Dibenzo[a,d]cycloheptenyl dibenzophosphole palladium dichloride: Synthesis, X-ray-crystal structure and application in the Suzuki-Miyaura coupling

Article abstract of DOI:10.1039/b417716a

A highly rigid dibenzo[a,d]cycloheptenyl dibenzophosphole with a pre-organized concave shaped binding site acts as an efficient ligand in the palladium catalyzed Suzuki-Miyaura coupling process between halogenoaromatics and phenylboronic acid. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b417716a

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Dibenzo[a,d]cycloheptenyl dibenzophosphole palladium dichloride:
Synthesis, X-ray-crystal structure and application in the Suzuki–
Miyaura coupling{
Claire Thoumazet,a Louis Ricard,a Hansjo¨rg Gru¨tzmacherb and Pascal Le Floch*a
Received (in Cambridge, UK) 25th November 2004, Accepted 11th January 2005
First published as an Advance Article on the web 28th January 2005
DOI: 10.1039/b417716a
spectroscopy, elemental analyses and X-ray crystallography
(Scheme 2). A view of one molecule of 3 is presented in Fig. 1.
As can be seen, the overall geometry around palladium is square
planar and coordination of the olefin group occurs in an g2-
fashion as expected. Bond lengths and bond angles fall in the usual
range.
A highly rigid dibenzo[a,d]cycloheptenyl dibenzophosphole
with a pre-organized concave shaped binding site acts as an
efficient ligand in the palladium catalyzed Suzuki–Miyaura
coupling process between halogenoaromatics and phenyl-
boronic acid.
There is a continuing interest in the elaboration of polydentate
ligands featuring electronically different binding sites. The fine
tuning of electronic and steric effects is a difficult task and no
definitive model allowing one to rationalize and predict the
optimal combination ligand–metal has been achieved yet.1
Combinations of two or more heteroatoms in the same ligand
already proved to be particularly active and most of the studies are
currently focussing on this topic.2 On the other hand, olefins have
been rarely used as ligands in homogeneous catalysis3 and the
combination of one phosphorus and one olefin as binding sites in
the same skeleton remains also largely unexploited.4 In this article
we present the synthesis of a mixed phosphole–dibenzotropylidene
ligand and its use in the palladium catalyzed formation of C–C
bonds through the Suzuki–Miyaura coupling process.
Comlex 3 contains a ligand combining the s-donor strength of a
phosphine group with the good p-accepting capability of an olefin.
Scheme 2 Synthesis of complex 3. i) [Pd(COD)Cl2], CH2Cl2, RT 10 min.
The synthesis of ligand 2 was conventionally achieved through
the reaction of the P–H phosphole 1 with chlorodibenzotropily-
dene.5 Compound 2 which proved to be slightly oxygen sensitive
was isolated in good yield after usual work-up and fully
characterized by NMR spectroscopy and elemental analyses
(Scheme 1).
Additional evidence was given by an X-ray crystal structure
analysis.{ Phosphole 2 is soluble in common organic solvents and
was reacted with [Pd(COD)Cl2] to quantitatively afford the
dichloride complex 3 which was fully identified by NMR
Scheme 1 Synthesis of phosphole 2. i) Chlorodibenzotropilydene (1 eq),
toluene, reflux 15 h.
{ Electronic supplementary information (ESI) available: General con-
siderations; syntheses and characterizations of P–H phosphole 1 and
complex 3; general procedure for catalytic reactions; X-ray crystal
structures of 2 and 3. See http://www.rsc.org/suppdata/cc/b4/b417716a/
*lefloch@poly.polytechnique.fr
Fig. 1 Solid state structure of complex 3. Hydrogen atoms are omitted
for clarity; thermal ellipsoids are at 50% probability.
1592 | Chem. Commun., 2005, 1592–1594
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Table 1 Cross-coupling reaction of halogenoaryls with phenylboronic acid using complex 3 as catalyst precursor and method A
Entry
Substrate
3/mol%
t/h
T/uC
GCa (%)
Yieldb (%)
TON
1
2
3
4
5
6
a
Bromobenzene
Bromobenzene
Bromobenzene
4-Bromotoluene
4-Bromoanisole
4-Bromoacetophenone
0.0001
0.0005
0.00001
0.0001
0.0001
0.0001
b
14
2
21
14
14
14
100
100
100
100
100
100
99.9
94.5
8.3
81
39
63
96
93
7
76
38
61
9.9 6 105
1.9 6 105
8.3 6 105
8.1 6 105
3.9 6 105
6.3 6 105
Based on GC analysis with external standards. Isolated yields by column chromatography; products fully characterized by NMR and MS
by comparison with literature data.
