Azobenzene Reduction and Derivatization and Al–H Bond Insertion with β-Diketiminate Gallium(I) Complexes

Using backbone modification of popular β-diketiminate ligands, ^RDipnacnac = HC-(RCNDip)₂, with R = Et, <i>i</i>Pr (Dip = 2,6-<i>i</i>Pr₂C₆H₃), we have prepared the new β-diketiminate gallium-(I) complexes [(^EtDipnacnac)-Ga] <b>2a</b> and [( ^{<i>i</i>PrDip}nacnac)-Ga] <b>2b</b> by salt metathesis/reduction using "GaI" in moderate to good (68%, <b>2a</b>) and poor (10%, <b>2b</b>) 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}] <b>4a</b> (R = Et) and <b>4b</b> (R = <i>i</i>Pr) with reduced former azobenzene fragments showing an <i>N</i>,<i>ortho</i>-C-(H)-chelating coordination to the Ga centers. Complex <b>4a</b> was further converted to its C-H-activated tautomer [(^EtDipnacnac)-Ga-{(C₆H₄)-N-(H)-NPh}] <b>5</b>, and reaction with DMSO and benzaldehyde afforded [(^EtDipnacnac)-Ga-(PhNNHPh)-(CH₂S-(O)-Me)] <b>6</b> after DMSO deprotonation and [(^EtDipnacnac)-Ga-(PhNN-(Ph)-CH-(Ph)-O)] <b>7</b> from C-N coupling, respectively. Compound <b>2a</b> also reacted with the aluminum-(III) hydride complexes (NHC)-AlH₃ (NHC = {MeCN-(<i>i</i>Pr)}₂C) and (Me₃N)-AlH₃ to the Ga-Al-bonded complex [(^EtDipnacnac)-Ga-(H)-Al-(H₂)-(NHC)] <b>8</b> and [(^EtDipnacnac)-GaH₂] <b>9</b>, respectively. Gallium-(I) complex <b>2a</b> is a good alternative to commonly used [(^MeDipnacnac)-Ga] (R = Me) for the study and application of low-oxidation-state gallium complexes.