A composition comprising a mixture of aluminum containing Lewis acids, said mixture corresponding to the formula: (Arf3Al)(AlQ13)y(-AlQ2-O-)z where Arf is a fluorinated aromatic hydrocarbyl moiety of from 6 to 30 carbon atoms; Q1 is C¿1-20? alkyl; Q?2¿ is C¿1-20? hydrocarbyl, optionally substituted with one or more groups which independently each occurrence are hydrocarbyloxy, hydrocarbylsiloxy, hydrocarbylsilylamino, di(hydrocarbylsilyl)amino, hydrocarbylamino, di(hydrocarbyl)amino, di(hydrocarbyl)phosphino, or hydrocarbylsulfido groups having from 1 to 20 atoms other than hydrogen, or, optionally, two or more Q?2¿ groups may be covalently linked with each other to form one or more fused rings or ring systems; y is a number from 0 to 1.0; z is a number from 0.1 to 20; and the moieties (Arf3Al)(AlQ13)y may exist as discrete entities or dynamic exchange products.