Reaction of [MnII(CH2tBu)2] with bidentate diimine ligands: From simple base adducts to C-C activation of the ligand

Article abstract of DOI:10.1002/1521-3773(20020816)41:16<3025::AID-ANIE3025>3.0.CO;2-B

Ligand transformations that depend on the substitution patterns of the diimine ligands occur upon their complexation with Mn¹¹ dialkyl complexes. For example the 1,3-migration of the neopentyl unit from Mn to a carbon atom and the 1,2-migration of the methyl in the putative intermediate 1 give the product 2.

Full text of DOI:10.1002/1521-3773(20020816)41:16<3025::AID-ANIE3025>3.0.CO;2-B

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[7] a) K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett. 1975,
4467 4470; b) K. Sonogashira in Comprehensive Organic Synthesis,
Vol. 3 (Eds.: B. M. Trost, I. Fleming, G. Pattenden), Pergamon,
Oxford, 1991, pp. 521 549.
[8] T. H. Chan, I. Fleming, Synthesis 1979, 761 786.
[9] a) S. Rousset, J. Thibonnet, M. Abarbri, A. DuchÜne, J.-C. Parrain,
Synlett 2000, 260 262; b) S. R. Wilson, L. A. Jacob, J. Org. Chem.
1986, 51, 4833 4836.
Ph
C6H13
Bu
PhB(OH)2
Me
[PdCl2(PPh3)2]
Na2CO3
81%
I
H
C6H13
SiMe3
Me
C6H13
Bu
C6H13
Bu
I2, AgNO3
Me
12
in EtOH,
0 °C
82%
H
X
H
C6H13
Bu
C6H13
C6H13
1) tBuLi
11
Me
7
[10] The stereochemistry of 11 was determined by NOESY NMR
spectroscopy.
2) Electrophile
H
C6H13
Electrophile
Product
X
H
Yield
H2O
13
14
15
95%
80%
73%
PhCHO
HC(O)NMe2
CH(OH)Ph
CHO
(95% purity)
Scheme 3. Transformation of 7 to the vinyl iodide 11 and the following
coupling reaction.
easily available in quantity, and the reaction operation is
easy.
Reaction of ™[MnII(CH2tBu)2]∫ with Bidentate
Diimine Ligands: From Simple Base Adducts to
ꢀ
C C Activation of the Ligand**
Experimental Section
Virginie Riollet, Christophe Copÿret,* Jean-
Marie Basset, Laurence Rousset, Denis Bouchu,
Laurent Grosvalet, and Monique Perrin
ꢀ
Typical procedure for the site-selective C C bond formation of 2 with
organocuprates (preparation of 3aa, Table 1, entry 1): To a stirred solution
ofCuI (1.99 g, 10.4 mmol) in Et O (10 mL) was added a 1.04m solution of
2
MeLi in ether (20.0 mL, 20.8 mmol) at 08C, under argon, to give a
homogeneous solution. The solution was cooled to ꢀ508C, then 2a (1.90 g,
3.48 mmol) was added to the solution. After stirring at ꢀ508C for 3 h, the
reaction mixture was quenched by the addition ofaqueous NH 4Cl and the
organic products were extracted with diethyl ether. The combined organic
layers were washed with brine, dried over Na2SO4, and concentrated
in vacuo to give a crude oil. Chromatography on silica gel (hexane)
afforded compound 3aa (1.35 g, 90%). 1H NMR (300 MHz, CDCl3): d ¼
0.16 (s, 9H), 0.85 0.90 (m, 6H), 1.25 1.60 (m, 16H), 1.65 (s, 3H), 2.18 (t, J ¼
8.0 Hz, 2H), 2.51 (t, J ¼ 7.1 Hz, 2H), 6.19 ppm (s, 1H); 13C NMR (75 MHz,
CDCl3): d ¼ 0.41, 14.18, 14.21, 19.67, 22.73, 22.76, 27.94, 28.84, 29.45, 29.85,
31.63, 31.91, 36.61, 45.06, 110.59, 131.35, 136.40, 149.32 ppm.
II
Base adducts ofdialkyl Mn
complexes are typically
monomeric tetrahedral high-spin systems;[1] our synthetic
target is to extend these adducts to bidentate diimine ligands.
