Inorg. Chem. 2004, 43, 6543−6545
(R/S)A2- or (R,S/S,R)p,p -[Pd(
K
2-P,P-
{
P(OC6H3But2-
′
2,4)2N(Me)C(O)N(Me)PPh2}Cl2]: Chirality Created by Ring Tilting
Olaf Ku1
hl*,†,‡ and Steffen Blaurock§
Institut fu¨r Chemie und Biochemie, EMAU Greifswald, Soldmannstrasse 16,
D-17487 Greifswald, Germany, and Institut fu¨r Anorganische Chemie,
UniVersita¨t Leipzig, Johannesallee 29, D-04103 Leipzig, Germany
Received June 15, 2004
The reaction of the unsymmetric bisphosphanyl urea ligand
P(OC6H3But2-2,4)2N(Me)C(O)N(Me)PPh2 with [Pd(cod)Cl2] (cod
1,5-cyclooctadiene) results in the chiral palladacycle (R,S)A2-[Pd-
2-P,P- P(OC6H3But2-2,4)2N(Me)C(O)N(Me)PPh2
Cl2]. The chirality
of the title compound is caused by the tilting of the central, six-
In the present contribution, we will describe a palladium
complex containing a bidentate phosphoramidate ligand
where the complex displays planar and axial chiral elements.
Title complex 1 can be synthesized by mixing THF solu-
tions of the ligand and [Pd(cod)Cl2] (cod ) 1,5-cycloocta-
diene) followed by precipitation with hexane.8 No attempt
was made to separate the pair of enantiomers.
)
(κ
{
}
membered PdP2N2C ring along one of the two P−N vectors and
comprises two chiral planes and one chiral axis.
Crystals of 1‚THF suitable for an X-ray diffraction study
were obtained from THF/hexane solution (Figure 1).9-12 The
palladium atom has the usual square planar coordination of
Pd(II) with a P1-Pd1-P2 angle of 93.20(3)°. The central
Pd1-P1-N1-C1-N2-P2 ring is tilted by 58° along the
N1-P2 vector effectively creating two chiral planes (Fig-
ure 2). The two Pd-Cl bond lengths are essentially equal
(233.1(1) and 233.60(9) pm) whereas the two Pd-P bond
lengths (217.77(9) and 221.78(9) pm) are not. A similar
Chirality is a very important concept in chemistry and has
major implications in catalysis, biochemistry, and pharma-
cology to name but a few.1 Chirality is described as central,
axial, and planar chirality depending on the dimension of
the chiral element.2 Prominent examples include asymmetric
carbon and metal atoms,3 a form of atropisomerism known
as “axial chirality”,4 and substituted arene transition metal
carbonyl complexes.5 Axial chirality is defined by any one-
dimensional chiral element known as an axis. This chirality
often, but not always, originates from a hindered rotation
along the phenyl-phenyl C-C bond and is therefore a form
of atropisomerism.4 Other examples of axially chiral com-
pounds include allenes, alkylidene cycloalkanes, and spi-
ranes.6 Chirality caused by a tilted ring system is compara-
tively rare7a whereas distorted chiral metalated macrocycles
play an important role in biochemistry.7b,c
(8) Complex 1 was prepared by adding 285 mg (1 mmol) of [Pd(COD)-
Cl2] to a solution of 713 mg (1 mmol) of P(OC6H3But2-2,4)2N(Me)-
C(O)N(Me)PPh2 in 20 mL of THF. After stirring for 2 h, the solution
was concentrated under reduced pressure and layered with 20 mL of
hexane. The pale yellow product was filtered off and dried in vacuo.
Crystals suitable for single crystal X-ray structure determination were
grown from the mother liquor at -20 °C. Yield 632 mg (73%); mp
178-80 °C (dec). NMR (CDCl3, 213 and 300 K): 1H δ 7.91 (m,
4H, o-Ph), 7.68 (m, 2H, p-Ph), 7.57 (m, 4H, m-Ph), 7.42 (s, 2H,
3
3
3-C6H3But2), 7.24 (d, JHH ) 8.4 Hz, 2H, 5-C6H3But2), 6.76 (d, JHH
) 8.4 Hz, 2H, 6-C6H3But2), 3.18 (d, JPH ) 5.2 Hz, 3H, Me), 3.01
3
(d, JPH ) 5.6 Hz, 3H, Me), 1.49 (s, 9H, But), 1.29 (s, 9H, But).
