Cycloruthenated tertiary amines and ethylene: Further insight to the Ru- mediated olefin-aryl coupling reaction

Article abstract of DOI:10.1039/a908703f

The reaction between cycloruthenated N,N-dimethylbenzylamine and ethylene under very mild conditions afforded 2-vinyl-N,N-dimethylbenzylamine and an organometallic Ru derivative resulting from the overall insertion of one carbon atom in the Ru-C bond of t

Full text of DOI:10.1039/a908703f

Cycloruthenated tertiary amines and ethylene: further insight to the
Ru-mediated olefin–aryl coupling reaction
Vincent Ritleng, Jean Pascal Sutter,† Michel Pfeffer* and Claude Sirlin
Laboratoire de Synthe`ses Me´tallo-Induites, UMR CNRS 7513 Universite´ Louis Pasteur, 4 rue Blaise Pascal, 67070
Strasbourg, France. E-mail: pfeffer@chimie.u-strasbg.fr
Received (in Basel, Switzerland) 29th October 1999, Accepted 6th December 1999
1
The reaction between cycloruthenated N,N-dimethylbenzyl-
amine and ethylene under very mild conditions afforded
2-vinyl-N,N-dimethylbenzylamine and an organometallic
Ru derivative resulting from the overall insertion of one
carbon atom in the Ru–C bond of the starting material.
Interestingly, only one enantiomeric pair was observed by H
NMR in both cases, indicating that these reactions occur with a
high level of diastereoselectivity. The stereochemistry of 3a has
1
6
been investigated by a H NOE experiment. The h -benzene
ring was found to interact strongly with one of the N-methyl and
with the C-methyl which also interacts with the proton of the
aryl ligand. The proton on the carbon a to Ru (CA) interacts
The insertion of an olefin in a transition metal–carbon s-bond is
a classical reaction in organometallic chemistry. With palla-
dium, this process is followed by b-hydrogen elimination and is
widely known as the Heck reaction.1 Recently, functionalisa-
tion reactions of aryl C–H bonds with terminal olefins catalysed
by ruthenium hydride complexes were reported.2,3 In these
reactions the products are alkyl substituted compounds resulting
from the ‘formal’ insertion of the olefinic double bond into a
C–H bond. We now report that air stable cycloruthenated N,N-
dimethylbenzylamine derivatives react at low pressure (1.5 atm)
and room temperature (RT) with ethylene to afford vinylbenzyl-
amines, as in the Heck reaction, and an organometallic
compound resulting from the insertion of ethylene into the Ru–
C bond.
6
neither with the latter nor with the h -benzene ring. Conse-
quently, 3a displays a boat conformation, with the C-methyl and
6
the h -benzene ring in the equatorial and the axial positions
respectively. The absolute configuration of the enantiomers are
thus (RRuRCA) and (SRuSCA).
In order to confirm the chiral control of the reaction, the
6
optically active complex (h -C6H6)Ru(C6H4-2-(R)-CH(Me)N-
Me2)Cl 1b (de = 90%)4 was treated with ethylene under the
same conditions. Surprisingly in addition to 2b and 3b,‡ the
respective analogues of 2a and 3a, a third product 4b‡ was
observed in trace amounts [eqn. (3)]. Its structure is that of a
new cyclometallated benzylamine derivative displaying an
ethyl substituent in position 3.
6
In a typical experiment, an orange suspension of (h -
C6H6)Ru(C6H4CH2NMe2)Cl 1a in methanol was stirred at
room temperature under 1.5 bar of ethylene over 1.5 h [eqn. (1)].
2-Vinyl-N,N-dimethylbenzylamine 2a‡ and the new organo-
ruthenium compound 3a‡ were isolated. The 1H and 13C NMR
spectra and combustion analyses of 3a are consistent with the
structure depicted in eqn. (1).
For complexes 3b and 4b, one diastereoisomer only was
observed by 1H NMR indicating that these compounds are the
result of highly diastereoselective processes. Unfortunately
owing to its instability, 3b could not be isolated as a pure solid.
Nevertheless its stereochemistry was investigated through a 1H
ROESY experiment of the crude reaction mixture. The methyl
substituent of the carbon atom s-bonded to Ru (CA) interacts
6
with the proton of the aryl ligand and with the h -C6H6 ring
We found that it was possible to influence the ratio of 2a to
3a by removing the chloride ligand of the starting material.
Thus, the yellow cationic derivative 1aA4c led to a much higher
yield of the red organometallic species 3aA when it was treated
with ethylene [eqn. (2)].
whereas the corresponding proton interacts with none of these.
These results indicate an equatorial position for the methyl
6
group and axial position for the h -benzene ring as in 3a. The
methyl group a to N interacts equally with both N-methyls and
6
with the proton of the aryl ligand but not with the h -benzene
indicating an equatorial position as well. Moreover, the absence
6
of any interaction between the h -benzene ring and the benzylic
proton attached to N, together with the deshielding of the latter
signal, indicate that this proton should be close to the chlorine
atom as in the starting material 1b. Consequently, 3b should
display a boat conformation with the protons a to Ru and N on
bridgehead positions and its absolute configuration should
therefore be (RCSRuSCA).
When 3b was left in solution it isomerised slowly into 4b
together with decomposition but no conversion into 2b was
detected. Thus 2b and 3b are independent products which,
however, are likely to come from the same intermediate (see
below). The important instability of 3b as compared to that of
3a might be due to steric congestion around the Ru atom. The
These reactions led to the formation of a chiral C atom s-
bonded to Ru, the Ru atom being itself a stereogenic center.4
† Present address: Institut de Chimie de la Matie`re Condense´e de Bordeaux
- UPR CNRS 9048-Avenue du Dr. Schweitzer 33608 Pessac, France.
Chem. Commun., 2000, 129–130
This journal is © The Royal Society of Chemistry 2000
129

