Preparation of chiral ruthenium(iv) complexes and applications in regio- and enantioselective allylation of phenols

Article abstract of DOI:10.1039/c0dt01812k

Facile preparations of chiral [Ru(Cp*)]- and [Ru(Cp′)]-based allyl complexes featuring N,O chelate derived from (+)-nopinone are described. Single crystal X-ray structural analysis of one complex revealed the preferential configuration of the ruthenium centre and the orientation of the unsymmetrical allylic substituent. Applications of these complexes in catalysis for nucleophilic allylic substitution allowed regio- and enantioselective formation of branched allyl ethers from phenols. The Royal Society of Chemistry.

Full text of DOI:10.1039/c0dt01812k

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PAPER
Preparation of chiral ruthenium(IV) complexes and applications in regio- and
enantioselective allylation of phenols†
Zeyneb Sahli, Nolwenn Derrien, Simon Pascal, Bernard Demerseman, Thierry Roisnel, Fre´de´ric Barrie`re,
Mathieu Achard and Christian Bruneau*
Received 22nd December 2010, Accepted 1st April 2011
DOI: 10.1039/c0dt01812k
Facile preparations of chiral [Ru(Cp*)]- and [Ru(Cp¢)]-based allyl complexes featuring N,O chelate
derived from (+)-nopinone are described. Single crystal X-ray structural analysis of one complex
revealed the preferential configuration of the ruthenium centre and the orientation of the
unsymmetrical allylic substituent. Applications of these complexes in catalysis for nucleophilic allylic
substitution allowed regio- and enantioselective formation of branched allyl ethers from phenols.
reactions,10,11 and recently, Kitamura has shown the high efficiency
of chiral naphthyl pyridine carboxylic acids with atropochirality
acting as N,O chelates associated to [Ru(Cp)(CH3CN)3][PF6] for
the enantioselective dehydrative cyclisation of w-hydroxy allyl
Introduction
Allylation reactions catalyzed by transition-metal complexes have
attracted much interest as a powerful tool in organic synthesis
for C–C and C-heteroatom bond formation.1 Among them,
allylation of phenols and alcohols has retained lot of interest
due to their potential applications in syntheses for the access of
bioactive compounds and polymers.2 In the last decade, ruthenium
precatalysts have been used in these reactions with unsymmetrical
allylic substrates to promote regio- and enantioselective formation
of branched compounds containing a chiral centre.3 Since the
seminal work of asymmetric alkylation and amination catalyzed
by ruthenium complexes starting from symmetrical substrates by
Takahashi,4 we reported the first ruthenium-catalyzed enantiose-
lective etherification starting from unsymmetrical allylic chlorides
using a catalytic system based on [Ru(Cp*)(CH3CN)3][PF6] I along
with chiral bisoxazolines reaching 82% ee but with moderate
regioselectivities.5 In a similar manner, enantioselective Caroll
rearrangement6 or decarboxylative etherification from allyl aryl
carbonate7 in the presence of iminopyridines and pyridine-
oxazolines afforded good regioselectivities and ee up to 87%.
Cyclopentadienyl ruthenium centres coordinated by chiral di-
amines have also been investigated in allylation reaction. The best
regioselectivity (94%) and enantioselectivity (54%) were obtained
during the substitution of cinnamyl chloride by phenol.8 More
recently, planar-chiral cyclopentadienyl ruthenium catalysts have
led to a breakthrough allowing excellent regio- and enantiose-
lectivities in etherification and other allylation reactions starting
from allylic chlorides.9 Ruthenium complexes featuring N,O
and P,O chelate have demonstrated good activities in allylation
alcohols.12 However, such N,O chelates require preparative chiral
HPLC for ligand purification and to date no N,O chelates
derived from the chiral pool have been applied in ruthenium-
catalyzed enantioselective etherification. Moreover, no structure
of chiral complexes was reported to determine the preferential
configuration of the ruthenium centre. We report herein the
straighforward synthesis of chiral allyl ruthenium(IV) complexes
containing an optically pure N,O chelate along with various
substituted cyclopentadienyl ligands, and their applications in
enantioselective allylation starting from cinnamyl carbonate.
