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Enantiomerically Pure Palladacycles Derived from -Ketosulfoxides.

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Enantiomerically Pure Palladacycles Derived
from fi-Ketosulfoxides**
Jose L. Garcia-Ruano,* Ana M. Gonzalez,
Isabel Lopez-Solera, JosC R. Masaguer,
Carmen Navarro-Ranninger,* Paul R. Raithby,
and Jesus H. Rodriguez
Thc coordination of the sulfinyl group to transition metal
atoms has been extensively investigated with particular reference to whether the ligand bonds through the sulfur or the
oxygen atoms.”] We are currently interested in ortho-metalation
reactionsL2]and the use of optically pure p-ketosulfoxides in
asymmetric synthesis.13] As part of these studies we therefore
decided to investigate the behavior of sulfinyls (RC(0)-CH,SO -p-Tol) toward palladium(@ salts. These compounds contain several possible coordination sites, for example the carbony1 and the sulfinyl oxygen atoms, and one chiral center
(sulfinyl sulfur atom). They may be obtained in high optical
purity, and the inherent chirality may be transferred to the metal
complexes derived from them. In addition, P-ketosulfoxides offer the possibility of forming diastereoisomeric ortho-metalated
species by the initial insertion of the electrophilic Pd“ salts into
the strongly acidic H - C bonds flanked by the SO and CO
groups,c41followed by the ortho-metalation of the para-tolyl
ring. Despite the interest in chiral compounds containing a
stereogenic sp3 hybridized C atom directly bonded to the palladium atom, very few are known.[51In this paper we describe the
synthesis and structure of the enantiomerically pure trimer 2,
which exhibits an unprecedented structure of a C-metalated
enolate (“palladium C-enolate”), unequivocally demonstrated
by X-ray diffraction.
The reaction of Pd(OAc), with (R)-3-para-tolylsulfinyl-2-propanone (1)[61under nitrogen for 48-72 hours, afforded, after
chromatographic pu0 0
rification, the com&g ....#,,. Pd(AcOh
[ Lp,j13
plex 2 as a solid in
H3C
p’ :Tol
$:;”
42% yield. The mi1
2
croanalytical data are
consistent with the
empirical formula CIoHloO,SPd, which indicates the structure
[LPd],,, and suggests that acetato ligands are not present. This
was confirmed by the IR spectra, which revealed the absence of
the two bands (1580 and 1420 cm-‘) typical of $-acetat0 ligands.[” The S=O stretch is tentatively assigned to the strong
band at 2127 cm- I , which suggests that the coordination is
through sulfur.[81The C=O stretching absorption appears at
1570 cm- I (139 cm-‘ lower than in the ligand l),which indicates that the carbonyl oxygen must be involved in the coordination; however, the high value observed for A5 is difficult to
explain.[”
The orrho-metalation of thepura-tolyl ring is evident from the
‘H NMR data (only three aromatic protons), and instead of the
methylene proton signal of 1 (6 = 3.83 (m, 2H)), a singlet with
an integral corresponding LO only one prolon appears for the
complex 2 (6 = 5.26 (s, 1H)) . Both facts suggest the formation
of a five-membered palladacycle with two Pd-C 0 bonds.
The I3C NMR parameters of 2 reveal the expected deshielding for the carbon atoms bonded to palladium, as well as of
those carbon atoms directly connected to the ligand coordination sites. In comparison with previously reported compounds,[”] the observed deshielding effect is larger for the
aliphatic carbon atom (AS(C2) =13-15) but smaller for the
aromatic one (Ab(C11) = 12). These differences are difficult to
explain unless we assume significant structural differences with
respect to both Pd-C bonds. Finally, the strong deshielding
observed for C1 (A6 = 15.6) is consistent with the structural
element Pd-O=C deduced from the IR data.
The structure of 2, which crystallizes as yellow prisms from
ethyl acetate/hexane ( l / l ) , was confirmed by an X-ray structure
determination.“ Views of the molecular structure are shown in
Figure 1. The complex is a trimer with crystallographic threefold symmetry. The core of the trimer is a nine-membered ring
of alternating S, Pd, and C(H) atoms. The plane defined by the
-
[‘I
Prof. J. L. Garcia-Ruano, Dr. J. H. Rodriguez
Departamento de Quimica Organica, Universidad Autonoma
Cantohlanco E-28049-Madrid (Spain)
Telefax’ Int code + (1) 3973-966
Prof. C. Naviirro-Ranninger. A . M. Gonzalez, Prof. J. R. Masaguer
Departamento de Quimica Inorganica, Universidad Aut6noma
Cantoblanco E-28049-Madrid (Spain)
Telefax: Int code ( 1 ) 3974-833
Dr. 1 Lhper-Solera, Dr. P. R. Raithby
Department of Chemistry, University of Cambridge (UK)
This work wab supported by CICYT Grants PB 93-0257 and SAF 93-1122,
HB-059. 1. L.-S. thanks the DGICYT for funding.
