Chloride-Promoted Synthesis of Cis Bis-Chelated Palladium(II) Complexes from Ortho-Mercurated tricarbonyl(η6-arene)chromium Complexes

Article abstract of DOI:10.1021/om030433l

A new method of synthesis of homo- and heteroleptic cis bis-chelated Pd(II) species by a transmetalation reaction of the ortho-mercurated 2-[tricarbonyl(η⁶-phenyl)chromium]pyridine with a series of bis(μ-chloro) palladacyclic aromatic compounds in the presence of a large excess of the chloride salt [NMe₄Cl is reported. These (CO) ₃Cr-bound bis-chelated Pd(II) species can be designed for the preparation of enantiopure planar chiral cyclopalladated (η ⁶-arene)Cr(CO)₃ complexes. The study of the mechanism of this transmetalation reaction reveals the key role of the excess of chloride salt, which is necessary for the isolation of persistent heteroleptic bis-chelated Pd(II) complexes. This method was further applied to the synthesis of highly enantioenriched (+) and (-) samples of the ortho-chloropalladated 2-[tricarbonyl(η⁶-phenyl)chromium]pyridine, whose enantiopurity was assessed with the aid of diamagnetic λ and δ TRISPHAT salts used as chiral shift ¹H NMR agents. The absolute configurations of the two enantioenriched complexes were obtained from the corresponding absolute structures determined by X-ray diffraction analyses. The molecular structures of six new heteroleptic bis-chelated Pd(II) complexes are reported.

Full text of DOI:10.1021/om030433l

Organometallics 2003, 22, 5243-5260
5243
Ch lor id e-P r om oted Syn th esis of Cis Bis-Ch ela ted
P a lla d iu m (II) Com p lexes fr om Or th o-Mer cu r a ted
Tr ica r bon yl(η6-a r en e)ch r om iu m Com p lexes†
Alexsandro Berger, J ean-Pierre Djukic,* and Michel Pfeffer*
Laboratoire de Synthe`ses Me´tallo-Induites, UMR 7513 CNRS, 4, rue Blaise Pascal,
F-67070 Strasbourg Cedex, France
J e´roˆme Lacour and Laurent Vial
De´partement de Chimie Organique, Universite´ de Gene`ve, 30, quai Ernest Ansermet,
CH-1211 Gene`ve 4, Switzerland
Andre´ de Cian‡ and Nathalie Kyritsakas-Gruber
Service Commun d’Analyse par Diffraction des Rayons X, UMR 7513 CNRS,
4, rue Blaise Pascal, F-67070 Strasbourg Cedex, France
Received J une 4, 2003
A new method of synthesis of homo- and heteroleptic cis bis-chelated Pd(II) species by a
transmetalation reaction of the ortho-mercurated 2-[tricarbonyl(η6-phenyl)chromium]pyridine
with a series of bis(µ-chloro) palladacyclic aromatic compounds in the presence of a large
excess of the chloride salt [NMe4]Cl is reported. These (CO)3Cr-bound bis-chelated Pd(II)
species can be designed for the preparation of enantiopure planar chiral cyclopalladated
(η6-arene)Cr(CO)3 complexes. The study of the mechanism of this transmetalation reaction
reveals the key role of the excess of chloride salt, which is necessary for the isolation of
persistent heteroleptic bis-chelated Pd(II) complexes. This method was further applied to
the synthesis of highly enantioenriched (+) and (-) samples of the ortho-chloropalladated
2-[tricarbonyl(η6-phenyl)chromium]pyridine, whose enantiopurity was assessed with the aid
1
of diamagnetic Λ and ∆ TRISPHAT salts used as chiral shift H NMR agents. The absolute
configurations of the two enantioenriched complexes were obtained from the corresponding
absolute structures determined by X-ray diffraction analyses. The molecular structures of
six new heteroleptic bis-chelated Pd(II) complexes are reported.
In tr od u ction
One obvious limitation of this deprotonation method
lies, however, in the high reactivity of the lithiated
(η6-arene)Cr(CO)3 intermediates, which prevents their
use at temperatures higher than -30 °C4 and their
storage in stock solutions over long periods of time.
One alternative method of direct metalation of
(η6-arene)Cr(CO)3 complexes is the mercuration reaction
by means of Hg(OAc)2, which affords compounds that
are both temperature and air stable as well as reason-
ably reactive. Surprisingly, until recently, only three
reports dealing with the matter were known.5 The
sparseness of data on such an important reaction ap-
plied to (η6-arene)Cr(CO)3 complexes was unusual,
There are no less than eight different procedures to
synthesize metalated (η6-arene)Cr(CO)3 complexes avail-
able in the literature,1 among which deprotonation-
lithiation certainly represents the method most studied
and applied since its discovery by Nesmeyanov in 1969.2
A good illustration of the impact of such a deprotonation
method applied to substituted (η6-arene)Cr(CO)3 com-
plexes is given by the number of articles and mono-
graphs dedicated to this very topic, which represents
more than 90% of all the published reports on metalated
(η6-arene)Cr(CO)3 complexes.3 Of course, this fact il-
lustrates the efficiency of organolithium bases for
deprotonating (η6-arene)Cr(CO)3 complexes, whatever
their nature, e.g. carbanionic or amide-like.
(3) (a) Semmelhack, M. F. In Comprehensive Organometallic Chem-
istry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon
Press: Oxford, U.K., 1995; Vol. 12, p 1017. (b) Rose-Munch, F.; Rose,
E. Curr. Org. Chem. 1999, 3, 445. (c) Gibson, S. E.; Reddington, E. G.
Chem. Commun. 2000, 989.
(4) (a) Card, R. J .; Trahanovsky, W. S. J . Org. Chem. 1980, 45, 2555.
(b) Semmelhack, M. F.; Ullenius, C. J . Organomet. Chem. 1982, 235,
C10. (c) Sandilands, L. M.; Lock, C. J . L.; Faggiani, R.; Hao, N.; Sayer,
B. G.; Quilliam, M. A.; McCarry, B. E.; McGlinchey, M. J . J . Orga-
nomet. Chem. 1982, 224, 267.
(5) (a) Magomedov, G. K. I.; Syrkin, V. G.; Frenkel, A. S. Russ. J .
Gen. Chem. (Engl. Transl.) 1972, 42, 2450. (b) Magomedov, G. K. I.;
Syrkin, V. G.; Frenkel, A. S.; Nekrassov, Yu. S.; Zabina, T. A. Zh.
Obshch. Khim. 1975, 45, 2533. (c) Magomedov, G. K. I. J . Organomet.
Chem. 1990, 385, 113.
* To whom correspondence should be addressed. Fax: +33 (0)-
390241526. Tel: +33 (0)390241523. E-mail: djukic@chimie.u-strasbg.fr
(J .-P.D.), pfeffer@chimie.u-strasbg.fr (M.P.).
† This article is dedicated to Prof. Dr. Karl Heinz Do¨tz on his 60th
birthday.
‡ To whom requests pertaining to X-ray diffraction analyses should
be addressed.
(1) Berger, A.; Djukic, J . P.; Michon, C. Coord. Chem. Rev. 2002,
225, 215.
(2) Nesmeyanov, A. N.; Kolobova, N. E.; Anisimov, K. N.; Markarov,
Yu. V. Izv. Akad. Nauk SSSR, Ser. Khim. 1969, 2665.
10.1021/om030433l CCC: $25.00 © 2003 American Chemical Society
Publication on Web 11/12/2003

5244 Organometallics, Vol. 22, No. 25, 2003
Berger et al.
Sch em e 1a
Ch a r t 1
scoring that the electrochemical compatibility of the
metal center that is to be attached to the Cr(0)-bound
arene ligand is a relevant issue. In this article, we
address an additional application of the transmetalation
of mercurated (η6-arene)Cr(CO)3 complexes. We present
a new method of synthesis of homo- and heteroleptic
cis bis-chelated Pd(II)12 species by an unusual reaction
between an ortho-mercurated (η6-arene)Cr(CO)3 com-
plex and a cyclopalladated aromatic compound. We show
how these (CO)3Cr-bound bis-chelated Pd(II) species can
be used for the preparation of enantiopure, planar
chiral cyclopalladated (η6-arene)Cr(CO)3 complexes.
a
Legend: (a) Hg(OAc)2, EtOH, 50 °C; (b) CaX2, EtOH; (c)
[Me4N]Cl, acetone, room temperature; (d) Pd(MeCN)2Cl2,
acetone -20 °C; (e) pyridine, room temperature.
especially if one considers the “popularity” of organo-
mercury(II) chemistry in the recent past6 and, of course,
the amount of work published on the same topic for
cymantrene, ferrocene, ruthenocene, and other metal-
locene derivatives.7 Such a factual absence could be the
consequence of at least two factors: (1) the persistent,
although supported, belief that (η6-arene)Cr(CO)3 com-
plexes react sluggishly or not at all with electrophiles,
a class of reagents to which Hg(II) salts belong,8 and
(2) the established general toxicity of mercury salts,9
which doubtless complicates possible large-scale devel-
opments.
In a previous report, it was demonstrated that various
(η6-arene)Cr(CO)3 complexes that bear an endogenous
ligand could be selectively ortho monomercurated to give
the corresponding bimetallic products.10 When they are
treated with simple labile palladium(II) chloride deriva-
tives, PdL2Cl2, these complexes exhibited exchange of
the Hg(II) center for Pd(II), which provided an efficient
route to ortho-palladated (η6-arene)Cr(CO)3 compounds
(Scheme 1).
Resu lts a n d Discu ssion
F or m a tion of a n “Od d P r od u ct”, th e Hom olep tic
Tr in u clea r Bis-Ch ela ted P d (II) Com p lex u -6.13 In
a previous report, we described the unexpected forma-
tion of minute amounts of crystalline u-6, a trinuclear
(Pd,Cr,Cr) homoleptic cis bis-chelated Pd(II) complex,
whose X-ray structure displays two Cr(CO)3 moieties in
a syn-facial relationship.10 This compound was believed
to be a secondary product of the transmetalation reac-
tion of complex 3 with Pd(MeCN)2Cl2, which yielded 5
as the main product after pyridine quenching (eq 1). The
Use of mercurated arenes for the synthesis of palla-
dated complexes can easily be justified11 by the failure
of all the direct palladation methods based on C-H bond
activation, as tested with various (η6-arene)Cr(CO)3
complexes. In all cases, such attempts led to the irre-
versible decomposition of the Cr(0) substrate, under-
(6) (a) Kobe, K. A.; Doumani, T. F. Ind. Eng. Chem. 1941, 33, 170.
(b) McMahon, K. S.; Kobe, K. A. Ind. Eng. Chem. 1957, 49, 42.
(7) (a) Rausch, M.; Vogel, M.; Rosenberg, H. J . Org. Chem. 1957,
22, 900. (b) Rausch, M. D. J . Org. Chem. 1963, 28, 3337. (c) Rausch,
M. D.; Genetti, R. A. J . Org. Chem. 1970, 35, 3888. (d) Slocum, D. W.;
J ones, W. E.; Ernst, C. R. J . Org. Chem. 1972, 37, 4278. (e) Kovar, R.
F.; Rausch, M. D. J . Org. Chem. 1973, 38, 1918. (f) Roling, P. V.;
Rausch, M. D. J . Org. Chem. 1974, 39, 1421. (g) Winter, C. H.; Han,
Y. H.; Heeg, M. J . Organometallics 1992, 11, 3169. (h) Kur, S. A.; Heeg,
M. J .; Winter, C. H. Organometallics 1994, 13, 1865. (i) Han, Y. H.;
Heeg, M. J .; Winter, C. H. Organometallics 1994, 13, 3009. (j) Kur, S.
A.; Winter, C. H. J . Organomet. Chem. 1996, 512, 39. (k) Wu, Y. J .;
Cui, X. L.; Liu, Y. H.; Yuan, H. Z.; Mao, X. A. J . Organomet. Chem.
1997, 543, 63. (l) Mayor-Lopez, M. J .; Weber, J .; Mannfors, B.;
Cunningham, A. F. Organometallics 1998, 17, 4983. (m) Wu, Y.; Huo,
S.; Gong, J .; Cui, X.; Ding, L.; Ding, K.; Du, C.; Liu, Y.; Song, M. J .
Organomet. Chem. 2001, 637-639, 27.
formation of u-6 was interpreted as the consequence of
some homocoupling of 3 with the latter Pd(II) salt, a
reaction that should have also yielded (rel)-l-6 (Chart
1). In fact, all our preliminary attempts at synthesizing
this compound from a reaction between 2a (or 3) and 4
failed.
Later, we decided to investigate further the formation
of such bis-chelated Pd(II) complexes, having in mind
their possible use for the synthesis of enantioenriched,
(8) Merlic, C. A.; Miller, M. M.; Hietbrink, B. N.; Houk, K. N. J .
Am. Chem. Soc. 2001, 123, 4904.
(12) Berger, A.; Djukic, J . P.; Pfeffer, M.; de Cian, A.; Kyritsakas-
Gruber, N.; Lacour, J .; Vial, L. Chem. Commun. 2003, 658.
(13) In the present paper, we use the u and l descriptors exclusively
for the description of the relative configurations of planar chiral
complexes and the associated “rel” prefix whenever we address
racemates: (a) Seebach, D.; Prelog, V. Angew. Chem., Int. Ed. Engl.
1982, 21, 654; Angew. Chem. 1982, 94, 696. (b) Moss, G. P. Pure Appl.
Chem. 1996, 68, 2193.
(9) Goldwater, L. J . In Mercury, Mercurials and Mercaptans; Miller,
M. W., Clarkson, T. W., Eds.; Charles C. Thomas: Springfield, IL, 1973;
p 56.
(10) Berger, A.; de Cian, A.; Djukic, J . P.; Fischer, J .; Pfeffer, M.
Organometallics 2001, 20, 3230.
(11) Constable, E. C.; Leese, T. A. J . Organomet. Chem. 1987, 335,
293.

