Remarkably Robust Monomeric Alkylperoxyzinc Compounds from Tris(oxazolinyl)boratozinc Alkyls and O-2
Department of Chemistry and United States Department of Energy Ames Laboratory, Iowa State University , Ames, Iowa 50011, United States.Journal of the American Chemical Society (Impact Factor: 12.11). 07/2012; 134(31). DOI: 10.1021/ja303440n
Metal alkylperoxides are remarkable, highly effective, yet often thermally unstable, oxidants that may react through a number of possible pathways including O-O homolytic cleavage, M-O homolytic cleavage, nucleophilic O-atom transfer, and electrophilic O-atom transfer. Here we describe a series of zinc alkyl compounds of the type To(M)ZnR (To(M) = tris(4,4-dimethyl-2-oxazolinyl)phenylborate; R = Et, n-C(3)H(7), i-C(3)H(7), t-Bu) that react with O(2) at 25 °C to form isolable monomeric alkylperoxides To(M)ZnOOR in quantitative yield. The series of zinc alkylperoxides is crystallographically characterized, and the structures show systematic variations in the Zn-O-O angle and O-O distances. The observed rate law for the reaction of To(M)ZnEt (2) and O(2) is consistent with a radical chain mechanism, where the rate-limiting S(H)2 step involves the interaction of (•)OOR and To(M)ZnR. In contrast, To(M)ZnH and To(M)ZnMe are unchanged even to 120 °C under 100 psi of O(2) and in the presence of active radical chains (e.g., (•)OOEt). This class of zinc alkylperoxides is unusually thermally robust, in that the compounds are unchanged after heating at 120 °C in solution for several days. Yet, these compounds are reactive as oxidants with phosphines. Additionally, an unusual alkylperoxy group transfer to organosilanes affords To(M)ZnH and ROOSiR(3)'.
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