Dehydrocoupling of phosphine–boranes using the [RhCp*Me(PMe₃)(CH₂Cl₂)][BAr^F₄] precatalyst: stoichiometric and catalytic studies

Abstract

Detailed experimental and computational studies are reported on the fundamental B–H and P–H bond activation steps involved in the dehydrocoupling/dehydropolymerization of primary and secondary phosphine–boranes, H3B·PPhR′H (R = Ph, H), using the [RhCp*(PMe3)Me(ClCH2Cl)][BArF4] catalyst.

(BB)-Carboryne Complex of Ruthenium: Synthesis by Double B–H Activation at a Single Metal Center

“…The complexes containing similar bridging R–BH 3 ···Ru interactions have been reported to exhibit dynamic (B H 3 ···Ru signals at δ = +3 to −4 ppm) or static (bridging B– H ···Ru signals at δ = −6 to −14 ppm) behavior in the 1 H NMR spectra at room temperature. 19 Complex 7 is a rare example of a carborane cluster with an exohedral B–B bond to a simple borane, and it is the first example of the regioselective formation of such a bond under metal-promoted conditions. 20 This compound may also be considered as a snapshot of a probable intermediate in transition-metal-catalyzed synthesis of diboranes, which is an increasingly important area of organometallic research due to the rise to prominence of diborane reagents for borylation chemistry.…”

Amine–Borane Dehydropolymerization: Challenges and Opportunities

“…An alternative chain termination process involves β‐hydride elimination from a M–amido‐ or M–boryl‐anchored polymer, possibly coupled with transfer hydrogenation of the aminoborane end group (Scheme C). Such processes have been modelled in related phosphine–borane model systems . In principle, such a β‐hydride transfer pathway could be probed by deuterium labelling of the substrate, as reported recently for N‐methylamine–borane .…”

“…The cationic rhodium bis(arylphosphine) system [Rh(Xantphos‐Ph){H 2 BNMe 3 (CH 2 ) 2 t Bu}][BAr F 4 ] shows behavior consistent with a single‐site coordination/dehydrogenation/insertion mechanism (Scheme A) . The mechanism suggested proceeds by on‐metal dehydrogenation to give H 2 B=NMeH coordinated to the metal, which inserts into the growing polymer chain at the metal center, postulated to be anchored by a Rh‐amido linkage, although Rh−B linkages are also possible …”

“…This Concept article serves to outline the current position of amine–borane dehydropolymerization, and identify key challenges and opportunities that the community may find useful to consider as the field develops. For brevity, closely related phosphine–borane dehydrocoupling is not discussed in detail, but concepts and catalysts developed in either field serve as useful comparisons …”

Synthesis, Characterization, and Properties of Poly(aryl)phosphinoboranes Formed via Iron‐Catalyzed Dehydropolymerization

“…[10a] Similar catalyst systems have been used to synthesize other polyphosphinoboranes, and demonstrate selective cross‐dehydrocoupling with no evidence for PP or BB homocoupling. [10h,17] Furthermore, work has been performed to elucidate a mechanism through experimental work with Rh catalysts . Recently, the precatalyst [( t BuPOCOP)IrH 2 ] ( t BuPOCOP = κ 3 ‐C 6 H 3 ‐1,3‐(OP t Bu 2 ) 2 ) has also been shown to dehydropolymerise primary phosphine–boranes (RPH 2 •BH 3 ) (R = Ph, p Tol, Mes) in solution at 100 °C.…”