Results and discussion
The ester 2 was synthesized in 45% overall yield from (+)-nopinone
using a reported methodology13 involving Michael addition,
imine formation and ring closure followed by triflation and
methoxycarbonylation. Its hydrolysis in the presence of lithium
hydroxide afforded the expected pyridine carboxylic acid 3 in 95%
yield (Scheme 1).
Scheme 1 Ligand preparation.
With this ligand in hand, we undertook the preparation of allyl
ruthenium(IV) complexes. Thus, reaction of the ligand 3 in the
presence of complex I followed by the addition of allyl alcohol
resulted in substitution of the labile acetonitrile ligands and to
the generation of water to yield the expected allyl ruthenium(IV)
complex II as a diastereoisomeric mixture in a 75/25 ratio and
almost quantitative yield (Scheme 2).11a
UMR6226 CNRS – Universite´ de Rennes, Sciences chimiques de Rennes,
Catalyse et Organome´talliques, Campus de Beaulieu, 35042, Rennes Cedex,
France. E-mail: christian.bruneau@univ-rennes1.fr; Fax: +33 223236939;
Tel: +33 223236283
† CCDC reference number 793151. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt01812k
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◦
˚
Table 1 Selected bond lengths (A), angles ( ), atom distances and sum-
mary of crystallographic parameters and refinement results for complex
VIa
Formula
C54H72F12N2 O4- Ru(1)–C(11)
P2Ru2
2.199(4)
F.W.
1305.22
Monoclinic
C2y
35.2478(14)
8.9626(4)
24.9400(10)
90
134.2050(10)
90
5647.9(4)
4
Ru(1)–C(12)
Ru(1)–C(13)
Ru(1)–N(18)
Ru(1)–O(15)
C(16)–O(17)
C(27)–N(18)
C(13)–C(14)
O(15)–C(16)
C(16)–C(19)
N(18)–C(19)
C(26)–C(6)
C(25)–C(6)
N(18)–Ru(1)–O(15) 77.87(13)
C(16)–O(15)–Ru(1) 118.6(3)
O(17)–C(16)–O(15) 124.1(4)
C(11)–Ru(1)–N(18) 87.38(16)
C(11)–Ru(1)–C(12) 37.81(18)
C(12)–Ru(1)–C(13) 36.14(18)
N(18)–C(27)–C(26) 122.3(4)
C(26)–C(25)–C(24) 85.7(4)
C(26)–C(28)–C(24) 84.8(3)
C(30)–C(28)–C(29) 110.2(5)
C(27)–C(26)–C(25) 107.4(3)
C(23)–C(24)–C(25) 107.8(4)
2.173(4)
2.302(4)
2.165(3)
2.068(3)
1.239(6)
1.361(6)
1.507(8)
1.280(6)
1.495(6)
1.379(6)
3.273
Cryst. Syst.
Space group
˚
a/A
˚
b/A
˚
c/A
Scheme 2 Complexes synthesis.
a/◦
b/◦
g /◦
The 1H NMR data of the fully characterized air stable complex
II gives two singlets at 0.8 ppm and 0.7 ppm that allow facile de-
termination of the major and minor diastereoisomer, respectively.
1H NMR analyses show evidence of a constant stereoisomeric
mixture but importantly, as indicated by disappearance of the
minor singlet, recrystallization of II by layering dichloromethane
and hexane in the presence of a small amount of methanol
allowed the formation of pure crystals of the major isomer in
51% yield and a major/minor ratio superior to 99/1. In a similar
manner, reactions of [Ru(Cp¢)(CH3CN)3][PF6] where Cp¢ contains
isopropyl, neopentyl or tertiobutyl groups led to the formation
of the expected complexes III, IV and V, respectively, also as a
stereoisomeric mixture (Scheme 2).14 Unfortunately, attempts to
isolate the major isomer of these complexes were unsuccessful.
