Communications
DOI: 10.1002/anie.200701727
Sequential Catalysis
Ruthenium(IV) Alkylidenes as Precatalysts for Direct Arylations of
Alkenes with Aryl Chlorides and an Application to Sequential
Catalysis**
Lutz Ackermann,* Robert Born, and Paula lvarez-Bercedo
Dedicated to Professor Herbert Mayr on the occasion of his 60th birthday
The development of chemo- and regioselective intermolecu-
activation of alkenes[19] with readily available aryl chlor-
ides.[20] Herein, we disclose our results on this economical and
ꢀ
lar functionalization reactions of C H bonds represents an
important and long-standing goal in synthetic chemistry.[1–4]
Diasteroselective olefin cross-metathesis[5–7] catalyzed by
single-component ruthenium carbene complexes was recog-
environmentally benign C H bond functionalization process,
ꢀ
the stereochemical outcome of which is complementary to
that observed in olefin cross-metathesis reactions (Scheme 1,
reaction B). The potential of our findings for tandem
ꢀ
nized as an alternative for the functionalization of vinylic C
H bonds (Scheme 1, reaction A).[8] Furthermore, rutheni-
um(IV) alkylidene complexes enabled other valuable cata-
lytic processes, such as isomerizations, hydrogenations, Khar-
asch additions, and dihydroxylations,[9] which ultimately
allowed for the development of elegant sequential catalytic
transformations.[10–12]
catalysis[21] is demonstrated with a C H bond functionaliza-
tion–hydrosilylation sequence.
ꢀ
At the outset of our studies we probed the catalytic
performance of different ruthenium compounds in the direct
arylation of alkene 1a with electron-rich aryl chloride 2a
(Table 1 and Table S1 in the Supporting Information).
Notably, we observed significant, though sluggish, product
formation under phosphine-free reaction conditions (Table 1,
entries 2, and 3). Significantly more efficient catalysis was
accomplished with a complex derived from secondary phos-
phine oxide 4 (Ad = adamantyl; Table 1, entry 4). Rutheni-
um(IV) carbene complexes 5 and 6 showed high catalytic
activities (Table 1, entries 5, and 6), while complex 7 out-
performed all studied catalysts (Table 1, entry 7). In view of
further catalyst development, it is notable that ruthenium(III)
ꢀ
Scheme 1. Indirect (A) versus direct (B) vinylic C H bond functionali-
zation catalyzed by a ruthenium(IV) carbene complex.
Table 1: Ruthenium catalyst screening for the direct arylation of
alkenes.[a]
Ruthenium-catalyzed direct arylations[13] using organic
electrophiles[14] have, to date, only been reported with
ruthenium(II) complexes as catalysts.[15–18] While conducting
mechanistic studies, we found that highly functional-group-
tolerant ruthenium(IV) carbene complexes can be employed
Entry
[Ru]
Yield [%][b]
ꢀ
for unprecedented direct arylation reactions via C H bond
1
2
3
4
[Ru3(CO)12]
[RuCl3 ·xH2O]
[{RuCl2(p-cymene)}2]
[{RuCl2(p-cymene)}2]/(1-Ad)2P(O)H (4)
–
27
34
78
[*] Prof. Dr. L. Ackermann, Dipl.-Chem. R. Born, P. lvarez-Bercedo
Institut für Organische und Biomolekulare Chemie
Georg-August-Universität
Tammannstrasse 2, 37077 Göttingen (Germany)
Fax: (+49)551-39-6777
E-mail: lutz.ackermann@chemie.uni-goettingen.de
5
54
[**] Support by the DFG (Emmy Noether-Programm), the Spanish
Ministerio de Educación y Ciencia (fellowship for P.A.B.), the Fonds
der Chemischen Industrie, the Dr. Otto Röhm Gedächtnisstiftung,
the Römer Foundation, and Sanofi-Aventis (Frankfurt) is gratefully
acknowledged.
[c]
=
6
7
[Cl2(PCy3)(IMes)Ru CHPh] (6)
78
85
=
[Cl2(PCy3)2Ru CHPh] (7)
[a] Reaction conditions: 1a (1.0 equiv), 2a (1.2 equiv), [Ru] (5.0 mol%),
K2CO3 (2.0 equiv), NMP (N-methylpyrrolidinone, 1 mL), 1208C, 22 h.
[b] Yields ofisolated product. [c] IMes =N,N’-bis-(2,4,6-trimethylphen-
yl)imidazol-2-ylidene.
Supporting information for this article is available on the WWW
6364
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 6364 –6367