| Abstract
| - Ring expansion of a platinacyclopropane to a platinacyclopentane was accomplished by insertion of isocyanides into each platinum−carbon bond of (η2-TCNE)Pt(η-CNC6H3-2,6-Me2)2 (1). Exchange between imidoyl CNC6H3-2,6-Me2 and coordinated CNC6H3-2,6-Me2 in the formed platinacyclopentane 4 in solution suggested the ring expansion to be reversible.
- A platinum isocyanide complex bearing a η2-TCNE ligand, (η2-TCNE)Pt(η-CNC6H3-2,6-Me2)2 (1),was synthesized, and its crystallographic study revealed the coordination mode of the η2-TCNE ligandto be a typical metallacyclopropane extreme, in which back-donation from metal to TCNE contributesprimarily to the stabilization of 1. Treatment of 1 with 2 equiv of CNC6H3-2,6-Me2 resulted in ringexpansion of the platinacyclopropane by insertion of CNC6H3-2,6-Me2 into each Pt−C bond of themetallacycle, leading to formation of a new complex having a platinacyclopentane structure, (TCNE)Pt(η-CNC6H3-2,6-Me2)4 (4). Although the molecular structures of palladium and nickel homologues of1 were close to the corresponding metallacyclopropane, no metallacyclopentane complex was obtainedunder similar conditions. Studies on variable-temperature NMR spectroscopy and spin-saturation transfermeasurement of 4 showed exchange of the imidoyl CNC6H3-2,6-Me2 group and the coordinated CNC6H3-2,6-Me2 ligand in solution, suggesting the ring expansion to be reversible.
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