[Bis(oxazolinyl)pyrrole]palladium complexes as catalysts in heck- and suzuki-type C-C coupling reactions

Article abstract of DOI:10.1002/ejic.200390148

The two bis(oxazoline)pyrrole ligand precursors 2,5-bis(4,4′-dimethyl-4,5-dihydrooxazol-2-yl)pyrrole ("dmoxpH", 2) and 2,5-bis(4,4′-dimethyl-4,5-dihydrooxazol-2-yl)-3,4-diethyl- pyrrole ("Et₂dmoxpH", 5) have been synthesised and metallated by treatment with n-butyllithium at -78°C in diethyl ether. Treatment of the lithium pyrrolide with 1.1 molequiv. of [PdCl₂(COD)] gave the corresponding helical dinuclear palladium complexes [Pd₂Cl₂(dmoxp)₂] (6) and [Pd₂Cl₂(Et₂dmoxp)₂] (7). In both complexes the tridentate bis(oxazolinyl)pyrrolide ligands bridge the two metal centres, with one of the oxazoline rings and the charged pyrrolide being coordinated to the one Pd centre while the second oxazoline ring is twisted relative to the pyrrolide unit and coordinates to the second palladium atom. Complexes 6 and 7 were found to be precursors for active catalysts for Heck coupling reactions of styrene and ethyl acrylate, with turnover numbers of over 9000 for the former, as well as for disubstituted alkenes such as methyl crotonate and methyl cinnamate. Complex 6 was found to be a very active catalyst for Suzuki coupling reactions of activated and deactivated bromoarenes. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

Full text of DOI:10.1002/ejic.200390148

FULL PAPER
[
Bis(oxazolinyl)pyrrole]palladium Complexes as Catalysts in Heck- and
Suzuki-Type C؊C Coupling Reactions
[a]
[a]
Cl e´ ment Mazet and Lutz H. Gade*
Keywords: Catalysis / Helical structures / N ligands / Palladium / Suzuki reaction / Heck reaction
The two bis(oxazoline)pyrrole ligand precursors 2,5-bis(4,4Ј-
dimethyl-4,5-dihydrooxazol-2-yl)pyrrole (‘‘dmoxpH’’, 2) and
cond oxazoline ring is twisted relative to the pyrrolide unit
and coordinates to the second palladium atom. Complexes 6
2
,5-bis(4,4Ј-dimethyl-4,5-dihydrooxazol-2-yl)-3,4-diethyl- and 7 were found to be precursors for active catalysts for
pyrrole (‘‘Et dmoxpH’’, 5) have been synthesised and Heck coupling reactions of styrene and ethyl acrylate, with
metallated by treatment with n-butyllithium at −78 °C in di- turnover numbers of over 9000 for the former, as well as for
2
ethyl ether. Treatment of the lithium pyrrolide with 1.1 mol-
equiv. of [PdCl (COD)] gave the corresponding helical di-
nuclear palladium complexes [Pd Cl (dmoxp) (6) and
Pd Cl (Et dmoxp) ] (7). In both complexes the tridentate
disubstituted alkenes such as methyl crotonate and methyl
cinnamate. Complex 6 was found to be a very active catalyst
for Suzuki coupling reactions of activated and deactivated
bromoarenes.
2
2
2
2
]
[
2
2
2
2
bis(oxazolinyl)pyrrolide ligands bridge the two metal
centres, with one of the oxazoline rings and the charged pyr-
rolide being coordinated to the one Pd centre while the se-
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
with the ligands containing a central pyridine unit would
be expected to result in somewhat different complex struc-
tures in comparison to pybox complexes. In a preliminary
study of their coordination chemistry we discovered that the
arrangement of its three N-donor atoms does not permit
meridional tris(coordination) to a single metal centre.[
This gives rise to dinuclear complexes that dissociate in so-
In recent years, nitrogen donor ligands have increasingly
been employed as ancillary ligands in molecular catalysis.
[
1]
This is due to the great variety of synthetic strategies avail-
able. Nitrogen-based catalysts may generate catalytically
active complexes complementary to the known phosphane-
based systems. Oxazolines and their derivatives have been
intensely studied in a wide range of applications, particu-
4]
[
6]
lution only at higher temperatures.
In this paper we report the synthesis of two achiral type
A bis(oxazolinyl)pyrroles, one of which is alkyl-substituted
in the 3- and 4-positions of the pyrrole ring, and the syn-
thesis of two helical dinuclear palladium complexes. The
principle focus was to assess their suitability as precursors
for efficient catalytic CϪC coupling reactions. To this end,
a series of Heck and Suzuki coupling reactions were carried
out as benchmark reactions in order to test these novel
molecular systems.
larly in asymmetric catalysis.[
2,3]
We recently began to develop the coordination chemistry
of a new class of potentially tridentate, monoanionic N-
donor ligands based on the combination of two oxazoline
rings and a central pyrrole unit (A).[4] This class of com-
pounds may be viewed as precursors to monoanionic ana-
logues of the well-established family of pybox ligands (B),
which have found widespread application in asymmetric
catalysis in recent years.[ The monoanionic charge of the
deprotonated molecule and the more open structure of this
derivative of the five-membered pyrrole ring in comparison
Results and Discussion
Synthesis of the Two Ligand Precursors 2,5-Bis[2-(4,4Ј-
dimethyl-4,5-dihydrooxazolyl)]pyrrole (‘‘dmoxpH’’, 2) and
2,5-Bis[2-(4,4Ј-dimethyl-4,5-dihydrooxazolyl)]-3,4-
5]
diethylpyrrole (‘‘Et dmoxpH’’, 5)
2
As a starting material in the synthesis of 2,5-bis(4,4Ј-di-
methyl-4,5-dihydrooxazol-2-yl)pyrrole (‘‘dmoxpH’’, 2) we
chose pyrrole-2,5-dicarbonitrile (1), for which we had previ-
ously developed an efficient synthetic route. Its cyclisation
with two mol-equiv. of 2-amino-2-methyl-1-propanol was
[
a]
Laboratoire de Chimie Organom e´ tallique et de Catalyse, CNRS
UMR 7513, Institut Le Bel, Universit e´ Louis Pasteur,
[
6]
4, rue Blaise Pascal, 67070 Strasbourg, France
Eur. J. Inorg. Chem. 2003, 1161Ϫ1168  2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ1948/03/0306Ϫ1161 $ 20.00ϩ.50/0 1161

C. Mazet, L. H. Gade
FULL PAPER
carried out by the method reported by Witte and Bolm.[7] ether and subsequent stirring of the lithium pyrrolide with
Heating at reflux in chlorobenzene in the presence of 0.5 1.1 mol-equiv. of [PdCl (COD)] gave the corresponding
2
mol-equiv. of activated ZnCl for 12 h gave crude 2, which palladium
complexes
[Pd Cl (dmoxp) ]
(6)
and
2
2
2
2
was purified by flash chromatography to give a cream-col- [Pd Cl (Et dmoxp) ] (7) after chromatographic workup
2
2
2
2
oured solid. The formulation of compound 2 was confirmed (Scheme 2).
