Bis‐(triphenylphosphane) Aluminum Hydride: A Simple Way to Provide, Store, and Use Non‐Polymerized Alane for Synthesis

Abstract

AlH3(PPh3)2 was synthesized as a stable solid being the first known 1 : 2 alane arylphosphane adduct. Although only weakly intra‐molecularly coordinated, it displays as a molecular crystal significant inertness against atmospheric humidity and oxygen due to strong steric screening of the alane unit. The compound readily dissociates PPh3 in solution allowing for its use as a Lewis acidic reducing agent. These features lead to an easy to store, easy to use reducing agent that may enable the quantitative investigation of aluminum hydride chemistry including reduction, complexation and hydroalumination reactions. The structure contains two non‐equivalent penta‐coordinated aluminum centers that despite long Al−P distances of ca. 2.7 Å display unusually high quadrupolar coupling constants CQ of 25.1 and 26.5 in 27Al solid state NMR measurements. The product was also tested as a reducing agent on a small set of selected compounds with various functional groups.

Highly accurate CCSD(T) homolytic Al–H bond dissociation enthalpies – chemical insights and performance of density functional theory

“…Recently, a 1:2 alane arylphosphane adduct has been synthesised, which was shown to be able to release essentially free non-polymerised AlH 3 , which could be used in reduction and hydroalumination reactions. [5] Bulkier aluminium hydride species, such as diisobutylaluminium hydride (DIBAl-H), have been employed in effecting a wide range of reduction processes, including the (i) reduction of ketones and aldehydes to the corresponding alcohols, (ii) transforming α,β-unsaturated esters into the corresponding allylic alcohols [6,7] and (iii) epoxide ring opening reactions. [8] While the reactions of alkylsubstituted aluminium hydrides have received considerable attention, other aluminium hydride species have also been used in synthesis, albeit with much more limited scope to date.…”