Cis Bis-Chelated Palladium(II) Complexes
Organometallics, Vol. 22, No. 25, 2003 5245
Sch em e 2
planar chiral metalated (η6-arene)Cr(CO)3 complexes,
as detailed in this article.
Sch em e 3
We performed a series of test experiments aimed at
understanding the conditions that would favor the
formation of such a bis-chelated Pd(II) complex. As a
model system we chose the reaction of the ortho-
palladated N,N-dimethylbenzylamine species 7a 14 with
the ortho-chloromercurated 2-[tricarbonyl(η6-phenyl)-
chromium]pyridine compound 2a (Scheme 2; note that
percentages correspond to yields of isolated compound).
A stoichiometric mixture (respective to the monomeric
form of the Pd(II) substrate) of 2a and 7a reacted at
low temperature to afford cleanly the cyclopalladated
monomer 5 and ortho-chloromercurated N,N-dimethyl-
benzylamine species 9a , upon quenching with pyridine
(Scheme 2, path A). Similar experiments carried out
with complexes 3 and 7a afforded 5 and 2a along with
moderate amounts of the new bimetallic heteroleptic
complex 8a (Scheme 2, path B), thus revealing the
importance of diarylmercury derivatives in the forma-
tion of the latter Pd(II) bis-chelate. Hence, we concen-
trated our efforts in finding an efficient way to favor
the formation of 3 from 2a , which was needed to
increase significantly the proportions of Pd(II) bis-
chelate 8a .
dated, an excess of chloride helps in decreasing the
reactivity of the Lewis acidic mercuric chloride that is
released in the solution, thus preventing the backward
reaction of R2Hg species with HgX2.15 Mercuric chloride
is therefore converted into a series of inert anionic
adducts such as [HgX3]- (Scheme 3).17 In concentrated
solutions, the latter may also exist as the dianionic
dimer [Hg2X6]2- and crystallize as such.17c Hence, we
reacted 2a with 7a and 1.5 equiv of [Me4N]Cl, expecting
the in situ formation of 3 and a significant overall
increase of the proportions of 8a . This was indeed
observed, as depicted in Scheme 2 (path C). We noticed
that complex 8a could be obtained cleanly as the major
product upon reacting 2a and 7a in the presence of 10
equiv of [Me4N]Cl (Scheme 2, path D). This result
suggested a priori a 2-fold role of the excess of halide:
(1) it promotes the steady formation of 3, which converts
readily into 8a upon reaction with 7a , and aids in
keeping the concentration of 2a at a low value and (2)
it “neutralizes” the Lewis acid HgCl2, which prevents
its reaction with 8a to yield 4 and eventually 5 after
Complex 3, which consists of a mixture of (rel)-l and
u stereoisomers, can be readily prepared from a reaction
of 2a with [Me4N]Cl in acetone. Vicente and co-workers
have, until recently, extensively used this method of
“symmetrization” that involves a halide as the pro-
moter.15 This important reaction was first addressed by
Whitmore almost 80 years ago.16 Although the mecha-
nism of this reaction, which produces a diarylmercury-
(II) complex and HgCl2, has not yet been fully eluci-
(17) (a) Mohana Rao, J . K.; Rajaram, R. K. Z. Kristallogr. 1982, 160,
219. (b) Goggin, P. L.; King, P.; McEwan, D. M.; Taylor, G. E.;
Woodward, P.; Sandstro¨m, M. J . Chem. Soc., Dalton Trans. 1982, 875.
(c) Sikirica, M.; Grdenic, D.; Vickovic, I. Cryst. Struct. Commun. 1982,
11, 1299. (d) Clegg, W. J . Chem. Soc., Dalton Trans. 1982, 593. Vezzosi,
I. M.; Benedetti, A.; Albinati, A.; Ganazzoli, F.; Cariati, F.; Pellicari,
L. Inorg. Chim. Acta 1984, 90, 1. (e) Terzis, A.; Mentzafos, D.; Tazmir-
Riahi, H. A. Inorg. Chim. Acta 1985, 101, 77.
(14) Cope, A. C.; Friedrich, E. C. J . Am. Chem. Soc. 1968, 90, 909.
(15) (a) Vicente, J .; Abad, J . A.; Fernandez de Bobadilla, R.; J ones,
P. G.; Ramirez de Arellano, M. C. Organometallics 1996, 15, 24. (b)
Vicente, J .; Abad, J . A.; Rink, B.; Hernandez, F. S.; Ramirez de
Arellano, M. C. Organometallics 1997, 16, 5269.
(16) Whitmore, F. C. J . Am. Chem. Soc. 1919, 41, 1841.

5246 Organometallics, Vol. 22, No. 25, 2003
Berger et al.
Sch em e 4
Sch em e 5
pyridine quenching. We show below that the role of the
halide in the overall transmetalation reaction leading
to Pd(II) bis-chelates is central and multiple in its
aspects.
Role of th e Ha lid e in th e So-Ca lled “Sym m etr i-
za t ion ” P r ocess. The “symmetrization” of 2a into 3
proceeded quantitatively when we subjected the former
to the action of [Me4N]Cl at -20 °C for 4 h. This result
clearly demonstrates that the conversion of 2a into 3
can readily take place at moderate subambient temper-
atures and likely occurs in the process leading to 8a . It
is well established that the nature of the halide greatly
influences the efficiency of the “symmetrization”. Simi-
larly to the above-mentioned early works of Whitmore
on the symmetrization of RHgX compounds, we studied
the effect of iodide, which is a far better promoter of
this reaction than chloride.
Ch a r t 2
The acetoxymercuration of 1 by Hg(OAc)2 followed by
treatment with a saturated solution of KI in EtOH
yielded complex 3 as the sole product 30 min after the
addition of halide. The isolation of the iodomercurated
complex 2b was possible only if nBu4NI was used in
stoichiometric amounts. The addition of 1 equiv of the
latter salt to the solution resulting from the acetoxy-
mercuration of 1, at room temperature after 30 min of
stirring, afforded complex 2b in 50% yield. The same
experiment carried out with 2 equiv of nBu4NI yielded,
after 30 min of reaction, a mixture containing 3 and 2b
(Scheme 4). It is worth noting that the treatment of the
chloromercuric compound 2a with 4 equiv of KI at 60
°C for 24 h yielded complex 3 quantitatively.
consideration the large amount of X- present in the
reaction medium (Scheme 5) and the known electron-
withdrawing effect of the Cr(CO)3 moiety. This proposal
implies a nucleophilic attack of the halide at the par-
ticularly electrophilic Hg(II) center of RHgX to give the
putative anionic mercurate intermediate [RHgX2]-,21
which might dimerize to give the bridged transient
species [RHgX2]22-; this species subsequently would
undergo an intramolecular transposition of the aryl
group and would yield the diarylmercury(II) product and
the inert [HgX3]- anion.17
Role of Cl- in th e Tr a n sm eta la tion P r ocess. It
must be noted that, in the course of the transmetalation
reaction leading to heteroleptic complex 8a , the chloride
can also interact with the cyclopalladated substrate 7a
to yield the palladate 10a (Chart 2).
As a rationale to the symmetrization reaction mech-
anism, it has been frequently postulated that RHgX
species are inherently in equilibrium with R2Hg and
HgX2 in solution (eq 2).18 Hence, the addition of the
Lewis base “B”, neutral or anionic in character, would
help to shift the equilibrium to the right as a result of
the formation of the corresponding stable HgX2‚B ad-
duct. Indeed, the symmetrizations of halogenomercu-
rated alkyls or aryls can also be promoted by bases19 or
chelating ligands20 as well as by halides, as previously
mentioned.
In the case of the symmetrization of chloro-/iodomer-
curated (η6-arene)Cr(CO)3 substrates addressed here, an
alternative mechanism can be proposed that takes into
A few examples of chloro-bridged cyclopalladated
aromatics have been shown to behave as Lewis acids
(18) (a) Whitmore, F. C.; Sobatzki, R. J . J . Am. Chem. Soc. 1933,
55, 1128. (b) Dessy, R. E.; Lee, Y. K.; Kim, J .-Y. J . Am. Chem. Soc.
1961, 113, 1163. (c) Reynolds, G. F.; Daniel, S. R. Inorg. Chem. 1967,
6, 480.
(19) (a) Whitmore, F. C.; Hanson, E. R.; Carnahan, F. L. J . Am.
Chem. Soc. 1929, 51, 894. (b) J ensen, F. R.; Rickborn, B. J . Am. Chem.
Soc. 1964, 86, 3784.
(20) Halpern, Y.; Garti, N. J . Organomet. Chem. 1975, 92, 291.
(21) Ibrahim, S. E.; Kreevoy, M. M. J . Phys. Chem. 1977, 81, 2143.

Cis Bis-Chelated Palladium(II) Complexes
Organometallics, Vol. 22, No. 25, 2003 5247
Sch em e 6
F igu r e 1. Negative mode electrospray mass spectrum of
a solution of 10b in acetone. The inset displays an enlarge-
ment of the parent peak of the anion with its associated
isotopic distribution.
stretching bands of the Cr(CO)3 group in 10b (1954 and
1877 cm-1) are shifted toward lower wavenumbers by
values of about 6 and 12 cm-1, respectively, as compared
to the corresponding bands of neutral complex 5 (1960
and 1889 cm-1), and by values of about 15 cm-1 as
compared to the averaged spectrum of a mixture of the
dimeric diastereomers 4 (1968 and 1893 cm-1). This
effect can be consistently interpreted in terms of an
increased flow of electron density in 10b from the Pd
center toward the Cr atom.23
toward halides to give dihalogenopalladates such as
10a .22 In a medium where the concentration of chloride
is high, the formation of palladates must be considered
(eq 3).
Treating 10b with an excess of pyridine in acetone
quantitatively yielded 5. A treatment of the same anion
by HgCl2 in excess was carried out in order to check
the possibility of forming 2a , which would indicate that
palladates play a role in the transmetalation reaction.
This hypothesis was ruled out, since the only product
recovered was 4. Nonetheless, we cannot exclude that
palladates are the major Pd(II) species in the early steps
of the transmetalation reaction.
We were able to prepare a very stable sample of 10b
from the reaction of 4 with [Me4N]Cl in acetone (eq 4).
We noted that HgCl2 was capable of attacking the
electron-rich Pd(II) center of 8a . The treatment of a pure
sample of the latter with 1 equiv of HgCl2 over 6 h
afforded, upon subsequent treatment with pyridine,
minute amounts of 2a and compounds 9a and 5 as the
major products. The latter was recovered in 60% yield
(Scheme 6). The outcome of this reaction can easily be
interpreted by a difference in reactivity of the two
CAr-Pd bonds of 8a . Given the established deactivating
effect of Cr(CO)3, the mercury center is more inclined
to bind and react with the “electron-rich” chelating lig-
and: i.e., the benzylamine fragment. The slight amounts
of 2a recovered from the reaction mixture may indicate
that only a small fraction of 8a underwent the cleavage
of the C-Pd bond related to the Cr-bound arene. This
result is reminiscent of those published several years
ago by van Koten and co-workers,24 who addressed the
reactivity of related heteroleptic bis-chelates of Pd(II)
and Pt(II) toward Hg(OAc)2. The authors demonstrated
that the site of the electrophilic attack was essentially
determined by electronic factors, the electrophilic attack
of the Hg(II) salt being directed at the carbon-metal
bond and the metal center of the Pd(II) and Pt(II)
This organometallic salt was successfully characterized
by electrospray mass spectroscopy (ESMS) in the nega-
tive mode. Figure 1 shows the ESMS spectrum obtained
after the injection of a solution of 10b in acetone in the
spectrometer. A large complex peak centered at 468 Da
corresponding to the organometallic anion of 10b as well
as a smaller one at around 332 Da corresponding to a
Cr(CO)3-free anion could be observed; the inset displays
an enlargement of the anion’s parent peak and the
isotopic distribution around the main signal at 468 Da.
The peak distribution fits almost ideally the theoretical
one calculated for C14H6NO3Cl2CrPd, the anionic part
of 10b.
Complex 10b, which proved to be stable in solution
in acetone, presented spectroscopic features different
from those related to other analogous heterodinuclear
complexes such as 5. The IR spectrum measured in
CH2Cl2 particularly illustrates the influence of the
negative charge on the d-π* back-bonding from the Cr
center to its carbonyl ligands. The two A1 and E
(23) (a) Bitterwolf, W. E. Polyhedron 1988, 7, 1377. (b) Neuse, E.
W. J . Organomet. Chem. 1975, 99, 287.
(22) Dehand, J .; Fischer, J .; Pfeffer, M.; Mitschler, A.; Zinsius, M.
Inorg. Chem. 1976, 15, 2675.
(24) van der Ploeg, A. F. M. J .; van Koten, G.; Vrieze, K. J .
Organomet. Chem. 1981, 222, 155.