1
by elemental analysis and mass spectrometry, while its H,
1
3
C NMR and infrared spectra were consistent with the
structure depicted in Scheme 1.
Scheme 2. Synthesis of the helical dinuclear palladium complexes
2 2 2 2 2 2 2
[Pd Cl (dmoxp) ] (6) and [Pd Cl (Et dmoxp) ] (7)
In order to establish their molecular structures, X-ray dif-
fraction studies of both complexes 6 and 7 were carried
out. Two views of their very similar molecular structures
are depicted in Figures 1 and 2, together with the principal
bond lengths and interbond angles.
Scheme 1. Synthesis of the two bis(oxazolinyl)pyrroles 2 and 5
The 3,4-diethylpyrrole analogue of 2, 2,5-bis(4,4Ј-dimethyl-
4
5
3
,5-dihydrooxazol-2-yl)-3,4-diethylpyrrole (‘‘Et dmoxpH’’,
2
) was synthesised in two steps, starting from the known
,4-diethylpyrrole-2,5-dicarboxylic acid (3).[ This has fre-
8]
quently been used as a starting material in porphyrin syn-
thesis, and several efficient preparative procedures have
been published in recent years.[ The purpose behind the
replacement of the central pyrrole ring by a diethylpyrrole
unit was the variation of the donor capacity of the pyrrolide
9]
ligand, an approach previously pursued in oligopyrrole
notably porphyrin) chemistry.[ In the first reaction step
9]
(
the dicarboxylic acid 3 was treated with 2.5 mol-equiv. of
the amino alcohol in the presence of the well-established
amide coupling reagent NЈ-[3-(dimethylamino)propyl]-N-
ethylcarbodiimide (EDC·HCl) and 1-hydroxybenzotriazole
[
10]
(
HOBt) (Scheme 1)· The diamide 4 was dimesylated and
then cyclized in the presence of an excess of NaOH in meth-
anol. After workup, the target compound 5 was obtained
as a pale yellow oil, which was characterised by elemental
1
13
analysis, mass spectrometry and infrared and H and
C
NMR spectroscopy.
Figure 1. Molecular structure of the palladium complex
˚
[
2 2 2
Pd Cl (dmoxp) ] (6); selected bond lengths [A] and angles [°]:
Synthesis and Structural Characterisation of the Helical
Dinuclear Palladium Complexes [Pd Cl (dmoxp) ] (6) and
Pd(1)ϪN(1) 2.052(8), Pd(1)ϪN(2) 2.039(8), Pd(1)ϪN(6) 2.036(8),
Pd(1)ϪCl(1) 2.296(3), Pd(2)ϪCl(2) 2.287(3), Pd(2)ϪN(3) 2.043(8),
Pd(2)ϪN(4) 2.025(7), Pd(2)ϪN(5) 2.039(8); N(2)ϪPd(1)ϪN(6)
97.7(3), N(1)ϪPd(1)ϪN(2) 79.8(3), Cl(1)ϪPd(1)ϪN(1) 96.5(2),
2
2
2
[
Pd Cl (Et dmoxp) ] (7)
2 2 2 2
N(3)ϪPd(2)ϪN(5)
N(2)ϪC(28)ϪC(8)ϪN(3)
Et dmoxpH (5) with n-butyllithium at Ϫ78 °C in diethyl 26.4(5)
97.7(3),
N(4)ϪPd(2)ϪN(5)
79.9(3),
Deprotonation of the pyrrole rings in dmoxpH (2) and
29.3(5),
N(5)ϪC(19)ϪC(22)ϪN(6)
2
1162
Eur. J. Inorg. Chem. 2003, 1161Ϫ1168

[Bis(oxazolinyl)pyrrole]palladium Complexes
FULL PAPER
the observation of two vibrational CϭN bands for the two
Ϫ1
inequivalent oxazoline rings at 1632 and 1608 cm for 6
Ϫ1
and at 1622 and 1600 cm for 7.
Heck Coupling Reactions with Mono- and 1,2-Disubstituted
Alkenes, Catalysed by [Pd Cl (dmoxp) ] (6) and
2
2
2
[
Pd Cl (Et dmoxp) ] (7)
2 2 2 2
Originally, Pd-catalysed Heck and Suzuki coupling reac-
tions were based almost entirely on phosphane or phos-
[
12]
phane-derived systems. In recent years, however, a whole
range of alternative ligand systems for this reaction has
been successfully tested. These include N-heterocyclic carb-
[
13,14]
[15,16]
enes,
N-, O- and S-containing palladacycles,
[
17]
[18]
cyclometallated imines and diazabutadienes which act
as mono- or polydentate ancillary ligands.
We tested the activities of compounds 6 and 7 in Heck
coupling reactions. In an initial study, the reaction condi-
tions (solvent, base, reaction temperature) were optimised
for the reference reaction between bromobenzene and styr-
ene, in the presence of 0.1 mol % of the catalyst precursor
Figure 2. Molecular structure of the palladium complex
˚
[
2 2 2 2
Pd Cl (Et dmoxp) ] (7); selected bond lengths [A] and angles [°]:
Pd(1)ϪN(1) 2.031(2), Pd(2)ϪN(3) 2.043(2), Pd(1)ϪCl(1) 2.2922(7), (Scheme 3). The best results were obtained at 110 °C in N-
Pd(1)ϪN(2) 2.036(2), Pd(2)ϪN(5) 2.031(2), Pd(2)ϪCl(2) 2.0311(7),
Pd(1)ϪN(4) 2.035(2), Pd(2)ϪN(6) 2.036(2); N(1)ϪPd(1)ϪCl(1)
methylpyrrolidone with K PO as a base, and these reaction
3
4
conditions were chosen for all subsequent catalytic runs. It
96.80(8), should be pointed out that the palladium catalysts were
9
4.94(6), N(6)ϪPd(2)ϪCl(2) 95.75(6), N(1)ϪPd(1)ϪN(2) 80.01(8),
N(3)ϪPd(2)ϪN(5)
94.48(8),
N(2)ϪPd(1)ϪN(4)
N(5)ϪPd(2)ϪN(6) 79.86(8), N(2)ϪC(7)ϪC(14)ϪN(3) 21.4(5),
N(4)ϪC(21)ϪC(24)ϪN(5) 28.3(5)
stable under these conditions throughout the conversions.
Precipitation of ‘‘Pd-black’’, potentially due to the degrada-
tion of the molecular catalysts, was not observed in any
Both compounds 6 and 7 are dinuclear complexes in
which the tridentate bis(oxazolinyl)pyrolide ligands bridge
the two metal centres. Whereas one of the oxazoline rings
and the charged pyrrolide are coordinated to the one Pd
centre, adopting an almost coplanar arrangement, the se-
cond oxazoline ring is twisted relative to the pyrrolide unit
case. The results of
a
comparative study with
[
Pd Cl (dmoxp) ] (6) and [Pd Cl (Et dmoxp) ] (7) are de-
2
2
2
2
2
2
2
picted in Table 1.
