Diastereoselectivity of the formation of planar chiral ruthenocenol in reactions of chiral tertiary phosphines with the (η4-cyclopentadienone)(η5-cyclopentadienyl)rutheni um cation

Article abstract of DOI:10.1023/A:1015030208262

The reactions of chiral benzyl- and ethyl(phenyl)ferrocenylphosphines with (acetonitrile)(η⁴-cyclopentadienone)(η⁵-cyclopenta dienyl)ruthenium trifluoromethylsulfonate proceed diastereoselectively through the attack on the cyclopenta

Full text of DOI:10.1023/A:1015030208262

2212
Russian Chemical Bulletin, International Edition, Vol. 50, No. 11, pp. 2212—2214, November, 2001
Diastereoselectivity of the formation of planar chiral
ruthenocenol in reactions of chiral tertiary phosphines with
the (η4-cyclopentadienone)(η5-cyclopentadienyl)ruthenium cation
L. L. Troitskaya,« S. T. Ovseenko, A. I. Krylova, and V. I. Sokolov
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5085. E mail: stemos@ineos.ac.ru
The reactions of chiral benzyl- and ethyl(phenyl)ferrocenylphosphines with (aceto-
nitrile)(η4-cyclopentadienone)(η5-cyclopentadienyl)ruthenium trifluoromethylsulfonate pro-
ceed diastereoselectively through the attack on the cyclopentadienone ring to form planar
chiral 2-phosphonioruthenocenols as mixtures of two diastereomers in ratios of 1.7 : 1 and
2 : 1, respectively.
Key words: (cyclopentadienone)(cyclopentadienyl)ruthenium cation, chiral phosphines,
benzyl(phenyl)ferrocenylphosphine, phosphonioruthenocenols, diastereoselectivity.
Organometallic analogs of phenols, viz., hydroxy-
cenol are generated in the reactions of 1 with low-
basicity aromatic amines. Although these reactions give
rise to planar chirality, the stereochemical aspect of the
reactions remained unknown. However, the use of chiral
phosphines in these reactions enables one to determine
the diastereoselectivity and offers a route to new opti-
cally active ruthenocene derivatives, which are currently
few in number.6
In the present study, we examined the reactions of
(acetonitrile)(η4-cyclopentadienone)(η5-cyclopenta-
dienyl)ruthenium salts (1) (X = CF3SO3 or PF6) with
P-chiral tertiary phosphines 2 or 3 yielding mixtures of
diastereomeric salts of benzyl- (4) or ethyl(ferro-
cenyl)(2-hydroxyruthenocenyl)phenylphosphonium (5),
respectively. Phosphines 2 and 3 are of particular inter-
est because products 4 and 5 contain simultaneously two
groups, which can be oxidized, viz., ferrocenyl and
ruthenocenyl, and in the limiting case they can revers-
ibly donate three additional electrons.
metallocenes, remain poorly studied because of their
instability, although the first representative, viz.,
ferrocenol, was prepared as early as 1959.1 Hydroxy-
metallocenes attracted our attention in view of the fact
that cyclopalladation of mixed phosphite esters of phenols
(hydroxyarenes) discovered by us2 was extended to
ferrocenol.* Hence, we are interested in hydroxy-
ruthenocene and its substituted chiral derivatives, which
are readily accessible due to the special features of the
chemistry of ruthenocene. Thus, Kirchner3—5 has devel-
oped an ingenious approach to these compounds involv-
ing the reactions of nucleophiles with the cations of the
–
salts [Ru(L)(Cp)(C5H4O)]+X (1), where L is a nitro-
gen-containing ligand, for example, acetonitrile, pyri-
dine, or thiourea. In these cations, either of the two
rings as well as the metal atom can be subjected to the
nucleophilic attack, the direction of the attack being
determined by the nature and properties of the nucleo-
phile and the ligand coordinated to the metal atom. The
evidence for the possibility of the addition of the cya-
nide and thiolate anions has been reported.4 The addi-
tion of tertiary phosphines has been studied in de-
tail.3,5 The latter reactions afford either 1,2-homo- or
1,1´-heteroannular phosphonioruthenocenols depending
on the basicity and steric characteristics of phosphines
and the capability of the ligand bound to the ruthenium
atom to be involved in complex formation. Based on the
intermediates detected in a number of reactions, several
reaction mechanisms were proposed. The reactions of
more basic dialkylaryl- or trialkylphosphines with cat-
ions 1 yield heteroannular 1,1´-phosphoniorutheno-
cenols, whereas homoannular 1,2-derivatives of rutheno-
The course of the reactions in acetone was moni-
1
tored by H NMR spectroscopy. After 2.5 h, approxi-
mately 50% of the initial cation 1 remained unconsumed,
whereas phosphines 2 and 3, which were taken in
amounts from one equivalent to a 50% excess,* disap-
peared, and the NMR spectra show three groups of new
signals both in the metallocenyl and aromatic regions.
