Small differences in the reactivity of weakly nucleophilic potassium aryltrifluoroborates are revealed in the silver-assisted Pd-catalyzed cross-coupling of K[4-RC6F4BF3] (R = H, Bu, MeO, EtO, PrO, iPrO, BuO, t-BuO, CH2=CHCH2O, PhCH2O, PhCH2CH2O, PhO, F, pyrazol-1-yl, pyrrol-1-yl, and indol-1-yl) with ArX (4-BrC6H4CH3, 4-IC6H4F and 3-IC6H4F). An assumed role of silver(I) compounds AgmY (Y = O, NO3, SO4, BF4, F) consists in polarization of the Pd–X bond in neutral complex ArPdLnX with the generation of the related transition state or formation of [ArPdLn][XAgmY] with a highly electrophilic cation and subsequent transmetallation with the weakly nucleophilic borate. Efficiency of AgmY as a polarizing agent decreases in order Ag2O > AgNO3 ≈ Ag2SO4 > Ag[BF4] > AgF. No clear correlation between the reactivity of K[4-RC6F4BF3] and substituent electron parameters, σI and σR°, of the aryl group 4-RC6F4 was found.
在
银辅助的Pd催化下,揭示了弱亲核性
钾芳基三
氟硼酸盐在K[4-RC
6F
4BF
3](R = H,Bu,MeO,EtO,PrO,iPrO,BuO,t-BuO,CH
2=CHCH
2O,PhCH
2O,PhCH
2CH
2O,PhO,F,
吡唑-1-基,
吡咯-1-基和
吲哚-1-基)与ArX(4-BrC
6H
4CH
3,4-IC
6H
4F和3-IC
6H
4F)的交叉偶联中的反应性的细微差异。
银(I)化合物Ag
mY(Y = O,NO
3,SO
4,BF
4,F)的假定作用在于极化中性配合物ArPdL
nX中的Pd–X键,生成相关的过渡态或形成[ArPdL
n][XAg
mY],其中阳离子具有高电子亲合性,随后与弱亲核性
硼酸盐进行
金属转移。作为极化剂的Ag
mY的效率按顺序降低为Ag
2O > AgNO
3 ≈ Ag
2SO
4 > Ag[BF
4] > AgF。未发现K[4-RC
6F
4BF
3]的反应性与取代基电子参数aryl group 4-RC
6F
4的σ
I和σ
R°之间的明确相关性。