17O NMR Study of Solvent Exchange in Some Aqueous [Co(tren)(X)(OH2/OH)]n+, [Co(cyclen)(X)(OH2/OH)]n+, and [Co
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- 作者：Nicola E. Brasch ; David A. Buckingham ; Charles R. Clark ; and Andrew J. Rogers
- 刊名：Inorganic Chemistry
- 出版年：1998
- 出版时间：September 21, 1998
- 年：1998
- 卷：37
- 期：19
- 页码：4865 - 4871
- 全文大小：120K
- 年卷期：v.37,no.19(September 21, 1998)
- ISSN：1520-510X
文摘
A 17O NMR study (I = 1.0 M, NaClO4 or NaOSO2CF3, 25.0 
es/entities/deg.gif">C) of solvent exchange in labeled p- and t-[Co(tren)(NH3)OH2]3+, [Co(tren)(OH2)2]3+, [Co(cyclen)(OH2)2]3+, and [Co(N-Mecyclen)(OH2)2]3+ ions (ca. 30% 17O)in aqueous solution has shown that loss of coordinated OH2 is slow for all of the complexes (kex/s-1 = 1.1 ×10-5, 1.2 × 10-5, 3.7 × 10-5 (p-site)/8.7 × 10-6 (t-site), 2 × 10-4, and 2 × 10-4, respectively). Values of kexfor solvent exchange in [Co(tren)(OH)2]+ have been determined as 9.7 × 10-5 s-1 (p-site) and 2.2 × 10-7 s-1(t-site) Coordinated OH- in both p- and t-[Co(tren)(NH3)OH]2+ also exchanges only slowly with solvent (kex/s-1= 1.7 × 10-4, and <1 × 10-6, respectively), whereas exchange of coordinated solvent in the aqua-hydroxocomplexes [Co(tren)(t-OH2)(p-OH)]2+, [Co(cyclen)(OH2)OH]2+, and [Co(N-Mecyclen)(OH2)OH]2+ is much morerapid (kex/s-1 = 0.03 (p-site)/0.01 (t-site), 12 and 15, respectively). Ligand-OH- exchange in these latter systemsis interpreted as occurring via (indirect) SN1(CB)-type processes on the corresponding aqua complexes: [Co(amine)OH]2+ es/entities/rlhar2.gif"> [Co(amine-H)OH2]2+ es/entities/rarr.gif"> exchange. This type of pathway is seen to be more efficient whenleaving-group departure is synchronous with proton transfer, and this appears to be more important for exchangein the cyclen and N-Mecyclen complexes where a reasonably acidic, adjacent syn NH proton is involved.