Two groups of signals, which are similar in shape and
differ only in the intensities, were assigned (taking into
account that each group has a pair of singlets of the
* The preliminary study demonstrated that compound 1 can be
completely consumed in the reaction; however, it is necessary
to use a substantial excess of phosphines, which are not easily
accessible and which are difficult to recuperate because they
are readily oxidized in solutions.
* The results will be published in J. Organomet. Chem.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2112—2114, November, 2001.
1066-5285/01/5011-2212 $25.00 © 2001 Plenum Publishing Corporation

Chiral phosphonium salts in the metallocene series Russ.Chem.Bull., Int.Ed., Vol. 50, No. 11, November, 2001 2213
unsubstituted cyclopentadienyl rings both of the rutheno-
cenyl and ferrocenyl fragments) to homoannular com-
pounds 4 and 5 with the diastereomeric ratios of 1.7 : 1
and 2 : 1, respectively. This is in agreement with the
31P NMR spectra, which have signals at δ 25.4 and 27.6
for 4 and at δ 28.97 and 30.38 for 5 in virtually the same
ratios.
MeCN ligand at the ruthenium atom followed by the
attack of the second phosphine molecule on the
cyclopentadienone ring to form the expected phosphonio-
ruthenocenols due to dissociation of the intermediate
complex. In our opinion, steric interactions of the sec-
ond phosphine molecule with the phosphine molecule
coordinated to the ruthenium atom may account for the
observed diastereoselectivity of the reaction.
The formation of phosphonium adducts 4 and 5 from
cation 1 and neutral fragments 2 and 3 is accompanied
by the distribution of the positive charge over two
metallocenyl systems, which is in accordance with the
downfield shifts of the signals for the protons of the
ferrocenyl group and the upfield shifts of the signals for
the protons of the ruthenocenyl fragment observed in
the 1H NMR spectra. At low field behind the aromatic
region, broadened singlets were found at δ 8.60 and 8.97
with the intensity ratio of 1.7 : 1 for 4 and at δ 8.68 and
8.91 with the intensity ratio of 1.94 : 1 for 5. These
signals were assigned to the hydroxyl protons of the
diastereomers of 4 and 5 and their broadening indicates
that these protons are involved in slow exchange pro-
cesses. The only difference in the behavior of 2 and 3 in
the reaction under study is that the reaction of 3 gave
rise to a small amount (about 10%) of heteroannular
ethyl(ferrocenyl)(1´-hydroxyruthenocenyl)(phenyl)phos-
phonium trifluoromethanesulfonate (6). This result dem-
onstrates that the replacement of the benzyl group by
the ethyl group leads to an increase in the nucleophilic-
ity of phosphine due to which it can attack the
nonsubstituted cyclopentadienyl ring. The use of the
pyridine complex of type 1 instead of the acetonitrile
complex in the reaction with phosphine 2 resulted in a
substantial decrease in its rate (after one day, the con-
version was at most 25%) and the complete loss of
diastereoselectivity. Hence, alkyldiarylphosphines 2 and
3 behave analogously to triarylphosphine rather than to
dialkylphenylphosphines as one might expect taking into
account the presence of the ferrocenyl group in 2 and 3.
