A novel chiral ferrocene-based amidine/amidinato ligand and its rhodium complexes

Article abstract of DOI:10.1021/om050845p

The N,N′-bisferrocenyl-substituted chiral formamidine 1 (N,N′-bis[(S)-2-{(1R)-1-(diphenylphosphino)-ethyl}ferrocen-1-yl] formamidine) was prepared from commercially available {(1R)-1-(dimethylamino)- ethyl}ferrocene by a multistep procedure in an overall yield of 29%. Deprotonation of 1 followed by addition of [Rh₂Cl₂(COD) ₂] yielded the (formamidinato)rhodium(I) complex 2 [(N,N′-bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-1-yl] formamidinato)rhodium(I)]. Direct reaction of formamidine 1 with [Rh ₂Cl₂(COD)₂] led to complex 10 [(κ-N,P-bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-1-yl] formamidine)(chloro)(η⁴-1,5-cyclooctadiene)rhodium(I)], which was converted to 2 upon addition of base. Oxidative addition of methyl chloride or methyl iodide to 2 yielded the trans adducts 11 [(N,N′-bis[(S)-2-{(1R)-1- (diphenylphosphino)ethyl}ferrocen-1-yl]formamidinato)(chloro)(methyl) rhodium(III)] and 12 [(N,N′-bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl} ferrocen-1-yl]formamidinato)(iodo)(methyl)-rhodium(III)], the configurations of which were determined by means of NMR and, in the case of the Rh(III) methyl chloride adduct 11, by X-ray analysis.

Full text of DOI:10.1021/om050845p

622
Organometallics 2006, 25, 622-630
A Novel Chiral Ferrocene-Based Amidine/Amidinato Ligand and Its
Rhodium Complexes
Andreas Bertogg and Antonio Togni*
Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology,
ETH Ho¨nggerberg, Wolfgang-Pauli Strasse 10, 8093 Zu¨rich, Switzerland
ReceiVed October 1, 2005
The N,N′-bisferrocenyl-substituted chiral formamidine 1 (N,N′-bis[(S)-2-{(1R)-1-(diphenylphosphino)-
ethyl}ferrocen-1-yl]formamidine) was prepared from commercially available {(1R)-1-(dimethylamino)-
ethyl}ferrocene by a multistep procedure in an overall yield of 29%. Deprotonation of 1 followed by
addition of [Rh2Cl2(COD)2] yielded the (formamidinato)rhodium(I) complex 2 [(N,N′-bis[(S)-2-{(1R)-
1-(diphenylphosphino)ethyl}ferrocen-1-yl]formamidinato)rhodium(I)]. Direct reaction of formamidine 1
with [Rh2Cl2(COD)2] led to complex 10 [(κ-N,P-bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-
1-yl]formamidine)(chloro)(η4-1,5-cyclooctadiene)rhodium(I)], which was converted to 2 upon addition
of base. Oxidative addition of methyl chloride or methyl iodide to 2 yielded the trans adducts 11 [(N,N′-
bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-1-yl]formamidinato)(chloro)(methyl)rhodium(III)]
and 12 [(N,N′-bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-1-yl]formamidinato)(iodo)(methyl)-
rhodium(III)], the configurations of which were determined by means of NMR and, in the case of the
Rh(III) methyl chloride adduct 11, by X-ray analysis.
Scheme 2
Introduction
Mononuclear rhodium complexes bearing amidinato ligands
are very rare,1-4 even though in the recent past an increasing
number of amidinato transition-metal complexes have been
reported.5 Surprisingly, neither molecules with both a phosphane
and an amidinato functionality nor chiral amidinates acting as
N,N-donors have ever been used as ligands in mononuclear
rhodium complexes of known composition. Consequently, the
ability of the latter to act as catalysts in asymmetric catalytic
transformations remains fully unexplored.6 We believe that
chiral amidinato ligands with pendant phosphane side chains
of appropriate size capable of forming chiral mononuclear
rhodium complexes might give access to a new class of chiral
catalyst systems worth exploring. Most importantly, the am-
photeric nature of the amidine functionality in close proximity
to the metal may fulfill the function of taking up or releasing
one proton, thereby taking advantage of its different possible
coordination modes (Scheme 1).5
motif into a ferrocenyl phosphane.8 To the best of our
knowledge, the only published examples of directly ferrocenyl-
substituted amidines are the achiral C-ferrocenyl-containing
amidines reported by Arnold4,9 and by Walton10 and the chiral
and achiral N,N′-bisferrocenyl-substituted amidines reported
from our laboratory.11,12
We disclose here the synthesis of the chiral N,N′-bisferro-
cenyl-substituted chelating phosphane-amidinato ligand 1 and
its Rh(I) complex 2 (Scheme 2). The unique pH-dependent
coordination modes of 1 to form Rh(I) complexes are described
(the latter were analyzed in solution by NMR). The constitutions
and configurations of Rh(III) complexes accessible by oxidative
addition of methyl chloride or methyl iodide have been
determined in solution. Furthermore, X-ray diffraction studies
were performed on the isolated and fully characterized methyl
chloride adduct.
Scheme 1. Possible Coordination Modes of Amidine/
Amidinato Ligands
Ferrocene-based phosphane ligands, on the other hand, are
well established in coordination chemistry and have proven to
be very successful in asymmetric catalysis.7 Nevertheless, no
attempts have been made to incorporate the amidinato structural
(5) For reviews, see: (a) Barker, J.; Kilner, M. Coord. Chem. ReV. 1994,
133, 219-300. (b) Edelmann, F. T. Coord. Chem. ReV. 1994, 137, 403-
481. For recent examples, see: (c) Munslow, I. J.; Wade, A. R.; Deeth, R.
J.; Scott, P. Chem. Commun. 2004, 2596-2597. (d) Li, J.-F.; Huang, S.-P.;
Weng, L.-H.; Liu, D.-S. Eur. J. Inorg. Chem. 2003, 810-813. (e) Zhang,
Y.; Keaton, R. J.; Sita, L. R. J. Am. Chem. Soc. 2003, 125, 8746-8747.
(6) The catalytic hydrogenation of unsymmetrical olefins using systems
consisting of [Rh2Cl2(C8H14)4] and different chiral amidinates was reported
by Brunner et al. Since no complexes were isolated or described, the possible
coordination mode (mono- or multinuclear, monocoordinating or chelating)
of the amidinate and thereby the nature of the catalytic species remain
unclear. The reported ee’s of 1.5-2.0% are low. See: Brunner, H.;
Agrifoglio, G. Monatsh. Chem. 1980, 111, 275-287.
* To whom correspondence should be addressed. E-mail: togni@
inorg.chem.ethz.ch.
(1) Piraino, P.; Tresoldi, G.; Faraone, F. J. Organomet. Chem. 1982,
224, 305-312.
(2) Piraino, P.; Bruno, G.; Tresoldi, G.; Faraone, G.; Bombieri, G. J.
Chem. Soc., Dalton Trans. 1983, 2391-2395.
(3) Lahoz, F. J.; Tiripicchio, A.; Tiripicchio-Camellini, M.; Oro, L. A.;
Pinillos M. T. J. Chem. Soc., Dalton. Trans. 1985, 1487-1493.
(4) Hagadorn, J. R.; Arnold, J. J. Organomet. Chem. 2001, 637-639,
521-530.
10.1021/om050845p CCC: $33.50 © 2006 American Chemical Society
Publication on Web 12/20/2005

Rh Complexes with a Chiral Amidinato Ligand
Organometallics, Vol. 25, No. 3, 2006 623
Scheme 3
represents a highly reactive functionality allowing for a wealth
of transformations, optionally leading to either planar-chiral or
both central and planar-chiral products. Apart from the highly
diastereoselective ionic additions to the vinylic double bond of
5 presented below, vinylferrocenes have been shown to par-
ticipate in pericyclic reactions such as 1,3-dipolar cycloaddi-
tions18 or Diels-Alder19 reactions.
Ligand Synthesis. To synthesize the amino acid 3 from Ugi’s
amine, the latter was lithiated and reacted in situ with gaseous
carbon dioxide following a modified procedure based on a
protocol of Cullen et al. (Scheme 3).20 As a direct elimination
of the amino function in 3 to yield the (S)-1-carboxyl-2-
vinylferrocene 4 could not be accomplished, we developed a
synthetic sequence consisting of three chemical transformations
serving this specific purpose. The methylation of both the amine
and acid functionalities of the amino acid 3 yielded an
intermediate tetraalkylammonium methyl carboxylate which
Results and Discussion
Direct Access to Planar-Chiral Aminoferrocenes. The Cbz-
protected aminoferrocene 5 was synthesized from the com-
mercially available Ugi amine13 in a protocol comprising three
synthetic operations (Scheme 3). Although most synthetic
operations involve more than one chemical transformation, only
one purification step is required. Thus, each of the three synthetic
operations can be accomplished without the isolation of
intermediate species within 1 day at most. The planar-chiral
2-vinyl-substituted Cbz-protected aminoferrocene 5 is easily
recognized as a central intermediate in the synthesis of 1
(Schemes 3 and 4).
