Unexpected Rearrangement of Palladacycles Derived from 2-Oxopropionaldehyde Phenylhydrazones. Synthesis of Palladium Complexes Containing a Bianionic Tridentate C, N, O Ligand

Abstract

The synthesis of bidentate monoanionic C−N derivatives of 2-oxopropionaldehyde phenylhydrazones, compounds 3, [Pd(2-{NHNCHC(O)Me}-3-RC6H3)Cl(PPh3)] is described. The structure of 3b (R = Me) was determined by X-ray diffraction. The bond distances and angles are similar to those reported for related metallacycles. The distance N(2)···O(1) (2.583(7) Å) shows the existence of a strong intramolecular hydrogen bond between the NH and COCH3 groups. The C(9)−O(1) (1.224(9) Å), C(8)−C(9) (1.46(1) Å), C(8)−N(1) (1.307(8) Å), and N1−N2 (1.325(7) Å) bond lengths indicate that 3b exists mainly in the keto−hydrazo form. The action of NaMeO on 3 in MeOH afforded deep violet compounds which did not contain chlorine atoms. The analytical data, the infrared spectra, and the NMR studies, including 1H−1H COSY and NOESY experiments, showed that deprotonation of the N−H bond took place to give 4, [Pd(2-{NN−CHC(O)Me}-3-RC6H3)(PPh3)] by means of an unexpected hydrazo−azo tautomerization. The structure of 4c (R = Et) was determined by X-ray diffraction. The C(10)−O(1) (1.32(1) Å), C(10)−C(9) (1.37(1) Å), C(9)−N(2) (1.33(1) Å), and N(1)−N(2) (1.25(1) Å) bond lengths indicate that 4c exists mainly in the azo−enol form. The action of HCl (0.5 N) on the tridentate metallacycles 4 regenerated the bidentate derivatives 3, showing the reversibility of this process.

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

“…The Pd-C(1) bond lengths are in the range 1.987(5)-2.011 (3) A in these complexes. These CPd-N angles and Pd-C bond lengths are comparable with the values reported for similar ortho-metallated complexes with Schiff bases [12,13,[17][18][19][20][21][22]32]. The Pd-N1 bond lengths are 2.011(4) and 2.059 (3) A in 3 and 6, respectively.…”

“…These shifts are by d 0.2-0.3. The upfield shift of the azomethine proton is consistent with the weakening of the C@N bond due to the N-coordination and the trans disposition of the Pd and the proton around the C@N [12,16,31,32]. The -NHproton of 3 and also of 6 is observed at d 8.47.…”

“…Formation of such complexes involves ligand C-H activation. Interest on this activation process and the corresponding metallated complexes stems from their utilization in insertion reactions, regio-and stereo-selective reactions and as catalysts in organic synthesis [8][9][10][11][12]. Thus there is a continuing quest for new cyclometallated species with different types of ligands.…”

“…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].…”

Synthesis, spectroscopic and thermal properties of nickel (II)–azo complexes with blue-violet light wavelength

“…The action of NaOMe on TIAD in THF solution converts the hydrazoketo form into the azoenol form (see Fig. 1) [13]. Their structures were confirmed by elemental analysis, spectroscopic data (MS, FT-IR, UVeVis) and magnetic data, respectively.…”