The third product did not contain ruthenocene and was
presumably the protonated form of the starting phos-
phine existing in equilibrium with the neutral form.
Protonation may occur due to the labile proton of the
hydroxy group in compounds 4 and 5 and hence, the
betaine structure of their diastereomers is not inconceiv-
able. Salt 4 was synthesized in a preparative amount and
was isolated as a mixture of diastereomers in a ratio of
approximately 1.2 : 1. The specimen was characterized
Scheme 1
Fc
Ph
R
RFcPhP (2, 3)
RFcPhP
Ru+
P
Ru+ NCMe
O
–RFcPhP
O
–
–
X
X
1
Fc
Ph
Bn
– RFcPhP
Ru
P
Ru
–
O
OH
–
P+
P+
X
Fc
(Ph)
Fc
(Ph)
R
R
Ph
(Fc)
Ph
(Fc)
4, 5
–
–
2, 4: R = Bn; 3, 5: R = Et, X = PF6 , CF3SO3
Experimental
All reactions were carried out under an atmosphere of
argon. Anhydrous solvents were prepared according to stan-
dard procedures. Acetone used as a solvent was distilled off
from the complex with NaI immediately before use. The 1H
and 31P NMR spectra were recorded on a Bruker AMX-400
instrument. The chemical shifts of the phosphorus atom were
measured relative to H3PO4.
Reaction of cation 1 with phosphine 2. NMR study. A
mixture of 1 and 2 taken in a ratio of 1 : 1.5 was dissolved in
acetone-d6 in an NMR tube. After 2—2.5 h, the 1H and
31P NMR spectra were recorded.
1H NMR, δ, for 1: 4.66 (m, 2 H, C5H4ORu); 5.83 (s, 5 H,
CpRu); 6.52 (m, 2 H, C5H4ORu); for major diastereomer of 4:
4.10 (br.s, 1 H, C5H3Ru); 4.32 (s, 5 H, CpFe); 4.46 and 4.50
(AB system, 2 H); 4.66 (s, 5 H, CpRu); 4.73 (br.s, 1 H,
C5H3Ru); 4.80 (m, 2 H); 4.87 (m, 2 H, C5H3Fe); 5.16 (br.s,
1 H, C5H3Ru); 7.14 (m, 2 H, Bn); 7.29 (m, 3 H, Bn); 7.60
(m, 3 H, Ph); 8.16 (m, 2 H, Ph), 8.60 (br.s, 1 H, OH); for
minor diastereomer of 4: 4.32 (br.s, 1 H, C5H3Ru); 4.40 (br.s,
5 H, CpFe); 4.56 and 4.60 (AB system, 2 H); 4.73 (br.s, 1 H,
C5H3Ru); 4.76 (s, 5 H, CpRu); 4.83 (m, 2 H, C5H3, Fe); 4.9
1
by the reliable data from elemental analysis, and its H
and 31P NMR spectral characteristics were identical
with those obtained in analysis of the reaction mixture.
Of several reactions with cation 1, which were exam-
ined for various tertiary phosphines, the reaction of the
pyridine complex of 1 with PMe3, like the reactions
with phosphines 2 and 3, was not brought to comple-
tion.5 We modified the scheme proposed in the cited
study5 (see Scheme 1) taking into account the ability of
phosphines 2 and 3 to attack the cyclopentadienone
ring. In the first stage, phosphines 2 and 3 replace the

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Russ.Chem.Bull., Int.Ed., Vol. 50, No. 11, November, 2001
Troitskaya et al.
(m, 2 H, C5H3Fe); 5.26 (br.s, 1 H, C5H3Ru); 7.06 (m, 2 H,
Bn); 7.86 (m, 3 H, Ph); 8.30 (m, 2 H, Ph); 8.97 (br.s, 1 H, OH).
