Arsenic MOF lifts rhodium yield past 95%
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- AsCM-102 — an arsenic-containing MOF built from arsenic-centered organic linkers connected to cobalt nodes — anchors organoarsine ligands inside its pore walls, solving the decades-old problem of arsenic ligands detaching from rhodium catalysts during reactions.
- RhI–AsCM-102 converted 1-hexene to aldehydes at over 95% yield with an iso:n ratio of 1.43 under 40 bar CO/H₂ at 70 °C, outperforming an analogous phosphine-based MOF catalyst.
- Arsenic leaching into solution measured just 0.689 parts per billion after one cycle, and what little framework dissolution occurred appeared to release intact cobalt-arsenic fragments rather than free toxic arsenic.
- RhI–AsCM-102 retained its activity across five consecutive reaction cycles, losing only about 1% per run.
- Single-crystal X-ray diffraction confirmed each rhodium atom sitting in a clean trans arrangement between paired arsenic atoms inside the pore channels — a level of atomic-level structural certainty rare for heterogeneous catalysts.
- The confined pore geometry itself drives iso selectivity by forcing alkenes into an end-on approach to rhodium, lowering the energy barrier toward the branched aldehyde product.
Why it matters: Hydroformylation produces over 12 million tons of aldehydes per year for detergents, plastics, and fine chemicals, and rhodium-phosphine catalysts have been the industrial workhorse for decades. Arsenic ligands have long been known to be faster and more selective than phosphines, but their tendency to fall off rhodium — releasing toxic arsenic — kept them confined to academic curiosity; this work shows that tethering them inside a MOF neutralizes that liability while delivering measurably better performance and recyclability than a phosphine-MOF benchmark.