Gambarotta and co-workers[2] recently reported an approach
to MnII analogues ofBrookhart Gibson complexes
and
[3]
compared their performance in olefin polymerization with
those ofFe II and NiII catalysts. In this approach, they showed
that the reaction of[MnCl 2L2] complexes with organolithium
reagents gave the corresponding MnI and Mn0 alkyl com-
plexes, that is, the lithium reagents alkylate and reduce the
MnII dichloro complex. These results have led us to disclose
Typical procedure for conversion of 4 into 5 (synthesis of 11; Scheme 3): To
a stirred solution of 7 (0.126 g, 0.345 mmol) in absolute ethanol (6 mL) was
added AgNO3 (0.088 g, 0.518 mmol) at 08C. The mixture was stirred for
10 min to ensure complete dissolution. Iodine (0.114 g, 0.449 mmol) was
added in one portion and stirred at 08C for 20 min. The reaction mixture
was diluted with diethyl ether, filtering through a celite pad. The filtrate
was washed with sodium thiosulfate solution, dried over Na2SO4, and
concentrated in vacuo to give a crude oil. Chromatography on silica gel
(hexane) afforded compound 11 (0.118 g, 82%). 1H NMR (300 MHz,
CDCl3): d ¼ 0.86 0.91 (m, 9H), 1.21 1.42 (m, 20H), 1.89 (t, J ¼ 7.4 Hz,
2H), 2.05 (t, J ¼ 7.1 Hz, 2H), 2.24 (t, J ¼ 7.1 Hz, 2H), 2.42 (s, 3H), 5.47 ppm
(s, 1H); 13C NMR (75 MHz, CDCl3): d ¼ 14.16, 14.20, 14.23, 22.74, 22.76,
23.13, 27.94, 28.04, 29.20, 29.27, 29.61, 30.75, 31.67, 31.82, 31.86, 35.47, 43.36,
96.24, 121.60, 142.69, 143.15 ppm.
II
our investigation on the reaction ofa bisneopentyl Mn
complex with bidentate Shiff base ligands that were designed
to generate complexes with structure 1 (Scheme 1). The major
difference in our approach is the reaction of diimine ligands
[*] Dr. C. Copÿret, V. Riollet, Dr. J.-M. Basset
Laboratoire de Chimie Organomÿtallique de Surface
UMR-9986 CNRS-ESCPE Lyon
43 bd du 11 Novembre 1918, 69616 Villeurbanne Cedex (France)
Fax : (þ 33)472-431-795
E-mail: coperet@cpe.fr
Received: May 2, 2002 [Z19197]
L. Rousset, Dr. D. Bouchu
Centre de Spectromÿtrie de Masse
Universitÿ Claude Bernard Lyon I
43 bd du 11 Novembre 1918, 69622 Villeurbanne Cedex (France)
[1] T. Hamada, D. Suzuki, H. Urabe, F. Sato, J. Am. Chem. Soc. 1999, 121,
7342 7344.
[2] Recent reviews ofsynthetic reactions mediated by a Ti(O- iPr)4/
2iPrMgX reagent: a) F. Sato, H. Urabe, S. Okamoto, Chem. Rev. 2000,
100, 2835 2886; b) F. Sato, S. Okamoto, Adv. Synth. Catal. 2001, 343,
759 784.
L. Grosvalet, Prof. Dr. M. Perrin
Laboratoire de Cristallographie UMR-5078
Universitÿ Claude Bernard Lyon I
43 bd du 11 Novembre 1918, 69622 Villeurbanne Cedex (France)
[3] S. Yamaguchi, R. Jin, K. Tamao, F. Sato, J. Org. Chem. 1998, 63,
10060 10062.
[**] We are indebted to the CNRS and ESCPE Lyon for financial support.
V.R. is grateful to the Rÿgion RhÙne-Alpes for
a predoctoral
[4] R. B. Miller, G. McGarvey, J. Org. Chem. 1979, 44, 4623 4633.
[5] a) G. H. Posner, Org. React. 1975, 22, 253 400; b) B. H. Lipshutz, S.
Sengupta, Org. React. 1992, 41, 135 631; c) B. H. Lipshutz in
Organometallics in Synthesis (Ed.: M. Schlosser), Wiley, Chichester,
1994, pp. 283 382.
fellowship. We also thank Prof. R. A. Andersen (U. C. Berkeley),
Prof. Dr. Koelher (TUM), Dr. R. Gauvin (LCOMS), and Dr. C.
