Synthesis of 2-(2-Pyridyl)phosphaalkenes [Mes*PC(R)Py] (R = H, SiMe3) and Their Complexes η1,η1-[Mes*PC(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 PdCl 2 (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 η 1,η 1 -[Mes*P C(R)Py]PdCl 2 ( 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 η 1,η 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 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 = SiMe 3 ).