+
[**I
Angrw. c%o)i. IN/. Ed. Engl. 1995, 34, No. 12
Fig. 1. Two views of the molecular structure of 2. Selected bond lengths [A] and
angles [“I: Pdl-S1 2.32(6), P d l - 0 2 2.16(1), Pdl-C2a 2.10(2). Pdl-C12a 1.95(2),
S1-01 1.44(2), S1-C2 1.82(2), S1-Cll 1.80(2), C1-02 1.24(3), C1-C2 1.49(3);
S l - P d l - 0 2 80.5(5). S1-Pdl -C12a 94.6(7), C1 2a-Pdl -C2d 85.2(9), C2d-Pdl-02
99.4(8). (Symmetry transformation used to generate the equivalent atoms.
a: - y
2. x - .v + 1, 2). The cavity diameter is 4.04 A.
0 VCH Vrrlugsgesellschufi mbH. 0-6945f
+
Weinheini,1995
0570-0833/95/12/2-1351$ 10.00+ .25%
1351
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palladium atoms is sandwiched between two planes, one of them
defined by the sulfur atoms and the other by the methyne carbon
atoms.
Each ligand is bonded to two palladium atoms. One palladium atom is joined through two dative bonds by using the lone
pairs of electrons at the sulfur and carbonyl oxygen, while the
other palladium atom is bonded to the ligand through two covalent bonds to the methyne carbon and the ortho-carbon of the
para-tolyl unit. The two five-membered rings supported by each
palladium atom (Fig. 2), adopt
an envelope shape, in which C2
( - 0.97 A) and S1 ( - 0.84 A) lie
out of the planes defined by the
Pdla, C11, C12, and S1 atoms
and the Pdl, 0 2 , C1, and C2
atoms, respectively. The angle between the coordination planes of
CH3
two adiacent Pd atoms is 62.3".
Fig. 2 . Section of the structure
Figure bottom shows that the
of 2. showing the coordination
trimer
forms a cavity, 4.04 8, in
sphere of the palladium atoms.
diameter. The sulfur atom and
the chiral carbon atom are both
R-configurated. As expected, the two Pd-C bonds are different.
The Pdl-C12a bond length is 1.95(2) A, similar to M-C bonds
in other cyclometalated aryl complexes[21where there is some
multiple-bond character because of metal-to-ligand back bonding.[121The Pdl -C2a bond length is longer (2.10(2) A) than
that for Pdl-C12a, but also similar to other Pd-C(sp3) o
bonds supporting a sulfur atom in the trans position (2.052.10 A).[131The value of the CI-C2-S1 angle (109(2)") supports
the palladium C-enolate structure of the compound 2. The
P d l - 0 2 distance of 2.16(1) is indicative of a carbon atom of
an aryl group lying in a trans
The Pdl -S1 distance
of 2.32(6)A is slightly longer than those observed for other
complexes containing a Pd-S bond (2.19-2.25 A).r151
The palladacycle containing the two Pd- C o bonds is almost coplanar
with the aromatic ring (angle between them is 3.2"). The sulfinyl
oxygen atoms are located outside the central framework of S,
Pd, and C(H) atoms, and they form a network of intermolecular
hydrogen bonds with the methyl groups joined to the carbonyl
groups [H3c.. ' 0 1 = 2.50(4) A, C3. ' 0 1 = 3.47(4) A, C3H 3 c . . . 0 1 =173(8)"; symmetry: 0.6667 - x + y , 1.3333 - x,
0.3333 21.
