**Ioannis D. Kostas \* and Barry R. Steele \***

Laboratory of Organic/Organometallic Chemistry & Catalysis, Institute of Chemical Biology, National Hellenic Research Foundation, Vas. Constantinou 48, 11635 Athens, Greece

**\*** Correspondence: ikostas@eie.gr (I.D.K.); bsteele@eie.gr (B.R.S.); Tel.: +30-2107273878 (I.D.K.); +30-2107273874 (B.R.S.)

Received: 2 September 2020; Accepted: 22 September 2020; Published: 24 September 2020

**Abstract:** Catalysis of cross-coupling reactions under phosphane-free conditions represents an important ongoing challenge. Although transition metal complexes based on the thiosemicarbazone unit have been known for a very long time, their use in homogeneous catalysis has been studied only relatively recently. In particular, reports of cross-coupling catalytic reactions with such complexes have appeared only in the last 15 years. This review provides a survey of the research in this area and a discussion of the prospects for future developments.

**Keywords:** thiosemicarbazone; metal complex; transition metal catalysis; cross-coupling reaction; Heck reaction; Suzuki reaction; Sonogashira reaction; Kumada reaction; Buchwald–Hartwig reaction
