A new concept for chelate ligands with planar chirality

Article abstract of DOI:10.1021/om970059n

The chiral donor substituted phosphaferrocene derivatives CpFe(3,4-Me₂-2-R-C₄HP) 6 (R =CH₂CH₂NMe₂), 7 (R=CH₂NMe₂), and 8 (R=CH₂OPPh₂) were synthesized as racemates starting from 2-formyl-3,4-dimethylphosphaferrocene. The P,N-ligand 6 reacted with [Cp*RuCl]₄ in THF to give the six-ring chelate complex Cp*RuCl(6) (≡10) which was characterized by single-crystal X-ray diffraction analysis. The complexation reaction was found to proceed diastereoselectively with respect to the newly created stereogenic center on the ruthenium atom. Under similar conditions, the reaction of ligand 7 with [Cp*RuCl]₄ did not lead to chelate formation. Instead, two isomers of the bis-P-coordinated complex Cp*RuCl(7)₂ (≡11) were observed by NMR spectroscopy. Reaction of the phosphinite ligand 8 with (PhCN)₂PdCl₂ in toluene produced the six-ring chelate complex cis-PdCl₂(8) (≡12). The crystal structure of 12 has been determined.

Full text of DOI:10.1021/om970059n

2862
Organometallics 1997, 16, 2862-2867
A New Con cep t for Ch ela te Liga n d s
w ith P la n a r Ch ir a lity†
Christian Ganter,* Lutz Brassat, Corinna Glinsbo¨ckel, and Beate Ganter
Institut fu¨r Anorganische Chemie, Technische Hochschule Aachen, D-52056 Aachen, Germany
Received J anuary 28, 1997X
The chiral donor substituted phosphaferrocene derivatives CpFe(3,4-Me2-2-R-C4HP) 6 (R
) CH2CH2NMe2), 7 (R ) CH2NMe2), and 8 (R ) CH2OPPh2) were synthesized as racemates
starting from 2-formyl-3,4-dimethylphosphaferrocene. The P,N-ligand 6 reacted with
[Cp*RuCl]4 in THF to give the six-ring chelate complex Cp*RuCl(6) (t10) which was
characterized by single-crystal X-ray diffraction analysis. The complexation reaction was
found to proceed diastereoselectively with respect to the newly created stereogenic center
on the ruthenium atom. Under similar conditions, the reaction of ligand 7 with [Cp*RuCl]4
did not lead to chelate formation. Instead, two isomers of the bis-P-coordinated complex
Cp*RuCl(7)2 (t11) were observed by NMR spectroscopy. Reaction of the phosphinite ligand
8 with (PhCN)2PdCl2 in toluene produced the six-ring chelate complex cis-PdCl2(8) (t12).
The crystal structure of 12 has been determined.
Ch a r t 1
In tr od u ction
Chiral ligands play an important role in coordination
chemistry. In particular, the increasing interest in
asymmetric catalysis over the past two decades has
stimulated the development of a huge number of chiral
ligands, among which the bidentate chelate ligands are
by far the most numerous.1 Whereas the C2 symmetry
of these chelate ligands was considered to be a prereq-
uisite for excellent asymmetric inductions,2 it has been
shown in recent years that ligands lacking any sym-
metry at all may perform equally well or even superior
in certain catalytic reactions.3 Ligands owing their
chirality to the presence of stereogenic centers are
legion, while those with planar chirality are so far
restricted to π-complexed disubstituted carbocycles (e.g.
1,2-disubstituted ferrocenes4 and tricarbonylchromium
complexes of ortho disubstituted benzene derivatives5).
We considered a new approach to a novel class of
bidentate chelate ligands with planar chirality via
π-complexed monosubstituted heterocycles which are
able to coordinate to a metal fragment M′L′m via both
the heteroatom X of the π-complexed heterocycle and
an appropriate donor group Y at the substituent (Chart
1). Within this arrangement the coordinated metal
atom M′ is positioned in immediate proximity to the
element of planar chirality. This situation may prove
advantageous for stereoselective reactions at the metal
center which involve chirality transfer from the ligand
to a metal-coordinated substrate as is the case in
asymmetric catalysis. We present here the first results
obtained from our studies with phosphaferrocenes, i.e.
the syntheses of appropriately substituted phosphafer-
rocene derivatives and their application as chelate
ligands toward transition metal fragments.
Resu lts
Ch oice of Liga n d s. Among the heterocycles con-
sidered as potential candidates were thiophene, pyri-
dine, and the pyrrolyl and phospholyl anions. The
CpFe+ and the Cr(CO)3 moieties might serve as ap-
propriate metal fragments for π-complexation of the
heterocycles. From the possible combinations of the
fragments, phosphaferrocene, i.e. the combination of the
phospholyl anion with the CpFe+ cation, was chosen for
several reasons. Firstly, from the pioneering work of
Mathey6 et al. it is known that the phosphorus atom in
the phosphaferrocene molecule is still nucleophilic
enough to act as a Lewis base toward metal centers.7
Secondly, the phosphaferrocenes are reasonably stable
and tolerate a wide range of experimental conditions
so that the risk of degradation in the course of the
intended complexation reactions is appreciably low.
Furthermore, the synthesis of phosphaferrocenes is
† Dedicated to Professor Gerhard E. Herberich on the occasion of
his 60th birthday.
X Abstract published in Advance ACS Abstracts, May 15, 1997.
(1) Brunner, H.; Zettlmeier, W. Handbook of Enantioselective Ca-
talysis; VCH: Weinheim and New York, 1993.
(2) Whitesell, J . K. Chem. Rev. 1989, 89, 1581.
(3) (a) Trost, B. M.; Van Vrancken, D. L. Chem. Rev. 1996, 96, 395
and literature cited therein. (b) Togni, A.; Burckhardt, U.; Gramlich,
V.; Pregosin, P. S.; Salzmann, R. J . Am. Chem. Soc. 1996, 118, 1031.
(c) Blo¨chl, P. E.; Togni, A. Organometallics 1996, 15, 4125. (d) Hayashi,
T.; Kawatsura, M.; Iwamura, H.; Yamaura, Y.; Uozumi, Y. J . Chem.