[
6: 26.4 and 29.3°; 7: 21.4 and 28.3°] and coordinates to the
second palladium atom. The coordination geometry at each
metal centre is distorted square-planar, with the chloro li-
gand disposed trans to the pyrrolide. Although neither of
the complexes 6 and 7 possesses exact crystallographic sym-
metry, both have an approximate twofold molecular sym-
metry axis relating the {Pd(ligand)Cl} fragments. Overall,
the two bis(oxazolinyl)pyrrolide ligands are wrapped
around the two metal centres to give helical arrange-
[
11]
˚
ments, with PdϪPd distances of 3.389 and 3.426 A for 6
and 7, respectively. It is interesting to note that complex 6
crystallised in the polar space group C2 as a conglomerate
Scheme 3. Application of the palladium complexes
[
2 2 2 2 2 2 2
Pd Cl (dmoxp) ] (6) and [Pd Cl (Et dmoxp) ] (7) in the Heck re-
of (P)- and (M)-helical enantiomers, although we were un- action between bromobenzene and styrene
able to separate them mechanically. For the solution of the
crystal structure of 6 we selected by chance a crystal con-
taining the (M) enantiomer, which is depicted in Figure 1.
The dimerisation of both 6 and 7 to give the helical di-
nuclear complexes implies the loss of all local symmetry
elements at the metal centres. Only the two tridentate li-
gands as a whole are related by a twofold rotational axis.
This loss in local symmetry is reflected in the signal patterns
Table 1. Comparative study of the catalytic activities of catalysts 6
and 7 in the Heck reaction between bromobenzene and styrene
Entry Catalyst Cat./Sub. Time Conv. [(Z) ϩ (E)] T.O.N.
Ϫ3
1
2
3
4
5
6
6
7
6
7
6
7
10
10
10
10
3 d
3 d
3 d
3 d
4 d
4 d
97.1%
96.6%
87.3%
85.4%
47.4%
43.2%
971
966
8730
8540
9480
8640
Ϫ3
Ϫ4
Ϫ4
1
13
of the H and C NMR spectra of both compounds, in
1
13
which all the H and C nuclei in the individual ligands
are chemically inequivalent. Consistent with this reduced
symmetry with respect to the ligand precursors 2 and 5 is
Ϫ5
Ϫ5
5·10
5·10
Eur. J. Inorg. Chem. 2003, 1161Ϫ1168
1163

C. Mazet, L. H. Gade
FULL PAPER
In general, there does not seem to be a significant differ-
The most remarkable aspect of these conversions is the
ence in the catalytic performances of complexes 6 and 7. A complete stereoselectivity in the positioning of the entering
Ϫ5
minimum catalyst/substrate ratio of 5·10 was employed, aryl group in the reaction products. The configuration was
and this, after 4 d reaction time at 110 °C, gave degrees of established by NOESY experiments, NOEs between the α-
conversion to the product stilbene of 47 and 43%, respect- olefin proton and the ortho-protons of the tolyl group pro-
ively. The electronic effect expected from the introduction viding the key assignment. It was not possible to detect any
of the ethyl substituent on the pyrrolide ring[ is not re- other stereoisomer even in trace quantities by GC, GCMS
flected in a modulation of the catalytic activity. It should or by NMR spectroscopy. The exclusive formation of the
be noted, though, that the turnover numbers of 9480 and (E) stereoisomers may be explained by the stereospecificity
9]
8
640 place these catalysts among the most efficient systems of the migratory insertion step resulting in the coupling of
[19,20]
containing exclusively nitrogen donor ligands.
the olefin and the Pd-bonded aryl group and of the sub-
The results of the coupling of methyl acrylate with several sequent β-elimination step (Scheme 6).
substituted bromobenzene derivatives catalysed by com- We have shown in a previous study that these dissociate
[
6]
pound 6 (Scheme 4) is shown in Table 2. The degree of con- in solution at temperatures above 70 °C, and it is within
version after a reaction time of 3 d was high and the stereo- this thermodynamic regime that their catalytic activities in
selectivity in favour of the (E) isomers essentially quantitat- Heck and Suzuki CϪC coupling reactions have been ob-
ive. In none of the cases did we observe traces of the gemin- served. We therefore only consider monomeric species in
ally disubstituted coupling product.[
21]
No activity was the following mechanistic discussion. The endo approach of
observed for derivatives of chlorobenzene for the coupling the aryl group in the intermediates Ia and IIa stereospecif-
either of styrene or of methyl acrylate.
ically generates the alkyl complexes Ib and IIb, in which
rotation around a CϪC bond gives access to a conforma-
tion (Ic and IIc, respectively) in which the β-H is oriented
towards the metal centre and from which β-elimination oc-
curs. This gives the intermediates Id and IId, both of which
liberate exclusively the (E) isomer.
Scheme 4. Coupling of methyl acrylate with substituted bromoben-
zene derivatives
Buchwald et al. have previously found a high degree of
stereoselectivity in non-phosphane/palladium-catalysed
Heck reactions of 1,2-substituted α,β-unsaturated carboxyl
Table 2. Results of the Heck reactions between methyl methacrylate
and substituted bromobenzene derivatives, catalysed by 6
[
20]
esters. They also pointed out that the generally accepted
mechanism of the catalytic Heck coupling implied a ste-
reospecific reaction sequence as detailed above. The devi-
ations from ideal stereoselection were interpreted as being
due to an isomerisation of the configuration at the CϭC
double bond after the Heck coupling step. For the two cases
described above we were unable to establish such an post-
Heck equilibration, which may be due to the short lifetime
of the hydridopalladium intermediate after decoordination
of the product olefin. In fact, such a hydrido species may
play a role either before or after the Heck reaction:
a) It may in principle coordinate the disubstituted alkene
starting material (IIIa in Scheme 6), which is isomerised to
the (Z)-1,2-disubstituted alkene in a sequence of migratory
insertion and β-elimination (liberated from IIId in
Scheme 6).
Entry
R
Time
Conversion
(E)/(Z)
1
2
3
2-Me
4-Me
4-OMe
3 d
3 d
3 d
77%
97%
85%
100:0
100:0
99:1
The use of the Heck coupling reaction for the synthesis
of trisubstituted alkenes has received much less attention
than the standard conversions affording disubstituted CϭC
[
20,22,23]
double bonds.