We took care to optimize the synthetic steps leading from
the Ugi amine to the carbamate 5 such that they can be carried
out on a large scale. In particular, all three purification steps
were carried out with relatively large amounts of material, and
no column chromatography is required. This highlights the
potential of the pathway presented here to give ready access to
enantiopure planar-chiral aminoferrocenes, a synthetic problem
that has attracted considerable interest in the past due to the
significance of aminoferrocenes as intermediates in the syntheses
of ligands and optically active materials.14-17 Furthermore, the
vinylic double bond in the Cbz-protected aminoferrocene 5
(14) Herberhold, M. Ferrocene Compounds Containing Heteroelements.
In Ferrocenes; Togni, A., Hayashi, T., Eds.; Wiley-VCH: Weinheim, 2002.
(15) Aminoferrocene was first synthesized by Nesmeyanov (ref 16), who
treated lithiated ferrocene with the O-benzyl ether of hydroxylamine and
isolated the product in 25% yield. In the same year Arimoto and Haven
synthesized aminoferrocene (ref 17) from ferrocenyl carboxylic acid by using
the Curtius synthetic strategy, but the overall yield was lower than 20%.
The planar-chiral (R)-1-amino-2-vinylferrocene presented here has not been
described previously.
(7) Togni, A., Hayashi, T., Eds. Ferrocenes; Wiley-VCH: Weinheim,
2002.
(16) Nesmeyanov, A. N.; Perevalova, E. G.; Golovnya, R. V.; Shilovt-
seva, L. S. Dokl. Akad. Nauk. SSSR 1955, 102, 535; Chem. Abstr. 1956,
50, 4925g.
(17) Arimoto, F. S.; Haven, A. C. J. Am. Chem. Soc. 1955, 77, 6295-
6297.
(8) N,N,N′-Trisubstituted chiral amidine ligands, not able to act as
amidinato donors, were reported by Hu, X.; Chen, H.; Dai, H.; Hu, X.;
Zheng, Z. Tetrahedron: Asymmetry 2003, 14, 2073-2080.
(9) (a) Hagadorn, J. R.; Arnold, Inorg. Chem. 1997, 36, 132-133. A
more recent paper describes the in-situ generation of boron complexes
bearing the ligand described by Hagadorn and Arnold. See: (b) Hill, N. J.;
Findlater, M.; Cowley, A. H. J. Chem. Soc., Dalton Trans. 2005, 3229-
3234.
(10) Reddy, N. D.; Fanwick, P. E.; Walton, R. A. Inorg. Chim. Acta
2001, 319, 224-228.
(11) Bertogg, A.; Camponovo, F.; Togni, A. Eur. J. Inorg. Chem. 2005,
347-356.
(18) (a) Shvekhgeimer, G. A.; Litim, M. IzV. Akad. Nauk, Ser. Khim.
1994, 1, 139. (b) Argyropoulos, N.; Coutouli-Argyropoulos, E. J. Orga-
nomet. Chem. 2002, 654, 117-122. (c) Nemeroff, N.; McDonnell, M. E.;
Axten, J. M.; Buckley, L. J. Synth. Commun. 1992, 22, 3271-3275.
(19) (a) Prokesova, M.; Solcaniova, E.; Toma, S.; Muir, K. W.; Torabi,
A. A.; Knox, G. R. J. Org. Chem. 1996, 61, 3392-3397. (b) Klimova, E.
I.; Garcia, M. M.; Klimova, T.; Toledano, C. A.; Toscano, R. A.; Ramirez,
L. R. J. Organomet. Chem. 2000, 598, 254-261. (c) Klimova, T.; Klimova,
E. I.; Martinez Garcia, M.; Alvarez Toledano, C.; Toscano, R. A. J.
Organomet. Chem. 2003, 665, 23-28.
(12) Knox et al. observed N-ferrocenyl-N′,N′-diisopropyl formamidine
as a trace byproduct in the decyanation of isocyanoferrocene. See: Know,
G. R.; Pauson, P. L.; Willison, D. Organometallics 1990, 9, 301-306.
(13) {(1R)-1-(Dimethylamino)ethyl}ferrocene.
(20) (a) Cullen, W. R.; Wickenheiser E. B. Can. J. Chem. 1990, 68,
705-707. (b) Beyer, L.; Richter, R.; Seidelmann, O. J. Organomet. Chem.
1998, 561, 199-201.

624 Organometallics, Vol. 25, No. 3, 2006
Bertogg and Togni
Scheme 4
allowed for a thermal elimination of trimethylamine, thereby
avoiding the risk of lactonization thanks to the methyl protection
of the carboxylic acid function. Saponification of this intermedi-
ate methyl ester then led to the targeted ferrocene carboxylate
4. Several methods to access the ferrocene-nitrogen bond such
as present in 5 have been described in the literature, including
protocols starting from bromoferrocene21 or ferroceneboronic
acid.22 As in our previous syntheses of aminoferrocenes,11 we
chose a different strategy based on a Curtius degradation
sequence that surpasses the aforementioned protocols in terms
of synthetic feasibility and that allows for a high-yielding large-
scale synthesis of the protected aminoferrocene 5. Using DPPA23
(diphenylphosphoryl azide) as both an activating reagent and
azide donor toward 4, we converted the carboxylic acid function
to the corresponding carbonyl azide, which rearranged in situ
to an isocyanate, which was further reacted with benzylic alcohol
to yield carbamate 5.
Tracing the chiral information present in 6 and 9 back to
Ugi’s amine reveals a chirality transfer from an element of
central chirality present in the starting material to the planar
chirality of the ferrocenyl core. In turn, we used this planar
chirality in going from 5 to either 6 or 9 to generate a new
stereocenter. Even though the one present in Ugi’s amine was
lost in the subsequent elimination sequence, its stereochemical
information was preserved in the planar-chiral ferrocene deriva-
tive and was finally recovered by performing diastereoselective
additions to the olefinic double bond of the vinylferrocene 5.
Reacting the latter with 3,5-dimethylpyrazole in acetic acid
yielded the internally hydrogen-bridged24 heterocyclic adduct
925 with a dr ) 9:1, whereas adding diphenylphosphane under
analogous conditions led to the phosphane 6 with complete
diastereoselectivity. We think that this difference in selectivity
is best explained by steric differences between the two
reagents.26
phosphorus lone-pair vector bisects the Cp-CH-CH3 angle,
thus minimizing steric strain (for a drawing and NMR data,
see Experimental Section). Hydrolysis of the Cbz-protected
amine 5 and subsequent reaction of the resulting primary amine
with s-triazine, which acts as a CH group donor,11,27 allows for
the isolation of the amidine 8. In its monoprotonated form, the
potential ligand precursor 8 crystallizes as a hydrogen-bonded
dimer. A representation of the solid-state structure is shown in
Figure 1, and selected bond lengths and angles are given in
Table 1. The observed C-N/CdN bond lengths have to be seen
as a result of the hydrogen-bridged structure, leading to bond
orders between one and two. The dihedral angles between the
ferrocenyl Cp plane and the amidine NdC(H)NH plane appear
to be mainly determined by crystal-packing effects.28
As can be seen in Scheme 4, we chose not to isolate the
aminoferrocene 7 for reasons of synthetic convenience, when
completing the preparation of the amidine 1 by reacting the
crude amine 7 with s-triazine. The access to ligand 1 therewith
consists of five synthetic operations mostly comprising several
chemical transformations and one purification step. Note again
that the first three operations have been performed on a relatively
large scale whereby only the final product requires a chromato-
graphic purification.
Synthesis of Rh(I) and Rh(III) Complexes. Much of our
interest in ligand 1 arises from its amphoteric nature, allowing
for either protonation or deprotonation at the nitrogen atoms,
thus leading to an amidinium cation, a neutral amidine, or an
Hydrolysis of the carbamate function in 6 leads to the air-
sensitive, though thermally stable amine 7, which could be
considered an interesting potential ligand in its own right.
Conformational analysis of the aminoferrocene 7 based on NMR
studies (full assignment and NOESY experiments) revealed
hindered rotation around the Ph2P-C bond such that the
(21) (a) Nesmejanow, A. N.; Ssasonowa, W. A.; Drosd, V. N. Chem.
Ber. 1960, 93, 2717-2729. (b) Sato, M.; Ebine, S.; Akabori, S. Synthesis
1981, 472-473. (c) Herberhold, M.; Ellinger, M.; Kremnitz, W. J.
Organomet. Chem. 1983, 241, 227-240.
(22) Montserrat, N.; Parkins, A. W.; Tomkins, A. R. J. Chem. Res.-
Synop. 1995, 8, 336-337.
Figure 1. ORTEP view of the hydrogen-bridged dimer of 8 (30%
thermal ellipsoids). The hydrogens on N(2) and N(4) were located
and refined.
(23) Ninoma, K.; Shioiri, T.; Yamada, S. Tetrahedron 1974, 30, 2151-
2157.
(24) 1H NMR and NOESY NMR data allowed for the identification of
a hydrogen bridge between the carbamate NH and the pyrazole 2-N, leading
to the formation of a seven-membered ring.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for 8
(25) The Cbz-protected aminoferrocene 9 can be regarded as a nitrogen
analogue of the well-known pyrazole-containing ferrocenyl phosphanes.
See: (a) Schnyder, A.; Hintermann, L.; Togni, A. Angew. Chem., Int. Ed.
Engl. 1995, 34, 931-933. (b) Burckhardt, U.; Hintermann, L.; Schnyder,
A.; Togni, A. Organometallics 1995, 14, 5415-5425. Togni, A.; Burckhardt,
U.; Gramlich, V.; Pregosin, P. S.; Salzmann, R. J. Am. Chem. Soc. 1996,
118, 1031-1037.