Comparing the influence of the substituent on the cyclopentadi-
3
˚
V/A
Z
d
calc/g cm-3
1.535
0.677
2672
3.433
m/mm-1
F(000)
no. of reflns collected 42236
no. of unique reflns
Rint
Parameters
T/K
GOF
12429
0.0427
692
100(2)
1.04
0.0455
0.1091
1.209
-0.755
R1 (all data)
wR2 (all data)b
-3
˚
Drmax/e A
Drmin/e A
-3
˚
a
2
Mo-Ka radiation (l = 0.71073 A). b w = 1/[s (Fo)2) + (0.0503P)2
+
˚
20.9699P] where P = (Fo + 2Fc2)/3.
2
1
enyl ligand, H NMR of complexes II–V revealed that the steric
hindrance of the substituent led to decrease of the diastereoisomers
ratio. Thus, the lowest ratio was obtained with complex V featuring
the highly sterically demanding tBu moiety. Interestingly, with the
use of the unsymmetrical crotyl alcohol, the reaction of complex I
afforded the enantiopure complex VI as sole stereoisomer after
recrystallization, which was confirmed by 1H NMR with the
disappearance of the singlet at 0.7 ppm corresponding to the minor
stereoisomer (Scheme 3). The structure of VI was unequivocally
elucidated by single crystal X-ray diffraction study (Fig. 1 and
Table 1). Complex VI presents a square- pyramidal structure,
with the nitrogen and oxygen atoms from the ligand 3 and the
3
terminal carbons of the h -allyl ligand at the basal positions.15 As
expected, the ligand is acting as a N,O chelate with the formation of
the five membered metallacycle. The chelate angle N(18)–Ru(1)–
O(15) is 77.87◦ and is consistent with similar previously described
complexes.10a,11a As already reported for allyl ruthenium complexes
featuring hindered Cp* ligand, the orientation of the allyl ligand
is endo relative to the Cp*.10a,15,16,17 More interestingly, only the
complex containing the carboxylate moiety in cis relationship
toward the methyl substituent of the allyl moiety is observed.10a,11a,c
Comparing ruthenium-carbon bonds, the unsubstituted terminal
allylic carbon atom is closer to the ruthenium centre than the
Fig. 1 Structure of enantiomerically pure complex VI. Thermal ellipsoids
are drawn at the 50% probability level. Hydrogen atoms, PF6 counter anion
are omitted for clarity.
stabilization of the major complex VI of 1.1 kcal mol-1 (Fig. 2). In
addition, theoretical investigation of the carboxylic/crotyl alcohol
intermediates shows optimized isoelectronic structures displaying
a hydrogen bond between the proton of the coordinated carboxylic
˚
substituted one with bonds of 2.199(4) and 2.302(4) A, respectively.
Gas phase DFT geometry optimization of the cation in VI and
of its diastereoisomer (Gaussian03 B3LYP/LanLD2Z) yields a
2
acid and the oxygen atom of the h -coordinated crotyl alcohol
(Fig. 3).18 Calculations on the earlier carboxylic/acetonitrile
intermediates yield a stabilization of 1.5 kcal mol-1 of the “pro-VI”
diastereoisomer. Taken together, these calculations indicate that
the synthesis yielding the major diastereoisomer of VI is probably
driven early in the synthetic sequence, and that the hydrogen-
bonded complex is a valid intermediate before dehydration.18
Scheme 3 Ruthenium complex VI from crotyl alcohol.
5626 | Dalton Trans., 2011, 40, 5625–5630
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Table 2 Regio- and enantioselective allylation of phenola
entry
solvent
catalyst
B/L
conv.
e.e.
1b
2b
3b
4b
5d
6d
7d
8d
9b
CH2Cl2
DCE
Acetone
THF
THF
THF
THF
THF
THF
II
98/2
87/13
99/1
98/2
98/2
97/3
96/4
97/3
97/3
99
99
99
29 (S)
8 (S)
II
II
71 (S)
76 (S)
75 (S)
68 (S)
67 (S)
63 (S)
76 (S)
Fig. 2 Optimized diastereoisomer complexes VI.
II
83(79)c
85
II
III
IV
V
64
70
75
VI
89(85)c
a Experimental conditions: all reactions were performed under an inert
atmosphere of argon and carried out at 0.12 M concentration with
4/5/base/precatalyst in 1/1.2/1.2/0.025 molar ratio at room temperature.
b entry 1–4: II dr = 99/1, entry 9 : VI dr = 99/1. c Isolated yield. d reaction
performed with precatalysts as a stereoisomeric mixture indicated in
Scheme 2.
