Topotactic Synthesis of Phosphabenzene‐Functionalized Porous Organic Polymers: Efficient Ligands in CO₂Conversion

Abstract

Progress toward the preparation of porous organic polymers (POPs) with task-specific functionalities has been exceedingly slow-especially where polymers containing lowoxidation phosphorus in the structure are concerned. At wostep topotactic pathway for the preparation of phosphabenzene-based POPs (Phos-POPs) under metal-free conditions is reported, without the use of unstable phosphorus-based monomers.T he synthetic route allows additional functionalities to be introduced into the porous polymer framework with ease.A sa ne xample,p artially fluorinated Phos-POPs (F-Phos-POPs) were obtained with as urface area of up to 591 m 2 g À1 .A fter coordination with Ru species,aRu/F-Phos-POPs catalyst exhibited high catalytic efficiency in the formylation of amines (turnover frequency up to 204 h À1 ) using aC O 2 /H 2 mixture,i nc omparison with the non-fluorinated analogue (43 h À1 )and aAu/TiO 2 heterogeneous catalysts reported previously (< 44 h À1 ). This work describes apractical method for synthesis of porous organic phosphorus-based polymers with applications in transition-metal-based heterogeneous catalysis.Organophosphorus compounds have emerged as powerful organocatalysts [1][2][3][4] and they are the ligands of choice for an umber of transition-metal-catalyzed processes. [5][6][7][8] In general, phosphine-containing catalysts are used mainly in homogeneous processes,w here they exhibit excellent catalytic activities and selectivities.N evertheless,h eterogeneous phosphine-based catalysts are more desirable for industrial applications because it is more convenient to recover and recycle them. However,o nly af ew examples of heterogeneous phosphine-based catalytic systems have been reported to date. [9][10][11][12][13] Fore xample,X iao et al. reported as eries of diphosphine-ligand-containing porous frameworks obtained by polymerization of the vinyl-functionalized diphosphine monomers.T hese materials demonstrated superior catalytic performance in the hydroformylation of alkenes after treatment with Rh species. [12] Mesoporous poly(triphenylphosphine) with azo functionality (poly(PPh 3 )-azo) was synthesized by oxidative polymerization of aP ( m-NH 2 Ph) 3 monomer. After coordination with metal ions (for example,R u 3+ and Ag + ), the resulting metalated poly(PPh 3 )-azo catalysts mediated CO 2 conversion reactions efficiently. [13] Despite the progress made,anumber of obvious drawbacks still need to be addressed:1 )tedious synthetic processes under an inert atmosphere are generally required for the preparation of vinyl-or amino-group-functionalizedp hosphine monomers (Scheme 1);2 )limited synthetic methods can be used for polymer construction because of the poor compatibility and stability of the phosphine monomers under harsh reaction conditions,asw ell as difficulties associated with the removal of metal catalysts that are strongly coordinated by phosphine ligands;3 )the introduction of additional functionalities into the polymer backbone is difficult by monomer design and synthesis,o rb yp ost-synthetic func...