Remarkably Robust Monomeric Alkylperoxyzinc Compounds from Tris(oxazolinyl)boratozinc Alkyls and O-2
ABSTRACT 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)'.
SourceAvailable from: Issam Kobrsi[Show abstract] [Hide abstract]
ABSTRACT: The reaction of 3,5-di-2-pyridyl-1,2,4-triazole with excess Al(CH3)3 and Ga(CH3)3 afforded (3,5-di-2-pyridyl-1,2,4-triazolate)Al(CH3)2•3Al(CH3)3 (1) and (3,5-di-2-pyridyl-1,2,4-triazolate) Ga(CH3)2•3Ga(CH3)3 (2) respectively. 1 and 2 reacted with oxygen gas to produce (CH3)2M(µ-3,5-di-2-pyridyl-1,2,4-triazolate)(µ-OCH3)M(CH3)2 (M = Al, 3; M = Ga, 4). 3 and 4 contain the non-bulky dimethylalumino moiety, yet they are indefinitely stable in the presence of oxygen gas. This increased stability towards oxygen is due to ancillary 2-pyridyl groups bonding to the metal centers producing a pseudo-trigonal pyramidal Al and Ga environments. This environment blocks oxygen from further inserting into the M-C bond. The Al-N(pyridine) and Ga-N(pyridine) bonds reported herein are extremely elongated yet inactive towards dissociation due to the chelate effect.PLoS ONE 08/2014; 9(6):e100626. DOI:10.1371/journal.pone.0100626 · 3.53 Impact Factor
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ABSTRACT: The epoxidation of enones by zinc alkylperoxides is a challenging task receiving considerable attention in contemporary research; however, until now no well-defined zinc alkylperoxide based systems have been described. Here, a new catalytic method of epoxidation of enones in the presence of zinc alkylperoxides supported by N,N-bidentate ligands and tert-butyl hydroperoxide is reported. A new dimeric zinc alkylperoxide complex supported by an aminotroponiminate ligand is also presented. The studied catalytic systems show high activity in the epoxidation of trans-chalcone, and in the case of a chiral catalyst with the (S,S)-N,N′-bis(1-phenylethyl)aminotroponiminate ligand a moderate enantioselectivity was achieved.Organometallics 09/2013; 32(19):5263–5265. DOI:10.1021/om400830e · 4.25 Impact Factor
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ABSTRACT: Ethylzinc derivatives of ortho-hydroxybiphenyl and 2,6-diphenylphenol that bear different nuclearity and dispositions of aromatic rings toward the metal center were synthesized and structurally characterized in the solid state and solution. This family of well-defined compounds was examined as a model system for the activation of dioxygen mediated by using complexes that feature lack of a redox-active metal center. Experimental and theoretical studies indicate an essential role in the oxygenation process of intramolecular interactions that involve aromatic subunits. Additionally, novel results for the oxygenation chemistry of alkylzinc compounds, including the isolation and structural characterization of the unique octanuclear aryloxide (hydroxide) compound Zn8(OAr)8(OH)6(O2) with an encapsulated peroxide species, are presented.Chemistry - A European Journal 11/2014; 20(45):14790–14799. DOI:10.1002/chem.201403851 · 5.70 Impact Factor