5248 Organometallics, Vol. 22, No. 25, 2003
Berger et al.
Sch em e 7
Sch em e 8
substrates, respectively. Hence, in the reaction of 2a
with 7a , the excess of halide did not only promote the
formation of 3 but also contribute in “preserving” the
heteroleptic Pd(II) complex 8a from a subsequent reac-
tion with HgCl2.
The experimental conditions previously optimized for
the formation of 8a proved to be also appropriate for
the synthesis of 8b (eq 5). Complex 8b was synthesized
indicative of its relative overall stability as compared
to that of (rel)-l-8c. We observed, indeed, that the latter
decomposed more rapidly in solution than its related
stereoisomer u-8c. Similarly, complexes 8d were ob-
tained by a stoichiometric reaction of 8a with (7R)-9c.
The two diastereomers (7R)-l-8d and (7R)-u-8d were
recovered with 31% conversion as a mixture containing
a majority of (7R)-u-8d (1:1.5 ratio) (eq 7). Complexes 6
in 50% isolated yield by reacting stoichiometric amounts
of 2a and 7b in the presence of a large excess of [Me4N]-
Cl in acetone at -20 °C.
were synthesized (isolated) by a reaction of 8a with 2a
in acetone at room temperature with 50% conversion
(eq 8).
Syn th eses of Cr (CO)3-Bou n d Hom o- a n d Heter o-
lep tic P d (II) Com p lexes. Given the importance of the
deactivation of the Pd-CAr bond by the electron-
withdrawing effects of the Cr-bound chelating unit and
the relative sensitivity of these bis-chelates toward
electrophiles such as HgCl2, we decided to check whether
compounds such as 8a could serve as substrates for the
synthesis of other Pd(II) bis-chelates. The reaction
would consist of a ligand-exchange step and the replace-
ment of the “electron-rich” benzylamine fragment by a
more electron-withdrawing chelating unit. In other
terms, the driving force of the reaction would be the
formation of a Pd(II) bis-chelate, stabilized by the com-
bined electron-withdrawing effects of the two chelating
units (Scheme 7).
8a + 2a acetone, room temp8 (rel)-l-6 and u-6 (1:10) (8)
50% conversion
In this experiment we also observed a marked air
sensitivity of diastereomer (rel)-l-6, illustrated by a
(rel)-l-6 to u-6 ratio of 1:10. In fact, complexes 6 could
be generated from a one-pot reaction of 2a with
Pd(MeCN)2Cl2 in the presence of a large excess of Cl-
with 33% conversion after chromatographic separation.
In this case the (rel)-l-6:u-6 ratio was 1:5 (eq 9).
(1) Pd(MeCN)2Cl2,
10 equiv of [Me4N]Cl,
acetone, -20 °C
2a
8 (rel)-l-6 and u-6
(9)
(2) pyridine, 33% conversion
Tri-nuclear complexes 8c were synthesized by react-
ing 8a with 9b in acetone at room temperature (eq 6).
Interestingly, the syn-facial compounds could be
readily separated from their anti-facial related isomers
by classical low-temperature chromatography on silica
gel, due to their predictable difference of polarity. The
coordination of an arene ligand to a Cr(CO)3 moiety
creates the dipolar moment component µAr-Cr along the
C3 axis of the facial Cr(CO)3 group, which is oriented
from the arene’s centroid toward the Cr atom.25 It is
therefore clear that the heterotrimetallic (Pd,Cr,Cr) syn-
facial complexes will possess a molecular dipolar mo-
ment higher than that of the anti-facial isomers. Ignor-
ing the in-plane dipolar moment component of the bis-
chelate, the two components µAr-Cr in syn-facial com-
The overall conversion after purification was 52%, and
the ratio between diastereomers (rel)-l-8c and (rel)-u-
8c was evaluated to be approximately 1:1.7, respec-
tively. In fact, this predominance of (rel)-u-8c is only

Cis Bis-Chelated Palladium(II) Complexes
Organometallics, Vol. 22, No. 25, 2003 5249
pounds such as u-6 and u-8c,d are roughly parallel,
while in anti-facial isomers they are anti-parallel (Scheme
8). Consistently, in all three cases silica gel column
chromatography delivered the anti-facial trinuclear
isomers, i.e., (rel)-l-6, (rel)-l-8c, and l-8d , before the syn-
facial isomers (see Experimental Section).
Syn th esis of P la n a r Ch ir a l En a n tioen r ich ed
P a lla d a ted (η6-a r en e)Cr (CO)3 Com p lexes fr om th e
Ch lor om er cu r a ted 2-[Tr ica r bon yl(η6-p h en yl)ch r o-
m iu m ]p yr id in e. We decided to turn the drawback of
the reactivity of bis-chelated Pd(II) complexes toward
HgCl2 into an advantage for the synthesis of enantioen-
riched, planar chiral cyclopalladated (η6-arene)Cr(CO)3
complexes, which could be of interest in various ap-
plications of homogeneous catalysis.26 In view of the
above-mentioned results, it seemed technically feasible
to introduce chiral information in the transmetalation
step by using, as a chiral auxiliary, one of the readily
available enantioenriched 7R or 7S cyclopalladated
dimers of R-methyl-N,N-dimethylbenzylamine.27 The
transmetalation reaction could therefore lead to couples
of enantioenriched diastereomers, which could be physi-
cally separated and submitted to HgCl2 in order to
initiate the release of the enantioenriched cyclopalla-
dated (η6-arene)Cr(CO)3 complex. If such a method
based on the use of heteroleptic Pd(II) complexes could
be applied more generally to other potent planar chiral
Pd(II) compounds, it would provide a convenient route
to valuable organometallic complexes.
F igu r e 2. Dichrograms of 0.13 mM solutions of (+)-(7S)-
endo-8e and (-)-(7R)-endo-8e in methanol at 20 °C.
Sch em e 9
ratio was found to be 1.3:1. All stereoisomers of 8e could
be readily characterized by X-ray diffraction analysis.
This task was made easier by the fact that each endo/
exo pair of compounds happened to cocrystallize in a
pseudo-centrosymmetric space group (vide infra). For-
tunately, we succeeded in physically separating the endo
and exo diastereomers by chromatography on silica gel.
Optimal separations were performed at +5 °C with
dry chloroform as the eluent. The exo isomers, more
polar in nature, were more difficult to purify and sepa-
rate from pollutants, consisting essentially of organic
substances and 2-[(η6-phenyl)Cr(CO)3]pyridine. We there-
fore concentrated our efforts on obtaining analytically
pure samples of (7R)- and (7S)-endo-8e, which were
cleanly released in the first eluted colored chromato-
graphic band. Their stereochemical relationship of
enantiomers was confirmed readily by the determina-
tion of their specific rotation, [R]D, at 20 °C and by the
measurement of their optical absorption circular dichro-
ism. Figure 2 displays the dichrograms of (7R)- and (7S)-
endo-8e, whose Cotton effects are reciprocal.
The reaction of complex 2a with either (7R)-7c or (7S)-
7c in the presence of 10 equiv of [Me4N]Cl afforded the
corresponding pairs of diastereomers: i.e., (7R)-endo-8e/
(7R)-exo-8e and (7S)-endo-8e/(7S)-exo-8e in 65 and 70%
yields, respectively (eq 10). In both cases the endo:exo
“Relea se” of Com p ou n d s (+)-5 a n d (-)-5 a n d
Deter m in a tion of Th eir En a n tiop u r ity a n d Abso-
lu te P la n a r Con figu r a tion . Enantioenriched samples
of 5 were efficiently obtained by the mild reaction of both
(7R)- and (7S)-endo-8e with stoichiometric amounts of
HgCl2 over 14 h followed by a treatment with dry
pyridine (Scheme 9). The optical activity of each sample
of enantioenriched 5 was assessed by classical polarim-
etry as well as by circular dichroism spectropolarimetry
(Figure 3). The enantiomeric purities of compounds
(-)-5 and (+)-5 were then determined using [n-Bu3NH]-
[Λ-TRISPHAT] and [n-Bu4N][∆-TRISPHAT] salts28 as
diamagnetic NMR chiral shift agents.29 The intrinsic
1
precision of this H NMR based technique is limited by
an error of (1.0% on the value of the ee, which was
established by a comparison with the values obtained
(25) Solladie´-Cavallo, A. Tetrahedron 1985, 4, 901 and references
therein.
(26) Delacroix, O.; Gladysz, J . A. Chem. Commun. 2003, 665.
(27) (a) Otsuka, S.; Nakamura, A.; Kano, T.; Tani, K. J . Am. Chem.
Soc. 1971, 93, 4301. (b) Tani, K.; Brown, L. D.; Ahmed, J .; Ibers, J . A.;
Yokota, M.; Nakamura, A.; Otsuka, S. J . Am. Chem. Soc. 1977, 99,
7876.
(28) (a) Lacour, J .; Ginglinger, C.; Grivet, C.; Bernardinelli, G.
Angew. Chem., Int. Ed. 1997, 36, 608. (b) Lacour, J .; Ginglinger, C.;
Grivet, C.; Bernardinelli, G. Angew. Chem. 1997, 109, 660.

5250 Organometallics, Vol. 22, No. 25, 2003
Berger et al.
are given in Table 1. ORTEP diagrams of each structure
with their atomic numbering schemes are given in
Figure 5. The structural parameters of both structures,
e.g. interatomic distances and angles, are in relatively
good agreement with those obtained previously for the
racemate (()-5, which crystallized in the monoclinic
crystal system with a P21/c space group.10 The enanti-
omer (+)-5 was found to crystallize with one disordered
molecule of CH2Cl2 in the monoclinic system and its
lattice to fit the P21 space group: the molecular struc-
ture revealed a pR configuration at the ipso carbon
bearing the palladium atom (see the Supporting Infor-
mation).
A pS configuration was found for (-)-5‚CH2Cl2, which
crystallizes in the orthorhombic system with a lattice
fitting the P212121 space group.12 In both cases, Flack’s
parameter was equal to 0.01 (less than 3 times the esd),
indicating that the coordinates correspond to the abso-
lute structures of the molecules in the studied crystal.30
Of course, the determination of these absolute planar
configurations made possible, a posteriori, the structural
assignment for all the diastereomers of 8e. Quite unex-
pected and disorienting was the fact that the two enan-
tiomers crystallized in different crystal systems and
space groups. From a crystallographic point of view the
structures of the two enantiomers differ from each other
by the orientation of the pyridine ligand bonded to the
Pd(II) (Figure 6a) and by a different position of the
solvating CH2Cl2 in the unit cell, a solvent molecule that
happens to be disordered in one case. This oddity was
not reproduced by growing new crystals from a different
mixture of solvents. The slow diffusion of acetone solu-
tions of the same two enantiomers in n-hexane produced
a more conventional result. The two newly obtained
crystals of (-)-5 and (+)-5 were found to be almost per-
fect enantiomorphs, both fitting the monoclinic system
and the P21 space group (see the Supporting Informa-
tion for complete acquisition and refinement data).31
Figure 6b displays the superimposition of the structure
of (pS)-5 with that of symmetry-inverted (pR)-5. Note
F igu r e 3. Dichrograms of 0.11 mM solutions of (+)-5 and
(-)-5 in methanol at 20 °C.
F igu r e 4. Enlargement of the 1H NMR (300 MHz) spectra
of the + and - enantiomers of 5 (1.5 mM) in the presence
of [n-Bu3NH][Λ-TRISPHAT] ((a), 6.1 mM) and [n-Bu4N]-
[∆-TRISPHAT] ((b), 6.1 mM) measured at 20 °C in a 1:4
mixture of d6-acetone and d6-benzene, respectively. The
reference spectrum measured for (()-5 displays the 1:1
spliting of the proton located at the position ortho to the
palladium at the Cr-bound arene.
(29) (a) Ratni, H.; J odry, J . J .; Lacour, J .; Ku¨ndig, E. P. Organo-
metallics 2000, 19, 3997. (b) Monchaud, D.; Lacour, J .; Coudret, C.;
Fraysse, S. J . Organomet. Chem. 2001, 624, 388. (c) Planas, J . G.; Prim,
D.; Rose, E.; Rose-Munch, F.; Monchaud, D.; Lacour, J . Organometallics
2001, 20, 4107. (d) Pasquato, L.; Herse, C.; Lacour, J . Tetrahedron
Lett. 2002, 43, 5517. (e) Hebbe, V.; Londez, A.; Goujon-Ginglinger, C.;
Meyer, F.; Uziel, J .; J uge´, S.; Lacour, J . Terahedron Lett. 2003, 44,
2467. (f) Bruylants, G.; Bresson, C.; Boisdenghien, A.; Pierard, F.;
Kirsch-De Mesmaeker, A.; Lacour, J .; Bartik, K. New J . Chem. 2003,
27, 748. (g) Wenzel, T. J .; Wilcox, J . D. Chirality 2003, 15, 256.
(30) (a) Flack, H. D.; Bernardinelli, G. J . Appl. Crystallogr. 2000,
33, 1143. (b) Flack, H. D. Helv. Chim. Acta 2003, 86, 905.
(31) (pS)-5‚C3H6O: formula, C22H19ClCrN2O4Pd; molecular weight,
569.26; crystal system, monoclinic; space group, P21; a ) 6.3044(2) Å;
b ) 12.8799(5) Å; c ) 13.7727(8) Å; â ) 97.445(5)°; V ) 1108.92(9) Å3;
Z ) 2; color, orange; crystal dimemsions, 0.10 × 0.10 × 0.02 mm; Dcalcd
) 1.70 g cm-3; F000 ) 568; µ ) 1.452 mm-1; minimum/maximum
transmission, 0.9670/1.0000; T ) 173 K.; hkl limits, -6, to +6, -16 to
+15, -17 to +17; θ limits, 2.5-27.48°; 3860 data measured; 3144 data
with I > 3σ(I); 279 variables; R ) 0.030; Rw ) 0.033; GOF ) 1.044;
largest peak in final difference, 0.820 e Å-3; Flack x parameter, 0.01-
(4). (pR)-5‚C3H6O: formula, C22H19ClCrN2O4Pd; molecular weight,
569.26; crystal system, monoclinic; space group, P21; a ) 6.3067(2) Å;
b ) 12.8659(5) Å; c ) 13.7717(7) Å; â ) 97.482(3)°; V ) 1107.94(8) Å3;
Z ) 2; color, orange; crystal dimensions, 0.10 × 0.10 × 0.08 mm; Dcalcd
) 1.71 g cm-3; F000 ) 568; µ ) 1.454 mm-1; minimum/maximum
transmission, 0.9570/1.0000; T ) 173 K; hkl limits, -8, to +8, -18 to
+16, -19 to +19; θ limits, 2.5/30.03°; 5264 data measured; 4296
data with I > 3σ(I); 279 variables; R ) 0.030; Rw ) 0.031; GOF )
1.033; largest peak in final difference, 0.771 e Å-3; Flack x parameter,
-0.01(3).
from chiral phase HPLC separations in a previous study
by Lacour, Ku¨ndig, and co-workers.28,29 A series of
solutions containing these salts and rac-5, in various
proportions and deuterated solvents, were analyzed by
1H NMR spectroscopy in order to find the optimal peak
separations arising from the formation of the tightest
(+)-5/TRISPHAT and (-)-5/TRISPHAT dipole-charge
association complexes. We found out that the mixture
of 4 equiv of TRISPHAT salts with 1 equiv of (()-5
dissolved in a 1:4 mixture of d6-acetone and d6-benzene
induced, at 20 °C, a 1:1 split of the signal of one ortho
proton of the Cr-bound arene (∆δ ) 0.1 ppm), the other
signals remaining mostly unchanged or only slightly
broadened. Compounds (-)-5 and (+)-5 were analyzed
under these conditions, and their spectra displayed only
3
one signal (δ 4.25 and 4.15 ppm, respectively, J ) 5.7
Hz) suggesting that each sample can be considered as
highly enantioenriched: e.g., with an ee higher than
96% (Figure 4).
Fortunately, both enantiomers could be crystallized
and their absolute structures determined by X-ray
diffraction analyses. Acquisition and refinement data

