**Szilvia Bunda 1,2, Krisztina Voronova 3, Ágnes Kathó 1, Antal Udvardy 1,\* and Ferenc Joó 1,4,\***


Received: 3 August 2020; Accepted: 31 August 2020; Published: 2 September 2020

**Abstract:** Water-soluble salan ligands were synthesized by hydrogenation and subsequent sulfonation of salens (*N*,*N*'-*bis*(slicylidene)ethylenediamine and analogues) with various bridging units (linkers) connecting the nitrogen atoms. Pd (II) complexes were obtained in reactions of sulfosalans and [PdCl4] <sup>2</sup>−. Characterization of the ligands and complexes included extensive X-ray diffraction studies, too. The Pd (II) complexes proved highly active catalysts of the Suzuki–Miyaura reaction of aryl halides and arylboronic acid derivatives at 80 ◦C in water and air. A comparative study of the Pd (II)–sulfosalan catalysts showed that the catalytic activity largely increased with increasing linker length and with increasing steric congestion around the N donor atoms of the ligands; the highest specific activity was 40,000 (mol substrate) (mol catalyst <sup>×</sup> h)−1. The substrate scope was explored with the use of the two most active catalysts, containing 1,4-butylene and 1,2-diphenylethylene linkers, respectively.

**Keywords:** catalysis in water; C–C cross-coupling; Suzuki–Miyaura reaction; palladium; sulfonated salan