We therefore carried out several tests
to investigate the activity of 6 towards (E)-1,2-disubstituted
alkenes. With a catalyst loading of 0.1 mol %, the reactions
of methyl crotonate and methyl cinnamate with 4-bromoto-
luene gave the corresponding trisubstituted olefins after a
reaction time of 7 d (Scheme 5).
b) Alternatively, given a sufficient lifetime of the hydrido-
palladium complex, the reaction products liberated from Id
and IId may recoordinate to the metal centre, and the mi-
gratory insertion into the PdϪH bond may then take place
in part with a reversed regioselectivity (migration of the H
atom to the C atom adjacent to the carboxyl function). A
subsequent β-elimination from such an intermediate may
indeed give the other isomer and, since all steps are revers-
ible, the product distribution may be under thermodyn-
amic control.
The fact that no isomerisation is observed in the case at
hand even after the considerable reaction time of 7 d, neces-
sary because of the low catalyst loadings of 0.1 mol %, in-
dicates the short lifetime of the hydridopalladium species.
Scheme 5. Heck reactions giving trisubstituted alkenes
1164
Eur. J. Inorg. Chem. 2003, 1161Ϫ1168

[Bis(oxazolinyl)pyrrole]palladium Complexes
FULL PAPER
Scheme 6. Mechanistic scheme representing the stereospecific migratory insertion-β-elimination sequence in the Heck reaction involving
,2-disubstituted alkenes
1
This may in part be due to the proximity of the relatively Table 3. Results of the Suzuki reactions between phenylboronic
acid and substituted bromobenzene derivatives, catalysed by 6
basic oxazoline functions attached to the pivotal pyrrolide
ligand.
Suzuki Coupling Reactions Catalysed by [Pd Cl (dmoxp) ]
2
2
2
(6)
Compound 6 was found to be a highly active catalyst for
the Suzuki-type coupling of phenylboronic acid with aryl
bromides at relatively moderate temperatures (Table 3). In
Ϫ4
the general procedure a catalyst/substrate ratio of 10 was
used and the aryl bromide and phenylboronic acid were
stirred at 70 °C in toluene in the presence of K CO as
2
3
auxiliary base.
to the reactivity towards aryl bromides, the catalyst proved
to possess only very low activity towards the aryl chlorides,
the reaction effectively stopping after a few cycles at 110
Scheme 7. Suzuki coupling between bromobenzene derivatives and
phenylboronic acid
°
C. As in the case of the Heck coupling reactions discussed
in the previous section, the use of the diethyl-substituted
derivative [Pd Cl (Et dmoxp) ] (7) gave essentially identical
2
2
2
2
results in the catalytic conversions.
As observed for the Heck-type coupling reactions discus-
sed above, catalyst 6 was found to be highly stable under
Suzuki coupling conditions, and no palladium-black was Conclusions
formed during the reaction. The catalytic reaction was
monitored by GC MS, and 100% conversion was obtained
Through the charging and deformation of the well-estab-
with both activated and deactivated bromides after 1Ϫ6 h. lished pybox ligand B systems by replacement of the central
Ϫ5
A decrease in the catalyst/substrate ratio to 10 still gave pyridine unit by a formally charged pyrrolide ring, the more
an 82% isolated yield of 4-bromoacetophenone and 54% of open ‘‘pyrrbox’’ ligands A have been obtained. The specific
4-methoxyacetophenone after 4 h, corresponding to turn- arrangement of the three nitrogen donor functions in these
over numbers of 82000 and 54000, respectively. In contrast has given rise to helical dinuclear complexes if coordinated
Eur. J. Inorg. Chem. 2003, 1161Ϫ1168
1165

C. Mazet, L. H. Gade
to palladium(). Whereas their activity is lower than those NHpyrr), 6.39 (s, 2 H, NH), 3.61 (s, 4 H, CH ), 2.64 (q, 4 H,
FULL PAPER
2
1
3
1
CH2,pyrr), 1.38 (s, 12 H, CH
NMR (75 MHz, CDCl ): δ ϭ 162.1 (C-3/4pyrr), 128.1 (CϭO or C-
/5pyrr), 123.9 (C-2/5pyrr or CϭO), 69.9 (CH ), 56.2 [C(CH ], 24.8
CH ), 17.9 (CH2,pyrr), 15.8 (CH3,pyrr) ppm. IR (CHCl
): ν˜ ϭ 3423
m), 2971 (s), 2253 (s), 1634 (s), 1516 (s), 1469 (s), 1301 (s), 1062
3
), 1.20 (t, 6 H, CH3,oxa) ppm. C{ H}
found for some Pd complexes bearing phosphane or N-het-
erocyclic arene ligands, they are nevertheless among the
most active catalysts containing exclusively nitrogen-donor
ligands. The observation of the high stereoselectivity in the
Heck reactions with 1,2-disubstituted alkenes described in
this work is remarkable and has initiated a more systematic
investigation into this aspect, currently underway in our
laboratory.
3
2
2
3 2
)
(
(
(
3
3
Ϫ1
m), 651 (s) cm . C18
31 3 4
H N O (353.23): calcd. C 61.17, H 8.84, N
1
1.89; found C 61.24, H 8.67 N 11.74.
Preparation of 2,5-Bis(4,4Ј-dimethyl-4,5-dihydrooxazol-2-yl)-3,4-di-
ethylpyrrole (‘‘Et dmoxpH’’, 5): MsCl (1.18 mL, 15.2 mmol) was
slowly added to an ice-cold solution of 3 (2.440 g, 6.9 mmol) and
Et N (3.30 mL, 30.4 mmol) in 20 mL of dichloromethane. The mix-
ture was allowed to warm to room temperature and was then
stirred for 1 h. After washing with water (5 mL), the organic phase
was dried with Na SO , and the volatiles were removed in vacuo
2 4
to give a yellow oil, which was used in the next step without puri-
fication. The bis(mesylated) compound was treated with KOH
2
3
Experimental Section
General: Solvents were dried by standard procedures and saturated
with nitrogen. Solids were separated from suspensions by centrifu-
gation, thus avoiding filtration procedures, with a Hettich Rotina
4
8 centrifuge equipped with a specifically designed Schlenk tube
(
0.4 g, 7.1 mmol) in 25 mL of an MeOH/H
reaction mixture was stirred at room temperature for 3 d, then
washed with water and dried with Na SO . The solvents were re-
moved to give the ligand precursor as a pale yellow oil in 73% yield
2
O mixture (5:1). The
[24]
rotor (Hettich Zentrifugen, Tuttlingen, Germany). Optical rota-
tions were recorded with a thermostated PerkinϪElmer Otopol III
2
4
1
13
instrument in a 1.0-dm cell. The H and C NMR spectra were
1
13
1
recorded with Bruker AC 300 ( H 300 MHz; C{ H} 75 MHz),
1
(
1.6 g). H NMR (300 MHz, CDCl
3
): δ ϭ 9.6 (br. s, 1 H, NHpyrr),
.24 (s, 4 H, CH2,oxa), 2.70 (q, 4 H, CH2,pyrr), 1.32 (s, 12 H, CH ),
): δ ϭ
56.6 (CϭNoxa), 130.1 (C-2/5pyrr), 118.6 (C-3/4pyrr), 79.0 (CH2,oxa),
6.9 [C(CH ], 28.2 (CH ), 17.7 (CH2,pyrr), 15.8 (CH3,pyrr) ppm.