C(1)-N(1)
1.262(6)
1.347(6)
1.268(6)
1.347(6)
124.4(4)
124.2(4)
N(2)-H(N2)
1.06(2)
1.08(2)
1.81(2)
2.04(4)
177(5)
161(9)
C(1)-N(2)
N(4)-H(N4)
C(26)-N(3)
C(26)-N(4)
N(1)-C(1)-N(2)
N(3)-C(26)-N(4)
N(3)-H(N2)
N(1)-H(N4)
N(2)-H(N2)-N(3)
N(4)-H(N4)-N(1)

Rh Complexes with a Chiral Amidinato Ligand
Organometallics, Vol. 25, No. 3, 2006 625
Scheme 5
amidinato anion. By assuming that the phosphorus atoms are
not protonated, the maximal theoretical hapticity of the ligand
can be set to either two, three, or four, depending on the presence
of weak acid or base. Thereby, ligand 1 can be used to form
different complexes with a given transition metal.
Reacting a lithium salt obtained after deprotonation of amidine
1 by n-butyllithium with [Rh2Cl2(COD)2] for several hours at
room temperature yields the fully saturated square planar Rh-
(I) complex 2 (Scheme 5).
bidentate PN coordination mode in complex 10. Further NMR
data supporting the structure of Rh(I) complex 10 can be found
in the Experimental Section. As expected, addition of base to
compound 10 led to the square-planar Rh(I) complex 2. The
observation that complex 2 can be accessed either by reacting
the lithium formamidinate with [Rh2Cl2(COD)2] or by simply
mixing 1 with [Rh2Cl2(COD)2], followed by the addition of base,
is crucial with regard to the use of 2 as catalyst under basic
reaction conditions.
Attempts to oxidatively add either methyl chloride or methyl
iodide to complex 2 proved successful and yielded both the Rh-
(III) complexes 11 and 12, respectively (Scheme 6). Most
probably, the anionic nature of the chelating formamidinato unit
and its ability to act as σ donor allow the oxidative addition of
methyl chloride to occur quickly at room temperature. We look
at this addition reaction as an initial experiment in the context
of the application of 2 as a catalyst in asymmetic transformations
involving oxidative addition and reductive elimination steps of
substrate molecules. That both 11 and 12 are formed as single
configurational isomers deserves mention. Obviously, this
complete selectivity in activating both methyl chloride and
methyl iodide, molecules that are generally thought to react via
different transition states, defines a promising starting point for
asymmetric catalysis studies.
Structure Elucidation of Rh(III) Complexes in Solution
and in the Solid State. While the structure elucidation proved
simple for the C2-symmetric Rh(I) complex 2, the configurations
of the methyl halide adducts 11 and 12 are less easily assigned
as a result of the considerable number of possible stereoiso-
mers.29 We discuss here the structure elucidation of 11;
anologous data for 12 can be found in the Experimental Section.
The 31P NMR spectral data proved crucial in view of
establishing the oxidation state of the Rh center by means of
However, shorter reaction times disclose the intermediate
formation of a Rh(I) species A of uncertain structural assignment
that reacts cleanly to the target compound 2 over several hours.
Even though a complete NMR characterization of this inter-
mediate species proved impossible due to its reactivity, the 31
P
NMR data strongly suggests the bidentate coordination mode
of the amidinato phosphane ligand. Evidence comes from the
inequivalence of the two phosphorus resonances out of which
one displays a 103Rh/31P coupling constant of 138 Hz at a
chemical shift of 54.0 ppm, thus demonstrating phosphorus
coordination, while the other one appears at higher field as a
singlet. Chloride and 1,5-cyclooctadiene complete the coordina-
tion sphere of the 18-e Rh(I) center.
To gain further evidence for the intermediate species and due
to our interest in the different coordination modes of amidines
and amidinates, we reacted amidine 1 with [Rh2Cl2(COD)2]
without prior deprotonation. The five-coordinate Rh(I) complex
10 was identified as the reaction product by performing
extensive NMR studies on the product solution. In addition to
the spectral data discussed above, 103Rh/1H coupling between
the Rh center and the formamidinate CH proton proves the
(26) Substitution reactions at planar-chiral derivatives of Ugi’s amine
occurring with replacement of the dimethylamino group by an incoming
nucleophile often proceed with high levels of diastereoselectivity. Since
such substitution reactions are known to follow a SN1 pathway in acetic
acid as a solvent, the intermediate carbocation is easily recognized as a
common intermediate in both the SN1 reactions and the addition reactions
presented here. Therefore, one must assume that the levels of diastereose-
lectivity for substitution reactions and addition reactions are based in either
case on the steric requirement of both the attacking reagent and the
substituent in ortho position. The nature of the leaving group and the way
in which the carbocation is generated, on the other hand, do not influence
the diastereoselectivity of the reaction.
Scheme 6
(27) Grundmann, C.; Kreutzberger, A. J. Am. Chem. Soc. 1955, 77,
6559-6562.
(28) For a conformational analysis of N-ferrocenyl-substituted N-
heterocyclic carbenes see ref 11.

626 Organometallics, Vol. 25, No. 3, 2006
Bertogg and Togni
Figure 2. NOESY contacts between the metal-bound methyl group
and hydrogen atoms (encircled) of the chelating ligand.
the 31P/103Rh coupling constantssJ(31P(a)/103Rh) ) 134 Hz;
J(31P(b)/103Rh) ) 131 Hz30swhile the 31P/31P coupling constantss
J(31P(a)/31P(b)) ) 18 Hzsprovided evidence for the mutual cis
arrangement of the two phosphorus atoms in the Rh(III)
complex. The 31P/1H couplingssJ(31P(a)/1H(Me)) ) 2.2 Hz;
J(31P(b)/1H(Me)) ) 2.2 Hzsmeasured by means of 1H NMR and
31P/1H correlation spectroscopy, provide direct evidence for the
methyl-rhodium bond. Furthermore, the couplings from either
phosphorus nuclei to their adjacent methyne and methyl groups,
as well as to the formamidinato proton, are indicative of the
tetradentate coordination mode of the formamidinato ligand. The
103Rh/1H correlation data gave additional evidence for this
coordination mode and provided the coupling constants between
the Rh(III) center and the hydrogen nuclei in its vicinity.
Conformational analysis of the two six-membered chelate rings
in the Rh(NP) structural motif based on those coupling constants
between the 103Rh nucleus and the two methyne hydrogen
Figure 3. ORTEP view of the Rh(III) complex 11 (30% thermal
ellipsoids).
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 11
N(1)-Rh
N(2)-Rh
C(50)-Rh
P(1)-Rh
P(2)-Rh
Cl-Rh
2.075(6)
N(1)-Rh-N(2)
N(1)-Rh-P(1)
N(2)-Rh-P(2)
P(1) -Rh-P(2)
N(1)-C(25)-N(2)
C(50)-Rh-Cl
C(25)-N(2)
63.4(3)
94.23(18)
93.73(19)
108.63(7)
109.9(7)
173.3(2)
1.311(10)
2.055(6)
2.071(6)
2.2824(19)
2.2623(19)
2.4998(19)
1.340(10)
C(25)-N(1)
is best described as an octahedral complex with a strongly
distorted arrangement of the donor atoms in a regular equatorial
plane occupied by the tetradentate formamidinato ligand. On
the other hand, the axial methyl and chloride ligands lie almost
in linesangle C(50)-Rh-Cl 173.3(4)°sand show the expected
bond lengths to the metalsC(50)-Rh 2.071(6) Å; Cl-Rh 2.4997-
(19) Å. Conformational freedom in the two six-membered
chelate rings appears to be rather restricted, partly due to the
necessity for phosphorus and nitrogen atoms to lie in the
equatorial coordination plane and partly due to the well-known
tendency of derivatives of Ugi’s amine to give rise to small
dihedral angles between the ferrocene Cp planes and their
atomss1,4J(103Rh/1H(methyne a)) ) 0.6 Hz; 1,4J(103Rh/1H(methyne b)
)
) 0.5 Hzsas compared to the couplings between 103Rh and
the formamidinato hydrogen atoms1,4J(103Rh/1H(formamidinato)) )
3.0 Hzsis not possible, as coefficients for an appropriate
Karplus equation are not available. Nevertheless, the apparent
pseudosymmetry of the formamidinato ligand with very similar
103Rh/1H couplings to either methyne hydrogen atom strongly
supports an equatorial arrangement of the tetradentate ligand.
The final proof for this trans chelation mode, thus ruling out
all other possible stereoisomers, is based on NOESY spectral
data that display contacts of the metal-bound methyl group to
parts of the formamidinato ligand, as expected for an equatorial
ligand arrangement (Figure 2). Most importantly, the observed
NOESY contacts between the metal-bound methyl group and
the ortho hydrogen atoms of both R-phenyl groups at phosphorus
P(a) and phosphorus P(b) are only consistent with an equatorial
arrangement of the tetradentate ligand. Furthermore, the contacts
to the methyne(b) hydrogen atom, to Cp(b), and to the forma-
midinato hydrogen atom clearly prove the trans Rh(III) complex
to be the only isomer of 11 present in solution.
neighboring methyl groups (dihedral angles C(24)-C(23)-C(14)
-
C
(15) 6.3(12)°; C(12)-C(11)-C(2)-C(3) -13.4(11)°). The bite angle
N(1)-Rh-N(2) of 63.4(3)° as well as the bond lengths of the
formamidinato unit are in a surprisingly exact agreement with
the sparse structural data available for Rh amidinato com-
plexes.3,4 In fact, two X-ray structures of mononuclear Rh
complexes containing amidinato ligands are known in the
literature. However, in contrast to the Rh(III) complex discussed
here, these are Rh(I) compounds. Although both of those
complexes lack further chelating atoms, they nevertheless exhibit
bonding parameters very similar to the ones measured for 11.
