Concept: Multiplet theory
Invented by: Aleksei Balandin 1929
Principle: catalytic reaction takes place when key atoms in a substrate are optimally positioned in relation to key metal atoms. There is no distinct difference between homogeneous catalysis (one metal center) and heterogeneous catalysis (several metal centers). The fields blur with advent of nanoparticles, nanosalts (incorporating heteroatoms) and homogeneous catalyst fixation (heterogenization), metal atoms are known to leach into solution from a solid catalyst. Likewise nanoparticles are known to form in mononuclear meta complexes. Ananikov & Beletskaya call this a cocktail of catalysts.
Main challenges: experimental evidence: all dynamic nanoscale processes, indirect kinetic evidence.
Literature: Ananikov & Beletskaya Organometallics 2012 (DOI). Relevant quote: ''we argue that research efforts should be concentrated on developing a unified concept of catalysis rather than spreading the field into repeating reports of one more
example of catalyst or ligand''