Organoarsine Metal–Organic Framework as a Solid-State Ligand for Rhodium(I) Olefin Hydroformylation Catalysis
Venkatesh Piradi, Wenrui Chai, Samuel K. Emslie, R. Eric Sikma, Chuning Zhang, Serhii Vasylevskyi, Graeme Henkelman, Simon M. Humphrey
Abstract
A new triaryl arsine (Ar 3 As)-based metal–organic framework (MOF) named AsCM-102 has been prepared by the reaction of As(C 6 H 4 -4-CO 2 H) 3 with Co(BF 4 ) 2 and 4,4′-bipyridine. AsCM-102 contains pairs of staggered As donors that function as trans- chelators for the facile incorporation of organometallic Rh I species via a single crystal-to-single crystal transformation. Coordination of Rh I is achieved by soaking crystals in a solution of [Rh(CO) 2 Cl] 2 at 70 °C. The originally closed and offset As 2 pockets expand to facilitate the trans- As 2 chelation of Rh I . The resulting metalated MOF displays trans -[(Ar 3 As) 2 Rh(CO)Cl n ] (1– n )+ complexes inside uniquely confined micropore reaction environments. Installation of the As–Rh–As moieties significantly enhances the internal porosity of the MOF. Crystalline Rh I –AsCM-102 is an air-stable and recyclable hydroformylation catalyst, which is more active than its phosphine-based analogue. It is also selective toward the formation of iso -aldehydes over n -aldehydes with various C 6 –C 8 olefin feedstocks. By leveraging the absolute atomic coordinates of Rh I –AsCM-102 obtained from single-crystal X-ray diffraction analysis, density functional theory (DFT) explains the experimentally observed iso -favored hydroformylation regioselectivity due to pore confinement. Rh I –AsCM-102 is resistant toward leaching of As into solution under forcing reaction conditions (40 atm of CO/H 2, 70 °C). This work demonstrates the premise that incorporation of organo(arsines) into MOF scaffolds is a safer and more convenient strategy for their deployment in catalysis, by alleviating M–As bond lability and As toxicity issues, which prevents their widespread use in homogeneous catalysis.