31P NMR, δ for 4: 25.4 (major diastereomer of 4), 27.6
(minor diastereomer of 4).
4.87 (m, 2 H, C5H3Fe); 4.90 (m, 2 H, C5H3Fe); 5.21 (m, 1 H,
C5H3Ru); 7.84 (m, 3 H, Ph); 8.68 (m, 2 H, Ph); 8.91 (br.s,
1 H, OH). 1H NMR of product 6 (some signals): 2.19—2.26
(m, 2 H, CH2); 4.42 (s, 5 H, CpFe); 5.03 (m, 1 H, C5H3Ru);
5.05 (m, 1 H, C5H3Ru); 5.07 (m, 1 H, C5H3Ru); 8.00 (br.s,
1 H, OH); 8.06—8.11 (m, 2 H, Ph).
Synthesis of (benzyl)(ferrocenyl)(2-hydroxyrutheno-
cenyl)(phenyl)phosphonium hexafluorophosphate (4). Phos-
phine 2 (46 mg, 0.12 mmol) was added to a solution of salt 1
(X = PF6) (50 mg, 0.12 mmol) in acetone (2 mL). The
reaction mixture was stirred for 2 h and kept for 12 h. Then the
solvent was evaporated and the residue was dried. The crude
product was obtained in a yield of 85 mg (94%). After washing
with ether, compound 4 was obtained as a yellow-brown solid.
Found (%): C, 52.16; H, 4.12; P, 7.96. C33H30F6FeOP2Ru.
Calculated (%): C, 51.11; H, 3.90; P, 7.96. The 1H and
31P NMR spectra correspond to a mixture of diastereomers
of 4 in a ratio of 1.3 : 1.
31P NMR, δ: 29.0 (major diastereomer of 5); 29.8 (6); 30.4
(minor diastereomer of 5).
References
1. A. N. Nesmeyanov, V. A. Sazonova, and V. N. Drozd,
Chem. Ber., 1960, 93, 2717.
2. V. I. Sokolov, L. A. Bulygina, O. Ya. Borbulevich, and O. V.
Shishkin, J. Organomet. Chem., 1999, 582, 246.
3. W. Simanko, N. Vallant, K. Mereiter, R. Schmid, and
K. Kirchner, Inorg. Chem., 1996, 35, 5923.
4. K. Kirchner and H. Taube, J. Am. Chem. Soc., 1991,
113, 7039.
5. K. Kirchner, K. Mereiter, R. Schmid, and H. Taube, Inorg.
Chem., 1993, 32, 5553.
6. I. A. Mamedyarova, M. N. Nefedova, and V. I. Sokolov.
J. Organomet. Chem., 1996, 524, 181.
Reaction of cation 1 with phosphine 3. NMR study. The
experiment was carried out as described above.
1H NMR, δ for major diastereomer of 5: 1.39—1.48 (m,
3 H, Me); 3.15—3.38 (m, CH2); 4.13 (m, 1 H, C5H3Ru); 4.37
(s, 5 H, CpFe); 4.54 (m, 1 H, C5H3Ru); 4.72 (s, 5 H, CpRu);
4.82 (m, 1 H, C5H3Ru); 4.87 (m, 2 H, C5H3Fe); 4.90 (m,
2 H, C5H3Fe); 5.13 (m, 1 H, C5H3Ru); 7.80 (m, 3 H, Ph);
8.20—8.25 (m, 2 H, Ph); 8.68 (br.s, 1 H, OH); for minor
diastereomer of 5: 1.28—1.37 (m, 3 H, Me); 3.15—3.38 (m,
CH2); 4.47 (m, 1 H, C5H3Ru); 4.44 (s, 5 H, CpFe); 4.47 (m,
1 H, C5H3Ru); 4.73 (s, 5 H, CpRu); 4.85 (m, 1 H, C5H3Ru);
Received February 2, 2001;
in revised form April 10, 2001