Boisson (LCPP) for helpful discussions.
Supporting information for this article is available on the WWW under
http://www.angewandte.org or from the author.
[6] N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457 2483.
Angew. Chem. Int. Ed. 2002, 41, No. 16
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with manganese(ii) dialkyl complexes, which
proceeds without reduction. Depending on the
structure ofthe ligand it is possible to isolate
either the desired base adduct or compounds in
which the imine functional group is alkylated.
A
brown solution of[{Mn(CH 2tBu)2}4]
(1 equiv) in toluene was added to a colorless
solution of trans-N,N’-bis(benzylidene)-1,2-cy-
clohexanediamine in toluene, and the solution
turned dark-purple. After 12 h, removal of
toluene and addition ofpentane led to precip-
itation ofunconsumed ligand (excess ligand:
vide infra). After complete removal of the ligand
and concentration to dryness, a concentrated
solution ofthe solid in toluene was cooled to
ꢀ308C to give single crystals as brown rectan-
gular parallelepipeds (20%). However, X-ray
analysis revealed the presence of 2 (Figure 1)
with a structure that was dramatically different
from that of the expected 1a.[4] Complex 2 is
ꢀ
dinuclear, and the Mn Mn distance of2.822 ä
Scheme 1. Generation of 2 via 1, through migration ofa neopentyl group and ufrther
reaction with the putative ™[Mn(CH2tBu)2]∫.
implies that there is no metal metal bond.
Mn(1) is bound to one neopentyl ligand as well
as to an imino and an amido ligand, whereas
Mn(2) is bonded to the electron lone pair ofthe nitrogen atom
ofthis amido group, but retains the two neopentyl ligands.
Complex 2 is probably obtained via the expected 1a
(Scheme 1), which then undergoes migration ofthe neopentyl
ligand onto the imine group[5] to generate a mononeopentyl
MnII complex with one imine and one amido ligand, which
further reacts with the putative ™[Mn(CH2tBu)2]∫ to give 2.
from the Si face of the imine moiety, that is, the face with the
ꢀ
methine hydrogen atom rather than the C C framework of
the cyclohexane ring.
Reaction ofa more highly substituted bisbenzylidene ligand
(Ar¼ mesityl (Mes)) with ™[Mn(CH2tBu)2]∫ gave the desired
base adduct 1b in 36% yield ofisolated product. X-ray
analysis shows that the geometry ofthe complex is a distorted
tetrahedron with a wide C-Mn-C bond angle of146.4 8
(Figure 2).[4] The methyl substituents ofthe aromatic ring
probably shield the imino group (see Scheme 1 and Figure 2)
and thus prevent the migration ofthe neopentyl ligand to the
imino group.
Thus, two equivalents of™[Mn(CH tBu)2]∫ are required for
2
each equivalent ofligand. This suggested reaction pathway is,
however, difficult to substantiate, since starting material and
product(s) contain high-spin MnII. Moreover, 2 was isolated as
a single stereoisomer. The stereochemistry at the carbon
center corresponds to the attack ofthe neopentyl rfagment
To understand the scope ofthis chemistry further, we also
investigated the reaction ofthe Brookhart imino ligand with
Figure 1. Thermal-ellipsoid plot of 2. Selected bond lengths [ä] and
ꢀ
ꢀ
ꢀ
angles [8]: Mn(1) C(24) 2.121(5), Mn(1) C(26) 2.419(5), Mn(1) N(1)
Figure 2. Thermal-ellipsoid plot of 1b. Selected bond lengths [ä] and
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2.132(4), Mn(1) N(2) 2.242(4), Mn(2) C(26) 2.223(5), Mn(2) C(231)
angles [8]: Mn C(40) 2.141(6), Mn C(50) 2.165(6), Mn N(1) 2.344(4),
ꢀ
ꢀ
2.122(5), Mn(2) N(1) 2.129(4); N(1)-Mn(1)-N(2) 79.35(2), N(1)-Mn(1)-
Mn N(2) 2.279(4); C(40)-Mn-C(50) 146.4(2), C(40)-Mn-N(1) 102.1(2),
C(24) 142.63(2), N(2)-Mn(1)-C(24) 118.48(2), N(1)-Mn(2)-C(26)
104.05(2), N(1)-Mn(2)-C(231) 129.99(2), C(26)-Mn(2)-C(231) 123.8(2).
