C O M M U N I C A T I O N S
W. A. In Applied Homogeneous Catalysis with Organometallic Com-
pounds. A ComprehensiVe Handbook in Two Volumes; Cornils, B.,
Hermann, W. A., Eds.; VCH Publishers: New York, 1996; Vol. 2, pp
712-732. (c) Farina, V.; Krishnamurthy, V.; Scott, W. J. Org. React.
1997, 50, 1.
(2) (a) Ehrentraut, A.; Zapf, A.; Matthias, B. AdV. Synth. Catal. 2002, 344,
209. (b) Harris, M. C.; Huang, X.; Buchwald, S. L. Org. Lett. 2002, 17,
2885. (c) Lautens, M.; Mancuso, J. Synlett 2002, 3, 394. (d) Ali, M. H.;
Buchwald, S. L. J. Org. Chem. 2001, 66, 2560. (e) Huang, X.; Buchwald,
S. L. Org. Lett. 2001, 3, 3417. (f) Jonkers, T. H. M.; Maes, B. U. W.;
Lemiere, G. L. F.; Dommisse, R. Tetrahedron 2001, 57, 7027. (g) Zapf,
A.; Beller, Mathias Chem.sEur. J. 2001, 7, 2908 (h) Andreu, M. G.;
Zapf, A.; Beller, M. Chem. Commun. 2000, 2475. (i) Baudoin, O.;
Guenard, D.; Gueritte, F. J. Org. Chem. 2000, 65, 9268. (j) Fox, J. M.;
Huang, X.; Chieffi, A.; Buchwald, S. L. J. Am. Chem. Soc. 2000, 122,
1360. (k) Old, D. W.; Harris, M. C.; Buchwald, S. L. Org. Lett. 2000, 2,
1403. (l) Wolfe, J. P.; Tomori, H.; Sadighi, J. P.; Yin, J.; Buchwald, S. L.
J. Org. Chem. 2000, 4, 1158. (m) Zhang, X.-X.; Buchwald, X. L. J. Org.
Chem. 2000, 65, 8027. (n) Mowery, M. E.; DeShong, P. Org. Lett. 1999,
1, 2137. (o) Wolf, J. P.; Buchwald, S. L. Angew. Chem., Int. Ed. 1999,
38, 3415. (p) Wolf, J. P.; Buchwald, S. L. Angew. Chem., Int. Ed. 1999,
38, 2413. (q) Wolf, J. P.; Singer, R. A.; Yang, B. H.; Buchwald, S. L. J.
Am. Chem. Soc. 1999, 121, 9550.
(3) (R3P)2Pd: (a) Portnoy, M.; Milstein, D. Organometallics 1993, 12, 1665.
(b) Ben-David, Y.; Portnoy, M.; Milstein, D. J. Am. Chem. Soc. 1989,
111, 8742. (c) Ben-David, Y.; Portnoy, M.; Milstein, D. J. Chem. Soc.,
Chem. Commun. 1989, 1816. (d) Ben-David, Y.; Gozin, M.; Portnoy, M.;
Milstein, D. J. Mol. Catal. 1992, 73, 173. (e) Fryzuk, M. D.; Clentsmith,
G. K. B.; Rettig, S. J. Organometallics 1996, 15, 2083.
(4) (R3P)Pd: (a) Galardon, E.; Ramdeehul, S.; Brown, J. M.; Cowley, A.;
Hii, K. K.; Jutand, A. Angew. Chem., Int. Ed. 2002, 41, 1761. (b) Hartwig,
J. P.; Roy, A. H. J. Am. Chem. Soc. 2001, 123, 1232.
Full line shape analysis16 of the variable temperature 31P{1H}
NMR spectra gave ∆H ) 2.04(5) kcal mol-1 and ∆S ) -2.09(9)
cal mol-1 K-1 for the equilibrium shown above. These small
differences in energy are consistent with a conformer equilibrium.
The thermodynamic parameters also reveal that conformer A, while
the minority species at very low temperatures as indicated, becomes
the predominant species near room temperature. The activation
parameters for A f B of ∆Hq ) 7.5(5) kcal mol-1 and ∆Sq )
-5(1) cal mol-1 K-1 reflect a fairly congested transition state for
the conformer interconversion.
Since 1 may be relevant to catalytic chemistry involving C-X
activation, the reaction of 1 with halobenzenes was investigated.
The reaction of 1 with excess PhX (X ) Cl, Br, I) in benzene at
room temperature resulted in the expected formation of the trans-
phenyl palladium halide complexes 2a-2c (Scheme 1). The reaction
times follow the expected order of PhI (minutes) < PhBr (1 day)
< PhCl (several days). The phenyl palladium iodide (2c) is unstable,
however, and quickly gives rise to the bridging diodide (3) and
free dcpBiph ligand. Complex 3 likely arises from ligand dissocia-
tion and dimerization of the resulting tricoordinate palladium
intermediate. Most interesting is the formation of the phosphonium
salts 4b,c as minor products (∼5% yields).17 These products
probably arise from the metalation of an ortho carbon of the distal
biphenyl ring of the phosphine ligand, followed by reductive
elimination a P-C bond from the palladium. This implies that a
palladium-arene interaction, similar to that observed in 1, may
exist for the Pd(II) complexes (2b,c). In the case of 2b,c, the
interaction has additional chemical significance in respect to arene
metalation.
