Fe Catalysis – Fact or Fiction?
Iron catalysis has been a growing area of interest in recent years helped by the low cost and toxicity of most iron catalysts particularly when compared to Pd, Ru, Rh etc. However a recent paper1 from Carsten Bolm and Steven Buchwald casts doubt on iron’s perceived role in some FeCl3 catalysed aryl coupling reactions between aryl iodides and phenols, thiophenols and imidazoles.
It now appears that, at least in some cases, the actual catalytic species is copper which is often a trace impurity in iron albeit at ppm levels.
| Metal Salt | Yield |
| >98% FECI3 (Merck) | 87% |
| >99.99% FECI3 (Aldrich) | 9% |
| >99.99% FECI3 + 5ppm Cu2O | 78% |
| No Fe + 5ppm Cu2O | 77% |
A follow up paper2 in the same issue of Angewandte from Carsten Bolm’s group describes some copper catalysed aryl couplings carried out with ppm levels of copper.
Whether the copper effect is true for other reactions involving iron catalysts remains to be seen.
1. S.L. Buchwald and C. Bolm, Angew. Chem. Internat. Ed., 2009, 48, 5586-5587.
2. P.-F, Larsson, A. Correa, M. Carril, P.-O. Norrby, and C. Bolm, Angew. Chem. Internat. Ed., 2009, 48, 5691-5693.