Activation of C-X (X = Cl or Br) bonds in 2-halobenzaldehydes as their 2-pyridylhydrazone derivatives: oxidative addition to tungsten(0) to give aryl-tungsten(II) complexes

Condensation of 2-pyridylhydrazine, (NC5H4)NHNH2, with the 2-halobenzaldehy des 2,6-dichlorobenzaldehyde, 2-chlorobenzaldehyde or 2-bromobenzaldehyde g ave the 2-pyridylhydrazones, (C6H3Cl2-2,6)CH=N-NH(C5H4N) (1a), (C(6)H(4)Cl2 )CH=N-NH(C5H4N) (1b) or (C6H4Br-2)CH=N-NH(C5H4N) (1c), respectively. Treatm ent of 1a with [W(CO)(3)(NCEt)(3)] in warm tetrahydrofuran caused oxidative addition of the C-Cl bond to give the aryl-tungsten(II) complex [W(CO)(3)C l{(C(6)H(3)Cl6)CH=N-NH(C5H4N)-C,N,N}] (2a). Similarly, the hydrazones 1b an d 1c, when treated with [W(CO)(3)(NCEt)(3)], gave the aryl-tungsten(II) Com plexes [W(CO)(3)Cl{(C6H4)CH=N-NH(C5H4N)-C,N,N] (2b) and [W(CO)(3)Br{(C6H4)C H=N-NH(C5H4N)-C,N,N}] (2c). H-1 and C-13-{H-1} NMR, IR and mass spectral da ta are given. (C) 2001 Elsevier Science B.V. All rights reserved.