Backbone Reactivity of Lithium β-Diketiminate (NacNac) Complexes with CO 2, tBuNCO and iPrNCO

Gauld, Richard M and McLellan, Ross and Kennedy, Alan R. and Barker, Jim and Reid, Jacqueline and Mulvey, Robert M. (2019) Backbone Reactivity of Lithium β-Diketiminate (NacNac) Complexes with CO 2, tBuNCO and iPrNCO. Chemistry - A European Journal. ISSN 0947-6539

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    Abstract

    Though alkali metal NacNac (β-diketiminate) complexes have been utilised in synthesis as NacNac-transfer agents, studies of them in their own right with small molecules are exceptionally rare. Here, the lithium compound of the common 2,6-diisopropylphenyl-β-methyldiketiminate [NacNac(Dipp, Me)] ligand is investigated with carbon dioxide and isocyanates. In all four cases reaction occurs at the backbone γ-C atom of the NacNac ligand, which redistributes electronically into a diimine. Insertion of CO 2 gives an eight-atom carboxylate (Li 2O 4C 2) ring at the γ-C site in a dimer. Insertion of tBuNCO gives a secondary amide at the γ-C site in a monomer with TMEDA chelating lithium. Double insertion of tBuNCO and (adventitious) oxygen gives a dimer with a (LiO) 2 central core involving the latter source. Insertion of less bulky (iPrNCO) gives a dimer with dimerisation through the C=O bonds of the emergent secondary amide function.