KINETICS AND MECHANISM OF REACTION OF TRANS-(DIAQUA)(N,N'-ETHYLENE-BIS-SALICYLIDENIMINE) CHROMIUM(LII) WITH SULFUR(IV) - THE LABILIZING EFFECT OF COORDINATED SULFITE

The reaction of trans-[Cr(Salen)(OH2)(2)](+) with aqueous sulfite yiel ds tuans[Cr(Salen)(OH2)(OSO2-O)](-) (O-bonded isomer). The rate and ac tivation parameter data for the Formation of the sulfito complex are c onsistent with a mechanism involving rate-limiting addition of SO2 to the Cr-III-OH bond. The complex ions, trans-[(OH2)Cr(Salen)(OSO2-O)](- ), and trans-[(OH)Cr(Salen)(OSO2-O)](2-), undergo reversible anation b y NCS-, N-3(-), imidazole, and pyridine resulting in the formation of trans-[XCr(Salen)(OSO2-O)]((n+1)-)(n = 1 for X = N-3(-),NCS-, and 0 fo r X = imidazole and pyridine) predominantly via dissociative interchan ge mechanism. The labilizing action of the coordinated sulfite on the trans-Cr-III-X bond in trans-[XCr(Salen)(OSO2)]((n+1)-) follows the se quence: NCS- < pyridine ca. N-3(-) ca. imidazole. Data analysis indica ted that the coordinated sulfite has little trans activating influence . (C) 1998 John Wiley & Sons, Inc.