Soc., Chem. Commun. 1996, 1767. (e) Uozumi, Y.; Tanahashi, A.; Lee,
S.-Y.; Hayahi, T. J . Org. Chem. 1993, 58, 1945. (f) Hayashi, T.;
Iwamura, H.; Naito, M.; Uozumi, Y.; Matsumoto, Y.; Miki, M.; Yanagi,
K. J . Am. Chem. Soc. 1994, 116, 775. (g) Hayashi, T.; Konishi, M.; Ito,
H.; Kumada, M. J . Org. Chem. 1986, 51, 3772.
(4) (a) Togni, A.; Hayashi, T. Ferrocenes; VCH: Weinheim and New
York, 1995. (b) A planar chiral ruthenocene ligand has been described
as well: Hayashi, T.; Ohno, A.; Lu, S.; Matsumoto, Y.; Fukuyo, E.;
Yanagi, K. J . Am. Chem. Soc. 1994, 116, 4221.
(6) For comprehensive reviews on the chemistry of phosphafer-
rocenes, see: (a) Mathey, F. Coord. Chem. Rev. 1994, 137, 1. (b)
Mathey, F. J . Organomet. Chem. 1990, 400, 149. (c) Mathey, F.,
Fischer, J .; Nelson, J . H. Structure Bonding 1983, 55, 154.
(7) (a) Mathey, F. J . Organomet. Chem. 1978, 154, C13. (b) Fischer,
J .; Mitschler, A.; Ricard, L.; Mathey, F. J . Chem. Soc., Dalton Trans.
1980, 2522. (c) Nief, F.; Mathey, F.; Ricard, L. J . Organomet. Chem.
1990, 384, 271. (d) Deschamps, B.; Mathey, F.; Fischer, J .; Nelson, H.
Inorg. Chem. 1984, 23, 3455. (e) De Lauzon, G.; Deschamps, B.;
Mathey, F. New J . Chem. 1980, 4, 683. (f) Roberts, R. M. G.; Silver,
J .; Wells, A. S. Inorg. Chim. Acta 1986, 119, 165.
(5) Uemura, M.; Miyake, R.; Nishimura,H.; Matsumoto, Y.; Hayashi,
T. Tetrahedron: Asymmetry 1992, 3, 213.
S0276-7333(97)00059-9 CCC: $14.00 © 1997 American Chemical Society

Chelate Ligands with Planar Chirality
Organometallics, Vol. 16, No. 13, 1997 2863
Sch em e 1. Syn th esis of Liga n d s 6, 7, a n d 8a
Sch em e 2
Ta ble 1. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 10
(a) Distances
Ru-Cl
Ru-P
2.475(2)
2.238(1)
2.296(5)
2.214(6)
2.145(6)
2.149(5)
2.184(6)
2.252(6)
1.752(5)
1.761(6)
1.425(8)
1.423(9)
1.421(8)
1.498(9)
Fe-P
2.262(2)
2.077(6)
2.048(6)
2.036(6)
2.070(6)
2.031(8)
2.037(8)
2.020(8)
2.037(8)
2.040(8)
1.51(1)
Fe-C2
Fe-C3
Fe-C4
Fe-C5
Fe-C12
Fe-C13
Fe-C14
Fe-C15
Fe-C16
C6-C7
N-C7
Ru-N
Ru-C20
Ru-C21
Ru-C22
Ru-C23
Ru-C24
P-C2
P-C5
C2-C3
C3-C4
C4-C5
C2-C6
1.512(8)
1.471(9)
1.479(8)
a
Reagents and conditions: (i) CH3NO2, MeOH, cat.; (ii)
N-C10
N-C11
NaBH4, NiCl2, MeOH; (iii) LiAlH4, Et2O; (iv) H2CO, NaBH3CN,
ZnCl2, MeOH; (v) HNMe2, NEt3, TiCl4, NaBH3CN, CH2Cl2; (vi)
LiAlH4, Et2O; then Ph2PCl, NEt3, Et2O.
(b) Angles
Ru-P-Fe
P-Ru-N
C2-P-C5
Ru-P-C5
P-C2-C6
C2-C3-C4
P-C5-C4
140.88(7)
84.4(1)
Cl-Ru-N
Cl-Ru-P
Ru-P-C2
P-C2-C3
C3-C2-C6
C3-C4-C5
85.0(1)
94.64(6)
126.4(2)
112.6(4)
125.3(5)
112.7(5)
quite straightforward. For synthetic reasons the di-
methyl-substituted derivative 3,4-dimethylphosphafer-
rocene (1) was chosen as the starting material, which
was prepared in 65% yield using an optimized modifica-
tion of Mathey’s original procedure7a (see the Experi-
mental Section). Introduction of a substituent in the
2-position of the phospholyl ring establishes the element
of planar chirality. Great progress has been achieved
in the stereoselective synthesis of planar chiral fer-
rocene derivatives via both diastereo8- and most recently
enantioselective9 deprotonation of monosubstituted fer-
rocenes. Unfortunately, the analogous approach of
enantioselective metalation in the 2-position of the
phospholyl ring of 1 is hampered by the fact that strong
nucleophiles such as BuLi add to the phosphorus atom
of phosphaferrocene,10 leading to subsequent degrada-
tion. We therefore decided to utilize the Vilsmeyer
formylation of 111 as an entry into 2-substituted phos-
phaferrocene derivatives although this reaction is not
stereoselective and leads to racemic 2-formyl-3,4-di-
methylphosphaferrocene (2). Starting from aldehyde 2
the P∧N ligands 6 and 7 and the P∧P ligand 8 were
prepared by standard organic transformations (Scheme
1). Reductive amination of 2 affords the (dimethylami-
no)methyl-substituted ligand 7, which should give rise
90.8(3)
141.9(2)
122.1(4)
111.9(5)
112.0(5)
to five-membered chelate rings on complexation to a
metal fragment. In contrast, nitroaldol condensation
of aldehyde 2 with nitromethane enables the extension
of the alkyl spacer by one CH2 unit and leads after
stepwise reduction and dimethylation to the amino
compound 6, appropriate for six-membered chelate ring
formation.