Compound 2 exhibits a very high specific rotation ([a];' =
- 486.5; c = 0.2 in chloroform). Its absolute configuration was
unequivocally established as ( R ,R ) by X-ray diffraction studies
(see above). Taking into account that compound 2 is the only
diastereoisomer obtained in the reaction (the NMR spectra of
the crude product reveals the presence of only one set of signals
corresponding to this kind of diastereoisomer) ,we can conclude
that the sequence involving the insertion of the palladium into
the C-H bond (resulting in the formation of the Pd" C-enolate)
followed by the ortlzo-metalation is highly stereoselective. This
behavior and the fact that the formation of the Pd-C,*,, o bond
does not require special activation, suggests that the formation
of the palladacycle involving the two G-Pd -C bonds must take
place after the formation of the chelate containing the S-Pd and
0 - P d bonds, since this chelation is responsible for the activation of the C-H methylene bonds.
The reactions of other 0-ketosulfoxides with Pd" acetate under conditions identical to those for compound 1, yield complexes with structures similar to that of 2.
In conclusion we have reported on the synthesis of a new type
of enantiomerically pure complex composed of three molecules
of ligand and three palladium atoms. The ligand supplies the
@ ?\
+
1352
8 VCH Verlu~sgesellschaftmhH, D-694S1 Weinheim.1995
two lone pairs of electrons to coordinate with Pd" by formation
of a stable five-membered ring and the two carbon atoms to
form the covalent Pd -C bonds of a five-membered palladacycle. This is the first stable palladium C-enolate unequivocally
characterized. The usefulness of this kind of compound as ferroelectric materials is currently under investigation.
Received: February 8, 1995
Revised version: March 19, 1995 [Z 7704 IE]
German version: Anxew. Chem. 1995, 107, 1452-1454
Keywords: complexes with sulfur ligands . ortho-metalation .
palladium compounds . sulfoxides
[ l ] E. L. M. Lempers. M. J. Bloemink, J. Reedijk. Inorg. Chem. 1991.30,201-206;
S . J. Lippard. Plufinunz, Gold und other Metol Chemotherapeutic Agents ( A C S
Symp. Ser. 1983.209); R. Melanson, C. Chevrotiere. F. Rochon, Actrr Crystall o p . Sect. C 1985, 41. 1428-1431; H. B. Kagan, B. Ronan, Rev. Herevoat.
Cliem. 1992, 7.92-116. and references therein; R. Riiger, W. Rittner, P. Jones,
W. Isenberg. G. M. Sheldrick, Angrn. Chem. 1981,93,389-390; Angew. Chem.
lnt. Ed. Engl. 1981. 20. 382-383.
[2] J. L. Garcia-Ruano, I. L6pez-Solera, J. R. Masaguer, C. Navarro-Ranninger,
J. H. Rodriguez. Orgunometallirs 1992,11,3013-3018; A. Alvarez-Valdes,J. L.
Garcia-Ruano. 1. Lopez-Solera, J. R. Masaguer, C. Navarro-Ranninger, J. H.
Rodriguez, ihid. 1993, 12, 4104-41 11.
131 J. L. Garcia-Ruano. A. M. Martin. J. H. Rodriguez. J Org. Chrm. 1994, 59.
533-536; I. Alonso, J. C. Carretero, J. L. Garcia-Ruano, rhid. 1994. 59, 14991508; E. Arce. M. C. Carreiio, B. Cid, J. L. Garcia-Ruano, ihid. 1994. 59,
3421 -3426.
141 One immediate precedent of these insertion processes I S the reactions of PtCI,
with (PhCOCH,),SO. which afforded a complex which contained a puckered
four-membered ring with two C-Pt bonds (W. Henderson. R. D. W. Kemmitt.
J. Fawcett. L. J. S. Prouse, D. R. Russell, J Chem. Soc. Chem. Commun. 1986,
1791-1793; W Henderson, R. D. W. Kemmitt. L. J. S. Prouse. D. R. Russell,
J Chem. Soc. Dalton Trans. 1990, 1853- 1859). Similar insertion reactions
have been observed starting from p-ketoesters (D. A. Clarke, R. D. W.
Kemmitt. M. A. Mazid, P. Mckenna, D. R. Russell, M. D. Schilling. L. J. S.
Sherry. ihid. 1984, 1993-2002) and p-ketosulfones (W. Henderson, R. D. W.
Kemmitt. L. J. S. Prouse. D. R. Russell, ihid. 1989, 259-266). With some of
these ligands (but not for sulfoxides), palladium complexes have also been
obtained.
[51 A. Yoneda. T. Hakushi, G. R. Newkome. F. R. Fronczek. Or~onometullics
1994. 13, 4912-4918, and references therein.