Therefore, one may assume that in 11 the position of the Rh-
(III) core is mainly determined by the formamidinato unit,
whereas the two phosphorus donor atoms further stabilize the
structure by creating a cavity that fits the radius of the Rh(III)
center. The two P/N bite angles of 93.73(19)° and 94.22(18)°
and the normal Rh-P bond lengths P(1)-Rh of 2.2824(19) Å
and P(2)-Rh of 2.2623(19) Å account for this view, whereas
the slight bending of the formamidinato unit out of the N/Rh/N
planesdihedral angle Rh-N(1)-C(25)-N(2) 10.0(4)°sis probably
best explained by crystal-packing effects.
Single-crystal X-ray analysis of the Rh(III) complex 11
revealed a structure that is in complete agreement with the
observed configuration in solution. The solid-state structure is
represented in Figure 3, whereas selected bond lengths and
angles can be found in Table 2. The organometallic species 11
(29) Ordering those possible isomers according to the arrangement of
the tetradentate ligand in the complex discloses one trans, two R-cis, and
four â-cis configurations. Only in the trans configuration does the ligand
not adopt a helical conformation. In the R-cis arrangement and in the â-cis
arrangement on the other hand, the helicity mentioned above gives rise to
∆ and Λ isomers. Furthermore, the â-cis arrangement allows for two
additional isomers by exchanging the two nonequivalent monodentate
ligands. As a result of the chirality of the formamidinato ligand, all seven
possible isomers are diasteroisomeric with respect to each other.
(30) For a collection of 31P and 13C NMR data on transition-metal
complexes see: Pregosin, P.; Kunz, R. W. 31P and 13C NMR of Transition
Metal Phosphine Complexes; Springer: Berlin, 1979.
Conclusions
The N,N′-bisferrocenyl-substituted chiral formamidine 1 was
prepared in 29% overall yield from the commercially available

Rh Complexes with a Chiral Amidinato Ligand
Organometallics, Vol. 25, No. 3, 2006 627
Ugi amine13 by applying a synthetic strategy exploiting a Curtius
degradation as the key step. As a direct product of the latter,
the planar-chiral, N-protected 2-vinyl aminoferrocene 5 not only
serves as a precursor to 1 but also allows for accessing planar-
chiral aminoferrocenes on a large synthetic scale in a short and
reliable synthetic route.
Deprotonation of the formamidine 1 followed by addition of
[Rh2Cl2(COD)2] yielded the (formamidinato)rhodium(I) complex
2, whereas in the absence of base the (chloro)(1,5-cycloocta-
diene)(formamidine)rhodium(I) complex 10 was formed. No-
tably, formamidine 1 acts as a P,N-bidentate ligand in 10, while
its anionic counterpart acts as a tetradentate donor in derivative
2. The latter was also accessible by adding base to a solution
of 10. These pH-dependent coordination modes of the amidinato/
amidine ligand system account for its ability to act as a proton
scavenger, which is of considerable interest with regard to
catalytic transformations. Currently, efforts are being undertaken
to use both 2 and 10 as catalysts, thereby taking advantage of
the amphoteric nature of ligand 1.
To study the activity of 2 toward the oxidative addition of
alkyl halides, we reacted it with both methyl chloride and methyl
iodide to give the corresponding Rh(III) complexes 11 and 12.
The configuration of the three complexes 2, 11, and 12 is such
that the four donor atoms share the main equatorial plane in
the coordination sphere of the metal. We think that this indicates
a significant conformational rigidity of the ligand in its
tetradentate form, which may be important in view of asym-
metric catalytic applications.
the immediate formation of a yellow solid. To make sure that the
lithiated intermediate had reacted completely, ca. 30 g of CO2(S)
was added to the reaction mixture followed by its slow warming
to rt. Then, the solvent was evaporated and a solution of the crude
product in MeOH was quickly filtered on silica gel (400 g, column
φ ca. 9 cm). After evaporation of the solvent, the crude product
was taken up in CH2Cl2, and the solution was dried over MgSO4,
filtered, and evaporated under reduced pressure, affording the
isolation of the title compound as a red amorphous solid. Yield:
1
27.6 g (95%). H NMR (CDCl3, 300.1 MHz): δ 1.42 (d, J ) 6.6
Hz, 3 H, CHCH3), 2.05 (bs, 3 H, NCH3CH3), 2.56 (bs, 3 H,
NCH3CH3), 4.20 (s, 5 H, Cpunsubst), 4.27-4.32 (m, 2 H, CHCp subst),
4.54 (q, J ) 6.8 Hz, 1 H,CHCH3), 5.02 (dd, J1 ) 2.4 Hz, J2 ) 1.5
Hz, 1 H, CHCp subst). CAS 211574-86-6 (other enantiomer), CAS
128713-34-8 (racemate).
(S)-1-Carboxyl-2-vinylferrocene (4). Treating a mixture of
compound 3 (25.43 g, 85.30 mmol, 1 equiv), K2CO3 (94.58 g, 684
mmol, 8 equiv), and acetone (510 mL) with MeI (43.67 mL, 684
mmol, 8 equiv) led to a clear, deep red solution with an underlying
precipitate (K2CO3) that was stirred at rt for 3.5 h. Filtration and
evaporation of the volatiles resulted in the formation of a red foam,
which was taken up in benzene (760 mL) and heated at 85 °C for
45 min. The red oil, which was isolated after filtration and
evaporation of the volatiles, was mixed with EtOH (450 mL), H2O
(450 mL), and NaOH (10.28 g, 256 mmol, 3 equiv) and stirred at
60 °C for 13 h. Addition of MTBE at rt, acidification, separation
of the resulting organic phase, drying over MgSO4, and evaporation
of the solvents afforded 4 as a yellow amorphous solid. Yield: 15.99
g (73%). 1H NMR (CDCl3, 300.1 MHz): δ 4.23 (s, 5 H, Cpunsubst),
4.53 (t, J ) 2.6 Hz, 1 H, CHCp subst), 4.85 (t, J ) 1.8 Hz, 1 H, CHCp
subst), 4.95 (dd, J1 ) 2.4 Hz, J2 ) 1.5 Hz, 1 H, CHCp subst), 4.95 (dd,
J1 ) 2.4 Hz, J2 ) 1.5 Hz, 1 H, CHCp subst), 5.22 (dd, J1 ) 10.8 Hz,
J2 ) 1.5 Hz, 1 H, CHCH2), 5.53 (dd, J1 ) 17.7 Hz, J2 ) 1.5 Hz,
1 H, CHCH2t), 7.27 (dd, J1 ) 17.7 Hz, J2 ) 10.8 Hz, 1 H, CHCH2).
13C{1H} NMR (CDCl3, 75.5 MHz): δ 69.1 (Cpsubst), 70.8
(Cpsubst,quat), 71.2 (Cpsubst), 71.4 (Cpunsubst), 72.3 (Cpsubst), 86.1
(Cpsubst,quat), 113.5 (Colefin), 133.2 (Colefin), 178.7 (CO2H). MS (HR
MALDI): m/z 256.0187 (calcd for C13H12FeO2); found 256.0181
[M+]. C13H12FeO2 (256.08): calcd C 60.97, H 4.72, O 12.5, Fe
21.81; found C 60.77, H 4.85. Mp ) 115.5 °C. [R]22 ) +820 (c 1,
CHCl3).
Experimental Section
General Considerations. All experiments were conducted under
an atmosphere of argon or dinitrogen using standard Schlenk-type
glassware or a glovebox. All solvents were stored over activated 4
Å molecular sieves unless otherwise indicated. In the case of freshly
distilled solvents, the following drying agents were used: Na/
benzophenone for THF and Et2O; Na for toluene, benzene, C6D6,
and d8-THF. Chromatography was carried out with Merck silica
gel 60. The NMR spectra were recorded on Bruker Avance 250
(250.1 MHz, 1H; 62.5 MHz, 13C; 101 MHz, 31P), 300 (300.1 MHz,
1H; 75.0 MHz, 13C; 122 MHz, 31P), 500 (500.2 MHz, 1H; 125 MHz,
1
13C; 203 MHz, 31P; 15.9 MHz, 103Rh), and 700 (700.1 MHz, H;
175 MHz, 13C; 284 MHz, 31P; 22.2 MHz, 103Rh) spectrometers. 1H
NMR, 13C NMR, 31P NMR, and 103Rh NMR chemical shifts (δ)
were referenced internally by the residual solvent signal. All spectra
were recorded at room temperature. Optical rotations were measured
in 1 dm cells on a Perkin-Elmer model 341 polarimeter at 22 °C.
High-resolution MALDI mass spectra were measured by the
analytical service of the Laboratorium fu¨r Organische Chemie of
the ETH Zu¨rich on a IonSpec ultima FT MALDI mass spectrometer.
Elemental analyses were obtained on a Leco CHN-900 analyzer.
