Synthesis of novel phosphaalkene-based bidentate ligands Mes*P=CH(3-R-Ar) (R = pyridyl, carbaldimino) and formation of three-membered palladacycles Mes*(Me)P-CH(3-R-Ar)-PdCl by carbapalladation of the P=C double bond

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 Mes*(Me)P-CH(3-R-Ar)-PdCl (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.