Cis Bis-Chelated Palladium(II) Complexes
Organometallics, Vol. 22, No. 25, 2003 5251
Ta ble 1. Ta ble of Acqu isition a n d Refin em en t Da ta Collected for Com p lexes 8a , 8b, u -8c, (7R)-u -8d , (7S)-8c,
(p R)-5, a n d (p S)-5a
8a
8b
u-8c
(7R)-u-8d
(7S)-8e
(pR)-5
(pS)-5
formula
C
23H20Cr-
N2O3Pd
C
25H16Cr-
N2O3Pd
C
26H20Cr2N2-
O6Pd‚CH2Cl2
C
27H22Cr2-
N2O6Pd
C
48H44Cr2-
N4O6Pd2
C
19H13ClCrN2-
O3Pd‚CH2Cl2
C
19H13ClCrN2-
O3Pd‚CH2Cl2
mol wt
cryst syst
space group
a (Å)
b (Å)
c (Å)
530.82
monoclinic
P21/n
11.0250(3)
16.3553(4)
11.6928(3)
103.800(5)
2047.55(9)
4
550.81
monoclinic
C2/c
28.457(2)
11.4642(8)
14.7537(9)
95.678(5)
4789.6(5)
8
751.78
monoclinic
P21/n
11.9974(2)
16.7208(2)
14.3988(3)
98.483(5)
2856.89(8)
4
680.88
1089.70
596.11
monoclinic
P21
6.4747(2)
12.4324(3)
14.0935(5)
96.103(5)
1128.04(6)
2
596.11
orthorhombic
P212121
18.0316(3)
18.0653(3)
6.6008(1)
orthorhombic monoclinic
P212121
10.2721(2)
12.4607(2)
20.8988(4)
P21
11.1217(3)
17.0324(4)
11.5570(3)
102.118(5
2140.45(9)
2
â (deg)
V (Å3)
2675.00(8)
4
2150.19(6)
4
Z
color
yellow
orange
red
orange
orange
orange
orange
0.20 × 0.08 ×
0.03
1.84
1176
1.739
0.9449/
1.0000
-25 to +25,
-25 to +25,
-9 to +9
2.5-30.03
6317
cryst dimens
(mm)
0.08 × 0.08 × 0.18 × 0.14 × 0.20 × 0.12 ×
0.04 0.01 0.10
1.72 1.53 1.75
1064
1.437
0.20 × 0.16 × 0.20 × 0.14 × 0.20 × 0.16 ×
0.14 0.14 0.10
1.69 1.69 1.75
1360
1.507
0.9759/
Dcalcd (g cm-3
F000
)
2192
1.232
0.8539/
1496
1.601
0.9597/
1096
1.377
0.9609/
588
1.658
0.9592/
1.0000
-9 to +9,
-17 to +17,
-19 to +19
2.5-30.04
6353
2879
µ (mm-1
)
transmissn min/ 0.8935/
max
hkl limits
1.0000
1.0000
1.0000
1.1181
1.0000
-15 to +15,
-19 to +23,
-16,16
-36 to +36,
-14 to +13,
-17 to +17
2.5-27.47
8042
-16 to +16,
-22 to +23,
-20 to +20
2.5-30.04
15 912
-14 to +14,
-17 to +17,
-29 to +29
2.5-30.03
7821
-7 to +15,
-20 to +23,
-15 to +16
2.5-30.03
12 332
θ limits (deg)
no. of data measd 9793
no. of data with
I > 3σ(I)
no. of variables
R
2.5-30.00
3421
2346
5810
3612
4310
5347
271
289
361
343
558
255
271
0.032
0.032
0.968
0.620
0.056
0.087
1.043
0.832
0.025
0.030
1.021
0.430
0.025
0.031
1.018
0.374
0.030
0.046
1.046
0.424
0.040
0.057
1.129
1.137
0.030
0.036
1.037
0.893
Rw
GOF
largest peak in
final diff map
(e Å-3
)
a
Reflections were collected at 173 K with a Nonius KappaCCD diffractometer using the Mo KR graphite-monochromated radiation (λ
) 0.710 73 Å).
F igu r e 5. Atom-numbering schemes and ORTEP diagrams of the structures of (a) (+)-(pR)-5 and (b) (-)-(pS)-5 drawn at
the 30% probability level. Hydrogen atoms and molecules of CH2Cl2 have been omitted for clarity purposes.
that, in these two structures, 5 is solvated by one
molecule of acetone.
Molecu la r Str u ctu r es of Hom o- a n d Heter olep tic
Cis Bis-Ch ela ted P d (II) Com p lexes. We succeeded
in obtaining crystals of complexes 8a (Figure 7), 8b
(Figure 8), (rel)-u-8c (Figure 9), (7R)-u-8d (Figure 10),
and (7R)- and (7S) endo-8e and exo-8e by the slow
diffusion of concentrated dichloromethane solutions of
each solute in n-hexane at -20 °C. Table 1 lists perti-
nent acquisition and refinement data for complexes

5252 Organometallics, Vol. 22, No. 25, 2003
Berger et al.
F igu r e 6. Accelerys ViewerPro drawings of the superimposed structures of inverted (+)-(pR)-5 (dark gray) and (-)-
(pS)-5 (light gray): (a) from the nonenantiomorphic structures containing one molecule of dichloromethane per complex;
(b) from the enantiomorphic structures containing one molecule of acetone per complex. Molecules of solvents have been
omitted for the sake of clarity.
F igu r e 8. Atom-numbering scheme and ORTEP drawing
for complex 8b drawn at the 30% probability level. Hy-
drogen atoms have been omitted for clarity purposes.
Selected interatomic distances (Å) and angles (deg):
Cr-Pd, 4.02(1); Cr-C4, 2.29(1); Cr-C5, 2.25(1); Cr-C8,
F igu r e 7. Atom-numbering scheme and ORTEP drawing
for complex 8a drawn at the 30% probability level. Hydro-
gen atoms have been omitted for clarity purposes. Selected
2.19(1); N1-Pd, 2.13(1); C4-Pd, 1.99(1); C15-Pd, 2.00(1);
interatomic distances (Å) and angles (deg): Cr1-Pd, 3.984-
N2-Pd, 2.11(1); N1-Pd, 2.13(1); C9-C4-C5, 114(1);
(3); Cr1-C3, 2.288(3); N2-Pd, 2.146(3); N1-Pd, 2.193(3);
C16-C15-C20, 115(1).
C4-Pd, 2.004(3); C13-Pd, 1.987(3); C5-C4-C9, 117.0(3);
C18-C13-C14, 121.7(3); N2-Pd-N1, 102.3(1); C13-Pd-
C4, 97.9(1); N2-Pd-C13, 81.0(1); N1-Pd-C4, 82.0(1).
opposite faces of the mean plane containing the pal-
ladium. This feature was already reported, in the past,
in numerous examples of cis bis-chelated Pd(II) and
Pt(II) complexes and elegantly used by von Zelewsky
and co-workers for the synthesis of enantiopure helical
objects.32 One must also mention the appealing applica-
tion by Yamaguchi and co-workers of Pt(II) bis-chelated
homoleptic complexes as helical building blocks for the
synthesis of helical inorganic polymers in which the Pt
8a -e (complete data for (7R)-8e are given in the
Supporting Information). As mentioned previously, the
couple of diastereomers of both (7S)- and (7R)-8e
cocrystallized in a pseudo centrosymmetric space group.
Figures 11 and 12 display the structures of the two
diastereomers of (7S)-8e extracted from a single set of
data. The main structural property of these heteroleptic
complexes is the distorted-square-planar coordination
geometry around the Pd(II) center. This distortion is
explained by the steric strain existing between the
proximal aryls of the bis-chelate, which tilts them to
(32) (a) Deuschel-Cornioley, C.; Stoeckli-Evans, H.; von Zelewsky,
A. J . Chem. Soc., Chem. Commun. 1990, 121. (b) Gianini, M.; Forster,
A.; Haag, P.; von Zelewsky, A.; Stoeckli-Evans, H. Inorg. Chem. 1996,
35, 4889. (c) Gianini, M.; von Zelewsky, A.; Stoeckli-Evans, H. Inorg.
Chem. 1997, 36, 6094.

Cis Bis-Chelated Palladium(II) Complexes
Organometallics, Vol. 22, No. 25, 2003 5253
F igu r e 10. Atom-numbering scheme and ORTEP drawing
for complex (7R)-u-8d drawn at the 30% probability level.
Hydrogen atoms have been omitted for clarity purposes.
Selected interatomic distances (Å) and angles (deg): Cr2-
Pd, 4000(5); Cr1-Pd, 3.887(5); Cr1-C17, 2.300(5); Cr2-
C23, 2.268(5); Cr1-C14, 2.245(4); Cr2-C26, 2.226(4); C23-
Pd, 2.000(3); N2-Pd, 2.144(3); N1-Pd, 2.162(3); C17-Pd,
1.978(3); Pd-Cr1, 3.887(5); Pd-Cr2, 4.000(5); C22-C23-
C24, 117.5(3); C12-C17-C16, 117.2(3); C17-Pd-C23,
96.0(1).
F igu r e 9. Atom-numbering scheme and ORTEP drawing
for (rel)-u-8c drawn at the 30% probability level. Hydrogen
atoms and the solvating molecule of CH2Cl2 have been
omitted for clarity purposes. Selected interatomic distances
(Å) and angles (deg): Cr1-Pd, 4.012(2); Cr2-Pd, 3.740(2);
Cr1-C7, 2.287(2); Cr2-C16, 2.276(2); C7-Pd, 2.001(2);
N1-Pd, 2.178(2); N2-Pd, 2.124(2); C16-Pd, 1.993(2);
Pd-Cr1, 4.012(2); Pd-Cr2, 3.740(2); C7-Pd-C16, 98.22-
(8); C7-Pd-N1, 81.45(8); N1-Pd-N2, 101.07(7); N2-Pd-
C16, 81.20(8).
center intervenes as a ditopic “double-sided” Lewis
base.33
The helical distortion of the square plane, or twist,
can be roughly quantified by the determination of the
interplanar angle Ψ between the two chelation planes
defined by the carbon, nitrogen, and palladium atoms
of each chelate (Figure 13). Table 2 gives the value of
Ψ for a series of published bis-chelates of Pd(II) and
Pt(II) as well as for those described in the present
article. It is clear that the presence of a Cr(CO)3 moiety
increases dramatically the torsion of the system of about
10° with respect to the three cases of mononuclear Pd
and Pt complexes 11,34 12, and 13,35 whose data were
extracted from the Cambridge Crystallographic Data-
base (Chart 3). The peculiar propensity of the aryl
group adjacent to the Cr-bound arene to point toward
the Cr(CO)3 rotor and not, as one might have expected,
outward to minimize steric interactions can be added
as yet another peculiarity of these polynuclear species.
Strikingly, this orientation is observed in all six cases
of binuclear (Cr,Pd) bis-chelated complexes that were
crystallized and analyzed by X-ray diffraction.
F igu r e 11. Atom-numbering scheme and ORTEP diagram
of (7S)-endo-8e extracted from the structure of the two
cocrystallized diastereomers and drawn at the 30% prob-
ability level. Hydrogen atoms have been omitted for clarity
reasons. Selected interatomic distances (Å) and angles
(deg): Cr1-Pd, 3.99(1); Cr1-C5, 2.290(9); Cr1-C7, 2.20-
(1); Cr1-C4, 2.28(1); C5-Pd1, 1.98(1); N1-Pd1, 2.149(9);
N2-Pd1, 2.187(8); C24-Pd1, 2.00(1); C6-C5-C4, 116.3-
(9); N1-Pd1-N2, 102.3(3); N2-Pd1-C24, 81.6(4); C24-
Pd1-C5, 97.5(4); C5-Pd1-N1, 81.5(4); C19-C24-C23,
119(1).
In a first approach to this problem, one could assume
that such a conformation of the bis-chelate stems from
a C-H‚‚‚[Cr(CO)3] interaction. In complex 8b, the close
contacts measured between the two phenyl groups
would suggest a diffuse multicenter interaction that
(33) Yamaguchi, T.; Yamazaki, F.; Ito, T. J . Am. Chem. Soc. 2001,
123, 743.
(34) Fuchita, Y.; Yoshinaga, K.; Hanaki, T.; Kawano, H.; Kinoshita-
Nagaoka, J . J . Organomet. Chem. 1999, 580, 273.
(35) Chassot, L.; Mu¨ller, E.; von Zelewsky, A. Inorg. Chem. 1984,
23, 4249.

5254 Organometallics, Vol. 22, No. 25, 2003
Berger et al.
F igu r e 14. Enlarged view of the endo tilting of the phenyl
fragment toward the Cr(CO)3 moiety in 8b. The dashed
lines indicate the shortest distances separating the H atom
of the endo phenyl fragment from the vicinal Cr-bound
arene.
F igu r e 12. Atom-numbering scheme and ORTEP diagram
of (7S)-exo-8e extracted from the structure of the two
cocrystallized diastereomers and drawn at the 30% prob-
ability level. Hydrogen atoms have been omitted for clarity
reasons. Selected interatomic distances (Å) and angles
(deg): Cr2-Pd2, 4.00(1); Cr2-C29, 2.295(9); Cr2-C30,
2.235(9); Cr2-C28, 2.25(1); Cr2-C31, 2.21(1); C29-Pd2,
2.00(1); C48-Pd2, 2.01(1); N3-Pd2, 2.165(9); N4-Pd2,
2.186(8); N3-Pd2-N4, 103.6(3); N3-Pd2-C29, 79.9(4);
C29-Pd2-C48, 98.6(4); N4-Pd2-C48, 81.1(4).
F igu r e 15. Nonbonding occupied orbitals putatively re-
sponsible for the endo tilting of the chelating ligand
adjacent to the Cr-bound one.
orbital located at the Cr atom,38 of which one of the
three lobes of which points toward the ipso position
bearing the Pd(II) center.
F igu r e 13. Distortion of the square-planar coordination
geometry at the Pd atom: definition of the torsion angle
Ψ.
A slight “endo” tilting of the Cr-free chelate sends the
lower lobe of the dz orbital far from the Cr(CO)3
Ta ble 2. Va lu es of Tor sion An gle Ψ for Sever a l
Bis-Ch ela ted P a lla d iu m a n d P la tin u m Com p lexes
2
fragment and minimizes the repulsive interaction (Fig-
ure 15). An “exo” tilting places the chelating ligand
above the Cr-bound arene and sends the lower lobe of
endo- exo-
11 12 13 8a
8b
8e
8e ul-6 ul-8c ul-8d
Ψ (deg) 6.8 8.6 4.0 20.7 23.6 20.0 21.0 24.0 16.3 17.3
2
the dz orbital toward the Cr(CO)3 group.
Strong electronic repulsion between the Cr(CO)3
group and mesomeric donor substituents can cause a
slight folding of the arene ligand.39 In the cases reported
here, such a distortion of the Cr-bound arene is not
noticed. To the best of our knowledge, what is witnessed
here in the solid state is an unprecedented electronically
induced oriented distortion of the square-planar coor-
dination geometry around the Pd(II) center. Preliminary
1H and 13C NMR studies of solutions of u-6 at 213 K
did not reveal any slowed rotation of the cluttered Cr-
involves the ortho hydrogen of the proximal aryl group
and at least two other centers, i.e., the chromium and
the carbon atoms of one CO ligand that syn-eclipses the
Pd (Figure 14). If the values of the interatomic distances
are compared to the data collected for other reported
cases of established intermolecular C-H‚‚‚CO interac-
tion, in 8b they fall far from what is actually expected
for a strong interaction.36 The reason for the endo tilting
of the aryl group toward the Cr(CO)3 therefore does not
seem to be a weak intramolecular interaction.
This peculiar distortion of the square plane reported
here very likely stems from an electronic repulsion
(37) Aullon, G.; Alvarez, S. Inorg. Chem. 1996, 35, 3137.
(38) Muetterties, E. L.; Bleeke, J . R.; Wucherer, E. J .; Albright, T.
A. Chem. Rev. 1982, 82, 499.
(39) (a) Hunter, A. D.; Shilliday, L.; Furey, W. S.; Zaworotko, M. J .
Organometallics 1992, 11, 1550. (b) Hunter, A. D.; Mozol, V.; Tsai, S.
D. Organometallics 1992, 11, 2251. (c) Djukic, J . P.; Rose-Munch, F.;
Rose, E.; Vaissermann, J . Eur. J . Inorg. Chem. 2000, 1295. (d) Suresh,
C. H.; Koga, N.; Gadre, S. R. Organometallics 2000, 19, 3008.
2
between the nonbonding populated dz orbital centered
at the Pd atom37 and a nonbonding populated hybrid
(36) Brown, M.; Zubkowsky, J . D.; Valente, E. J .; Yang, G. Z.; Henry,
W. P. J . Organomet. Chem. 2000, 613, 111.

