 with (COD)PdCl2
Into a 100 cm3 flask was placed 5 (0.436 g, 0.318 mmol) and
Summary. The reactions of some cobalt-containing bulky
monodentate phosphine ligands toward palladium com-
plexes have been carried out. These cobalt-containing bulky
(COD)PdCl2 (0.091 g, 0.318 mmol) with 15 ml of CH2Cl2. The
D a l t o n T r a n s . , 2 0 0 3 , 3 8 9 2 – 3 8 9 7
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Table 1 Crystal data for 5, 6, 7 and 8
Compound
5
6
7
8
Formula
Formula weight
Crystal system
Space group
C63H49Co4O11P5
1372.59
C61H40 Cl2Co4O9P4Pd C63H49Cl2Co4O11P5Pdؒ2CH2Cl2ؒCH3OH C55H42Cl2Co2O5P4PdؒCH2Cl2
1453.83
Monoclinic
P21/n
1549.98
Monoclinic
P21/c
1286.85
Triclinic
P1
Triclinic
¯
¯
P1
a/Å
b/Å
c/Å
α/Њ
13.7890(19)
13.8536(19)
18.622(2)
86.151(3)
85.941(3)
61.916(2)
3128.3(7)
2
15.029(4)
23.761(7)
17.180(5)
90
98.846(7)
90
6062(3)
4
1.593
16.5696(12)
19.5107(13)
23.8716(17)
90
109.1480(10)
90
7290.4(9)
4
1.597
11.1922(8)
13.1178(9)
19.4159(14)
94.9880(10)
100.917(2)
101.4100(10)
2720.7(3)
2
β/Њ
γ/Њ
V/Å3
Z
Dc/Mg mϪ3
λ(Mo-Kα)/Å
µ/mmϪ1
1.457
0.71073
1.228
1.571
0.71073
1.291
0.71073
1.611
0.71073
1.520
θ Range/Њ
Observed reflections
(F > 4σ(F))
No. of refined parameters
R1a
1.96–26.03
7388
1.68–25.98
3819
1.38–26.00
4570
1.81–26.04
7517
748
730
865
451
0.0662
0.1697
0.959
0.0889
0.2158
0.986
0.0494
0.1409
0.906
0.0385
0.0993
0.983
wR2b
GoFc
a R1 = |Σ(|Fo| Ϫ |Fc|)/|ΣFo|| for significant reflections. b wR2 = {Σ[w(Fo2 Ϫ Fc2)2/Σ[w(Fo )2}}1/2 for significant reflections; w = 0.118, 0.1525, 0.1129 and
2
0.0705 for 5, 6, 7 and 8, respectively. c GoF = [Σw(Fo 2 Ϫ Fc2)2/(Nrflns Ϫ Nparams)]1/2
.
solution was stirred at 25 ЊC for 1 h. Purification with centri-
fugal thin-layer chromatography (CTLC) was carried out. The
first band, yellow-brown in color, [Co2(CO)4{P(OMe)3}{µ-P,P-
determinations were based on a check of the Laue symmetry
and systematic absences, and confirmed using structure solu-
tion. The structures were solved by direct methods using the
SHELXTL package.17 All non-H atoms were located from suc-
cessive Fourier maps and hydrogen atoms were refined using a
riding model. Anisotropic thermal parameters were used for all
non-H atoms, and fixed isotropic parameters were used for H
atoms.18 Crystallographic data for 5, 6, 7, and 8 are summarized
in Table 1.
᎐
᎐
(µ-PPh C᎐CPPh )}][Co (CO) {µ-P(µ-PPh C᎐CPPh )}]PdCl 7
᎐
᎐
2
2
2
4
2
2
2
(0.2216 g, 0.1429 mmol), was eluted with mixed solvent (ethyl
acetate–CH2Cl2 (1 : 1)); yield 45.0%.
3.4.1 Characterization of 7. 1H NMR (CD2Cl2, δ/ppm):
3.62 (d, JH–H = 10.81 Hz, 9H, CH3), 7.04–7.86 (m, 40H, arene);
13C NMR (CDCl3, δ/ppm): 127.38–134.08 (m, 40C, arene),
201.13–205.80 (m, terminal CO); 31P NMR (CD2Cl2, δ/ppm):
24.31 (s, 1P, dppa), 50.53 (s, 1P, dppa), 59.08 (s, 1P, dppa),
158.76 (s, 1P, POMe3). Anal. Calc: C, 48.82; H, 3.19. Found: C,
45.35; H, 3.34%; IR (KBr)/cmϪ1: νCO 1980, 2007, 2068; mp 100
ЊC (decomp.).
