Phosphorus containing porous organic polymers: synthetic techniques and applications in organic synthesis and catalysis

The phosphorus-containing porous organic polymer is a trending material for the synthesis of heterogeneous catalysts. Decades of investigations have established phosphines as versatile ligands in homogeneous catalysis. Recently, phosphine-based heterogeneous catalysts were synthesized to exploit the same electronic properties while leveraging extra stability and reusability. In the last few decades, the catalysts were applied in diverse organic transformations, including hydroformylation, hydrogenation, C-C, C-N and C-X coupling, hydrosilylation, oxidative-carbonylation reactions, and so on. However, even though these polymers possess a multifunctional character, they face multiple synthetic issues in controlling the pore size, increasing the surface area, and creating a single type of active site. This review summarizes the developments in this field over the last few decades, highlighting the current limitation and future scope.

Orthogonally Bimetallized Phosphane-ene Photopolymer Networks

The development of batteries and fuel cells has brought to light a need for carbon anode materials doped homogeneously with electrocatalytic metals. In particular, combinations of electrocatalysts in carbon have shown promising activity. A method to derive functional carbon materials is the pyrolysis of metallopolymers. This work describes the synthesis of a bifunctional phosphonium-based system derived from a phosphane-ene network. The olefin functionality can be leveraged in a hydrogermylation reaction to functionalize the material with Ge. Unaffected by this radical addition, the bromide counterion of the phosphonium cation can be used to subsequently incorporate a second metal in an ion-complexation reaction with CuBr₂ . The characterization of the polymers and the derived ceramics are discussed.

"Lignophines": lignin-based tertiary phosphines with metal-scavenging ability

Methacrylated lignin was reacted with PH₃(g) to prepare a phosphorus rich bio-based polymer containing PH/PH₂ functional groups, which were converted to tertiary phosphine units via the phosphane-ene reaction. This represents a straightforward method for the upconversion of low-value biomass waste to useful inorganic polymer with potential utility in metal scavenging applications.

Metallized Phosphane-Ene Polymer Networks as Precursors for Ceramics with Excellent Shape Retention

Our research group has reported the synthesis of phosphane-ene photopolymer networks, where the networks are composed of cross-linked tertiary alkyl phosphines. Taking advantage of the rich coordination chemistry of alkyl phosphines and the material's susceptibility to solution chemistry, we were able to generate Co, Al, and Ge macromolecular adducts. The metallized polymer networks can be pyrolyzed to make metal-doped carbon, commodity materials in the areas of battery, and fuel cell research. The polymer precursors can also be shaped by spin coating and lithography, before being metallized and pyrolyzed to give patterned ceramics, which display excellent shape retention of the original patterns.

Phosphorous(v) Lewis acids: water/base tolerant P3-trimethylated trications

The water/base intolerance of the previously reported electrophilic phosphonium cations has been overcome by replacing the labile electron-withdrawing groups generally attached to phosphorus (e.g. -F, -OAr, -CF3) with methyl groups. Tri-phosphorus(v) tricationic species, accessible in one-pot from commercially available materials, are air and water/base tolerant, yet are sufficiently Lewis acidic for catalysis.

Antimony-Functionalized Phosphine-Based Photopolymer Networks

The synthesis of phosphane-ene photopolymer networks, where the networks are composed of crosslinked tertiary alkyl phosphines are reported. Taking advantage of the rich coordination chemistry of alkyl phosphines, stibino-phosphonium and stibino-bis(phosphonium) functionalized polymer networks could be generated. Small-molecule stibino-phosphonium and stibino-bis(phosphonium) compounds have been well characterized previously and were used as models for spectroscopic comparison to the macromolecular analogues by NMR and XANES spectroscopy. This work reveals that the physical and electronic properties of the materials can be tuned depending on the type of coordination environment. These materials can be used as ceramic precursors, where the Sb-functionalized polymers influence the composition of the resulting ceramic.