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

The trichromium cluster ( ^tbs L)Cr ₃ (thf) ([ ^tbs L] ^6- =[1,3,5-C ₆ H ₉ (NC ₆ H ₄ -o-NSi ^t BuMe ₂ ) ₃ ] ^6- ) exhibits steric- and solvation-controlled reactivity with organic azides to form three distinct products: reaction of ( ^tbs L)Cr ₃ (thf) with benzyl azide forms a symmetrized bridging imido complex ( ^tbs L)Cr ₃ (μ ³ -NBn); reaction with mesityl azide in benzene affords a terminally bound imido complex ( ^tbs L)Cr ₃ (μ ¹ -NMes); whereas the reaction with mesityl azide in THF leads to terminal N-atom excision from the azide to yield the nitride complex ( ^tbs L)Cr ₃ (μ 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.
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