Com p lexa tion Stu d ies. Complexation reactions of
the P∧N ligands 6 and 7 were carried out using
[Cp*RuCl]4 9,12 which is known to provide a source of
Cp*RuCl fragments with two vacant coordination sites
and reacts with a variety of hard and soft bidentate
ligands L∧L including phosphines and nitrogen donors
to give chelate complexes of the type Cp*RuCl(L∧L).13
Different results were obtained for the reaction of
[Cp*RuCl]4 with ligands 6 and 7, respectively. When
ligand 6 was treated with 0.25 equiv of 9 in THF at room
temperature, we observed within minutes the formation
of the desired chelate complex [Cp*RuCl(6)] 10 (Scheme
2), which was isolated in analytically pure form as an
orange red powder in quantitative yield simply by
evaporating the solvent. Recrystallization from acetone
afforded red crystals suitable for X-ray diffraction.
Selected bond distances and angles are given in Table
1; a PLATON plot of the structure of 10 is depicted in
Figure 1 and reveals the chelating coordination of ligand
6 to the ruthenium atom. The phospholyl ring shows
only slight deviation from planarity and forms an angle
of 4(2)° with the Cp ring plane. The Ru-P vector is
tilted from the mean phospholyl plane by 8.2(2)° away
from iron. A similar tilt angle of 8.4(2)° was found for
the Fe-P vector in tetracarbonyl(3,4-dimethylphospha-
(8) (a) For a compilation of recent advances with planar chiral
ferrocenes, see: Togni, A. Angew. Chem. 1996, 108, 1581; Angew.
Chem., Int. Ed. Engl. 1996, 35, 1475. (b) Marquarding, D.; Klusacek,
H.; Gokel, G.; Hoffmann, P.; Ugi, I. J . Am. Chem. Soc. 1970, 92, 5389.
(c) Togni, A.; Breutel, C.; Schnyder, A.; Spindler, F.; Landert, H.; Tijani,
A. J . Am. Chem. Soc. 1994, 116, 4062. (d) Rebie`re, F.; Riant, O.; Ricard,
L.; Kagan, H. B. Angew. Chem. 1993, 105, 644; Angew. Chem., Int.
Ed. Engl. 1993, 32, 568. (e) Riant, O.; Samuel, O.; Kagan, H. B. J .
Am. Chem. Soc. 1993, 115, 5835. (f) Ganter, C.; Wagner, T. Chem. Ber.
1995, 128, 1157. (g) Richards, C. J .; Damilidis, T.; Hibbs, D. E.;
Hursthouse, M. B. Synlett 1995, 74. (h) Nishibayashi, Y.; Uemura, S.
Synlett 1995, 79. (i) Sammakia, T.; Latham, H. A.; Schaad, D. R. J .
Org. Chem. 1995, 60, 10.
(9) (a) Price, D.; Simpkins, N. S. Tetrahedron Lett. 1995, 36, 6135.
(b) Tsukazaki, M.; Tinkl, M.; Roglans, A.; Chapell, B. J .; Taylor, N. J .;
Snieckus, V. J . Am. Chem. Soc. 1996, 118, 685. (c) Nishibayashi, Y.;
Arikawa, Y.; Ohe, K.; Uemura, S. J . Org. Chem. 1996, 61, 1172.
(10) (a) Deschamps, B.; Fischer, J .; Mathey, F.; Mitschler, A. Inorg.
Chem. 1981, 20, 3252. (b) Deschamps, B.; Fischer, J .; Mathey, F.;
Mitschler, A.; Ricard, L. Organometallics 1982, 1, 312.
(12) Fagan, P. J .; Mahoney, W. S.; Calabrese, J . C.; Williams, I. D.
Organometallics 1990, 9, 1843.
(13) (a) Wang, M. H.; Englert, U.; Ko¨lle, U. J . Organomet. Chem.
1993, 453, 127. (b) Ko¨lle, U.; Kossakowski, J . J . Organomet. Chem.
1989, 362, 383.
(11) De Lauzon, G.; Deschamps, B.; Fischer, J.; Mathey, F.; Mitschler,
A. J . Am. Chem. Soc. 1980, 102, 994.

2864 Organometallics, Vol. 16, No. 13, 1997
Ganter et al.
Sch em e 3
25.5 ppm in 10. No sign of line broadening was
observed for the 31P resonance down to -80 °C. Al-
though we cannot as yet exclude tentatively a fast
epimerization of the chiral ruthenium center on the
NMR time scale which should also lead to a single 31P
resonance for the interconverting diastereomers, we
believe that the formation of 10 proceeds stereoselec-
tively and only one diastereomer is present in the crystal
as well as in solution. The fact that Consiglio et al. were
able to observe both diatsereoisomers of CpRuCl(P∧P)
with chiral bidentate diphosphines15,18 points to an
appreciable epimerization barrier for the ruthenium
atom and supports our assumption.
F igu r e 1. Thermal ellipsoid plot (PLATON)28 of complex
10. Ellipsoids are scaled to 30% probability.
ferrocene-P)iron.7b The six-membered chelate ring shows
a half-chair conformation with only C7 and N deviating
considerably from its mean plane by -0.300(7) and
0.614(5) Å, respectively. The Ru-P distance of 2.238(1)
Å is remarkably short and falls in the range observed
for Cp*RuCl{P(OR)3}2 complexes [2.212(9)-2.250(9) Å]14
while 2.276(2) and 2.278(2) Å are found in Cp*RuCl-
(Ph2PCH2CHMePPh2).15 The Ru-N and Ru-Cl dis-
tances are comparable to those found in related
complexes.13a,16 A new stereogenic center is created on
the ruthenium atom in the course of the complexation
reaction. The crystal examined contains only one di-
astereomer with the relative configuration of the central
and planar elements of chirality as depicted in Figure
1, i.e. (RRu),(S)17 and sconsistent with the centrosym-
metric space group P21/csits (SRu),(R) enantiomer as we
started from the racemic ligand 6. Since the quantita-
tively obtained crude product of 10 as well as the
crystals give identical NMR spectra, we conclude that
complex 10 is formed diastereoselectively since we
observe only one set of NMR signals consistent with the
presence of only one diastereomer. In the 1H NMR
spectrum of 10 the protons of the Cp* ligand appear as
a doublet due to the coupling with the phosphorus atom
of coordinated 6 with J HP ) 2.7 Hz. The coupling
Completely different results were obtained for the
reaction of ligand 7 with the ruthenium complex 9. No
chelate formation was observed. Instead, when 7 was
reacted with 0.25 equiv of [Cp*RuCl]4 in THF-d8, we
observed the formation of the 2:1 complex [Cp*RuCl-
(7)2] 11 by NMR spectroscopy while half of the [Cp*-
RuCl]4 remains unreacted and insoluble (Scheme 3).
