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

Alexa Caise, Dafydd Jones, Eugene L. Kolychev, Jamie Hicks, Jose M. Goicoechea, Simon Aldridge*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

51 Citations (Scopus)

Abstract

A series of β-diketiminate stabilized aluminium hydrides of the type (Nacnac)Al(R)H has been synthesized offering variation in the auxiliary R substituent and in the Nacnac backbone. These show significant variation in the nature of the Al−H bond: electron-donating R groups give rise to weaker (and presumably more hydridic) Al−H bonds, leading to enhanced rates of reactivity towards CO2. The resulting κ1-formate complexes (Nacnac)Al(R){OC(O)H} have been isolated and their reactivity towards B−H-containing reductants probed. In the case of HBpin no reaction is observed (even under forcing conditions), while the more reactive boranes HBcat and {H(9-BBN)}2 ultimately yield boryloxy complexes of the type (Nacnac)Al(R)(OBX2) (X2=cat, 9-BBN). However, no hint of Al−O/B−H metathesis is observed even under forcing conditions. With BH3⋅SMe2 the major product is a related boryloxy system, although (uniquely) in this case a minor product is observed which contains an Al−H bond. We hypothesize that (Nacnac)Al(R)(κ2-BH4) is formed (despite the unfavourable thermodynamics of Al−O/B−H metathesis) due to the additional driving force provided by coordination of the strongly Lewis acidic BH3 unit to the Al−H bond. That said, we find that (unlike the analogous gallium systems) no catalytic turnover can be achieved in the reduction of CO2 by boranes mediated by these aluminium hydrides.

Original languageEnglish
Pages (from-to)13624-13635
Number of pages12
JournalChemistry - A European Journal
Volume24
Issue number51
DOIs
Publication statusPublished - 12 Sept 2018
Externally publishedYes

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