Ligand-Based Control of Single-Site vs. Multi-Site Reactivity by a Trichromium Cluster

The trichromium cluster (L-tbs)Cr-3(thf)([L-tbs](6-) = [1,3,5-C6H9(NC6H4-o-(NSiBuMe2)-Bu-t)(3)](6-)) exhibits steric- and solvation-controlled reactivity with organic azides to form three distinct products: reaction of (L-tbs)Cr-3(thf) with benzyl azide forms a symmetrized bridging imido complex (L-tbs)Cr-3(mu(3)-NBn); reaction with mesityl azide in benzene affords a terminally bound imido complex (L-tbs)Cr-3(mu(1)-NMes); whereas the reaction with mesityl azide in THF leads to terminal N-atom excision from the azide to yield the nitride complex (L-tbs)Cr-3-(mu(3)-N). The reactivity of this complex demonstrates the ability of the cluster-templating ligand to produce a well-defined polynuclear transition metal cluster that can access distinct single-site and cooperative reactivity controlled by either substrate steric demands or reaction media.