SYNTHESIS AND STRUCTURE
289
FIG. 2. Molecular structure of complex Ka. shows 30% probability displacement ellipsoids. H atoms are omitted for clarity. Selected interatomic distances (Å)
and angles (◦): Pd (1)-C (1) = 1.830(19), Pd (1)-C (1)#1= 1.830 (19), Pd (1)-Br (1) = 2.499(2), Pd (1)-Br (1)#1 = 2.499(2), C (1)-Pd (1)-Br (1) = 90.0(4), C (1)-Pd
(1)-Br (1)#1 = 166.8(6), C (1)#1-Pd (1)-C (1) = 93.1(8).
¨
CHCl3. On the basis of X-ray diffraction, the structure of com-
plex Fa was unambiguously determined. Its molecular structure
is depicted in Figure 2.
248, 2239. (e) Gu¨rbu¨z, N.; Ozdemir, Y.; Cetinkaya, B. Tetrahedron Lett.
2005, 46, 2273. (f) Burling, S.; Whittlesey, M.K.; Williams, J.M.J. Adv.
Synth. Catal. 2005, 347, 591.
2. For a review, see Herrmann, W.A. Angew. Chem., Int. Ed. 2002, 41, 1290.
3. (a) Herrmann, W.A.; Elison, M.; Fisher, J.; Kocher, C.; Artus, G.R.J. Angew.
Chem. Int. Ed. 1995, 34, 2371. (b) Albert, K.; Gisdakis, P.; Rosch, N.
Organometallics 1998, 17, 1608. (c) Zhang, C.; Trudell, M.L. Tetrahedron
Lett. 2000, 41, 595. (d) Perry, M. C.; Cui, X.-H.; Burgess, K. Tetrahe-
dron: Asymmetry. 2002, 13, 1969. (e) Lee, H.M.; Lu, C.Y.; Chen, C.Y.;
Chen, W.L.; Lin, H.C.; Chiu, P.L.; Cheng, P.Y. Tetrahedron 2004, 60, 5807.
(f) Marshall, C.; Ward, M.F.; Harrison, W.T.A. Tetrahedron Lett. 2004, 45,
5703. (g) Clyne, D.S.; Jin, J.; Genest, E.; Gallucci, J.C.; RajarBabu, T.V.
Org. Lett. 2000, 2, 1125.
As expected, the dianionic ligand is coordinated to palladium
in a dentate fashion by the two carbene atoms, forming a nine-
membered chelate rings. X-ray analysis of these crystals showed
the geometry of the ligand around the metal to be distorted
square planar. The Pd (1)-C (1) bond length was 1.830 Å and Pd
(1)-Br (1) bond length was 2.499 Å. The C (1)-Pd-C (1ꢁ) bond
angle was determined to be 93.1◦. The Br (1)-Pd (1)-(Brꢁ) bond
angle was 89.9◦.
4. Liao, C.Y.; Chan, K.T.; Zeng, J.Y.; Hu, C.H.; Tu, C.Y.; Lee, H.M.
Organometallics 2007, 26, 1692.
CONCLUSION
5. (a) Muci, A.R.; Buchwald, S.L., Curr. Chem. 2002, 219, 131. (b) Littke,
A.F.; Fu, G.C. Angew. Chem. Int. Ed. 2002, 41, 4176.
6. For an early example of the use of chelating NHC ligands in Heck coupling
reactions, see Herrmann, W.A.; Elison, M.; Fischer, J.; Kocher, C.; Artus,
G.R.J. Angew. Chem. Int. Ed. Engl. 1995, 34, 2371.
7. For an early example of the use of chelating NHC ligands in Suzuki-Miyaura
and Sonogashira coupling reactions, see Herrmann, W.A.; Reisinger, C.P.;
Spiegler, M. J. Organomet. Chem. 1998, 557, 93.
8. Chelating NHC ligands have been successfully employed in the following
catalytic reactions. Pd-catalyzed Heck coupling: (a) Peris, E.; Loch, J.A.;
Mata, J.; Crabtree, R.H. Chem. Commun. 2001, 201. Pd-catalyzed Suzuki-
Miyaura coupling: (b) Zhang, C.; Trudell, M.L. Tetrahedron Lett. 2000,
41, 595. (c) Vargas, V.C.; Rubio, R.J.; Hollis, T.K.; Salcido, M.E. Org.
Lett. 2003, 5, 4847. Pd-catalyzed ethylene/CO copolymerization: (d) Gar-
diner, M.G.; Herrmann, W.A.; Reisinger, C.P.; Schwarz, J.; Spiegler, M. J.
Organomet. Chem. 1999, 572, 239. Rh-catalyzed transfer hydrogenation:
(e) Albrecht, M.; Crabtree, R.H.; Mata, J.; Peris, E. Chem. Commun. 2002,
32. Ir-catalyzed transfer hydrogenation: (f) Albrecht, M.; Miecznikowski,
J.R.; Samuel, A.; Faller, J.W.; Crabtree, R.H. Organometallics 2002, 21,
3596. (g) Miecznikowski, J.R.; Crabtree, R.H. Organometallics 2004,
23, 629. Rh-catalyzed hydrosilylation: (h) Poyatos, M.; Mas-Marza, E.;
In summary, we have synthesized a new class of biphenyl-
chelated bidentate-type NHC ligand precursors and cyclomet-
alated biphenyl-chelated bidentate NHC-palladium (II) com-
plexes Fa-b. On the basis of X-ray diffraction, the structure of
the complexes was determined. Complexes Fa-b are stable un-
der moisture and air at room temperature. The present ligands
are versatile because they can be further modified by changing
the aromatic ring substituents or N-substituents in the imida-
zole moiety, thus tuning either the sterics or the electronics,
which are very promising for the construction of highly active
transition-metal catalysts.
REFERENCES
1. (a) Herrmann, W.A. Angew. Chem. Int. Ed. 2002, 41, 1290. (b) Hillier, A.C.;
Grasa, G.A.; Viciu, M.S.; Lee, H.M.; Yang, C.; Nolan, S.P. J. Organomet.
Chem. 2002, 65, 69. (c) Crudden, C.M.; Allen, D.P. Coord. Chem. Rev.
2004, 248, 2247. (d) Peris, E.; Crabtree, R.H. Coord. Chem. Rev. 2004,