Cyclopropenylidene carbene ligands in palladium catalysed coupling reactions: carbene ligand rotation and application to the Stille reaction
作者:Ratanon Chotima、Tim Dale、Michael Green、Thomas W. Hey、Claire L. McMullin、Adam Nunns、A. Guy Orpen、Igor V. Shishkov、Duncan F. Wass、Richard L. Wingad
DOI:10.1039/c1dt10109a
日期:——
Reaction of [Pd(PPh3)4] with 1,1-dichloro-2,3-diarylcyclopropenes gives complexes of the type cis-[PdCl2(PPh3)(C3(Ar)2)] (Ar = Ph 5, Mes 6). Reaction of [Pd(dba)2] with 1,1-dichloro-2,3-diarylcyclopropenes in benzene gave the corresponding binuclear palladium complexes trans-[PdCl2(C3(Ar)2)]2 (Ar = Ph 7, p-(OMe)C6H48, p-(F)C6H49). Alternatively, when the reactions were performed in acetonitrile, the complexes trans-[PdCl2(NCMe)(C3(Ar)2)] (Ar = Ph 10, p-(OMe)C6H411 and p-(F)C6H4) 12) were isolated. Addition of phosphine ligands to the binuclear palladium complex 7 or acetonitrile adducts 11 and 12 gave complexes of the type cis-[PdCl2(PR3)(C3(Ar)2)] (Ar = Ph, R = Cy 13, Ar = p-(OMe)C6H4, R = Ph 14, Ar = p-(F)C6H4, R = Ph 15). Crystal structures of complexes 6·3.25CHCl3, 10, 11·H2O and 12–15 are reported. DFT calculations of complexes 10–12 indicate the barrier to rotation about the carbene-palladium bond is very low, suggesting limited double bond character in these species. Complexes 5–9 were tested for catalytic activity in C–C coupling (Mizoroki–Heck, Suzuki–Miyaura and, for the first time, Stille reactions) and C–N coupling (Buchwald–Hartwig amination) showing excellent conversion with moderate to high selectivity.
四(三苯基膦)钯[Pd(PPh3)4]与1,1-二氯-2,3-二芳基环丙烯的反应生成cis-[PdCl2(PPh3)(C3(Ar)2)]类型的配合物(Ar = Ph 5, Mes 6)。在苯中,[Pd(dba)2]与1,1-二氯-2,3-二芳基环丙烯反应生成了相应的双核钯配合物trans-[PdCl2(C3(Ar)2)]2(Ar = Ph 7, p-(OMe)C6H4 8, p-(F)C6H4 9)。另一种情况是,当反应在乙腈中进行时,生成了trans-[PdCl2(NCMe)(C3(Ar)2)]类型的配合物(Ar = Ph 10, p-(OMe)C6H4 11, p-(F)C6H4 12)。向双核钯配合物7或乙腈加合物11和12中加入膦配体,生成了cis-[PdCl2(PR3)(C3(Ar)2)]类型的配合物(Ar = Ph, R = Cy 13, Ar = p-(OMe)C6H4, R = Ph 14, Ar = p-(F)C6H4, R = Ph 15)。报告了配合物6·3.25CHCl3, 10, 11·H2O和12–15的晶体结构。对配合物10–12的DFT计算表明,卡宾-钯键的旋转能垒非常低,表明这些物种中的双键特性有限。对配合物5–9进行了催化活性测试,用于C–C偶联(Mizoroki–Heck, Suzuki–Miyaura,以及首次用于Stille反应)和C–N偶联(Buchwald–Hartwig胺化),显示出优良的转化率和中等至高的选择性。