Synthesis of 2-(2-pyridyl)phosphaalkenes [Mes*P=C(R)Py] (R=H, SiMe(3)) and their complexes eta(1),eta(1)-[Mes*P=C(R)Py]XPdCl (X=Cl, Me, Ac)

Bidentate ligands of the type Mes*P=C(R)Py ((E)-2, R = H; (Z)-9, R = SiMe(3); Mes* = supermesityl 2,4,6-tri-tert-butylphenyl; Py = 2-pyridyl) were synthesized. Ligand (E)-2 was synthesized by reacting Mes*P(Li)SiMe(2)(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(SiMe(3))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 eta(1),eta(1)-[Mes*P=C(R)Py]PdCl2 (11, R = H; 12, R = SiMe(3)) were prepared by the reaction of bis(benzonitrile)palladium dichloride with (E)-2 and (Z)-9, respectively. The complexes eta(1),eta(1)-[Mes*P=C(R)Py]MePdCl (13, R = H; 14, R = SiMe(3)) 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 determination. Both 13 and 14 reacted with CO, resulting in the acetyl complexes eta(1),eta(1)-[Mes*P=C(R)Py]AcPdCl (16, R = H; 17, R = SiMe(3)).