Synthesis, X-ray structure and reactivity of cyclopalladated complexes of hydrazones of 1H-indole-3-carboxaldehyde

Cyclopalladated complexes with N-(benzoyl)-N′-(2,4-dimethoxybenzylidene)hydrazine: syntheses, characterization and structural studies

“…These are assigned to the N-H, aromatic C-H and methyl C-H stretches, respectively. Two strong bands observed at 1642 and 1603 cm À1 are likely to be due to the C@O and C@N stretches [20][21][22]. The spectra of 2, 3, 5 and 6 display a weak peak in the range 3289-3206 cm À1 .…”

“…In an unlikely situation of the bridging chlorine atom being a stronger trans directing group than PPh 3 , the C@O stretch will appear at a lower frequency compared to that in 5. On the other hand, if HL À is C,N,O-donor in 2, the amide C@O stretch should shift to the lower wavenumber [20][21][22] compared to that for the free Schiff base (1) due to the O-coordination to the metal. The formation of 3, 5, and 6 from 2 does not differentiate the dichloro bridged or a mononuclear structure as both structures can give the same products either by cleavage of Pd-Cl (bridging) bond or by cleavage of Pd-O bond.…”

“…However structurally characterized cyclometallated species of this class of ligands are scarce. To the best of our knowledge the lone example reported Journal of Organometallic Chemistry 689 (2004) 352-360 www.elsevier.com/locate/jorganchem is a cationic palladium(II) complex with a monoaninoic C,N,O-donor acetylhydrazone having triphenylphosphine as the ancillary ligand [22]. A couple of cyclopalladated complexes are reported with benzoylhydrazones of phenyl 2-pyridyl ketone [23] and 2,6-diacetyl pyridine [24].…”

“…Thus there is a continuing quest for new cyclometallated species with different types of ligands. Compounds containing two non-carbon donor atoms are well known to act as tridentate ligands for palladium(II) or platinum(II) via ortho-metallation and can produce cyclometallated complexes having two fused rings at the metal centre [12][13][14][15][16][17][18][19][20][21][22][23]. Thiosemicarbazones and semicarbazones of aromatic aldehydes belong to this type of ligands [18][19][20][21].…”

“…Unlike the previously reported complexes with benzoylhydrazones [23,24], in the present complexes the cyclometallation occurs at the benzylidene ring. In the cationic cyclopalladated compounds of semicarbazone [20,21] and acetylhydrazone [22] containing monodentate PPh 3 , the ligands act as monoanionic C,N,O-donor. In contrast the analogous compound with H 2 L contains dianionic C,N,O-donor ligand (L 2À ).…”