Low-Valent Niobium Catalysis for the Polymerization of Electron-Rich Diphenylacetylenes

Abstract

A low-valent niobium (Nb) species formed in situ from NbCl5 with PhSiH3 induces the polymerization of diphenylacetylenes having electron-donating groups to afford the corresponding poly(diphenylacetylene)s (PDPAs) with high molecular weights in good yield. An insertion ring-expansion mechanism would be involved in the polymerization and would produce cyclic PDPAs, as suggested by results of atomic force microscopy (AFM) observations and NMR analysis of the obtained polymers. The present polymerization method was applicable to the synthesis of symmetrically substituted PDPAs having chiral alkoxy pendants at para- and meta-positions, and their chiroptical properties were investigated.

Metallacyclobuta‐(2,3)‐diene: A Bidentate Ligand for Stream‐line Synthesis of First Row Transition Metal Catalysts for Cyclic Polymerization of Phenylacetylene

“…This strategy has been pioneered by Veige and co-workers utilizing a high-valent [W VI ] catalyst and a variety of terminal alkynes. [22][23][24][25][26][27][28][29] Likewise, Maeda and co-workers have also reported cyclic polyalkynes of tolanes invoking Nb, [30] Ta, [31] and W [32] alkyne adducts. More recently, we have identified [V V ] alkylidynes (Scheme 1, A) [33][34] as pre-catalysts for the cyclic polymerization of phenylacetylene (cyclic-PPA, B).…”

Metallacyclobuta‐(2,3)‐diene: A Bidentate Ligand for Stream‐line Synthesis of First Row Transition Metal Catalysts for Cyclic Polymerization of Phenylacetylene

“…This strategy has been pioneered by Veige and co-workers utilizing a high-valent [W VI ] catalyst and a variety of terminal alkynes. [22][23][24][25][26][27][28][29] Likewise, Maeda and co-workers have also reported cyclic polyalkynes of tolanes invoking Nb, [30] Ta, [31] and W [32] alkyne adducts. More recently, we have identified [V V ] alkylidynes (Scheme 1, A) [33][34] as pre-catalysts for the cyclic polymerization of phenylacetylene (cyclic-PPA, B).…”