Fig. 3 Depiction of computed transient intermediates for complex VI.
Complexes II–VI were evaluated for their activities in regio-
and enantioselective allylation, using cinnamyl carbonate as linear
substrate in the presence of phenol acting as nucleophile and
potassium carbonate as mineral base (Table 2). Complexes II–
VI were efficient in acetone or halogenated solvent such as
dichloromethane or 1,2-dichloroethane, and gave conversions
located in the range 64–89% in THF (entries 5–9). Notably, for all
the solvents and complexes evaluated, excellent regioselectivities
toward the branched compound 7 were obtained when potassium
carbonate was used as base. In contrast, lower regioselectivities
were obtained with the use of caesium carbonate using THF as
solvent (not presented in the Table). However, although conver-
sions and regioselectivities were satisfactory, enantioselectivities
were found to be strongly solvent dependent. Thus, when the
reactions were carried out in low polar halogenated solvent such
as CH2Cl2 or DCE, branched product 7 was formed with low
levels of enantioselectivity of 29 and 8%, respectively (entries 1
and 2). On the contrary, reactions in THF or acetone afforded
promising enantioselectivities (entries 3–9). It is important to
note that the best enantioselectivity was obtained with the less
hindered pentamethylcyclopentadienyl ligand (entry 4, 5 and 9).
Complexes II and VI differ only from the nature of the allylic
ligand, which is removed during the first catalytic cycle and as
a result, the same ee value of 76% was reached when complex
II and VI were used as precatalyst (entries 4 and 9). Concerning
the stereoisomeric purity of the precatalysts, entries 4 and 5 with
complex II emphasized that the presence of the other stereoisomer
is not prejudicial for the enantioselectivity and almost identical
conversion, ratio and ee were obtained. This result might be
explained by the formation of a transient intermediate during
the catalytic cycle demonstrating a possible equilibrium between
the two ruthenium(II) species leading after reaction with the
allylic derivatives to the formation of both allylruthenium(IV)
stereoisomer intermediates (Fig. 4).18 We cannot also exclude an
inner sphere mechanism during allylation reaction leading to the
formation of unchelated species by exchange of the carboxylate
Fig. 4 Proposed equilibrium of the two ruthenium(II) intermediates.
moiety and the nucleophile.9a,c The absolute configuration of
the major enantiomer of ether 7 determined by optical rotation
measurement was S(+),19 which tends to demonstrate that an
inner sphere mechanism seems unprobable and thus supports
the possible equilibrium of Fig. 4 prior to allylic activation and
nucleophilic attack.
With regard to the use of other phenol derivatives such as o-
cresol 8, reaction in the presence of pure precatalyst II proceeded
smoothly allowing the exclusive formation of the branched
allyl ether 10 in 85% isolated yield and 72% enantioselectivity
(Scheme 4).
Scheme 4 Allylation with o-cresol.
The nature of the leaving group of the allylic derivative was
then investigated. Thus, when the reaction was carried out in the
presence of cinnamyl chloride 11 and phenol 5, branched product
7 was also formed preferentially but with poor enantioselectivity
of 17% (Scheme 5). This result highlights the complementarity of
the complexes featuring a chiral N,O chelate, which give better
enantioselectivity from carbonate derivatives, with the reported
chiral planar cyclopentadienyl ruthenium complexes9 or ruthe-
nium complexes featuring bis-oxazoline ligand,5 which afforded
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wR(F2) = 0.1076 (R(F) = 0.0427) for 11682 observed reflections
with I > 2s(I). For parameters see Table 1.
Synthesis of compound 3
A solution of ester 2 (389 mg, 1.68 mmol, 1 eq.) in THF–MeOH
(5 : 1, 6 mL) was slowly added at 0 ◦C to a solution of lithium
hydroxide (201.1 mg, 8.40 mmol, 5 eq.) in water (2 mL). After
stirring the resulting mixture for one hour at 0 ◦C, the solution was
allowed to warm at room temperature and stirred for four hours.
