| prov:value
| - M* is aluminum or boron; R1 independently each occurrence is a compound selected from the group consisting of a halide, alkyl, aryl, alkoxide, aryloxide, dialkylamido, halogenated alkyl, halogenated aryl, halogenated alkoxide, halogenated aryl oxide and mixtures thereof, said R1 having up to twenty carbon atoms, and Arf1???Arf2 in combination is independently, a divalent aromatic group of 6 to 20
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