Moreover, this push–pull ligand is especially rigid and contains no
rotating groups. We evaluated the activity of 3 in a catalyzed C–C
cross-coupling process. These transformations are thought to be
facilitated by ligands that combine a good s-donor strength (to
favour the oxidative addition) with a good p-accepting capacity (to
favour reductive elimination).
featuring the tropylidene backbone and their use as highly rigid
ligand in different catalytic processes.
Claire Thoumazet,a Louis Ricard,a Hansjo¨rg Gru¨tzmacherb and
Pascal Le Floch*a
aDepartment of Chemistry, Laboratory ‘‘He´te´roe´le´ments et
Coordination’’ UMR CNRS 7653, Ecole Polytechnique, 91128,
Palaiseau cedex, France. E-mail: lefloch@poly.polytechnique.fr;
Fax: (+33).1.69.33.39.90; Tel: (+33).1.69.33.45.70
bDepartment of Chemistry and Applied Biosciences (D-CHAB), ETH
Ho¨nggerberg, Wolfgang-Pauli Str, 8093, Zu¨rich, Switzerland.
E-mail: gruetzmacher@inorg.chem.eth.ch; Fax: (+41).1.633.10.32;
Tel: (+41).1.632.28.55
3 was reacted with some halogenoarenes in the presence of
phenylboronic acic under various conditions to form the
corresponding biphenyl derivatives.6 These data are summarized
in Tables 1 and 2.
A very good activity was obtained with bromoarenes using a
low loading of catalyst in toluene at 100 uC using K2CO3 as a base.
Under these conditions, 1024 mol% of complex 3 is sufficient to
convert bromobenzene into biphenyl in 14 h (TON 5 9.9 6 105,
Table 1, entry 1). Conversions of 4-bromoacetophenone, and
4-bromotoluene proceeded with TON’s of 6.3 6 105 and 8.1 6
105 respectively, under the same experimental conditions (Table 1,
entries 4–6). Under exactly the same conditions, less than 15% of
bromobenzene was converted into biphenyl with 1024 mol% of
Pd(OAc)2 (GC yield). We can therefore assume that our catalyst
does not decompose at this temperature. Coupling reactions with
chlorobenzene were also attempted. Among different experimental
conditions, the most satisfactory results were obtained using
iPrOH as solvent and t-BuOK as base with 1–2 mol% of catalyst.
Unfortunately, as can be seen in Table 1, only low conversions
were observed (Table 2, entry 1–2) and the formation of benzene
as side-product could not be avoided. Note that under these
conditions, bromobenzene could also be converted into biphenyl
but here again the formation of benzene could not be totally
precluded. A yield of 90% was obtained by using 1022 gmol% of
catalyst 3 at 60 uC for 12 h (Table 2, entry 4).
Notes and references
{ Crystal data for 2: (C27H19P), M 5 374.39: monoclinic, space group P21/
˚
c, a 5 10.4290(10), b 5 10.1650(10), c 5 18.9660(10) A, b 5 101.6900(10)u,
3
U 5 1968.9(3) A , Z 5 4, dcalc 5 1.263 g cm23, F(000) 5 784, m 5
˚
0.149 cm21, (MoKa, l 5 0.71069 A), T 5 150.0(1) K, R1 5 0.0526,
˚
wR2 5 0.1697, GoF 5 1.096, unique data 5 5724 (Rint 5 0.0184,
KappaCCD diffractometer), 254 refined parameters. CCDC 256941.
Crystal data for 3: C27H19Cl2PPd,2(CH2Cl2), M 5 721.54, orthorhombic,
˚
space group P212121, a 5 10.3990(10), b 5 15.8850(10), c 5 17.0640(10) A,
3
U 5 2818.8(4) A , Z 5 4, dcalc 5 1.700 g cm23, F(000) 5 1440, m 5
˚
1.304 cm21 (MoKa, l 5 0.71069 A), T 5 150.0(1) K, R1 5 0.0356,
˚
wR2 5 0.0858, GoF 5 1.017, unique data 5 8152 (Rint 5 0.0000,
KappaCCD diffractometer), 353 refined parameters, Flack’s
parameter 5 20.05(2). CCDC 256942. See http://www.rsc.org/suppdata/
cc/b4/b417716a/ for crystallographic data in .cif or other electronic format.
