The cyclopalladation of the stabilized iminophosphoranes Ph 3 PdNC(O)C 6 H 4 R (R ) H 1a, 4-OMe 1b, 3-OMe 1c, 2-Me 1d, 3-Me 1e) results in the regioselective activation of the ortho CH bond of the benzamide ring, giving exo-[Pd(µ-Cl){C,N-C 6 H 3 (R){C(O)NdPPh 3 -2}}] 2 (R ) H 2a, 5-OMe 2b, 4-OMe 2c, 3-Me 2d, 4-Me 2e). The palladated ligand behaves as a strong C,N-chelating group and cannot be easily displaced by other chelating ligands. This is clear from the reaction of 2c with Tl(acac), py, or AgClO 4 /L∧L, which gives [Pd(acac){C,N-C 6 H 3 (MeO-4){C(O)NdPPh 3 -2}}] (3c), [PdCl{C,N-C 6 H 3 (MeO-4){C(O)NdPPh 3 -2}}(py)] (4c), or [Pd{C,N-C 6 H 3 (MeO-4){C(O)NdPPh 3 -2}}(L∧L)]ClO 4 (L∧L ) dppe 5c, bipy 6c, phen 7c). However, Pd(OAc) 2 reacts with the ylides Ph 3 PdCHC(O)C 6 H 4 R (R ) H 8a, 3-OMe 8b, 2,5-(OMe) 2 8c) to give the C,C-orthometalated complexes [Pd(µ-Cl){C,C-[C 6 H 4 (PPh 2 CHC-(O)C 6 H 4 R)-2]}] (R ) H 9a, 3-OMe 9b, 2,5-(OMe) 2 9c), which are also regioselectively obtained. The C,C-metalated chelate is very stable, as shown by the reactions of 9b with Tl(acac), PPh 3 , and AgClO 4 / L∧L. The X-ray structures of 2d and 9b have been determined. Unexpectedly, the reaction of Pd(OAc) 2 with the ylide [Ph 3 PdCHC(O)C 6 H 3 -2,4-(OMe) 2 ] (16) gives the polymer [ 17) as a result of a double palladation, giving two types of metalacycles: in one of them, the Pd atom is bonded to the ylidic CR atom and has activated an ortho C(Ph)-H bond of the PPh 3 group; in the other one, the Pd atom is bonded to the carbonyl oxygen and has activated an ortho C-H bond of the C 6 H 3 (OMe) 2 unit. This tetradentate ylide ligand is remarkably stable.

No abstract