C(40)-Mn-N(2) 110.3(2), C(50)-Mn-N(1) 105.62(2), C(50)-Mn-N(2)
95.71(2), N(1)-Mn-N(2) 73.12(2).
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™[Mn(CH2tBu)2]∫. In this case the reaction yield is higher
(51% ofsingle crystals), but structural analysis again showed
major reorganization ofthe putative base adduct by carbon
carbon migration within the ligand (Figure 3).[4] The reaction
probably involves adduct formation followed by the events
outlined in Scheme 2. Migration ofone neopentyl ligand in 4
metal carbon bonds. Most interestingly, we have uncovered
¼
pathways in which the C N bonds undergo alkylation to
amido groups. These reactions might be important deactiva-
tion pathways in some olefin polymerization reactions. [6]
Received: April 12, 2002 [Z19085]
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V. C. Gibson, B. S. Kimberley, P. J. Maddox, S. J. Mctavish, G. A. Solan,
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f) G. J. P. Britovsek, M. Bruce, V. C. Gibson, B. S. Kimberley, P. J.
Maddox, S. Mastroianni, S. J. McTavish, C. Redshaw, G. A. Solan, S.
Strˆmberg, A. J. P. White, D. J. Williams, J. Am. Chem. Soc. 1999, 121,
8728; g) G. J. P. Brotovsek, S. Mastroianni, G. A. Solan, S. P. D. Baugh,
C. Redshaw, V. C. Gibson, A. J. P. White, D. J.
Figure 3. Thermal ellipsoid plot of 6. Selected bond lengths [ä] and
ꢀ
ꢀ
ꢀ
angles [8]: Mn C(13) 2.105(3), Mn N(1) 1.960(2), Mn N(2) 2.185(3);
C(13)-Mn-N(1) 150.86(12), C(13)-Mn-N(2) 129.68(11), N(1)-Mn-N(2)
79.11(10).
Willimas, M. R. J. Elsegood, Chem. Eur. J.
2000, 6, 2221; h) E. L. Dias, M. Brookhart,
P. S. White, Chem. Commun. 2001, 423;
i) V. C. Gibson, M. J. Humphries, K. P. Tell-
mann, D. F. Wass, A. J. P. White, D. J. Wil-
liams, Chem. Commun. 2001, 2252; j) T. M.
Kooistra, Q. Knijnenburg, J. M. M. Smits,
A. D. Horton, P. H. M. Budzelaar, A. W. Gal,
Angew. Chem. 2001, 113, 4855; Angew. Chem.
Int. Ed. 2001, 40, 4719.
[4] CCDC-183390, CCDC-183147, and CCDC-
182472 contain the supplementary crystallo-
graphic data for this paper (2, 1b, and 6,
respectively). These data can be obtained free
ofcharge via www.ccdc.cam.ac.uk/conts/re-
trieving.html (or from the Cambridge Crys-
tallographic Data Centre, 12, Union Road,
Scheme 2. Proposed mechanism for the migration reaction.
Cambridge CB21EZ, UK; fax: (þ 44)1223-
336-033; or deposit@ccdc.cam.ac.uk).
onto the imino group to give 5 is apparently followed by a 1,2-
migration to the vicinal imino group. This rearrangement
could also be a two-step process involving successive rever-
sible 1,3-migration ofthe Me group rfom the C atom to the
Mn atom and then to the other C atom to give an apparent
overall 1,2-migration. Complex 6 has an MnII center in a
trigonal environment with an imino, an amido, and a
neopentyl ligand, like in 2, but does not undergo further
reaction with ™[Mn(CH2tBu)2]∫, probably because the 2,6-
diisopropylphenyl substituent prevents access to the lone pair
ofthe amido ligand.
In conclusion, we have shown that diimine MnII dialkyl
complexes are accessible without reduction ofthe Mn center,
which demonstrates the importance to access perhydrocarbyl
metal complexes with the appropriate oxidation state. We
have also demonstrated the necessity to protect the imino
group with bulky substituents to avoid their reaction with
[5] a) J. M. Klerks, D. J. Stufkens, G. van Koten, K. Vrieze, J. Organometal.
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[6] No ethylene polymerization activities were found in either case using
MAO or B(C6F5)3 as co-catalysts.
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