Large transition-metal clusters are possible models for metal particles with chemisorbed species, and potential intermediates in size-dependent transition from molecular to bulk metallic behaviour. The major obstacle to their study is the lack of facile high-yielding syntheses. We have developed a remarkably easy route into certain high-nuclearity ruthenium carbonyl clusters (the figure shows a Ru12 cluster, the largest Ru cluster so far); this project will explore the chemistry of these unique compounds.