(5) de Graaf, W.; Boersma, J.; Smeets, W. J. J.; Spek, A. L.; van Koten, G.;
Organometallics 1989, 8, 2907.
(6) (a) Krause, J.; Cestaric, G.; Haack, K.-J.; Seevogel, K.; Storm, W.;
Po¨rschke, K.-R. J. Am. Chem. Soc. 1999, 121, 9807. (b) Andreu, M. G.;
Zapf, A.; Beller, M. Chem. Commun. 2000, 2475.
(7) Reid, S. M.; Mague, J. T.; Fink, M. J. J. Am. Chem. Soc. 2001, 17, 4081-
4082.
(8) Experimental: A solid mixture of dcpBiph (900 mg, 2.568 mmol) and
(tmeda)PdMe2 (324 mg, 1.284 mmol) was dissolved in 17 mL of benzene
and stirred at 55 °C (tmeda ) N,N,N′N′-tetramethylethylenediamine).
Within 5 min the color changed to yellow. After 16 h, 31P{H} NMR
indicated the full consumption of dcpBiph. Volatiles were removed in
vacuo to leave a foamy yellow solid that was then dissolved in 20 mL of
Et2O. The product began to crystallize at 20 °C; the mixture was chilled
to 0 °C after which the mother liquor was removed from yellow crystals
that were washed quickly with 2 × 10 mL of cold pentane and dried in
vacuo for 16 h; yield 855 mg (82%): 1H NMR (C6D6) δ 1.22 (m, 6),
1.48-1.93 (m, 14), 1.99 (m, 2), 7.03 (m, 1), 7.14-7.25 (m, 5), 7.51 (m,
2), 7.94 (m, 1); 13C{H} NMR (C6D6) δ 26.80, 27.51 (t), 27.60 (t), 30.51
(t), 31.60 (t), 37.80 (t), 126.08, 126.12, 126.29, 126.66 (t), 128.45, 131.74
(t), 134.10 (t), 135.63 (br), 142.59 (t), 148.71 (t); 31P{H} NMR (C6D6) δ
30.81 (br). Anal. Calcd for C48H62P2Pd: C, 71.41; H, 7.74. Found: C,
71.17; H, 8.19.
Scheme 1
(9) The conformation of the phosphine substituents, viewed down the P-P
axis, result in a torsion angle of only 37.8° between the biphenyl
substituents. This conformation may be in part stabilized by a weak
C-H-π interaction between the distal rings of the two biphenyl groups.
Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond; Oxford University
Press: New York, 2001.
(10) Typically, PdP2 complexes adopt a linear or nearly linear coordination
geometry. (a) Paul, F.; Patt, J.; Hartwig, J. F. Organometallics 1995, 14,
3030. (b) Tanaka, M. Acta Crystallogr., Sec. C 1992, 4, 739. (c) Otsuka,
S.; Yoshida, T.; Matsumoto, M.; Nakatsu, K. J. Am. Chem. Soc. 1976,
98, 5850.
(11) (a) Falvello, L. R.; Fornie´s, J.; Navarro, R.; Sicilia, B., Toma´s, M. Angew.
Chem., Int. Ed. Engl. 1990, 29, 891. (b) Falvello, L. R.; Fornie´s, J.;
Navarro, R.; Sicilia, B., Toma´s, M. J. Chem. Soc., Dalton Trans. 1994,
3143.
(12) η1-arene complexes may be classified as π or σ. In the case of 1, it is
best designated as a η1-π complex. Hubig, S. N.; Lideman, S. V.; Kochi,
S. K. Coord. Chem. ReV. 2000, 200-202, 831-873.
Acknowledgment. We thank the Dow Corning Corp., NSF
(CHE-0092001) and the Tulane Institute for Macromolecular and
Engineering Sciences (NASA NAG-102070 and NCC3-946) for
financial support. The NSF (CHE-0078054) is acknowledged for
the purchase of a 400 MHz NMR.
(13) Yin, Y. J.; Rainka, M. P.; Zhang, X.-X.; Buchwald, S. L. J. Am. Chem.
Soc. 2002, 124, 1163.
(14) Marshall, W. J.; Grushin, V. V. Organometallics 2003, 22, 585.
(15) The relative broadness of the resonance at 13.5 ppm may result from an
ensemble of closely related conformers, all of which possess two biphenyl
groups with noncoordinating arenes. A specific arene interaction of
conformer B with toluene-d8 solvent is unlikely since the VT 1H and 31P-
{1H} NMR spectra of 1 in THF-d8 are virtually identical.
(16) Full line shape analysis was performed with the gNMR 4.1 software
package (Budzelaar, P. H. M. Cherwell Scientific Limited, 1999). Erying
plots of the rate constants afforded the activation parameters. A van’t
Hoff plot of the equilibrium constants afforded the thermodynamic
parameters.
Supporting Information Available: Crystallographic data for 1
(CIF and PDF) and experimental procedures (PDF). This material is
available free of charge via the Internet at http:/pubs.acs.org.
(17) X-ray crystal structures of 2b, 3, 4b, and 4c have been obtained. Details
References
will be presented in a full paper.
(1) (a) Hegedus, L. S. In Organometallics in Synthesis; Schlosser, M., Ed.;
John Wiley and Sons: Ltd.: New York, 1994; pp 383-459. (b) Hermann,
JA0361493
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