After complete conversion (TLC), the mixture was acidified to
pH = 2 with 1 N HCl. After evaporation of THF, the remaining
solution was extracted three times with dichloromethane. The
combined organic layers were dried over sodium sulfate and
concentrated to afford ligand 3 as a white powder in 92% yield
Scheme 5 Allylation with cinnamyl chloride.
better results with allylic chlorides and poor enantioselectivities
with carbonates.
Conclusions
Chiral allyl ruthenium(IV) complexes featuring a N,O chelate
derived from (+)-nopinone were easily prepared. As expected from
our previous results with ruthenium catalysts featuring an achiral
N,O ligand derived from quinaldic acid,11a the nucleophilic allylic
substitution of cinnamyl carbonate by phenol, was highly regios-
elective in favour of branched chiral aryl allyl ethers. In addition,
with the new ligand 3, both high regioselectivity and satisfactory
enantioselectivity were obtained. Studies in enantioselective ally-
lation reactions demonstrate the influence of the substituent on
the cyclopentadienyl group for the enantioselectivity. The results
also highlight the crucial importance of the leaving group of the
allylic substrate for synthetic applications.
1
(336 mg). H NMR (200 MHz, CDCl3) d 8.02 (d, J = 7.3 Hz,
1H), 7.66 (d, J = 7.5 Hz, 1H), 6.00 (brs, 1H), 3.06–3.02 (m, 3H),
2.84–2.74 (m, 1H), 2.46–2.38 (m, 1H), 1.46 (s, 3H), 1.29 (d, J =
10.1 Hz, 1H), 0.66 (s, 3H); 13C NMR (50 MHz, CDCl3) d 166.6,
165.3, 142.3, 137.5, 136.6, 122.2, 50.2, 40.2, 39.6, 31.9, 30.9, 26.3,
21.7; [a]2D0 = -24.6 (c 0.5, CH2Cl2).
General procedure for the preparation of complexes II–VI
A resulting violet solution containing [Ru(Cp*)(CH3CN)3][PF6]
or [Ru(Cp¢)(CH3CN)3][PF6] (0.4 mmol) and ligand 3 (0.4 mmol)
in dichloromethane (6 mL) was stirred for thirty minutes at room
temperature. Allyl alcohol or crotyl alcohol (0.8 mmol) was then
added and the solution turned immediately to yellow. After stirring
overnight, the mixture was concentrated leaving a yellow solid,
which was washed several times with degassed diethyl ether. The
remaining powder was dried to afford complex as a stereoisomeric
mixture. Further crystallization was possible with complexes II
and VI by layering dichloromethane and hexane allowing the
isolation of the major complex.
Experimental section
Unless otherwise stated, all manipulations were performed under
inert atmosphere (argon) following conventional Schlenk tech-
niques. Solvents were purified according to standard procedures.
[Ru(Cp*)(CH3CN)3][PF6] was prepared according to the literature
method.11a [Ru(Cp¢)(CH3CN)3][PF6] complexes were prepared
following reported protocols.14 Chiral ester 2 was synthesized
according Kocˇovsky´ methodology.13 All other reagents were ob-
tained from the usual commercial suppliers, and used as received.
NMR spectra were recorded in Bruker GPX (200 MHz) in CDCl3
or CD2Cl2, at room temperature unless otherwise stated. NMR
[Ru(C5Me5)(N–O)(g3-CH2CHCH2)][PF6] complex II
1
Prepared from ligand
3 (100 mg, 0.46 mmol, 1 eq.),
spectra are referred to the internal residual solvent peak for H
and 13C{1H} NMR.