Addition of another equivalent of ligand 7 to the mixture
results in complete consumption of 9 with complex 11
again being the only detectable species in the NMR
spectrum. The 2:1 stoichiometry of complex 11 is
evident from the integration of the Cp and Cp* protons
which appear in a 10:15 ratio. Both phosphaferrocene
molecules 7 are coordinated via their phosphorus atoms
to the ruthenium center, which leads to a triplet
structure of the signal for the Cp* protons due to
coupling to the two phosphorus nuclei with J HP ) 2.7
Hz. The 31P NMR spectrum consists of a singlet [δ(31P)
) 30.7 ppm] and a pair of doublets at δ(31P) ) 35.5 and
δ(31P) ) 24.7 ppm, respectively, with J PP ) 56.8 Hz in
a 4:1 ratio. We assume that two isomers of 11 are
formed in the complexation reaction. While the Cs
symmetric 11a gives rise to one 31P NMR signal for the
two equivalent phosphorus atoms, the phosphorus
nuclei in the C1 symmetric isomer 11b are inequivalent
and lead to the observed AB pattern. Consistently, the
1H NMR spectrum shows, besides the signal set for Cs
symmetric 11a , the expected resonances for the C1
symmetric isomer 11b in the same 4:1 ratio. Due to
the lower symmetry of 11b, two singlets for the Cp
protons are observed and the signal for the Cp* protons
appears as a doublet of doublets with identical coupling
constants to the two inequivalent P atoms of J HP ) 2.5
Hz. Attempts to separate and isolate the isomers 11a
2
constant J HP for the R phospholyl H decreases on
complexation from 36.0 Hz in 6 to 31.7 Hz in 10, which
is a known phenomenon in the coordination chemistry
of phosphaferrocenes.7a,d,e At room temperature the
protons of the NMe2 group give one broad signal, which
coalesces on cooling to 6 °C (500 MHz) and splits into
two sharp resonances (∆ν ) 212 Hz) at -40 °C. We
attribute this observation to a dynamic hemilabile
behavior of dissociation/association of the NMe2 moiety
that is fast on the NMR time scale at ambient temper-
ature. For this dangling process an activation enthalpy
of ∆Gq ) 53.6 ( 1 kJ mol-1 is calculated from the
recorded data. In the 31P NMR spectrum the signal of
6 (-80.2 ppm) experiences a downfield shift to δ(31P) )
(14) Serron, S. A.; Luo, L.; Stevens, E. D.; Nolan, S. P.; J ones, N.
L.; Fagan, P. J . Organometallics 1996, 15, 5209.
(15) Morandini, F.; Consiglio, G.; Straub, B.; Ciani, G.; Sironi, A. J .
Chem. Soc., Dalton Trans. 1983, 2293.
(16) (a) Bruce, M. I.; Wong, F. S.; Skelton, B. W.; White, A. H. J .
Chem. Soc., Dalton Trans. 1981, 1398. (b) Balavoine, G. G. A.; Boyer,
T.; Livage, C. Organometallics 1992, 11, 456.
(17) The “non central” descriptor for the planar chirality as originally
proposed by Schlo¨gl is used here: Schlo¨gl, K.; Fried, M.; Falk, H.
Monatsh. Chem. 1964, 95, 576.
(18) (a) Consiglio, G.; Morandini, F. Chem. Rev. 1987, 87, 761. (b)
Consiglio, G.; Morandini, F.; Bangerter, F. Inorg. Chem. 1982, 21, 455.
(c) See also: White, C.; Cesarotti, E. J . Organomet. Chem. 1985, 287,
123.

Chelate Ligands with Planar Chirality
Organometallics, Vol. 16, No. 13, 1997 2865
Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 12
(a) Distances
Pd-Cl1
Pd-Cl2
Pd-P1
Pd-P2
P1-C2
P1-C5
C2-C3
C3-C4
C4-C5
C2-C6
O-C6
2.329(4)
2.367(3)
2.201(4)
2.243(3)
1.74(1)
1.74(1)
1.40(2)
1.42(2)
1.42(2)
1.49(2)
1.44(1)
1.604(9)
Fe-P1
2.224(4)
2.08(1)
2.06(1)
2.03(2)
2.06(1)
2.05(1)
2.03(1)
2.03(1)
2.05(1)
2.06(2)
1.82(1)
1.81(1)
Fe-C2
Fe-C3
Fe-C4
Fe-C5
Fe-C10
Fe-C11
Fe-C12
Fe-C13
Fe-C14
P2-C20
P2-C30
P2-O
(b) Angles
F igu r e 2. Thermal ellipsoid plot (PLATON)28 of complex
12. Ellipsoids are scaled to 30% probability.
Pd-P1-Fe
C2-P1-C5
Cl1-Pd-Cl2
Cl1-Pd-P1
Cl1-Pd-P2
Pd-P1-C5
C2-C3-C4
P1-C5-C4
142.1(3)
92.8(7)
93.5(1)
176.6(1)
88.7(1)
143.8(6)
113(1)
Pd-P2-O
117.0(4)
89.3(1)
88.6(1)
176.9(1)
121.7(5)
111.2(9)
113(1)
P1-Pd-P2
Cl2-Pd-P1
Cl2-Pd-P2
Pd-P1-C2
P1-C2-C3
C3-C4-C5
Sch em e 4
110(1)
than the Pd-Cl2 distance of 2.367(3) Å reflecting the
different donor/acceptor properties of the two phospho-
rus centers. The mean planes for the Cp and phospholyl
rings form an angle of 8(2)°. The Pd-P1 vector is
inclined against the phospholyl mean plane by 10.4(2)°.
In the 31P NMR spectrum the signal for the phospholyl
P atom is shifted downfield from -78.0 ppm in ligand
8 to -14.3 ppm in the complex 12, while the signal for
the phosphinite phosphorus atom remains practically
unchanged (8, 116.7 ppm; 12, 109.7 ppm).
and 11b in pure form have so far been unsuccessful.
