Trace metal impurities in catalysis

Abstract

Metal-catalysed transformations are a powerful tool in organic chemistry and the enormous progress, which has been made in the last few decades, was one more time honoured by the Nobel Prize in Chemistry in 2010. Many metal-containing compounds have been applied in carbon-carbon and carbon-heteroatom bond formations. However, not every component originally claimed as catalyst turned out to be the active ingredient in the end. Sometimes trace metal impurities were the actual catalytic species. In this tutorial review, we will highlight recent findings in transition metal-catalysed cross-coupling reactions and detail several reports from the past, which illustrate that "trace metal catalysis" is not a newly discovered phenomenon.

A Zinc Catalyzed C(sp3)−C(sp2) Suzuki–Miyaura Cross‐Coupling Reaction Mediated by Aryl‐Zincates

“…Although highly selective cross‐coupling was observed in both dioxane and 2‐MeTHF, 2‐MeTHF was utilized for this study due to its superior safety profile. Control reactions were performed next to examine the possibility of trace‐metal catalysis 18. ZnBr 2 obtained from multiple sources and of different purity (including 99.999 % purity) produced similar coupling outcomes.…”

Trace Amounts of Second Metal Elements Can Play a Key Role in the Generation of Organometallic Compounds

“…Magnesium plays three different roles in the Grignard reaction: (1) to provide electrons as an electron pool for reduction of organic halides (first step), (2) to stabilize and activate the reactive intermediates, carbanions, as organomagnesium compounds, and (3) to provide reaction fields for the transition state and to control selectivities (second step) (Scheme 1). 1 In organic chemistry textbooks, carboncarbon bond formation usually receives more attention than the first step, the formation of organometallic compounds.…”

“…1 In organic chemistry textbooks, carboncarbon bond formation usually receives more attention than the first step, the formation of organometallic compounds. Acceleration of the second step with catalytic amounts of a second metal element, 2 for example, palladium-catalyzed cross-coupling reactions, is well known and utilized even in practical industrial processes. In this manuscript, however, I focus on the effects of the second metal elements on the first step, the formation of organometallic compounds under reductive conditions.…”

Recent Advances of Transition Metal-Catalyzed Aerobic Dehydrative Reactions of Alcohols and Amines and Related Researches

“…总之, Xu 等在该报 道中的这些实验证据很好地解释了 Cu(II)和空气促进反 应的真正原因, 也对机理中的各个步骤进行了实验证 明, 因此该反应也应该通过接力机理进行(Scheme 14). [46] . 因此, 这一报道中底物和碱中 残留过渡金属的检测及其对反应的影响, 也有待通过进 一步的研究确定.…”