Synthesis of ligand 2: to a solution of the P–H phosphole 1 (0.54 mmol,
100 mg) in toluene (1 mL), under an inert atmosphere of nitrogen, was
slowly added
a solution of dibenzo[a,d]cyclohepten-5-yl chloride
(0.54 mmol, 123 mg) in toluene (1 mL). The mixture was then refluxed
for 15 h during which time evolution of gaseous HCl was observed. The
solvent was then evaporated and the product was filtered in hexanes and
washed with dry deoxygenated acetonitrile. Ligand 2 was obtained as a
white, air and moisture sensitive solid (150 mg, 74%). Crystallization was
achieved from hot acetonitrile. 31P NMR (121.5 MHz, CD2Cl2, 25 uC):
However, these preliminary results are very encouraging and
further investigations on this unusual type of ligand combination
are worth the effort. In our laboratories, we are currently pursuing
our studies on the synthesis of other phosphole based derivatives
d 219.7. 1H NMR(300 MHz, CD2Cl2, 25 uC, TMS): d 3.61 (d, JPH
5
8.1 Hz, 1H, H13), 6.41 (dvd, AA9XX9, S J 5 11.6 Hz, 2H, H5–H8), 6.61
(vd, AA9XX9, S J 5 7.6 Hz, 2H, H15–H26), 7.03 (vt, AA9XX9, S J 5
17.6 Hz, 2H, H3–H10), 7.11 (s, 2H, H20–H21), 7.18 (vt, AA9XX9, S J 5
14.9 Hz, 2H, H17–H24), 7.31 (vt, AA9XX9, S J 5 14.9 Hz, 2H, H16–H25),
7.38 (vt, AA9XX9, S JHH 5 14.7 Hz, 2H, H4–H9), 7.42 (vt, AA9XX9,
S JHH 5 17.1 Hz, 2H, H18–H23), 7.89 (vd, AA9XX9, S J 5 7.8 Hz, 2H, H5–
H8); 13C NMR (75.5 MHz, CD2Cl2, 25 uC) : d 58.6 (d, JPC 5 22.1 Hz, C13),
121.3 (s, C2–C11), 126.7 (d, JPC 5 6.8 Hz, C3–C10), 127.4 (d, JPC 5 1.8 Hz,
C16–C25), 128.6 (s, C4–C9), 128.8 (s, C17–C24), 130.0 (d, JPC 5 1.8 Hz, C18–
C23), 130.6 (d, JPC 5 3.4 Hz, C15–C26), 131.0 (d, JPC 5 20.5 Hz, C5–C8),
132.7 (d, JPC 5 4.4 Hz, C20–C21), 135.6 (d, JPC 5 5.3 Hz, C14–C27), 137.9
(d, JPC 5 8.9 Hz, C19–C22), 143.2 (d, JPC 5 11.9 Hz, C1–C12), 144.1 (s, C6–
C7). General procedures for the coupling reactions: Method A: preparation of
the catalyst was achieved by dilution of 3 (3 mg, 0.0056 mmol) in
dichloromethane (30 mL) at room temperature under an inert atmosphere.
22 mL (0.0001%) of the solution was taken with a syringe, poured into a
Schlenck tube, and the solvent was evaporated. The Schlenk tube was then
filled with phenylboronic acid (6 mmol, 731.6 mg), K2CO3 (8 mmol, 1.1 g)
and the halogenoarene (4 mmol) in toluene (6 mL). The mixture was heated
Table 2 Cross-coupling reaction of halogenoaryls with phenyl-
boronic acid using complex 3 as catalyst and method B
GCa Yieldb
Entry Substrate
3/mol% t/h T/uC (%)
(%)
TON
1
2
3
4
a
Chlorobenzene
Chlorobenzene
Bromobenzene 0.1
Bromobenzene 0.01
2
1
96 RT
16 50
3 RT
12 60
32.4 31
16.2
14.6
776
14.6 13
77.6 76
91.3 90
b
9130
Based on GC analysis with external standards. Isolated yields by
column chromatography; products fully characterized by NMR and
MS by comparison with literature data.
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at 100 uC for 14 h. The progress of the reaction was monitored by GC.
When the reaction reached completion, a small amount of silica gel was
added and the solvent was evaporated in vacuo. The product was then
isolated by column chromatography on silica gel (petroleum ether 40–
65 uC) and characterized by comparison with the literature.Method B: the
catalyst 3 (5.5 mg, 1%), phenylboronic acid (1.4 eq, 170.7 mg), KOtBu
(1.5 eq, 168.3 mg) and chlorobenzene (1 mmol) were mixed in iPrOH
(1.5 mL). The mixture was stirred at ambient temperature and the progress
of the reaction was monitored by GC. Purification was carried out as
above.
2002, 124, 13597; (n) R. Weber, U. Englert, B. Ganter, W. Keim and
M. Mo¨thrath, Chem. Commun., 2000, 1419; (o) G. P. Suranna,
P. Mastrorilli, C. F. Nobile and W. Keim, Inorg. Chim. Acta, 2000,
305, 151.