1
13
1
Bruker AM 400 ( H 400 MHz; C{ H} 100 MHz), and Bruker
4
1
1
6
3
1
13
1
ARX 500 ( H 500 MHz;
C{ H} 125 MHz) spectrometers.
13
1
.15 (t, 6 H, CH3,oxa) ppm. C{ H} NMR (75 MHz, CDCl
3
Infrared spectra were recorded with a PerkinϪElmer 1600 FT-IR
spectrometer. EI mass spectra were recorded with a Shimadzu
QP5050-GC/MS system. The elemental analyses were carried out
by the Service Commun de Microanalyse de l’Universit e´ Louis
3
)
2
3
IR (CHCl
3
): ν˜ ϭ 3437 (m), 2969 (s), 1640 (s), 1461 (m), 1353 (m),
Ϫ1
ϩ
1305 (m), 1197 (m), 651 (s) cm . MS (EI, 70 eV): m/z ϭ 317 [M] ,
[6]
Pasteur at Strasbourg. Pyrrole-2,5-dicarbonitrile, 3,4-diethylpyr-
ϩ
ϩ
3
02 [M Ϫ CH
3
] , 160 [M Ϫ 2 CH
2
CH
3
] . C18
H
27
N
3
O
2
(317.21):
role-2,5-dicarboxylic acid[ and [PdCl (1,5-COD)][25] were pre-
8]
2
calcd. C 68.11, H 8.57, N 13.24; found C 68.02, H 8.52 N 13.15.
pared by published procedures. All other chemicals used as starting
materials were obtained commercially and used as received without
further purification.
General Procedure for the Preparation of the Palladium Complexes
[Pd
nBuLi (1.6 ) in hexanes (3.59 mL) was added to a diethyl ether
50 mL) solution of the bis(oxazolinyl)pyrrole (5.74 mmol), which
2 2 2 2 2 2 2
Cl (dmoxp) ] (6) and [Pd Cl (Et dmoxp) ] (7): A solution of
Preparation of 2,5-Bis(4,4Ј-dimethyl-4,5-dihydrooxazol-2-yl)pyrrole
(
2
(‘‘dmoxpH’’, 2): ZnCl (1.164 g, 8.54 mmol, 0.5 equiv.) was melted
was cooled to Ϫ78 °C. The reaction mixture was stirred for 15 min
and then allowed to warm to room temperature. After an addi-
tional hour, a suspension of dichlorobis(1,5-cyclooctadiene)pallad-
ium (1.639 g; 5.74 mmol) in diethyl ether (20 mL) was added and
the resulting mixture was stirred for 12 h at room temperature. The
reaction mixture was then filtered and the resulting orange oil was
purified by flash chromatography (silica gel, hexanes/EtOAc, 1:1)
to give 6 (and 7) as orange, air-stable solids.
under vacuum and then cooled under nitrogen for 15 min. A slurry
of pyrrole-2,5-dicarbonitrile (2 g, 17.6 mmol) and 2-amino-2-
methyl-1-propanol (4.263 g, 47.82 mmol, 2.8 equiv.) in chloroben-
zene (25 mL) was added, and the mixture was heated at reflux for
24 h. The solvent was removed in vacuo and the orange-brown
residue was chromatographed on silica gel (hexanes/EtOAc, 1:1);
1
R
f
ϭ 0.43, yielding 4.263 g of an off-white solid (yield 72%). H
NMR (300 MHz. CDCl ): δ ϭ 11.40 (br. s, 1 H, NHpyrr), 6.71 (s,
H, H3/4,pyrr), 4.05 (s, 4 H, CH2,oxa), 1.34 (s, 12 H, CH3,oxa) ppm. [Pd
3
1
2
2
Cl
): δ ϭ 155.6 (CϭNoxa), 123.0 (C- CDCl
/5pyrr), 112.9 (C-3/4pyrr), 79.0 (CH2,oxa), 67.4 (Cquat,oxa), 28.2 4.24 (t, 2 H, CH2,oxa), 4.17 (d, 1 H, CH2,oxa), 1.92 (s, 3 H, CH3,oxa),
2
(dmoxp)
2
] (6): Yield: 42%. R
f
ϭ 0.56. H NMR (300 MHz,
13
1
C{ H} NMR (75 MHz. CDCl
3
3
): δ ϭ 6.64 (br. d, 2 H, 3/4-Hpyrr), 4.38 (d, 1 H, CH2,oxa),
2
(
CH3,oxa) ppm. IR (KBr): ν˜ ϭ 3436 (s), 2969 (m), 1660 (s), 1612
1.57 (s, 3 H, CH3,oxa), 1.43 (s, 3 H, CH3,oxa), 1.15 (s, 3 H, CH3,oxa
)
Ϫ1
13
1
(
2
C
6
m), 1499 (s), 1404 (m), 702 (m) cm . MS (EI, 70 eV): m/z ϭ ppm. C{ H} NMR (125 MHz, CDCl
3
): δ ϭ 167.8 (CϭNoxa),
ϩ
ϩ
ϩ
61 [M] , 246 [M Ϫ CH
(261.15): calcd. C 64.35, H 7.33, N 16.08; found C
3.89, H 7.25 N 15.99.
3
] , 174 [M Ϫ CH
3
Ϫ (CH
3
)
2
CCH
2
O] . 164.9 (CϭNoxa), 133.1 (C-2/5pyrr), 131.9 (C-5/2pyrr), 117.1 (C-3/
pyrr), 112.2 (C-3/4pyrr), 83.2 (CH2,oxa), 80.0 (CH2,oxa), 67.9
[C(CH ], 65.9 [C(CH ], 30.4 (CH3,oxa), 27.8 (CH3,oxa), 27.5
CH3,oxa), 26.7 (CH3,oxa) ppm. IR (KBr): ν˜ ϭ 2964, 1632, 1608,
H
19
N
3
O
2
4
14
3
)
2
3 2
)
(
1
Preparation of Compound 4: A mixture of 3,4-diethylpyrrole-2,5-
dicarboxylic acid (4.1 g, 19.4 mmol), amino alcohol (5.191 g,
Ϫ1
521, 1376, 721, 362 cm . C28
H38Cl
2
N
6
O
5
Pd
2
(822.36): calcd. C
41.81, H 4.51; found C 41.95, H 4.73.
