Metallopolymers via thermal dealkylation of unstrained bisphosphanylferrocene precursors

Abstract

Ferrocenylene-bridged polyphosphanes [Fc′P₂]_n^tBu₂ and [Fc′P₂]_n (Fc′ = 1,1′-ferrocenediyl; ^tBu = tert-butyl), previously prepared via thermal ring expansion polymerization from strained ferrocenophane precursors, are reported to be accessible from unstrained secondary phosphanes. The thermal reaction and polymerization of Fe(C₅H₄-PH^tBu)₂ proceed through the elimination of ^tBuH and consequent formation of ^tBu-substituted diphospha[2]FCP, along with ferrocene substituted cyclic P₄-species and di-^tBu-substituted linear P₄-species. The resulting polymer shows similar ¹³C and ³¹P solid-state NMR, IR, and UV-vis spectra and elemental analysis results, when compared to those of authentic samples of previously published [Fc′P₂]_n^tBu₂ and [Fc′P₂]_n obtained via strained ferrocenophanes. In contrast, the thermal reaction of all-^tBu-substituted tertiary phosphane Fc′(P^tBu₂)₂ entails loss of the P-containing moiety along with formation of Fc^tBu instead of a polymeric material. Thermodynamic assessment of the decomposition pathways of both precursors based on density functional theory calculations is consistent with the experimental findings. Overall, the unstrained 1,1′-ferrocenylene bridged secondary bisphosphane provides a simplified approach for thermal polymerization to linear one-dimensional P_n-chains.