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A literature survey of the P–C coupling reactions of 1,4-and 1,2-bromo-iodobenzenes with diphenylphosphine oxide or diethyl phosphite under different conditions comprising Pd-, Ni-, or Cu-catalysis revealed that, depending on the experimental details, the yields of the corresponding >P(O)-bromobenzenes were rather diverse and occasionally contradicting. Therefore, the reactivity of a series of 1,4-, 1,3- and 1,2-dibromo- and bromo-iodobenzenes with the above mentioned P-reagents was evaluated under the "P-ligand-free" microwave (MW)-assisted conditions elaborated by us. Starting from dibromobenzenes and iodo-bromoarenes, practical and competent syntheses were developed for phosphonoyl- and phosphinoyl-bromoarenes, and, in a few instances, for arenes with two P-functions. The cheaper dibromobenzenes may be substituted for the bromo-iodo derivatives. In all, 12 products were prepared in yields of 45–82%. They were fully characterized. The method described does not require the use of traditional P-ligands. [ABSTRACT FROM AUTHOR]

A literature survey of the P–C coupling reactions of 1,4-and 1,2-bromo-iodobenzenes with diphenylphosphine oxide or diethyl phosphite under different conditions comprising Pd-, Ni-, or Cu-catalysis revealed that, depending on the experimental details, the yields of the corresponding >P(O)-bromobenzenes were rather diverse and occasionally contradicting. Therefore, the reactivity of a series of 1,4-, 1,3- and 1,2-dibromo- and bromo-iodobenzenes with the above mentioned P-reagents was evaluated under the “P-ligand-free” microwave (MW)-assisted conditions elaborated by us. Starting from dibromobenzenes and iodo-bromoarenes, practical and competent syntheses were developed for phosphonoyl- and phosphinoyl-bromoarenes, and, in a few instances, for arenes with two P-functions. The cheaper dibromobenzenes may be substituted for the bromo-iodo derivatives. In all, 12 products were prepared in yields of 45–82%. They were fully characterized. The method described does not require the use of traditional P-ligands.

Our group described a green, “P-ligand-free”, Pd(OAc)2- or NiCl2-catalyzed synthesis under MW conditions. The reactivity of a few aryl derivatives in the Pd(OAc)2-catalyzed, “P-ligand-free” P–C coupling reactions under MW condition was also studied. An induction period was observed. Finally, the less known copper(I)-promoted reactions were investigated experimentally. The mechanism was explored by quantum chemical calculations.

The Hirao reaction involving the phosphinoylation or phosphonation of aryl halides by >P(O)H reagents is a P–C bond forming transformation belonging to the recently very hot topic of cross-couplings. The Pd- or Ni-catalyzed variations take place via the usual cycle including oxidative addition, ligand exchange, and reductive elimination. However, according to the literature, the nature of the transition metal catalysts is not unambiguous. In this feature article, the catalysts described for the Pd(OAc)2-promoted cases are summarized, and it is concluded that the “(HOY2P)2Pd(0)” species (Y = aryl, alkoxy) is the real catalyst. In our model, the excess of the >P(O)H reagent served as the P-ligand. During the less studied Ni(II)-catalyzed instances the “(HOY2P)(−OY2P)Ni(II)Cl−” form was found to enter the catalytic cycle. The newest conclusions involving the exact structure of the catalysts, and the mechanism for their formation explored by us were supported by our earlier experimental data and theoretical calculations.

• New variation for the Hirao P–C coupling reaction. • Cu(II) salts may be novel precursors for P- and N-complexes. • Excess of the > P (O)H reagent can substitute usual P-ligands via its tautomeric form. • Efficient synthesis of tertiary phosphine oxides and phosphonates. • The mechanism involves a Cu(II) → Cu(I) transition. After surveying the most important results described on the Pd(0)/Pd(II)- and Ni(II)-catalyzed P–C couplings of bromobenzene and diethyl phosphite or diphenylphosphine oxide, the simple Hirao reactions catalyzed by different Cu(II) salts were investigated. In these instances, the more reactive iodobenzene had to be used. CuSO 4 and Cu(OAc) 2 · H 2 O were found suitable catalyst precursors in case they were used together with two equiv. of triethylamine suggesting the role of the amine in the complexation. Theoretical calculations suggested that the corresponding Cu(I) species formed from the initial Cu(II) salt is involved in the catalytic cycle. [Display omitted] [ABSTRACT FROM AUTHOR]

The Hirao reaction involving the phosphinoylation or phosphonation of aryl halides by >P(O)H reagents is a P–C bond forming transformation belonging to the recently very hot topic of cross-couplings. The Pd- or Ni-catalyzed variations take place via the usual cycle including oxidative addition, ligand exchange, and reductive elimination. However, according to the literature, the nature of the transition metal catalysts is not unambiguous. In this feature article, the catalysts described for the Pd(OAc)2-promoted cases are summarized, and it is concluded that the "(HOY2P)2Pd(0)" species (Y = aryl, alkoxy) is the real catalyst. In our model, the excess of the >P(O)H reagent served as the P-ligand. During the less studied Ni(II)-catalyzed instances the "(HOY2P)(−OY2P)Ni(II)Cl−" form was found to enter the catalytic cycle. The newest conclusions involving the exact structure of the catalysts, and the mechanism for their formation explored by us were supported by our earlier experimental data and theoretical calculations. [ABSTRACT FROM AUTHOR]