3
13C{1H}: δ 157.24 (s, CO), 148.04 (s, C1), 147.88 (s, C6), 139.51 (d,
† EMAU Greifswald.
JPC ) 7.55 Hz, i-Ph), 133.99 (s, C2), 133.87 (s, C4), 133.61 (d, JPC
)
‡ Current address: Institut fu¨r Angewandte Photophysik, TU Dresden,
George-Ba¨hr-Strasse 1, D-01069 Dresden, Germany. E-mail: kuhl@iapp.de.
§ Universita¨t Leipzig.
2.31 Hz, o-Ph), 130.17 (s, m-Ph), 130.04 (s, p-Ph), 117.90 (s, C5),
117.79 (s, C3), 38.27 (s, NMe), 35.89 (s, CMe), 35.18 (s,CMe), 32.46
(s, NMe), 32.05 (s, CMe), 31.01 (s, CMe). 31P{1H}: δ 86.99 (s, PO2N),
72.49 (s, PNPh2). IR (KBr, cm-1): 1680 (s, CO). Anal. Calcd for
C47H66Cl2N2O4P2Pd (962.44): C 58.65, H 6.91, N 2.92. Found: C
58.23, H 7.12, N 2.76.
(1) ComprehensiVe Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A.,
Yamamoto, H., Eds.; Springer: Berlin, 1999.
(2) (a) Cahn, R. S.; Ingold, C. K. J. Chem. Soc. 1951, 612. (b) Cahn, R.
S.; Ingold, C. K.; Prelog, V. Experienta 1956, 12, 81. (c) Cahn, R. S.;
Ingold, C. K.; Prelog, V. Angew. Chem. 1966, 78, 413. (d) Prelog,
V.; Helmchen, G. Angew. Chem. 1982, 94, 614.
(3) (a) Paiaro, G.; Panunzi, A. J. Am. Chem. Soc. 1964, 86, 5148. (b)
Flood, T. C.; Campbell, K. D.; Downs, H. H.; Nakanishi, S.
Organometallics 1983, 2, 1590.
(9) Crystallographic study (215 K): a ) 1100.4(2) pm, b ) 1232.3(2)
pm, c ) 1909.2(3) pm, R ) 104.548(3)°, â ) 99.170(3)°, γ )
91.801(3)°, with Z ) 2 in the triclinic space group P1h. R(int) ) 0.0214,
R1 ) 0.0595, wR2 ) 0.1253 for 14310 unique reflections. All
hydrogen atoms were found and refined. Absorption correction was
performed with SADABS.
(4) Bringmann, G.; Menche, D. Acc. Chem. Res. 2001, 34, 615.
(5) Salzer, A. Coord. Chem. ReV. 2003, 242, 59.
(10) Sheldrick, G. M. SADABS, A Program for Empirical Absorption
Correction; University of Go¨ttingen: Go¨ttingen, Germany, 1998.
(11) SHELXTL PLUS, XS, Program for Crystal Structure Solution, XL,
Program for Crystal Structure Determination, XP, InteractiVe Mo-
lecular Graphics; Siemens Analytical X-ray Institute Inc.: Madison,
WI, 1990.
(6) Hauptmann, S. Organische Chemie; Deutscher Verlag fu¨r Grund-
stoffindustrie: Leipzig, 1985.
(7) (a) Sumby, C. J.; Steel, P. J. Organometallics 2003, 22, 2358. (b)
Fekner, T.; Gallucci, J.; Chan, M. K. J. Am. Chem. Soc. 2004, 126,
223. (c) Fekner, T.; Gallucci, J.; Chan, M. K. Org. Lett. 2004, 6, 989.
(12) Farugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
10.1021/ic049222e CCC: $27.50
Published on Web 09/16/2004
© 2004 American Chemical Society
Inorganic Chemistry, Vol. 43, No. 21, 2004 6543