| 18189351 |
Na YM, Noh TH, Chun IS, Lee YA, Hong J, Jung OS: Subtle ring-constraint effects on the formation of metallacycles. Inorg Chem. 2008 Feb 18;47(4):1391-6. Epub 2008 Jan 12.
Cyclodimer versus cyclotrimer of bis (chloro)-1,4-bis (dimethyl-3 or 4-pyridylsilyl) benzenepalladium (II) complexes.. Stepwise modulation of the ring size of metallacyclic compounds via subtle ring-constraint effects has been established. The reactions of (COD) PdCl 2 with p- or m-psb ligand [COD = 1,5-cyclooctadiene; p-psb = 1,4-bis (dimethyl-4-pyridylsilyl) benzene; m-psb = 1,4-bis (dimethyl-3-pyridylsilyl) benzene] in a mixture of acetone and ethanol at room temperature produce the metallacyclodimers [PdCl 2 ( p- or m-psb)] 2. The cyclodimeric species of [PdCl 2 ( p-psb)] 2 at the boiling temperature or via the sonication of the chloroform solution is completely converted to the cyclotrimer [PdCl 2 ( p-psb)] 3. Direct reaction of (COD) PdCl 2 with p-psb in a mixture of acetone and ethanol at reflux temperature yields the same trimer, [PdCl 2 ( p-psb)] 3. Furthermore, equilibria between the kinetic product, [PdCl 2 ( p-psb)] 2, and the thermodynamic product, [PdCl 2 ( p-psb)] 3, have been observed in N, N-dimethylformamide as well as in dimethyl sulfoxide. In contrast, the cyclodimeric structure of [PdCl 2 ( m-psb)] 2 is retained under the same treatment conditions for 40 h; that is, the trimeric species, [PdCl 2 ( m-psb)] 3, is not formed. Such a notable difference between [PdCl 2 ( p-psb)] 2 and [PdCl 2 ( m-psb)] 2 might be explained by their different angle constraints. |
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