Structure and Thermal Reactivity of a Novel Pd(0) Metalloenediyne

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• 作者：Nicole L. Coalter ; Thomas E. Concolino ; William E. Streib ; Chris G. Hughes ; Arnold L. Rheingold ; and Jeffrey M. Zaleski
• 刊名：Journal of the American Chemical Society
• 出版年：2000
• 出版时间：April 5, 2000
• 年：2000
• 卷：122
• 期：13
• 页码：3112 - 3117
• 全文大小：117K
• 年卷期：v.122,no.13(April 5, 2000)
• ISSN：1520-5126

文摘

We report the X-ray diffraction structure and thermal reactivity of the metalloenediyne compoundbis(1,2-bis(diphenylphosphinoethynyl)benzene)palladium(0) (Pd(dppeb)₂, 1). The structure of 1 features atetrahedral Pd(0) center with four phosphorus atoms from two chelating ligands. The P-Pd-P bond anglesnearly match the idealized 109.5es/entities/deg.gif"> geometry expected for a d¹⁰ metal center in a tetrahedral ligand field. Thetetrahedral geometry of the metal center forces the alkyne termini separation of the enediyne ligand to a distanceof 3.47 Å, which results in a thermally stable compound at room temperature. However, at 115 es/entities/deg.gif">C 1 exhibitssolvent-dependent reactivity. In o-fluorotoluene, 1 decomposes via ligand dissociation, while in o-dichlorobenzene, carbon-halide bond activation of solvent occurs leading to the oxidative addition producttrans-Pd((2-chlorophenyl)diphenylphosphine)₂Cl₂ and free (2-chlorophenyl)diphenylphosphine. The thermalreactivity of 1 is markedly more endothermic (44 kcal/mol) than that of the known Pd(dppeb)Cl₂ analogue(12.3 kcal/mol). The diminished reactivity can be attributed to two factors: the increased alkyne terminiseparation in 1 (3.47 vs 3.3 Å) due to the metal-mandated tetrahedral geometry of the Pd(0) center, and theresistance of the Pd(0) to adopting a planar transition state geometry to promote Bergman cyclization. Overallthis study demonstrates that metal binding can impose structural consequences upon the enediyne ligand governedby the oxidation state and corresponding ligand field geometry of the metal center.