Calix[4]pyrrolato Aluminate Catalyzes the Dehydrocoupling of Phenylphosphine Borane to High Molar Weight Polymers

Abstract

High molar weight polyphosphinoboranes represent materials with auspicious properties, but their preparation requires transition metal-based catalysts. Here, calix[4]pyrrolato aluminate is shown to induce the dehydropolymerization of phosphine boranes to high molar mass polyphosphinoboranes (up to M n = 43 000 Da). Combined GPC and 31 P DOSY NMR spectroscopic analyses, quantum chemical computations, and stoichiometric reactions disclose a PÀ H bond activation by the cooperative action of the square-planar aluminate and the electron-rich ligand framework. This first transition metal-free catalyst for PÀ B dehydrocoupling overcomes the problem of residual d-block metal impurities in the resulting polymers that might interfere with the reproducibility of the properties for this emerging class of inorganic materials.

Polyphosphinoborane Block Copolymer Synthesis Using Catalytic Reversible Chain‐Transfer Dehydropolymerization

“…1 H Diffusion Ordered Spectroscopy (DOSY, CDCl 3 , 298 K) provides further evidence for the formation of a block copolymer, Figure 1C. DOSY has been used previously for the analysis of polyphosphinoborane homopolymers [30] as well as hydrocarbon-based block copolymers. [51] Taking each homopolymer of similar MW (CCC, M n = 44 000-33 000 g mol À1 ) shows that ficients (1.5(2) and 3.9(8) × 10 À10 m 2 s À1 , respectively, Figure S42).…”

“…[33] Such catalyst-dependent changes in mechanism has been noted before for group 13/15 dehydropolymerizations. [30,35,36] We now report, by using the simple pre-catalyst [Rh-(Ph 2 PCH 2 CH 2 PPh 2 ) 2 ]Cl, 1, and harnessing a step-growth like mechanism in which reversible chain transfer also occurs, [36] a polyphosphinoborane block copolymer can be prepared containing aromatic and alkyl substituted segments. We also describe that this material shows sufficient amphiphilicity to self-assemble in solution to form rod-like micelle nanostructures, Scheme 2B.…”

“…While initial reports used melt conditions at temperatures of up to 130 °C with catalysts such as [Rh(COD)Cl] 2 , [27] more recently catalyst systems that operate in solution at lower temperatures (e.g. arenes, 100 °C) have been reported, [28][29][30][31] exemplified by [Cp*RhCH 3 (PMe 3 )(ClCH 2 Cl)][BAr F 4 ], I, [32] and versatile CpFe(CO) 2 OTf, II. [18,33,34] A step-growth-like mechanism is suggested to operate using catalyst I.…”

Polyphosphinoborane Block Copolymer Synthesis Using Catalytic Reversible Chain‐Transfer Dehydropolymerization

“…1 H Diffusion Ordered Spectroscopy (DOSY, CDCl 3 , 298 K) provides further evidence for the formation of a block copolymer, Figure 1C. DOSY has been used previously for the analysis of polyphosphinoborane homopolymers [30] as well as hydrocarbon-based block copolymers. [51] Taking each homopolymer of similar MW (CCC, M n = 44 000-33 000 g mol…”

Recent developments in calix[4]pyrrole (C4P)-based supramolecular functional systems

“…20). 129 Strikingly, it was proposed that the dehydrocoupling of 130 via the p-block metal ion (Al III )-inserted ligand/ catalyst 116 offers the resultant polymers (131) with higher purity than that obtained via d-block metal ion-inserted catalysts, where residual metal ion impurities remain in the resultant polymeric materials.…”