Titanium‐Catalyzed Polymerization of a Lewis Base‐Stabilized Phosphinoborane

Abstract

The reaction of the Lewis base‐stabilized phosphinoborane monomer tBuHPBH2NMe3 (2a) with catalytic amounts of bis(η5:η1‐adamantylidenepentafulvene)titanium (1) provides a convenient new route to the polyphosphinoborane [tBuPH‐BH2]n (3a). This method offers access to high molar mass materials under mild conditions and with short reaction times (20 °C, 1 h in toluene). It represents an unprecedented example of a transition metal‐mediated polymerization of a Lewis base‐stabilized Group 13/15 compound. Preliminary studies of the substrate scope and a potential mechanism are reported.

Mono-Alkyl-Substituted Phosphinoboranes (HRP–BH2–NMe3) as Precursors for Poly(alkylphosphinoborane)s: Improved Synthesis and Comparative Study

“…In contrast to other phosphinoboranes, the iPr-substituted phosphinoborane 2 revealed a considerably lower tendency for polymerization. Thermal polymerization at room temperature only led to minimal conversion, while [Ti]-based catalytic polymerization revealed an unexpected behavior; similar to what was reported for the parent phosphinoborane [49], the formation of polymeric species was not observed. Instead, a significant broadening of the signal corresponding to 2 in the 31 P NMR spectra was perceived, which increased with higher catalyst load without any new signals emerging (Figure 6).…”

“…Via this pathway, the formation of alkyl-substituted arsenic-boron oligomers has also been reported recently [47]. Moreover, the titanium-catalyzed polymerization of I under very mild conditions and with shorter reaction times was achieved (Figure 1) [48,49]. As yet, the scope of accessible polymers has been limited by the range of suitable starting materials, as only a few mono-alkylsubstituted phosphinoboranes have been reported so far; these are essential for accessing a broader variety of properties.…”

“…Polymerization experiments with compounds 1a-c were performed under varying conditions, both via thermal elimination of the stabilizing NMe 3 Lewis base as well as via catalytic conditions using the recently reported bispentafulvene [(η 5 :η 1 [49,52]. Overall, the influence of temperature, reaction time, concentration and solvent as well as the presence and concentration of the catalyst were investigated to be discussed in the following.…”

“…When the polymerization reaction was performed in the presence of the recently reported bispentafulvene [Ti] catalyst [49,52], significant differences could be observed: The presence of the [Ti] catalyst leads to drastically reduced reaction times in the range of hours, but in all cases, the reaction stops at around 80% conversion. In this case, neither an increase of temperature nor longer reaction times lead to an improvement.…”