[61 R. Annunziata. M. Cinquini, F. Lozzi, J. Chem. Soc. Perkin nuns. 1 1979.
1687- 1690.
[7] K. Nakamoto, IR and Ruman Sprclru of Inorganic und Coordination Cumpounds, 3rd ed., Wiley-Interscience. New York, 1978, p. 232.
[8] J. A. Davies, Adv. Inorg. Cliem. Rurliochem. 1981, 24, 135-187; B. R. James,
H. R. Morris, Cun. J. Chem. 1980.58, 399-408.
[9] A similar A: value has been observed for the carbonyl group associated to
palladium when the a-carbon atom is also bonded to a metal atom [J. Fawcett,
W Henderson, R. D. W. Kemmitt, L. J. S. Prouse, D. R. Russell, J. Chem. Soc.
Dalton Trans. 1991, 2595-25991.
[ l o ] A. R. Garber. P. E. Garrou, G. E. Hartwell, M. J. Smas. 1. R. Wilkinson, J.
Orgunomet. Chem. 1975.86, 219-223.
( 1 1 1 Crystal data for 2: C,,H,,O,Pd,S,~ H,O, rhombohedral, space group R3,
u = 13.935(2). h = 13.935(2), c = 17.1 14(2)A, Y = 2878.0(8) A'. Z = 3.
pGSlcd
=1.589gcm-'; F(000) =1356; p(MoKa)= I S 9 1 mm-'. T=153(2) K ;
3271 reflections with 5" < 20 < 45'. of which 1660 are independent were collected on a Stoe four-circle diffractometer using graphite monochromated
Mo,, (i.= 0.71073 A) radiation. Three standard reflections were measured
every 60 minutes. There was no evidence of crystal decomposition. The data
were corrected for absorption. The structure was solved by a combination of
Patterson and Fourier difference techniques [SHELXTL PLUS, Program version 4.0, Siemens Analytical X-Ray Instruments. Madison, WI, 19901 and refined by a full-matrix least-square methodology based on F Z to R = 0.079 with
all non-H atoms anisotropic [SHELX 93, Program for Crystal Structure Refinement, G. M. Sheldrick, University of Gottingen, 19931; H atoms were
placed in idealized positions and allowed to ride on the relevant C atom.
Largest peak and hole in the final difference map 0.784 and - 1.658 e k ' .
respectively. A H,O solvate was located in three disordered positions, and an
occupancy factor of 0.33 was assigned according to the height of the Fourier
synthesis. Further details of the crystal structure investigation are available on
request from the Director of the Cambridge Crystallographic data Centre, 12
Union Road, GB-Cambridge CB2 1EZ (UK). on quoting the full journal citation.
0570-0U3/95/1212-1j52 3 10.00+ 2510
Angew. Chem. Inl. Ed. Engl. 1995. 34, No. 12
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[12] G. Minghetti. M. A. Cinellu. G . Chelucci, S . Gladiali. F. Demartin, M. Manassero, J. Orgunoniel. Cheni. 1986, 307, 107-114; J. Selbln. K. Abboud. S. F.
Watkins. M . A. Gutierrez, F. R. Fronczek, ihid. 1983. 241. 259-268.
1131 K . Osakada. Y. Orawa. A. Yamamoto. Bull. Chern. SOL.Jpn. 1991. 64. 20022004: D L. Reger. D . G . Garza, L. Lebioda. Orgunomrtullics 1991. 10, 902906. ihid 1992. ii. 4285-4292.
[14] A. L. Rheingold. D. L. Staley, Acta Cry.sruilogr.Sect. C 1988, 44. 572-574: J.
Fornies. R. Kiavarro. M. Tomas. E. P. Urriolabeitia. Organornetullic.\ 1993, 12,
940 943
[15] R . Ruger. W. Rittner, P. G . Jones. W. Isenberg. G . M. Sheldrick. A n g c w Cliem
1981. 93. 3x9 390; Angew. Clirm. I n / . Ed. EngI. 1981, 20. 382-383; G. Annibale. L. C'att;rlini. V. Bertolasi, V. Ferretti, G. Gilli, M. L Tobe. J. Chem. Soc
Dalron Purr\ 1989. 1265-1271; 8 . F. G. Johnson, J. Puga. P. R. Raithby. Acru
Ct-i,,%/d/oEr
S t z f r . B 1981. 37, 953-956: S. Y. M. Chooi. P.-H. Leung. F. F
Mok. Inorg. Clirrn. Airu 1993. 205. 245-247.