5
5
8.2 mmol), EDC·HCl (11.164 g, 58.2 mmol), and HOBt (7.870 g,
8.2 mmol) in 75 mL of CH Cl and 75 mL of DMF was stirred
[Pd
6 6
(500 MHz, C D ϭ
): δ ϭ 3.72 (m, 3 H, CH2,oxa), 3.52 (d, 3JH,H
Cl (Et dmoxp) ] (7): Yield 30%. R ϭ
2 2 2 2 f
0.47. 1H NMR
2
2
under nitrogen at room temperature for 48 h. The reaction mixture
was poured into a saturated NH Cl/CH Cl solution, and the aque-
ous layer was extracted with CH Cl . The combined organic layers
were washed with 1  HCl, water, saturated NaHCO and brine,
and then dried with anhydrous Na SO
4
2
2
8.3 Hz, 1 H, CH2,oxa), 2.92 (m, 1 H, CH2,pyrr), 2.79 (m, 2 H,
2
2
CH2,pyrr), 2.68 (m, 1 H, CH2,pyrr), 1.77 (s, 3 H, CH3,oxa), 1.53 (s, 3
3
3
H, CH3,oxa), 1.41(m, 6 H, CH3,oxa and CH3,pyrr), 1.32 (t, JH,H
ϭ
. After removal of the solv- 8 Hz, 3 H, CH3,pyrr), 1.04 (s, 3 H, CH3,oxa) ppm. 13C{ H} NMR
1
2
4
ent, the product was isolated as a pale yellow oil (5.2 g, 14.7 mol,
6 6
(125 MHz, C D ): δ ϭ 168.3 (CϭNoxa), 165.5 (CϭNoxa), 133.0 (C-
7
7% yield). 1H NMR (300 MHz, CDCl
166
3
): δ ϭ 10.4 (br. s, 1 H, 2/5pyrr), 131.1 (C-3/4pyrr), 130.0 (C-3/4pyrr), 128.4 (C-3/4pyrr), 83.2
1
Eur. J. Inorg. Chem. 2003, 1161Ϫ1168

[Bis(oxazolinyl)pyrrole]palladium Complexes
FULL PAPER
(
(
(
(
(
(
CH2,oxa), 80.0 (CH2,oxa), 67.4 [C(CH ], 65.2 [C(CH
3
)
2
3
)
2
], 31.0 be obtained free of charge at www.ccdc.cam.ac.uk/conts/
CH3,oxa), 27.6 (CH3,oxa), 27.4 (CH3,oxa), 26.6 (CH3,oxa), 18.8 retrieving.html [or from the Cambridge Crystallographic Data
CH2,pyrr), 17.9 (CH2,pyrr), 17.3 (CH3,pyrr), 17.2 (CH3,pyrr) ppm. IR Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (internat.)
KBr): ν˜ ϭ 2965 (m), 1622 (s), 1600 (s), 1519 (m), 1406 (s), 1189 ϩ 44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
s), 1151 (s), 965 (m), 742 (m), 349 (w) cmϪ1. C36
914.15): calcd. C 47.17, H 5.72; found C 47.21, H 5.56.
2 6 5 2
H52Cl N O Pd
Table 4. X-ray experimental data of compounds 6 and 7
General Procedure for the Heck Coupling Reactions: The aryl brom-
ide (1.1 mmol), the olefinic substrate (1.0 mmol, 6.0 mmol in the
6
7
case of methyl acrylate) and K
3 4
PO (1.1 mmol) were dissolved in
Empirical formula
Formula mass
Crystal system
Space group
C
822.36
monoclinic
C2
19.733(1)
9.9775(5)
16.8832(9)
95.021(5)
3311.3(3)
4
1.65
1656
1.293
173
0.71073
Mo-K
2.5/27.09
5478
28
H
36Cl
2
N
6
O
4
Pd
2
·H
2
O
C
36 2 6 4 2
H52Cl N O Pd
3
mL of dry NMP. The catalyst (or a solution of the catalyst) was
916.56
monoclinic
P2 /c
11.4766(1)
18.3485(3)
19.8285(3)
103.820(5)
4054.58(9)
4
1.50
1872
1.063
173
then added the reaction mixture was purged three times with nitro-
gen and heated to 110 °C. The reaction was monitored by GCMS
analysis until the generation of the product olefin had ceased. The
1
˚
a [A]
˚
(Z)/(E) ratio and the degree of conversion were determined by
b [A]
˚
c [A]
GC analysis.
β [°]
˚
3
General Procedure for the Heck Coupling Reactions with 1,2-Disub-
stituted Alkenes: The aryl bromide (1.1 mmol), the olefin
V [A ]
Z
D
calcd. [g cmϪ3
]
3 4
(1.0 mmol) and K PO (1.1 mmol) were dissolved in 3 mL of dry
F(000)
µ [mmϪ1]
T [K]
NMP. The catalyst (0.1%) was then added and the reaction mixture
was purged three times with nitrogen and heated to 110 °C. When
the reaction was complete, as determined by GCMS analysis, the
reaction mixture was allowed to cool to room temperature, diluted
with diethyl ether and washed three times with water. The organic
˚
λ [A]
0.71073
Mo-K
α
2.5/30.03
20064
Radiation
θ limits [°]
Number of data
measured
Number of data
with I Ͼ 3σ(I)
α
layer was dried with MgSO
crude product. Purification by flash chromatography (hexane
00%, then hexanes/EtOAc, 1:1) afforded the analytically pure al-
4
and concentrated in vacuo to give the
4263
7971
1
kene product.
Number of variables 387
451
R
Rw
GOF
0.048
0.066
1.179
0.029
0.036
1.159
1.267
General Procedure for the Suzuki Cross-Coupling Reactions: The
arylboronic acid and K CO (2 equiv.) were placed in a Schlenk
2 3
tube equipped with a stirring bar. Three nitrogen/vacuum cycles
were performed before addition of dry toluene (5 mL), the aryl
bromide (1.1 equiv.) and the palladium catalyst (or a solution of the
palladium catalyst). The reaction was performed at the temperature
indicated in Table 3. On completion of the reaction, the mixture
Largest peak in final 1.758
difference [e·A
˚
Ϫ3
]
2
was diluted with Et O, filtered through a pad of Celite, washed
Acknowledgments
We thank the CNRS (France), the Institut Universitaire de France,
and the Minist e` re de l’Education Nationale, de la Recherche et de
la Technologie (PhD grant for C. M.) for funding. We are grateful
three times with water, concentrated and purified by column chro-
matography or recrystallisation. All the products were charac-
terised by standard spectroscopic and analytical methods. Their
spectroscopic data are in agreement with those found in the literat-
to Dr. Andre
´
De Cian and N. Gruber for X-ray diffraction studies
[
26]
ure.
X-ray Crystallographic Study of 6 and 7: Suitable crystals of the
complexes 6 and 7 were obtained by layering concentrated solu-
tions of the compounds in dichloromethane with n-hexane and al-
lowing slow diffusion at room temperature. The crystal data were
collected at Ϫ100 °C with a Nonius Kappa CCD diffractometer
and transferred to a DEC Alpha workstation; for all subsequent
[1]
A. Togni, L. M. Venanzi, Angew. Chem. 1994, 106, 517Ϫ546;
Angew. Chem. Int. Ed. Engl. 1994, 33, 497Ϫ526.
