Donor‐influenced Structure–Activity Correlations in Stoichiometric and Catalytic Reactions of Lithium Monoamido‐Monohydrido‐Dialkylaluminates

Abstract

A series of heteroleptic monoamido‐monohydrido‐dialkylaluminate complexes of general formula [iBu2AlTMPHLi⋅donor] were synthesized and characterised in solution and in the solid state. Applying these complexes in catalytic hydroboration reactions with representative aldehydes and ketones reveals that all are competent, however a definite donor substituent effect is discernible. The bifunctional nature of the complexes is also probed by assessing their performance in metallation of a triazole and phenylacetylene and addition across pyrazine. These results lead to an example of phenylacetylene hydroboration, which likely proceeds via deprotonation, rather than insertion as observed with the aldehydes and ketones. Collectively, the results emphasise that reactivity is strongly influenced by both the mixed‐metal constitution and mixed‐ligand constitution of the new aluminates.

Comparing Neutral (Monometallic) and Anionic (Bimetallic) Aluminum Complexes in Hydroboration Catalysis: Influences of Lithium Cooperation and Ligand Set

“…Stoichiometric reactions of TMP‐containing 1 and 4 with terminal alkyne phenylacetylene (PhCCH) in C 6 D 6 , reveal deprotonation of PhCCH at room temperature, in agreement with the fact that hydroboration of PhCCH with 1 implicated deprotonation as a key step 8b. Alternatively 3 is unreactive with PhCCH, and 6 only very slowly hydroaluminates PhCCH, at room temperature.…”

Alkali‐Metal Mediation: Diversity of Applications in Main‐Group Organometallic Chemistry

“…Recently Harder and co‐workers used it as a catalyst for the hydrogenation of imines [7c] . Our own group employed various derivatives of LiAlH 4 for catalytic hydrophosphination [5a] and hydroboration [3g–i] processes. For the latter we carried out a comparative study on the performance of neutral (monometallic) and anionic (bimetallic) aluminium complexes (depicted in Scheme 3), and found that the bimetallic catalysts ([( i Bu) 2 Al(TMP)(H)Li] 2 ( 4 ), [(HMDS) 2 Al(H)(μ‐H)Li⋅(THF) 3 ] ( 5 ), [( i Bu) 3 Al(H)Li] ( 6 )) outperform their monometallic counterparts ([( i Bu) 2 Al(TMP)] ( 7 ), [(HMDS) 2 Al(H)] ( 8 ), [( i Bu) 3 Al(H)] ( 9 )) in the conversion of aldehydes, ketones, and imines.…”

Insights into LiAlH4 Catalyzed Imine Hydrogenation

“…[5] Although these applications are based on stoichiometric use of LiAlH 4 ,t he last decades have seen some interesting examples of LiAlH 4 (or related compounds) in catalysis. [6][7][8][9][10][11][12][13] During the development of early main group metal catalyzed imine hydrogenation, [14] we found that commercially availableL iAlH 4 can be used under relatively mild conditions in catalytic instead of stoichiometric quantities (2.5 mol %c atalyst loading, 1bar H 2 and 85 8C). [13,15] Such an on-stoichiometric route prevents the generally hazardous aqueous work-up anda voids considerable amountso fL i/Al salts as side-products.…”