Cis Bis-Chelated Palladium(II) Complexes
Organometallics, Vol. 22, No. 25, 2003 5255
Ch a r t 3
(CO)3 moiety. The 13C nuclei of the two Cr(CO)3 groups
in u-6 are isochronous and give a singlet at 235.1
ppm.
Con clu d in g Rem a r k s
Homo- and heteroleptic bis-chelated Pd(II) complexes
can be synthesized by several methods that are based
on the transmetalation of metalated C-L type (L ) N,
O, P) chelating ligands with electrophilic Pd salts.40-42
In almost all cases, the sole products of the transmeta-
lation reaction are the cis isomers. Several authors
stated that the origin of this stereoselectivity lies in the
lower steric strains observed in cis stereoisomers as
compared to trans isomers.40e,h,i Using these methods,
homoleptic palladium complexes can be obtained in
yields ranging from 20 up to 90% in some cases,40c,h
whereas the synthesis of heteroleptic complexes is much
less convenient for the formation of homoleptic com-
plexes, as byproducts cannot be completely avoided in
most cases.40e We have described here a method of
synthesis of stable heteroleptic complexes based on the
use of mercurated substrates and cyclopalladated aro-
matics, which in some ways complements the early
studies of Vicente and co-workers on simpler systems.41
We also verified the validity of this method for the
synthesis of simple homoleptic Pd(II) complexes such
as 14a (eq 11) and 14b (eq 12).
those of original samples prepared according to less
efficient published procedures.40a,h It is worth noting
that attempts at obtaining heteroleptic Pd(II) complexes
from 2a and the ferrocene-derived Pd(II) chelate 7d ,43
in the presence of a large excess of Cl-, only resulted in
the quantitative formation of 5 upon quenching with
pyridine (eq 13).
The one-pot reaction of 2 equiv of complexes 9a and
9d , respectively, with (MeCN)2PdCl2 in the presence of
large amounts of [Me4N]Cl in acetone at room temper-
ature yielded the two homoleptic complexes in good
yields. Their analytical data were found to agree with
Scheme 10 summarizes our findings on the mecha-
nism of formation of bis-chelated Pd(II) compounds from
2a , [NMe4]Cl, and a bis(µ-chloro) palladacycle. The
persistence of the Pd(II) bis-chelate is clearly condi-
tioned by the balance existing between the relative rates
of those reactions that create (transformations C and
D, Scheme 10) and consume it (transformations F and
G, Scheme 10). The chloride salt, which ensures the
continuous trapping of HgCl2 (equilibrium B, Scheme
10), the steady formation of 3 (path A, Scheme 10) and
the equilibrated monomerization of the chloropallada-
cycle (equilibrium E, Scheme 10), plays a key role. In
the reactions leading to 8a ,b and 8e, processes desig-
nated by letters F and G are obviously inefficient under
the conditions we have used, probably because the
(40) (a) Kasahara, A.; Izumi, T. Bull. Chem. Soc. J pn. 1969, 42, 1765.
(b) Longoni, G.; Fantucci, P.; Chini, P.; Canziani, F. J . Organomet.
Chem. 1972, 39, 413. (c) Abicht, H. P.; Issleib, K. J . Organomet. Chem.
1980, 185, 265. (d) Dehand, J .; Mauro, A.; Ossor, H.; Pfeffer, M.; Santos,
R. H.; Lechat, J . R. J . Organomet. Chem. 1983, 250, 537. (e) J anecki,
T.; J effreys, J . A. D.; Pauson, P. L.; Pietrzykowski, A.; McCullough,
K. J . Organometallics 1987, 6, 1553. (f) Maassarani, F.; Pfeffer, M.;
Le Borgne, G.; J astrzebski, J . T. B. H.; van Koten, G. Organometallics
1987, 6, 1111. (g) Cornioley-Deuschel, C.; von Zelewsky, A. Inorg.
Chem. 1987, 26, 3354. (h) J olliet, P.; Gianini, M.; von Zelewsky, A.;
Bernardinelli, G.; Stoeckli-Evans, H. Inorg. Chem. 1996, 35, 4883. (i)
Fuchita, Y.; Yoshinaga, K.; Hanaki, T.; Kawano, H.; Kinoshita-
Nagaoka, J . J . Organomet. Chem. 1999, 580, 273.
(41) (a) Vicente, J .; Chicote, M. T.; Martin, J .; Artigao, M.; Solans,
X.; Font-Altaba, M.; Aguilo, M. J . Chem. Soc., Dalton Trans. 1988,
141. (b) Sokolov, V. I.; Troitskaya, L. L.; Reutov, O. A. J . Organomet.
Chem. 1975, 93, C11.
(42) Valk, J . M.; Boersma, J .; van Koten, G. Organometallics 1996,
15, 4366.
(43) (a) Lednicer, D.; Hauser, C. R. Org. Synth. 1960, 40, 31. (b)
Gaunt, J . C.; Shaw, B. L. J . Organomet. Chem. 1975, 102, 511.

5256 Organometallics, Vol. 22, No. 25, 2003
Berger et al.
Sch em e 10
8a + 14b acetone8 8b + ?
(15)
In our opinion the electron-withdrawing effect of the
Cr(CO)3 group associated with its bulkiness makes the
cleavage of C-Pd bonds less likely than in mononuclear
“Cr-free” species. Only the exchange of ligand leading
to a less electron-rich but strongly chelated Pd center
operates, as exemplified by the latter reaction of 8a with
14b. This information would be consistent with a
mechanism implying a “face to face” approach of the two
bis-chelated Pd(II) complexes as proposed previously by
von Zelewsky and co-workers.40h
In conclusion, almost enantiopure, planar chiral
complexes derived from 2-phenylpyridine can readily be
obtained by the method described here. This methodol-
ogy offers great advantages over other known methods
of introduction of planar chirality applied to similar Cr
complexes.3c The synthesis of compounds such as 8e
does not require extreme low temperatures and high-
grade dry solvents. Provided that extreme caution is
applied in the handling and disposal of toxic mercury
derivatives and wastes, both organomercury and -pal-
ladium substrates are readily available from very simple
procedures; they display a relative inertness to air and
moisture, which allows their storage over long periods
of time. In the future, we shall concentrate our efforts
on establishing further alternative routes to enantioen-
riched, planar chiral metalated complexes that use the
methods described in this article.
electron-withdrawing Cr(CO)3 moiety deactivates the
Pd(II) center toward electrophilic attacks. However, one
must expect these steps to predominate whenever the
Pd(II) is “richer” in electron density, which might be the
reason why we have not recovered any heteroleptic bis-
chelated species in the reaction of 2a with 7d . Both
reactions C and D have their rates limited by the
amount of electrophilic palladium dimer released in
solution upon displacement of the monoanionic palla-
date, which must affect the relative rate of the trans-
metalation step.
The chemical stability of bis-chelated Pd(II) complexes
was probed by many authors, who focused essentially
on the behavior of these electron-rich complexes toward
various sorts of electrophiles. One interesting property,
which has been addressed for the first time by von
Zelewsky and co-workers, is the chemical fluxionality
of bis-chelated palladium(II) complexes such as 14b,c
and their ability to cross-exchange chelating units and
give 14d (eq 14).40h
Exp er im en ta l Section
All experiments were carried out under a dry atmosphere
of argon, with dry and degassed solvents. Chloromercurated
and cyclopalladated compounds such as 2a , (7S)-9c, 4,10 bis-
(µ-chloro)(N,N-dimethylbenzylamine-2C,N)dipalladium(II) (7a),14
(+)- and (-)-bis(µ-chloro)[(S)- and (R)-N,N-dimethyl-R-phenyl-
ethylamine-2C,N]dipalladium(II) (7c),27 and 7b44 were syn-
thesized according to published procedures. Neutral silica gel
(Si 60, 40-63 µm) for column chromatography was purchased
from Merck and tetramethylammonium chloride from Avo-
cado. NMR spectra were acquired with Bruker DRX 500 (13C
1
and H nuclei) and Bruker AV-300 (1H) spectrometers at room
temperature unless otherwise stated. Chemical shifts are
reported in parts per million downfield of Me4Si. IR spectra
were measured on a Perkin-Elmer FT spectrometer. Elemental
analyses (reported in percent mass) were performed at the
analytical centers of “Universite´ Louis Pasteur” and the
“Institut Charles Sadron” in Strasbourg. CD spectra were
recorded in Geneva with a J ASCO J R 7 spectropolarimeter
using 1 cm optical length quartz cells. ∆ꢀ is expressed in units
of cm2 mmol-1. High-resolution mass spectra were carried out
with the fast atom bombardment (FAB) method, and electro-
spray mass spectra were acquired in the negative mode at the
“Service de Spectrome´trie de Masse de Strasbourg”.
None of the heteroleptic binuclear bis-chelated
Pd(II) complexes that we report in this paper underwent
such a spontaneous disproportionation in solution, even
after several days of stirring at room temperature. In
fact, we found it difficult to discriminate between the
result of a departure of the Cr(CO)3 moiety and that of
a disproportionation reaction. However, we could ob-
serve a ligand exchange in the stoichiometric reaction
of 8a with 14b, which afforded a new mixture containing
50 mol % of complexes 8b, 8a , and 14b as well as other
unidentified species, after 3 h of stirring at room
temperature (eq 15).
Exp er im en ta l P r oced u r e for th e X-r a y Diffr a ction
An a lysis of Com p ou n d s 8a , 8b, u -8c, (7R)-u -8d , (7S)-8e,
(7R)-8e, (p R)-5‚CH2Cl2, a n d (p S)-5‚CH2Cl2. Acquisition and
processing parameters are displayed in Table 1. Reflections
were collected with a Nonius KappaCCD diffractometer using
Mo KR graphite-monochromated radiation (λ ) 0.710 73 Å).
The structures were solved using direct methods; they were
refined against |F|, and for all pertaining computations, the
(44) (a) Kasahara, A. Bull. Chem. Soc. J pn. 1968, 41, 1272. (b)
Constable, E. C.; Thompson, A. M. W. C.; Leese, T. A.; Reese, D. G. F.;
Tocher, D. A. Inorg. Chim. Acta 1991, 182, 93.

