An EPR study of the C-O bond activation of 1,2-epoxybutane by ground-state Al atoms

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 (CH3CH2CHOCH2) and its isotopomers, 1,2-epoxybutane-1,1-d(2) (CH3CH2CHOCD2) and 1,2-epoxybutane-2-d(1) (CH3CH2CDOCH2). 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(A1) = 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 CH3CH2CHCH2AlO. Species B, thought to result from the insertion of Al atoms into the C-2-O bond, CH3CH2CHCH2OAl, has the magnetic parameters g = 2.0003, a(A1) = 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 CH3CH2CH(O-) CH2 center dot 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.