Abstract
Cooperativity between the Li and Al centres is implicated in catalytic hydroboration reactions of aldehydes and ketones with pinacolborane via heteroleptic lithium diamidodihydridoaluminates. In addition to implementing hydroalumination, these versatile heteroleptic ates can also perform as amido bases as illustrated with an acidic triazole.
Highlights
Cooperativity between the Li and Al centres is implicated in catalytic hydroboration reactions of aldehydes and ketones with pinacolborane via heteroleptic lithium diamidodihydridoaluminates
In addition to implementing hydroalumination, these versatile heteroleptic ates can perform as amido bases as illustrated with an acidic triazole
Its compounds have been the focus of an increasing number of studies and find application in a range of chemical processes including as catalysts for dehydrocoupling, hydrosilylation and hydroboration,[1,2,3] as well as small molecule activation by frustrated Lewis pairs (FLP)[4,5,6] and trans-metal-trapping.[7]
Summary
The 1H NMR chemical shifts for the hydride signals in LiAlH4ÁMe6-TREN appear as a broad singlet at 3.86 ppm.[17] A high temperature 27Al NMR experiment on 3 shows that as the temperature is increased the signal becomes sharper, and at 70 1C a triplet is resolved (1JAl–H, 173.6 Hz) (Fig. 3) This is consistent with reported 1JAl–H couplings (e.g., for [AlH2(NEt2)2]À, 175 Hz).[18] Despite the SSIP structures in solid 5 and 6, DOSY NMR studies for 1–6 indicate that all species are CIP in C6D6 solution (see ESI‡). This fact may be due to the ease of displacement of THF compared with one arm of the PMDETA ligand, which would inhibit access of substrate to the active metal centre(s) in a catalytic regime Expanding upon this idea we repeated hydroboration of acetophenone with 1 and 4 in bulk THF-d8, rationalising that catalysis would proceed in similar rates, since excess THF replaces the PMDETA ligand from 4. In that case hydride was the base, but we pondered
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