rearrangement process 3b ? 4b remains unclear yet. Running
the reaction in CD3OD did not result in deuterium incorporation
in the new ethyl group. Moreover, when a sample of the crude
reaction mixture was left in an aprotic solvent such as CDCl3
this demetallation–remetallation process also occured. These
observations tend to indicate that 4b may be formed through an
intramolecular rearrangement as demonstrated by Steenwinkel
et al. for a related ruthenocyclic molecule.5
To the best of our knowledge the only precedent of a Ru-
mediated functionalization of a C–H bond to afford a vinyl
derivative such as 2a,b was reported by Murai and coworkers6
when reacting aromatic imines or imidates with mono-
substituted olefins in the presence of catalytic amounts of
Ru3(CO)12. It is generally assumed that this type of product is
formed by b-H elimination from a carbometallation inter-
mediate. Consequently the formation of 2a,b and 3a,b can be
rationalised according to the reaction path depicted in Scheme
1. The first step involves the insertion of ethylene into the C–Ru
bond followed by a b-H elimination leading to an olefin–
hydride complex.7 This leads on one hand to the metal free
substituted olefin 2a,b as in the Heck reaction and on the other
hand to the one carbon-atom insertion complex 3a,b by anti-
Markovnikov hydrometallation of the olefinic unit (Scheme
1).
We thank INTAS (INTAS-97-166) for financial support of
this work.
Notes and references
‡ Selected data (J/Hz): 2a: dH(200 MHz, CDCl3) 7.55 (m, 1H, C6H4), 7.26
(m, 3H, C6H4), 7.17 (dd, 1H, CHNCH2, 3J 17.5, 3J 11.0), 5.68 (dd, 1H,
CHNCHEHZ, 3J 17.5, 2J 1.4), 5.30 (dd, 1H, CHNCHEHZ, 3J 11.0, 2J 1.4),
3.44 (s, 2H, CH2N), 2.24 (s, 6H, NMe2). 2b: dH(200 MHz, CDCl3) 7.44 (m,
2H, C6H4), 7.24 (m, 2H, C6H4), 7.23 (dd, 1H, CHNCH2, 3J 17.4, 3J 11.0),
3
2
3
5.57 (dd, 1H, CHNCHEHZ, J 17.4, J 1.6), 5.29 (dd, 1H, CHNCHEHZ, J
11.0, 2J 1.6), 3.53 (q, 1H, CHCH3, 3J 6.6), 2.21 (s, 6H, NMe2), 1.31 (d, 3H,
CHCH3). 3a: Anal. Calc. (found) for C17H22NClRu·0.25CH2Cl2: C, 52.04
(52.27); H, 5.70 (5.72); N, 3.52 (3.66)%. dH(300 MHz, CDCl3) 7.58 (d, 1H,
C6H4, 3J 7.7), 7.33 (m, 2H, C6H4), 6.88 (d, 1H, C6H4, 3J 4.0), 4.90 (s, 6H,
C6H6), 3.53 (q, 1H, CHCH3, 3J 7.1), 3.39 and 2.29 (AB, 2H, CH2N, 2J 11.4),