All commercially available chemicals were used without further
purification. We were generously supplied with {(1R)-1-(dimeth-
ylamino)ethyl}ferrocene (ee ≈ 96%) by Solvias AG (Basel,
Switzerland). Prior to use, the latter was recrystallized as tartrate
salt according to the procedure reported by Gokel et al.31 in order
to completely separate it from its antipode.
(1S)-1-Carboxyl-2-{(1R)-1-(dimethylamino)ethyl}ferrocene (3).
In a flame-dried 1 L Schlenk vessel, optically pure [(1R)-1-
(dimethylamino)ethyl]ferrocene (24.81 g, 96.50 mmol, 1 equiv) was
dissolved in 200 mL of freshly distilled Et2O, cooled to -78 °C,
and treated with tBuLi (59.6 mL, 101.3 mL, 1.05 equiv). After
stirring for 1 h, the clear red solution was warmed to rt and further
stirred for 3 h, which resulted in the formation of a yellow
precipitate. The addition of CO2(g) during 1 h at -78 °C caused
Benzyl N-{(S)-2-Vinylferrocenyl}carbamate (5). Dry NEt3
(9.82 mL, 70.3 mmol, 1.5 equiv) and diphenylphosphoryl azide
(11.3 mL, 51.5 mmol, 1.1 equiv) were added in this order to a
solution of 4 (11.97 g, 46.80 mmol, 1 equiv) in freshly distilled
toluene (68 mL) at rt. The clear, deep red solution was stirred for
20 min and then quickly heated to 95 °C. After 10 min the formation
of a gas (N2) was observed. Thirty minutes later benzylic alcohol
(9.70 mL, 93.6 mmol, 2.0 equiv) was added, and after another 5
min of stirring at 95 °C, the reaction mixture was cooled to rt.
Extraction with MTBE/H2O, drying of the organic phases with
MgSO4, and evaporation of the solvents gave a crude product that
was purified by filtration on passivated aluminum oxide (basic,
activity II) to give 5 as an amorphous red solid. Yield: 12.00 g
(71%). 1H NMR (CDCl3, 300.1 MHz): δ 4.10 (s, 5 H, Cp A), 4.11
(dd, J1 ) 2.7 Hz, J2 ) 2.7 Hz, 1 H, Cp D), 4.31 (t, J ) 2.7 Hz, 1
H, Cp C), 4.81 (bs, Cp B), 5.18 (dd, J1 ) 11.1 Hz, J2 ) 1.5 Hz, 1
H, vinyl F), 5.18 (s, 2 H, methylene E), 5.42 (dd, J1 ) 17.7 Hz, J2
) 1.5 Hz, 1 H, vinyl H), 6.02 (bs, 1H, NH), 6.50 (dd, J1 ) 17.5
Hz, J2 ) 10.8 Hz, 1 H, vinyl G), 7.32-7.45 (m, 5 H, phenyl J,K,L).
13C{1H} NMR (CDCl3, 75.5 MHz): δ 62.5 (D), 63.9 (B), 64.9
(31) Gokel, G. W.; Ugi, I. K. J. Chem. Educ. 1972, 49, 294-296.

628 Organometallics, Vol. 25, No. 3, 2006
Bertogg and Togni
(C), 67.2 (E), 70.4 (A), 76.1 (P), 92.9 (O), 113.2 (F,H), 127.9 (K,L),
128.6 (J), 131.4 (G), 136.2 (M), 154.2 (N). MS (HR MALDI): m/z
361.0765 (calcd for C20H19FeNO2); found 361.0760 [M+]. C20H19-
FeNO2 (361.22): calcd C 66.50, H 5.30, N 3.88, O 8.86, Fe 15.46;
found C 66.31, H 5.32, N 3.87. [R]22 ) +167 (c 1, CHCl3).
F), 104.0 (s, E), 128.2 (P), 128.5 (Q), 128.8 (d, JP ) 6.8 Hz, L),
129.4 (M), 133.7 (d, JP ) 17.4 Hz, O), 134.9 (d, JP ) 19.9 Hz, K),
136.9 (d, JP ) 18.6 Hz, J), 138.7 (d, JP ) 18.7 Hz, N). 31P NMR
(C6D6 121.5 MHz): δ 3.9. MS (HR MALDI): m/z 413.0996 (calcd
for C24H24FeNP); found 413.0950 [MH+]. C24H24FeNP (413.27):
calcd C 69.75, H 5.85, N 3.39 P 7.49, Fe 13.51; found C 69.46, H
6.10, N 3.32. The optical rotation and the melting point of 7 were
not determined due to its air sensitivity.
N,N′-Bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-1-
yl]formamidine (1). A suspension of 6 (2.45 g, 4.48 mmol) in
iPrOH (30 mL) and H2O (20 mL) was degassed with Ar using an
ultrasonic bath and then treated with KOH (11.0 g). Stirring at 90
°C for 12 h led to a clear, red organic phase and a colorless aqueous
phase. Drying of the organic phase with MgSO4, filtration, and
evaporation of the solvents gave 7 as a orange to red solid. After
the addition of s-triazine (2.25 g, 27.8 mmol, 6.2 equiv) and dioxane
(6.0 mL), the resulting solution was stirred at 90 °C for 21 h and
the solvent was evaporated at reduced pressure using a distillation
apparatus. The product 1 was isolated as an orange foam after
column chromatography (SiO2, hexane/AcOEt/NEt3 ) 3:1:0.04).
Benzyl N-[(S)-2-{(1R)-1-(Diphenylphosphino)ethyl}ferrocenyl]-
carbamate (6). Diphenylphosphane (3.86 mL, 22.2 mmol, 4 equiv)
was added to a solution of 5 (2.00 g, 5.54 mmol, 1 equiv) in dry
acetic acid (9.0 mL) at rt. Stirring for 16 h at 65 °C, evaporation
of the solvent and of excess diphenylphosphane under reduced
pressure using a distillation apparatus, and washing with pentane
yielded a crude product that was recrystallized from iPrOH to give
6 as a red crystalline solid. Yield: 2.51 g (83%). Since no signal
1
Yield over the two steps from 6 to 1: 1.42 g (72%). H NMR
(CDCl3, 250.1 MHz): δ 1.54 (q, J ) 6.9 Hz, 6 H, 2 CH3), 3.44
(dq, Jq ) 6.5 Hz, Jd ) 6.0 Hz, 2 H, 2 CHmethyne), 3.93-3.99 (m, 4
H, 4 CHCp subst), 4.06-4.19 (m, 12 H, 2 CHCp subst and 2 Cpunsubst),
6.86 (s, 1 H, CHformamidinato), 6.99-7.08 (m, 4 H, CHarom.), 7.11-
7.19 (m, 4 H, CHarom.), 7.19-7.25 (m, 2 H, CHarom.), 7.36-7.43
(m, 6 H, CHarom.), 7.50-7.58 (m, 4 H, CHarom.). 13C{1H} NMR
(CDCl3, 62.9 MHz): δ 18.2 (bs, 2 CH3 methyl), 29.1 (bs, 2 CHmethyne),
63.1 (s, 2 CHCp subst), 63.2 (s, 2 CCp subst), 64.1 (s, 2 CHCp subst), 64.7
(s, 2 CCp subst), 69.5 (s, 2 Cpunsubst), 69.8 (s, 2 CHCp subst), 127.9 (2
CHarom.), 128.0 (2 CHarom.), 129.0 (2 CHarom.), 129.0 (2 CHarom.),
133.2 (2 CHarom.), 134.7 (2 CHarom.), 136.5 (2 CHarom.), 138.1 (2
CHarom.), 147.9 (bs, CHformamidinate). 31P NMR (CDCl3 101.3 MHz):
δ 6.1. IR (CHCl3) ν˜(cm-1) 1640 {ν(CdN) of amidine}. MS (HR
MALDI): m/z 837.1908 (calcd for C49H47Fe2N2P2); found 837.1916
[MH+]. C49H46Fe2N2P2‚1/2AcOEt (880.59): calcd C 69.56, H 5.72,
N 3.18, O 1.82, P 7.03, Fe 12.68; found C 69.58, H 5.70, N 3.21.
[R]22 ) -633 (c 1, CHCl3).
1
of a diastereomeric species could be detected in either the H or
31P NMR spectra, we assume a dr > 100:1. 1H NMR (CDCl3, 250.1
MHz): δ 1.55 (q, J ) 7.0 Hz, 3 H, A), 3.25 (dq, Jq ) 6.8 Hz, Jd
) 4.3 Hz, 1 H, B), 3.87-3.89 (m, 1H, E), 3.99 (dd, J1 ) 2.6 Hz,
J2 ) 2.6 Hz, 1 H, D), 4.12 (s, 5 H, T), 4.59 (bs, 1 H, C), 4.81 (bs,
1 H, NH), 4.98-5.11 (m, 2 H, H,J), 6.99-7.18 (m, 5 H, P,Q,R.),
7.31-7.45 (m, 8 H, L-N,X-Z), 7.49-7.58 (m, 2 H, L-N,X-Z).
