The new selenated Schiff bases L1–L4 which differ in the chain lengths (longest in L4) of non-coordinating substituents and their square planar complexes [Pd(L–H)Cl] (1–4) [L = L1–L4, behaving as (Se, N, O⁻) ligand] have been synthesized and characterized by multinuclei NMR. The molecular structure of 1 has been elucidated by X-ray diffraction on its single crystal [Pd–Se = 2.3965(9) Å]. All the complexes 1–4 (0.5 mol%) have been found suitable to catalyze Suzuki–Miyaura coupling reactions under mild conditions. The activity of 4 which has ligand L4 has been found highest. The formation of palladium(0) nano-particles (NPs) stablilized by organoselenium species appears to be the catalytic pathway. The length of the pendent alkyl chain present in the complex molecule unprecedentedly controls the dispersion and composition of these particles and consequently the catalytic activity.