~
torted ellipsoid is covered by a total 9 x 11 + 8 x 3 = 123
hydrogen substituents (Fig. 1 top).
Crystals of the title compound and other related coinpounds
were first produced serendipitously,"
and then also deliberately under well-de~igned''~- d l conditions. They will be called
"lipophilically wrapped polyion aggregates", which are defined
as follows:[3]A cluster nucleus of cations and anions provides the
essential contributions to the thermodynamic stability, whereas
predominantly the largely impenetrable hydrocarbon skin lends
kinetic stability. Other specimens of a different type,[21prepared
shortly thereafter, provided evidence of a wide-spread, generalizable crystallization (self-organization) prin~iple.'~'
3
The Lipophilically Wrapped Polyion Aggregate
([Ba6Li3021'1 -I[ - o c ( ~ ~ 3 ) ~ ~ 1 1 ( 0 C ~ H ~ ) ~ ~ ,
a Face-Sharing (Octahedron Prismane)
Ba6Li,02 Polyhedron in a Hydrocarbon
Ellipsoid : Preparation, Single Crystal Structure
Analysis, and Density Functional Calculations * *
+
Hans B o c k , * Tim H a u c k , Christian N a t h e r ,
Notker R o s c h , * Markus S t a u f e r ,
and O l i v e r D. Hiiberlen
Dedicated to Professor Gerhard Ertl
When barium metal is treated with fert-butyl alcohol, n-butyllithium in n-hexane added, the precipitate filtered off, dissolved
in tetrahydrofuran, and the resulting solution layered with n-hexane, colorless monoclinic prisms of a novel type of cluster crystallize [Eq. (a)]. According to the single crystal structure deter-
mination (Fig. 1 center), its nucleus [Ba,Li,O,]'
consists
of a Ba;' octahedron surrounding an 0'- ion and of an
analogously 0'- centered prismate Ba:+Li:,
formed by connecting three Li' centers to one of the triangular faces Ba:+.
The polyion aggregate with eleven positive charges is lipophilically wrapped by eleven tert-butyl alcoholate ions and three
tetrahydrofuran solvent molecules. The surface of the dis+
[*J Prof Dr. H. Bock. DipLChem. T. Hauck. Dr. C. NHther
Chemische Institute der Universitit
Marie-Curie-Straw 11, D-60439 Frankfurt (Germany)
Telefax' Int. code (69)5800-9188
Prof. Dr. N. R(isch, M. Staufer, Dr. 0. D. Hiberlen
Lehrstuhl fur 'l'heoretische Chemie der Technischen Universitat Munchen
D-85747 Garching (Germany)
Telefax: lnt code (89)3209-3622
Fig. 1. Single-crystal structure of {[Ba,Li,O,]"'[~OC(CH,),],,(OC,H,),)
at
150 K . Top: Space-filling representation; center: side view; bottom: unit cell
(monoclinic. P2,jm, 2 = 2) viewed along the z axis. Selected bond lengths [pm] and
angles ['I: BaBa(Ba) 381, BaBa(Li) 373. BaLi 307, LiLi 238; BaBaBa 90 and 60.
BaLiLi 103, LiLiLi 60; BaO(Ba) 260, 276, 277, BaO(Li) 266, LiO(Ba) 195, 199.
BaO(R) 264 to 278, BaO(R,) 295, LiO(R) 178 to 191, OC(R,) 140. An additional
T H F molecule is disordered in the crystal cavities.
+
+
[**I
Lipophilically wrapped polyion aggregates, Part 1. and Interactions in Crystals, Part 69. The research project was supported by the Adolf Messer Foundation. the Deutschen Forschungsgemeinschaft, the state of Hesse, and the Fonds
der Chemischen Industrie. - Part 68. N. Nagel, C. Nlther, H. Bock, Actu
Cr~.siullogr.Swr. C , 1995, in print.
The following structural details are emphasized : The Ba octahedron is slightly distorted, since the interbarium distances are
8 pm shorter on its lithium side [BaBa(Li)]. The 0'- center is
shifted by about 15 pm out of the center of the octahedron
towards the outer Ba, triangle and that of the prismane by
about 8 pm towards the Li, triangular face. Of the eleven terfbutyl alcoholate anions, seven are above Ba, octahedral faces,
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