[Ru(Cp*)(CH3CN)3][PF6] (232 mg, 0.46 mmol, 1 eq.) and allyl
alcohol (78 mL, 2 eq.) to yield after recrystallization 66% (195 mg)
of a yellow complex in a ratio superior to 99 : 1. 1H NMR
(200 MHz, CD2Cl2) : 7.96 (d, J = 7.8 Hz, 1H ( CH)), 7.93 (d,
J = 7.8 Hz, 1H ( CH)), 4.76 (m, 1H (allylic CH)), 4.18 (dd,
J = 2.3, 5.9 Hz, 1H (syn allylic CH)), 3,65 (dd, J = 2.3, 5.9 Hz,
1H (syn allylic CH)), 3.36 (d, J = 10.3 Hz, 1H (anti allylic CH)),
3.16 (m, 2H), 3.06–2.93 (m, 1H), 2.69 (d, J = 10.5 Hz, 1H (anti
allylic CH)), 2.59–2.47 (m, 2H), 1.72 (s, 1H), 1.67 (s, 15H (Cp*)),
1.55 (s, 3H (Me)), 1.29 (d, J = 10 Hz, 1H), 0.82 (s, 3H (Me));
13C NMR (50 MHz, CD2Cl2) : 171.9 (CO2), 169.2 (N C–CO2),
146.6 (N C), 141.4 (CH C), 140.1 (C C), 127.5 (CH C),
108.6 (C5Me5), 100.8 (CH allyl), 78.3 (CH2 allyl), 64.6 (CH2 allyl),
54.3 (CH), 39.5 (CMe2), 39.5 (CH), 32.6 (CH2), 32.2 (CH2), 25.3
(Me), 21.3 (Me), 9.7 (C5Me5); anal. calcd for C26H34F6NO2PRu :
C 48.90, H 5.37 found: C 48.79, H 5.41; HRMS calculated for
C24H34NO2Ru+: [M]+ 494.16330, found [M]+ 494.1634; [a]2D0 = +120
(c 0.492, CH2Cl2).
X-ray diffraction studies
Suitable crystals were collected on a APEXII, Bruker-AXS
diffractometer equipped with a CCD detector, using graphite-
monochromated Mo-Ka radiation (l = 0.71073 A) at T =
˚
100(2) K. The structure was solved by direct methods using
the SIR97 program,20 and then refined with full-matrix least-
square methods based on F2 (SHELX-97) with the aid of the
WINGX21 program. The contribution of the disordered solvents
to the calculated structure factors was estimated following the
BYPASS algorithm,22 implemented as the SQUEEZE option in
PLATON23 A new data set, free of solvent contribution, was then
used in the final refinement. All non-hydrogen atoms were refined
with anisotropic atomic displacement parameters. H atoms were
finally included in their calculated positions. A final refinement on
F2 with 12429 unique intensities and 692 parameters converged at
5628 | Dalton Trans., 2011, 40, 5625–5630
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[Ru(C5Me5)(N–O)(g3-CH2CHCHMe)][PF6] complex VI
Prepared from ligand (90 mg, 0.41 mmol,
(N C), 141.4 (CH C), 140.1 (C C), 127.6 (CH C), 113.1
(Cp¢), 111.6 (Cp¢), 110.5 (Cp¢), 106.7 (Cp¢), 104.8 (Cp¢), 101.2 (CH
allyl), 79.5 (CH2 allyl), 65.6 (CH2 allyl), 52.5 (CH), 39.4 (CMe2),
.39.4 (CH), 37.8 (CH2CMe3), 35.7 (CMe3), 32.6 (CH2), 32.3 (CH2),
30.6 (CMe3), 25.3 (CMe2), 21.2 (CMe2), 11.7 (Me), 11.4 (Me),
10.3 (Me), 10.05 (Me); HRMS calculated for C30H42NO2Ru+: [M]+
550.22590, found [M]+ 550.2258.
3
1 eq.),
[Ru(Cp*)(CH3CN)3][PF6] (208 mg, 0.41 mmol, 1 eq.) and croty-
lalcohol (70 mL) to yield after recrystallization 55% (148 mg) of a
brown complex in a ratio superior to 99 : 1. 1H NMR (200 MHz,
CD2Cl2) : 7.96 (d, J = 7.6 Hz, 1H ( CH)), 7.87 (d, J = 7.6 Hz,
1H ( CH)), 4.46 (dt, J = 10.3, 6.2 Hz, 1H (allylic CH)), 4.12 (dq,
J = 10.3, 6.2 Hz, 1H (allylic CHMe)), 3.58 (dd, J = 0.6, 6.2 Hz, 1H
(syn allylic CH)), 3.16 (m, 2H), 2.96 (td, J = 5.9, 11.6 Hz, 1H), 2.61
(t, J = 5.4 Hz, 1H), 2.54–2.45 (m, 2H), 1.63 (s, 15H (Cp*)), 1.56 (s,
3H (Me)), 1.37 (d, J = 6.2 Hz, 3H (Me)), 1.27 (d, J = 10 Hz, 1H),
0.81 (s, 3H); 13C NMR (50 MHz, CD2Cl2) : 171.8 (CO2), 168.1
(N–C–CO2), 146.4 (N C), 141.4 (CH C), 139.9 (C C), 126.3
(CH C), 107.5 (C5Me5), 101.3 (CH allyl), 85.0 (CH-Me allyl),
62.3 (CH2 allyl), 54.5 (CH), 40.1 (CMe2), 40.0 (CH), 32.5 (CH2),
32.4 (CH2), 25.3 (Me), 21.1 (Me), 17.3 (Me), 9.5 (C5Me5); anal.