13C{1H} NMR (CDCl3, 62.9 MHz): δ 18.2 (d, J ) 18.2 Hz, A),
30.0 (d, J ) 15.0 Hz, B), 59.9 (s, C), 63.2 (s, E), 63.4 (s, D), 66.7
(s, H,J), 69.5 (s, T), 83.1 (d, J ) 14.7 Hz, V), 93.9 (s, U), 128.0-
129.3 (m, L-N,Q-R,Y-Z), 133.0 (d, J ) 17.6 Hz, P), 134.0 (d,
J ) 19.6 Hz, X), 135.9 (d, J ) 16.0 Hz, O or W), 136.3 (d, J )
16.7 Hz, O or W), 153.3 (s, S). 31P NMR (CDCl3 101.3 MHz): δ
3.4. MS (HR MALDI): m/z 548.1442 (calcd for C32H31FeNO2P);
found 548.1436 [MH+]. C32H30FeNO2P (547.40): calcd C 70.21,
H 5.52, N 2.56, O 5.85, P 5.66, Fe 10.20; found C 69.99, H 5.63,
N 2.53, P 5.76. Mp ) 153.5 °C. [R]22 ) -375 (c 1, CHCl3).
N,N′-Bis{(S)-2-vinylferrocen-1-yl}formamidine (8). The Cbz-
protected aminoferrocene 5 (605 mg, 1.67 mmol, 1.0 equiv) was
suspended in iPrOH (12 mL) and KOH(aq) (12 mL, 5 M) and
quickly heated to 90 °C. After stirring for 4 h and cooling to rt, the
organic phase was separated from the aqueous layer, dried with
MgSO4, filtered, and concentrated to dryness under reduced
pressure. The orange solid was mixed with s-triazine (679 mg, 8.37
mmol, 5.0 equiv), dissolved in dioxane (3.0 mL), degassed, and
stirred at 100 °C for 28 h. After the addition of another portion of
s-triazine (679 mg, 8.37 mmol, 5.0 equiv) and further stirring for
26 h and cooling to rt, the reaction mixture was concentrated to
dryness under reduced pressure. Excess s-triazine was sublimed
by heating during 3 h at 80 °C, after which the crude product
obtained was subjected to column chromatography (SiO2, hexane/
EtOAc/NEt3 ) 3:1:0.04). Yield: 143 mg (37%) of a red amorphous
(S)-2-{(1R)-1-(Diphenylphosphino)ethyl}aminoferrocene (7;
the picture shows its conformation in solution). A suspension of 6
(2.39 g, 4.36 mmol) in iPrOH (30 mL) and H2O (30 mL) was
degassed with Ar using an ultrasonic bath and then treated with
KOH (16.5 g, results in a 9.8 M aqueous solution). Stirring at 90
°C for 17 h led to a clear, red organic phase and a colorless aqueous
phase. Drying of the organic phase with MgSO4, filtration, and
evaporation of the solvents gave 7 as a red solid. Yield: 1.66 g
(92%). For the yield of the direct conversion of 6 to 1 see the next
1
solid. H NMR (CDCl3, 250.1 MHz): δ 4.10-4.14 (m, 12 H, 10
CHCp subst and 2 CHCp unsubst), 3.34-3.38 (m, 2 H, 2 CHCp unsubst),
3.38-4.40 (m, 2 H, 2 CHCp unsubst), 5.20 (dd, J1 ) 11.0 Hz, J2 )
1.5 Hz, 1 H, vinyl H), 5.51 (dd, J1 ) 17.5 Hz, J2 ) 1.5 Hz, 1 H,
vinyl H), 6.67 (dd, J1 ) 17.5 Hz, J2 ) 11.0 Hz, 1 H, vinyl H),
8.00 (s, 1 H, CHformamidinato). 13C{1H} NMR (CDCl3, 125.8 MHz):
δ 61.1 (2 CH, Cpsubst), 63.2 (2 CH, Cpsubst), 64.8 (2 CH, Cpsubst),
70.6 (2 CH, Cpunsubst), 76.8 (2 C, Cp subst), 101.8 (2 C, Cpsubst), 113.0
(CHvinyl), 132.4 (CH2 vinyl), 151.5 (CHformamidinate). MS (HR MAL-
DI): m/z 465.0717 (calcd for C25H25Fe2N2); found 465.0703 [MH+].
C25H24Fe2N2 (464.17): calcd C 64.69, H 5.21, Fe 24.06, N 6.04;
found C 64.52, H 5.38, N 6.07. [R]22 ) -66.2 (c 1, CHCl3).
Benzyl N-[(S)-2-{(1R)-1-(3,5-dimethylpyrazol-1-yl)ethyl}-
ferrocenyl]carbamate (9). 3,5-Dimethylpyrazole (639 mg, 6.65
mmol, 5 equiv) was added to a solution of 5 (500 mg, 1.38 mmol,
1 equiv) in dry acetic acid (30 mL) at room temperature. Stirring
1
paragraph. H NMR (C6D6 500.2 MHz): δ 1.53 (bs, 2 H, NH2),
1.67 (dd, J1 ) 7.0 Hz, J2 ) 6.5 Hz, 3 H, H), 3.59 (dq, Jq ) 3.0 Hz,
Jd ) 6.0 Hz, 1 H, G), 3.79 (t, J ) 2.0 Hz, 1 H, D), 3.83 (t, J ) 2.5
Hz, 1 H, C), 3.89-3.90 (m, 1 H, B), 4.12 (m, 5 H, A), 7.05-7.11
(m, 3 H, P,Q), 7.23-7.29 (m, 3 H, L,M), 7.33-7.38 (m, 2 H, O),
7.67-7.72 (m, 2 H, K). 13C{1H} NMR (C6D6, 125.8 MHz): δ 18.6
(d, JP ) 17.9 Hz, H), 29.9 (d, JP ) 15.2 Hz, G), 59.9 (s, D), 61.9
(s, C), 63.4 (d, JP ) 4.7 Hz, B), 69.8 (s, A), 84.2 (d, JP ) 16.1 Hz,

Rh Complexes with a Chiral Amidinato Ligand
Organometallics, Vol. 25, No. 3, 2006 629
for 105 min at 60 °C and evaporation of the solvent under reduced
pressure yielded a mixture of the crude product and residual 3,5-
dimethylpyrazole. The product was purified by column chroma-
tography (SiO2, hexane/EtOAc/NEt3 ) 10:1:0.05). Yield: 450 mg
(82%) of a red oil. The dr of 9:1 was determined by integration of
relevant peaks in the H NMR spectrum. H NMR (CDCl3, 300.1
MHz): δ 1.67 (d, J ) 7.2 Hz, 3 H, CHCH3), 2.25 (s, 3 H, CCH3),
2.36 (s, 3 H, CCH3), 3.81 (s, 5 H, CHCp unsubst), 3.90-3.92 (m, 2
H, 2 CHCp subst), 5.04 (q, J ) 7.2 Hz, 1 H, CHCH3), 5.15-5.27 (m,
3 H, CH2 and CHCp subst), 5.84 (s, 1 H, CHtriazole), 7.31-7.44 (m, 5
H, CHphenyl), 10.06 (bs, 1 H, NH).
