COMPARATIVE REACTIVITIES OF PHOSPHATE ESTER CLEAVAGES BY METALLOMICELLES

The hydrolytic efficiency of the hydrophilic Cu(II) complex of tetrame thylethylenediamine (TMED C-1 . Cu(II)) and the amphiphilic N-n-hexade cyl-N,N',N'-trimethylethylenediamine complex (TMED C-16. Cu(II)) in co micelles with CTANO(3) was studied toward a series of phosphate triest ers and diesters that were either neutral (1-7) or cationic and amphip hilic (8-10). While the pseudo-first-order rate constants at [catalyst ] = 1 x 10(-3) M are larger (ca. one order of magnitude) for the micel lar catalyst, the second-order rate constants are higher for the hydro philic catalyst. With phosphate triesters, regardless of the structure of the substrate, TMED C1(.) Cu(II)-bound OH- is a better nucleophile than free OH-, while TMED C-16. Cu(II)-bound OH- is poorer. This is e xplained by electrophilic assistance of the metal center which greatly diminishes in micelles. With phosphate diesters the OH- bound to both TMED C-1 . Cu(II) and TMED C-16. Cu(II) is a better nucleophile than free OH-. Partial neutralization of the negative charge of the substra te may explain this behavior. In all cases the amphiphilic substrates are intrinsically more reactive than the neutral ones. Comparison with an iodosobenzoate-based catalyst shows that this is ineffective with phosphate diesters while it is a better reagent than the metallomicell ar one with phosphate triesters. Its higher effectiveness, however, se ems to vanish as the substrate becomes less reactive.