. . . " Mg, RMgCl , R3 Al , R3 B, R2 AlCl , R2 BCl , RAlCl2, RBCl2, R3 Al2 Cl3, R3 B2 Cl3 where R=H1, CH3, C2 H5, n-C3 H7, i-C3 H7, n-C4 H7, i-C4 H9, t-C4 H9, C6 H5 or other alkyl group, or aryl group, or substituted aryl group." . .