The Ru atom in the achiral isomer 11a is an achirotopic
but stereogenic unit, i.e. it is a center of pseudoasym-
metry. Thus, the formation of another achiral diaste-
reomer may be anticipated, which can formally be
constructed by interchanging the positions of the two
phosphaferrocene ligands in formula 11a . This would
result in a ligand arrangement with the aminoalkyl side
chains pointing toward each other, a situation which is
very likely less favorable for steric reasons as compared
to the arrangement depicted in formula 11a with the
side chains lying far apart from each other. The NMR
spectra indicate the presence of only one achiral com-
plex, and we therefore consider the arrangement 11a
to belong to the observed species.
Discu ssion
Some aspects of the reported findings deserve a
further comment. Comparing ligands 6 and 7, we note
that chelate formation only occurs with 6 leading to a
six-membered chelate ring, while no five-membered ring
was observed with ligand 7. As both ligands can be
supposed to have similar donor/acceptor properties,
their different coordination modes toward the Cp*RuCl
fragment must be attributed to their different confor-
mational flexibility resulting in a better ring size fit for
ligand 6. Complexation of two molecules of 7 via their
phosphorus atoms shows that P-coordination of the
ligand is prefered for electronic reasons as compared to
coordination via the NMe2 donor moiety. In the chelate
complex 10 on the other hand, this electronic preference
is overcome by the chelate effect. A further, quite
encouraging point concerns the diastereoselectivity
observed in the formation of the Ru complex 10. Con-
siglio et al. have reported the synthesis of several
CpRuCl(P∧P) chelate complexes with chiral diphos-
phine ligands. In most cases, low diastereoselectivities
were observed for the formation of the stereogenic center
on the ruthenium atom resulting in almost 1:1 mixtures
of diastereomers.15,18 An argument for the increased
stereoselectivity observed in the complexation reaction
with our new ligand 6 is provided by inspection of the
structure of the ruthenium complex 10: formally,
interchanging the positions of the Cl and Cp* ligands
on the ruthenium atom results in the other diastere-
omer. Model inspection of that hypothetical ligand
Another complexation experiment was carried out
with the P∧P ligand 8. The synthesis of the phosphinite
8 was complicated by the formation of Ph2P(O)PPh2 in
a consecutive reaction.19 Furthermore, since it is quite
sensitive and decomposes on chromatography, 8 could
not be obtained in pure form. Therefore, ligand 8 was
prepared in situ without isolation and immediately
treated with (PhCN)2PdCl2 in toluene (Scheme 4). The
resulting red precipitate was collected and recrystallized
from dichloromethane and ether to give the palladium
chelate complex 12 in low yield as dark red crystals
suitable for an X-ray diffraction study (Figure 2, Table
2). The structure determination confirms the chelating
coordination mode of the phosphinite ligand 8, which
leads to a boat conformation for the six-membered
chelate ring. The structure shows a distorted square
planar geometry about the palladium atom with a
rather short Pd-P1 distance of 2.201(4) Å, which is
comparable to 2.229(1)
Å
found for cis-PdCl2-
[P(OSiMe3)3]2.20 The distance Pd-P2 of 2.243(3) Å falls
in the range observed for other PdCl2 complexes with
chelating diphosphines.21 The bite angle P1-Pd-P2
adopts a value of 89.3(1)°. The Pd-Cl1 distance of
2.329(4) Å trans to the phospholyl phosphorus is shorter
(21) (a) Steffen, W. L.; Palenik, G. J . Inorg. Chem. 1976, 15, 2432.
(b) Hayashi, T.; Konishi, M.; Kobori, Y.; Kumada, M.; Higuchi, T.;
Hirotsu, K. J . Am. Chem. Soc. 1984, 106, 158. (c) Hayashi, T.; Kumada,
M.; Higuchi, T.; Hirotsu, K. J . Organomet. Chem. 1987, 334, 195.
(19) Fluck, E.; Binder, H. Inorg. Nucl. Chem. Lett. 1967, 3, 307.
(20) Gebauer, T.; Frenzen, G.; Dehnicke, K. Z. Naturforsch. 1993,
48b, 1661.

2866 Organometallics, Vol. 16, No. 13, 1997
Ganter et al.
Hz, R-C), 96.06 (d, J ) 4.4 Hz, â-C), 99.83 (d, J ) 7.6 Hz, â-C),
134.36 (d, J ) 14.8 Hz, dCH), 144.49 (d, J ) 17.0 Hz, dCH).
31P{1H} NMR (CDCl3): δ ) -75.6. MS: 303 (M+). Anal.
Calcd for C13H14FePNO2: C, 51.52; H, 4.66; N, 4.62. Found:
C, 51.14; H, 4.67; N, 4.34.
arrangement suggests an unfavorable approach of the
Cp and Cp* ligands for that particular diastereomer.
Con clu sion a n d Ou tlook
P r ep a r a tion of 4. NaBH4 (211 mg, 5.58 mmol) was added
to a solution of NiCl2‚6H2O23 (439 mg, 1.85 mmol) in 25 mL of
MeOH portionwise, and the mixture was stirred vigorously
for 0.5 h. A solution of 3 (1.12 g, 3.7 mmol) in 10 mL of MeOH
and 3 mL of THF was then added followed by 485 mg (12.83
mmol) of NaBH4 in several portions. Stirring was continued
for 0.5 h at room temperature, and the mixture was filtered
through Kieselguhr. The filtrate was evaporated to dryness,
dissolved in 30 mL of CH2Cl2, and washed with 0.1 N HCl and
brine. The organic phase was dried over Na2SO4 and filtered,
and the solvent was removed under vacuum to yield 1.00 g
(89%) of 4 as a red oil. 1H NMR (500 MHz, CDCl3): δ ) 2.14
(s, 3H, Me), 2.16 (s, 3H, Me), 2.84 (m, 2H, CH2), 3.72 (d, J )
36.9 Hz, R-H), 4.10 (s, 5H, Cp), 4.34 (t, J ) 7.8 Hz, 2H, CH2-
NO2). 13C{1H} NMR (125.7 MHz, CDCl3): δ ) 13.50 (Me),
16.89 (Me), 28.93 (d, 19.7 Hz, CH2), 72.23 (Cp), 76.03 (d, J )
58.7 Hz, R-CH), 76.38 (d, J ) 6.6 Hz, CH2NO2), 92.33 (d, J )
59.2 Hz, R-C), 93.36 (d, J ) 5.0 Hz, â-C), 96.26 (d, J ) 6.6 Hz,
â-C). 31P{1H} NMR (CDCl3): δ ) -79.6. HRMS: calcd for
Phosphaferrocene derivatives bearing donor substit-
uents in the 2-position have been synthesized and were
shown to react as bidentate chelate ligands forming
metal complexes with six-membered chelate rings. The
planar chirality of the ligand 6 provided effective
stereocontrol in the formation of the stereogenic ruthe-
nium center in complex 10 which was obtained diaste-
reoselectively. This clearly demonstrates that our
approach to a topologically new class of planar chiral
chelate ligands bears a potential for stereoselective
reactions being carried out at a coordinated metal
center. We are currently investigating the resolution
of the racemic aldehyde 2 in order to obtain enantiopure
ligands. Further work will be directed toward the
development of ligands with other donor substituents
as well as their use in coordination chemistry and
asymmetric catalysis.
