Reaction of elemental phosphorus with α-methylstyrenes: one-pot synthesis of secondary and tertiary phosphines, prospective bulky ligands for Pd(II) catalysts

α-Methylstyrene and 4-chloro-α-methylstyrene react readily with elemental (red) phosphorus under microwave-irradiation in the superbase KOH/DMSO suspension to afford, depending on the reactant ratio and reaction time, either corresponding bis(2-arylpropyl)phosphines or tris(2-arylpropyl)phosphines in 46–54% and 69–77% yields, respectively. Upon the heating only (110–130 °C, 3 h), this reaction provides mainly tris(2-arylpropyl)phosphine oxides (up to 78% yield) along with (2-arylpropyl)phosphinic acids (up to 43%). The synthesized phosphines are prospective bulky ligands for metal catalysts that has been demonstrated by the preparation of a new Pd(II) complex, trans-[Pd(PR3)2Cl2], which proves to be active in the Sonogashira couplings.

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