Cis Bis-Chelated Palladium(II) Complexes
Organometallics, Vol. 22, No. 25, 2003 5257
Nonius OpenMoleN package was used.45 Hydrogen atoms were
introduced as fixed contributors. The absolute structures of
(7R)-u-8d (x ) 0.03(3)), (7S)-8e (x ) 0.03(3)), (7R)-8e (x ) 0.01-
(2)), (pR)-5‚CH2Cl2 (x ) -0.04(5)), and (pS)-5‚CH2Cl2 (x )
-0.05(5)) were determined by refining the corresponding Flack
x parameters.
[Tr ica r bon yl(η6-1-(iodom er cu r o)p h en yl)ch r om iu m ]py-
r id in e (2b). A solution of 1 (300 mg, 1.03 mmol) and Hg(OAc)2
(394 mg, 1.24 mmol) in EtOH (15 mL) was stirred at reflux
over 3 h under argon. The resulting medium was cooled to
room temperature and filtered over Celite. Then, [n-Bu4N]I
(380 mg, 1.03 mmol) was added and the mixture stirred for
30 min. A yellow-orange solid, which precipitated upon addi-
tion of H2O, was filtered, washed several times with water,
and dried under vacuum. Flash chromatography over silica
gel, with a mixture of 50-60% CH2Cl2 in hexane, afforded the
orange-yellow complex 2b (320 mg, 0.52 mmol, 50% yield).
97.9, 93.4, 91.6. Complex 4b: 1H NMR (C3D6O, 500 MHz) δ
8.80 (d, 3J ) 4.9 Hz, 1H, Py), 8.09 (t, 3J ) 7.5 Hz, 1H, Py),
7.95 (d, 3J ) 8.2 Hz, 1H, Py), 7.54 (t, 3J ) 5.7 Hz, 1H, Py),
6.43 (d, 3J ) 5.7 Hz, 1H, ArCr), 5.92 (d, 3J ) 6.2 Hz, 1H, ArCr),
5.80 (t, 3J ) 6.2 Hz, 1H, ArCr), 5.50 (t, 3J ) 6.2 Hz, 1H, ArCr);
13C{1H} NMR (C3D6O, 125 MHz) δ 235.1, 163.4, 149.7, 140.1,
127.2, 124.8, 120.1, 111.9, 100.7, 98.0, 93.4, 90.4. Complexes
4c,d : 1H NMR (C3D6O, 500 MHz) δ 8.63 (broad, 1H, Py), 8.12
(broad, 1H, Py), 7.88 (broad, 1H, Py), 7.46 (broad, 1H, Py), 6.26
(broad, 2H, ArCr), 5.62 (broad, 1H, ArCr), 5.48 (broad, 1H,
ArCr).
(r el)-l a n d u -(SP -4-4)-Bis[{tr ica r bon yl(η6-p h en yl-KC1)-
ch r om iu m (0)}p yr id in e-KN]p a lla d iu m (II) (6). A solution of
Pd(MeCN)2Cl2 (153 mg, 0.95 mmol) in dry acetone (10 mL)
was added dropwise to a mixture of 2a (1.0 g, 1.90 mmol) and
[Me4N]Cl (2.08 g, 19.0 mmol) in acetone (40 mL) at -20 °C.
The resulting mixture was vigorously stirred and slowly
warmed to room temperature over 7 h. The brown-orange
mixture was filtered through Celite and the filtrate stripped
of solvents. The residue was separated by low-temperature (0
°C) flash chromatography over silica gel. The unreacted
complexes 2a and 3 were eluted first with 20% and 30%
acetone/hexane mixtures. Then, the two diasteroisomers of 6
were separated with 40% and 50% acetone/hexane mixtures;
the orange-beige fraction corresponding to (rel)-l-6 (35 mg) was
eluted and followed by the fraction identified as being u-6 (180
HRMS: calcd for
C
14H8NO3I52Cr199Hg, 615.8636; found,
615.8637. IR (CH2Cl2): ν(CdO) 1897, 1968 cm-1
.
1H NMR
3
3
(C3D6O, 300 MHz): δ 8.60 (d, J ) 4.8 Hz, 1H, Py), 8.08 (d, J
3
3
) 8.1 Hz, 1H, Py), 8.02 (dd, J ) 8.1 Hz, 1H, Py), 7.58 (dd, J
3
3
) 4.8 Hz, 1H, Py), 6.55 (d, J ) 6.6 Hz, 1H, ArCr), 6.08 (d, J
3
3
) 5.8 Hz, 1H, ArCr), 5.85 (m, J ) 6.6 Hz, J ) 5.8 Hz, 2H,
ArCr). 13C{1H} NMR (CDCl3, 125 MHz): δ 232.5 (CO), 153.6,
147.6, 138.3, 126.9, 124.4, 119.9, 106.3, 100.8, 93.6, 92.7, 91.1.
199Hg NMR (CDCl3): δ -886. MS (FAB+): m/e 619 [M]+, 563
[M - 2CO]+, 483 [M - Cr(CO)3]+.
mg). Complex 6: dr ) 1:5 ((rel)-l:u), 215 mg, 0.313 mmol, 33%
52
Dir ect Syn th esis of (r el)-u - a n d l-Bis[{tr ica r bon yl(η6-
p h en yl-KC1)ch r om iu m (0)}p yr id in e-KN]m er cu r y(II) (3). A
mixture of 1 (200 mg, 0.68 mmol) and Hg(OAc)2 (328 mg, 1.03
mmol) in EtOH (15 mL) was stirred at reflux over 3 h under
argon. The resulting medium was cooled to room temperature
and filtered through Celite. A small amount of yellow solid
precipitated upon addition of a saturated solution of KI in
EtOH. The mixture was vigorously stirred for 30 min and then
filtered through Celite. The yellow filtrate was treated with
H2O and the precipitate filtered off and dried under vacuum.
Recrystallization from dry CH2Cl2/hexane afforded complex 3
(185 mg, 0.24 mmol, 69% yield). Spectroscopic and analytical
data were identical with those published previously.
conversion. Complex (rel)-l-6: HRMS calcd for C28H16N2O6
-
Cr2105Pd 684.8869, found: 684.8902; IR (CH2Cl2) ν(CdO) 1881,
1953 cm-1; 1H NMR (C3D6O, 500 MHz) δ 8.86 (d, J ) 5.1 Hz,
3
2H, Py), 8.14 (t, 3J ) 7.6 Hz, 2H, Py), 8.05 (d, 3J ) 7.8 Hz, 2H,
Py), 7.60 (t, 3J ) 6.4 Hz, 2H, Py), 6.52 (d, 3J ) 6.5 Hz, 2H,
ArCr), 6.08 (d, 3J ) 6.3 Hz, 2H, ArCr), 5.89 (t, 3J ) 6.6 Hz,
2H, ArCr), 5.60 (t, 3J ) 6.4 Hz, 2H, ArCr); 13C{1H} NMR
(C3D6O, 125 MHz) δ 235.6 (CO), 163.3, 149.8, 140.3, 128.7,
124.8, 120.1, 112.5, 101.3, 98.0, 93.4, 91.5; MS (FAB+) m/e
686 [M]+, 602 [M - 3CO]+, 550 [M - Cr(CO)3]+. Complex u-6:
HRMS calcd for C28H16N2O652Cr2105Pd 684.8869, found 684.8903;
IR (CH2Cl2) ν(CdO) 1879, 1965 cm-1
;
1H NMR (C3D6O, 500
3
3
MHz) δ 8.75 (d, J ) 5.1 Hz, 2H, Py), 8.06 (t, J ) 7.8 Hz, 2H,
Py), 7.91 (d, 3J ) 8.1 Hz, 2H, Py), 7.51 (t, 3J ) 6.3 Hz, 2H,
Bis(µ-ch lor o)[2-{tr ica r bon yl(η6-p h en yl-KC)ch r om iu m -
(0)}p yr id in e-KN]p a lla d iu m (II) (4; Mixtu r e of Isom er s).
A solution of PdCl2(MeCN)2 (0.49 g, 1.90 mmol) in dry acetone
(20 mL) was added dropwise to a solution of 2a (1.00 g, 1.90
mmol) in acetone (60 mL) at -20 °C. The resulting mixture
was vigorously stirred and slowly warmed to room temperature
over 6 h. The solution was filtered through Celite and the
solvent removed under reduced pressure. The crude residue
was submitted to low-temperature (5 °C) flash chromatography
over silica gel. Unreacted yellow complex 2a was eluted with
mixtures of 20% and 30% acetone in n-hexane, followed by one
large orange-red fraction corresponding to a mixture of ste-
reoisomers of 4 (0.67 g, 1.71 mmol, 90% yield), which was
cleanly separated with a mixture of 50% acetone in hexane.
Attempted separations of the four possible stereoisomers of 4
by a second flash chromatography at 5 °C over SiO2 afforded
only two fractions enriched in 4a and 4b, respectively, and a
third fraction containing probably the two other swiftly
interconverting isomers 4c and 4d . Data for the mixture of
steroisomers 4a -d are as follows. Anal. Calcd for C28H16N2O6-
Cl2Cr2Pd2: C, 38.88; H, 1.85; N, 3.24. Found: C, 38.73; H, 2.07;
N, 2.99. IR (CH2Cl2) ν(CO): 1893, 1968 cm-1. Complex 4a : 1H
3
3
Py), 6.38 (d, J ) 6.4 Hz, 2H, ArCr), 5.88 (d, J ) 6.4 Hz, 2H,
ArCr), 5.76 (t, 3J ) 6.2 Hz, 2H, ArCr), 5.46 (t, 3J ) 6.3 Hz,
2H, ArCr); 13C{1H} NMR (C3D6O, 125 MHz) δ 235.1 (CO),
163.4, 149.7, 140.0, 127.4, 124.7, 120.1, 111.9, 100.7, 98.0, 93.4,
90.4; MS (FAB+) m/e 686 [M]+, 602 [M - 3CO]+, 550 [M -
Cr(CO)3]+. Anal. Calcd for C28H16N2O6Cr2Pd‚CH2Cl2: C, 45.14;
H, 2.33; N, 3.63. Found: C, 44.78; H, 2.36; N, 3.54.
Alter n a tive Meth od for th e Syn th esis of 6 fr om 8a . A
solution of 8a (100 mg, 0.18 mmol) and 2a (116 mg, 0.22 mmol)
in acetone (10 mL) was stirred at room temperature for 14 h.
The mixture was filtered over Celite and the solvent evapo-
rated under vacuum. Low-temperature (0 °C) flash chroma-
tography over silica gel delivered first the byproduct 9a and
the unreacted product 2a (yellow fraction) with 20% and 30%
acetone in hexane mixtures. A large orange fraction corre-
sponding to 6 (dr ) 1:10 ((rel)-l:u), 65 mg, 0.095 mmol, 50%
conversion) was eluted with 40% and 50% acetone in hexane
mixtures.
r a c-(SP -4-4)-[2′-{Tr icar bon yl(η6-ph en yl-kC1′)ch r om iu m -
(0)}p y r id in e -KN ](N ,N -d im e t h y lb e n zy la m in e -KC1,N )-
p a lla d iu m (II) (8a ). A solution of 7a (460 mg, 0.79 mmol) in
dry acetone (20 mL) was added dropwise to a mixture of 2a
(830 mg, 1.58 mmol) and [Me4N]Cl (1.73 g, 15.8 mmol) in
acetone (40 mL) at -20 °C. The resulting mixture was
vigorously stirred and slowly warmed to room temperature
over 7 h. Then, the mixture was filtered through Celite to
remove [Me4N]2[Hg2Cl6] and the remaining [Me4N]Cl. The
filtrate was striped of solvents. The residue was separated by
low-temperature (5 °C) flash chromatography over silica gel,
and the starting chloromercurated compound 2a was eluted
3
NMR (C3D6O, 500 MHz) δ 8.85 (d, J ) 4.8 Hz, 1H, Py), 8.14
3
3
(t, J ) 8.0 Hz, 1H, Py), 8.02 (d, J ) 7.9 Hz, 1H, Py), 7.58 (t,
3J ) 5.5 Hz, 1H, Py), 6.48 (d, J ) 6.6 Hz, 1H, ArCr), 6.08 (d,
3
3J ) 6.1 Hz, 1H, ArCr), 5.86 (t, J ) 6.4 Hz, 1H, ArCr), 5.59
3
3
(t, J ) 6.4 Hz, 1H, ArCr); 13C{1H} NMR (C3D6O, 125 MHz):
δ 235.6, 163.4, 149.9, 140.3, 128.5, 124.8, 120.1, 112.5, 101.4,
(45) Fair, C. K. In MolEN: An Interactive Intelligent System for
Crystal Structure Analysis; Nonius: Delft, The Netherlands, 1990.

