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Azobenzene Reduction and Derivatization and Al-H Bond Insertion with β‑Diketiminate Gallium(I) Complexes
Huanhuan Dong1, Connor Bourne1, Aidan P McKay1
1EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews KY16 9ST, United Kingdom.
Abstract:
Using backbone modification of popular β-diketiminate ligands, RDipnacnac = HC-(RCNDip)2, with R = Et, iPr (Dip = 2,6-iPr2C6H3), we have prepared the new β-diketiminate gallium-(I) complexes [(EtDipnacnac)-Ga] 2a and [( iPrDipnacnac)-Ga] 2b by salt metathesis/reduction using "GaI" in moderate to good (68%, 2a) and poor (10%, 2b) isolated yields, respectively, highlighting the influence of the ligand backbone substitution on the reaction success. The gallium-(I) complexes were converted with azobenzene to the gallium-(III) complexes [(RDipnacnac)-Ga-{(C6H5)-NNPh}] 4a (R = Et) and 4b (R = iPr) with reduced former azobenzene fragments showing an N,ortho-C-(H)-chelating coordination to the Ga centers. Complex 4a was further converted to its C-H-activated tautomer [(EtDipnacnac)-Ga-{(C6H4)-N-(H)-NPh}] 5, and reaction with DMSO and benzaldehyde afforded [(EtDipnacnac)-Ga-(PhNNHPh)-(CH2S-(O)-Me)] 6 after DMSO deprotonation and [(EtDipnacnac)-Ga-(PhNN-(Ph)-CH-(Ph)-O)] 7 from C-N coupling, respectively. Compound 2a also reacted with the aluminum-(III) hydride complexes (NHC)-AlH3 (NHC = {MeCN-(iPr)}2C) and (Me3N)-AlH3 to the Ga-Al-bonded complex [(EtDipnacnac)-Ga-(H)-Al-(H2)-(NHC)] 8 and [(EtDipnacnac)-GaH2] 9, respectively. Gallium-(I) complex 2a is a good alternative to commonly used [(MeDipnacnac)-Ga] (R = Me) for the study and application of low-oxidation-state gallium complexes.
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