3.24 and 2.28 (2s, 6H, NMe2), 2.14 (d, 3H, CHCH3). dC(75 MHz, CDCl3)
153.8, 133.3, 129.4, 129.0, 121.6 and 120.4 (C6H4), 83.0 (C6H6), 64.7
(CH2N), 56.5 and 56.3 (NMe), 36.8 (CHRu), 24.5 (CHCH3). 3aA: dH(200
MHz, CD3CN) 7.62 (d, 1H, C6H4, 3J 7.4), 7.34 (m, 2H, C6H4), 6.99 (d, 1H,
C6H4, 3J 6.6), 5.14 (s, 6H, C6H6), 3.24 and 2.63 (AB, 2H, CH2N, 2J 11.8),
3.09 (q, 1H, CHCH3, 3J 7.4), 3.01 and 2.38 (2s, 6H, NMe2), 2.14 (s, 3H,
CH3CN), 2.08 (d, 3H, CHCH3). 3b: dH(500 MHz, CD2Cl2) 7.57 (d, 1H,
3
C6H4, J 7.7), 7.29 (t, 1H, C6H4), 7.02 (d, 1H, C6H4). 6.90 (t, 1H, C6H4),
4.88 (s, 6H, C6H6), 3.57 (2q, 2H, CHCH3Ru and CHCH3N), 3.32 and 2.07
(2s, 6H, NMe2), 2.11 (d, 3H, CHCH3Ru, 3J 7.1), 1.29 (d, 3H, CHCH3N, 3J
6.9). 4b: dH(500 MHz, CD2Cl2) 7.51 (d, 1H, C6H3, 3J 7.4), 6.94 (t, 1H,
C6H3). 6.68 (d, 1H, C6H3), 5.32 (s, 6H, C6H6), 3.45 (q, 1H, CHCH3, 3J 6.6),
3.10 and 2.33 (2s, 6H, NMe2), 2.44 (q, 2H, CH2CH3, 3J 7.6), 1.16 (d, 3H,
CHCH3), 1.14 (t, 3H, CH2CH3).
1 R. F. Heck, Org. React. (New York), 1982, 27, 345.
2 S. Murai, F. Kakiuchi, S. Sekine, Y. Tanaka, A. Kamatani, M. Sonoda
and N. Chatani, Nature, 1993, 366, 529; F. Kakiuchi, S. Sekine, Y.
Tanaka, A. Kamatani, M. Sonoda, N. Chatani and S. Murai, Bull. Chem.
Soc. Jpn., 1995, 68, 62.
3 Y. Guari, S. Sabo-Etienne and B. Chaudret, J. Am. Chem. Soc., 1998, 120,
4228.
4 (a) H. C. L. Abbenhuis, M. Pfeffer, J. P. Sutter, A. de Cian, J. Fischer, H.
Li Ji and J. H. Nelson, Organometallics, 1993, 12, 4464; (b) S. Attar, J. H.
Nelson, J. Fischer, A. de Cian, J. P. Sutter and M. Pfeffer, Organome-
tallics, 1995, 14, 4559; (c) S. Fernandez, M. Pfeffer, V. Ritleng and C.
Sirlin, Organometallics, 1999, 18, 2390.
5 P. Steenwinkel, S. L. James, R. A. Gossage, D. M. Grove, H. Kooijman,
W. J. J. Smeets, A. L. Spek and G. van Koten, Organometallics, 1998, 17,
4680.
6 F. Kakiuchi, M. Yamauchi, N. Chatani and S. Murai, Chem. Lett., 1996,
111; F. Kakiuchi, T. Sato, M. Yamauchi, N. Chatani and S. Murai, Chem.
Lett., 1999, 19.
Scheme 1
7 For a leading reference concerning olefin–hydride complexes, see: J. W.
Faller and K. J. Chase, Organometallics, 1995, 14, 1592.
Studies are currently under way to determine the conditions
that would allow us to direct the reaction toward the exclusive
formation of one of these products.
Communication a908703f
130
Chem. Commun., 2000, 129–130