5258 Organometallics, Vol. 22, No. 25, 2003
Berger et al.
with a mixture of 20% acetone in hexane. The orange-brown
product 8a (520 mg, 0.98 mmol, 62% yield) was eluted with a
mixture of 50% acetone in hexane. Complex 8a : IR (CH2Cl2)
ν(CO) 1951, 1875 cm-1; 1H NMR (CDCl3, 500 MHz) δ 8.41 (d,
3J ) 5.4 Hz, 1H, Py), 7.84 (t, 3J ) 7.6 Hz, 1H, Py), 7.64 (d,
(CO’s), 162.8, 149.6, 140.3, 128.0, 125.3, 124.8, 120.1, 112.3,
102.8, 100.9, 98.3, 96.7, 94.5, 93.5, 90.8, 90.6, 71.1, 49.8, 49.2.
Anal. Calcd for C26H20N2O6Cr2Pd: C, 46.85; H, 3.00; N, 4.20.
Found: C, 47.07; H, 2.89; N, 4.10. Complex (rel)-u-8c: HRMS
calcd for C26H20N2O652Cr2104Pd 663.9172, found 663.9188; IR
(CH2Cl2) ν(CdO) 1866, 1963 cm-1; 1H NMR (C3D6O, 500 MHz)
δ 8.75 (d, J ) 5.2 Hz, 1H, Py), 8.06 (t, J ) 7.2 Hz, 1H, Py),
7.96 (d, 3J ) 8.1 Hz, 1H, Py), 7.47 (t, 3J ) 6.4 Hz, 1H, Py),
6.44 (d, 3J ) 6.2 Hz, 1H, ArCr), 6.21 (d, 3J ) 6.1 Hz, 1H, ArCr),
5.78 (t, 3J ) 6.1 Hz, 1H, ArCr), 5.67 (d, 3J ) 5.7 Hz, 1H, ArCr),
5.58 (d, 3J ) 4.9 Hz, 1H, ArCr), 5.44 (t, 3J ) 6.4 Hz, 2H, ArCr),
5.39 (t, 3J ) 6.1 Hz, 1H, ArCr), 4.23 (d, 2J ) 13.1 Hz, 2H, CH2),
3.30 (d, 2J ) 13.3 Hz, 2H, CH2) 3.01 (s, 3H, NMe3), 2.64 (s,
3H, NMe3); 13C{1H} NMR (C3D6O, 125 MHz) δ 236.3 (CO),
235.3 (CO), 163.3, 149.6, 140.2, 129.0, 127.0, 124.2, 120.9,
119.5, 110.2, 105.5, 99.5, 98.5, 95.3, 93.1, 92.0, 91.1, 90.0, 71.2,
50.0, 48.0; MS (FAB+) m/e 666 [M]+, 582 [M - 3CO]+, 530 [M
- Cr(CO)3]+.
l- a n d u -(SP -4-4)-(7R)-[Tr ica r bon yl(η6-7-m eth yl- N,N-
d im eth ylben zyla m in e-KC1,N)ch r om iu m (0)][2-{tr ica r bo-
n yl(η6-p h e n yl-KC1)ch r om iu m (0)}p yr id in e ]p a lla d iu m -
(II) (8d ). The procedure for this reaction was similar to that
described for 8c. The conditions were slightly changed as
follows: 8a (700 mg, 1.32 mmol) and (7R)-9c (726 mg, 1.45
mmol) solution in acetone (10 mL) at room temperature for
16 h. Low-temperature (0 °C) chromatography over silica gel
carried out with a mixture of 60% CH2Cl2 in hexane delivered
first colorless (7R)-7c and unreacted (7R)-9c. The large orange
fraction corresponding to the two stereoisomers of 8d (l:u dr
) 1:1.5, 280 mg, 0.41 mmol, 31% conversion) was eluted with
a mixture of 60% and 70% CH2Cl2 in hexane. The two
diasteroisomers (7R)-l-8d and (7R)-u-8d (280 mg) were sepa-
rated by low-temperature (0 °C) flash chromatography over
silica gel with mixtures of CH2Cl2 in hexane ranging from 50%
up to 80%. The orange fraction corresponding to (7R)-l-8d (40
mg) was first eluted, followed by (7R)-u-8d (60 mg). Complex
(7R)-l-8d : [R]D (CH2Cl2, 25 °C) -1100° (c ) 0.04 g/100 mL);
3
3
3J ) 7.4 Hz, 1H, Ph), 7.58 (d, J ) 8.0 Hz, 1H, Py), 7.26 (t, J
3
3
) 4.2 Hz, 1H, Py), 7.12 (m, 1H, Ph), 7.04 (m, 2H, Ph), 5.99 (d,
3
3J ) 6.5 Hz, 1H, ArCr), 5.89 (d, J ) 6.4 Hz, 1H, ArCr), 5.62
(t, 3J ) 6.4 Hz, 1H, ArCr), 5.17 (t, 3J ) 6.4 Hz, 1H, ArCr),
4.35 (d, 2J ) 12.8 Hz, 1H, CH2), 3.54 (d, 2J ) 12.8 Hz, 1H,
CH2), 2.86 (s, 3H, NMe2), 2.57 (s, 3H, NMe2); 13C{1H} NMR
(CDCl3, 125 MHz) δ 234.7 (CO), 162.7, 157.6, 147.8, 147.6,
138.5, 137.4, 130.0, 126.5, 123.8, 122.6, 122.1, 118.4, 109.1,
101.4, 97.7, 92.4, 88.4, 73.0, 50.1, 49.1. Anal. Calcd for
C
23H20N2O3CrPd: C, 52.07; H, 3.77; N, 5.28. Found: C, 51.57;
H, 3.69; N, 5.08.
(SP -4-4)-[2-{Tr ica r bon yl(η6-p h en yl-KC1)ch r om iu m (0)}-
p yr id in e-KN][2-(p h en yl-KC1)-p yr id in e-KN]p a lla d iu m (II)
(8b). The procedure for this reaction was similar to that
described for 8a . The conditions were slightly changed as
follows: 7b (190 mg, 0.32 mmol) in dry acetone (20 mL) was
added dropwise to a mixture of 2a (337 mg, 0.64 mmol) and
[Me4N]Cl (703 mg, 6.42 mmol) in acetone (40 mL) at -20 °C.
Low-temperature (5 °C) flash chromatography over silica gel
delivered first the byproducts upon elution with mixtures of
10% and 20% acetone in hexane. The large orange fraction
corresponding to 8b (178 mg, 0.32 mmol, 50% yield) was eluted
with a mixture of 30% acetone in hexane. Complex 8b: IR
(CH2Cl2) ν(CdO) 1879, 1953 cm-1; 1H NMR (C3D6O, 500 MHz)
3
3
δ 8.89 (d, J ) 5.2 Hz, 1H, Py), 8.79 (d, J ) 5.3 Hz, 1H, Py),
3
3
3
8.11 (t, J ) 7.7 Hz, 2H), 8.07 (d, J ) 8.5 Hz, 1H), 7.99 (d, J
3
3
) 8.1 Hz, 1H), 7.87 (d, J ) 7.6 Hz, 1H), 7.76 (d, J ) 7.6 Hz,
3
3
1H), 7.55 (t, J ) 6.3 Hz, 1H), 7.47 (t, J ) 5.7 Hz, 1H), 7.23
(t, 3J ) 7.4 Hz, 1H), 7.13 (t, 3J ) 7.9 Hz, 1H), 6.45 (d, 3J ) 6.3
3
3
Hz, 1H, ArCr), 6.11 (d, J ) 6.3 Hz, 1H, ArCr), 5.84 (t, J )
6.3 Hz, 1H, ArCr), 5.55 (t, 3J ) 6.3 Hz, 1H, ArCr); 13C{1H}
NMR (C3D6O, 125 MHz) δ 235.9 (CO), 165.7, 163.3, 161.8,
149.9, 149.6, 147.7, 139.9, 139.8, 138.0, 130.2, 129.4, 124.8,
124.6, 124.4, 123.6, 120.1, 120.0, 112.8, 102.5, 98.1, 93.5, 91.2.
Anal. Calcd for C25H16N2O3CrPd: C, 54.54; H, 2.90; N, 5.09.
Found: C, 54.64; H, 3.11; N, 4.87.
IR (CH2Cl2) ν(CdO) 1874, 1950 cm-1
;
1H NMR (C3D6O, 300
3
3
MHz) δ 8.76 (d, J ) 5.2 Hz, 1H, py), 8.09 (t, J ) 7.8 Hz, 1H,
py), 7.96 (d, 3J ) 8.1 Hz, 1H, py), 7.53 (t, 3J ) 6.2 Hz, 1H, py),
6.43 (d, 3J ) 6.3 Hz, 1H, ArCr), 6.13 (d, 3J ) 6.3 Hz, 1H, ArCr),
5.79 (d, 3J ) 5.1 Hz, 2H, ArCr), 5.65 (t, 3J ) 6.1 Hz, 2H, ArCr),
5.55 (t, 3J ) 6.1 Hz, 1H, ArCr), 5.37 (t, 3J ) 6.2 Hz, 1H, Ar
(r el)-l- a n d u -(SP -4-4)-[Tr ica r bon yl(η6-N,N-d im eth yl-
ben zylam in e-KC1,N)ch r om iu m (0)][2-{tr icar bon yl(η6-ph en -
yl-KC1)ch r om iu m (0)}p yr id in e-KN]p a lla d iu m (II) (8c). A
solution of 8a (200 mg, 0.37 mmol) and 9b (225 mg, 0.44 mmol)
in acetone (10 mL) was stirred at room temperature for 7 h.
The mixture was filtered through Celite and the filtrate
stripped from solvent under vacuum. Low-temperature (5 °C)
flash chromatography over silica gel afforded first the byprod-
uct 9a (colorless fraction) and some amounts of unreacted
product 9b upon elution with mixtures of 30% and 40% acetone
in hexane. A large orange fraction corresponding to a mixture
of the two stereoisomers of 8c ((rel)-l:u dr ) 1:1.7, 133 mg,
0.19 mmol, 52% conversion) was eluted with a mixture of 50-
60% acetone in hexane. Diasteroisomers rac-l-8c and u-8c (133
mg) were separated by low-temperature (0 °C) flash chroma-
tography over silica gel using mixtures of 60% and 80% of CH2-
Cl2 in hexane, respectively. The first orange band of (rel)-l-8c
(20 mg) was followed by the orange fraction of u-8c (25 mg).
Mixture of diastereomers 8c: Anal. Calcd for C26H20N2O6Cr2-
Pd: C, 46.85; H, 3.00; N, 4.20. Found: C, 46.45; H, 2.85; N,
3
Cr), 4.08 (q, J ) 6.7 Hz, 1H, CH), 3.17 (s, 3H, NMe3), 2.62 (s,
3H, NMe3), 1.48 (d, 3J ) 6.7 Hz, 3H, CH3); 13C{1H} NMR
(C3D6O, 125 MHz) δ 236.4 (CO), 235.7 (CO), 162.8, 149.5,
140.2, 129.5, 125.6, 124.9, 124.7, 120.2, 112.5, 102.6, 101.2,
98.0, 97.4, 94.3, 93.6, 90.9, 90.4, 71.8, 48.3, 42.4, 13.7. Anal.
Calcd for
C27H22N2O6Cr2Pd: C, 47.65; H, 3.23; N, 4.12.
Found: C, 47.93; H, 2.91; N, 4.08. Complex (7R)-u-8d : [R]D
(CH2Cl2, 25 °C) +550° (c ) 0.04 g/100 mL); IR (CH2Cl2) ν(Cd
1
3
O) 1867, 1962 cm-1; H NMR (C3D6O, 300 MHz) δ 8.78 (d, J
3
3
) 5.1 Hz, 1H, py), 8.06 (dd, J ) 7.8 Hz, 1H, py), 7.95 (d, J )
3
3
7.8 Hz, 1H, py), 7.48 (dd, J ) 6.5 Hz, 1H, py), 6.42 (d, J )
6.0 Hz, 1H, ArCr), 6.28 (d, 3J ) 5.8 Hz, 1H, ArCr), 5.79 (dd, 3J
3
) 6.2 Hz, 1H, ArCr), 5.63 (d, J ) 6.2 Hz, 1H, ArCr), 5.44 (m,
3
3
3H, ArCr), 5.36 (dd, J ) 6.0 Hz, 1H, ArCr), 4.41 (q, J ) 6.8
Hz, 1H, CH), 3.11 (s, 3H, NMe2), 2.47 (s, 3H, NMe2), 1.32 (d,
3J ) 6.8 Hz, 3H, CH3); 13C{1H} NMR (C3D6O, 125 MHz) δ 236.1
(CO), 235.3 (CO), 163.2, 149.4, 140.2, 130.7, 129.3, 124.3, 124.1,
119.5, 109.9, 105.5, 99.3, 99.0, 96.2, 93.4, 92.0, 90.8, 89.7, 70.6,
46.8, 40.5, 8.0. Anal. Calcd for C27H22N2O6Cr2Pd: C, 47.65; H,
3.23; N, 4.12. Found: C, 47.94; H, 3.06; N, 3.96.
4.05. Complex (rel)-l-8c: IR (CH2Cl2) ν(CdO) 1875, 1950 cm-1
;
1H NMR (C3D6O, 500 MHz) δ 8.72 (d, 3J ) 5.1 Hz, 1H, Py),
8.10 (t, 3J ) 8.1 Hz, 1H, Py), 7.97 (d, 3J ) 8.1 Hz, 1H, Py),
exo- a n d en d o-(SP -4-4)-(7S)-(7-Meth yl-N,N-d im eth yl-
ben zylam in e-KC1,N)[2-{tr icar bon yl(η6-ph en yl)ch r om iu m -
(0)}p yr id in e]p a lla d iu m (II) ((7S)-8e). A solution of (7S)-7c
(860 mg, 1.48 mmol) in dry acetone (20 mL) was added
dropwise to a mixture of 2a (1.56 g, 2.96 mmol) and [Me4N]Cl
(3.2 g, 29.6 mmol) in acetone (60 mL) at -20 °C. The reaction
medium was vigorously stirred and slowly warmed to room
temperature over 7 h. The resulting mixture was filtered over
3
3
7.53 (t, J ) 6.1 Hz, 1H, Py), 6.47 (d, J ) 6.2 Hz, 1H, ArCr),
6.05 (d, 3J ) 6.4 Hz, 1H, ArCr), 5.82 (t, 3J ) 6.2 Hz, 1H, ArCr),
5.77 (d, 3J ) 6.4 Hz, 1H, ArCr), 5.69 (d, 3J ) 6.1 Hz, 1H, ArCr),
5.64 (t, 3J ) 6.2 Hz, 1H, ArCr), 5.54 (t, 3J ) 6.2 Hz, 1H, ArCr),
5.40 (t, 3J ) 6.1 Hz, 1H, ArCr), 3.94 (d, 2J ) 13.9 Hz, 2H, CH2),
3.64 (d, 2J ) 13.9 Hz, 2H, CH2), 3.07 (s, 3H, NMe3), 2.77 (s,
3H, NMe3); 13C{1H} NMR (C3D6O, 125 MHz) δ 236.5 and 235.6