C
13H16FePNO2 305.026 804, found 305.026 764.
P r ep a r a tion of 5. To a suspension of 500 mg (13.16 mmol)
Exp er im en ta l Section
of LiAlH4 in 25 mL of ether was added a solution of 4 (1.00 g,
3.3 mmol) in 5 mL of THF dropwise at 0 °C, and the mixture
was strirred for 1 h at room temperature. Water (0.5 mL), 1
mL of NaOH (2 M), and again 1 mL of water were added
subsequently to give a granular precipitate which could easily
be removed by filtration through Kieselguhr. The filtrate was
evaporated to dryness under vacuum and treated with ether,
water and HCl (2 M). The acidic aqueous phase was sepa-
rated, treated with 2 M NaOH until pH 11, and extracted twice
with ether. The combined extracts were washed with brine
and dried over Na2SO4, and the solvent was removed under
vacuum to give 667 mg (74%) of 5 as a red oil. 1H NMR (500
MHz, CDCl3): δ ) 1.32 (br s, 2H, NH2), 2.14 (s, 3H, Me), 2.19
(s, 3H, Me), 2.24 (m, 1H, CH2), 2.36 (m, 1H, CH2), 2.78 (m,
2H, CH2NH2), 3.68 (d, J ) 36.0 Hz, 1H, R-H), 4.08 (s, 5H, Cp).
13C{1H} NMR (125.7 MHz, CDCl3): δ ) 13.61 (Me), 16.85 (Me),
35.62 (d, J ) 16.4 Hz, CH2), 43.74 (br s, CH2), 71.85 (Cp), 75.35
(d, J ) 58.2 Hz, R-CH), 93.12 (d, J ) 4.9 Hz, â-C), 95.58 (d, J
) 6.6 Hz, â-C), 96.48 (d, J ) 58.7 Hz, R-C). 31P{1H} NMR
Gen er a l P r oced u r es. Reactions were carried out under
an atmosphere of dinitrogen by means of conventional Schlenk
techniques. Solvents were purified and deoxygenated by
conventional methods. Kieselguhr and alumina (Woelm, N-
o
super O, activity I) were heated at 250 C for 12 h, cooled to
room temperature under high vacuum, and stored under
dinitrogen. Alumina was deactivated with 5% deoxygenated
water after cooling.
NMR spectra were recorded on a Varian Unity 500 spec-
trometer (1H, 500 MHz; 13C{1H}, 125.7 MHz; 31P{1H}, 202.3
MHz), a Bruker AM 250 PFT (1H, 250 MHz; 13C, 62.9 MHz),
and a Bruker WP 80 PFT (1H, 80 MHz). 1H and 13C spectra
are referenced to internal TMS and 31P spectra to external H3-
PO4 (85%). Mass spectra were recorded on a Finnigan MAT-
95 spectrometer (EI, 70 eV nominal electron energy). 3,4-
Dimethylphosphaferrocene (1) was prepared by an optimized
modification of Mathey’s original procedure7a (see below).
2-Formyl-3,4-dimethylphosphaferrocene (2),11 2-(hydroxy-
methyl)-3,4-dimethylphosphaferrocene,11 and [Cp*RuCl]4 (9)12
were prepared as described in the literature.
(CDCl3):
δ ) -79.06. HRMS: calcd for C13H18FeNP
275.052 625, found 275.052 317.
P r ep a r a tion of 6. To a solution of 5 (590 mg, 2.14 mmol)
and 3 equiv of formaldehyde (37% aqueous solution) in 15 mL
of MeOH and 5 mL of THF was added a solution of NaBH3-
CN24 (135 mg, 2.14 mmol) and ZnCl2 (146 mg, 1.07 mmol) in
5 mL of MeOH, and the mixture was stirred for 3 h. Water
was added and the pH adjusted to 10. The organic solvents
were removed under vacuum, more water was added and the
mixture was extracted with three portions of ether which were
dried over Na2SO4 and evaporated to dryness. The oily residue
was chromatographed on alumina with hexane/ether (1:1) to
give 468 mg (72%) of 6 as a red oil after removal of the eluent
under vacuum. 1H NMR (500 MHz, CDCl3): δ ) 2.10 (s, 3H,
Me), 2.14 (s, 3H, Me), 2.21 (s, 6H, NMe2), 2.27 (m, 4H, CH2-
CH2), 3.63 (d, J ) 36.0 Hz, R-H), 4.04 (s, 5H, Cp). 13C{1H}
NMR (125.7 MHz, CDCl3): δ ) 13.89 (Me), 16.81 (Me), 28.96
(d, J ) 18.1 Hz, CH2), 45.31 (NMe2), 61.64 (d, J ) 7.1 Hz, CH2-
NMe2), 71.72 (Cp), 75.23 (d, J ) 58.2 Hz, R-CH), 92.85 (d, J )
5.5 Hz, â-C), 95.31 (d, J ) 6.0 Hz, â-C), 96.81 (d, J ) 58.7 Hz,
R-C). 31P{1H} NMR (CDCl3): δ ) -80.2. MS: 303 (M+). The
methylammonium iodide was prepared for the purpose of an
elemental analysis by addition of an excess of MeI to a solution
P r ep a r a t ion of 3,4-Dim et h ylp h osp h a fer r ocen e (1).
