Experimental Evidence Supporting Related Mechanisms for Ru(II)-Catalyzed Dehydrocoupling and Hydrolysis of Amine-Boranes

Abstract

A family of ruthenium­(II) half-sandwich complexes was tested for the hydrolytic decomposition of amine-boranes. The analysis of the catalytic results, together with a multilateral approach based on 1H, 11B NMR, and ESI-MS were used to propose a plausible and conceptually unified mechanism for both the hydrolysis and competitive dehydrogenation of amine-boranes. We propose the intermediacy of solvent-stabilized borenium cations during the catalytic cycle, evolving toward dehydrogenation products in distilled THF or releasing amine-hydroxyboranes in aqueous media. Both reaction pathways would liberate up to 1 equivalent of hydrogen through a metal-catalyzed process, but an out-of-cycle low-barrier hydrolysis of amine-hydroxyboranes would produce the 2 additional equivalents of hydrogen in aqueous solutions. Metal-catalyzed deuteration of (non hydrogen-productive) trisubstituted amine-boranes by using D2O as deuterium source was observed, and included as part of the mechanism proposal.

Cu@Pd/C with Controllable Pd Dispersion as a Highly Efficient Catalyst for Hydrogen Evolution from Ammonia Borane

“…A lot of catalysts were reported to be effective for the hydrogen evolution reaction from AB. Noble metals usually had very high activity for the hydrolysis of AB [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ]. However, as noble metals are expensive, the full utilization of the noble metal atoms is a significant issue in the production of noble metal-based catalysts.…”

A General, Rhodium‐Catalyzed, Synthesis of Deuterated Boranes and N‐Methyl Polyaminoboranes

“…[14] This proceeds via initial oxidative cleavage of aR h···H-B sigma interaction to give a base-stabilized boryl hydride, as indicated by complementary studies using phosphine-boranes. [14a] Existing methods for the formation of D 3 B·NMe 3 include acid-or ruthenium-catalyzed H/D exchange of H 3 B·NMe 3 using D 2 O( which suffers from competitive hydrolysis), [21] ion exchange, [22] or crownether-catalyzed reaction of NaBD 4 with NMe 3 HCl. H 3 B·NMe 3 is an ideal substrate for such BH/BD exchange as it can be sublimed, is air-stable, does not have NÀHg roups neededf or onward dehydrogenation,a nd also forms a s-complex with 2,aprecursor to BÀHa ctivation.…”

“…H 3 B·NMe 3 is an ideal substrate for such BH/BD exchange as it can be sublimed, is air-stable, does not have NÀHg roups neededf or onward dehydrogenation,a nd also forms a s-complex with 2,aprecursor to BÀHa ctivation. [14a] Existing methods for the formation of D 3 B·NMe 3 include acid-or ruthenium-catalyzed H/D exchange of H 3 B·NMe 3 using D 2 O( which suffers from competitive hydrolysis), [21] ion exchange, [22] or crownether-catalyzed reaction of NaBD 4 with NMe 3 HCl. [23] Initial screening showedt hat 2 promotesB H/BD exchange in H 3 B·NMe 3 with D 2 in Et 2 O, THFor1,2-F 2 C 6 H 4 solvents.…”

One‐Pot Fabrication of Pd Nanoparticles@Covalent‐Organic‐Framework‐Derived Hollow Polyamine Spheres as a Synergistic Catalyst for Tandem Catalysis

“…[28] The furtherh ydrolysis of the hydroxyborane adduct generates two additive equivalents of H 2 . [29] After the catalytic reaction is complete, the aqueous solution was examined by 11 BNMR spectroscopy. As shown in Figure S13 (in the Supporting Information), the 11 B peak at À23.90 ppm for aqueous NH 3 BH 3 disappears, whereas the solutiong ives a 11 Bp eak at d = 10.17 ppm, which was attributed to the formed borate species.…”

“…The coordination of amine to Pd NPs increases the electron density on the Pd NP surface, which would favor the cleavage of the O−H bond in water; this is proposed to be the rate‐limiting step . The further hydrolysis of the hydroxyborane adduct generates two additive equivalents of H 2 . After the catalytic reaction is complete, the aqueous solution was examined by 11 B NMR spectroscopy.…”