Cis Bis-Chelated Palladium(II) Complexes
Organometallics, Vol. 22, No. 25, 2003 5259
Celite and the solvent evaporated under reduced pressure.
Low-temperature (5 °C) chromatography over silica gel using
mixtures of 20% and 50% of acetone in hexane afforded the
unreacted chloromercurated compound 2a and an orange
fraction corresponding to a mixture of diastereoisomers (7S)-
8e (endo:exo dr ) 1.3:1, 1.14 g, 2.09 mmol, 70% conversion),
respectively. The two diasteroisomers (7S)-endo- and exo-8e
(400 mg) were separated by low-temperature (0 °C) chroma-
tography (column: 40 cm length × 3 cm diameter) over silica
gel with dry CHCl3. The orange-red fraction corresponding to
(+)-(pR,7S)-endo-8e (83 mg) was eluted first, followed by a
mixture of (pS,7S)-exo-8e and the products of decomposition
identified as 1 and (7S)-7c. Unfortunately, (pS,7S)-exo-8e could
not be obtained completely free of impurities, mostly because
of its air sensitivity. NMR spectroscopic data were deduced
by difference from the spectra of the mixture of (7S)-endo- and
exo-8e and pure (pR,7S)-endo-8e. Mixture of diastereoisomers
(7S)-8e: Anal. Calcd for C24H22N2O3CrPd: C, 52.89; H, 4.04;
N, 5.14. Found: C, 52.96; H, 4.02; N, 5.04. (+)-(pR,7S)-endo-
8e: [R]D (CH2Cl2, 298 K) ) +788° (c ) 0.04 g/100 mL); IR (CH2-
Cl2) ν(CO) 1951, 1875 cm-1; 1H NMR (CDCl3, 300 MHz) δ 8.48
5.57 (t, 3J ) 6.1 Hz, 1H, ArCr), 5.24 (t, 3J ) 6.2 Hz, 1H, ArCr),
3
3.47 (q, J ) 6.6 Hz, 1H, CH), 2.83 (s, 3H, NMe2), 2.54 (s, 3H,
3
NMe2), 1.92 (d, J ) 6.5 Hz, 3H, CH3); 13C{1H} NMR (CDCl3,
125 MHz) δ 234.7 (CO), 162.7, 155.5, 154.1, 147.7, 138.2, 137.7,
130.4, 126.0, 123.6, 122.4, 121.4, 118.2, 109.2, 101.9, 96.6, 91.0,
89.4, 76.4, 50.9, 46.8, 23.7; CD (MeOH, 20 °C): λ 275 (-10.2),
281 (-10.6), 324 (13.3), 380 (-3.6), 435 nm (-5.3). Anal. Calcd
for C24H22N2O3CrPd: C, 52.89; H, 4.04; N, 5.14. Found: C,
52.59; H, 4.24; N, 4.86.
(+)-(pR)-(SP -4-4)-Ch lor o(p yr id in e)[2′-{tr ica r bon yl(η6-
ph en yl-KC1′)ch r om iu m (0)}pyr idin e-KN]palladiu m (II) ((+)-
5). A mixture of (pR,7S)-endo-8e (80 mg, 0.15 mmol) and HgCl2
(60 mg, 0.22 mmol) in dry acetone (20 mL) was stirred at room
temperature for 14 h. An excess of pyridine was added
dropwise, and the resulting mixture was stirred for an ad-
ditional 15 min and then filtered through Celite. The filtrate
was stripped of solvents. The product was purified by low-
temperature (0 °C) flash chromatography over silica gel. The
colorless (7S)-9d byproduct was eluted with a 10% acetone in
hexane mixture, followed by the orange product (+)-(pR)-5 (50
mg, 0.098 mmol, 65% yield), which was cleanly eluted with a
40% acetone in hexane mixture. The spectroscopic data of this
complex were in agreement with those published for the
racemate. (+)-(pR)-5: [R]D (CH2Cl2, 298 K) +751° (c ) 0.04
g/100 mL); UV-vis (CH2Cl2, 20 °C) λ 271 (1.26 × 106 mol-1
dm2), 315 (9.1 × 104), 444 nm (3.3 × 104); CD (MeOH, 20 °C)
λ 246 (-8.5), 268 (+4.6), 326 (-10.0), 445 nm (+6.2). Anal.
Calcd for C19H13N2O3ClCrPd: C, 44.62; H, 2.54: N, 5.48.
Found: C, 44.45; H, 2.51; N, 5.38.
(-)-(p S )-(S P -4-4)-Ch lor o(p yr id in e )[2′-{t r ica r b on yl-
(η6-p h en yl-KC1′)ch r om iu m (0)}p yr id in e-KN]p a lla d iu m -
(II) ((-)-5). The procedure was similar to that described for
(+)-5: (pS,7R)-endo-8e (74 mg, 0.14 mmol) and HgCl2 (55 mg,
0.20 mmol) in dry acetone (20 mL), room temperature, 14 h.
An excess of pyridine was added. Low-temperature (0 °C) flash
chromatography over silica gel afforded (7R)-9d byproduct
with 10% acetone in hexane mixture, followed by the orange
product (-)-(pS)-5 (50 mg, 0.098 mmol, 72% yield), which was
eluted with a 40% acetone in hexane mixture. (-)-(pS)-5: [R]D
(CH2Cl2, 298 K) -733° (c ) 0.04 g/100 mL); CD (MeOH): λ
247 (+6.6), 268 (-3.7), 326 (+8.8), 445 (-5.3) nm.
3
3
(d, J ) 5.1 Hz, 1H, Py), 7.83 (t, J ) 7.5 Hz, 1H, Py), 7.61 (d,
3
3
3J ) 7.4 Hz, 1H, Ph), 7.58 (d, J ) 8.1 Hz, 1H, Py), 7.26 (t, J
3
) 6.0, 1H, Py), 7.09 (m, 1H, Ph), 7.03 (m, 2H, Ph), 5.95 (d, J
3
) 6.5 Hz, 2H, ArCr), 5.57 (t, J ) 6.2 Hz, 1H, ArCr), 5.24 (t,
3J ) 6.2 Hz, 1H, ArCr), 3.47 (q, J ) 7.0 Hz, 1H, CH), 2.83 (s,
3
3H, NMe2), 2.54 (s, 3H, NMe2), 1.92 (d, 3J ) 6.4 Hz, 3H, CH3);
13C{1H} NMR (CDCl3, 125 MHz) δ 234.7 (CO), 162.7, 155.5,
154.1, 147.7, 138.2, 137.7, 130.4, 126.0, 123.6, 122.4, 121.4,
118.2, 109.2, 101.9, 96.6, 91.0, 89.4, 76.4, 50.9, 46.8, 23.7; UV-
vis (CH2Cl2) λ 275 (1.6 × 105), 436 nm (3.3 × 104); CD (MeOH,
20 °C): λ 275 (11.1), 281 (11.6), 325 (-14.4), 378 (3.9), 435
(5.75) nm. Anal. Calcd for C24H22N2O3CrPd: C, 52.89; H, 4.04;
N, 5.14. Found: C, 52.82; H, 4.33; N, 4.89. (pS,7S)-exo-8e: IR
1
(CH2Cl2) ν(CO) 1951, 1875 cm-1; H NMR (CDCl3, 300 MHz)
3
3
δ 8.45 (d, J ) 5.2 Hz, 1H, Py), 7.83 (t, J ) 7.2 Hz, 1H, Py),
7.66 (d, 3J ) 7.2 Hz, 1H, Ph), 7.58 (d, 3J ) 8.1 Hz, 1H, py)
7.26 (t, 1H, py), 7.14 (t, J ) 7.2 Hz, 1H, Ph), 7.06 (t, J ) 7.2
Hz, 1H, Ph), 6.93 (d, 3J ) 7.3 Hz, 1H, Ph), 5.97 (d, 3J ) 6.5
Hz, 1H, ArCr), 5.88 (d, J ) 6.3 Hz, 1H, ArCr), 5.60 (t, J )
3
3
3
3
3
3
6.3 Hz, 1H, ArCr), 5.18 (t, J ) 6.2 Hz, 1H, ArCr), 4.26 (q, J
) 6.5 Hz, 1H, CH), 2.89 (s, 3H, NMe2), 2.47 (s, 3H, NMe2),
(7S)-Tr ica r b on yl(η6-1-ch lor om er cu r o-7-m et h yl-N,N-
d im eth ylben zyla m in e)ch r om iu m (0) ((7R)-9c). A solution
of (7S)-(η6-7-methyl-N,N-dimethylbenzylamine)tricarbonyl-
chromium46 (800 mg, 2.80 mmol) and Hg(OAc)2 (1.34 g, 4.20
mmol) in EtOH (25 mL) was stirred at reflux over 4 h under
argon. The resulting solution was cooled to room temperature
and filtered over Celite. Addition of a saturated solution of
CaCl2 in EtOH to the filtered solution afforded a yellow pale
solid, which was filtered, washed with water, and dried over
vacuum. Recrystallization with dry Et2O/hexane afforded the
yellow complex (7R)-9c (820 mg, 1.58 mmol, 56% yield): [R]D
(CH2Cl2, 298 K) -64.5° (c ) 1.7 × 10-3M). Anal. Calcd for
C13H14NO3ClCrHg: C, 29.94; H, 2.68; N, 2.68. Found: C, 29.84;
H, 2.85; N, 2.62. The 1H and 13C NMR as well as IR
spectroscopic data of this complex were identical with those
measured for (7S)-9c.10
Tetr a m eth yla m m on iu m (SP -4-3)-Dich lor o[2-{tr ica r bo-
n yl(η6-p h en yl-KC1)ch r om iu m (0)}p yr id in e-KN]p a lla d a te-
(II) (10b). A solution of 4 (50 mg, 0.058 mmol) with [Me4N]Cl
(127 mg, 1.16 mmol) in dry acetone (10 mL) was stirred for 4
h at room temperature. The mixture was filtered over Celite
and the solvent evaporated under vacuum. Recrystallization
with CH2Cl2/hexane affords the product 10b (25 mg, 0.046
1.55 (d, J ) 6.5 Hz, 3H, CH3); 13C{1H} NMR (CDCl3) δ 234.6
3
(CO), 162.4, 158.5, 151.8, 147.5, 138.2, 137.1, 130.4, 126.4,
123.4, 122.5, 121.8, 118.3, 109.2, 101.7, 97.5, 92.3, 88.1, 72.4,
47.9, 42.9, 23.6.
exo- a n d en d o-(SP -4-4)-(7R)-(7-Meth yl-N,N-d im eth yl-
b e n zy la m in e -KC1,N )[2-{t r ic a r b o n y l(η6-p h e n y l-KC1)-
ch r om iu m (0)}p yr id in e-KN]p a lla d iu m (II) ((7R)-8e). The
procedure for this reaction was similar to that described
previously for (7R)-8e, as follows: (7R)-7c (550 mg, 0.95 mmol)
solution in acetone (20 mL), mixture of 2a (1.0 g, 1.90 mmol)
and [Me4N]Cl (2.1 g, 19 mmol) in acetone (60 mL) at -20 °C.
Low-temperature (5 °C) chromatography over silica gel with
a mixture of 20% and 50% acetone in hexane delivered a raw
mixture of the two diastereoisomers (7R)-8e (dr )1.3:1 (endo:
exo), 670 mg, 1.23 mmol, 65% conversion), which were
separated by a second flash chromatography. A pure sample
of complex (7R)-8e (74 mg) was obtained from a mixture of
(7R)-endo- and exo-8e (300 mg). The NMR spectroscopic data
of (pR,7R)-exo-8e were identical with those observed for
(pS,7S)-exo-8e and were deduced by difference between the
NMR spectra of the mixture of (7R)-endo- and exo-8e and pure
(pS,7R)-endo-8e. Mixture of the two stereoisomers: Anal.
Calcd for C24H22N2O3CrPd: C, 52.89; H, 4.04; N, 5.14. Found:
C, 53.03; H, 3.81; N, 5.00. (-)-(pS,7R)-endo-8e: [R]D (CH2Cl2,
298 K) -813° (c ) 0.04 g/100 mL); IR (CH2Cl2) ν(CO) 1951,
mmol, 79% yield). 10b: IR (CH2Cl2) ν(CO) 1877, 1954 cm-1
;
1H NMR (C3D6O, 300 MHz) δ 9.60 (d, 3J ) 5.2 Hz, 1H, py),
8.00 (t, 3J ) 7.5 Hz, 1H, py), 7.78 (d, 3J ) 8.0 Hz, 1H, py),
3
3
3
1875 cm-1; 1H NMR (CDCl3, 300 MHz) δ 8.48 (d, J ) 5.0 Hz,
7.34 (t, J ) 6.5 Hz, 1H, py), 6.44 (d, J ) 6.3 Hz, 1H, ArCr),
6.20 (d, 3J ) 6.5 Hz, 1H, ArCr), 5.56 (t, 3J ) 6.3 Hz, 1H, ArCr),
1H, py), 7.83 (t, 3J ) 7.5 Hz, 1H, py), 7.61 (d, 3J ) 7.4 Hz, 1H,
Ph), 7.58 (d, 3J ) 8.1 Hz, 1H, py), 7.26 (t, 1H, py), 7.09 (m,
1H, Ph), 7.03 (m, 2H, Ph), 5.94 (d, 3J ) 6.3 Hz, 2H, ArCr),
3
5.41 (t, J ) 6.3 Hz, 1H, ArCr), 3.47 (s, 12H, NMe4); 13C{1H}
NMR (C3D6O, 125 MHz) δ 235.7 (CO), 164.5, 151.8, 139.4,

5260 Organometallics, Vol. 22, No. 25, 2003
Berger et al.
1
123.7, 122.6, 119.2, 112.4, 100.0, 95.7, 92.2, 91.0, 56.0 (NMe4).
Anal. Calcd for C18H20N2O3Cl2CrPd: C, 39.91; H, 3.72; N, 5.17.
Found: C, 39.95; H, 3.65; N, 5.08.
Zelewsky and co-workers,40h except for the H NMR spectrum
in CDCl3, which we found was incompletely listed by the latter
authors. Complex 14b: 1H NMR (CDCl3, 300 MHz) δ 8.63 (d,
3
3
(SP -4-4)-[Bis(N,N-d im et h ylb en zyla m in e-KC,N)]p a lla -
d iu m (II) (14a ). A solution of PdCl2(MeCN)2 (110 mg, 0.42
mmol) in dry acetone (5 mL) was added dropwise to a mixture
of 9a (315 mg, 0.84 mmol) and [Me4N]Cl (466 mg, 4.25 mmol)
in acetone (15 mL) at -20 °C. The resulting mixture was
vigorously stirred and warmed to room temperature over 6 h.
Then, the pink-brown mixture was filtered over Celite and the
filtered solution was stripped of solvents. It is important to
note that flash chromatography purification of the crude
product was avoided, due to the sensitivity of 14a to SiO2.
Recrystallization from dry CH2Cl2/hexane afforded the yellow
pale solid 14a (95 mg, 0.25 mmol, 60% yield). Analytical data
were in agreement with those reported in the literature.
(SP -4-4)-[Bis(2-p h en ylp yr id in e-KC,N)]p a lla d iu m (II)
(14b). The procedure for this reaction was similar to that
described for 14a . The conditions were slightly changed as
follows: PdCl2(MeCN)2 (133 mg, 0.51 mmol) in dry acetone (5
mL) was added dropwise to a mixture of 9d (400 mg, 1.02
mmol) and [Me4N]Cl (1.12 g, 10.2 mmol) in acetone (20 mL)
at -20 °C. The gray-white mixture was filtered over Celite to
afford a yellow solution, which was stripped of solvent under
reduced pressure. Recrystallization from dry CH2Cl2/hexane
afforded 14b (164 mg, 0.40 mmol, 80% yield). Flash chroma-
tography purification was avoided for the same reasons
mentioned previously for 14a . All analytical data were in
agreement with those reported for the same complex by von
3J ) 5.0 Hz, 2H, py), 8.08 (d, J ) 7.4 Hz, 2H, Ph), 7.88 (d, J
3
3
) 7.7 Hz, 2H, py), 7.83 (t, J ) 7.6 Hz, 2H, py), 7.64 (d, J )
7.5 Hz, 2H, Ph), 7.29 (m, 4H), 7.16 (t, 3J ) 7.4 Hz, 2H, Ph).
Ack n ow led gm en t. We thank the Centre National
de la Recherche Scientifique (J .-P.D., M.P., A.d.C., N.K.-
G.), the Swiss National Science Foundation (L.V., J .L.),
the Sandoz Family Foundation (J .L.), and the Coorde-
nac¸a˜o de Aperfeic¸oamento de Pessoal de N´ıvel Superior
(A.B.) for financial support. We also gratefully acknowl-
edge the expertise provided by Prof. Howard Flack and
Dr. Gerald Bernardinelli, from the University of Gene-
va, in helping us analyzing some of our chiral structures.
Su p p or tin g In for m a tion Ava ila ble: Complete listings
of pertinent X-ray diffraction analysis acquisition and refine-
ment data and of interatomic distances and angles for com-
plexes 8a -e mentioned in this article and for complexes (pS)-5
and (pR)-5 (both dichloromethane and acetone solvates); these
data are also available as CIF files. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM030433L
(46) Maisse, A.; Djukic, J . P.; Pfeffer, M. J . Organomet. Chem. 1998,
567, 65.