calcd for C27H36F6NO2PRu : C 49.69, H 5.56 found: C 49.59, H
5.59; [a]2D0 = +145 (c 0.5, CH2Cl2).
[Ru(C5Me4t-Bu)(N–O)(g3-CH2CHCH2)][PF6] complex V
Prepared from ligand 3 (30 mg, 0.14 mmol, 1 eq.), [Ru(C5Me4t-
Bu)(CH3CN)3][PF6] (75 mg, 0.14 mmol, 1 eq.) and allyl alcohol
(30 mL) to yield after treatment 89% (83 mg) of a brown complex
as a stereoisomeric mixture in a 60/40 ratio. Only major isomer
is described : 1H NMR (200 MHz, CD2Cl2) : 8.01 (d, J = 7.8 Hz,
1H ( CH)), 7.94(d, J = 7.7 Hz, 1H ( CH)), 4.73–4.56 (m, 1H
(allylic CH)), 4.42 (d, J = 5.6 Hz, 1H (syn allylic CH)), 3.66 (d,
J = 5.4. Hz, 1H (syn allylic CH)), 3.52 (d, J = 10 Hz, (anti allylic
CH)), 3.18 (brs, 2H), 3.07–2.94 (m, 1H), 2.70 (d, J = 10.5 Hz, 1H
(anti allylic CH)), 2.52–2.46 (m, 2H), 1.87 (s, 3H (Me)), 1.85 (s, 3H
(Me)), 1.72 (s, 3H (Me)), 1.64 (s, 3H, (Me)), 1.55 (s, 3H (Me)), 1.33
(brs, 9H (CMe3)), 0.81(s, 3H (Me)); 13C NMR (75 MHz, CD2Cl2) :
172.1 (CO2), 169.2 (N C–CO2), 146.6 (N C), 141.4 (CH C),
140.2 (C C), 127,4 (CH C), 119,8 (Cp¢), 117,7 (Cp¢), 110.6
(Cp¢), 104.8 (Cp¢), 101.7 (Cp¢), 100.7 (CH allyl), 79.4 (CH2 allyl),
65.3 (CH2 allyl), 53.4 (CH), 39.5 (CMe2), 39.4 (CH), 36.4 (CMe3),
32.6 (CH2), 32.4 (CH2), 30.5 (CMe3), 25.3 (CMe2), 21.2 (CMe2),
13.8 (Me), 13.1 (Me), 11.1 (Me), 10.3 (Me); HRMS calculated for
C29H40NO2Ru+: [M]+ 536.21025, found [M]+ 536.2110.
