Over the last 25 years the Weller group have made contributions to the organometallic chemistry of the transition metals and homogeneous catalysis, with particular expertise in the use of Platinum Group Metals. The group has developed novel synthetic techniques, and mechanism-led designs of catalyst systems, for challenging bond activation processes. In particular, they develop new routes to highly reactive and novel organometallic complexes that contain, so-called sigma-interactions in which an alkane, borane or C–C single bonds act as a ligand to a metal by coordination through a saturated sigma-bond. The group has advanced single-crystal to single-crystal solid-state molecular organometallic chemistry (SMOM) techniques and new routes to highly reactive “operationally unsaturated” organometallic pre-catalysts to do this. A unifying concept is the removal of any unfavourable competing pre-equilibria prior to key bond activation steps in catalytic processes that invoke sigma-interactions. Exploitation of this idea leads to highly efficient, selective, catalysis with low-energy input for a wide variety of important processes in both solution and single-crystalline phases. Collaborations with computational chemists (Professor Stuart Macgregor St Andrews), experts in the study of mechanism using kinetics (Professor Guy Lloyd–Jones, Edinburgh) and novel analytical techniques (Professor J. S. McIndoe, University of Victoria), and Materials Chemists (Professor Nicole Grobert) also lead to a deeper understanding of structures and reactivity and applications of many of the new complexes and catalytic systems discovered.