2] [2a]
[
R. E. Lowenthal, A. Abiko, S. Masamune, Tetrahedron
Lett. 1990, 31, 6005Ϫ6008. [ D. A. Evans, K. A. Woerpel,
2b]
M. M. Hinman, M. M. Faul, J. Am. Chem. Soc. 1991, 113,
7
26Ϫ728. [ D. Müller, G. Umbricht, B. Weber, A. Pfaltz,
2c]
[2d]
[27]
Helv. Chim. Acta 1991, 74, 232Ϫ240.
E. J. Corey, N. Imai,
calculations the Nonius OpenMoleN package was used.
The
H. Y. Zhang, J. Am. Chem. Soc. 1991, 113, 728Ϫ729. For re-
structures were solved by direct methods with absorption correc-
tions being part of the scaling procedure of the data reductions.
After refinement of the heavy atoms, difference Fourier maps re-
vealed the maxima of residual electron density close to the posi-
tions expected for the hydrogen atoms; they were introduced as
fixed contributors in the structure factor calculations with fixed
views of chiral oxazoline ligands in asymmetric catalysis, see:
[2e]
F. Fache, E. Schulz, M. Lorraine Tommasino, M. Lemaire,
[2f]
Chem. Rev. 2000, 100, 2159Ϫ2231.
M. Gomez, G. Muller,
[
2g]
M. Rocamora, Coord. Chem. Rev. 1999, 193, 769Ϫ835.
A.
K. Ghosh, P. Mathivanan, J. Cappiello, Tetrahedron: Asym-
metry 1998, 9, 1Ϫ45.
Selected recent references:
[3]
[3a]
˚
MukaiyamaϪMichael reactions:
coordinates (CϪH: 0.95 A) and isotropic temperature factors
˚
2
D. A. Evans, K. A. Scheidt, J. N. Johnston, M. C. Willis, J.
[
B(H) ϭ 1.3 Bequiv(C) A ] but not refined. Full least-squares refine-
Am. Chem. Soc. 2001, 123, 4480Ϫ4491. [ Cycloadditions of
3b]
2
ments on F . A final difference map revealed no significant maxima
silyl ketenes: D. A. Evans, J. M. Janey, Org. Lett. 2001, 3,
of electron density. The scattering factor coefficients and the anom-
[3c]
2
125Ϫ2128.
Henry reactions: C. Christensen, K. Juhl, K.
[28]
alous dispersion coefficients were taken from ref.
Crystal data
[3d]
A. Jørgensen, Chem. Commun. 2001, 2222Ϫ2223.
FriedelϪCrafts reactions: W. Zhuang, N. Gathergood, R. G.
Hazell, K. A. Jørgensen, J. Org. Chem. 2001, 66, 1009Ϫ1013-
and experimental details for the crystals of compounds 6 and 7 are
given in Table 4. CCDC-173019 (6) and -194957 (7) contain the
supplementary crystallographic data for this paper. These data can
[3e]
Hetero DielsϪAlder reactions: D. A. Evans, J. S. Johnson,
Eur. J. Inorg. Chem. 2003, 1161Ϫ1168
1167

C. Mazet, L. H. Gade
FULL PAPER
E. J. Olhava, J. Am. Chem. Soc. 2000, 122, 1635Ϫ1649. [3f] Mol-
ybdenum-catalysed allylic alkylation: F. Glorius, A. Pfaltz, Org.
Lett. 1999, 1, 141Ϫ144.
[13] [13a]
W. A. Herrmann, C. P. Reisinger, M. Spiegler, J. Or-
ganomet. Chem. 1998, 557, 93Ϫ96. [
13b]
T. W. Weskamp, V. P.
Böhm, W. A. Herrmann, J. Organomet. Chem. 1999, 585,
[
[
4]
[13c]
C. Mazet, L. H. Gade, Organometallics 2001, 20, 4144Ϫ4146.
348Ϫ352.
J. Org. Chem. 1999, 64, 3804Ϫ3805.
ell, Tetrahedron Lett. 2000, 41, 595Ϫ598.
W. Skelton, A. H. White, C. C. Williams, J. Chem. Soc., Dalton
C. Zhang, J. Huang, M. L. Trudell, S. P. Nolan,
5] [5a]
[13d]
H. Nishiyama, H. Sakagushi, T. Nakamura, M. Horihata,
C. Zhang, M. L. Trud-
M. Kondo, K. Itoh, Organometallics 1989, 8, 846Ϫ848. [ H.
5b]
[13e]
M. V. Baker, B.
Nishiyama, M. Kondo, T. Nakamura, K. Itoh, Organometallics
991, 10, 500Ϫ508. [ D. A. Evans, M. C. Kozlowski, J. A.
5c]
Trans. 2001, 111Ϫ120.
[13f]
D. A. Albisson, R. B. Bedford, S.
1
Murry, C. S. Burgey, K. R. Campos, B. T. Connell, R. J.
Staples, J. Am. Chem. Soc. 1999, 121, 669Ϫ685. [5d] D. A. Ev-
ans, C. S. Burgey, M. C. Kozlowski, S. W. Tregay, J. Am. Chem.
Soc. 1999, 121, 686Ϫ699. [ D. A. Evans, D. M. Barnes, J. S.
Johnson, T. Lectka, P. von Matt, S. J. Miller, J. A. Murry, R.
D. Norcross, E. A. Shaughnessy, K. R. Campos, J. Am. Chem.
Soc. 1999, 121, 7582Ϫ7594. [ D. A. Evans, Z. K. Sweeney, T.
Rovis, J. S. Tedrow, J. Am. Chem. Soc. 2001, 123, 12095Ϫ12096.
E. Lawrence, P. N. Scully, Chem. Commun. 1998, 2095Ϫ2096.
[13g]
R. B. Bedford, S. M. Draper, P. N. Scully, S. L. Welch, New
J. Chem. 2000, 24, 745Ϫ747. [
Chem. Commun. 2001, 129Ϫ130.
14] [14a]
13h]
R. B. Bedford, S. L. Welch,
5e]
[
[
S. Gründemann, M. Albrecht, J. A. Loch, J. W. Faller, R.
[
14b]
H. Crabtree, Organometallics 2001, 20, 5485Ϫ5488.
E.
5f]
Peris, J. A. Loch, J. Mata, R. H. Crabtree, Chem. Commun.
2001, 201Ϫ202. [
14c]
J. A. Loch, M. Albrecht, E. Peris, J. Mata,
J. W. Faller, R. H. Crabtree, Organometallics 2002, 21,
[
5g]
H. Nishiyama, Y. Itoh, H. Matsumoto, K. Itoh, J. Am.
Chem. Soc. 1994, 116, 2223Ϫ2224. [ H. Nishiyama, Y. Itoh,
Y. Sugawara, H. Matsumoto, K. Aoti, K. Itoh, Bull. Chem.
Soc. Jpn. 1995, 68, 1247Ϫ1262. [ Y. Motoyama, K. Murata,
O. Kurihara, T. Naitoh, K. Aoki, H. Nishiyama, Organometal-
lics 1998, 17, 1251Ϫ1253. [ H. Nishiyama, T. Naitoh, Y. Mo-
toyama, K. Aoki, Chem. Eur. J. 1998, 5, 3509Ϫ3513.