[Ru(C5Me4i-Pr)(N–O)(g3-CH2CHCH2)][PF6] complex III
Prepared from ligand 3 (30 mg, 0.14 mmol, 1 eq.), [Ru(C5Me4i-
Pr)(CH3CN)3][PF6] (73 mg, 0.14 mmol, 1 eq.) and allyl alcohol
(18 mL) to yield after treatment 90% (82 mg) of a brown complex
as a stereoisomeric mixture in a 72/29 ratio. Only the major isomer
is described: 1H NMR (200 MHz, CD2Cl2) : 8.00 (d, J = 7.5 Hz,
1H ( CH)), 7.9 (d, J = 7.5 Hz, 1H ( CH)), 4.62–4.79 (m, 1H
(allylic CH)), 4.27 (dd, J = 2.1, 5.14 Hz, 1H (syn allylic CH)), 3.65
(dd, J = 2.0, 5.4 Hz, 1H (syn allylic CH)), 3.39 (d, J = 10.6 Hz,
1H (anti allylic CH)), 3.17 (m, 2H), 3.02–2.94 (m, 1H), 2.75 (d,
J = 10.7 Hz, 1H (anti allylic CH)), 2.66–2.49 (m, 3H), 1.77 (s, 3H),
1.69 (s, 6H), 1.65 (s, 3H), 1.56 (s, 3H), 1.29 (d, J = 9.8 Hz, 1H),
1.16 (d, J = 7 Hz, 6H, C(CH3)2), 0.82 (s, 3H); 13C NMR (75 MHz,
CD2Cl2) d (ppm): 171.7 (CO2), 169.4 (N C–CO2), 146.6 (N C),
141.4 (CH C), 139.9 (C C), 127.5 (CH C), 118.0 (Cp¢), 112.8
(Cp¢), 109.0 (Cp¢), 106.2 (Cp¢), 104.1 (Cp¢), 100.9 (CH allyl), 78.2
(CH2 allyl), 64.5 (CH2 allyl), 52.4 (CH), 39.5 (CMe2), 39.5 (CH),
32.5 (CH2), 32.0 (CH2), 26.9 (CHMe2), 25.3 (Me), 20.9 (Me), 20.2
(CHMe2) 15.4 (CHMe2), 11.2 (Me),10.0 (Me), 9.9 (Me), 9.8 (Me).
anal. calcd for C28H38F6NO2PRu : C 50.45, H 5.75 found: C 50.36,
H 5.81; HRMS calculated for C28H38NO2Ru+: [M]+ 522.19405,
found [M]+ 522.1948.
General procedure for the allylation of phenols
In a Schlenk tube containing cinnamyl carbonate (50 mg,
0.24 mmol, 1 eq.), phenol (27 mg, 0.29 mmol, 1.2 eq.) in THF
(2 mL), potassium carbonate (40 mg, 0.29 mmol, 1.2 eq.) and
precatalyst (2.5 mol%) were sequentially added. After stirring the
solution at room temperature for 16 h, the solution was filtered
through a silica plug using diethyl ether as eluent. Conversions
and B/L ratio were determined by 1H NMR. Enantioselectivities
were determined by HPLC using chiralcel-OJ, H/I 99.5/0.5,
0.8 mL min-1, l = 220, 250 nm; t1(maj) = 29.1 min. and t2(min) =
32 min.
Acknowledgements
[Ru(C5Me4CH2CMe3)(N–O)(g3-CH2CHCH2)][PF6] complex IV
The authors wish to thank Dr C. Guillaume and Dr S. Guillaume
for the methoxycarbonylation reaction. Z. S. thanks the Ministry
of Higher Education and Research of Algeria for PNE fellowship.
Prepared from ligand
3 (30 mg, 0.14 mmol, 1 eq.),
[Ru(C5Me4CH2CMe3)(CH3CN)3][PF6] (78.5 mg, 0.14 mmol, 1 eq.)
and allyl alcohol (28 mL) to yield after treatment 88% (86 mg) of a
brown complex as a stereoisomeric mixture in a 66/34 ratio. Only
1
Notes and references
the major isomer is described: H NMR (200 MHz, CD2Cl2) :
7.99 (d, J = 7.6 Hz, 1H ( CH)), 7.92 (d, J = 7.6 Hz, 1H ( CH)),
4.62–4.81 (m, 1H (allylic CH)), 4.24 (dd, J = 2.2, 5.5 Hz, 1H (syn
allylic CH)), 3.70 (d, J = 5.4 Hz, 1H (syn allylic CH)), 3.45 (d,
J = 10.5 Hz, 1H (anti allylic CH)), 3.17 (brs, 2H), 2.94–3.08 (m,
1H), 2.73 (d, J = 11.0 Hz, 1H (anti allylic CH)), 2.50–2.60 (m,
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NMR (75 MHz, CD2Cl2): 171.8 (CO2), 169.2 (N C–CO2), 146.5
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5630 | Dalton Trans., 2011, 40, 5625–5630
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