Mechanochemical dehydrocoupling of dimethylamine borane and hydrogenation reactions using Wilkinson's catalyst

Abstract

Mechanochemistry enabled the selective synthesis of the recherché orange polymorph of Wilkinson's catalyst [RhCl(PPh3)3]. The mechanochemically prepared Rh-complex catalysed the solvent-free dehydrogenation of Me2NH·BH3 in a ball mill. The in situ-generated hydrogen (H2) could be utilised for Rh-catalysed hydrogenation reactions by ball milling.

Boron−Boron Dehydrocoupling of Boranes Initiated by Reaction with Iodine

“…In contrast, ab oron-boron-dehydrocoupling reaction to give the diborane(4) (P-P)(BH 2 ) 2 was not observed, neither after heatingt he solution nor after addition of potential catalysts that were previously used in dehydrocoupling reactions, for example ( 3 ]. [23][24][25][26][27][28] The reactiono f( P-P)(BH 3 ) 2 (5)w ith Cr(CO) 6 showed the characteristic 1 HNMR signals for the dehydrocoupling complex [{(OC) 4 Cr} 2 (BH 2 BH 2 (P-P))]a td = À8.8 ppm, as reportedb yS himoia nd co-workers, [29] but this complex was never formed in isolable quantities. The BÀHs tretching modes in the IR spectrum of (P-P)(BH 2 I) 2 (6)g ave rise to bands at ñ = 2363 and 2260cm À1 ,c lose to the corresponding bands fort he BÀHs tretchingm odes of borane adduct 5 (2382, 2360 and 2338 cm À1 )a nd (L + H)·BH 3 (2).…”

“…In contrast, a boron–boron‐dehydrocoupling reaction to give the diborane(4) ( P‐P )(BH 2 ) 2 was not observed, neither after heating the solution nor after addition of potential catalysts that were previously used in dehydrocoupling reactions, for example ([Rh(μ‐Cl)cod] 2 , ([Ir(μ‐Cl)cod] 2 , the Brookhart catalyst [(C 6 H 3 ‐2,6‐[CH 2 P( t Bu) 2 ] 2 )IrH 2 ], or the Wilkinson catalyst [RhCl(PPh 3 ) 3 ] . The reaction of ( P‐P )(BH 3 ) 2 ( 5 ) with Cr(CO) 6 showed the characteristic 1 H NMR signals for the dehydrocoupling complex [{(OC) 4 Cr} 2 (BH 2 BH 2 ( P‐P ))] at δ =−8.8 ppm, as reported by Shimoi and co‐workers, but this complex was never formed in isolable quantities.…”

Mechanochemistry of Gaseous Reactants

“…More recently, other mechanochemical metal‐catalyzed hydrogenations have also been reported . Specifically, the Wilkinson rhodium complex [RhCl(PPh 3 ) 3 ] was demonstrated to facilitate the dehydrocoupling of dimethylamine borane in a mixer mill (Scheme ; top).…”

Mechanochemie gasförmiger Reaktanten

“…Oft kann die Chemoselektivitätd es Prozesses (Hydroformylierung versus Hydrierung des Alkens oder des Produkts) durch die Wahl des Metallkatalysators geändert werden. [51] Wenn in Gegenwart von Styrolderivaten gemahlen wurde, verlief die Reaktion mit einer hohen Chemoselektivität, und die Hydroformylierung der Olefine lieferte ausschließlich Aldehyde (Schema 2). [48] Alternativ wurde gezeigt, dass der Gebrauch von supramolekularen Liganden die Regioselektivitätm etallkatalysierter Hydroformylierungen beeinflusst.…”

“…[50] Interessanterweise erlaubte die Robustheit des Rhodiumkatalysators [HRh-(CO)(PPh 3 ) 3 ]s eine In-situ-Darstellung in der Kugelmühle durch Mahlen von Rh(CO) 2 (acac) (acac = Acetylacetonat), PPh 3 und Sacchariden in einem unter Druck stehenden ZrO 2 -Mahlbecher mit CO/H 2 (1:1) bei 15 bar und 850 min À1 . [51] Wenn in Gegenwart von Styrolderivaten gemahlen wurde, verlief die Reaktion mit einer hohen Chemoselektivität, und die Hydroformylierung der Olefine lieferte ausschließlich Aldehyde (Schema 2). Das Kugelmahlen von Substraten mit acyclischen Sacchariden fçrderte das Mischen und die Diffusion der Alkene in der heterogenen Reaktionsmischung und führte zu verzweigten Aldehyden in hohen Ausbeuten.…”