Barder Timothy E, Buchwald Stephen L
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
J Am Chem Soc. 2007 Oct 3;129(39):12003-10. doi: 10.1021/ja073747z. Epub 2007 Sep 12.
We present results on the binding of a variety amines to monoligated oxidative addition complexes of the type L1Pd(Ar)Cl, where L is 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (SPhos, 1) or 2-dicyclohexylphosphino-2',4',6'-tri-ispropylbiphenyl (XPhos, 2). The binding of an amine to oxidative addition complexes composed of 1 and 2 is more complex than with smaller ligands as intermediate Pd(II) complexes with bulky biaryl phosphine ligands disfavor amine binding to favorable conformations of oxidative addition complexes. Additionally, thermodynamic and kinetic parameters for reductive elimination from complexes of the type L1Pd(amido)Ph (where amido = EtNH, Me2N, PhNH) are discussed. From this data, we suggest a possible mechanism for (biaryl phosphine) Pd-catalyzed amination reactions that is more intricate than previously thought.
我们展示了多种胺与L1Pd(Ar)Cl型单配位氧化加成配合物的结合结果，其中L为2-二环己基膦基-2',6'-二甲氧基联苯（SPhos，1）或2-二环己基膦基-2',4',6'-三异丙基联苯（XPhos，2）。与较小的配体相比，胺与由1和2组成的氧化加成配合物的结合更为复杂，因为具有庞大联芳基膦配体的中间Pd(II)配合物不利于胺与氧化加成配合物的有利构象结合。此外，还讨论了L1Pd(酰胺基)Ph型配合物（其中酰胺基=EtNH、Me2N、PhNH）还原消除的热力学和动力学参数。根据这些数据，我们提出了一种比之前认为的更为复杂的(联芳基膦)Pd催化胺化反应的可能机理。
