Pradhumn Singh

Chalcogenated Schiff bases: Complexation with palladium(II) and Suzuki coupling reactions

AbstractChalcogenated Schiff bases of 5–chloroisatin (L1–L3), 2–(methythio)benzaldehyde (L4), 2–acetylpyridine (L5) and benzaldehyde (L6–L7) have been synthesized. Both the carbonyl groups of 5–chloroisatin appear to be reactive (noticed for the first time) for making >C=N bond, of course one at a time only. The 1H, 13C{1H}, 77Se{1H} and 125Te{1H} NMR spectroscopy have been used to establish the co-existence of two products, which were found in the ratio 53:47 (E = S), 55:45 (E = Se) and 81:19 (E = Te). The larger amount is of the one in which C=O group away from NH is derivatized. The two products are not separable. Palladium complexes (1–4) of Schiff bases of other three aldehydes were synthesized. The ligands as well as complexes were characterized by multinuclear NMR spectroscopy. The crystal structures of [Pd(L4/L5)Cl][ClO4] (1/2) have been solved. The Pd–Se bond lengths are 2.4172(17) and 2.3675(4) Å, respectively for 1 and 2. The Pd–complexes (3–4) of L6–L7 were explored for Suzuki–Miyaura coupling and found promising as 0.006 mol % of 3 is sufficient to obtain good conversion with TON up to 1.58 × 104. Graphical AbstractChalcogenated Schiff bases of 5–chloroisatin (L1–L3), 2–(methythio)-benzaldehyde (L4), 2–acetylpyridine (L5) and benzaldehyde (L6–L7) and palladium complexes of L4–L7 have been synthesized and characterized by 1H, 13C{1H}, 77Se{1H} and 125Te{1H} NMR. The Pd–complexes of L6–L7 even at 0.006 mol% give good conversions in Suzuki−Miyaura coupling (TON upto 1.58 × 104).