1-tert-Butyl-3,4-dimethylphosphole22 (10.4 g, 62 mmol) and
12.0 g (34 mmol) of [CpFe(CO)2]2 were refluxed in 75 mL of
xylene for 15 h. The solvent was evaporated under vacuum
and the residue dissolved in dichloromethane (30 mL). Alu-
mina (30 g) was added, and the solvent was removed under
vacuum. The dry residue was loaded onto a 20 cm alumina
column and eluted with hexane. Evaporation of the dark
orange main band gave 9.3 g (65%) of 1 as an orange solid
which yielded spectroscopic data similar to those quoted in the
literature.7a Crystalline 1 can be obtained by recrystallization
of the crude product from hot methanol.
P r ep a r a tion of 3. Aldehyde 2 (2.45 g, 9.4 mmol), ni-
tromethane (0.63 g, 10.3 mmol), and ethylenediamine diacetate
(170 mg, 0.94 mmol) were stirred in methanol (20 mL) at room
temperature for 4 days. The solvent was removed, and the
residue was chromatographed on alumina (15 cm) with hex-
ane/ether (4:1) to give 2.23 g (78%) of 3 as a dark purple
powder after removal of the eluent under vacuum. 1H NMR
(500 MHz, CDCl3): δ ) 2.23 (s, 3H, Me), 2.27 (s, 3H, Me), 4.21
(s, 5H, Cp), 4.24 (d, J ) 37.3 Hz, 1H, R-H), 7.27 (dd, J ) 13.1/
1.2 Hz, 1H, CCH), 7.98 (dd, J ) 13.1/12.2 Hz, 1H, CHNO2).
13C{1H} NMR (125.7 MHz, CDCl3): δ ) 13.94 (Me), 16.97 (Me),
73.60 (Cp), 80.99 (d, J ) 59.7 Hz, R-CH), 82.34 (d, J ) 59.2
(23) For nickel-mediated boranate reductions, see: Osby, J . O.;
Ganem, B. Tetrahedron Lett. 1985, 26, 6413.
(24) For reductive methylations of amines using formaldehyde/
NaBH3CN, see: Kim, S.; Oh, C. H.; Ko, J . S.; Ahn, K. H.; Kim, Y. J . J .
Org. Chem. 1985, 50, 1927.
(22) Mathey, F. Tetrahedron 1972, 28, 4171.

Chelate Ligands with Planar Chirality
Organometallics, Vol. 16, No. 13, 1997 2867
of 6 in ether and collecting the resulting precipitate [Me-6]I-
on a frit. Anal. Calcd for C16H25NPFeI: C, 43.17; H, 5.66; N,
3.15. Found: C, 42.94; H, 5.83; N, 3.11.
Ta ble 3. Cr ysta llogr a p h ic Da ta , Da ta Collection
P a r a m eter s, a n d Refin em en t P a r a m eter s for
10 a n d 12
P r ep a r a tion of 7. To a solution of 2 (2.054 g, 7.90 mmol),
dimethylamine (356 mg, 7.90 mmol), and trimethylamine
(1.60g, 15.8 mmol) in 30 mL of dichloromethane was added
1.50 g (7.9 mmol) of TiCl4, and the mixture was stirred
overnight at room temperature. A solution of NaBH3CN (750
mg, 11.94 mmol) in 5 mL of dichloromethane was added
dropwise at 0 °C, and stirring was continued for another 2 h
at ambient temperature. The mixture was hydrolyzed by the
careful addition of 2 mL of water, filtered through Kieselguhr,
and concentrated under vacuum. CH2Cl2 (15 mL) was added,
and the solution was washed with NaHCO3 solution and brine
and dried over Na2SO4. The solvent was removed under
vacuum, and the residue was chromatographed on alumina
with hexane/ether (1:1). Evaporation of the eluent yielded 1.43
g (63%) of 7 as a dark red oil which solidified slowly on
standing. 1H NMR (500 MHz, CDCl3): δ ) 2.15 (s, 3H, Me),
2.16 (br s, 9H, Me + NMe2), 2.88 (dd, J ) 13.0/6.0 Hz, 1H,
CH2), 3.10 (dd, J ) 16.0/13.0 Hz, 1H, CH2), 3.73 (d, J ) 35.7
Hz, 1H, R-H), 4.07 (s, 5H, Cp). 13C{1H} NMR (125.7 MHz,
CDCl3): δ ) 14.02 (Me), 17.00 (Me), 45.17 (NMe2), 59.33 (d, J
) 19.2 Hz, CH2), 72.02 (Cp), 76.63 (d, J ) 55.1 Hz, R-CH),
94.23 (d, J ) 5.0 Hz, â-C), 94.42 (d, J ) 58.0 Hz, R-C), 96.10
(d, J ) 6.0 Hz, â-C). 31P{1H} NMR (CDCl3): δ ) -72.9. MS:
289 (M+). Anal. Calcd for C14H20FePN: C, 58.15; H, 6.97; N,
4.84. Found: C, 58.08; H, 7.14; N, 4.78.
10
12
formula
fw
cryst syst
space group
a, Å
C25H37ClFeNPRu
574.92
C24H24Cl2FeOP2Pd
623.56
monoclinic
P21/c (No. 14)
10.479(2)
16.171(3)
14.647(6)
95.32(2)
2471(2)
monoclinic
P21/n (No. 14)
8.728(5)
13.65(1)
20.12(1)
94.21(5)
2391(5)
b, Å
c, Å
â, deg
V, Å3
dcalcd, g‚cm-3
Z
1.545
4
1184
13.72
1.733
4
1248
17.23
F(000)
µ, cm-1
cryst dimens, mm
T, K
0.10 × 0.20 × 0.28
0.25 × 0.25 × 0.10
203
ω-2θ
203
ω-2θ
scan mode
scan range, deg
total no. of data
no. of unique obsd data
no. of variables
3 < θ < 28
6479
4002 (I > σ(I))
3 < θ < 28
6353
2962 (I > σ(I))
418
280
R, Rw [w-1 ) σ2(Fo)], GOF 0.057, 0.049, 1.090
0.084, 0.066, 1.193
max resid density, e Å-3 0.83 (1.13 Å from Ru) 1.23 (1.36 Å from O)
dichlorobis(benzonitrile)palladium (289 mg, 0.76 mmol) in 30
mL of toluene. A red voluminous precipitate formed instan-
taneously, which was collected on a frit after the mixture was
stirred for 0.5 h. The solid was dried under vacuum, dissolved
in dichloromethane (20 mL), and layered with ether (30 mL)
to give 12 (56 mg, 12%) as dark red crystals. 1H NMR (500
MHz, CD2Cl2): δ ) 2.07 (s, 3H, Me), 2.18 (s, 3H, Me), 4.46 (s,
5H, Cp), 7.5 (m, 5H, Ph), 8.0 (m, 5H, Ph). 31P{1H} NMR (CD2-
Cl2): δ ) -14.3 (br s), 109.7 (br s). Anal. Calcd for
C24H24FeP2OPdCl2: C, 46.23; H, 3.88. Found: C, 47.21; H,
3.89.