and Its Conversion to (N,N′-Bis[(S)-2-{(1R)-1-(diphenylphos-
phino)ethyl}ferrocen-1-yl]formamidinato)rhodium(I) (2). The
formamidine ligand 1 (76.0 mg, 90.8 µmol, 1 equiv) was dissolved
in freshly distilled C6D6 (2.4 mL) at rt. Addition of [Rh2Cl2(COD)2]
(22.4 mg, 45.4 µmol, 0.5 equiv) resulted in the immediate formation
of 10. Upon addition of KOtBu (15.3 mg, 136 µmol, 1.5 equiv),
1
1
1
10 was converted in situ to 2, as ascertained by H NMR and 31P
NMR. 1H NMR (C6D6, 500.2 MHz): δ 1.13 (t, JP ) 8.4 Hz, 3 H,
CH3(methyl a)), 1.60-1.71 (m, 5 H, CH3(methyl b) + CH2(COD)), 2.10-
2.19 (m, CH2(COD)), 2.26-2.38 (m, CH2(COD)), 3.08-3.12 (m,
CH(Xa)), 3.12-3.23 (m, CH2(COD)), 3.42-3.50 (m, 1 H, CH(methyne
a)), 3.55-3.58 (m, CH(Ya)), 3.58-3.61 (m, CH(Xb)), 3.86-3.90 (m,
CH(Yb)), 3.91-3.95 (m, CH(Za)), 4.11-4.19 (m, 7 H, Cp(a)
+
CH(COD)), 4.20-4.28 (m, CH(COD)), 4.43-4.46 (m, CH(Zb)), 4.58
(s, 5 H, Cp(b)), 5.35-5.45 (m, 1 H, CH(methyne b)), 7.20-7.25 (m, 4
CH, phenylâ(b) para + phenylâ(b) meta + phenylâ(a) para), 7.25-7.29 (m,
2 H, phenylâ(a) meta), 7.32 (t, J ) 7.5 Hz, 1 H, phenylR(b) para), 7.36
(t, J ) 7.1 Hz, 1 H, phenylR(a) para), 7.43 (t, J ) 7.1 Hz, 2 H,
phenylR(a) meta), 7.50 (t, J ) 7.5 Hz, 2 H, phenylR(b) meta), 7.58 (t, J
) 7.1 Hz, 2 H, phenylR(a) ortho), 7.69-7.75 (m, 2 H, phenylâ(b) ortho)
,
7.87 (t, J ) 7.3 Hz, 2 H, phenylâ(a) ortho), 8.20 (t, J ) 6.4 Hz, 2 H,
phenylR(b) ortho), 8.49 (d, J ) 9.7 Hz, 1 H, CHformamidinato), 12.44 (d,
J ) 9.7 Hz, 1 H, NH). 13C{1H} NMR (C6D6, 125.0 MHz): δ 11.4-
11.6 (m, CH3(methyl a)), 16.0 (CH3(methyl b)), 28.6 (CH(methyne b)), 28.7
(CH2(COD)), 29.8 (d, JP(a) ) 8.7 Hz, CH(methyne a)), 35.0 (CH2(COD)),
61.2 (CH(Ya)), 61.8 (CH(Za)), 63.7 (CH(Xa)), 64.0 (CH(Yb)), 65.2
(CH(Zb)), 65.4 (CH(Xb)), 69.8 (Cp(a)), 70.6 (Cp(b)), 73.7 (2 CH(COD)),
83.5 (2 CH(COD)), 84.6 (C(Va)), 87.0 (C(Vb)), 94.6 (C(Wb)), 111.6
(C(Wa)), 127.5 (Cphenyl), 128.0 (Cphenyl), 128.0 (Cphenyl), 128.4 (Cphenyl),
128.5 (Cphenyl), 129.1 (Cphenyl), 129.3 (Cphenyl), 130.2 (Cphenyl), 131.5
(d, J ) 21.4 Hz, Cphenyl R(a) ipso), 132.8 (d, J ) 7.7 Hz, 2 CHphenyl
(N,N′-Bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-
1-yl]formamidinato)rhodium(I) (2). The formamidine ligand 1
(116 mg, 138.6 µmol, 1 equiv) was dissolved in freshly distilled
THF (4.2 mL), treated with nBuLi (112 µL, 180 µmol, 1.3 equiv)
at 0 °C, and then slowly warmed to rt. After 2.5 h, [Rh2Cl2(COD)2]
(34.2 mg, 69.3 µmol, 0.5 equiv) was added inside the glovebox
and stirred overnight. The reaction mixture was filtered, and the
volatiles were evaporated under reduced pressure to yield the
1
product as an orange powder. Yield: 111 mg (85%). H NMR
(d8-THF, 700.1 MHz): δ 1.09 (dd, JP ) 7.0 Hz, JP ) 4.2 Hz, 6 H,
2 CH3), 3.70-3.72 (m, 2 H, 2 CH(X)), 3.78 (t, J ) 2.5 Hz, 2 H,
2 CH(Y)), 3.90 (s, 10 H, 2 Cp), 4.01-4.15 (m, 2 H, 2 CHmethyne),
4.50-4.52 (m, 2 H, 2 CH(Z)), 6.98 (t, J ) 7.7 Hz, 4 H, 4
CHphenyl meta), 7.01 (t, J ) 7.7 Hz, 4 H, 4 CHphenyl meta), 7.14 (dd, J1
) 9.1 Hz, J2 ) 7.7 Hz, 4 H, 4 CHphenyl para), 7.40-7.44 (m, 4 H,
4 CHphenyl ortho), 7.53-7.58 (m, 4 H, 4 CHphenyl ortho), 9.36 (t, J )
3.2 Hz, 1 H, CHformamidinato). 13C{1H} NMR (d8-THF, 75.5 MHz):
δ 16.2 (s, 2 CH3), 30.7 (t, J ) 11.2 Hz, 2 CHmethyne), 54.4
(a) ortho), 133.3 (d, J ) 14.8 Hz, 2 CHphenyl R(b) ortho), 136.4 (d, J )
R
20.9 Hz, 2 CHphenyl â(b) ortho), 137.1 (d, J ) 12.7 Hz, 2 CHphenyl â(a)
ortho), 139.1 (d, J ) 18.9 Hz, Cphenyl R(b) ipso), 163.4 (CHformamidinato),
two (2 Cphenyl ipso) not found. 31P NMR (C6D6, 203 MHz): δ 9.8 (s,
P(b)), 56.0 (dd, JRh ) 137.3 Hz, P(a)). 103Rh NMR (C6D6, 15.9
MHz): δ 990.
(s, 2 CH(Z)), 60.5 (s, 2 CH(Y)), 63.9 (s, 2 CH(X)), 68.6 (s, 2 Cquat.
)
69.4 (s, 2 Cp), 83.4 (t, J ) 4.2 Hz, 2 Cquat.), 126.7 (t, J ) 4.6 Hz,
4 CHphenyl meta), 127.5 (t, J ) 4.3 Hz, 4 CHphenyl meta), 128.2 (s, 2
CHphenyl ), 132.4 (t, J ) 5.6 Hz, 4 CHphenyl ortho), 133.0-133.0 (m,
para
2 Cphenyl ipso), 134.4 (t, J ) 6.1 Hz, 2 CHphenyl ortho), 135.3-136.2
(m, 2 Cphenyl ipso), 160.4 (ddd, JRh ) 2.5 Hz, JP ) 2.3 Hz, JP ) 2.3
Hz, one (2 Cphenyl ipso) not found. 31P NMR (d8-THF, 121.5 MHz):
δ 74.8 (d, JRh ) 201 Hz). 103Rh NMR (d8-THF, 22.1 MHz): δ
-42.5. MS (HR MALDI): m/z 938.0812 (calcd for C49H45Fe2N2P2-
Rh); found 938.0828 [M+], 938.0864 [MH+]. Due to the air
sensitivity of the product, no correct elemental analysis could be
obtained.
(N,N′-Bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-
1-yl](chloro)(methyl)formamidinato)rhodium(III) (11). The for-
mamidine ligand 1 (116 mg, 138.6 µmol, 1 equiv) was dissolved
in freshly distilled THF (4.2 mL) and treated with nBuLi (113 µL,
180 µmol, 1.3 equiv) at 0 °C. After warming to rt and stirring for
2.5 h, [Rh2Cl2(COD)2] (34.2 mg, 69.3 µmol, 0.5 equiv) was added
and the red solution was stirred for 22 h and filtered. As a stream
of MeCl was passed over the clear, red solution for 10 min, its
color darkened considerably. All volatiles were evaporated under
reduced pressure, and the crude product was taken up in benzene
(3.5 mL). Pentane was allowed to slowly diffuse overnight into
the solution, leading to the formation of red crystals. After decanting
the mother liquor, the crystals were dried in vacuo. Complete
evaporation of the solvent in order to obtain the pure product
suitable for elemental analysis required extensive drying at low
1
pressure. Yield: 101 mg (77%). H NMR (C6D6, 500.2 MHz): δ
0.68 (ddd, JRh ) 2.2 Hz, JP(a) ) 2.2 Hz, JP(b) ) 2.2 Hz, 3 H, CH3(Rh)),
1.17 (dd, JP ) 12.5 Hz, JP ) 12.0 Hz, 3 H, CH3(methyl b)), 1.48 (dd,
JP ) 13.0 Hz, JP ) 13.0 Hz, 3 H, CH3(methyl a)), 3.72 (dd, J1 ) 2.5
Hz, J2 ) 2.5 Hz, 1 H, CH(Xb)), 3.85 (dd, J1 ) 6.5 Hz, J2 ) 6.5 Hz,
(K-N,P-Bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-
1-yl]formamidine)(chloro)(η4-1,4-cyclooctadiene)rhodium(I) (10)

630 Organometallics, Vol. 25, No. 3, 2006
Bertogg and Togni
1 H, CH(methyne b)), 3.96 (dd, J1 ) 2.8 Hz, J2 ) 2.8 Hz, 1 H, CH(Yb)),
4.01 (dd, J1 ) 2.5 Hz, J2 ) 2.5 Hz, 1 H, CH(Ya)), 4.13 (s, 5 H,
Cp(b)), 4.30-4.31 (m, 1 H, CH(Xa)), 4.40 (dd, J1 ) 2.5 Hz, J2 )
