An EPR Study of the C−O Bond Activation of 1,2-Epoxybutane by Ground-State Al Atoms

Abstract

Group 13 metal atoms react with ethers under matrix isolation conditions to give a number of interesting products. This work has been extended to include the reaction of Al atoms with 1,2-epoxybutane (CH(3)CH(2)H(2)) and its isotopomers, 1,2-epoxybutane-1,1-d(2) (CH(3)CH(2)D(2)) and 1,2-epoxybutane-2-d(1) (CH(3)CH(2)H(2)). The paramagnetic species generated in the reaction have been studied by electron paramagnetic resonance (EPR) spectroscopy. Two divalent Al insertion products were spontaneously formed. Species A, with the magnetic parameters a(Al) = 855 MHz, a(H)(1) = 28.8 MHz, a(H)(2) = 13.6 MHz, and g = 2.0014, is the C(1)-O insertion radical CH(3)CH(2). Species B, thought to result from the insertion of Al atoms into the C(2)-O bond, CH(3)CH(2), has the magnetic parameters g = 2.0003, a(Al) = 739 MHz, a(H)(1) = 15.1 MHz, a(H)(2) = 18.5 MHz, and a(H)(1) = 37.8 MHz. Support for these assignments was obtained by comparing the experimental values of the Al and H hyperfine interaction (hfi) with those calculated using a DFT method. At temperatures < 150 K, there is evidence for the formation of the alkyl radical CH(3)CH(2)CH(O(-))CH(2)* due to ring opening at the C(1)-O bond, while at higher temperatures a radical with magnetic parameters similar to those reported for 1-methallyl was detected.

Al Atom Activation of C–S Bonds: Characterization of the Aluminathietane Formed in the Reaction of Al Atoms with 1,2-Butylene Sulfide

“…The formation of a mixture of cis-and trans-methallyl radicals was reported in the Al atom + 1,2-butylene oxide study. 12 The spectra that developed upon annealing of the Al atom + 1,2-BuS, 1,2-BuS-2-d 1 , and 1,2-BuS-1,1-d 2 reaction mixtures closely resemble those in the Al atom + 1,2-butylene oxide study. However, spectral simulation suggests that mainly cis-methallyl, cis-methallyl-2-d 1 , and cis-methallyl-1,1-d 2 , respectively, form.…”

“…In contrast, the C 2 −O insertion product of 1,2-butylene oxide yields a superhyperfine pattern demonstrating the contribution of two C 1 hydrogens with a H = 18.5 MHz, a C 2 hydrogen with a H = 15.5 MHz, and a C 3 hydrogen with a H = 37.8 MHz. 12 We therefore assign BuS-1 as the Al atom C 1 −S insertion product of 1,2-BuS (1). As well, we are able to attribute the values of the H hfi to the respective hydrogens by monitoring the effect of isotopic substitution.…”

“…Details of the synthesis of 1,2butylene oxide-1,1-d 2 and 1,2-butylene oxide-2-d 1 are described elsewhere. 12 i. 1,2-BuS-2-d 1 .…”

“…11 Insertion of Al atoms into the C 1 −O and C 2 −O bonds of 1,2-butylene oxide to form the novel aluminaoxetanes CH 3 CH 2 CHCH 2 AlO and CH 3 CH 2 CHCH 2 OAl, respectively, has also been observed. 12 Like the above-mentioned magnesacycles, the aluminum analogues present new potential routes for the preparation of carbocyclic and heterocyclic compounds.…”

Electron spin resonance

“…There is also evidence for the formation of the alkyl radical CH 3 CH 2 CH(O-)CH 2 d from ring opening at the C 1 -O bond, while at temperatures above 150 K, a radical with magnetic parameters similar to those reported for the 1-methylallyl radical was detected. 124 The same group have reported their results for the reaction of ground-state Al atoms with cyclopropylamine (CpNH 2 ) in an adamantane matrix at 77 K. Four paramagnetic species were identified from their ESR spectra. The isotropic 27 Al hyperfine couplings for these species vary in the range 801-962 MHz and can therefore be grouped with other structurally similar aluminium-containing radicals.…”