P r ep a r a tion of 10. 6 (83.0 mg (0.274 mmol) was added to
a suspension of [Cp*RuCl]4 9 (74.4 mg, 0.068 mmol) in 5 mL
THF at room temperature, and the mixture was stirred for 5
min until a clear dark red solution had formed. Evaporation
of the solvent under vacuum gave pure 10 as an orange brown
powder in quantitative yield. The crude product could be
recrystallized by cooling an acetone solution to -20 °C to give
102 mg (65%) of 10 as dark red crystals. 1H NMR (500 MHz,
THF-d8): δ ) 1.62 (d, J ) 2.7 Hz, 15H, Cp*), 2.08 (s, 3H, Me),
2.22 (s, 3H, Me), 2.49 (m, 2H, CH2), 2.64 (br s, 6H, NMe2),
3.57 (d, J ) 31.7 Hz, 1H, R-H), 3.97 (m, 2H, CH2), 4.36 (s, 5H,
Cp). 13C{1H} NMR (125.7 MHz, THF-d8): δ ) 10.92 (Cp*),
12.80 (Me), 16.62 (Me), 28.20 (d, J ) 14.1 Hz, CCH2), 54.29
(NMe2), 59.97 (d, J ) 7.3 Hz, CH2NMe2), 73.08 (Cp), 74.02 (d,
J ) 35.2 Hz, R-CH), 83.03 (Cp*), 88.72 (â-C), 89.56 (â-C), 91.01
(d, J ) 35.4 Hz, R-C). 31P{1H} NMR (THF-d8): δ ) 25.5. SIMS
X-r a y Str u ctu r e Deter m in a tion s. Geometry and inten-
sity data were collected on an ENRAF-Nonius CAD4 diffrac-
tometer with Mo KR radiation (λ ) 0.710 73 Å, graphite
monochromator). A summary of crystallographic data, data
collection parameters, and refinement parameters are collected
in Table 3. The structures were solved with Patterson
methods and refined on structure factors.25 In the final least
squares full-matrix refinement, all non-hydrogen atoms for
both structures were refined with anisotropic thermal dis-
placement parameters. Hydrogen atoms for compound 10
were refined isotropically and for 12 were included as riding
atoms with an idealized geometry (C-H ) 0.98 Å, BH ) 1.3
Bc). For 10 an empirical absorption correction (Ψ scans) was
applied.26,27
(DTE/DTT matrix): 540 (M+
25H37NPClFeRu: C, 52.23; H, 6.49; N, 2.44. Found: C, 52.16;
H, 6.63; N, 2.29.
- Cl). Anal. Calcd for
C
Com p lexa tion Exp er im en t w ith Liga n d 7. A NMR tube
was charged with 24.0 mg (0.088 mmol) of 9 and THF-d8.
Ligand 7 (51.1 mg, 0.177 mmol) was added, and the NMR tube
was shaken several times until a clear solution resulted. 1H
NMR (500 MHz, THF-d8): major isomer (Cs symmetry): δ )
1.82 (t, J ) 2.7 Hz, 15H, Cp*), 2.10 (s, 12H, NMe2), 2.15 (s,
6H, Me), 2.21 (s, 6H, Me), 2.48 (dm, J ) 12.2 Hz, 2H, CH2),
3.41 (dm, J ) 12.2 Hz, 2H, CH2), 3.88 (dm, J ) 26.6 Hz, 2H,
R-H), 4.01 (s, 10H, Cp); minor isomer (C1 symmetry) δ ) 1.60
(t, J ) 2.5 Hz, 15H, Cp*), 2.07 (s, 6H, NMe2), 2.17 (s, 6H,
NMe2), 2.25 (s, 3H, Me), 2.26 (s, 3H, Me), 2.27 (s, 3H, Me),
2.28 (s, 3H, Me), 2.88 (m, 2H, CH2), 3.03 (m, 2H, CH2), 4.19
(s, 5H, Cp), 4.28 (s, 5H, Cp). 31P{1H} NMR (THF-d8): major
isomer (Cs symmetry) δ ) 30.7; minor isomer (C1 symmetry)
δ ) 24.7 (d, J ) 56.8 Hz), 35.5 (d, J ) 56.8 Hz). Ratio major/
minor isomer: 4:1.
Ack n ow led gm en t. We thank Prof. Dr. G. E. Her-
berich for his support.
Su p p or tin g In for m a tion Ava ila ble: Complete tables of
unit cell parameters, H atom parameters, thermal parameters,
bond distances, bond angles, and positional and anisotropic
thermal parameters for 10 and 12 (11 pages). Ordering
information is given on any current masthead page.
OM970059N
P r ep a r a tion of 12. To a solution of 2-(hydroxymethyl)-
3,4-dimethylphosphaferrocene11 (198 mg, 0.76 mmol) and
triethylamine (0.5 mL) in 30 mL of ether was added a solution
of chlorordiphenylphosphine (167 mg, 0.76 mmol) in 5 mL of
ether dropwise at 0 °C. After the mixture was stirred for 1 h
at room temperature, hexane (10 mL) was added and the
precipitated hydrochloride was removed by filtration through
Kieselguhr. The filtrate was evaporated to dryness under
vacuum, and the residue was dissolved in toluene (5 mL). The
resulting solution of ligand 8 was added to a solution of
(25) MolEN, An Interactive Structure Solution Procedure;
ENRAF-Nonius: Delft, The Netherlands, 1990.
(26) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.
(27) Further details of the crystal structure analysis are available
on request from the Fachinformationszentrum Karlsruhe, Gesellschaft
fu¨r wissenschaftlich-technische Information mbH, D-76344 Eggenstein-
Leopoldshafen, Germany, on quoting the depository numbers CSD-
406694 for 10 and CSD-406695 for 12, the names of the authors, and
this journal citation.
(28) Spek, A. L. Acta Crystallogr. 1990, A46, C34.