Reversible borohydride formation from aluminium hydrides and {H(9-BBN)}₂: structural, thermodynamic and reactivity studies

Abstract

Aluminium borohydrides of the type (Nacnac)Al(R){H2(9-BBN)} are characterized by borane dissociation in solution under ambient conditions. This behaviour is critical to the ability of such complexes to reduce CO2.

Molecular Main Group Metal Hydrides

“…Interestingly, when the amine-boranes DippNH 2 ·BH 3 or t BuNH 2 ·BH 3 are used, amine elimination is observed and the κ 2 -borohydride complexes 500 and 501 can be isolated (Scheme ). , Related borohydride complexes have also been generated by the addition of 9-BBN to β-diketiminate-bound aluminum hydrides . ( Mes Nacnac)­AlH 2 ( 486 ) was also found to readily reduce an equivalent of CO 2 (per Al center), forming the formate-bridged aluminum hydride dimer [{( Mes Nacnac)­Al­(μ-H)­(μ-OC­(H)­O)] 2 ( 498 ) .…”

“…703,704 Related borohydride complexes have also been generated by the addition of 9-BBN to β-diketiminate-bound aluminum hydrides. 705 ( Mes Nacnac)AlH 2 (486) was also found to readily reduce an equivalent of CO 2 (per Al center), forming the formate-bridged aluminum hydride dimer [{( Mes Nacnac)Al(μ-H)(μ-OC(H)O)] 2 (498). 706 Structurally related ketiminate supported aluminum hydrides are known to yield aluminum formate species.…”

Aluminium complexes: next-generation catalysts for selective hydroboration

“…For the sake of developing a sustainable world in general, recently Earth-abundant and less toxic metals have revived their importance in hydroboration and borylation chemistry, among which the suitable candidates are aluminium complexes as catalysts. 36–38 The reactivity of aluminium complexes can be controlled by suitably tuning their ligands, and selective reduction of various functionalities via hydroboration can be achieved (Scheme 2A). Moreover, the amount of catalyst can be decreased to as low as 0.5–1 mol% in several Al-catalysed hydroboration reactions.…”

Hydroboration of a Diolate Complex Obtained by Carbon Dioxide Capture with Acenaphthenediimine Aluminum Hydride

“…9 β-Diketiminate aluminum hydrides capture CO 2 giving formates; however, a further reaction of them with HBX 2 yields boryloxy complexes [(NacNac)Al(R)-(OBX 2 )] and no hint to Al−O/B−H metathesis is observed. 10,11 In the field of catalytic hydrosilylation of carbon dioxide using 13 group hydrides, only one example is known� the reduction of CO 2 with triethylsilane to methane, 12 but there are many examples of application of other organoaluminum and -gallium compounds. 13−17 Previously, we have demonstrated the diverse reactivity of aluminum complexes of sterically hindered diimine ligands dpp-bian ( For instance, the reaction of dialane [(dpp-bian)Al−Al(dppbian)] with CO 2 results in two different products depending on solvent�a cycloadduct in toluene and an oxo-bridged carbamato derivative in diethyl ether.…”

“…Selective reduction of CO 2 with formation of pinBOMe (99%) takes place when β-diketiminate gallium hydride [(NacNac)­Ga­( tBu )­H] is used . β-Diketiminate aluminum hydrides capture CO 2 giving formates; however, a further reaction of them with HBX 2 yields boryloxy complexes [(NacNac)­Al­(R)­(OBX 2 )] and no hint to Al–O/B–H metathesis is observed. , In the field of catalytic hydrosilylation of carbon dioxide using 13 group hydrides, only one example is knownthe reduction of CO 2 with triethylsilane to methane, but there are many examples of application of other organoaluminum and -gallium compounds. − …”