Bidentate ligands of the type Mes*PC(R)Py ((E)- 2, R = H; (Z)- 9, R = SiMe3; Mes* = supermesityl = 2,4,6-tri-tert-butylphenyl; Py = 2-pyridyl) were synthesized. Ligand (E)- 2 was synthesized by reacting Mes*P(Li)SiMe2(t-Bu) (4) with 2-pyridinecarboxaldehyde. Ligand (Z)- 9 was synthesized via a PdCl2(dppb)-catalyzed coupling reaction between 2-bromopyridine and Mes*PC(SiMe3)M ((E)- 7, M = ZnCl; (Z)- 8, M = MgBr). Compound (E)- 2 was also characterized by an X-ray crystal structure determination; it has a planar structure with the (E)-configuration. The complexes η1,η1-[Mes*PC(R)Py]PdCl2 (11, R = H; 12, R = SiMe3) were prepared by the reaction of bis(benzonitrile)palladium dichloride with (E)- 2 and (Z)- 9, respectively. The complexes η1,η1-[Mes*PC(R)Py]MePdCl (13, R = H; 14, R = SiMe3) were obtained by a ligand exchange reaction of MePdCl(COD) with (E)- 2 and (Z)- 9, respectively. Complex 13 was alternatively prepared by reaction of 11 with methylmagnesium chloride. Complex 14 was unambiguously identified by an X-ray crystal structure determination. Both 13 and 14 reacted with CO, resulting in the acetyl complexes η1,η1-[Mes*PC(R)Py]AcPdCl (16, R = H; 17, R = SiMe3).

Novel functionalized phosphaalkene-based bidentate ligands of the type 1-[(E)-Mes*PC(H)]-3-R-benzene (8, R = N-phenylcarbaldimino; 2, R = 2-pyridyl; Mes* = 2,4,6-tri-tert-butylphenyl) were prepared via a Pd(0)-catalyzed cross-coupling reaction of (Z)-bromophosphaalkene (Z)- 1 with Grignard reagents. The reaction of 8 and 2 with MePdCl(COD) furnished three-membered phosphapalladacycles of the type (9, R = N-phenylcarbaldimino; 10, R = 2-pyridyl), displaying intramolecular coordination between the phosphine ligand and palladium(II). The structure of 10 was established by an X-ray structure determination, showing a dimeric structure. The addition of triphenylphosphine to 9 and 10 causes rupture of the interconnecting Pd−N bonds, furnishing 11 and 12, respectively.