2.5 Hz, 1 H, CH(Za)), 4.45 (dd, J1 ) 2.5 Hz, J2 ) 2.5 Hz, 1 H,
CH(Zb)), 4.51 (s, 5 H, Cp(a)), 5.52 (dd, J1 ) 6.8 Hz, J2 ) 6.8 Hz, 1
H, CH(methyne a)), 6.65 (t, J ) 8.5 Hz, 2 H, 2 CHphenyl (Ra) ortho), 6.89
(td, Jt ) 8.0 Hz, Jd ) 2.0 Hz, 2 H, 2 CHphenyl (Ra) meta), 6.95-7.04
(m, 5 H, 2 CHphenyl (âa) meta, CHphenyl (Ra) para, 2 CHphenyl (Rb) meta), 7.10
(td, Jt ) 7.5 Hz, Jd ) 1.5 Hz, 1 H, CHphenyl (âa) para), 7.14-7.19 (m,
3 H, 1 CHphenyl (Rb) para, 2 CHphenyl (Rb) ortho, 7.20-7.26 (m, 3 H, 1
CHphenyl (âb) para, 2 CHphenyl (âb) meta, 8.36-8.40 (m, 2 H, CHphenyl (âb)
ortho), 8.50 (bs, 2 H, CHphenyl (âa) ortho), 9.22 (ddd, JRh ) 3.0 Hz, JP )
2.5 Hz, JP ) 2.5 Hz, 1 H, CHformamidinato). 13C{1H} NMR (C6D6,
176.0 MHz): δ 7.9 (ddd, JRh ) 22.3 Hz, JP ) 6.3 Hz, JP ) 6.3
Hz, 3 H, CH3(Rh)), 13.3 (d, JP(b) ) 6.2 Hz, CH3(methyl b)), 13.5 (d,
JP(a) ) 7.4 Hz, CH3(methyl a)), 31.5 (d, JP(b) ) 22.2 Hz, CH3(methyne
b)), 32.6 (d, JP(a) ) 22.4 Hz, CH3(methyne a)), 56.5 (d, JP(b) ) 3.7 Hz,
CH(Zb)), 57.5 (d, JP(a) ) 5.2 Hz, CH(Za)), 62.5 (s, CH(Ya)), 62.9 (s,
CH(Yb)), 64.5 (d, JP(ab) ) 2.5 Hz, CH(Xa)), 65.3 (s, CH(Xb)), 70.3 (s,
Cp(b)), 71.6 (s, Cp(a)), 79.8 (d, J ) 7.0 Hz, C(Wb)), 81.4 (d, J ) 4.0
Hz, C(Wa)), 97.7 (d, J ) 3.4 Hz, C(Va)), 101.9 (d, J ) 3.4 Hz, C(Vb)),
126.6 (d, J ) 35.1 Hz, Cphenyl ipso), 126.9 (d, J ) 9.3 Hz, 2 CHphenyl
and the red solution was stirred for 22 h and filtered. The addition
of dry MeI (26 µL, 59 mg, 416 µmol, 3.0 equiv) caused a slight
darkening of the clear, red solution, which was evaporated to
dryness after 3 h of stirring. The resulting red powder was taken
1
up in C6D6. Yield: 132 mg (88%). H NMR (C6D6, 700.1 MHz):
δ 0.81-0.85 (m, 3 H, CH3(Rh)), 1.04 (dd, JP ) 12.6 Hz JP ) 7.0
Hz, 3 H, CH3(methyl b)), 1.46 (dd, JP ) 12.6 Hz, JP ) 7.0 Hz, 3 H,
CH3(methyl a)), 3.81-3.83 (m, 1 H, CH(Xb)), 3.89 (dd, J1 ) 7.0 Hz,
J2 ) 6.3 Hz, 1 H, CH(methyne b)), 3.99 (dd, J1 ) 2.8 Hz, J2 ) 2.8
Hz, 1 H, CH(Yb)), 4.03 (dd, J1 ) 2.5 Hz, J2 ) 2.5 Hz, 1 H, CH(Ya)),
4.10 (s, 5 H, Cp(b)), 4.27-4.29 (m, 1 H, CH(Xa)), 4.45 (dd, J1 ) 2.1
Hz, J2 ) 1.4 Hz, 1 H, CH(Za)), 4.50 (dd, J1 ) 2.1 Hz, J2 ) 1.4 Hz,
1 H, CH(Zb)), 4.52 (s, 5 H, Cp(a)), 5.56 (dd, J1 ) 7.0 Hz, J2 ) 3.5
Hz, 1 H, CH(methyne a)), 6.50-55 (m, 2 H, 2 CHphenyl (Ra) ortho), 6.86
(t, J ) 7.0 Hz, 2 H, 2 CHphenyl (âb) meta), 6.95-7.00 (m, 4 H, 2 CHphenyl
(âa) meta), 2 CHphenyl (Rb) meta), 7.02 (t, J ) 7.0 Hz, 1 H, CHphenyl (Ra)
para), 7.13 (t, J ) 7.4 Hz, 1 H, CHphenyl (âa) para), 7.16 (t, J ) 7.4 Hz,
1 H, CHphenyl (Rb) para), 7.18-7.25 (m, 3 H, 3 CHphenyl (Ra) meta and phenyl
(âb) para), 7.27-7.30 (m, 2 H, CHphenyl (Rb) ortho), 8.15 (t, J ) 8.4 Hz,
2 H, CHphenyl (âb) ortho), 8.39 (t, J ) 9.1 Hz, 2 H, CHphenyl (âa) ortho),
8.97 (ddd, JRh ) 3.5 Hz, JP ) 4.9 Hz, JP ) 4.9 Hz, 1 H,
CHformamidinato). 13C{1H} NMR (C6D6, 62.9 MHz): δ 13.7 (d, JP(b)
) 6.3 Hz, CH3(methyl b)), 14.2 (d, JP(a) ) 7.1 Hz, CH3(methyl a)), 16.2
(âb) meta), 127.4 (d, J ) 10.0 Hz, 2 CHphenyl (âa) meta), 127.6 (2 CHphenyl
(Ra) meta), 127.8 (2 CHphenyl (Rb) meta), 128.7 (s, CHphenyl (Rb) para), 128.8
(d, J ) 2.1 Hz, CHphenyl (Ra) para), 129.4 (d, J ) 40.7 Hz, Cphenyl ipso),
130.1 (d, J ) 2.3 Hz, CHphenyl (âb) para), 130.6 (d, J ) 2.3 Hz, CHphenyl
(âa) para), 131.4 (d, J ) 35.2 Hz, Cphenyl ipso), 132.1 (d, J ) 36.4 Hz,
(dd, JRh ) 22.3 Hz, J2 ) 6.7 Hz, 3 H, CH3(Rh)), 31.0 (d, JP(b) )
23.5 Hz, CH3(methyne b)), 35.9 (d, JP(a) ) 22.5 Hz, CH3(methyne a)), 56.8
(d, JP(b) ) 4.5 Hz, CH(Zb)), 57.0 (d, JP(a) ) 4.3 Hz, CH(Za)), 62.6 (s,
CH(Ya)), 63.1 (s, CH(Yb)), 64.2 (s, CH(Xa)), 65.8 (s, CH(Xb)), 70.5 (s,
Cp(b)), 71.4 (s, Cp(a)), 79.3 (d, J ) 6.9 Hz, C(Wb)), 81.5 (d, J ) 3.6
Hz, C(Wa)), 99.0 (t, J ) 3.5 Hz, C(Va)), 100.7 (t, J ) 3.9 Hz, C(Vb)),
126.6 (2 CHphenyl (Ra) meta), 127.0 (2 CHphenyl (âa) meta or 2 CHphenyl (Rb)
meta), 127.3 (2 CHphenyl (âb) meta), 127.8 (2 CHphenyl (âa) meta or 2 CHphenyl
(Rb) meta), 128.8 (CHphenyl (Ra) para), 128.8 (CHphenyl (âa) para), 130.0 (d,
J ) 40.7 Hz, Cphenyl ipso), 130.4 (s, CHphenyl (âb) para), 130.7 (d, J )
35.4 Hz, Cphenyl ipso), 130.9 (s, CHphenyl (Rb) para), 132.8 (d, J ) 6.7
Hz, 1 CHphenyl (Ra) ortho), 133.0 (d, J ) 3.6 Hz, 1 CHphenyl (Rb) ortho),
135.6 (d, J ) 8.5 Hz, 1 CHphenyl (âb) ortho), 139.0 (d, J ) 11.0 Hz, 1
C
phenyl ipso), 132.6 (d, J ) 7.0 Hz, 2 CHphenyl (Ra) ortho), 132.7 (d, J )
7.2 Hz, 2 CHphenyl ortho), 135.8 (d, J ) 8.6 Hz, 2 CHphenyl
(Rb)
(âb)
ortho), 137.1 (d, J ) 9.5 Hz, 2 CHphenyl (âa) ortho), 158.6 (dt, Jd ) 3.3
Hz, Jt ) 3.3 Hz, 1 CHformamidinato)). 31P NMR (C6D6, 121.5 MHz):
δ 45.0 (dd, JRh ) 131.0 Hz, JP ) 17.5 Hz, P(a)), 53.5 (dd, JRh
)
134.1 Hz, JP ) 17.5 Hz, P(b)). 103Rh NMR (C6D6, 22.2 MHz): δ
1600. MS (HR MALDI): m/z 953.1047 (calcd for C50H48Fe2N2P2-
Rh); found 953.1041 [M - Cl+]. C50H48ClFe2N2P2Rh (988.93):
calcd C 60.73, H 4.89, Cl 3.59, Fe 11.29, N 2.83, P 6.26, Rh 10.41;
found C 60.50, H 4.90, N 2.58.
CHphenyl
ortho), 156.6 (d, J ) 3.5 Hz, 1 CHformamidinato), two (2
(âa)
Cphenyl ipso) not found. 31P NMR (C6D6, 121.5 MHz): δ 44.2 (dd, JRh
) 131.1 Hz, JP ) 16.2 Hz, P(b)), 53.5 (dd, JRh ) 129.0 Hz, JP )
16.3 Hz, P(a)). 103Rh NMR (C6D6, 22.2 MHz): δ 1471. MS (HR
MALDI): m/z 953.1047 (calcd for C50H48Fe2N2P2Rh); found
953.1036 [M - I+].
Acknowledgment. Support from the Swiss National Science
Foundation is gratefully acknowledged. We thank Dr. Heinz
Ru¨egger for NMR assistance and Dr. Isabelle Haller for
performing the X-ray crystallographic studies of compounds 8
and 11.
(N,N′-Bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-
1-yl]formamidinato)(iodo)(methyl)rhodium(III) (12). The for-
mamidine ligand 1 (116 mg, 138.6 µmol, 1 equiv) was dissolved
in freshly distilled THF (4.2 mL) and treated with nBuLi (113 µL,
180 µmol, 1.3 equiv) at 0 °C. After warming to rt and stirring for
2.5 h, [Rh2Cl2(COD)2] (34.2 mg, 69.3 µmol, 0.5 equiv) was added
Supporting Information Available: Crystallographic data as
CIF files. These data are available free of charge via the Internet
at http://pubs.acs.org.
OM050845P