Abstract
Bimetallic lithium aluminates and neutral aluminum counterparts are compared as catalysts in hydroboration reactions with aldehydes, ketones, imines and alkynes. Possessing Li–Al cooperativity, ate catalysts are found to be generally superior. Catalytic activity is also influenced by the ligand set, alkyl and/or amido. Devoid of an Al−H bond, iBu2Al(TMP) operates as a masked hydride reducing benzophenone through a β‐Η transfer process. This catalyst library therefore provides an entry point into the future design of Al catalysts targeting substrate specific transformations.
Highlights
Bimetallic lithium aluminates and neutral aluminum counterparts are compared as catalysts in hydroboration reactions with aldehydes, ketones, imines and alkynes
Our groups interests lie in exploiting the synergistic reactivity imparted by two distinct metal centres[7,8] installed within a bimetallic complex. In this regard we introduced ate complexes (Figure 1), detailing that heteroleptic lithium diamido-dihydridoaluminates and lithium monoamido-monohydrido-dialkylaluminates implicate that the alkali metal influences the ensuing “aluminum reactivity” in the hydroboration of aldehydes, ketones and terminal alkynes.[8]
Hydroboration of unsaturated substrates under aluminum catalysis is gaining a foothold in the literature, and a variety of neutral aluminum complexes are displaying excellent potential in this role.[2a,3,10] Previously, we reported that bimetallic lithium [iBu2AlTMP(H)Li]2 (1) and [(HMDS)2AlH(mH)Li·3 THF)] (2) are both efficient bimetalliccatalysts in the hydroboration of aldehydes and ketones.[8]
Summary
International Edition: DOI: 10.1002/anie.201806168 German Edition: DOI: 10.1002/ange.201806168 Comparing Neutral (Monometallic) and Anionic (Bimetallic) Aluminum Complexes in Hydroboration Catalysis: Influences of Lithium Cooperation and Ligand Set Victoria A. Pollard, M. ngeles Fuentes, Alan R. Kennedy, Ross McLellan,* and Robert E. Mulvey*
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