Aluminum Monohydride Catalyzed Selective Hydroboration of Carbonyl Compounds

Abstract

The well-defined aluminum monohydride compound [{(2,4,6-Me3-C6H2)NC(Me)}2(Me)(H)]AlH·(NMe2Et) (1) catalyzes hydroboration of a wide range of aldehydes and ketones under mild reaction conditions. Moreover, compound 1 displayed chemoselective hydroboration of aldehydes over ketones at rt.

On the Viability of Catalytic Turnover via Al−O/B−H Metathesis: The Reactivity of β‐Diketiminate Aluminium Hydrides towards CO2 and Boranes

“…Several systems, for example, are capable of effecting the catalytic hydroboration of alkenes and alkynes . Most interesting to us, however (given our interests in oxygen‐containing substrates) are a number of recent reports detailing the use of aluminium hydrides in the catalytic hydroboration of aldehydes and ketones (Figure ) …”

“…[29][30][31][32][33] Most interesting to us, however (given our interests in oxygen-containing substrates) are a number of recent reports detailing the use of aluminium hydrides in the catalytic hydroboration of aldehydes and ketones ( Figure 1). [32,[34][35][36] These systems are proposed to turn over by initial hydroalumination of the C=Ofunctionality to yield an aluminiumalk-oxide, followed by reactionw ith HBpin (via AlÀO/BÀH s-bond metathesis) to regenerate the active AlÀHb ond. [34] This mechanism is superficially similar to that reported for the [ Dipp 1]Ga(tBu)H catalysed reduction of CO 2 (Scheme 1), [23] and this, together with the knownc apabilities of aluminium hydrides in the stoichiometric hydroalumination of CO 2 ,s uggested to us that they might be capable of functioning as catalysts for this process.…”

Electronically Unsaturated Three‐Coordinate Aluminum Hydride and Organoaluminum Cations

“…Similar to the formation of adducts 5 – 8 , the reaction of 3 with an equivalent amount of PhCHO formed an analogous adduct A1 ; however, this adduct was labile enough to undergo hydride migration to the carbonyl carbon to easily afford a stable benzyloxide intermediate A2 , [ L Al‐O‐CH 2 Ph] + [HB(C 6 F 5 ) 3 ] − (Figure ). Intermediates similar to A2 have been proposed to be key species in Lewis acid catalysis with carbonyl compounds;, however, A2 remains to be the first example of such low‐coordinate stable species that has been isolated and spectroscopically characterized. Formation of A2 appears to be the overall rate‐limiting step (see the Supporting Information, Figures S39–S43).…”

Catalytic Hydroboration of Organic Nitriles Promoted by Aluminum Complex

“…[9][10][11][12][13][14] As a result, innumerable procedures have been evolved to accomplish the addition of boranes to nitriles. All these procedures require more or less effective catalysts based on transition-metal complexes such as Co, Fe, Ru, [15][16][17][18][19][20][21][22][23] alkaline earth metal (Mg), [24][25][26][27][28][29][30][31][32][33][34][35] but the processes culminate in frustrated Lewis pairs. [36][37][38] On the other hand, while the reduction of aryl and alkyl nitriles can be achieved using stoichiometric quantities of maingroup reducing agents such as LiAlH 4 and NaBH 4 , [39] the combustible nature of these reagents and large quantities of inorganic waste by-products they generate render the process unattractive, and hence reductive hydroboration is preferable in order to provide further functionality to the resultant amine.…”