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Article: Structural and mechanistic studies of co-ordination compounds. Part 22. Preparation and ligand-substitution kinetics of some trans-di-halogeno- and trans-halogenoisothiocyanato-cobalt(III) complexes of 2,12-dimethyl- and 2,7,12-trimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]-heptadeca-1(17),2,11,13,15- pentaene
Title | Structural and mechanistic studies of co-ordination compounds. Part 22. Preparation and ligand-substitution kinetics of some trans-di-halogeno- and trans-halogenoisothiocyanato-cobalt(III) complexes of 2,12-dimethyl- and 2,7,12-trimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]-heptadeca-1(17),2,11,13,15- pentaene |
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Authors | |
Issue Date | 1978 |
Citation | Journal of the Chemical Society, Dalton Transactions, 1978, n. 9, p. 1180-1185 How to Cite? |
Abstract | Complexes trans-[CoL1(NCS)X]+ {L1 = 2,7,12-trimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1(17),2,11,13,15- pentaene; X = NCS, Cl, or Br} have been prepared and characterized. The kinetics of thiocyanate-substitution reactions of trans-[CoLX2]+ {L = L1 or L2 (2,12-dimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]hepta-deca-1(17),2,11,13,15- pentaene); X = Cl or Br} have been studied over a range of temperature. The rate constants for the replacement of the first chloride from the dichloro-complexes are virtually independent of the nature of L [kCl = 1.1 × 10-2 (L1 and 2.9 × 10-2 s-1 at 25.0 °C (L2)] whereas those for the replacement of the second halide are much faster for L2 (kCl = 7.6 × 10-4 and kBr = 9.1 × 10-4 s-1 at 25.0 °C) than for L1 (kCl = 2.8 × 10-6 and kBr = 4.5 × 10-6 s-1 at 25.0 °C) by two orders of magnitude. This observation seems to indicate that the first step of substitution involves the release of the halide farther away from the N-R group of the L1 (R = Me) and L2 (R = H) macrocycles. The role played by the amine proton in promoting the rates of substitution of the second halide in the L2 complexes is discussed. The hydrolysis of trans-[CoL1(NCS)X]+ involves concurrent release of both isothiocyanate and halide. This, coupled with a relatively low value of kBr/kCl, is taken to indicate that the cobalt(III) ion in these L1 and L2 complexes is much softer than that in complexes of saturated macrocyclic amines. |
Persistent Identifier | http://hdl.handle.net/10722/194203 |
ISSN | |
ISI Accession Number ID |
DC Field | Value | Language |
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dc.contributor.author | Poon, C-K | - |
dc.contributor.author | Liao, SST | - |
dc.date.accessioned | 2014-01-30T03:32:18Z | - |
dc.date.available | 2014-01-30T03:32:18Z | - |
dc.date.issued | 1978 | - |
dc.identifier.citation | Journal of the Chemical Society, Dalton Transactions, 1978, n. 9, p. 1180-1185 | - |
dc.identifier.issn | 1472-7773 | - |
dc.identifier.uri | http://hdl.handle.net/10722/194203 | - |
dc.description.abstract | Complexes trans-[CoL1(NCS)X]+ {L1 = 2,7,12-trimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1(17),2,11,13,15- pentaene; X = NCS, Cl, or Br} have been prepared and characterized. The kinetics of thiocyanate-substitution reactions of trans-[CoLX2]+ {L = L1 or L2 (2,12-dimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]hepta-deca-1(17),2,11,13,15- pentaene); X = Cl or Br} have been studied over a range of temperature. The rate constants for the replacement of the first chloride from the dichloro-complexes are virtually independent of the nature of L [kCl = 1.1 × 10-2 (L1 and 2.9 × 10-2 s-1 at 25.0 °C (L2)] whereas those for the replacement of the second halide are much faster for L2 (kCl = 7.6 × 10-4 and kBr = 9.1 × 10-4 s-1 at 25.0 °C) than for L1 (kCl = 2.8 × 10-6 and kBr = 4.5 × 10-6 s-1 at 25.0 °C) by two orders of magnitude. This observation seems to indicate that the first step of substitution involves the release of the halide farther away from the N-R group of the L1 (R = Me) and L2 (R = H) macrocycles. The role played by the amine proton in promoting the rates of substitution of the second halide in the L2 complexes is discussed. The hydrolysis of trans-[CoL1(NCS)X]+ involves concurrent release of both isothiocyanate and halide. This, coupled with a relatively low value of kBr/kCl, is taken to indicate that the cobalt(III) ion in these L1 and L2 complexes is much softer than that in complexes of saturated macrocyclic amines. | - |
dc.language | eng | - |
dc.relation.ispartof | Journal of the Chemical Society, Dalton Transactions | - |
dc.title | Structural and mechanistic studies of co-ordination compounds. Part 22. Preparation and ligand-substitution kinetics of some trans-di-halogeno- and trans-halogenoisothiocyanato-cobalt(III) complexes of 2,12-dimethyl- and 2,7,12-trimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]-heptadeca-1(17),2,11,13,15- pentaene | - |
dc.type | Article | - |
dc.description.nature | link_to_subscribed_fulltext | - |
dc.identifier.doi | 10.1039/DT9780001180 | - |
dc.identifier.scopus | eid_2-s2.0-37049097169 | - |
dc.identifier.issue | 9 | - |
dc.identifier.spage | 1180 | - |
dc.identifier.epage | 1185 | - |
dc.identifier.isi | WOS:A1978FP89500035 | - |
dc.identifier.issnl | 1364-5447 | - |