Remarkably Robust Monomeric Alkylperoxyzinc Compounds from Tris(oxazolinyl)boratozinc Alkyls and O2
摘要:
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-C3H7, i-C3H7, t-Bu) that react with O-2 at 25 degrees 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)-O-center dot and To(M)ZnR. In contrast, To(M)ZnH and To(M)ZnMe are unchanged even to 120 degrees C under 100 psi of O-2 and in the presence of active radical chains (e.g., (OOEt)-O-center dot). This class of zinc alkylperoxides is unusually thermally robust, in that the compounds are unchanged after heating at 120 degrees 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 ROOSiR3'.
Remarkably Robust Monomeric Alkylperoxyzinc Compounds from Tris(oxazolinyl)boratozinc Alkyls and O2
摘要:
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-C3H7, i-C3H7, t-Bu) that react with O-2 at 25 degrees 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)-O-center dot and To(M)ZnR. In contrast, To(M)ZnH and To(M)ZnMe are unchanged even to 120 degrees C under 100 psi of O-2 and in the presence of active radical chains (e.g., (OOEt)-O-center dot). This class of zinc alkylperoxides is unusually thermally robust, in that the compounds are unchanged after heating at 120 degrees 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 ROOSiR3'.
Divergent reaction pathways of tris(oxazolinyl)borato zinc and magnesium silyl compounds
作者:Debabrata Mukherjee、Nicole L. Lampland、KaKing Yan、James F. Dunne、Arkady Ellern、Aaron D. Sadow
DOI:10.1039/c2cc36953b
日期:——
Synthesis and reactivity of monomeric magnesium and zinc silyl compounds To(M)M-Si(SiHMe2)3 and To(M)M-Si(SiMe3)3 are described (To(M) = tris(4,4-dimethyl-2-oxazolinyl)phenylborate). The magnesium compounds react slowly with water and air, while the zinc compounds are inert. With CO2, To(M)Mg-Si(SiHMe2)3 provides To(M)MgO2CSi(SiHMe2)3 through CO2 insertion, whereas To(M)Zn-Si(SiHMe2)3 affords To(M)ZnOCHO