Base-promoted vinyl carbon-bromine bond cleavage of styryl bromide by group 9 metalloporphyrin complexes was achieved to give the metal(III) porphyrin styryls M(ttp)(styryl) (ttp = 5,10,15,20-tetra:p-tolylporphyrinato dianion). Mechanistic studies suggest that [M-II(ttp)](2) (M = Rh, Ir) cleaves the vinyl C-Br bond via an addition-elimination mechanism. The much less reactive Co-II(ttp) undergoes a radical recombination with styryl radical which is generated by the hydroxide reduction of styryl bromide to give a radical anion with subsequent C-Br cleavage.
Base-Promoted Selective Aryl C–Br and C–I Bond Cleavage by Iridium(III) Porphyrin: Reduction of Ir<sup>III</sup>–OH to Ir<sup>II</sup> for Metalloradical Ipso Substitution of Aryl–Halogen Bonds
作者:Chi Wai Cheung、Kin Shing Chan
DOI:10.1021/om200251k
日期:2011.8.22
center to give iridium(II) porphyrin dimer ([IrII(ttp)]2) and H2O2. In a competitive pathway, [IrII(ttp)]2 disproportionates in the presence of base and residual water to give an iridium(III) hydride (IrIII(ttp)H) and Ir(ttp)OH. In a productive process, [Ir(ttp)]2 undergoes IrII(ttp) metalloradical-mediated ipso substitution of Ar–X via an addition–elimination pathway to form Ir(ttp)Ar and Ir(ttp)X. Ir(ttp)X
在存在下,通过铱(III)卟啉羰基氯(Ir III(TTp)(CO)Cl)裂解碱促进的选择性芳基碳溴和碳碘键(Ar–X,X = Br,I)裂解。碱(K 2 CO 3,NaOH)得到铱(III)卟啉芳基(Ir III(TTp)Ar)。机理研究表明,碱经Ir(ttp)(CO)Cl进行配体取代,生成铱(III)羟基物种(Ir III(TTp)OH)。羟基配体最有可能还原Ir(III)中心,得到铱(II)卟啉二聚体([Ir II(TTp)] 2)和H 2 O 2。在竞争途径中,[Ir II(TTp)] 2在碱和残留水的存在下歧化,得到氢化铱(III)(Ir III(TTp)H)和Ir(TTp)OH。在一个生产过程中,物[Ir(TTP)] 2经历的Ir II(TTP)经由加成-消除途径metalloradical介导的本位的Ar-X的取代,以形成的Ir(TTP)中的Ar和Ir(TTP)X。Ir(