3 (a) C. Fischer, C. Defieber, T. Suzuki and E. M. Carreira, J. Am. Chem.
Soc., 2004, 1628; (b) T. Hayashi, K. Ueyama, N. Tokunaga and
K. Yoshida, J. Am. Chem. Soc., 2003, 125, 11508; (c) R. Shintani,
K. Ueyama, I. Yamada and T. Hayashi, Org. Lett., 2004, 6, 3425; (d)
N. Tokunaga, Y. Otomaru, K. Okamoto, K. Ueyama, R. Shintani and
T. Hayashi, J. Am. Chem. Soc., 2004, 13584.
4 (a) P. Maire, S. Deblon, F. Breher, J. Geier, C. Bohler, H. Ruegger,
H. Schonberg and H. Grutzmacher, Chem. Eur. J., 2004, 10, 4198; (b)
J. Yin, M. P. Matthew, X.-X. Zhang and S. L. Buchwald, J. Am. Chem.
Soc., 2002, 124, 1162; (c) N. Feiken, P. S. Pregosin, G. Trabesinger,
A. Albinati and G. L. Evoli, Organometallics, 1997, 16, 5756; (d)
P. Kocovsky, S. Vyskocil, I. Cisarova, J. Sejbal, I. Tislerova, M. Smrcina,
G. C. Lloyd-Jones, S. C. Stephen, C. P. Butts, M. Murray and V. Langer,
J. Am. Chem. Soc., 1999, 121, 7714; (e) T. Hayashi, Acc. Chem. Res.,
2000, 33, 354; (f) P. Dotta, P. G. A. Kumar, P. S. Pregosin, A. Albinati
and S. Rizzato, Organometallics, 2003, 22, 5345.
5 J. Thomaier, S. Boulmaaˆz, H. Scho¨nberg, H. Ru¨egger, A. Currao,
H. Gru¨tzmacher, H. Hillebrecht and H. Pritzkow, New J. Chem., 1998,
947.
6 (a) D. A. Albisson, R. B. Bedford, S. E. Lawrence and P. N. Scully,
Chem. Commun., 1998, 2095; (b) A. F. Littke, C. Y. Dai and G. C. Fu,
J. Am. Chem. Soc., 2000, 122, 4020; (c) O. Navarro, R. A. Kelly and
S. P. Nolan, J. Am. Chem. Soc., 2003, 125, 16194; (d) X. Sava, L. Ricard,
F. Mathey and P. Le Floch, Organometallics, 2000, 19, 4899; (e)
J. P. Wolfe, R. A. Singer, B. H. Yang and S. L. Buchwald, J. Am. Chem.
Soc., 1999, 121, 9550.
1 P. Braunstein and F. Naud, Angew. Chem. Int. Ed., 2001, 40,
680.
2 (a) M. Doux, N. Mezailles, M. Melaimi, L. Ricard and P. Le Floch,
Chem. Commun., 2002, 1566; (b) M. R. Eberhard, S. Matsukawa,
Y. Yamamoto and C. M. Jensen, J. Organomet. Chem., 2003, 687, 185;
(c) S. R. Gilbertson, D. G. Genov and A. L. Rheingold, Org. Lett., 2000,
2, 2885; (d) G. Helmchen and A. Pfaltz, Acc. Chem. Res., 2000, 33, 336;
(e) K. K. Hii, M. Thornton-Pett, A. Jutand and R. P. Tooze,
Organometallics, 1999, 18, 1887; (f) Y. X. Liang, S. A. Gao,
H. H. Wan, Y. C. Hu, H. L. Chen, Z. Zheng and X. Q. Hu,
Tetrahedron Asymmetry, 2003, 14, 3211; (g) M. Sauthier, F. Leca,
L. Toupet and R. Reau, Organometallics, 2002, 21, 1591; (h)
J. T. Singleton, Tetrahedron, 2003, 59, 1837; (i) C. Thoumazet,
M. Melaimi, F. Mathey and P. Le Floch, Organometallics, 2003, 22,
1580; (j) M. E. Van der Boom and D. Milstein, Chem. Rev., 2003, 103,
1759; (k) M. J. Baker, M. F. Giles, A. G. Orpen, M. J. Taylor and
R. J. Watt, Chem. Commun., 1995, 197; (l) H. Liang, K. Nishide, S. Ito
and M. Yoshifuji, Tetrahedron Lett., 2003, 44, 8297; (m) L. Gonsalvi,
H. Adams, G. J. Sunley, E. Ditzel and A. Haynes, J. Am. Chem. Soc.,
1594 | Chem. Commun., 2005, 1592–1594
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