Pd(0)-Catalyzed Phosphorus−Carbon Bond Formation. Mechanistic and Synthetic Studies on the Role of the Palladium Sources and Anionic Additives

Abstract

Pd(PPh 3 ) 4 , Pd(dba) 2 , Pd(OAc) 2 , and PdCl 2 , have been evaluated as possible Pd(0) sources for the palladium-catalyzed P-C bond formation via a cross-coupling of aryl halides with H-phosphonate diesters. It was found that the most efficient catalytic system can be generated from Pd(OAc) 2 with a key role being played by Pd(II) and Pd(0) species with coordinated acetate ions. The reactivity of differently ligated Pd(II) complexes was determined, and 31 P NMR spectroscopy studies were carried out to provide mechanistic interpretations for the observed differences between the catalytic systems.

Preparation of Arylphosphonates by Palladium(0)‐Catalyzed Cross‐Coupling in the Presence of Acetate Additives: Synthetic and Mechanistic Studies

“…As far as the palladium source is concerned, it was found that in contrast to PdA C H T U N G T R E N N U N G (PPh 3 ) 4 used in Hiraos original procedure, [1] catalytic systems generated in situ from PdA C H T U N G T R E N N U N G (OAc) 2 and appropriate phosphine ligands, were usually superior in terms of reactivity for promoting the C À P bond formation. [9,11,[20][21][22]24,27] All these improvements, for which a mechanistic basis has been provided in recent years, [19,27,28,[29][30][31] lend themselves into a modified catalytic cycle for the palladium-mediated formation of the C À P bond as shown in Scheme 2. Scheme 1.…”

Pd-Catalyzed P-Arylation of Triarylantimony Dicarboxylates with Dialkyl H-Phosphites without a Base: Synthesis of Arylphosphonates

“…First, we performed the reactions of 9a (1.2 eq) with a variety of antimony reagents (1a-6) to compare the reactivity using 5 mol% of Pd(PPh 3 ) 4 as catalyst in 1,4-dioxane at 60°C under argon atmosphere (entries [1][2][3][4][5][6][7][8]. In comparison with these results, triphenylantimony dicarboxylates (1a, 2) and pentavalent bismuth(V) compounds (7,8) afforded the expected diethyl phenylphosphonate (10) in good to high yields along with homo-coupling product (11) and reductive products (12,13). Among these, triphenylantimony diacetate (1a) appeared to be the best substrate for this reaction in terms of the yield (77%) of the cross-coupling product (10) and reaction time (6 h).…”

“…We also examined a similar reaction using other catalytic systems such as Pd(dba) 2 , Pd(dba) 2 -dppf, PdCl 2 , Pd(OAc) 2 , and PdCl 2 (PPh 3 ) 2 . They were inferior to Pd(PPh 3 ) 4 in the terms of the reaction time and yield of the cross-coupling product (entries [12][13][14][15][16]. The screening of solvent showed that the reaction proceeded effectively in dioxane (94%), 1,2-dichloroethane (DCE) (78%), 1,2-dimethoxyethane (DME) (75%) and tetrahydrofuran (THF) (71%) whereas toluene, CH 3 CN, N-methylpyrrolidone (NMP) and EtOH gave inferior results (entries [17][18][19][20][21][22][23].…”

“…The Pd-catalyzed P-arylation of aryl halides with dialkyl H-phosphites is promoted by acetate ions, and ArPdOAc (C) is the key intermediate for reaction mechanism. 12,13,19) The ligand exchange of ArPdOAc (C) with dialkyl H-phosphite (9) gives ArPdP(O)(OR) 2 intermediate D, which undergo reductive elimination to form the coupling product and regenerate the Pd(0) species (A).…”

“…[7][8][9] With regard to the synthesis of arylphosphonates, the Pd-catalyzed cross-coupling reactions of aryl halides with dialkyl H-phosphites (i.e., Hirao P-arylation) have proved to be a powerful method. [10][11][12][13][14][15][16][17][18][19][20][21] The general procedure of these P-arylations involves a Pd-phosphine complex as the catalyst with the use of a stoichiometric or an excess amount of a base. Recently, different aryl substances were investigated for their reactivity with phosphorus agents.…”