Activation of C-Cl by ground-state aluminum atoms: an EPR and DFT investigation

The reaction of ground-state Al atoms with dichloromethane (CH 2 Cl 2 ) in an adamantane matrix at 77 K yielded two mononuclear Al species. The magnetic parameters, extracted from the axial EPR spectrum of Species A/A′ ( g 1 = 2.0037, g 2 = g 3 = 2.0030, a Al,1 = 1307 MHz, a Al,2 = a Al,3 = 1273 MHz, a 35Cl = 34 MHz and a 37Cl = 28 MHz) were assigned to the Al-atom insertion product, ClCH 2 AlCl. Density functional theory (DFT) calculations of the values of the Al and Cl hyperfine interaction (hfi) of the Cl 1 -Cl 2 gauche conformer were in close agreement with the experimental values of ClCH 2 AlCl. The second species, B/B′, had identical magnetic parameters to those of ClCH 2 AlCl with the exception that the Al hfi was 15% smaller. Coordination of a ligand, possessing a lone pair of electrons, to the Al atom of the insertion product, [ClCH 2 AlCl]:X, could cause the a Al to decrease by 15%. Alternatively, it is possible that the Cl 1 -Cl 2 anti conformer of ClCH 2 AlCl is also isolated in the matrix. Support for the spectral assignments is given by calculation of the nuclear hfi of [ClCH 2 AlCl]:H 2 O and the Cl 1 -Cl 2 anti conformer of ClCH 2 AlCl using a DFT method. The potential energy hypersurface for an Al atom approaching CH 2 Cl 2 , calculated at the B3LYP level, suggests that Al atom abstraction of Cl forming AlCl and CH 2 Cl is favoured in the gas phase. When produced in a matrix, the close proximity of AlCl and CH 2 Cl could account for the formation of ClCH 2 AlCl. EPR evidence was also found for the formation of the CHCl 2 radical. Characterization of ClCH 2 AlCl formed in the Al atom-dichloromethane reaction in adamantane at 77 K.