Crowding controls whether carbon chains or a hydrogen atom will transfer from transition metal molecular complexes to acceptor molecules. To gain this new insight into the factors governing the onset of hydrogen abstraction from metal alkyls, researchers carefully designed experiments involving series of cobalt and chromium alkyls. The results show that when the alkyl chain is only one carbon long, the alkyl group will transfer to a rhodium acceptor molecule. But, if the chain is made up of two or more carbons, crowding makes it hard for the alkyl group to transfer. In these cases the reaction finds another pathway, one in which a single hydrogen atom, rather than the entire alkyl group, is transferred. The transfer of hydrogen and carbon chains from transition metal molecular complexes to an acceptor molecule is involved in many catalytic reactions of industrial and biological significance. These results provide key fundamental information about these processes.
Alkyl Group versus Hydrogen Atom Transfer from Metal Alkyls to Macrocyclic Rhodium Complexes