CCDC reference numbers 209741–209744.
See http://www.rsc.org/suppdata/dt/b3/b306228g/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
We thank the National Science Council of the R.O.C. (Grant
NSC-91-2113-M-005-017) for support.
3.5 Reaction of 3 with (COD)PdCl2
Into a 100 cm3 flask was placed 3 (0.673 g, 0.656 mmol) and
(COD)PdCl2 (0.187 g, 0.656 mmol) with 15 ml of CH2Cl2. The
solution was stirred at 25 ЊC for 1 h. Purification with centri-
fugal thin-layer chromatography (CTLC) was carried out. The
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᎐
(CO) {µ-PPh C᎐CP(O)Ph }]PdCl 8 (0.455 g, 0.384 mmol), was
᎐
4
2
2
2
eluted with mixed solvent (ethyl acetate–CH2Cl2 (1 : 1); yield
57.7%.
3.5.1 Characterization of 8. 1H NMR (CD2Cl2, δ/ppm):
3.83 (m, 1H, CH2), 6.79 (m, 1H, CH2), 6.71–8.41 (m, 40H,
arene); 13C NMR (CDCl3, δ/ppm): 31.57 (s, 1C, CH2), 116.86–
136.66 (m, 40C, arene), 201.13–205.80 (m, terminal CO); 31P
NMR (CD2Cl2, δ/ppm): 24.76 (s, 1P, dppa), 28.70 (s, 1P, dppa),
33.92 (s, 2P, dppm). Anal. Calc: C, 54.96; H, 3.52. Found: C,
50.62; H, 3.93%; IR(KBr)/cmϪ1: νCO 1969, 2019, 2052; MS: m/z
1166 (Pϩ Ϫ Cl); mp 210 ЊC (decomp.).
3.6 X-Ray crystallographic studies
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capillaries under nitrogen atmosphere and mounted on a
Bruker AXS SMART 1000 diffractometer. Intensity data were
collected in 1350 frames with increasing ω (width of 0.3Њ per
frame). Absorption corrections were based on symmetry equiv-
alent reflections using the SADABS program. Space group
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D a l t o n T r a n s . , 2 0 0 3 , 3 8 9 2 – 3 8 9 7
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14 31P NMR chemical shift (δ/ppm): 1 (12.98)
6 (23.65); 5 (13.00)
7 (24.31); 3 (0.80)
8 (24.76).
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16 Suzuki coupling reaction was performed according to Wolfe’s
procedure. Into a oven-dried Schlenk flask, which was previously
evacuated and backfilled with nitrogen, was placed 0.01 mmol of
6 (or 7, 8), boronic acid (183 mg, 1.5 mmol), and KF (174 mg, 3.0
mmol). This was then followed by adding
1 mmol of 2-
bromothiophene and 1 ml of THF. The solution was stirred at 60 ЊC
for 19 h. Consequently, the reaction mixture was diluted with ether
(30 mL) and poured into a separatory funnel. The mixture was
washed with aqueous NaOH (1 M, 20 mL); the aqueous layer was
then extracted with ether (20 mL) again. The combined organic
layers were washed with saturated NaCl (20 mL), and dried with
anhydrous magnesium sulfate, filtered, and concentrated in vacuo.
The crude material was purified by flash chromatography on silical
gel. The reaction yield was calculated based on the isolated product.
17 G. M. Sheldrick, SHELXTL PLUS User’s Manual . Revision 4.1
Nicolet XRD Corporation, Madison, WI, USA, 1991.
10 The commonly observed hydrogen-bonding range is from 2.05 to
2.40 Å: R. Taylor and O. Kennard, J. Am. Chem. Soc., 1982, 104,
5063.
11 C. M. Lukehart, Fundamental Transition Metal Organometallic
Chemistry, Brooks/Cole Publishing Company, Monterey, CA, 1985,
ch. 1.
12 The statistics search from the Cambridge Structure Data base by the
enquired Pd–Co distance from 16 citations reveals that the distances
range from 2.511 to 2.942 Å: (a) P. Braunstein, J.-M. Jud,
18 The hydrogen atoms were ride on carbons or oxygens in their
idealized positions and held fixed with the C–H distances of 0.96 Å.
D a l t o n T r a n s . , 2 0 0 3 , 3 8 9 2 – 3 8 9 7
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