5h]
700Ϫ706.
15] [15a]
I. P. Beletskaya, A. V. Chuchurjukin, H. P. Dijkstra, G.
5i]
P. M. van Klink, G. van Koten, Tetrahedron Lett. 2000, 41,
[
15b]
1075Ϫ1079.
I. P. Beletskaya, A. N. Kashin, N. B.
5j]
Karlstedt, A. V. Mitin, A. V. Cheprakov, G. M. Kazankov, J.
Organomet. Chem. 2001, 622, 89Ϫ96.
D. Zim, A. S. Gruber, G. Ebeling, J. Dupont, A. L. Monteiro,
Org. Lett. 2000, 18, 2881Ϫ2884.
H. Weissman, D. Milstein, Chem. Commun. 1999, 1901Ϫ1902.
G. A. Grasa, A. C. Hillier, S. P. Nolan, Org. Lett. 2001, 3,
1077Ϫ1080.
[
[
6]
[16]
[17]
C. Mazet, L. H. Gade, Chem. Eur. J. 2002, 8, 4308Ϫ4318.
7] [7a]
C. Bolm, K. Weickhardt, M. Zehnder, D. Glasmacher, Helv.
Chim. Acta 1991, 74, 717Ϫ726. [ C. Bolm, K. Weickhardt,
7b]
[18]
M. Zehnder, T. Ranff, Chem. Ber. 1991, 124, 1173Ϫ1180.
[
8] [8a]
[8b]
8c]
L. Knorr, Ber. Dtsch. Chem. Ges. 1884, 17, 1635Ϫ1642.
L. Knorr, Justus Liebigs Ann. Chem. 1886, 236, 290Ϫ332. [
U. Eisner, A. Lichtarowicz, R. P. Linstead, J. Chem. Soc. 1957,
7
[19]
W. Cabri, I. Candiani, A. Bedeschi, R. Santi, Synlett 1992,
871Ϫ872.
[
8d]
[20]
[21]
33Ϫ738.
J. B. Paine, III, R. B. Woodward, D. Dolphin,
C. Gürtler, S. L. Buchwald, Chem. Eur. J. 1999, 5, 3107Ϫ3112.
V. C e´ sar, S. Bellemin-Laponnaz, L. H. Gade, Organometallics
2002, 21, 5204.
[8e]
J. Org. Chem. 1976, 41, 2826Ϫ2835.
H. W. Whitelock, R.
Hanauer, J. Org. Chem. 1968, 33, 2169Ϫ2171.
[
9]
[22]
The Porphyrins Handbook (Eds.: K. M. Kadish, K. M. Smith,
R. Guilard), Academic, San Diego, CA, 2000.
A. F. Littke, G. C. Fu, J. Am. Chem. Soc. 2001, 123,
6989Ϫ7000.
[
[
10] [10a]
[23] [23a]
Y. S. Klausner, M. Bodansky, Synthesis 1972, 453Ϫ463.
S. R. Gilbertson, C. W. T. Chang, J. Org. Chem. 1998,
S. Cacchi, P. G. Ciattini, E. Morera, G. Ortar, Tetrahedron
[
10b]
[23b]
Lett. 1987, 28, 3039Ϫ3042.
A. Amorese, A. Arcadi, E.
63, 8424Ϫ8431.
Bernocchi, S. Cacchi, S. Cerrini, W. Fedeli, G. Ortar, Tetrahed-
11]
12]
[11a]
[23c]
For reviews of helical complexes, see:
E. C. Constable, Tet-
C. Piguet, G. Bernardi-
ron 1989, 45, 813Ϫ829.
M. Moreno-Manas, M. P e´ rez, R.
rahedron 1992, 48, 10013Ϫ10059. [
11b]
Pleixats, Tetrahedron Lett. 1996, 37, 7449Ϫ7452.
[23d]
M. Mor-
[
11c]
nelli, G. Hopfgartner, Chem. Rev. 1997, 97, 2005Ϫ2062.
eno-Manas, R. Pleixats, A. Roglans, Synlett 1997, 1157Ϫ1158.
M. Albrecht, Chem. Rev. 2001, 101, 3457Ϫ3498. [
11d]
U. Knof,
[23e]
M. Beller, T. H. Riermeier, Tetrahedron Lett. 1996, 37,
6535Ϫ6538. [ M. Beller, T. H. Riermeier, Eur. J. Inorg. Chem.
23f]
A. von Zelewsky, Angew. Chem. Int. Ed. 1999, 38, 302Ϫ322.
[
For recent reviews of the cross-coupling of organoboron com-
1998, 29Ϫ35.
[
12a]
[24]
[25]
pounds, see:
A. Suzuki, Pure Appl. Chem. 1991, 63,
N. Miaura, A. Suzuki, Chem. Rev. 1995, 95,
12c]
K. W. Hellmann, L. H. Gade, Verfahrenstechnik (Berlin) 1997,
31(5), 70Ϫ71.
D. Drew, J. R. Doyle, Inorg. Synth. 1972, 13, 47Ϫ65.
[
12b]
4
2
1
19Ϫ422.
457Ϫ2483.
47Ϫ168. Selected references:
[
A. Suzuki, J. Organomet. Chem. 1999, 576,
[
12d]
[26] [26a]
M. Beller, H. Fischer, W. A.
A. F. Littke, G. C. Fu, J. Org. Chem. 1999, 64, 10Ϫ11.
A. F. Littke, C. Dai, G. C. Fu, J. Am. Chem. Soc. 2000,
[26b]
Herrmann, K. Öfele, C. Brossmer, Angew. Chem. Int. Ed. Engl.
995, 34, 1848Ϫ1849. [
Beller, Chem. Commun. 2000, 2475Ϫ2476.
C. Fu, Angew. Chem. Int. Ed. 1998, 37, 3387Ϫ3388. [
Wolfe, S. L. Buchwald, Angew. Chem. Int. Ed. 1999, 38,
12e]
M. Gomez Andreu, A. Zapf, M.
122, 4020Ϫ4028.
1
[12f]
[27]
[28]
A. F. Littke, G.
Nonius OpenMoleN, Interactive Structure Solution, Delft, 1997.
D. T. Cromer, J. T. Waber, International Tables for X-ray Crys-
tallography, The Kynoch Press, Birmingham, 1974.
Received October 7, 2002
12g]
J. P.
[
12h]
2413Ϫ2416.
J. P. Wolfe, R. A. Singer, B. H. Yang, S. L.
Buchwald, J. Am. Chem. Soc. 1999, 121, 9550Ϫ9561.
[I02552]
1168
Eur. J. Inorg. Chem. 2003, 1161Ϫ1168